Method and system for laser hardening a surface of a workpiece

Abstract

A method for laser hardening a surface of a journal (1001, 1002) of a crankshaft (1000), wherein the journal has a surface region to be hardened, wherein the surface region extends in a first direction parallel to a rotational axis (X) of the crankshaft and in a second direction corresponding to a circumferential direction (W) of the journal, wherein the surface region comprises at least one more heat-sensitive sub-region and at least one less heat-sensitive sub-region, wherein the at least one more heat-sensitive sub-region comprises a region adjacent to an oil lubrication hole (1003) of the crankshaft, the method comprising: projecting a laser beam (2) from a laser source (1) onto the surface region so as to produce an effective laser spot (2A, 2B, 2C, 2D, 5) on the surface region, wherein the effective laser spot (2A, 2B, 2C, 2D,5) extends in the first direction over the main part of the area to be hardened; generating a relative movement between the surface of the crankshaft (1000) and the laser source (1) in the circumferential direction so as to project the effective laser spot (2A, 2B, 2C, 2D, 5) successively onto different parts of the surface area in the circumferential direction; during the relative movement, repeatedly scanning the laser beam (2) over the respective part of the surface area in two dimensions so as to produce the effective laser spot (2A, 2B, 2C, 2D, 5) as a two-dimensional effective laser spot (2A, 2B, 2C, 2D, 5) on the surface area, wherein the effective laser spot (2A, 2B, 2C, 2D, 5) is an equivalent laser spot exhibiting a two-dimensional energy distribution; wherein the method comprises dynamically adjusting the two-dimensional energy distribution so that the two-dimensional energy distribution when the less heat-sensitive sub-area is heated is different,as if the more heat-sensitive sub-region adjacent to an oil lubrication hole (1003) is heated so as to avoid overheating of the region adjacent to an oil lubrication hole (1003), and wherein during at least 50% of the time of applying the effective laser spot (2A, 2B, 2C, 2D, 5) to the surface region, the effective laser spot has a width in the circumferential direction (W) of at least 5 mm.

Description

Technical area

[0001] The following invention relates to the field of surface hardening of products made of ferrous materials, such as steel, for example crankshafts, by means of lasers. State of the art

[0002] It is well known in the art to harden ferrous materials, such as medium-carbon steel, by heating the material to a high temperature below its melting point and subsequently quenching it—that is, cooling it rapidly enough to form hard martensite. Heating can be done in combustion chambers or by induction heating, and cooling can be achieved by applying a cooling fluid, such as water mixed with water or other components.

[0003] Often, it's only the surface that needs to be hardened. Surface hardening increases the wear resistance of the material and can sometimes be used to increase fatigue strength, which is caused by the residual compressive stresses. Surface hardening can be useful for hardening surfaces that will be subject to severe wear during use, for example, bearing surfaces such as crankshaft journal surfaces.

[0004] Laser surface hardening is a surface treatment process in which high-energy laser light is used as a heat source to harden the surface of a substrate. It is known to use laser light to achieve surface hardening, for example: - F. Vollertsen, et al., “State of the art of Laser Hardening and Cladding”, Proceedings of the 3rd International WLT Conference on Lasers in Manufacturing 2005, June 2005; - M. Seifert, et al., „High Power Diode Laser Beam Scanning in Multi-Kilowatt Range“, Berichte des 23. Internationalen Kongresses zu Anwendungen von Lasern und Electro-Optics 2004; - S. Safdar, et al., „An Analysis of the Effect of Laser Beam Geometry on Laser Transformation Hardening“, Journal of Manufacturing Science and Engineering, Aug. 2006, Band 128, Seiten 659-667; - H. Hagino, et al., „Design of a computer-generated hologram for obtaining a uniform hardened profile by laser transformation hardening with a high-power diode laser“, Precision Engineering 34 (2010), Seiten 446-452, - US 4 313 771 A; - DE 41 23 577 A1; - EP 1 308 525 A2; - EP 2 309 126 A1; - JP 2008-202438 A; - JP S61-58950 A; - US 4 797 532 A.

[0005] The use of laser light for surface hardening offers several advantages: The laser beam is essentially independent of the workpiece, is easily controlled, does not require a vacuum, and does not produce combustion products. Since the laser beam generally only heats the metal product or workpiece locally, the rest of the workpiece can also act as a heat sink, ensuring rapid cooling, which is also known as self-quenching: The cold interior of the workpiece forms a sufficiently large heat sink to quench the hot surface through heat conduction to the interior at a rate high enough to allow martensite to form on the surface. This eliminates the need for external cooling media, such as cooling fluids.

[0006] A problem associated with the use of laser light as a heat source in metal hardening processes is that the width of the hardening zone is limited by the dimensions of the laser spot. It is known to use optics to modify the shape of the spot, for example, to provide a substantially rectangular spot with a more or less uniform intensity distribution. As an alternative, scanning devices (such as a scanning mirror connected to drive means) can be used to repeatedly move the spot across the track, so that the heat source can be considered a rectangular source moving along the track.

[0007] Despite these advantages, laser hardening is often not used because it is assumed that the production rate will not be high enough for many practical applications of this technique, and because it is difficult to ensure that all parts requiring hardening are hardened to the desired degree. Proper heating is essential to ensure that hardening and tempering are achieved to the required depths without causing damage due to overheating.

[0008] For example, a crankshaft (the part of the engine that translates a reciprocating linear piston motion into rotation) is a complex product that is often considered difficult to harden by laser light. An example of a crankshaft is shown in Fig. 1. The crankshaft 1000 is a forged or cast steel product having two or more centrally located coaxial cylindrical journals 1001 (also known as the "main journals") and one or more offset cylindrical crankpins 1002 (also known as "rod journals") separated by counterweights and legs forming walls 1005 extending substantially perpendicular to the surfaces of the journals. The complex shape of the product can make it difficult to "scan" the surface with the laser beam; the tracks or surfaces to be hardened may have different widths and / or be asymmetrical and / or arranged in different planes (which is the case with the walls 1005 and the surfaces of the journals 1001 and 1002). Thus, high-frequency induction heating followed by a polymer-based water quench process is now commonly used for hardening crankshafts.However, this process has certain disadvantages, although it has proven useful for achieving the desired hardening. For example, the inductors used to generate heat by induction must be designed according to the specific design of the crankshaft, which reduces flexibility: adapting an induction machine to a new type of crankshaft can be time-consuming and expensive. Furthermore, heating by induction is expensive in terms of the energy required to heat the crankshaft to the desired temperature. Furthermore, the cooling process is complex, expensive, and environmentally challenging due to the large quantities of cooling fluid required. Therefore, parameters such as cooling fluid temperature and flow must be carefully controlled to ensure a correct hardening process.

[0009] Thus, curing using laser light as a heat source can be an attractive alternative in terms of flexibility, environmental friendliness, energy consumption and costs.

[0010] DE 10 2005 005 141 B3 discloses a method for laser hardening the surfaces of the journals of a crankshaft. According to this method, a six-axis industrial robot is used to hold the crankshaft and subsequently rotate it around the axis of the main journal and the axes of the crankpins while the respective journals are heated with laser light. Thus, by utilizing the motion capabilities of the industrial robot, the distance between the laser source and the surface onto which the laser beam is projected can be kept constant.

[0011] US 2004 / 0244529 A1 also teaches the use of a laser to harden a small region of the crankshaft. In this case, the laser light is used to harden a plurality of spaced-apart areas, with the size of the areas varying across the region to be hardened. Since these spaced-apart areas only harden a small area of the crankshaft, there is no need to worry about overheating other, more heat-sensitive areas.

[0012] DE 3905551 A1 teaches a system for hardening a crankshaft surface, in which a laser beam is projected onto a crankshaft and in which there is a relative movement between the beam and the crankshaft, such that the beam is projected essentially onto different areas of the crankshaft. The power or power distribution in the beam is adjusted depending on the geometry of the respective area of the crankshaft and the desired penetration depth of the laser beam. One problem with the approach taught by DE 3905551 A1 is that it does not allow for a high fluctuation rate.To achieve a sufficient depth of the hardened layer (in the engine industry, case depths of at least 800, 1000, 1500, 2000, or even 3000 µm are typically required for effective case depths; on the other hand, it is often desirable to have 100% converted martensite down to depths of 200 µm or more), it is not enough to simply increase the temperature of the specific area of the surface; energy must be applied for a sufficiently long time to heat not only the surface but also the subsurface material to a sufficient depth. Since excessive heating of the surface is undesirable, the best solution to achieve the desired penetration is not simply to increase the amount of laser beam power, but rather to increase the time during which laser heating is applied to the relevant area.In the system disclosed in DE 3905551 A1, in which the laser beam is held stationary and applied to a specific area, achieving adequate heating and penetration across the main areas of the main journals or crankpins would require a significant amount of time. Thus, while DE 3905551 A1 may describe a method suitable for hardening very specific areas of the surface of a crankshaft, it is not suitable for hardening the general surfaces of the journals.

[0013] EP 1972694 A2 also addresses the hardening of specific areas of a crankshaft, namely the grooves, using only one or more lasers. The laser light is directed onto the area to be hardened, and the crankshaft is rotated. The disclosed method may include a preheating step, a main heating step, and a postheating step. It appears that the laser radiation is kept constant while the crankshaft rotates. EP 1972694 A2 does not address the risk of overheating more heat-sensitive areas of the crankshaft surface.

[0014] US 2004 / 0108306 A1 confirms that car manufacturers use induction heating to harden crankshaft bearings, i.e., the surfaces of the main journals and crankpins, while a mechanical rolling process is used to roll the fillets and improve compressive stresses. However, according to US 2004 / 0108306 A1, these processes are described as capital-intensive, time-consuming, a pathway for non-uniformity, and prone to cracking at the oil lubrication holes, which requires a tempering process. US 2004 / 0108306 A1 teaches a laser heat treatment of the fillets, which aims to eliminate the need for a mechanical rolling process. Tight temperature control using an optical pyrometer is proposed. The use of a controllable x, y mechanism to maintain a fixed heating distance between the laser and the fillet is proposed.

[0015] SM Shariff, et al., "Laser Surface Hardening of a Crankshaft," SAE 2009-28-0053 (SAE International) discusses laser surface hardening of a crankshaft with the goal of achieving a hardened case depth of over 200 µm with a hardness of 500 to 600 HV at various specified locations. The document mentions the problem of melting at the periphery of the holes due to a reduced heat sink effect and heat buildup at the edge. It is stated that the problem can be resolved by reducing the preheating effect at the hole edge, choosing a suitable start-up location, and varying process parameters within the allowable range.

[0016] One reason why laser hardening has not been used more frequently in the context of complex products, such as crankshafts, is that it is believed that it can be difficult to obtain correct heating of the parts, i.e. sufficient heating to ensure correct hardening (in general, the hardened layer must have an effective case depth of at least 800 µm or more, for example at least 1000, 1500, 2000 µm and / or have 100% unformed martensite to a depth of, for example, 200 µm or more), while avoiding overheating of sensitive areas. In the case of a crankshaft, for example, such as the one in Fig. 1, care must be taken regarding the heating of the bearings in relation to the oil lubrication holes 1003 and optionally also with regard to the grooves 1004. For example, if a large laser spot is projected onto the bearing surface while the bearing is rotating in order to heat the entire surface, and if the rotation speed and the power of the laser beam are kept constant so that each area of the surface receives the same amount of energy, and if this is sufficient to achieve adequate heating of the majority of the surface to produce the desired hardening, the heating at the edges of the oil lubrication holes may become excessive and thus damage the edges. The same can occur at the grooves, which are usually undercut; thus, there are edges there that can suffer damage if overheated.

[0017] US 2008 / 0053384 A1 discloses a method for laser hardening a workpiece surface, in which the laser beam is projected off-center onto the workpiece surface. The workpiece rotates relative to the laser beam, which strikes the workpiece surface at an angle of less than 90°.

[0018] According to DD 291 717 A5, during the laser treatment of differently shaped workpieces, the workpiece surface is divided into grids, which are scanned with differently adjustable pulse energies and thus different power inputs. Pulse frequencies of up to 100 kHz are possible. Description of the invention

[0019] A first aspect of the invention relates to a method for laser hardening a surface of a journal of a crankshaft, wherein the journal comprises a surface region to be hardened, wherein the surface region extends in a first direction parallel to the rotational axis (X) of the crankshaft and in a second direction corresponding to a circumferential direction (W) of the journal, wherein the surface region comprises at least one more heat-sensitive partial region and at least one less heat-sensitive partial region, wherein the at least one more heat-sensitive partial region comprises a region adjacent to an oil lubrication hole of the crankshaft, the method comprising: Projecting a laser beam from a laser source onto the surface area so as to create an effective laser spot on the surface area, the effective laser spot being in the first direction, transverse to the main part of the surface area to be hardened (for example more than 50%, more than 75%, more than 85% or more than 90% or 95%, such as more than 99% or even 100% in the transverse direction and particularly over the main part, if not over 100%, of the surface area to be hardened, for example the surface area in which an effective case hardening depth of, for example, at least 800 µm or more is desired); Generating a relative movement between the surface of the crankshaft and the laser source in the circumferential direction so as to sequentially or continuously project the effective laser spot onto different parts of the surface area in the circumferential direction; where the effective laser spot exhibits a two-dimensional energy distribution (in terms of how the energy or power of the laser beam is distributed within the effective laser spot).

[0020] The method further comprises adjusting the energy distribution so that when heating the less heat-sensitive sub-area, the energy distribution is different than when heating the more heat-sensitive sub-area adjacent to an oil lubrication hole, thus avoiding overheating of the area adjacent to an oil lubrication hole. By performing this adjustment, it is possible to achieve efficient and adequate heating of the surface area to be hardened without, for example, overheating and damaging the edges of the oil lubrication holes.

[0021] In some embodiments of the invention, the effective laser spot has a width (or linear extension along the curvature of the surface of the stud) in the circumferential direction of at least 5 mm, preferably 7 mm, more preferably at least 10 mm, and even more preferably at least 15 mm, 20 mm, 30 mm or more, such as at least 50 mm, during a substantial portion (such as at least 50%, 75%, 90%, 95%, or more) of the application time of the effective laser spot on the surface area. The use of a sufficient extension in the circumferential direction, i.e., in the direction of the relative movement generated between the laser source and the surface of the stud, makes it possible to heat each portion of the surface area to be hardened for a sufficient time while simultaneously completing the hardening process within a reasonably short time.This means that a sufficient extension of the effective laser spot in the circumferential direction makes it possible to perform the relative movement at a relatively high speed, as sufficient penetration or curing depth is achieved without using excessively high temperatures. For this reason, a significant width of the effective laser spot in the circumferential direction may be preferable. Of course, a balance must be struck between the capacity in terms of the power of the laser used and the surface area covered by the effective laser spot, as the available power must be sufficient to ensure adequate heating of the area.It has been found that when working with automotive crankshafts, which have journals with widths on the order of one to a few centimeters in the first direction, and using lasers with an output power in the range of a few kW, such as 3-4 kW, the effective spot can have a circumferential width of, for example, 1 cm, while the relative linear velocity between the laser and the journal surface can be on the order of 60 cm / minute. For many industrial purposes, it is assumed that the laser beam should have a power of at least 3 kW, preferably more, such as 6 kW.

[0022] In some embodiments of the invention, the effective laser spot is an equivalent or virtual laser spot obtained by scanning the laser beam in the first direction and in the second direction, including directions between these two directions, i.e., directions oblique to the first and second directions, for example, along a straight or curved path or lines, and repeatedly following a scanning pattern in which the laser spot is arranged at a scanning speed, such that the two-dimensional energy distribution during a scanning cycle is determined by the scanning speed, the scanning pattern, the size of the laser spot, the power of the laser beam, and the power distribution within the laser beam. Thus, one or more of these parameters can be used to dynamically adjust the two-dimensional energy distribution.This makes it possible to easily adjust and modify the size and shape of the effective laser spot as well as the two-dimensional energy distribution within the effective laser spot during the relative displacement between the laser source and the surface of the workpiece, e.g., during rotation of the crankshaft about its longitudinal axis, and thereby adjust the two-dimensional energy distribution to avoid overheating of the more heat-sensitive sub-regions, such as the regions adjacent to the oil lubrication holes.In some embodiments of the invention, the energy distribution adjustment is performed for adjusting at least one of the scanning speed, the scanning pattern, the size of the laser spot, the power of the laser beam, and the power distribution within the laser beam, such that when the less heat-sensitive sub-region is heated, the energy distribution is different than when the more heat-sensitive sub-region, including the region adjacent to an oil lubrication hole, is heated, thus avoiding overheating of the region adjacent to an oil lubrication hole. In some embodiments of the invention, the energy distribution adjustment is performed by adjusting the power of the laser beam, for example, by switching the laser beam on and off while scanning the laser spot along the scanning pattern.For example, if a laser is used, such as a fiber laser, the laser beam can be switched on and off very quickly, making it possible to achieve a desired energy distribution by switching the laser beam on and off as it follows the scan pattern. Thus, heating can be achieved by switching the laser beam on during specific lines or portions of lines of the scan pattern.

[0023] In some embodiments of the invention, the energy distribution is controlled at least in part by selectively adjusting the power of the laser beam while scanning the laser spot along the scan pattern so as to place the laser beam into a plurality of available power states at least 300 times per second, more preferably at least 600 times per second, more preferably at least 1000 times per second, more preferably at least 5000 times per second, and even more preferably at least 10,000 times per second. The term "power state" refers to a state in which the laser beam has a predetermined average power, such that different power states correspond to different power levels of the laser beam, such as 0 kW, 1 kW, 4 kW, 5 kW, 6 kW, 9 kW, and 10 kW.In some embodiments of the invention, for example, there may be two power states, namely an "ON" state when the laser beam is switched on, and an "OFF" state when the laser beam is switched off, i.e., at 0 power (or close to 0 power). However, any other available power state may be used, i.e., even power states where the average power is higher than 0 but lower than the maximum power of the laser beam. For example, if the maximum power of the laser beam is 10 kW, there may be two available power states corresponding to 0 kW and 10 kW, and / or there may be available power states corresponding to intermediate values, such as 2 kW, 4 kW, 5 kW, 6 kW, and / or 8 kW. The term "available" refers to the fact that the power states can be achieved with the laser equipment used.The term "shift into" does not mean that there must be an actual change in state that many times per second (e.g., several adjacent sections may have the same power state associated with it, so there is no need to change the laser power when moving from one section to the next), but indicates that the laser is arranged so that it is capable of changing power states as many times as necessary, for example, when following commands provided by a control system. This makes it possible to achieve segmentation or "pixelation" of the energy distribution with 300, 600, 1000, 5000, or 10,000 segments or pixels per second, with the laser beam having an average power during each segment or pixel, or at least during a sub-segment or pixel, as determined by the power state associated with the segment or pixel.For example, if the scanning pattern is repeatedly followed at a frequency of 50 Hz, the energy distribution along the scanning pattern can be determined by, for example, the power states associated with 6, 12, 20, 100, or 200 segments or pixels distributed along the scanning pattern, corresponding to 300, 600, 1000, 5000, and 10,000 segments or pixels per second, respectively. For the same throughputs of pixels per second and for a scanning speed of 100 Hz, the energy distribution would be determined by, respectively, 3, 6, 10, 15, and 100 segments or pixels of the scanning pattern. In general, it is preferred to use at least six segments and / or pixels, i.e., the scanning pattern can comprise, for example, two rows of three segments each, each segment having a power state associated with it.Obviously, when switching between different power states, there may be transition periods during which the power of the laser beam differs from the power determined by the previous power state and the new power state, for example, the beam power may increase or decrease, so that there is a slope / decline in the power curve as the laser beam is scanned along the scan pattern, transitioning from one segment to the next.

[0024] This approach, i.e., changing the beam power at different segments or pixels of the scanning pattern, provides high flexibility in energy distribution and makes it easy to adjust and dynamically modify the energy distribution to avoid overheating, for example, of the edges of oil lubrication wipers. The segment- and / or pixel-based approach also makes it easy to find suitable energy distribution patterns through trial-and-error testing, in which the power states assigned to the different segments are adjusted until a suitable heating pattern is achieved. Switching between different power states can occur at high speed when adequate lasers are used, such as commercially available fiber lasers.Fiber lasers may be more expensive than other available lasers, but may be advantageous due to the reduced operating time for controlled switching between, for example, an "ON" and "OFF" state or between other power states / power levels. The on / off or off / on switching times of such lasers may be less than 1 ms, such as 0.1 ms or less. In some embodiments of the invention, the scanning pattern may comprise a plurality of segments, each of the segments having one of the available power states associated with it at a given instant. The power state associated with at least one of the segments may be different during heating of the less heat-sensitive sub-region than during heating of the more heat-sensitive sub-region, which includes the region adjacent to an oil lubrication hole.This means that the energy distribution can be dynamically adjusted by adjusting it in specific segments or all segments, for example when the effective laser spot approaches an oil lubrication hole.

[0025] Alternatively or additionally, the energy distribution can be further adjusted by adjusting the scanning speed while scanning the laser spot along the scanning pattern. For a given laser beam power, a higher speed means less energy is applied, and vice versa.

[0026] In some embodiments of the invention, scanning is performed at a scanning speed sufficiently high such that temperature fluctuations at points within the effective laser spot have an amplitude of less than 200°C, preferably less than 150°C, preferably less than 130°C, and more preferably less than 50°C between a local maximum and a local minimum of the temperature. In this context, the amplitude of the fluctuations refers to the amplitude of the repeated variations between local maxima and minima of the temperature curve, excluding the initial baseline heating to a maximum temperature at the leading edge of the effective laser spot and the subsequent cooling to a lower temperature at the trailing edge of the effective laser spot.For proper hardening, it is desirable that the metal quickly reaches a sufficiently high temperature and that the metal subsequently remains at the sufficiently high temperature for a reasonable period of time without significant fluctuations in temperature, as such fluctuations can have a negative impact on the quality of the hardening. Scanning speeds greater than 10, 25, 50, 75, 100, 150, 200, or 300 Hz (i.e., repetitions of the scanning pattern per second) may be suitable to prevent the temperature of the heated spot from dropping too much before the spot is reheated by the laser beam during the next scan cycle. Adequate hardening requires certain minimum temperatures, and if desired hardening depths are to be achieved quickly, high temperatures are preferred. However, excessive temperatures can negatively impact quality due, for example, to grain size growth.Thus, a compromise temperature must be found, and deviations from this temperature should be as small as possible. Thus, a high sampling rate, essentially cycles per second, may be preferable to reduce the amplitude of temperature fluctuations or fluctuations.

[0027] In some embodiments of the invention, the energy distribution in the effective laser spot is such that more energy is applied towards the ends of the effective laser spot in the first direction than towards the center of the effective laser spot in the first direction. It has been found that, due to the way in which thermal energy is absorbed and distributed in the crankshaft, applying more energy towards the lateral ends of the effective laser spot is helpful in obtaining a substantially uniform thickness of the hardened layer, i.e., a substantially rectangular cross-section rather than a cross-section in which the hardened layer is very thin towards the lateral ends and gradually increases, following a curve, towards the center. However, care should be taken to avoid overheating of the undercuts or grooves at the ends of the journal.

[0028] In some embodiments of the invention, the energy distribution exhibits a higher energy density at a front region or leading edge of the effective laser spot than at a rear region or trailing edge of the effective laser spot, such that an area scanned by the effective laser spot first receives laser radiation with a higher average power and subsequently receives laser radiation with a lower average power. This increases efficiency in that a suitable temperature for curing is quickly reached, thus reducing the time during which the effective laser spot must be applied to a specific area to achieve a required cure depth. Thus, it takes less time to complete the curing of, for example, the surface of a stud.

[0029] In some embodiments of the invention, the method comprises the step of applying the effective laser spot to the surface area on both sides of an oil lubrication hole in the first direction, wherein the oil lubrication hole extends obliquely inward such that it extends not under a first of the sides, but under a second of the sides, wherein the effective laser spot is configured to apply more energy to the first of the sides than to the second of the sides. Due to the presence of the oil lubrication hole under the second of the sides, the heat sink effect is lower on this side. Therefore, less energy should preferably be applied there than on the other side, where the absence of such an oil lubrication hole ensures better heat dissipation. In this way, the use of thermal energy is optimized and the risk of overheating is minimized.That is, according to these embodiments of the invention, not only the surface to be hardened is taken into account, but also the structure below the surface with respect to the oil lubrication holes.

[0030] In some embodiments of the invention, the effective laser spot has a first shape in the less heat-sensitive sub-region and is configured to have a substantially U-shape when approaching an oil lubrication hole and a substantially inverted U-shape when leaving the oil lubrication hole, or vice versa, and wherein the first shape is optionally a substantially rectangular or triangular shape. The terms "U" and "inverted U" refer to the situation when the oil lubrication hole is approached "from above." In principle, a substantially rectangular, trapezoidal, or triangular effective laser spot, which is suitable for providing fairly homogeneous heating on the surface of the pin, may not be suitable for heating around the oil lubrication hole.Therefore, the effective laser spot can be given a substantially "U" shape (including a "V" shape or similar) to receive the oil lubrication hole without substantially directly heating it or its edges, and can then be reversed to allow the oil lubrication hole to exit without directly heating the oil lubrication hole or its edges by the effective laser spot. The change in the shape of the effective laser spot can be achieved by modifying the shape of the scanning pattern and / or by changing the power state associated with one or more portions or segments of the scanning pattern.For example, when using a scanning pattern having a plurality of lines formed by a plurality of segments, a "U" shaped effective laser spot can be obtained by changing the power state associated with one or more of the segments in the central region of one or more lines, for example, by assigning an off state to the segments or by assigning the segments a power state corresponding to a low power level of the laser beam.

[0031] A further aspect of the invention relates to the method of laser hardening a surface of a journal of a crankshaft, wherein the journal has a surface region to be hardened, wherein the surface region extends in a first direction parallel to the rotational axis of the crankshaft, and in a second direction corresponding to a circumferential direction of the journal, wherein the surface region has at least one more heat-sensitive sub-region and at least one less heat-sensitive sub-region, wherein at least one heat-sensitive sub-region includes a region at an oil lubrication hole, the method comprising: Projecting a laser beam from a laser source onto the surface area; Generating a relative movement between the surface of the crankshaft and the laser source in the circumferential direction so as to successively project the laser beam onto different parts of the surface area in the circumferential direction, so as to harden a circumferential segment of the surface area to be hardened; and translating the laser beam in the first direction so as to increase the extent of the circumferential segment in the first direction until hardening of the surface area to be hardened is completed.

[0032] The method includes adjusting the manner in which energy is applied to the crankshaft by the laser beam in synchronization with the relative movement between the laser source and the surface of the crankshaft so as to apply less energy with respect to the more heat-sensitive sub-region, including a region adjacent to an oil lubrication hole, than in the less heat-sensitive sub-region, so as to avoid overheating of the region adjacent to an oil lubrication hole.

[0033] According to this aspect of the invention, the hardening of the surface region is carried out such that the hardening first occurs at one end of the surface region in the first direction and subsequently extends toward the other end of the surface region to be hardened until the entire surface region has been hardened. An advantage of the method is that at the end of the hardening, there is no overlap with an already hardened region. This reduces the risk of problems associated with repeated heating and excessive tempering of an already hardened region.

[0034] In some embodiments of the invention, the method comprises the step of creating a relative movement between the surface of the crankshaft and the laser source in the circumferential direction by rotating the crankshaft at a high speed, such as at a speed greater than 3000 rpm or 6000 rpm. This can help to avoid significant fluctuations in temperature within the area currently undergoing a hardening process.

[0035] In some embodiments of the invention, the method comprises the step of simultaneously applying more than one laser beam to the surface region so as to simultaneously heat, in terms of effective laser spots, a plurality of sections or sectors in the circumferential direction of a circumferential segment of the journal. For example, two laser beams from opposite sides of the journal can illuminate and thus heat two sections or sectors, each up to 180° of a circumferential or annular segment of the journal. This requires a lower rotational speed of the crankshaft to prevent significant temperature fluctuations within the heated region compared to the case where only one laser beam is used to heat only one such reaction or sector.

[0036] In some embodiments of the invention, the method comprises the step of applying energy to heat the surface area on both sides of an oil lubrication hole in the first direction, the oil lubrication hole extending inwardly in an oblique manner such that it extends not under a first of the sides but under a second of the sides, the method comprising applying more energy to the first of the sides than to the second of the sides. This optimizes the use of energy and minimizes the risk of overheating, as explained above.

[0037] In some embodiments of the invention, the method comprises the step of providing movement of the effective laser spot in the circumferential direction of the journal (the movement of the laser beam and / or the crankshaft, for example by rotating the crankshaft about its longitudinal axis) at a first speed so as to repeatedly heat a circumferential portion of the journal, and moving the effective laser spot in the first direction at a second speed which is lower than the first speed so as to heat new circumferential portions while allowing the previously heated circumferential portions to cool, so as to provide self-hardening to progressively increase the size of a hardened circumferential segment.That is, by the rapid relative movement between the effective laser spot and the surface of the pin in the circumferential direction, an annular segment of the pin can be heated to a desired hardening temperature and maintained at this temperature for a sufficiently long time without excessive fluctuations in temperature to ensure hardening, and due to the movement in the first direction, the hardened segment is output in the first direction until the hardening process of the substantially entire surface of the pin is completed.

[0038] In some embodiments of the invention, the effective laser spot is projected in an off-center manner. This can help make the laser spot larger, which is sometimes necessary to better distribute heat. This approach can also be useful because a leading edge of the laser spot can have a higher power density than a trailing edge due to different angles of incidence of the laser beam on the surface at the leading and trailing edges of the laser spot. As explained here, this can shorten the heating time required for the surface to reach the desired temperature. This approach can be used, for example, in combination with fixed optics that provide a substantially square or rectangular laser spot. Offsetting the laser beam laterally also has the advantage of reducing the risk of damage or defects due to print reflections.

[0039] A further aspect of the invention relates to a method for laser hardening a surface of a workpiece, wherein the workpiece comprises at least one surface region to be hardened, wherein the surface region comprises at least one more heat-sensitive sub-region and at least one less heat-sensitive sub-region, the method comprising: Projecting a laser beam from a laser source onto the surface area to create a laser spot on the area; Creating a relative movement between the surface of the workpiece and the laser source, thereby enabling the laser spot to be projected successively onto different parts of the surface area; during the relative movement, repeatedly scanning the laser beam over the respective part of the surface area in two dimensions so as to generate a two-dimensional equivalent or virtual effective laser spot on the surface area, wherein the effective laser spot has an energy distribution; wherein the energy distribution is designed such that it is different in a more heat-sensitive sub-area than in a less heat-sensitive sub-area in order to prevent overheating of the more heat-sensitive sub-area.

[0040] In some embodiments of the invention, the method comprises scanning the laser beam along a scanning pattern within the effective laser spot and modifying the power of the laser beam along the scanning pattern to obtain an energy distribution, optionally by switching the laser beam on and off along the scanning pattern.

[0041] In some embodiments of the invention, the energy distribution is controlled by selectively adjusting the power of the laser beam during the scanning process of the laser spot along the scanning pattern so as to place the laser beam into one of a plurality of available power states at least 300 times per second, preferably at least 600 times per second, more preferably at least 1000 times per second, more preferably at least 5000 times per second, and even more preferably 100,000 times per second. For example, the scanning pattern may comprise a plurality of segments, wherein each segment is assigned one of the available power states, and the power state assigned to at least one of the segments may be selected such that it is different in the less heat-sensitive sub-region than in the more heat-sensitive sub-region.This means that the power states assigned to one, some or more of the segments can be dynamically modified during the process to avoid overheating, for example, the edges of the oil lubrication holes or excessive repeated heating of an already hardened part of a journal, etc.

[0042] As explained above, the term "power state" refers to a state in which the laser beam has a predetermined average power, such as "on" or "off," or a power level between maximum and 0 (or close to 0). The term "available" refers to the fact that the power states can be achieved with the laser equipment used. The term "shift to" does not imply that an actual change does not have to occur that many times per second, but indicates that the laser is arranged in such a way that it is capable of changing the power state whenever appropriate, for example, when following commands provided by a control system. This allows segmentation or "pixelation" of the energy distribution to be achieved with 300, 600, 1000, 5000, or 10,000 segments or pixels per second.For example, 300 segments per second can form a scan pattern with six (6) segments at a scan sequence of 50 Hz. As explained above, when switching between different power states, there are transition periods during which the laser beam power differs from the power determined by the previous power state and the new power state. For example, the beam power may increase or decrease, resulting in a slope / decline in the power curve as the transition from one segment to the next occurs while the laser beam is scanned along the scan pattern.

[0043] The greater the laser's ability to switch between different power states, the greater the number of segments or pixels that can be used to generate the scan pattern for a given scan sequence. For example, in the case of a laser source capable of switching between power levels at a rate of 1,000 times per second, a 100 Hz scan sequence can be used for a scan pattern with ten (10) segments, each of which is assigned a desired power state and can be adjusted during operation to prevent overheating of heat-sensitive parts, such as the edges of a crankshaft's oil lubrication holes.

[0044] In some embodiments of the invention, the method comprises the step of using a different scanning pattern for the laser beam within the effective laser spot in the more heat-sensitive sub-region compared to the less heat-sensitive sub-region.

[0045] In some embodiments of the invention, the method comprises the step of adjusting the energy distribution by adjusting the scanning speed so that it is different in at least a portion of the effective laser spot in the more heat-sensitive sub-region compared to the less heat-sensitive sub-region.

[0046] In some embodiments of the invention, the effective laser spot comprises a front region with an energy distribution and density selected to heat a surface region of the workpiece to a hardening temperature, a middle region with an energy distribution and density (such as a very low energy density, such as 0 power or close to 0 power) selected to enable cooling of a heated surface region for quenching, and a rear region with an energy distribution and density selected to heat the quenched portion to produce tempering thereof. Generally, many workpieces, such as crankshafts, require tempering in addition to hardening to reduce hardness, improve ductility, and reduce brittleness.For tempering, the workpiece must be heated to a temperature that is generally lower than the temperature used for hardening. If a workpiece has been hardened using a laser treatment, tempering can be done in a combustion chamber or furnace, but it is also possible to temper it by applying a laser treatment similar to that used for hardening, but with a different energy density and / or distribution. In the case of a crankshaft, for example, tempering can take place by applying a tempering cycle after the hardening cycle. For example, after hardening over 360° of a journal, the effective laser spot can be moved around and along the journal again, this time to temper it. However, it is also possible to provide hardening and tempering in the same cycle or process, which includes an effective laser spot. a front region for heating the surface of the workpiece to a desired hardening temperature and for maintaining the surface at that temperature for a sufficient time to achieve the desired hardening depth; an intermediate region with a low energy density, such as an energy or power density of essentially 0 W / cm 2to allow the heated area to cool to produce quenching or self-quenching, and a rear area with an energy distribution and density to reheat the quenched area to the extent necessary for the desired tempering. Thus, to produce both quenching and tempering, it may be sufficient to sweep the effective laser spot over the previously treated surface, for example, in the case of the surface of a crankshaft journal, by rotating the crankshaft once around its rotational axis.

[0047] In some embodiments of the invention, the effective laser spot is established by repeatedly scanning the laser beam across the workpiece following a pattern comprising a plurality of lines, such as straight and curved lines, each of the plurality of lines comprising a plurality of segments or pixels, the method comprising assigning a predetermined laser beam power value to each of the segments so as to selectively adjust the output power of the laser beam to a different level among some of the segments compared to others of the segments. Assigning the laser beam power to segments may include specifying that the laser beam should be "on" for selected ones of the segments and "off" for others of the segments, which may be achieved by turning the laser on and off during the scan. Thus, a pixelated energy distribution is easily achieved.This approach can be useful to provide a desired energy distribution that can be easily varied as the effective laser spot sweeps along the surface to be heated, for example, by rotating the workpiece about an axis.

[0048] In some embodiments of the invention, the scanning frequency is at least 50 Hz (such that the laser beam is controlled to complete the virtual laser spot at least 50 times per second), and preferably at least 100 Hz, and the plurality of lines comprises at least two lines, preferably at least three lines, more preferably at least four lines, such as about five to ten lines, and each line comprises at least three segments, preferably at least five segments, and more preferably at least ten segments, such as about ten to twenty segments. This type of arrangement may be suitable for establishing a desired energy distribution, with sufficient detail and at a sufficient frequency so as to avoid significant temperature variations of a segment within the scanning pattern during a scanning cycle. The use of lasers, such as fiber lasers, which enable rapid on- and off-axis scanning, may be advantageous.Allowing switching off makes it possible to achieve a large number of segments or pixels even at relatively high sampling frequencies, such as sampling frequencies above 50 Hz. Each segment can have a beam power state associated with it, indicating the intended power of the laser beam during that segment or part of it. The power states associated with the segments can be dynamically modified during the curing process, for example, to prevent overheating of more heat-sensitive sub-areas. This means that by adjusting the power states associated with the segments, the energy distribution of the effective laser spot can be adjusted.

[0049] In the various aspects of the invention described above, which comprise scanning the laser beam or laser spot along or across a region of the workpiece, this scanning can be carried out such that the laser spot repeatedly follows a scanning pattern comprising a plurality of segments, wherein at least one parameter value influencing the two-dimensional energy distribution is associated with each of the segments, for example stored in a memory of a control system, so as to be used to adapt the operation with respect to the respective segment each time the laser spot is moved along this segment.This at least one parameter value can be dynamically adjusted during the operation so that the at least one parameter value for at least one of the segments is different when the effective laser spot heats the more heat-sensitive sub-region than when it heats the less heat-sensitive sub-region. For example, different parameter values (or combinations of parameter values) can be stored in different memory locations for a given segment, and the parameter values can be retrieved from one memory location or another depending on the sub-region being heated. However, this is only an example, and other implementations are within the scope of the invention. The use of a segmented scanning pattern has proven beneficial in making it easier to find and implement an energy distribution tailored to the specific design of a crankshaft.By adjusting one or more parameters that influence the two-dimensional energy distribution, it is easy to modify the energy distribution, for example, to apply less power / energy to more heat-sensitive parts of the workpiece, such as the area around the edges of a crankshaft's oil lubrication hole. Thus, by assigning different values to specific parameters for each segment, an operator can define different energy distributions. By switching between different energy distributions during the hardening process of a part of a workpiece, such as the surface of a crankshaft journal, adequate hardening can be achieved while avoiding local overheating of heat-sensitive parts.Using a segmented scanning pattern and assigning parameter values per segment makes it easy to find suitable values, for example, with a few trial-and-error tests. For example, to account for an oil lubrication hole, the values assigned to specific segments can be selected to reduce the energy applied adjacent to the oil lubrication holes when the effective laser spot arrives at the corresponding sub-areas of the workpiece.

[0050] The parameter values may indicate at least one of the scanning speed, laser spot size, laser beam power, power distribution within the laser beam, length of the corresponding segment, and orientation of the corresponding segment. In many embodiments of the invention, the laser beam power and / or the scanning speed may be preferred parameters. The choice of parameter may depend on factors such as the speed at which the laser beam can be switched between different power levels, such as on / off or between different intermediate power levels, and the extent to which the scanning system allows for rapid and controlled changes in scanning speed on a segment-by-segment basis.When using lasers that allow rapid and controlled changes in output power, the power of the laser beam can advantageously be used as at least one of the parameters that determines the energy distribution.

[0051] The method may include, for each segment, the step of storing the corresponding at least one parameter value in a memory, wherein, for at least one segment, at least two different values are stored in the memory: a first to be used when heating the less heat-sensitive sub-region, and a second to be applied when heating the more heat-sensitive sub-region. Thus, the parameter values corresponding to different two-dimensional energy distributions may be stored in different memory locations, and depending on whether a more heat-sensitive or less heat-sensitive sub-region is being heated, the control system utilizes the parameter values from one memory location or the other.Thus, when adapting the system and method to a new type of crankshaft, the operator can determine a set of different energy distributions by specifying the scanning pattern and parameter values. For example, a first energy distribution is determined to be used during the main heating of a crankshaft journal, a second energy distribution to be used when the effective laser spot approaches the sub-area of an oil lubrication hole, and a third energy distribution to be used when the effective laser spot leaves the sub-area of the oil lubrication hole. The two-dimensional energy distribution patterns can thus be easily adapted to account for, for example, the width of the journal and the size and / or location of an oil lubrication hole.Scanning may, for example, be performed at an average speed of at least 300 segments per second, preferably at least 600 segments per second, more preferably at least 1000 segments per second, more preferably at least 5000 segments per second, and even more preferably at least 10,000 segments per second. A high scanning speed may be preferred in order to repeat the scanning pattern at a high frequency in order to avoid significant temperature fluctuations between each scanning cycle in the heated region and at the same time to achieve a sufficiently large number of segments to provide flexibility in the two-dimensional energy distribution. For example, with a scanning speed of 300 segments per second, a scanning pattern with six segments or pixels can be repeated at a frequency of 50 Hz.A high number of segments or pixels can be useful to maximize the possibilities of adapting the energy distribution to the properties of the surface to be cured, while a high frequency of repetition of the scanning pattern reduces the risk of unwanted temperature fluctuations within the heated area between each scanning cycle.

[0052] In some embodiments of the aspects of the invention described above, the step of reducing the energy density at a leading edge of the effective laser spot is included when the effective laser spot reaches a previously hardened portion of the surface area, such as a previously hardened portion of a journal of the hardened crankshaft, by shifting the effective laser spot around the journal in a circumferential direction. This can prevent undesired heating of an already heated and hardened portion of the journal. In some embodiments of the invention, the power / energy density of the leading edge of the effective laser spot is only reduced, but the effective laser spot continues its trajectory, for example, around the journal in the circumferential direction, so as to reheat the hardened portion to some extent for the purpose of tempering it.In other embodiments of the invention, the method comprises the step of, when the effective laser spot arrives at a previously hardened portion of the surface area, such as a previously hardened portion of a crankshaft journal that has been hardened by circumferentially translating the effective laser spot around the journal, interrupting the movement of the effective laser spot at a leading portion of the effective laser spot while the trailing portion of the effective laser spot continues its circumferential movement, thereby progressively reducing the size of the effective laser spot in the circumferential direction until the effective laser spot disappears. That is, the effective laser spot essentially stops when it arrives at the previously hardened portion, that is, the leading edge stops, for example, and the trailing edge catches up with the leading edge and completes the hardening cycle.

[0053] In both cases, the implementation of the method can be substantially facilitated if the effective laser spot is composed of segments, such as the segments of a scanning pattern. The reduction or elimination of the effective laser spot starting at its leading edge can be achieved by adjusting the energy density at the segments, such as by reducing the beam power and / or increasing the scanning speed, and / or by simply eliminating or rearranging segments. Thus, the segment approach, in combination with the use of two-dimensional scanning of the laser beam to generate the effective laser spot, provides flexibility and makes it easy for the skilled person to manage the arrival of the effective laser spot at the previously hardened wedge of the path tracks, for example, in the case of circumferential laser hardening of crankshaft journals.

[0054] A further aspect relates to a method for laser hardening a surface of a workpiece, such as a medium carbon steel workpiece, for example a crankshaft; reference to "a surface" does not imply that the entire surface needs to be hardened; in the case of a crankshaft, for example, it may be sufficient that parts of the surface, for example one or more journals and / or the walls adjacent to the journals, need to be hardened.

[0055] The workpiece comprises at least one surface area to be hardened (for example, the surface of one or more main journals and / or one or more test journals of the crankshaft and / or side walls of the crankshaft), the surface area having at least one or more more heat-sensitive sub-areas (for example, in the case of a crankshaft, the area immediately around an oil lubrication hole and / or the area of the edge of an undercut groove; here the absence of material reduces the heat sink capacity and implies an increased risk of overheating);Furthermore, the sharp edges are more likely to be damaged by overheating than the smooth and uniform surface of the rectangular journal) and at least one less heat-sensitive sub-area (for example, in the case of a crankshaft, the part of the journal surface further away from the oil lubrication hole and / or the undercut groove, the absence of edges and cavities implying a reduced risk of overheating).

[0056] The procedure includes: Projecting a laser beam from a laser source onto the surface area to create a laser spot on the area; Generating a relative movement between the surface of the workpiece and the laser source (for example, by rotating the workpiece about an X-axis and / or by translating the workpiece and / or the laser source along a Y- and / or Z-axis perpendicular to the X-axis), thereby enabling the laser spot to be projected successively onto different parts of the surface area (that is, depending on the relative position between the workpiece and the laser source along, for example, the X-, Y- and Z-axes, whenever the laser source in combination with scanning means can direct the laser spot, for example, onto a specific part or section of the surface area, and depending on whether the scanning means provide for a one-dimensional or two-dimensional movement on a line of the area, with a thickness corresponding to the diameter, length or width of the laser spot,or to, for example, substantially a rectangular portion of the area); during the relative movement, scanning the laser beam over the respective part of the area. The scanning can be performed in only one dimension, for example parallel to the axis of rotation of the workpiece and / or perpendicular to the direction of movement of the surface of the workpiece with respect to the position of the laser source, or in two dimensions, so that a path or pattern is followed, such as a rectangular pattern, an oval pattern, a triangular pattern, a trapezoidal pattern, a hexagonal pattern, an octagonal pattern, etc., or an area outlined by such a pattern is sensed, for example by performing a meandering or triangular scan, back and forth along and / or across the part enables scanning of the laser beam along a plurality of lines, such as substantially parallel lines.The term “scanning the laser beam” should be interpreted to mean that the laser beam itself is shifted using some kind of optical scanning means or similar, such as one or more scanner mirrors.

[0057] Scanning is performed such that the laser spot follows a scanning pattern and / or path on the surface area.

[0058] According to this aspect of the invention, at least one of (i) a scanning speed; and / or (ii) a laser beam power; and / or (iii) a laser spot size different in one part of the scan pattern than in another part of the scan pattern so as to avoid (or reduce the risk of) overheating of the workpiece in the more heat-sensitive sub-region.

[0059] Thus, in the more heat-sensitive sub-region, the scanning speed may be higher, and / or the laser beam power may be reduced, and / or the laser spot area may be larger—something that can be achieved, for example, by moving a focus lens—than in the less heat-sensitive sub-region, so as to reduce the amount of energy per unit of surface area transferred in the more heat-sensitive region compared to the less heat-sensitive region.

[0060] In some embodiments of the invention, the scanning pattern comprises a plurality of segments and each of the segments is associated (i) a scanning speed; and / or (ii) a laser beam power; and / or (iii) a laser spot size;wherein at least one of the scanning speed, the laser beam power, and the laser spot size is selected differently with respect to at least one of the segments compared to at least one other of the segments.

[0061] The segments can be straight or curved and can form a polygon or other geometric figure. They can form a closed curve, which the laser spot follows during the scanning process, or an open curve, which the laser spot can repeatedly follow in both directions. The segments can be short and can even include points where the laser beam can be stopped for a specific period of time. Thus, by assigning at least one value of a parameter that influences the energy transfer to the surface during the scanning process to each segment, an adequate distribution of heat transfer and heating can be achieved.For example, in a computer-controlled scanning system, this approach makes it easy for the user to try out different energy transfer profiles along the scanning pattern and, through such trial and error, arrive at a suitable profile for a specific product, such as a specific crankshaft. Furthermore, this approach can be easily implemented in a computer-controlled simulation system, allowing one to experiment with different energy transfer profiles, modify the scanning speed, laser beam power, and / or laser spot size for one or more segments, and even modify the geometric layout of the scanning pattern until adequate heating of the workpiece is achieved.Computer input means may be provided that allow variation of the scanning pattern (for example, by adjusting the length of the segments), and / or the scanning speed, and / or the laser beam power, and / or the laser spot size. Of course, additional parameters may also be included.

[0062] For example, the scanning speed can be selected to be higher in a segment located closer to a more heat-sensitive sub-area than in two adjacent segments located farther from the heat-sensitive sub-area. In the case of a crankshaft, for example, the scanning speed can be selected to be higher for one or two segments that actually cross the oil lubrication hole(s) at one stage of the process than for adjacent segments. Using different scanning speeds for different segments along the path followed by the laser spot has the advantage of being easily implemented in commercially available scanner devices.

[0063] In some embodiments of the invention, the laser power is selected such that it is lower in a segment located closer to a more heat-sensitive sub-region than in two adjacent segments located farther from the heat-sensitive sub-region. In the case of a crankshaft, for one or two segments that cross the oil lubrication holes at a stage of the process—or are crossed by the oil lubrication holes—the scanning speed can be selected to be higher and / or the laser beam power lower than for the adjacent segments.

[0064] In some embodiments of the invention, the laser spot is selected to cover a larger area in a segment closer to a more heat-sensitive sub-region than in two adjacent segments farther from the more heat-sensitive sub-region. Thus, by "defocusing" during a certain portion of the path followed by the laser beam, the power concentration per unit surface area is reduced, which is useful in preventing overheating of more heat-sensitive regions, such as those corresponding to the oil lubrication holes of crankshafts.

[0065] In some embodiments of this aspect of the invention, (i) the scanning speed; and / or (ii) the laser beam power; and / or (iii) the laser spot size associated with one or more of the segments is modified at least once while the workpiece surface moves relative to the laser source, for example, each time the pattern or segment reaches or leaves a more heat-sensitive sub-area. In this way, for example, the scanning speed and / or the laser beam power and / or the laser spot size can be modified corresponding to one or more segments of the pattern during the process, for example, when one or more of the segments arrive at or near a more heat-sensitive sub-area, such as the oil lubrication holes of a crankshaft, and also when the segment(s) leaves the more heat-sensitive sub-area. In this way, the heat treatment can be easily optimized for surfaces of the workpiece in adjustment with their heat sensitivity.

[0066] This aspect of the invention may further comprise the step of programming an electronic control means, such as a personal computer, a PLC or the like, to control the laser beam by assigning to each of the segments: (i) at least one scanning speed; and / or (ii) at least one laser beam power; and / or (iii) at least one laser spot size.

[0067] In some embodiments of the invention, the scanning pattern has a geometric shape (e.g., formed by the segments), wherein the geometric shape of the scanning pattern is modified at least once while the surface of the workpiece moves relative to the laser source. For example, at one stage of the process, such as during rotation of the workpiece, e.g., when an oil lubrication hole approaches the scanned portion of the surface area, one or more segments may simply be omitted to avoid overheating a more heat-sensitive sub-area, or the scanning pattern may be modified to reduce the power density in one or more areas.

[0068] A further aspect of the invention relates to the method of laser hardening a surface of a workpiece (such as a medium carbon steel workpiece, for example a crankshaft; reference to "a surface" does not mean that the entire surface has to be hardened; for example, in the case of a crankshaft, it may be sufficient that part of the surface, for example the surfaces of one or more journals and / or the walls adjacent to the journals, is hardened), the workpiece having at least one surface area to be hardened (for example the surface of one or more main journals and / or one or more crankpins of the crankshaft and / or the wall surfaces of the crankshaft).The surface area comprises at least a more heat-sensitive sub-area (for example, in the case of a crankshaft, the area immediately around an oil lubrication hole and / or the area near the edge of an undercut groove; here, the absence of material reduces the heat sink capacity and implies an increased risk of overheating; moreover, the sharp edges can be more easily damaged during overheating than a smooth and uniform surface of the rest of the journal) and a less heat-sensitive surface area (for example, in the case of a crankshaft, the part of the surface of the journal that is further away from the oil lubrication hole and / or the undercut groove, where the absence of edges and cavities implies a reduced risk of overheating).

[0069] The procedure includes: Projecting a laser beam from a laser source onto the laser area to create a laser spot on the laser area; Generating a relative movement between the surface of the workpiece and the laser source (for example, by rotating the workpiece about an X-axis and / or translating the workpiece and / or the laser source along a Y- and / or Z-axis, perpendicular to the X-axis), whereby the laser spot is enabled to be subsequently projected onto different parts of the surface area (that is, depending on the relative position between the workpiece and the laser source in accordance with, for example, the X-, Y- and Z-axis, whereby the laser source can at any time, in combination with a scanner device, direct the laser spot, for example, onto a specific part or section of the area, and depending on whether the scanner device provides for movement in one dimension or in two dimensions on a line of the area with a thickness,which corresponds to the diameter of the length or width of the laser spot or, for example, to a substantially rectangular section of the area; during the relative movement, scanning the laser beam across the respective part of the surface area (the scanning can be carried out in only one dimension, for example parallel to the axis of rotation of the workpiece, and / or perpendicular to the direction of movement of the surface of the workpiece with respect to the position of the laser source or in two dimensions, then following a pattern, such as a rectangular pattern, an oval pattern, a triangular pattern, a trapezoidal pattern, a hexagonal pattern, an octagonal pattern, etc.or filling an area outlined by such a pattern, for example by performing a meandering or triangular scanning back and forth along and / or across the area or by tracking a plurality of lines, such as a plurality of parallel lines; the term "scanning the laser beam" should be interpreted to mean translating the laser beam itself using some type of optical scanning device, such as one or more scanner mirrors). wherein the scanning is performed such that the laser spot follows a scanning pattern and / or path on the surface, the scanning pattern having a geometric configuration.

[0070] In accordance with this aspect of the invention, the geometric configuration of the scanning pattern is modified at least once during the relative movement between the surface region and the laser source. For example, the scanning pattern may comprise a plurality of segments, and one or more segments may simply be omitted to avoid overheating of a more heat-sensitive sub-region, or the pattern may be modified to reduce the power density in one or more areas. For example, in the case of a crankshaft, if one or more oil lubrication holes approach the area being scanned during the relative movement between the laser source and the surface of the workpiece, the scanning pattern may be adjusted, for example, by reducing the energy density of the path, i.e., by separating segments and / or by omitting one or more segments.For example, a segment can be omitted, changing an originally closed-curve scanning pattern to an open-curve scanning pattern, allowing the laser spot to trace the open curve back and forth; if the omitted segment corresponds to the position of the oil lubrication hole, it will not contribute to heating the edges of the oil lubrication hole.

[0071] Another aspect of the invention relates to a method of laser hardening a surface of a workpiece (such as a workpiece made of ferrous material, such as medium carbon steel, for example a crankshaft), the workpiece comprising at least one surface region to be hardened (for example, in the case of a crankshaft, the surface of one or more main journals and / or one or more crankpins of the crankshaft, and / or the main surfaces of the crankshaft), the surface region having at least one more heat-sensitive sub-region (for example, in the case of a crankshaft, the region immediately around an oil lubrication hole and / or the surface near the edge of an undercut groove; here, the absence of the material reduces the heat sink capacity and implies an increased risk of overheating);also, the sharp edges are more likely to be damaged by overheating than the smooth and uniform surface of the rest of the journal) and at least one less heat-sensitive sub-area (for example, the part of the journal surface further away from the oil lubrication hole and / or the undercut groove, the absence of edges and cavities implying a reduced risk of overheating).

[0072] The procedure includes: Projecting a laser beam from a laser source onto the surface area to thereby create a laser spot on the surface area; Generating a relative movement between the surface of the workpiece and the laser source (for example, by rotating the workpiece about an X-axis and / or translating the workpiece and / or the laser source along the Y- and / or Z-axis, perpendicular to the X-axis), thereby enabling the laser spot to be subsequently projected onto different parts of the surface area (that is, depending on the relative position between the workpiece and the laser source in accordance with, for example, the X-, Y- and Z-axis), whereby the laser source can at any time, in combination with a scanning device, direct the laser spot onto, for example, a specific part or section of the surface and, depending on whether the scanning device provides a one-dimensional or two-dimensional movement onto a line of the area with a thickness corresponding to the diameter of the length or width of the laser spot,or to, for example, a substantially rectangular portion of the area); during the relative movement, scanning the laser beam transversely to the respective part of the area (the scanning can be carried out in only one dimension, for example parallel to a rotation axis of the workpiece, or in two dimensions, thus following a pattern, such as a rectangular pattern, an oval pattern, a triangular pattern, a trapezoidal pattern, etc., or filling an area outlined by a pattern, for example by performing a meandering or triangular scan back and forth along and / or transversely to the area, or in that the laser beam can follow a pattern with a plurality of lines, such as parallel lines; the expression “scanning the laser beam” should be interpreted to mean that the laser beam itself is translated), and from use in some kind of optical scanning device, such as one or more scanner mirrors;In the case of an XYZ scanner, in addition to the possibility of moving the spot in the X and Y directions, a focusing lens is provided which can be adjusted in the Z direction by some type of drive device, thus enabling dynamic adjustment of the size of the laser spot; this allows both the positions of the spot and its size to be controlled and adjusted to optimize the manufacturing process); and modulating the laser beam.

[0073] In this setting, with this aspect of the invention, the laser beam is modulated differently when the laser spot is located in the more heat-sensitive sub-area than when it is located in the less heat-sensitive sub-area, thus preventing overheating of the respective area of the workpiece. In particular: A- The laser beam is modulated in its power (for example, so that its power is lower when the laser spot is in the more heat-sensitive sub-area than when the laser spot is in the less heat-sensitive sub-area; modulating the power may even involve temporarily reducing the power to 0 or close to 0); and / or B- The laser beam is modulated in its scanning speed (for example, so that the laser spot moves across the surface of the workpiece faster when the laser spot is in the more heat-sensitive sub-area than when the laser spot is in the less heat-sensitive area; modulating the scanning speed may even involve temporarily stopping the movement of the laser beam); and / or C- The laser beam is modulated in its scanning pattern so that the laser spot is subjected to a different scanning pattern in relation to the more heat-sensitive sub-area than in relation to the less heat-sensitive sub-area (thus, a scanning pattern can be selected for the more heat-sensitive sub-area which reduces the risk of overheating at, for example, the edges of the oil lubrication holes and / or the undercut grooves of a crankshaft); and / or D- The laser beam is modulated in its laser spot size so that the laser spot size is different (e.g. larger) in relation to the more heat-sensitive sub-area than in relation to the less heat-sensitive sub-area (for example, the spot size for the more heat-sensitive sub-area can be used to reduce heating at, for example, the edges of oil lubrication holes or the undercut grooves of a crankshaft. Increasing the spot size by, for example, defocusing the laser beam reduces the amount of power per unit of the surface area of the laser spot).

[0074] For example, in all these aspects of the invention, and in the case of heating the bearing surfaces of a crankshaft, i.e., the surfaces of the main journal and the crankpins, the laser beam can be focused on one of the journals, and the beam can then be scanned across the journal and / or across a portion of the journal. On the other hand, the relative movement between the laser light source and the surface of the crankshaft can scan the entire circumference of the crankshaft. Now, instead of using an optical device to generate, for example, a square or rectangular laser spot of substantial size, such as a laser spot with a width on the order of the width of the journal, a small spot can be used, which is then scanned across the journal.In this way, the modulation of the beam in terms of scanning speed, power, scanning pattern and / or laser spot size allows the heat treatment to be adapted to the specificities of different areas of the surface, for example, to the heat sensitivity of the regions, such as the oil lubrication holes and grooves in the case of a crankshaft.Thus, instead of treating all areas of the surface in the same way by simply applying a large laser spot to the surface and moving the surface relative to the laser source, for example, by rotating the workpiece (which is apparently suggested by DE-10 2005 005 141-B3), a small spot can be used, and scanning and modulating can be carried out such that different parts of the surface receive different amounts of energy to achieve sufficient heating of all parts, while simultaneously avoiding overheating of certain parts. By modulating the beam, different parts of the surface can be treated differently. For example, the scanning pattern in the area near the oil lubrication holes can be modified to prevent the edges of the oil lubrication holes from overheating.Additionally, or alternatively, the beam intensity can be reduced and / or the speed increased and / or the size of the laser spot can be increased by defocusing or by adjusting the angle of incidence of the laser beam on the surface to prevent overheating. Thus, instead of homogeneously heating the entire surface area to be hardened, care can be taken to reduce the risk of overheating in areas such as the areas around the oil lubrication holes and / or the areas near the undercut grooves. In these areas, the absence of material reduces the heat flow away from the heated surface, implying a significantly increased risk of overheating; moreover, the sharp edges in these areas are much more likely to suffer damage from overheating than the smooth surfaces of the other parts of the journal.

[0075] Thus, by modifying one or more of these parameters, the risk of overheating can be reduced.

[0076] When utilizing one of the aspects of the invention discussed above, and particularly when an equivalent or virtual effective laser spot is generated by scanning a laser beam in one or two dimensions, one skilled in the art can utilize computer simulations and / or practical trial-and-error testing to determine modulation techniques suitable for each specific crankshaft design. Adapting the system to a new type of crankshaft thus requires only a change in the software, for example, by introducing new scanning speed profiles, new laser light intensity profiles, scanning patterns, and / or spot sizes, for example, by assigning different values of these parameters to different segments of a scanning pattern.This makes it easy to conduct trial-and-error simulations and dynamically modify the scanning pattern and related parameters during trial-and-error simulations and also during real-time operation (e.g., using a pyrometer and associated software and a suitable feedback-based controller) to achieve adequate performance. Indeed, the beam modulation or energy distribution approach for a particular crankshaft can often be easily adapted to a particular crankshaft type by taking into account changes in the dimensions and positions of, for example, the oil lubrication holes. Thus, this technique is much more flexible than one based on induction heating. When using embodiments of the invention, adaptation may essentially involve software adaptation rather than hardware adaptation.

[0077] For example, each of the modulation alternatives A, B, C, and D can be used individually, or A can be used together with B or C, or B can be used with C, or A, B, and C can be used together, and D can optionally be used with any of the above combinations. Thus, the various aspects of the invention described above provide an extremely flexible platform for adapting laser heating of the workpiece to different workpiece designs, significantly reducing the need to adapt hardware; this implies another important advantage over inductive heating of workpieces such as crankshafts.For example, the choice of option(s) from A, B, C and D may be made based on practical considerations, e.g., the costs associated with different types of lasers and scanning systems, the capacity to vary scanning speed and / or intensity of laser beam power, the capacity to vary scanning patterns - for example, depending on whether a uniaxial or biaxial scanning system is used, etc.

[0078] This modulation approach is not only useful for preventing overheating at the oil lubrication holes and at the grooves and undercuts, but can also be useful in the case of workpieces with respect to the overall circumference to be hardened, such as the circumference of the journals of a crankshaft: Once almost the entire 360° of the circumference has been subjected to heat treatment, the laser beam once again reaches an area that has already been hardened and this area should not be significantly heated again; by modulating the laser beam appropriately (in terms of speed, scanning pattern, power and / or spot size, and / or by adjusting the energy distribution within the effective laser spot, such as a virtual or equivalent laser spot), adequate heating can be achieved even in this boundary region between the first heated area of the circumference and the last heated area.

[0079] Another aspect of the invention relates to a method of laser hardening a surface of a workpiece (such as a workpiece made of a ferrous material, such as a medium carbon steel, for example, a crankshaft), wherein the workpiece has at least one surface area to be hardened (for example, the surface of one or more main journals and / or one or more crankpins of the crankshaft). The method comprises: Projecting a laser beam from a laser source onto the surface area to form a laser spot on the surface area; Generating a relative movement between the surface of the workpiece and the laser source (for example, by rotating the workpiece about an X-axis and / or translating the workpiece and / or the laser source along a Y- and / or Z-axis perpendicular to the X-axis), thereby allowing the laser spot to be projected successively onto different parts of the surface area (i.e., depending on the relative position between the workpiece and the laser source in accordance with, for example, the X-, Y- and Z-axes, the laser source can, at any time in combination with a scanner device, direct the laser spot, for example, onto a part or a portion of the area, and, depending on whether the scanner device provides one-dimensional or two-dimensional movement, onto a line of the area with the thickness of the laser spot or onto, for example, a substantial portion of the area); during the relative movement, scanning the laser beam transversely to the respective part of the area (wherein the scanning can be carried out in one dimension, for example parallel to the axis of rotation of the workpiece, or in two dimensions, thus following a pattern such as a rectangular pattern, an oval pattern, a triangular pattern, a trapezoidal pattern, etc., or by moving the laser beam within the boundaries of such a pattern, for example in a meandering manner filling such a pattern; the term "scanning the laser beam" should be interpreted to mean that the laser beam itself is translated using some kind of optical scanning device or the like, such as one or more scanning mirrors); wherein the heating is carried out such that a portion of the workpiece surface entering a laser beam-swept area first receives laser radiation with a higher average power and subsequently receives laser radiation with a lower average power. This can be achieved by using a scanning pattern with a front area with a higher scanning density and a rear area with a lower scanning density, so that the laser spot remains in the front area for a longer time per unit area than in the rear area, whereby the surface area to be treated first enters the front area and subsequently the rear area. The term "average power" should be understood as the average amount of power per surface area during an entire scanning cycle.Another way to achieve this goal is to project the laser beam at least partially off-center, so that the laser beam hits the surface at an angle of less than 90°. Offsetting the laser beam off-center also has the advantage of reducing the risk of damage or errors due to back reflections.

[0080] Another aspect of the invention relates to a method of laser hardening a surface of a part of a workpiece (such as a workpiece made of ferrous material, such as medium carbon steel, for example, a crankshaft) having a substantially circular cross-section (such as for the surface of a main journal or a crankpin of a crankshaft). The method comprises: Projecting a laser beam from a laser source onto the surface to create a laser spot on the surface; Creating a relative movement between the surface of a workpiece and the laser source (for example, by rotating the workpiece about an X-axis and / or translating the workpiece and / or the laser source along a Y- and / or Z-axis perpendicular to the X-axis), thereby allowing the laser spot to be projected sequentially onto different parts of the surface along the perimeter of the surface.

[0081] In accordance with this aspect of the invention, the laser beam is projected onto the surface in an off-center manner, i.e., the laser beam is not aligned with a line passing through the center of the circular cross-section. This can help make the laser spot larger, which is sometimes useful for better heat dissipation. Furthermore, this approach can be useful because a leading edge of the laser spot has a different power density than the trailing edge due to different angles of incidence of the laser beam on the surface at the leading and trailing edges of the laser spot. This approach can, for example, be used in combination with fixed optics, which provide a substantially square or rectangular laser spot. Furthermore, off-centering the laser beam has the advantage of reducing the risk of damage or feathering due to back reflections.

[0082] Another aspect of the invention relates to a method for laser hardening a surface of a part of a workpiece, the method comprising: Projecting a laser beam from a laser source onto the surface to create a laser spot on the surface; Creating a relative motion between the surface of the workpiece and the laser source, thereby allowing the laser spot to be projected sequentially onto different areas of the surface. The laser beam is projected onto the surface in a direction that is not perpendicular to the surface, preferably forming an angle of less than 70° with the surface, such as less than 60° or even less than 45°. This can help increase the size of these spots and thus reduce the amount of power per surface area, and for a given relative speed between the surface and the laser source, increases the interaction time between the laser spot and a given point on the surface. This can contribute to an increased depth of the hardened layer.

[0083] Another aspect of the invention relates to a method of laser hardening a surface of a workpiece (such as a medium carbon steel workpiece, e.g., a crankshaft). The method comprises: Projecting laser light from a laser source onto surface areas to be heated.

[0084] In accordance with this aspect of the invention, laser light is projected (simultaneously or subsequently or sequentially) onto a first surface region and onto a second surface region extending substantially perpendicular to the first surface region. The method comprises splitting a laser beam into a first laser beam component having an s-polarization and a second laser beam component having a p-polarization, and using the first laser beam component to heat the first surface region and using the second laser beam component to heat the second surface region. In this way, the relationship between power absorption and angular incidence, and the way in which this relationship depends on polarization, can be used to increase heating efficiency.

[0085] In all the aspects of the invention described above, the step of generating relative motion between the workpiece and the laser source may comprise rotating the workpiece about the rotational axis (which may be parallel to the so-called X-axis of the system) so that the laser light spot can cover the entire circumference of the surface area to be hardened. For example, a crankshaft may be rotated about a longitudinal axis passing through the center of the main journal.

[0086] Furthermore, the step of generating a relative movement between the workpiece and the laser source may comprise generating a relative movement in a first direction perpendicular to the rotation axis (e.g., parallel to an X-axis) and in a second direction perpendicular to the rotation axis (e.g., parallel to a Z-axis). In this way, the distance between the laser light source and the surface to be treated can be kept constant, even in the case of an eccentrically arranged object, such as the crankpins of the crankshaft, which rotate around the central axis of the main journals. If the main axis corresponds to the X-axis of the system, generating relative movement between the laser light source in two other directions, such as the Y-axis and Z-axis, can help ensure that the distance between the laser light source and the surface to be treated is kept constant. For example, movement in the first direction can be generated by moving the workpiece (e.g., horizontally), and movement in the second direction can be generated by moving the laser source (e.g., vertically). Furthermore, the laser source can optionally be movable parallel to the rotation axis. For example, the laser light source can subsequently be used to act on different journals of a crankshaft.

[0087] In many embodiments of the invention, the workpiece may be a crankshaft having a plurality of oil lubrication holes.

[0088] Another aspect of the invention relates to the method of laser hardening a surface of a crankshaft, wherein the crankshaft includes main journals, crankpins, and oil lubrication holes. The method comprises: Projecting a laser beam from a laser source onto a surface of a stud to be hardened to create a laser spot on a surface and Moving the surface relative to the laser source in which the crankshaft is rotated (for example, around an axis that may correspond to a center axis of the main journals).

[0089] In accordance with this aspect of the invention, during rotation of the crankshaft, the laser beam is scanned over at least a portion of the surface of the journal in accordance with a predetermined scanning pattern to heat the surface. The scanning is performed such that less energy is applied to more heat-sensitive sub-areas than to less heat-sensitive sub-areas of the surface. The term "predetermined" does not exclude the possibility of dynamically adjusting the scanning pattern during operation in a predetermined manner and / or in accordance with a control system based on feedback from some type of temperature sensor or temperature camera.

[0090] For example, scanning may be performed by maintaining the substantially constant power of the laser beam and adjusting the scanning speed and / or the scanning pattern (i.e., the pattern and path followed by the laser beam on the surface) so as to apply less energy to more heat-sensitive subregions than to less heat-sensitive subregions of the surface. In other aspects of the invention, scanning is performed by keeping the scanning pattern substantially constant and adjusting the scanning speed and / or the beam power so as to apply less energy to more heat-sensitive subregions than to less heat-sensitive subregions of the surface, for example, by dynamically adjusting the on / off state of the laser beam with respect to segments of the scanning pattern.In some embodiments of the invention, more heat-sensitive areas include those adjacent to oil lubrication holes and those adjacent to grooves at the axial ends of crankshaft journals.

[0091] In some embodiments of the invention, the scanning pattern comprises a plurality of segments, and a beam power state is associated with each of the segments to adjust the power of the laser beam with respect to each segment to a power level corresponding to the power state. The laser is arranged to change the power of the laser beam as required by the beam power states, so that the beam power at some of the segments will be different compared to other segments, as determined by the power states.The scanning of the laser spot along the scanning pattern preferably occurs at a rate of at least 300 segments per second, preferably at least 600 segments per second, more preferably at least 1000 segments per second, more preferably at least 5000 segments per second, and even more preferably at least 10,000 segments per second, and the scanning pattern is repeated at a frequency of at least 10 Hz, more preferably at least 50 Hz, and even more preferably at least 100 Hz. Thus, segmentation or pixelation of the scanning pattern can be achieved, which allows the power or energy distribution across the heated area to be adjusted in accordance with, for example, the thermal sensitivity of the scanned area, while at the same time the scanning pattern is repeated at a high frequency, thereby reducing temperature fluctuations within the area being heated.

[0092] In many embodiments of the invention, the laser source comprises a fiber laser, such as a fiber laser that requires approximately 100 µs or less to switch from an "on" state to an "off" state. Fiber lasers are typically more expensive than other types of lasers that produce beams with sufficient power for hardening purposes, such as diode lasers, and one skilled in the art may thus be reluctant to use fiber lasers for hardening workpieces such as crankshafts. However, fiber lasers allow for on / off switching instead and can thus be particularly useful for obtaining adequate energy distribution by switching the laser on and off while the laser beam follows a predetermined scanning pattern across an effective laser spot, thus distributing the energy along lines or within subregions or pixels of the equivalent laser spot.Fiber lasers also produce beams of high quality and relatively small diameter, so the focal length between the focused laser spot and the focal point of the beam can be large, which can be an advantage in the case of scanning, since the movements of the scanning mirrors or the like can be smaller, and also in the case of scanning the laser beam over the surface of complex objects, such as crankshafts, where the counterweights and walls can pose obstacles for laser emitters with short focal lengths.

[0093] Another aspect of the invention relates to a system for hardening at least a portion of the surface of a workpiece, the system comprising a laser source and means for generating relative movement between a surface of the workpiece and the laser source. In some embodiments of the invention, the laser source is provided with or connected to a scanning device for scanning the laser beam across a portion of the surface of the workpiece in one or two dimensions. The system further comprises an electronic control device, such as a computer, computer system, PLC, etc., for controlling the operation of the system.

[0094] In accordance with this aspect of the invention, the electronic control means for operating the system are arranged so as to carry out the method according to any of the aspects described above.

[0095] By modifying parameters such as the geometric configuration of the scanning pattern, i.e., the path of the pattern, and / or the scanning speed and / or the laser beam power and / or the laser spot size and / or even parameters such as the wavelength or the angle of incidence of the laser beam on the surface to be cured, the system provides flexibility for optimizing heating along and across the surface to be cured. Trial-and-error experiments can be performed on test workpieces or using computer simulations, and the user can dynamically modify the values of the parameters, the length and position / orientation of segments, scanning speed for each segment, laser beam power at each segment, etc., until a combination of parameters is achieved that provides acceptable curing properties without excessive degradation of the more heat-sensitive areas or objects.

[0096] A further aspect of the invention relates to a computer program comprising program instructions for carrying out the method of any of the above aspects of the invention when executed in a system as described above, and to an information carrier (such as a suitable type of storage device or an electrical signal) storing the computer program.

[0097] A further aspect of the invention relates to a device for laser hardening surfaces of journals of a crankshaft, wherein the journals comprise at least two centrally arranged main journals and at least one offset crank journal, the device comprising: a crankshaft holder arranged to hold the crankshaft and, optionally, to rotate the crankshaft about a longitudinal axis of the crankshaft; at least one laser source arranged to project a laser beam onto a journal of the crankshaft so as to generate a laser spot on the laser spot on the journal; wherein the laser source comprises a bi-directional scanner device for scanning the laser beam in two dimensions to produce a two-dimensional scanning pattern on the surface of the pin.The use of a two-dimensional scanning pattern makes it possible to create an effective laser spot by repeatedly scanning a laser spot over the surface hardening points to be hardened, the effective laser spot having a sufficient dimension in one direction parallel to the longitudinal axis of the crankshaft so as to allow the hardening of an entire journal of the crankshaft during a single rotation of a crankshaft about its longitudinal axis or a single 360° sweep of the effective laser spot around the journal, and in another direction corresponding to a circumferential direction of the crankshaft so as to allow heating to take place for a sufficient period of time to achieve the desired hardening depth, while at the same time being able to rotate the curve at a sufficient speed to obtain an adequate production rate in terms of crankshafts produced per hour.This bi-directional scanning may, for example, be combined with the division of the scanning pattern into a plurality of segments assigned different power levels to obtain an energy distribution that can be dynamically adjusted during operation of the device to avoid overheating of the heat-sensitive sub-regions, such as the regions adjacent to the oil lubrication holes.

[0098] In some embodiments of the invention, the crank carrier and the laser source are adjustable relative to each other in at least two different clearances perpendicular to the longitudinal axis so as to allow a constant distance between a crank pin and the laser source during rotation of the crankshaft about the longitudinal axis, wherein the crank pin is offset with respect to the longitudinal axis.

[0099] For example, the laser source may be translatable in a first direction, preferably vertically, and the crankshaft may be translatable in a second direction, preferably horizontally, wherein the first and second directions are perpendicular to the longitudinal axis. In some embodiments of the invention, the laser source may further be translatable parallel to the longitudinal axis of the crankshaft so as to be able to act sequentially on a plurality of journals of the crankshaft. The laser source may comprise a laser, such as a fiber laser or other laser capable of rapid on / off switching and / or rapid switching between, for example, beam power levels, so as to be capable of rapid switching between power levels when the laser spot follows a scanning pattern having segments assigned to different power states, i.e., desired power levels.

[0100] The apparatus may comprise a control unit having a memory for storing parameter values associated with the scan pattern comprising a plurality of sets of parameter values, wherein a first set of the parameter values determines a first two-dimensional energy distribution on a journal of the crankshaft and a second set of the parameter values determines a second two-dimensional energy distribution on the journal. The control system may be configured to apply a first set of parameter values during hardening of a substantial portion of a journal of a crankshaft and to apply a second set of parameter values when heating an area adjacent to an oil lubrication hole. It will be appreciated that further sets of parameter values may be applied.Thus, for example, during rotation of the crankshaft around a longitudinal axis, the two-dimensional energy distribution can be dynamically adjusted to avoid overheating of more heat-sensitive subregions. The parameter values can include any of the parameters discussed above, including beam power and scan speed.

[0101] The control unit can be arranged to initiate the hardening process during rotation of the crankshaft about its longitudinal axis by selectively applying the first set of parameter values and the second set of parameter values, and optionally, further sets of parameter values stored in memory, synchronously with the occurrence of a more heat-sensitive sub-area relative to the two-dimensional scanning pattern, such as within or adjacent to the area covered by the scanning pattern. For example, the control unit modifies the two-dimensional energy distribution when the area adjacent to an oil lubrication hole is to be heated, i.e., when, for example, the oil lubrication hole approaches the area currently covered by the laser beam during rotation of the crankshaft.

[0102] In some embodiments of the invention, the scanning pattern may be a segmented scanning pattern comprising a plurality of segments, each of which has been assigned at least one of the parameter values. This may indicate at least one of scanning speed, laser spot size, laser beam power, power distribution within the laser beam, length of the corresponding segment, and orientation of the corresponding segment. For example, a suitable selection of the scanning speed, i.e., the speed of the laser spot along the segment, and / or the laser beam power, can be used to determine the energy distribution over the entire area covered by the scanning pattern. Some of the advantages of the segment approach for implementing dynamic variable energy distribution and adapting it to a crankshaft have been explained above.

[0103] In some embodiments of the invention, the device may be arranged to perform a scanning operation at an average speed of at least 300 segments per second, preferably at least 600 segments per second, more preferably at least 1000 segments per second, more preferably at least 5000 segments per second, and even more preferably at least 10,000 segments per second. As explained above, the number of segments per second may be useful for combining a scanning pattern with a reasonable number of segments, such as, for example, 6 or more, with a short cycle time, i.e., a high repetition rate for the scanning operation, for example, 50 Hz or 100 Hz.

[0104] Another aspect of the invention relates to a machine or apparatus for hardening a surface area of a workpiece. The term "surface area" is to be interpreted broadly: it may refer to part of the surface of the workpiece or to the entire surface of the workpiece; for example, it may refer to the surface of a crankshaft journal or to part of the surface. It is clear that the machine may be useful for hardening more than one surface area of the workpiece; for example, in the case of a crankshaft, the machine may be arranged to harden the surfaces, or most of the surfaces, of several or all of the main journals and / or crankpins. The surface area (or at least one of the surface areas) comprises at least one more heat-sensitive sub-area and at least one less heat-sensitive sub-area.

[0105] The device comprises a laser source arranged to project an effective laser spot onto the surface area (by simply directing a beam configured to have a desired cross-section onto the surface area or by generating a virtual or equivalent effective laser spot by scanning a "real" laser spot along a scanning pattern on the surface area), and means for generating a relative movement between the surface area and the effective laser spot (in some embodiments of the invention, these means comprise or consist of rotating the workpiece about an axis so as to sweep the effective laser spot around a part of the workpiece, such as a journal of a crankshaft), so that the effective laser spot is moved along the surface area,in order to successively and progressively heat different areas or parts of the surface area to a temperature suitable for the hardening process. This means that as the effective laser spot advances along the surface area, for example, in the circumferential direction of a crankshaft journal or along such a journal—from one end of it to the other end, in the longitudinal direction of the crankshaft—the effective laser spot progressively heats new areas, while previously heated areas can cool, thereby allowing quenching to occur. The effective laser spot is arranged in such a way that it implements a two-dimensional energy distribution. For example, the energy can be distributed more or less evenly across and along the effective laser spot, or more energy / power can be applied to the surface in some areas of the effective laser spot than in others.

[0106] The device further comprises a control system, such as an electronic control system with one or more programmable devices, for controlling the operation of the device, the control system being arranged to modify the two-dimensional energy distribution so that it is different in the more heat-sensitive sub-region than in the less heat-sensitive sub-region. This allows the heating of the surface region to be optimized to achieve a desired cure depth and quality around all or most of the surface region to be cured and to prevent overheating of more heat-sensitive sub-regions while simultaneously allowing sufficient heating of the less heat-sensitive sub-regions.The terms "more heat-sensitive" and "less heat-sensitive" should be interpreted broadly and generally refer to different surface areas that, due to their properties, should receive less or more energy from the effective laser spot. For example, a less heat-sensitive sub-area may be an area that requires more energy to achieve a desired hardening than the more heat-sensitive sub-area, which should receive less energy, for example, to avoid damage or simply because less heating is required to achieve the desired hardening, for example, due to the structure of the workpiece.

[0107] Reference to a laser source implies the presence of at least one laser source, but does not exclude the presence of further laser sources that can be used together to form an effective laser spot and / or to generate a plurality of different effective laser spots.

[0108] In some embodiments of the invention, the at least one heat-sensitive subregion comprises - an area adjacent to a hole in the surface area, such as an oil lubrication hole; and / or - a groove, such as an undercut groove; and / or - a previously hardened part of the surface area, such as the part where the effective laser spot arrives at the end of a 360° trajectory along the circumference of an object, such as a cylindrical journal of a crankshaft.

[0109] The less heat-sensitive sub-area may, for example, correspond to the surface of a crankshaft journal that is located away from the oil lubrication holes and / or away from the grooves and / or a part that has been previously hardened.

[0110] In some embodiments of the invention, the device is configured or programmed to operate such that the effective laser spot has a size and moves along the surface region at a speed such that during at least a portion of the movement of the effective laser spot along the surface region, preferably during at least 50% and more preferably at least 90% and even more preferably during 100% of the movement of the effective laser spot along the surface region, hardened portions within the surface region are heated by the effective laser spot for at least 0.5 s, preferably at least 1 s. This has been found to help achieve a sufficient depth of hardened layer for many applications. A sufficiently long heating time may be desirable to allow the heat to sufficiently penetrate the material.Times of at least 0.5 to 1 second, optionally less than 5 seconds or even less than 3 seconds may be suitable for, for example, the hardening of crankshaft journals, in order to allow sufficient heat penetration to achieve hardening depths commonly required in, for example, the automotive industry, while at the same time not requiring temperatures so high as to negatively affect the quality of the hardening, for example temperatures close to or above the melting temperature of the workpiece.In some of these embodiments of the invention, the size of the effective laser spot in the direction in which the effective laser spot moves along the surface area (such as in the circumferential direction of a crankshaft journal when the effective laser spot is translated circumferentially around the journal, for example, by rotation of the crankshaft about its longitudinal axis) is at least 5 mm, preferably at least 7 mm, more preferably at least 10 mm, and even more preferably at least 15 mm, 20 mm, 30 mm or more, such as 50 mm. The need to keep each part to be hardened heated for a sufficient period of time, such as at least 0.5 seconds or at least 1 second, limits the speed at which the effective laser spot can safely move along the surface area to be hardened.If an effective laser spot has the typical size of a laser spot with a diameter or width on the order of only a few millimeters, the required heating time would imply that the laser spot would have to move along the surface area to be hardened at a fairly low speed, which would negatively impact productivity in terms of, for example, workpieces per hour. Thus, using an effective laser spot with a larger length or width in the direction in which the effective laser spot moves along the surface area to be hardened can increase productivity, as the effective laser spot can move at a higher speed while still ensuring sufficient heating time.

[0111] In some embodiments of the invention, the apparatus is arranged to generate the effective laser spot by generating a plurality of segments of the effective laser spot, the plurality of segments comprising at least six segments, wherein the control system is arranged to modify the two-dimensional energy distribution by selectively modifying the energy density and / or distribution of the segments (i.e., the energy corresponding to each segment during a particular period of time, such as, in the case of segments of a scanning pattern, of a scanning cycle), and in accordance with parameter values associated with the segments, the parameter values being stored in a memory of the control system.As explained above, the segment approach implies important advantages, for example due to the flexibility and simplicity with which different energy distribution patterns can be generated to adapt the heating of the surface area to the properties of the surface area.For example, if a simple pattern with six segments arranged in two rows of three segments each is used, reducing the power of one or both of the central segments when the effective laser spot reaches an oil lubrication hole placed in the center of a journal of a crankshaft being hardened can reduce the energy applied adjacent to the oil lubrication hole compared to the energy applied to the surrounding part of the surface of the journal, thereby reducing the risk of overheating the area adjacent to the oil lubrication hole, while at the same time maintaining adequate surface hardening also further away from the oil lubrication hole, such as on the sides of the oil lubrication hole, away from edges of the oil lubrication hole.A large number of segments can allow for very precise adjustment of the two-dimensional energy distribution to the heat-sensitivity properties of the surface to be cured. The segments can, for example, be arranged in an array with rows and columns of segments.

[0112] In some embodiments of the invention, the laser source comprises a scanning device arranged to two-dimensionally scan a laser beam from the laser source, wherein the control system is arranged to scan the laser beam in two dimensions to generate the effective laser spot, following a scanning pattern (in the case of a segmented effective laser spot, the scanning pattern may comprise a plurality of segments in many embodiments of the invention), wherein the scanning pattern is repeated at a repetition rate of at least 10 Hz, preferably at least 50 Hz, more preferably at least 100 Hz, and even more preferably at least 200 Hz. Scanning the laser beam to move a small laser spot along and across the surface area to generate the larger effective laser spot is advantageous because it provides greater flexibility with regard to the energy distribution across the entire effective laser spot.On the other hand, a high repetition rate of the scanning pattern allows:. - a relatively large size of the effective laser spot, which is about one or more cm 2, which, on the other hand, allows a relatively large width of the laser spot in a direction perpendicular to the direction of movement of the effective laser spot. For example, in the case of hardening crankshaft journals, where the effective laser spot moves in the circumferential direction, the effective laser spot can have a relatively large width in the direction transverse to the journal (i.e., in the longitudinal direction of the crankshaft), allowing the effective laser spot to extend over a large part or the entire width of the journal, allowing the entire surface area of the journal to be heated by the effective laser spot passing once around the journal.On the other hand, at the same time, the size of the effective laser spot in each direction of movement of the effective laser spot along the surface area to be hardened can also be large enough to allow for movement at a relatively high speed in combination with a sufficient duration of the heating process, as explained above. - At the same time, significant temperature fluctuations within the area just heated are avoided, which is advantageous for the reasons mentioned above: a high repetition rate ensures that a heated area can be heated again before the temperature to which it was previously heated has dropped too low.

[0113] The scanning pattern may be in the form of adjacent segments forming a loop, or in the form of a plurality of lines, such as parallel lines, or it may have any other suitable concentration. Adjusting the two-dimensional energy distribution may involve adjusting the lengths and / or positions of some or all of the segments.

[0114] In some embodiments of the invention, the parameter values are indicative of a beam / power level and / or a scanning speed of a beam relative to the corresponding segment of the scanning pattern. Thus, the two-dimensional energy distribution to be applied at each specific instant of movement of the effective laser spot along the surface area to be hardened by heating can be determined by a beam power value and / or a scanning speed associated with each segment. The choice between one option, the other option, or both may depend, for example, on the properties of the laser source and the scanning system, as explained above. In other embodiments of the invention, the parameter values may be indicative of the position or length of the corresponding segment.Other options are also possible, as explained above, and one or more of these options can be used in combination.

[0115] In some embodiments of the invention, the device is programmed to harden at least one journal on the crankshaft, wherein the device is programmed to generate the effective laser spot such that it extends in the longitudinal direction of the crankshaft over more than 50% of the journal of the crankshaft, preferably over more than 75%, more than 85% or more than 90% or 95%, such as more than 99% or even 100%, and in particular over the majority, if not 100%, of the surface area to be hardened, for example the surface area where an effective case-specific hardening depth of, for example, at least 800 µm or more is desired. It is generally known to use a small laser spot to harden very specific parts of a crankshaft surface.However, the present invention allows the hardening of major surfaces (such as the general surfaces of the crankshaft journal) in a single pass or in a few passes, while at the same time adjusting the heating according to the properties of the parts of the surface area being heated, taking into account the presence of, for example, oil lubrication holes and / or other more heat-sensitive sub-areas.

[0116] In some embodiments of the invention, the control system comprises a memory arranged to store a plurality of data sets, each of the data sets representing a two-dimensional energy distribution of the effective laser spot, the device being adapted to adapt the two-dimensional energy distribution of the effective laser spot as the effective laser spot moves along the surface region by using one of the plurality of data sets to operate the laser source when the effective laser spot is projected onto the less heat-sensitive sub-region and by combining at least one other of the plurality of data sets to operate the laser source when the effective laser spot is projected onto the more heat-sensitive sub-region.Thus, when the device is adapted to a specific product, such as a specific crankshaft, the user can determine adequate energy distributions for different parts of the crankshaft, for example, a first two-dimensional energy distribution for a part of a journal remote from an oil lubrication hole and one or more different two-dimensional energy distributions for areas adjacent to an oil lubrication hole, store the corresponding sets of parameters in the memory of the control system, and program the control system so as to dynamically modify the energy distribution of the effective laser spot as the effective laser spot moves around or along the journal, and in synchronization with the occurrence of oil lubrication holes and other areas requiring adjustment of how the heating is carried out.

[0117] Another aspect of the invention relates to a method of laser hardening at least one surface area of a workpiece, such as a crankshaft, comprising the step of heating the surface area of the workpiece to a temperature for hardening using an apparatus as described above, and the step of allowing the heated portions of the surface area to cool to produce a quench.

[0118] Another aspect of the invention relates to a crankshaft having a plurality of journals, wherein at least one of the journals has a surface hardened by a method according to any of the aspects of the invention described above.

[0119] A further aspect of the invention relates to a method for programming a device, as described above, for laser hardening crankshaft journals, comprising the steps of assigning parameter values related to the energy distribution, such as a laser beam power and / or a scanning speed and / or a length of a segment and / or an orientation of a segment, to a plurality of segments (such as segments of a scanning pattern to be followed by the laser beam spot in order to establish the effective laser spot), in order to create a plurality of data sets, each data set corresponding to a specific two-dimensional energy distribution of an effective laser spot to be projected onto a surface area to be hardened and to be displaced along the surface area, Saving the data records,

[0120] Programming the device to adjust the energy distribution of the effective laser spot in synchronization with the movement of the effective laser spot along the surface region by adjusting the energy distribution in accordance with at least one of the data sets to heat a less heat-sensitive sub-region of the surface region and by adjusting the energy distribution in accordance with at least one other of the data sets to heat more heat-sensitive sub-regions of the surface region.As explained above, the segment approach makes it easy for the skilled person to set up, test and select suitable two-dimensional energy distributions and to assign them to different sub-regions of an area to be hardened, for example, specific data sets, the area around an oil lubrication hole and other specific data sets to assign an area of overlap with a previously hardened area of a crankshaft.

[0121] In some embodiments of the invention, this method comprises, after the step of creating a data set, the step of calculating and visualizing a corresponding two-dimensional energy distribution on a screen. In many cases, the visualization can help the person skilled in the art determine whether a selected two-dimensional data set corresponding to a specific assignment of parameter values to segments, such as segments of a scanning pattern, is likely to result in adequate heating of the corresponding part on the crankshaft.

[0122] Although pure mathematical methods and computers can be used to calculate the optimal assignment of parameter values to the segments, visualization can be a useful tool in the hands of a professional.

[0123] It has been found that suitable lasers that can be used are those that provide high beam power, such as a beam with a power output of 2 kW to 10 kW (the upper and lower limits are included in the range). Such lasers may be particularly suitable for surface hardening of crankshafts, for example.

[0124] Typically, with this type of laser and for the purpose of surface hardening, for example, the surface of a crankshaft, the laser spot projected onto the surface to be hardened can preferably have a diameter in the range of 2 mm to 5 mm, such as 3 mm. This type of spot is considered suitable for hardening a crankshaft surface when using a 2 kW to 10 kW laser beam.

[0125] Hardening is often preferably performed to obtain an effective case depth of the hardened layer of at least 800 µm or more (such as at least 1200 µm or at least 1500 µm or even 2000 µm or more) in the hardened area, except, optionally, near more heat-sensitive sub-areas and / or at the edges or end portions of the hardened area. These case depths are suitable for, for example, crankshafts.It is believed that using a laser with a power in the range of 2kW to 10kW, these hardening depths can be achieved by applying the laser beam to the crankshaft for approximately 2–6 minutes (the exact time will depend on properties such as beam power, surface area to be hardened, and the depth of the layer). By machining multiple crankshafts in parallel, the cycle time can be significantly reduced: for example, by machining two or three crankshafts in parallel, typical cycle times in the order of 1 minute can be achieved. The required depth can typically range from 800 µm up to 2000 µm or more.

[0126] Adjusting the scanning pattern and other parameters, such as beam power, laser spot size, scanning speed, and / or laser beam incidence angles, makes it possible to increase the duration of interaction between the laser beam and a specific area, which can help increase the depth of the first layer.For example, if a given pattern is extended in the direction of relative motion between the laser source and the surface to be hardened and / or if the angle of incidence between the laser beam and the surface is reduced (for example, by locating the beam off-center with respect to a surface of a part having a circular cross-section or by tilting the beam with respect to a flat surface), the duration of interaction between the beam and a given point on the surface can be increased, which can contribute to an increased depth of the hardened layer.

[0127] The scanning speed (i.e., the speed at which the laser spot is moved by the scanning system over the surface to be hardened) can be varied along the scanning pattern or path, as explained above, but the average scanning speed can typically be in the range of 2000 mm / s up to 8000 mm / s; such scanning speeds may be suitable for the surface hardening of crankshafts when a laser beam with a power in the range of 2 kW to 10 kW is used.

[0128] Of course, the different aspects described above can be combined whenever they are compatible with each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0129] To complete the description and provide a better understanding of the invention, a set of drawings is provided. The drawings form an integral part of the description and illustrate various ways of carrying out the invention, which should not be interpreted as limiting the scope of protection, but merely as examples of how the invention may be carried out. The drawings include the following figures: Fig. 1 is a schematic perspective view of a crankshaft as known in the art. Fig. Figure 2 is a schematic perspective view of a system in accordance with a possible embodiment of the invention. Fig. Figure 3 is a schematic enlarged front view of a portion of the laser source 1 and a portion of a workpiece, in accordance with a possible embodiment of the invention. Fig. 4A and Fig. 4B are schematic plan views of a portion of the workpiece in the embodiment of Fig. 3, at two different times during the curing process. Fig. 5A and Fig. 5B are schematic plan views of a portion of a workpiece at two different times in the hardening process in accordance with a variant embodiment of the invention. Fig. 6A, Fig. 6B, Fig. 6C and Fig. 6D are schematic plan views of virtual laser spots with a front region of higher power density and at least one rear region of lower power density. Fig. 7A and Fig. 7B are two schematic enlarged side views in cross-section in the YZ plane of a variant of the Fig. 3 layouts shown. Fig. Figure 8 schematically shows a polarizer that can be used as part of the laser source in some embodiments of the invention. Fig. 9 schematically shows a computer system and a scanning pattern generated in and / or by the computer system. Fig. Figure 10 schematically shows memory locations within the computer system. Fig. 11 schematically shows memory locations within a computer system in accordance with an alternative embodiment of the invention. Fig. 12A-12C schematically show how the energy distribution of a laser spot is adjusted when hardening the area around an oil lubrication hole. Fig. Figure 13 schematically shows how the expansion of the oil lubrication hole can be taken into account in accordance with some embodiments of the invention. Fig. 14A and Fig. 14B schematically show the amplitude of the fluctuation of the surface fracture of a heated area as a function of the frequency with which a laser scans the effective laser spot. Fig. 15A and Fig. 15B schematically show how an effective laser spot can be applied to produce a hardening of a journal of a crankshaft by hardening an annular segment thereof. Fig. 16A, Fig. 17A and Fig. 18A represent the energy or power distribution over an effective laser spot, calculated for a scanning pattern as shown in the Fig. 16B and Fig. 16C, Fig. 17B and Fig. 17C, Fig. 18B and Fig. 18C. Fig. 16B, Fig. 17B and Fig. 18B show schematically the arrangement of the segments of different scanning patterns and the Fig. 16C, Fig. 17C and Fig. 18C schematically show different scanning speeds associated with different segments of the pattern. Fig. 19A-19C schematically show the arrival of the effective laser spot at a previously hardened region of the path. DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0130] Fig. Figure 2 shows a system in accordance with a possible embodiment of the invention. The system comprises a frame structure housing a laser source 1 mounted on a laser carriage 11, which is displaceable in the vertical direction, parallel to a Z-axis of the system, by a first laser carriage drive device 12, for example, a servomotor or other type of drive device. On the other hand, the laser source 1 can also be driven horizontally, parallel to a horizontal X-axis of the system, along a horizontal path 14, driven by a second laser carriage drive device 13, such as another servomotor or other suitable drive device.

[0131] On the other hand, the system comprises two workpiece carriages 20, each workpiece carriage capable of receiving two workpieces 1000 in parallel (in this embodiment, the workpieces are crankshafts), and a drive device (not shown) for rotating each workpiece along a central axis (in this embodiment, the central axis corresponds to the longitudinal axis passing through the centers of the main journals of the crankshaft), the axes being parallel to the X-axis of the system. On the other hand, each workpiece carriage 20 is connected to a workpiece carriage drive device 21 (such as a servomotor or other suitable drive device) arranged to translate the workpiece carriage horizontally, parallel to a Y-axis of the system, perpendicular to the X-axis.

[0132] The references to the horizontal and vertical directions are used only to simplify the explanation, and any other orientation of the axes is of course possible and within the scope of the invention.

[0133] In the following case, the laser source 1 is first used to harden relevant parts of the surface of one of the workpieces 1000 in a first of the workpiece carriages 20. It is then used to harden the relevant parts of the surface of the other workpiece 1000 in the first of the workpiece carriages 20, and then it is moved along the path 14 to face the second of the workpiece carriages 20 and harden the surfaces of the workpieces 1000 arranged therein. While the laser source 1 is working on the workpieces in the second of the workpiece carriages, the workpieces in the first of the workpiece carriages can be unloaded and replaced with new workpieces to be treated by the laser source, and vice versa.

[0134] It is clear that there are many alternative possibilities. For example, there may be only one workpiece per workpiece carriage or there may be more than two workpieces per workpiece carriage. There may be one laser source per workpiece carriage (i.e., a second laser source carriage with a corresponding laser source may be added to the guideway 14). In addition, several arrangements, such as those shown in Fig. 2, or variants thereof, can be arranged in parallel. In addition, each laser carriage 11 can be provided with more than one laser source 1, so that several workpieces in a workpiece carriage can be subjected to the laser hardening treatment simultaneously. The relationship between the number of laser sources, the number of workpiece carriages, and the number of workpieces can be selected to optimize the use of larger parts of the system and thus optimize productivity, for example by allowing loading and unloading of workpieces without interrupting the operation of the system. In some embodiments of the invention, the plurality of laser sources can be used to direct laser beams simultaneously onto the same crankshaft, for example to act simultaneously on different journals of the crankshaft or on the same journal of the crankshaft.

[0135] In some embodiments of the invention, when the workpiece of a crankshaft 1000 with main journal 1001 and crank pin 1002 is heat-treated, the laser source does not move in the Z-axis direction, and the workpiece carriage does not move in the Y-axis direction, since the surface of the main journal is circular and symmetrical about the rotation axis of the crankshaft. In some embodiments of the invention, there may be movement of the laser source and / or the workpieces along the X-axis (if it is necessary to apply the laser heat treatment along the entire extension of the main journal in the X-axis direction). This depends on the power capacity of the laser source and the capacity of the scanning device (not shown) to translate the laser beam in the X-axis direction.If the laser beam can be scanned along the path of the main journal 1001 along its extension in the X-axis direction, there may be no need to move the laser source 1 in the X-axis direction during the heat treatment of, for example, one of the main journals 1001 of a crankshaft, but only when switching from the treatment of one journal to the treatment of another; the same applies to the heat treatment of, for example, the crank pins 1002 of a crankshaft.

[0136] However, during the heat treatment of a crankpin 1002 whose center axis is radially offset from the center axes of the main journals, while the respective crankshaft workpiece 1000 rotates in the workpiece carriage 20, the laser light source 1 is moved vertically parallel to the Z-axis, and the workpiece carriage 2 is moved horizontally parallel to the Y-axis, so as to maintain a constant distance between the laser source (such as the output of the laser device of the laser source or the surface of a lens) and the surface onto which the laser beam is projected. In other embodiments of the invention, the crankshaft can be moved parallel to the Z- and Y-axes. Additionally or alternatively, the laser source can be arranged such that it is movable parallel to the Z- and Y-axes.The operation of the first 12 and second 13 laser carriage drive means as well as the operation of the workpiece carriage drive means 21 and the drive means for rotating the workpieces 1000 in the workpiece carriage 20 can be controlled by an electronic control device such as a computer, a computer system or a PLC (in . Fig. 2 not shown).

[0137] In some embodiments of the invention, the laser source 1 comprises a scanning system arranged to modify the direction of the laser beam. Such scanning systems are well known in the art and often comprise one or more scanning mirrors whose angles can be modified in accordance with scanning functions and the control of a computer, such as sine functions, triangular functions, etc. A single-axis scanning system (for example, a scanning system with a scanning mirror pivotable about an axis or the like) can be used to scan the laser beam parallel to the X-axis, i.e., perpendicular to the direction of movement of the surface of the workpiece 1000 relative to the laser source 1, due to the rotation of the workpiece 1000.A rapid scan over the relevant area of the surface can thus produce a virtual spot with a much larger extent in the X-direction than the extent of the spot without scanning: thus, the original spot is transformed into a wider virtual spot (with a larger extent in the X-direction), but with a smaller power density, since the power of the beam is spread over a larger area.

[0138] With a two-axis scanning system (e.g., a scanning system with a biaxial mirror or two uniaxial mirrors), the laser beam can be moved in two directions, for example, parallel to the X-axis on the one hand and parallel to the X-axis on the other, or combinations thereof. Thus, in addition to scanning the surface perpendicular to the direction of movement of the surface relative to the laser source, i.e., in addition to scanning the surface "along" the surface of the journal in the X-axis direction, the laser beam can also scan the surface in the direction of its movement, i.e., parallel to the Y-axis; this allows the surface of a crankshaft journal to be scanned in the circumferential direction of the journal. Furthermore, the laser beam can describe paths that combine movement in the X-direction and the Y-direction (i.e., when projected onto the circular journal of a crankshaft, in the circumferential direction W, see, for example, Fig. 12A-12B). This allows the beam to follow paths with complex shapes, such as rectangles, ovals, trapezoids, etc. The laser spot can be scanned across the surface to create a virtually filled rectangle with a substantial height in the Y (or W) direction (for example, by following a meandering pattern within a rectangular boundary or following a plurality of separate lines within the boundary) or to repeatedly trace the edges of a rectangle or other geometric figure. Thus, using the capability of the scanning system, a virtual or equivalent effective laser spot can be created having a desired configuration and shape in both the X and Y or W directions.In the case of a so-called X-scanner, in addition to the possibility of movement in the X and Y directions, a focusing lens is provided that can be adjusted in the Z direction by some type of drive device, thus enabling the dynamic adjustment of the size of the laser spot. This allows both the position of the spot and its size to be controlled and adjusted to optimize the curing process. Furthermore, as an alternative or in addition to adjusting a focusing lens or the like, the size of the laser spot can be controlled and adjusted by moving the laser source parallel to the Z axis using the laser carriage drive device. Furthermore, the system can comprise means for varying the power distribution within the laser spot, as is known, for example, from the above-mentioned DE-3905551-A1.

[0139] Fig. Figure 3 schematically shows the laser source 1 with a schematically shown two-axis scanning system 3, which is based on a biaxial mirror or uniaxial mirror and is arranged so that it deflects the incoming laser beam 2 in the vertical plane parallel to the X-axis and in the vertical plane parallel to the Y-axis; the angle α represents the maximum range in the vertical plane parallel to the X-axis and the angle β represents the maximum range in the plane parallel to the Y-axis. Fig. Figure 3 schematically shows a laser source 1 arranged above a workpiece, and in particular above the main journal 1001 of a crankshaft, which includes an oil lubrication hole 1003 and which is rotated in the workpiece carriage (not shown) in the direction indicated by the arrow. Fig. 3 illustrates an area or section 1006 swept by the laser spot as the laser beam is scanned. Thus, using this type of laser source, a small laser spot produced on top of the workpiece can be offset by a large virtual or equivalent spot obtained by repeatedly scanning at high speed a pattern with a desired shape in the section 1006, which is determined by the maximum range allowed by the scanning system in accordance with the angles α and β. In this way, instead of heating a single small spot with the laser beam, a large area can be heated over a period of time by scanning the area within the laser beam (but with less power per unit area).In other words, instead of providing a large spot (such as a large rectangular spot) using, for example, suitable fixed optics, a corresponding power distribution can be obtained by scanning a smaller or more powerful spot over a large area. This has an important advantage: it provides the possibility of dynamically applying different amounts of energy to different areas of the surface by adjusting the scanning pattern, scanning speed, beam power, and / or spot size according to different properties of different areas of the surface, for example, depending on heat sensitivity and the risk of damage from overheating.For example, a scanning pattern, scanning speed, beam power, and / or laser spot size can be selected (and dynamically adjusted during the curing process) to limit the amount of energy applied to the surface near oil lubrication holes or near undercut grooves. To achieve adequate cure depth and quality, scanning is performed repeatedly and preferably at a high frequency, such as greater than 10 Hz, or more preferably greater than 50, 100, 150, 200, or 250 Hz, to avoid significant temperature fluctuations within the heated area.

[0140] The Fig. 4A and Fig. 4B show plan views of a portion of a crankshaft, namely a main journal 1001 of the crankshaft, during two different stages of a hardening process. The crankshaft is rotated in the workpiece carriage (not shown) in the direction indicated by the arrow.

[0141] In Fig. 4A, reference numeral 2A denotes the scanning pattern: the laser spot essentially follows the rectangular path 2A; in an alternative embodiment, the laser spot is moved in a scanning manner within the essentially rectangular surface 2A, for example, following a meander pattern or other patterns within the rectangular surface 2A, so as to fill the rectangle, i.e., to act on the entire area of the rectangle. In both cases, the scanning process is carried out at high speed, so that the result is that the projection of the laser beam onto the surface of the workpiece 1001 is, from a heating point of view, essentially equivalent to the heating that would have been achieved if the laser beam had been projected in the form of an empty rectangle 2A or a filled rectangle 2A, respectively. Fig. 4A, the area swept by the laser beam is a less heat-sensitive sub-area because the workpiece is solid in this area.

[0142] Now Fig. 4B, the oil lubrication hole 1003 reaches the section or area that is grazed by the laser beam. The area immediately adjacent to the oil lubrication hole 1003 is more heat sensitive because the edges of the oil lubrication hole can be damaged by overheating and because the absence of metal in the hole reduces the heat sink capacity of the workpiece in that area. Thus, if the laser beam were projected onto the area immediately adjacent to the oil lubrication hole 1003 in the same way as it is projected onto the less heat sensitive region, such as in Fig. 4A, overheating could occur with damage to the edges of the oil lubrication hole 1003.

[0143] Therefore, in this embodiment of the invention, a different scanning pattern 2B is used when the workpiece is in the Fig. 4B: in this case, the laser beam follows a path in the shape of a large rectangle 2B or follows a meandering pattern or a plurality of parallel lines to fill the bounded area of the large rectangle 2B. This implies that the power of the laser beam is spread over a large area, thus reducing the risk of overheating. In other words, the modulation of the laser beam with respect to the scanning pattern is in the Fig. 4B is different from the situation shown in the Fig. 4A to reduce the risk of overheating.

[0144] It is clear that there is no need to use a rectangular pattern or a meandering pattern that fills a rectangle. Those skilled in the art are free to use the pattern they consider most suitable. For example, when using a fiber laser or other laser that allows rapid on / off switching of the laser beam, a pattern comprising a plurality of parallel lines may be used, and the spacing between the lines may be smaller when scanning a less heat-sensitive area or sub-area than when scanning a more heat-sensitive area or sub-area.Or, more preferably, the spacing between the lines can be kept substantially constant, and only the beam power and / or the scanning speed along the lines can be adjusted, such that a scanning speed is higher and / or the beam power is lower in the more heat-sensitive region than in the less heat-sensitive region. Combinations of these approaches can also be used. For scanning along a plurality of parallel lines, polygonal mirrors can be used in many embodiments of the invention.In addition, or as an alternative to modifying the pattern or the path followed by a laser spot, the skilled person may choose to modify the power of the laser beam and / or the scanning speed of the laser beam and / or the size of the laser spot and / or the power distribution within the laser spot, so as to ensure adequate hardening with an acceptable degree of reduction in sensitive areas, such as the edges of the oil lubrication holes 1003 of a crankshaft. This type of measure can be taken with respect to sensitive areas, such as the undercut grooves or the area at the end of a hardening path, i.e., basically the area where, once the workpiece has been rotated almost 360°, the laser beam approaches an area previously hardened by it and which should not be subsequently reheated, thus avoiding an excessive tempering effect that would lead to an unacceptable hardness reduction.

[0145] The Fig. 5A and Fig. 5B are plan views of a portion of a crankshaft, namely a main journal 1001 of the crankshaft, during two different stages of the hardening process in accordance with an alternative embodiment of the invention. Fig. 4A and Fig. 4B applies mutatis mutandis. In Fig. 5A and Fig. 5B, the scanning pattern extends almost across the entire width of the stud, essentially from one of the grooves 1004 to the other. As in Fig. 4A and Fig. 4B, the scanning pattern is designed to provide a low power density in the more heat-sensitive sub-region around an oil lubrication hole 1003 (see Fig. 5B) than in the less heat-sensitive sub-area or region further away from the oil lubrication hole (see Fig. 5A); in this case, this is achieved by a greater height of the trapezoidal scanning pattern when scanning the area around the oil lubrication hole 1003.

[0146] In this case, however, the area adjacent to the grooves 1004 is also considered a more heat-sensitive area, for example, using undercut grooves. Thus, the scanning pattern is arranged to ensure a low power density in this area as well; this is achieved by using a trapezoidal scanning pattern, which, at a substantially constant scanning speed, results in less energy being received near the grooves than if a rectangular scanning pattern were used. Analogous to the case of the embodiment of the Fig. 4A and Fig. 4B, the laser beam can follow the outlines of the trapezoids 2C and 2D, which in Fig. 5A or Fig. 5B, or it may cover or fill trapezoids, for example, following a meandering path within the trapezoid or a plurality of lines within the trapezoid.

[0147] It will be obvious to the person skilled in the art that these patterns are only examples and that the person skilled in the art will be able to choose from an unlimited number of possible patterns if the method and system are to be adapted to a specific workpiece design.

[0148] Fig. Figure 6A is a plan view of a virtual laser spot 5 with a rectangular cross-section and having a front region 2E with a higher power density and a rear region 2F with a lower power density. The virtual laser spot is obtained by repeatedly scanning a smaller real laser spot following a meandering pattern covering the rectangular region. In this case, the higher power density is obtained by using a more compact meander pattern in a first part of the rectangular region and a less compact meander pattern in the second part of the rectangular region. The case indicates the direction in which a surface of the workpiece moves relative to the virtual laser spot.In this way, a portion of the workpiece to be heated is first impacted by the leading edge of the virtual laser spot and then receives a comparatively large amount of power per unit of surface area. This promotes rapid heating, which in the case of laser hardening means that the area of the workpiece will quickly reach the austenitizing temperature range. This means that for a given laser beam power and for a given velocity of the surface to be heated, the heated area of the workpiece can be maintained at or above the austenitizing temperature range for a longer time than if the power had been evenly distributed across the virtual laser spot: had the power been evenly distributed, it would have taken a longer time for the surface to reach the austenitizing temperature zone.

[0149] Fig. 6B shows an alternative embodiment in which, instead of using a meander pattern, the laser spot follows a plurality of parallel lines to form the (virtual or equivalent) effective laser spot 5. The laser beam power is higher and / or the scanning speed is lower than the lines at the front region 2E with higher power density compared to the rear region 2F with a lower power density, where the laser beam power is lower and / or the scanning speed is higher. In this way, the desired energy distribution across the effective laser spot 5 can be obtained. Instead of lines, a different type of scanning pattern can be used to create a desired two-dimensional energy distribution.Using a laser that allows rapid switching of the laser beam on / off and / or rapid variation in power, very complex patterns can be used, allowing a very precise energy distribution that can be tailored according to the properties of the surface to be hardened, for example, so that less energy is applied in more heat-sensitive regions or areas, such as near the oil lubrication holes of a crankshaft. For example, a fiber laser can be useful for implementing this type of energy distribution, for example, using a "pixel" approach by which very specific subregions are heated according to a desired two-dimensional energy distribution. For fast scanning along parallel lines, polygonal mirrors can be used, as is known in the art.

[0150] Fig. Figure 6C shows an effective laser spot 5 with three different regions, namely a first region 2H comprising a plurality of lines of the scanning pattern, a second region 2I without such lines, and a third region 2J comprising a plurality of lines of the scanning pattern. The first region 2H can optionally have a front sub-region 2E with a high energy density and a rear sub-region 2F with a lower energy density. On the other hand, the energy density in the first region 2I can be higher than the energy density in the third region 2J, which in turn can be higher than the energy density in the second region 2I, in which the energy density can be 0 or close to 0. The effective laser spot 5 can be obtained by repeatedly scanning the laser beam along all lines of the scanning pattern.by adjusting the scanning speed and / or the beam power and / or switching the laser beam on / off in different segments of a line to distribute the energy according to a desired power or energy distribution pattern. Because of the second region, where no heating occurs, the first region 2H of the scanning pattern can be designed to bring the surface temperature of the workpiece to a high temperature as quickly as possible, such as in the order of 1400 °C (due to the high power density at the front sub-region 2E) and maintain it there for a sufficient period of time to achieve a desired hardening depth (by correctly selecting the length of the first region 2H in the direction of relative movement between the effective laser spot and the surface of the workpiece, taking into account the speed of the relative movement).The second region 2I can allow quenching by cooling the heated region, such as self-quenching, and the third region 2J can have a scanning pattern, speed, and beam power suitable for heating the workpiece to a temperature, such as in the range of 400 to 500°C, to temper the hardened region. In this way, hardening and tempering can be performed sequentially during a single step of moving or sweeping the effective laser spot 5 over the surface to be hardened and tempered. This can serve to accelerate the entire hardening and tempering sequence. (The temperature to which the surface is to be heated depends on the workpiece material, for example, the type of steel used and its composition. The value of 1400°C is intended only as an example.)

[0151] Fig. Figure 6 D schematically shows a scanning pattern with six lines 51, each line comprising five segments or pixels 51A, 51B. For each segment, the beam is on (segments or pixels 51A) or off (segments or pixels 51B), depending on the desired energy distribution, which can be dynamically varied during the curing process. Thus, the layout in Fig. 2D represents a 6x5 pixelation and can be easily obtained with commercially available laser and scanner systems. Using a laser that allows rapid on / off switching, such as a fiber laser, can increase the number of pixels of the scanning pattern for a predetermined scanning frequency. The number of lines that can be achieved for a given scanning frequency, such as 50 Hz or 100 Hz or more, will depend, among other things, on the scanning device used.

[0152] Instead of or in addition to switching the laser on and off, other beam power states can also be used, i.e., different power levels between maximum power and 0 power (or close to 0). The power states corresponding to the different segments can be stored in a memory and dynamically modified during the manufacturing process, for example, to reduce the energy density in an area adjacent to an oil lubrication hole by reducing the power level assigned to one or more of the segments, if necessary. This segmented or pixelated approach is very practical and allows the user to find the correct energy distributions across the effective laser spot by trying out different combinations of power states, i.e.,the power the beam should have at different segments until a combination is found that produces a desired result. If the laser allows rapid switching between different power states or levels, a high number of segments can be completed per second, allowing a sufficiently high scan pattern repetition rate to avoid significant temperature fluctuations while still encompassing a reasonable number of segments. For example, if the laser allows 1000 power state changes per second, a scan pattern repetition frequency of 100 Hz can be combined with a scan pattern that has 10 segments.

[0153] Fig. Figure 7A is a cross-sectional view of a main journal 1001 in a variant in Fig. 3. Here, the laser source is slightly offset with respect to the vertical plane of symmetry of the main pivot 1001 along the X-axis. This means that the laser beam, when moved within the range of the β-angle, will reach the surface of the workpiece at different angles between the angle γ1, which in this case is approximately 90°, and the angle y2, which in this case is substantially less than 90°. If the scanning speed and the scanning pattern are constant during the scanning process and if the power of the beam is also kept constant, this means that the power density per unit surface area is higher at the leading edge (i.e., where the surface of the rotating body enters the area reached by the laser beam during scanning) due to the larger angle γ1 and lower at the trailing edge due to the smaller angle y2. As with respect to Fig. As explained in Figure 6A, this arrangement can help the surface temperature to quickly reach the austenitizing temperature zone.

[0154] Fig. Figure 7B shows an alternative arrangement in which the laser beam is kept stable or is only scanned in the vertical plane parallel to the X-axis, ie in accordance with the angle α in Fig. 3. In this case, the offset position of the laser beam relative to the plane of symmetry implies that the laser beam hits the surface at an angle α of substantially less than 90°. This can have two effects: first, the spot area becomes larger, which can be advantageous as it distributes the laser beam power over a wider area. Even if the thickness of the laser beam (along the X-axis) is not so small that it can be ignored, this creates a difference between the angle of incidence between the laser beam and the workpiece surface at the leading edge of the spot and the corresponding angle at the trailing edge of the spot. This means that the aforementioned effect of rapid heating of the surface as it enters the spot can be achieved due to a high power density at the leading edge.This embodiment can, for example, be advantageously used with fixed optics that provide a substantially rectangular laser spot. Additionally or alternatively, this concept can be used in combination with a one-dimensional scan parallel to the X-axis, creating a virtual rectangle with a width corresponding to the diameter or width of the laser spot and a length corresponding to the range of the laser beam parallel to the X-axis.

[0155] To increase the size of the laser spot, similar approaches can be taken when the surface area to be hardened is flat and not circular: the laser beam can be projected onto a flat area so that it is not perpendicular to the flat area.

[0156] Sometimes it is desirable to harden surfaces that are difficult to reach with the laser, only at very small angles. In the case of crankshafts, for example, the wall surfaces 1005 extending substantially perpendicularly from the surfaces of the main journals and the crankpins are often hardened almost parallel to the surfaces emitted by a laser source 1 in an arrangement such as that shown in Fig. 2 emitted laser beams must be nearly parallel. This can reduce the power absorption rate at such surfaces, making curing more difficult and energy-consuming: laser light received at a very small angle relative to the surface may be absorbed much less effectively than laser light received at a large angle, such as 90°, i.e., perpendicular to the surface.

[0157] However, the absorption also depends on the polarization. Thus, if for one polarization (s or p) the power is better absorbed when the laser beam is directed perpendicularly to the surface (i.e. at 90° with respect to the surface), with an opposite polarization the absorption of power is higher when the laser beam is directed at the surface at a small angle, such as an angle close to 0, i.e. with a direction of the beam almost aligned with the surface. In the case of workpieces such as crankshafts, where the walls are sometimes very large and separated by a fairly short pin, an arrangement such as the one in Fig. 2, project the laser beam at a relatively small angle onto the walls 1005, at least on the part of the walls that is close to the pins.

[0158] Fig. Figure 8 shows a polarization system 4 that can be used as part of the laser source 1: it comprises a beam-splitting polarizer 41, such as a polarizing cube, which splits an incident laser beam into an s-polarized beam 2' and a p-polarized beam 2", one of which can then be used to harden the surface, preferably the main pin 1001 and the crank pin 1002, and the other of which can be used to harden the surfaces of the walls 1005. Mirrors 42, 43, and 44 can be used to align the s-polarized beam 2' and the p-polarized beam 2" to make them substantially parallel.

[0159] Fig. Figure 9 schematically shows a computer device or system 100, such as a personal computer or other programmable device or means, having a computer input device 101, such as a keyboard and / or a mouse, and a computer screen 102. A scan pattern 2G is shown on the screen. In this case, the scan pattern is a polygon having a plurality of segments a, b, c, d, e, f, g, and h. In the illustrated embodiment, the segments form a polygon, namely an octagon. However, a larger or smaller number of segments may be used, and one or all of the segments may be curved rather than straight, and the segments may be distributed in other ways, such as in a plurality of more or fewer parallel lines.The computer system may be arranged such that a user can change the layout of the pattern, for example, by using a mouse or other input means, for example by moving a cursor on the screen. As an alternative, a touchscreen may be used, allowing the user to change the shape of the pattern by touching the segments, thereby changing their position, orientation, and / or length. The shape of the pattern represents the path that the laser spot will describe when scanned over the surface to be cured, for example, to create a virtual or equivalent effective laser spot with a two-dimensional energy distribution. Also present on the screen are a plurality of lines AH, each of which corresponds to one of the segments ah. Each of the lines AH represents a property of the laser spot in relation to the corresponding segments ah, for example, a range of scanning speeds.In the embodiment, the arrow near each line indicates a specific scanning speed selected for each segment, i.e., the speed at which the laser spot moves along the corresponding segment while following the scanning pattern. In the present case, the highest scanning speed was assigned to segments c and g. A slightly lower scanning speed was assigned to segments a and e, and an even lower scanning speed was assigned to segments b, d, h, and f.In other embodiments of the invention, in addition to or as an alternative to assigning different scanning speeds to different segments, different laser beam powers may be assigned to the different segments, such as by selecting the laser beam to be "on" or "off" or in another available power state (such as 10%, 25%, 50%, 75%, or 90% of maximum power) for different segments in accordance with a desired energy distribution. The segments may indicate the route followed by the center of the scanning spot, and the scanning spot may, for example, have a diameter equal to one-half the length of segments a and c.If this is so, each time the spot completes the route determined by the segments ah, the entire area inside the segments is directly heated by the laser, as well as part of the area outside the segments, up to a distance equal to half the diameter of the laser spot.

[0160] The octagon 2G can, for example, be used instead of the rectangle 2A / 2B or the trapezoid 2C / 2D in the embodiments of the Fig. 4 and Fig. 5. In this case, for example, the higher scanning speed in segments c and g can reduce heating in the area of the oil lubrication holes 1003, and the increased speed in segments a and e can help prevent overheating in the area of the undercut grooves 1004. Furthermore, the computer system can be programmed so that any one type of pattern 2G can be used when scanning an area remote from the oil lubrication holes, and a different type of pattern (for example, a pattern with different and / or differently oriented segments and / or with different speeds or beam powers associated with some or all of the segments) when scanning the area adjacent to or including the oil lubrication holes.For example, the same outline of the segments can be used, but with different speed (and / or beam power) on segments c and g, depending on whether the area around the oil lubrication holes is scanned or not.

[0161] This system can be used in conjunction with a pyrometer to allow trial adjustment of the scanning pattern 2G, for example, by laser hardening test workpieces and modifying the scanning pattern (shape, scanning speed, laser beam intensity, laser spot size, etc.) for one or more segments depending on the results. Additionally, or alternatively, a computer system 100 can be provided with simulation software to simulate the heating that would result from a selected pattern 2G and the scanning speeds (and / or other parameters such as laser beam power, laser spot size, etc.) associated with the different segments ah, so that the user can quickly find a pattern configuration that appears useful. The result of the simulation can be displayed, for example, on the screen 102.The user can dynamically modify the 2G pattern and the various associated parameters and observe the resulting heating. This tool can be helpful for easily finding or designing a suitable scanning pattern with appropriate parameter values assigned to the different segments for a given workpiece design.

[0162] For example, this type of system can be advantageously used to find a suitable scanning pattern for a given crankshaft, for example, by dynamically adjusting parameters of the pattern (its shape and dimensions, e.g., by enlarging or shortening segments) and / or the parameters associated with each segment, such as, for example, a laser spot speed (by modifying the scanning speed), a power (e.g., by modifying the amount of power of the laser beam), and / or a power density (e.g., by changing the size of the laser spot, e.g., by defocusing, e.g., by adjusting a focus lens or by changing the angle of incidence between the laser beam and the surface). In some embodiments of the invention, the power distribution within the laser beam can also be adjusted.In some embodiments of the invention, a specific scanning pattern, such as one in accordance with one of . Fig. 6D and adjustment of the energy distribution can be established by selecting the beam power and / or the scanning speed to be assigned to each segment 51A, 51B.

[0163] It has been found that using this type of segment-based definition of the scanning pattern, which, on the one hand, allows the creation of a pattern contour by reducing the number of segments and / or the length of the segments and / or modifying their orientation and / or position, and by selecting and assigning different parameter values for power and energy, such as values for scanning speed, beam power, and / or spot size for each segment, makes it easy to achieve adequate heating of the different areas of the surface to be heated. More heat-sensitive sub-areas, such as the area adjacent to the oil lubrication holes 1003 of a crankshaft, can be handled appropriately: - By using the same scanning pattern (in terms of the path followed by the spot) for both the more heat-sensitive areas and the less heat-sensitive areas, but adjusting other parameters to avoid overheating of the more heat-sensitive areas, for example, choosing a higher scanning speed (and / or lower beam power, etc.) for a selected segment; in the case of Fig. 9, by increasing the speed at segments c and g, help to reduce overheating at the oil lubrication holes 1003 centrally located in a pin over which the laser beam is moved in accordance with the pattern 2G; in the case of Fig. 6D, assigning a low (such as 0 or close to 0) beam power to some of the central segments 51B of the lines 51 may also help prevent overheating at an oil lubrication hole passing through the central region of the pattern, in the direction of the arrow in Fig. 6D. - By using different sets of scanning patterns and associated parameter values for different sub-ranges; for example, during the rotation of a crankshaft, a journal can be detected as Fig. 5A, but with a scanning pattern that reflects the layout of Fig. 9; when the oil lubrication hole 1003 reaches or approaches the area of the surface being scanned, the speed value associated with segments c and g can be modified so that the laser beam scans these segments at a higher speed, thereby reducing the risk of overheating the area adjacent to the oil lubrication hole. - By changing the shape of the pattern, for example, by modifying the length and orientation of the segments, and even by omitting segments. For example, segment g of the scanning pattern 2G can be omitted throughout the rotation of the workpiece, or when scanning an area of the workpiece adjacent to or including an oil lubrication hole; in this case, the laser spot can follow the path from segment h through segments a, b, c, d, e, and to segment f, and then turn in the opposite direction, i.e., around segments f, e, d, c, b, and a, until it reaches the end of segment h.

[0164] Thus, a computer system that provides control of the laser beam based on a segmented scanning pattern, with different values for, for example, - the scanning speed (i.e. the speed of movement of the laser spot along its path) - the laser beam power, and / or- The laser spot size assigned to different segments can be useful for adjusting the scanning pattern to ensure optimal energy distribution and optimized heating of a surface, for the purpose of adequately heating the surface with reduced damage or reduced risk of damage to the sensitive areas. The above explanation primarily referred to the scanning speed, but heating can of course also be modified by modifying the laser beam power or power density, for example, by defocusing, for example, by moving a lens. For many currently existing lasers and scanning devices, modifying the speed may be a preferred option.When using lasers that allow rapid on / off switching or rapid changes in the beam power (such as many fiber lasers, which currently require approximately 100 µs to switch between "on" and "off"), modifying the power of the laser beam, for example by switching it on and off, becomes an increasingly interesting option; the option is even more interesting in view of the trend towards shorter switching times.

[0165] To provide a virtual laser spot (such as an “octagonal” laser spot by quickly scanning the area in which the pattern 2G of Fig. 9, or a segmented effective laser spot such as the one from Fig. 6D), scanning must be performed at high frequency, i.e., at high speed. In a practical embodiment, for example, the laser beam may complete one scanning cycle along segments ah in a time period of, for example, 8 ms; often, it may be difficult or expensive, such as when using diode lasers or other lasers where on / off switching is slow, to modify the beam power quickly enough to bring it to the correct level at each and all segments; it will often be more practical to modify the scanning speed, something that is within the capacity of commercially available scanning systems. However, depending on the capacity of the laser to switch power levels, modulation of the beam power may be preferable.

[0166] The scanning pattern from Fig. Figure 9 shows a set of interconnected segments. However, depending on the type of laser and / or scanning device used, unconnected segments may also be used. For example, the scanning pattern may comprise a plurality of lines, dots, or pixels; this type of scanning pattern may often be preferred when using a laser that allows rapid on / off switching, such as a fiber laser. This allows very complex and sophisticated patterns to be used, allowing for very precise selection of the energy distribution in the area being scanned. Thus, the system can be tailored to deliver exactly the energy distribution necessary when considering the presence of more heat-sensitive regions, such as oil lubrication holes in a crankshaft.

[0167] Fig. Figure 10 schematically shows a first 110 and a second 120 computer memory area associated with the computer system 100, each memory area comprising a memory matrix with a plurality of columns, each column containing a memory location associated with each of the segments ah of the scanning pattern 2G. The columns may contain the following data: The data in the sample pattern segment columns 111 and 121 can define the shape of the pattern, ie, the arrangement of the segments (such as start and end points of each segment). The data in scan speed columns 112 and 122 can define, for each segment, the scan speed associated with that segment, i.e., the speed at which the laser spot will move along the corresponding segment of the scan pattern or scan path. The data in beam power columns 123 and 133 can define, for each segment, the beam power, i.e., the power of the laser beam as it moves along the corresponding segment. The data in the spot size columns 114 and 124 can define the size of the laser spot for each segment as it moves along the corresponding segment. By focusing / defocusing the laser beam, for example, by moving a motorized focusing lens or by moving the laser source parallel to the system's Z-axis, the size of the spot and thus the power density per unit surface area can be changed. This can also be achieved by modifying the angle of incidence of the laser beam onto the surface, for example, by offsetting the laser beam, as shown, for example, in Fig. 7A and Fig. 7B is proposed.

[0168] In some embodiments of the invention, there is only one of these computer memory areas, meaning that the speed, beam power, and spot size can remain constant throughout the entire process. In other embodiments, there are two or more of these memory areas, and a pointer 130 can be used to dynamically modify the scanning process during the relative movement between the surface of the workpiece 1000 and the laser source 2: for example, as an oil lubrication hole 1003 approaches the area of the surface currently being scanned, a first scanning pattern (with its associated set of parameter values for, for example, the scanning speed, laser beam power, laser spot size, and / or angle of incidence) defined by the first memory area 110 can be replaced by a second scanning pattern (with its associated set of parameter values for scanning speed, laser beam power, and / or laser spot size, etc.).defined by the second storage area 120, so as to prevent overheating of the edges of the oil lubrication hole. For example, the second scanning pattern may have a higher scanning speed and / or a lower laser beam power and / or a larger laser spot size associated with the segments crossed by the oil lubrication hole during scanning, compared to the first scanning pattern.

[0169] In some embodiments of the invention, there will be only one or some of the columns 111-114, or there may be multiple columns specifying data related to other aspects of the process. In some embodiments of the invention, only one or two of the scan speed, laser spot size, and laser beam power will vary between different segments and patterns. In some embodiments, there may be only one memory area 110, since the path followed by the laser spot and its associated parameter values will remain constant throughout the entire process.

[0170] Fig. Figure 11 schematically shows two computer memory areas in accordance with an alternative embodiment of the invention, in which each computer memory area 140, 150 comprises a plurality of memory locations 141, each corresponding to a pixel or segment of a region to be scanned. Each memory location may have a power state value indicative of a laser power, such as a value indicative of an on / off state of the laser or a value indicative of a particular power level. Thus, as the laser beam is moved across a region to be scanned (for example, by allowing the laser beam to follow a plurality of parallel lines extending across the region), the laser beam may be turned on or off according to the value of the corresponding memory location.In some embodiments of the invention, each memory location may correspond to a "line" on the scanning pattern, and in other embodiments of the invention, each memory location may correspond to a region or segment of a line, such that a pixelated energy distribution may be obtained (an example of a scanning pattern with such a segmented or pixelated energy distribution is shown in . Fig. 6D). The degree of accuracy of pixelation or subdivision of the area to be scanned into subsegments with different laser power levels (such as on / off and / or intermediate power levels) associated therewith may depend on features such as the scanning speed and the laser on / off switching capacity. As in the case of the embodiment shown in Fig. As shown in Figure 10, a pointer 130 may be used to switch between one type of scanning pattern and another, thus adjusting the energy distribution depending on the characteristics of the area being scanned, for example, to take into account the presence of an oil lubrication hole.

[0171] The 20x20 pixelation, which is Fig. 11 is only an example, and any other suitable number of targets and pixels per line may be used. For example, the number of lines may be limited by the speed of the scanner and the scanning frequency (i.e., the frequency at which the scanning pattern is repeated), and the number of pixels or pixels per line may be limited, for a given scanning frequency and number of lines, by the laser's on / off switching capacity. For example, in the case of a laser that requires 100 µs to turn on and 100 µs to turn off, i.e., 200 µs for one on / off cycle, and a scanning frequency of 100 Hz, using a scanning pattern of 5 lines to complete the effective virtual laser spot, the number of pixels per line may be approximately 10.

[0172] The Fig. 12A-12C show how the energy distribution of an effective laser spot can be adjusted to accommodate an oil lubrication hole. The oil lubrication hole 1003 is positioned in a surface of a crankshaft journal, and the surface extends in a first direction parallel to the crankshaft's rotational axis and in a second circumferential direction W. In Fig. 12A, a substantially rectangular equivalent effective laser spot 5 is used, which has a front region 2E with higher power density and a rear region 2F with lower power density. However, if, as in Fig. 12B, as the oil lubrication hole 1003 approaches the effective laser spot due to the relative movement between the surface of the crankshaft and the laser source, due, for example, to rotation of the crankshaft about its longitudinal axis, the energy distribution is substantially adjusted by reducing the power or energy density toward the center of the front region 2E, so as to avoid overheating of the region adjacent to the oil lubrication hole 1003. Here, the effective laser spot is substantially U-shaped. Thereafter, when the oil lubrication hole 1003 has passed the front region 2E, the original energy distribution is restored at the front region, whereas the energy distribution at the rear region 2F is adjusted to account for the oil lubrication hole 1003 by reducing the energy or power density toward the center of the rear region.Here, the effective laser spot 5 essentially assumes an inverted U-shape (which in some embodiments of the invention is obtained using segmentation or pixelation in accordance with a method disclosed in . Fig. 6D and adjusting the power states associated with the different segments to provide the corresponding shapes of the effective laser spot. That is, as the oil lubrication hole passes through the effective laser spot, the energy distribution is adjusted to apply less energy to the more heat-sensitive area adjacent to the oil lubrication hole than that applied to the surface to be hardened remote from the oil lubrication hole. The area around the oil lubrication hole can be hardened without damaging the more heat-sensitive sub-area adjacent to the oil lubrication hole; the lateral areas of the U-shaped effective laser spot serve to harden the areas on the sides of the oil lubrication hole. The change in energy distribution that occurs in Fig. 12A-12C can be obtained, for example, by adjusting the scanning pattern and / or by adjusting the path in which the beam power is distributed along the scanning pattern (for example, by adjusting the path in which the laser beam is turned on and off during different segments of the scanning pattern) and / or by adjusting the scanning speed in accordance with different segments of the scanning pattern, etc.

[0173] Fig. Figure 13 schematically shows how the energy distribution is adjusted to take into account the skewed position of an oil lubrication hole 1003 by applying more energy 5A to the side 1003A of the oil lubrication hole that is not located above the oil lubrication hole 1003, and less energy to the side 1003B of the oil lubrication hole that is located above the oil lubrication hole, i.e., on the side toward which the oil lubrication hole extends in the body of the crankshaft. This can be achieved, for example, by correctly selecting the power states associated with the different segments of a scanning pattern. This difference in the application of energy takes into account the fact that the absence of conductive material due to the presence of the Fig. 13 downwards to the right side extending oil lubrication hole reduces the capacity with which heat applied to the right side of the oil lubrication hole 1003 can be carried away from the heated area. Applying the same amount of energy on both sides would essentially result in an excess of energy, as this would cause the thicker hardened layer on the right side 1003W of the oil lubrication hole in Fig. 13 than on the left side 1003A; however, if it becomes necessary to comply with the requirement of a minimum thickness of the hardened layer, the thinnest area of the hardened layer must meet this requirement. Thus, making the hardened layer extra thick on the right side of the oil lubrication hole 1003 makes no sense in terms of meeting the requirements set by the consumer and only represents a waste of energy. Furthermore, applying the same amount of energy to both sides could imply an increased risk of overheating on one of the sides. This risk is greater due to the fact that the angle between the inner wall of the oil lubrication hole and the surface of the path to be hardened is more acute on the side towards which the oil lubrication hole extends, i.e., the angle is more acute on the right side of the oil lubrication hole in Fig. 13 than on the left, which means that the edge on the right side is sharper, increasing the risk of damage in case of overheating.

[0174] As stated above, the scanning process is preferably rapid to avoid significant temperature fluctuations. As the laser beam repeatedly scans along a two-dimensional scan pattern—such as a plurality of parallel lines—to form an equivalent or virtual effective laser spot, regions of the workpiece will be repeatedly heated if the regions remain within the scan pattern. The actual laser spot will heat different points on the surface as it is repeatedly scanned across the entire virtual laser spot, and these points will thus be repeatedly heated to a maximum temperature. Each time after being heated, they will cool until they are heated again during the next sweep of the laser beam along the scan pattern, i.e., during the next cycle of the scanning process.It is desirable to keep these fluctuations between local temperature maxima and minima as small as possible. For this purpose, a high sampling speed and high frequency are preferred. Fig. 14A, Fig. 14B schematically show the result of the test performed on a crankshaft using a fixed scanning pattern and a fixed power. In the case of Fig. 14A or the scanning frequency of 50 Hz (i.e., the laser beam followed the complete scanning pattern 50 times per second). It can be seen that after reaching the maximum temperature, fluctuations between local maxima and minima with an amplitude of more than 100 °C, in fact, close to 200 °C, occurred. This could be problematic, as it could imply a risk of overheating and / or a risk of inadequate curing or cure depth.

[0175] Fig. Figure 14B shows schematically the result of a test carried out under the same conditions as those in Fig. 14A, but with a sampling frequency of 250 Hz. Here, it can be observed how the temperature fluctuations between the local maxima and minima, corresponding to the thickness of the graph, have an amplitude of significantly less than 100 °C.

[0176] The Fig. 15A and Fig. 15B schematically show how an effective laser spot 5 can be applied to a journal 1001 of a crankshaft with an oil lubrication hole 1003 and undercut grooves 1004, so as to heat a portion such as approximately 30-180° of an annular segment 1001A thereof. Since the effective laser spot 5 extends no more than 180° in the circumferential direction W of the journal in order to heat the entire annular segment, the journal can be arranged to rotate about its rotation axis X and / or the laser source can be adjusted relative to the crankshaft. Heating can begin at a lateral end of the journal 1001, as in Fig. 15A, near the undercut groove 1004, and the stud can be rotated, for example, to heat the entire circumference to heat the ring segment 1001A to a sufficient temperature and for a sufficient time to ensure a required hardening depth. To harden the entire surface of the stud, the effective laser spot 5 is progressively shifted along the stud in a direction parallel to the rotation axis X, for example, by shifting the laser source parallel to the X-axis or by shifting the beam parallel to the X-axis using a scanning mirror. Thus, the heated ring segment 1001A is expanded in this direction, and the subsequent heat region can begin to cool, thereby achieving quenching. Fig. 15B, it can be observed how the effective laser spot was moved over the main area of the stud, heating it and then allowing quenching as it moved further. The effective laser spot is moved until it reaches the groove at the right end of the Fig. 15B. The two-dimensional energy distribution is adjusted near the grooves 1004 and also in correspondence with the oil lubrication hole 1003 to prevent overheating of these parts. An advantage of this method of carrying out the hardening process is that there is no reheating of an already heated area, since the growth of the hardened area occurs in the direction from one end of the journal to the other, i.e., in the first direction parallel to the X-axis of rotation of the journal and not in the circumferential direction W. That is, hardening occurs from left to right and not in the circumferential direction. Thus, there is fundamentally no risk of undesirable reheating and excessive tempering of an already hardened surface area.

[0177] When hardening the surface of the journal circumferentially, special attention must be paid to the overlap area, i.e., the area where the effective laser spot, near the end of its travel along the circumferential path, arrives at a previously hardened area. Reheating a previously hardened area to a high temperature, such as the temperature used for hardening, should generally be avoided. Fig. 19A-19C show an arrangement similar to that of Fig. 12A-12C, but instead of the oil lubrication holes, the more heat-sensitive sub-area that the laser spot approaches corresponds to a previously hardened area 1001B of the journal. In this embodiment, as shown in Fig. 19A, the effective laser spot is composed of an array of segments (similar to that of Fig. 6D), and when the leading edge of the effective laser spot arrives at the previously heated area 1001B, the segments in the first row are deleted (see Fig. 19B), for example, by setting the laser to an “off” state in accordance with the segments. In Fig. 19C, additional rows of segments were removed, shrinking the effective laser spot circumferentially. This means that the effective laser spot progressively disappears at its leading edge or front region as it reaches the previously hardened region 1001B, while the trailing edge or rear region catches up with the front region until the effective laser spot disappears.

[0178] In other embodiments of the invention, the effective laser spot is not eliminated, but rather its entire power / energy is reduced. This allows the effective laser spot to move only once around the stud and heat the surface to a temperature suitable for tempering.

[0179] In further embodiments of the invention, a plurality of laser sources can be used to heat multiple sections of the ring segment simultaneously, for example, to heat the entire 360° of the ring segment 1001A simultaneously. This reduces the need for rapid rotation of the crankshaft to avoid temperature fluctuations that could negatively affect the hardening quality, as discussed above. A very high rotation speed of the crankshaft can be expensive to implement and can make it more difficult to adjust the energy distribution of the effective laser spot or effective laser spots to avoid overheating the area adjacent to a fast-moving oil lubrication hole.

[0180] The following invention thus provides an extremely flexible approach to hardening a laser surface and can therefore be very useful for, for example, laser hardening workpieces with surface areas that have significantly different properties with regard to heat transfer sensitivity and / or significantly different requirements with regard to, for example, aspects such as the depth of the hardened layer.

[0181] The system can be operated with feedback from a pyrometer and, for example, PID control.

[0182] The following is an example of how the invention may be implemented in accordance with a practical embodiment thereof: The Fig. 16A, Fig. 17A and Fig. 18A represent the power or energy distribution over an effective laser spot, calculated for a scanning pattern of the Fig. 16B and Fig. 16C, Fig. 17B and Fig. 17C, Fig. 18B and Fig. 18C. The scanning pattern is of the type shown in Fig. 9, discussed above, namely a scanning pattern with eight segments, which the user can rearrange in terms of their position, orientation, and lengths, and for which the user can select and adjust one or more power / energy-related parameter values, for example, the power of the laser beam and / or the speed of the projected laser spot along the scanning pattern. In this example, a constant power was used, and the speed was adjusted on a segment-by-segment basis. As explained above, the computer system 100 can be provided with calculation / simulation software to calculate / simulate the heating or energy distribution resulting from a selected pattern 2G and from the scanning speeds (and / or other parameters, such as the laser beam power, the laser spot size, etc.).) assigned to different segments ah, allowing the user to quickly identify a pattern configuration that seems useful. The calculated energy distributions, such as those of the . Fig. 16A, Fig. 17A and Fig. 18A can be visualized on a screen 102 to help the user estimate whether the energy distributions are likely to be suitable.

[0183] The Fig. 16A, Fig. 17A and Fig. 18A show how a calculated energy / power distribution can be made over the effective laser spot, calculated based on the specific patterns and velocities from the Fig. 16B, Fig. 17B, Fig. 18B and Fig. 16C, Fig. 17C and Fig. 18C for the following values: d1-d12 indicate the dimensions of the sample in accordance with the example shown; the values in mm according to this example are as follows: d1=16; de=2.8; d3=3.1; d4=3.9; d5=7; d6=1.4; d7=0.4; d8=13; d9=5.1; d10=6; d11=2.8; d12=0.2. v1-v10 indicate the scanning speeds associated with the different parts of the scanning pattern; the values in mm / s according to this example are as follows: v1=3600; v2=8000; v3=4600; v4=3500; v5=6000; v5=5500; v7=3600; v8=8000; v9=5430; v10=8000; v11=5500

[0184] In Fig. 16A, Fig. 17A and Fig. 18A shows the corresponding power or energy distribution patterns. Fig. 16A-16C refer to a pattern that may be suitable for heating the surface of a crankshaft journal across the journal in a direction parallel to the longitudinal axis of the crankshaft, into a less heat-sensitive sub-area, away from an oil lubrication hole. Thus, the pattern and speeds of the Fig. 16A-16C in a situation like that in Fig. 12A is shown. The Fig. 17A-17C show a pattern and the corresponding energy distribution across the effective laser spot when the effective laser spot reaches an oil lubrication hole, such as when the effective laser spot is at the position shown in Fig. 12B, and takes on a “U-shape” or similar. Here, taking into account the Fig. 9 shown scanning pattern of one of the central segments, such as the segment “c” according to Fig. 9, to avoid overheating of the heat-sensitive sub-area adjacent to the oil lubrication hole. In a corresponding manner, the Fig. 18A-18C the energy distribution and the scanning pattern when the effective laser spot is just about to leave the area adjacent to the oil lubrication hole, ie at a position such as that shown in Fig. 12C is shown.

[0185] Using this configuration and a laser beam applying a 3.4 mm diameter laser spot to journals made of low-carbon (0.40%) steel (type 1538MV), an effective case depth (hardness >HRC45) of 2.5 mm was achieved with a 1 mm layer of pure martensite. The laser beam power was 2700 W, and the journal was a main journal with a width of 21 mm. Very similar results were also obtained when hardening a 19 mm wide crankpin surface, using essentially the same setup and parameters, except that the laser beam power was set to 2400 W and the scanning pattern width was reduced to 14 mm. In both cases, the effective laser spot moved along the surface in the circumferential direction at a speed of 168 mm / minute.

[0186] The scanning pattern was applied with an offset center with respect to the center of the hardened pin, in accordance with what was Fig. 7A: an offset (in the direction perpendicular to the plane containing the laser source and the central longitudinal axis of the journal) was 31 mm for the main journal with a radius of 34.45 mm and 25.2 mm for the crank pin with a radius of 28.45 mm. Due to the offset, the total area of the effective laser spot projected onto the journal was larger than it would have been if it had been projected without the offset.

[0187] Reference numerals used in the present invention: 1 laser source 2 laser beam 2' s-polarized laser beam 2" p-polarized laser beam 2A Path scanned by the laser beam, or area scanned by the laser beam 2B Path scanned by the laser beam, or area scanned by the laser beam 2C Path scanned by the laser beam, or area scanned by the laser beam 2D path scanned by the laser beam, or area scanned by the laser beam 2E Area of a virtual, rectangular laser spot with high power density 2F area of a virtual, rectangular laser spot with low power density 2G scanning pattern; path scanned by the laser beam 2H area of an effective laser spot with power density adjusted for a hardening process 2I Area of an effective laser spot with a power density adapted for quenching 2J area of an effective laser spot with power density adapted to a tempering process 3 scanning system 4 Polarization system 5 Effective laser spot 5A, 5B Energy distribution around an inclined oil lubrication hole 11 laser sleds 12 First laser carriage drive device for vertical movement of the laser source 13 Second laser carriage drive device for horizontal movement of the laser source 14 Horizontal path for moving the laser source 20 workpiece slides 21 Workpiece slide drive device 41 Polarizer 42 mirrors 43 mirrors 44 mirrors 51 lines of a scanning pattern 51A “On” segments or pixels 52B “Off” segments or pixels 100 computer systems 101 Computer Input Devices 102 computer screen 110 First computer memory area 111 Sample pattern segment column 112 Scanning speed column 113 Beam power column 114 Spot size column 120 Second computer memory area 121 Sample pattern segment column 122 Scanning speed column 123 Beam power column 124 Spot size column 130 hands 140 First computer memory area 141 Memory location for storing a pixel value (On / Off) 150 Second computer memory area 151 Memory location for storing a pixel value (On / Off) 1000 crankshaft 1001 main journals 1001A Heated / hardened ring segment of the surface of a main journal 1001B Previously hardened area of a tenon 1002 crank pins 1003 oil lubrication holes 1003A, 1003B Areas of the pin on the sides of the opening of an oil lubrication hole 1004 grooves 1005 Surface perpendicular to the cones 1006 Area or section that can be scanned by the laser beam a, b, c, d, e, f, g, h Segments of a scanning pattern A, B, C, D, E, F, G, H speed indicators α, β, γ, γ1, γ2 angles referred to in the description X, Y, Z directions in space W is the circumferential direction d1-d12 Indication of different dimensions of a scanning pattern, in mm v1-v11 Indications of a scanning speed corresponding to different segments of a scanning pattern, in mm / s

[0188] In this document, the term “effective laser spot” refers to an area onto which a laser beam is effectively projected to illuminate and heat the area.The effective laser spot may be a laser spot obtained by reshaping a U-shaped laser beam using optics to shape the laser spot and distribute the power across the effective laser spot in a desired manner, or a virtual or equivalent laser spot obtained by rapidly and repeatedly scanning the laser beam along a scanning pattern to repeatedly apply the laser beam to the same area or substantially the same area such that the heating effect of the laser beam is substantially the same as it would have been if a stationary laser beam with a power distribution corresponding to the power distribution across the virtual or equivalent laser spot during a scanning cycle had been used.Here, the term "fast" means that the scanning speed is much greater than the speed of the relative movement between the laser source and the surface of the crankshaft, for example, in the circumferential direction, so that parts of the surface area to be hardened are repeatedly hardened by the laser spot. For example, the scanning speed can typically be selected to achieve at least 10, 50, or 100 scanning cycles per second.Preferably, when the effective laser spot is a virtual or equivalent laser spot obtained by repeatedly scanning an actual or real laser spot over the surface to be hardened, the scanning is preferably carried out in two dimensions and the size of the virtual laser spot in both dimensions is preferably at least 2, 3, 4, 5, 10, 20 or even a multiple of the size of the actual or real laser spot in that dimension, for example in the direction parallel to a rotation axis of a crankshaft and in the circumferential direction of a journal of the crankshaft. The term "scanning" is preferably intended to imply the movement of the laser beam and the scanning pattern is preferably intended to refer to the pattern that the beam would follow on a stationary surface, i.e., without taking into account the relative movement between the laser source and the surface of the workpiece.

[0189] Generally speaking, the increment of the hardened area or segment is achieved by a relative movement between the effective laser spot and the surface to be hardened, for example, in the case of a crankshaft, by rotation of the crankshaft. To achieve a sufficient hardening depth, for example, a case hardening depth of 1000 µm or more, it is preferred that substantially every portion of the surface area to be hardened remains in the area of the effective laser spot for a sufficiently long period of time, such as typically 0.5-5 seconds in the case of crankshaft journals, such as 1-3 seconds, so that not only will the surface temperature be high enough, but such that the workpiece is sufficiently heated to the required depth.Increasing the laser beam's power density is no substitute for sufficient heating time, as the surface area should not be overheated, as this could cause damage to the workpiece. Therefore, the surface temperature should remain within an adequate range for a sufficient period of time.Therefore, a significant size of the effective laser spot is desired in one dimension to ensure a sufficient width of the hardening path (for example, to cover substantially the entire width of a crankshaft journal) and in another dimension to allow a high relative speed between the effective laser spot and the surface to be treated (thus ensuring a high production speed), while at the same time allowing the areas to be hardened to remain within the effective laser spot for a sufficient period of time to achieve the desired and required hardening depth.

[0190] In this document, the term "crankshaft" preferably refers to the part of an engine that translates reciprocating linear piston motion into rotation, for example, the type of crankshaft used in internal combustion engines such as those used in many types of motor vehicles, such as trucks, automobiles and motorcycles.

[0191] In the present document, the hardening depth preferably refers to the effective case depth, which preferably refers to the distance perpendicular to the surface of the hardened insert to the furthest point at which a specified hardness level is obtained. The level can be in the range of, for example, 40-55 HRC, preferably 45 HRC. In the field of crankshafts, hardness levels are generally determined taking into account the carbon content of the steel, but a typical level is 45 HRC. In the context of the present invention and with regard to the hardening of crankshaft journals, a hardening depth of at least 1000, 2000, or 3000 µm is preferred.

[0192] Another aspect of interest may be the degree or depth to which 100% transformed martensite can be observed. In the context of the present invention and with regard to the hardening of crankshaft journals, this depth may preferably be at least 200, 300, 500, 800, 1000 µm or more.

[0193] When a segmented scanning pattern is used, a scanning speed of at least 300 segments per second may be preferred, with speeds of, for example, at least 600, 1000, 5000 and 10 0000 segments per second being even more preferred, preferably in combination with repetition frequencies of the scanning pattern of at least 10 Hz, more preferably at least 50 Hz, even more preferably at least 100 Hz or 200 Hz.

[0194] Although the present invention has been described with several references to the surface hardening of crankshafts, the scope of protection is in no way limited to the surface treatment of crankshafts.

[0195] In this text, the term "comprises" and its inflections (such as "comprehensive" etc.) should not be understood in an exclusive sense, that is, these expressions should not be interpreted in such a way as to exclude the possibility that what is described and defined may include further elements, steps, etc.

[0196] On the other hand, the invention is not limited to the specific embodiment(s) described here, but also includes any variations that may be considered by a person skilled in the art to be within the general scope of protection as defined in the claims (for example, with regard to the choice of materials, dimensions, components, configuration, etc.).

Claims

[1] A method for laser hardening a surface of a journal (1001, 1002) of a crankshaft (1000), wherein the journal has a surface region to be hardened, wherein the surface region extends in a first direction parallel to a rotational axis (X) of the crankshaft and in a second direction corresponding to a circumferential direction (W) of the journal, wherein the surface region comprises at least one more heat-sensitive sub-region and at least one less heat-sensitive sub-region, wherein the at least one more heat-sensitive sub-region comprises a region adjacent to an oil lubrication hole (1003) of the crankshaft, the method comprising: Projecting a laser beam (2) from a laser source (1) onto the surface area so as to produce an effective laser spot (2A, 2B, 2C, 2D, 5) on the surface area, wherein the effective laser spot (2A, 2B, 2C, 2D, 5) extends in the first direction over the main part of the area to be hardened; Generating a relative movement between the surface of the crankshaft (1000) and the laser source (1) in the circumferential direction so as to project the effective laser spot (2A, 2B, 2C, 2D, 5) successively onto different parts of the surface area in the circumferential direction; during the relative movement, repeatedly scanning the laser beam (2) over the respective part of the surface area in two dimensions so as to produce the effective laser spot (2A, 2B, 2C, 2D, 5) as a two-dimensional effective laser spot (2A, 2B, 2C, 2D, 5) on the surface area, wherein the effective laser spot (2A, 2B, 2C, 2D, 5) is an equivalent laser spot exhibiting a two-dimensional energy distribution; wherein the method comprises dynamically adjusting the two-dimensional energy distribution such that the two-dimensional energy distribution is different when the less heat-sensitive sub-region is heated than when the more heat-sensitive sub-region adjacent to an oil lubrication hole (1003) is heated, so as to avoid overheating of the region adjacent to an oil lubrication hole (1003), and wherein during at least 50% of the time of application of the effective laser spot (2A, 2B, 2C, 2D, 5) on the surface region, the effective laser spot has a width in the circumferential direction (W) of at least 5 mm. [2] A method according to claim 1, in which during at least 50% of the time of applying the effective laser spot (2A, 2B, 2C, 2D, 5) on the surface area, the effective laser spot has a width in the circumferential direction (W) of at least 7 mm, preferably at least 10 mm and more preferably at least 15 mm, 20 mm, 30 mm or more, such as at least 50 mm. [3] A method for laser hardening a surface of a journal (1001, 1002) of a crankshaft (1000), wherein the journal has a surface region to be hardened, wherein the surface region extends in a first direction parallel to a rotational axis (X) of the crankshaft and in a second direction corresponding to a circumferential direction (W) of the journal, wherein the surface region comprises at least one more heat-sensitive sub-region and at least one less heat-sensitive sub-region, wherein the at least one more heat-sensitive sub-region comprises a region adjacent to an oil lubrication hole (1003) of the crankshaft, the method comprising: Projecting a laser beam (2) from a laser source (1) onto the surface area so as to produce an effective laser spot (2A, 2B, 2C, 2D, 5) on the surface area, wherein the effective laser spot (2A, 2B, 2C, 2D, 5) extends in the first direction over the main part of the area to be hardened; Generating a relative movement between the surface of the crankshaft (1000) and the laser source (1) in the circumferential direction so as to project the effective laser spot (2A, 2B, 2C, 2D, 5) successively onto different parts of the surface area in the circumferential direction; during the relative movement, repeatedly scanning the laser beam (2) over the respective part of the surface area in two dimensions so as to produce the effective laser spot (2A, 2B, 2C, 2D, 5) as a two-dimensional effective laser spot (2A, 2B, 2C, 2D, 5) on the surface area, wherein the effective laser spot (2A, 2B, 2C, 2D, 5) is an equivalent laser spot exhibiting a two-dimensional energy distribution; wherein the method comprises dynamically adjusting the two-dimensional energy distribution such that the two-dimensional energy distribution is different when the less heat-sensitive sub-region is heated than when the more heat-sensitive sub-region adjacent to an oil lubrication hole (1003) is heated, so as to avoid overheating of the region adjacent to an oil lubrication hole (1003), wherein the effective laser spot extends in said first direction over more than 50% of the pin (1001, 1002). [4] The method of claim 3, wherein the effective laser spot extends over more than 75% of the stud in said first direction. [5] A method according to any one of the preceding claims, in which the effective laser spot (2A, 2B, 2C, 2D, 5) is an equivalent laser spot obtained by scanning the laser beam (2) in the first direction and in the second direction, repeatedly following a scanning pattern along which the laser spot is moved at a scanning speed, such that the two-dimensional energy distribution during a scanning cycle is determined by the scanning speed, the scanning pattern, the size of the laser spot, the power of the laser beam and the power distribution within the laser beam. [6] A method according to claim 5, in which an adjustment of the energy distribution is carried out by adjusting at least one of scanning speed, scanning pattern, Size of the laser spot, Power of the laser beam, and Power distribution within the laser beam, such that the energy distribution when the less heat-sensitive sub-region is heated is different from when the more heat-sensitive sub-region, including the region adjacent to an oil lubrication hole (1003), is heated, so as to avoid overheating of the region adjacent to an oil lubrication hole (1003). [7] Method according to claim 6, in which an adjustment of the energy distribution is carried out by adjusting the power of the laser beam (2), for example by switching the laser beam (2) on and off during a scanning operation of the laser spot along the scanning pattern. [8] A method according to claim 5, in which the energy distribution is controlled by selectively adjusting the power of the laser beam during a scan of the laser spot along the scan pattern so as to selectively place the laser beam into one of a plurality of available power states at least 300 times per second, preferably at least 600 times per second, more preferably at least 1000 times per second, more preferably at least 5000 times per second and even more preferably at least 10 000 times per second. [9] The method of claim 8, wherein the scanning pattern comprises a plurality of segments (51A, 51B; a, b, c, d, e, f, g, h), each of the segments being associated with one of the available power states, and wherein the power state associated with at least one of the segments is different during heating of the less heat-sensitive sub-region than during heating of the more heat-sensitive sub-region, including the region adjacent to an oil lubrication hole (1003). [10] A method according to any one of claims 6-9, in which the adjustment of the energy distribution is carried out by adjusting the scanning speed during a scanning operation of the laser spot along the scanning pattern. [11] A method according to any one of claims 5-10, in which the scanning operation is carried out at a scanning speed which is sufficiently high such that the temperature variations at points within the effective laser spot have an amplitude of less than 200 °C, preferably less than 150 °C, more preferably less than 100 °C and even more preferably less than 50 °C between a local maximum and the following local minimum of the temperature. [12] A method according to any one of the preceding claims, in which the energy distribution in the effective laser spot (2A, 2B, 2C, 2D, 5) is such that more energy is applied towards the ends of the effective laser spot in the first (X) direction than towards the center of the effective laser spot in the first (X) direction. [13] Method according to one of the preceding claims, in which the energy distribution shows a higher energy density at a front region (2E) of the effective laser spot than at a rear region (2F) of the effective laser spot, such that a region swept over by the effective laser spot first receives laser radiation with a higher average power and subsequently receives laser radiation with a lower average power. [14] A method according to any one of the preceding claims, comprising the step of applying the effective laser spot to the surface area on both sides of the oil lubrication hole (1003) in the first direction, said oil lubrication hole (1003) extending inwardly in an oblique manner so as to extend not under a first (1003A) of the sides but onto a second (1003B) of the sides, said effective laser spot being adapted to apply more energy (5A) to the first (1003A) of the sides than to the second (1003B) of the sides. [15] A method according to any one of the preceding claims, in which the effective laser spot (5) has a first shape in the less heat-sensitive sub-region and is formed to have a substantially U-shape when arriving at an oil lubrication hole (1003) and a substantially inverted U-shape when leaving the oil lubrication hole (1003), or vice versa, and wherein the first shape is optionally a substantially rectangular or triangular shape. [16] A method of laser hardening a surface of a workpiece, wherein the workpiece comprises at least one surface region to be hardened, wherein the surface region comprises at least one more heat-sensitive sub-region and at least one less heat-sensitive sub-region, the method comprising: Projecting a laser beam (2) from a laser source (1) onto the surface area to produce a laser spot on the area; Generating a relative movement between the surface of the workpiece (1000) and the laser source (1), thereby enabling the laser spot to be projected successively onto different parts of the surface area; during the relative movement, repeatedly scanning the laser beam (2) over the respective part of the surface area in two dimensions so as to produce a two-dimensional equivalent effective laser spot (2A, 2B, 2C, 2D, 5) on the surface area, the effective laser spot having a two-dimensional energy distribution; wherein the two-dimensional energy distribution is dynamically adjusted during the relative movement so that it is different in a more heat-sensitive sub-region than in a less heat-sensitive sub-region, in order to prevent overheating of the more heat-sensitive sub-region. [17] Method according to claim 16, comprising scanning the laser beam along a scanning pattern within the effective laser spot (5) and modifying the power of the laser beam along the scanning pattern so as to obtain the energy distribution, optionally by switching the laser beam on / off along the scanning pattern. [18] A method according to claim 16, in which the energy distribution is controlled by selectively adjusting the power of the laser beam during a scan of the laser spot along the scan pattern so as to selectively place the laser beam into one of a plurality of available power states at least 300 times per second, more preferably at least 600 times per second, more preferably at least 1000 times per second, more preferably at least 5000 times per second and even more preferably at least 10 000 times per second. [19] A method according to claim 18, in which the scanning pattern comprises a plurality of segments (51A, 51B; a, b, c, d, e, f, g, h), each of the segments being associated with one of the available power states, and wherein the power state associated with the at least one of the segments is different in the less heat-sensitive sub-region than in the more heat-sensitive sub-region. [20] A method according to any one of claims 16-19, comprising the step of using a different scanning pattern for the laser beam within the effective laser spot in the more heat-sensitive sub-region compared to the less heat-sensitive sub-region. [21] A method according to any one of claims 16-20, comprising the step of adjusting the energy distribution by adjusting the scanning speed so that it is different in the more heat-sensitive sub-region compared to the less heat-sensitive sub-region in at least a part of the effective laser spot. [22] A method according to any one of the preceding claims, in which the effective laser spot (5) comprises a front region (2H) with an energy distribution and an energy density selected to heat a surface region of the workpiece to a hardening temperature, an intermediate region (2I) with an energy distribution and energy density selected to allow cooling of a heated region for quenching, and a rear region (2J) with an energy distribution and energy density designed to heat the quenched region to produce its tempering. [23] A method according to any preceding claim, in which the effective laser spot is established by repeatedly scanning the laser beam over the workpiece along a pattern comprising a plurality of lines (51), the lines preferably being substantially parallel, the scanning being repeated at a scanning frequency, and each of the plurality of lines comprising a plurality of segments (51A, 51B), the method comprising assigning a predetermined laser beam power value to each of the segments so as to selectively adjust the output power of the laser beam at some of the segments to a different level than at others of the segments. [24] A method according to claim 23, in which the sampling frequency is at least 50 Hz, preferably 100 Hz, wherein the plurality of lines comprises at least two lines, preferably at least 3 lines, more preferably at least 4 lines, such as 5-10 lines, and wherein each line comprises at least 3 segments (51A, 51B), preferably at least 5 segments and more preferably at least 10 segments, such as 10-20 segments. [25] A method according to claim 5 or 16, in which the scanning of the laser beam is carried out such that the laser spot repeatedly follows a scanning pattern having a plurality of segments (51A, 51B; a, b, c, d, e, f, g, h) and wherein at least one parameter value influencing the two-dimensional energy distribution is associated with each of the segments, and in which the at least one parameter value is dynamically adjusted during operation such that the at least one parameter value is different for at least one of the segments when the effective laser spot heats the more heat-sensitive sub-region than when it heats the less heat-sensitive sub-region. [26] The method of claim 25, wherein said one parameter value is indicative of at least one of scanning speed, laser spot size, laser beam power, power distribution within the laser beam, length of the corresponding segment, and orientation of the corresponding segment. [27] A method according to claim 25, in which the one parameter value is indicative of the power of the laser beam in accordance with the respective segment. [28] Method according to one of claims 25-27, comprising the step of storing for each segment the corresponding at least one parameter value in a memory, wherein for at least one segment at least two different parameter values are stored in the memory, a first to be used when heating the less heat-sensitive sub-region and a second to be applied when heating the more heat-sensitive sub-region. [29] A method according to any one of claims 25-28, in which the scanning is carried out at an average speed of at least 300 segments per second, preferably at least 600 segments per second, more preferably at least 1000 segments per second, more preferably at least 5000 segments per second and even more preferably at least 10 0000 segments per second. [30] Method according to one of the preceding claims, comprising the step of reducing the energy density at a front region of the effective laser spot (5) when the effective laser spot arrives at a previously hardened part of the surface area, such as a previously hardened area (1001B) of a journal (1001, 1002) of a hardened crankshaft, by shifting the effective laser spot around the journal in the circumferential direction (W). [31] A method according to any preceding claim, comprising the step of interrupting a movement of the effective laser spot at a front portion of the effective laser spot when the effective laser spot arrives at a previously hardened part of the surface area, such as a previously hardened portion (1001B) of a journal (1001, 1002) of a crankshaft hardened by shifting the effective laser spot around the journal in the circumferential direction (W), while a rear portion of the effective laser spot continues to move in the circumferential direction, whereby the size of the effective laser spot is progressively reduced in the circumferential direction until the effective laser spot disappears. [32] A method according to claim 16, wherein the scanning operation is carried out such that the laser spot follows a scanning pattern (2G) on the surface area, wherein at least one of (i) a scanning speed; and / or (ii) a laser beam power; and / or (iii) a laser spot size; in one part of the scanning pattern is different from that in another part of the scanning pattern, so as to avoid overheating of the workpiece in the more heat-sensitive sub-region. [33] A method according to claim 32, in which the scanning pattern (2G) comprises a plurality of segments (a, b, c, d, e, f, g, h; 51A, 51B) and in which each of the segments is assigned there (i) a scanning speed; and / or (ii) a laser beam power; and / or (iii) a laser spot size; whereby at least one of the scanning speed, the laser beam power, and the laser spot size is selected differently with respect to at least one of the segments compared to at least one other of the segments. [34] A method according to claim 33, in which the scanning speed is selected so that it is higher in a segment (c, g; a, e) which is closer to a more heat-sensitive sub-region than in two adjacent segments (b, d; h, f) which are further away from the heat-sensitive sub-region. [35] A method according to claim 33 or 34, in which the laser beam power is selected such that it is lower in a segment (c, g; a, e) which is closer to a more heat-sensitive sub-region than in two adjacent segments which are further away from the heat-sensitive sub-region (b, d; h, f). [36] A method according to any one of claims 33-35, in which the laser spot is selected to have a larger area (c, g; a, e) in a segment closer to a more heat-sensitive sub-region than in two adjacent segments (b, d; h, f) further away from the heat-sensitive sub-region. [37] Method according to any one of claims 33-36, in which the (i) scanning speed; and / or (ii) laser beam power; and / or (iii) laser spot size; associated with one or more of the segments, is modified at least once when the surface of the workpiece (1000) moves relative to the laser source (1). [38] A method according to any one of claims 32-37, in which the scanning pattern (2G) has a geometric shape, the geometric shape of the scanning pattern (2G) being modified at least once when the surface of the workpiece (1000) moves relative to the laser source (1). [39] A method according to claim 16, wherein the scanning is performed such that the laser spot follows a scanning pattern (2A, 2B, 2C, 2D, 2E, 2F, 2G) on the area, the scanning pattern having a geometric configuration, the geometric configuration of the scanning pattern being modified at least once during the relative movement between the surface area and the laser source. [40] A method according to claim 16, wherein the method comprises: Modulating the laser beam (2); wherein the laser beam (2), when the laser spot is located in the more heat-sensitive sub-area, is modulated differently than when it is located in the less heat-sensitive sub-area, in order to prevent overheating of the respective area of the workpiece; where A- the laser beam is modulated in its power; and / or B- the laser beam is modulated in its scanning speed; and / or C- the laser beam is modulated in its scanning pattern such that the laser spot follows a different scanning pattern (2B, 2D) in accordance with the more heat-sensitive sub-area than in accordance with the less heat-sensitive sub-area; and / or D- the laser beam is modulated in its laser spot size so that the laser spot size is different in accordance with the more heat-sensitive sub-area than in accordance with the less heat-sensitive sub-area. [41] The method of claim 16, wherein the heating is performed such that the portion of the surface of the workpiece entering a region swept by the laser beam first receives laser radiation having a higher average power and thereafter receives laser radiation having a lower average power. [42] A method according to any one of the preceding claims, in which producing a relative movement between the workpiece (1000) and the laser source (1) comprises rotating the workpiece about a rotation axis so that the laser light spot can access the entire circumference of the surface area to be hardened. [43] The method of claim 42, wherein producing a relative movement between the workpiece (1000) and the laser source (1) comprises producing a relative movement in a first direction perpendicular to the rotation axis and in a second direction perpendicular to the rotation axis, wherein the movement in the first direction is produced by translating the workpiece, and wherein the movement in the second direction is produced by translating the laser source, and optionally wherein the laser source (1) is movable parallel to the rotation axis. [44] A method according to any one of claims 16-43, wherein the workpiece is a crankshaft (1000) having a plurality of oil lubrication holes (1003). [45] The method of claim 44, wherein the at least one surface area to be hardened is the general surface of a journal (1001, 1002) of the crankshaft. [46] Method according to claim 44, wherein the effective laser spot extends over more than 50% of a journal (1001, 1002) of the crankshaft, preferably over more than 75% of the journal in a direction parallel to a longitudinal direction of the crankshaft. [47] A method according to claim 16, in which the scanning operation is carried out by keeping the power of the laser beam substantially constant and adjusting the scanning speed and / or the scanning pattern so as to apply less energy to more heat-sensitive sub-regions than to less heat-sensitive sub-regions of the surface. [48] A method according to claim 16, wherein the scanning operation is performed by keeping the scanning pattern substantially constant and adjusting the scanning speed and / or the beam power so as to apply less energy to more heat-sensitive sub-regions than to less heat-sensitive sub-regions of the surface, for example by dynamically adjusting an on / off state of the laser beam in accordance with segments (51A, 51B) of the scanning pattern. [49] A method according to claim 16, in which the scanning pattern comprises a plurality of segments, and in which each of the segments is assigned a beam power state to adjust the power of the laser beam in correspondence with each segment to a power level corresponding to the power state, and in which the laser is arranged so that the power of the laser beam is changed as required and by the beam power states, and in which the scanning process takes place at a speed of at least 300 segments per second, preferably at least 600 segments per second, more preferably at least 1000 segments per second, more preferably at least 5000 segments per second, and even more preferably at least 10 000 segments per second, the scanning pattern being carried out at a frequency of at least 10 Hz, preferably at least 50 Hz, most preferably at least 100 Hz,and in which the power state associated with at least one of the segments is different in accordance with the more heat-sensitive sub-region than in accordance with the less heat-sensitive sub-region. [50] A method according to any one of claims 47-49, in which the more heat-sensitive sub-regions comprise regions adjacent to the oil lubrication holes (1003) and optionally regions adjacent to grooves (1004) at the axial ends of the journals of the crankshaft. [51] A method according to any one of the preceding claims, in which the laser source comprises a fiber laser. [52] Device for hardening a surface area of a workpiece (1000), wherein the surface area comprises at least one less heat-sensitive sub-area and at least one more heat-sensitive sub-area, wherein the device comprises a laser source (1) arranged to project an effective laser spot onto the surface area, and a device (12, 13, 21) for generating a relative movement between the surface area and the effective laser spot, so that the effective laser spot is moved along the surface area in order to successively and progressively heat different parts of the surface area to a temperature suitable for hardening, wherein further during the relative movement a repeated scanning of the laser beam (2) over the respective part of the surface area takes place in two dimensions in order to thus generate the effective laser spot (2A, 2B, 2C, 2D, 5) as a two-dimensional effective laser spot (2A, 2B,2C, 2D, 5) on the surface area, wherein the effective laser spot is arranged such that it is an equivalent laser spot exhibiting a two-dimensional energy distribution, the device further comprising a control system (100) for controlling the operation of the device, the control system being arranged such that it dynamically controls the two-dimensional energy distribution such that it is different in the more heat-sensitive sub-area than in the less heat-sensitive sub-area, the laser source comprising a scanning device arranged for two-dimensional scanning of a laser beam from the laser source, the control system being arranged for scanning the laser beam in two dimensions along a scanning pattern having a plurality of segments to thereby generate the effective laser spot, the scanning pattern being repeated at a repetition rate of at least 10 Hz. [53] Apparatus according to claim 52, in which the at least one more heat-sensitive sub-region comprises: - an area adjacent to a hole in the surface area, such as an oil lubrication hole (1003); and / or - a groove (1004), such as an undercut groove; and / or - a previously hardened part of the surface area, such as the part at which the effective laser spot arrives at the end of a 360° trajectory along the circumference of an object, such as a cylindrical journal (1001, 1002) of a crankshaft (1000). [54] Apparatus according to any one of claims 52-53, configured to operate such that the effective laser spot has a size and moves along the surface area at a speed such that during at least part of the movement of the effective laser spot along the surface area, preferably during at least 50% and more preferably during at least 90% and even more preferably during 100% of the movement of the effective laser spot along the surface area, it heats parts within the surface area heated by the effective laser spot for at least 0.5 second, preferably at least 1 second, and wherein the size of the effective laser spot in the direction in which the effective laser spot moves along the surface area is at least 5 mm, preferably at least 7 mm, more preferably at least 10 mm and even more preferably at least 15 mm, 20 mm, 30 mm or more, such as at least 50 mm. [55] Apparatus according to any one of claims 52-54, arranged to generate the effective laser spot by generating a plurality of segments (a, b, c, d, e, f, g, h; 51A, 51B) of the effective laser spot, the plurality of segments comprising at least six segments, wherein the control system is arranged to modify the two-dimensional energy distribution by selectively modifying the energy density and / or the distribution of the segments in accordance with the parameter values associated with the segments, the parameter values being stored in a memory of the control system. [56] Apparatus according to claim 55, in which the parameter values are indicative of a beam power level and / or a scanning speed of the beam in accordance with the corresponding segment of the scanning pattern. [57] Apparatus according to any one of claims 52-54, wherein the scanning pattern is repeated at a repetition rate of at least 50 Hz, preferably at least 100 Hz and more preferably at least 200 Hz. [58] Apparatus according to any one of claims 52-57, programmed to harden at least one journal of a crankshaft, the apparatus being programmed to generate the effective laser spot such that it extends over more than 50% of the journal of the crankshaft, preferably over more than 75% of the journal of the crankshaft. [59] Apparatus according to any one of claims 52-58, in which the control system comprises a memory (110, 120; 140, 150) arranged to comprise a plurality of data sets (111-114; 121-124; 141; 151), each of the data sets being indicative of a two-dimensional energy distribution of the effective laser spot, the apparatus being arranged to adjust the two-dimensional energy distribution of the effective laser spot as the effective laser spot is moved along the surface region by using one of the plurality of data sets to operate the laser source when the effective laser spot is projected onto the less heat-sensitive sub-region, and at least one other of the plurality of data sets to operate the laser source when the effective laser spot is projected onto the more heat-sensitive sub-region. [60] Apparatus according to claim 52 for laser hardening surfaces of journals of a crankshaft (1000) comprising at least two centrally arranged main journals (1001) and at least one offset crank pin (1002), the apparatus comprising: a crankshaft holder (20) arranged to support the crankshaft and optionally rotate the crankshaft about a longitudinal axis of the crankshaft; at least one laser source (1) arranged to project a laser beam (2) onto a journal of the crankshaft (1000) so as to generate a laser spot on the journal; wherein the laser source comprises a bi-directional scanning device (3) for scanning the laser beam in two dimensions so as to establish a two-dimensional scanning pattern on the surface of the pin. [61] Apparatus according to claim 60, in which the crankshaft holder (20) and the laser source (1) are displaceable with respect to each other in at least two different directions perpendicular to the longitudinal axis so as to ensure a constant distance between a crank pin (1002) and the laser source (1) during rotation of the crankshaft about the longitudinal axis, the crank pin being concealed with respect to the longitudinal axis. [62] Device according to claim 61, in which the laser source (1) is displaceable in a first direction (Z), preferably vertically, and in which the crankshaft holder (20) is displaceable in a second direction (Y), preferably horizontally, both the first and the second direction being perpendicular to the longitudinal axis. [63] Apparatus according to claim 62, in which the laser source (1) is further displaceable parallel to the longitudinal axis of the crankshaft. [64] Apparatus according to any one of claims 60-63, comprising a control unit (100) comprising a memory storing parameter values associated with the scan pattern, including a plurality of sets of parameter values, wherein a first set of the parameter values determines a first two-dimensional energy distribution on a journal of the crankshaft and a second set of the parameter values determines a second two-dimensional energy distribution on the journal. [65] Apparatus according to claim 64, in which the control unit (100) is arranged to control the hardening process by selectively applying the first set of parameter values and the second set of parameter values and, optionally, further sets of parameter values stored in the memory during rotation of the crankshaft about its longitudinal axis, synchronously with the occurrence of a more heat-sensitive sub-region within the two-dimensional scanning pattern. [66] Apparatus according to claim 64 or 65, in which the scanning pattern is a segmented scanning pattern comprising a plurality of segments (a, b, c, d, e, f, g, h; 51A, 51B) and in which at least one of the parameter values is associated with each segment, the at least one parameter value being an indication of at least one of the scanning speed, size of the laser spot, power of the laser beam, power distribution within the laser beam, length of the corresponding segment and orientation of the corresponding segment. [67] Apparatus according to claim 66, arranged to carry out the scanning operation at an average speed of at least 300 segments per second, preferably at least 600 segments per second, more preferably at least 1000 segments per second, more preferably at least 5000 segments per second and even more preferably at least 10 000 segments per second.

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