Method and system for heating using energy beam

Abstract

A method for heating a selected portion of an object comprises the following steps: projecting an energy beam (1) onto a surface of an object (100), and repeatedly scanning the beam according to a scanning pattern (11A, 11B) to establish an effective spot (12A, 12B) on the surface, and shifting the effective spot (12A, 12B) along a trajectory (101) to gradually heat a selected portion (102) of the object. The selected portion (102) has a first width (W1) at a first position along the trajectory (101) and a second width (W2) at a second position along the trajectory (101). The second width (W2) is less than 75% of the first width (W1). The scanning pattern is repeated at a first frequency corresponding to the first position and at a second frequency corresponding to the second position, the second frequency being greater than 60% of the first frequency and less than 140% of the first frequency.

Description

Technical Field

[0001] The present invention relates to heating an object using an energy beam, such as a laser beam. Background Art

[0002] It is known in the art to heat an object by directing an energy beam (such as a light beam, e.g., a laser beam) onto the object. For example, it is well known in the art to harden an iron-containing material such as steel (e.g., medium carbon steel) by heating the material to a high temperature below its melting temperature and then quenching it (that is, cooling it quickly enough to form hard martensite). The heating can be performed in a furnace or by induction heating, and the cooling can be performed by applying a cooling fluid (such as water or water mixed with other ingredients). It is also known to use an energy beam such as a light beam to perform a specific hardening process, for example, for complex products such as crankshafts. Crankshafts have complex surfaces and very high requirements for wear resistance during use. For example, WO-2014 / 037281-A2 explains how a laser beam can be used to harden the surface of a journal of a crankshaft, for example, without overheating in the area near the oil lubrication hole. Other objects may also be heat treated by methods and systems consistent with the methods and systems taught by WO-2014 / 037281-A2, the contents of which are incorporated herein by reference. WO-2014 / 037281-A1 discusses, among other things, how a workpiece may be selectively heated by projecting a beam onto the surface of the workpiece so as to produce a primary spot on the surface, the beam being repeatedly scanned in two dimensions according to a scanning pattern so as to establish an effective spot on the surface of the workpiece, the effective spot having a two-dimensional energy distribution. The effective spot is displaced relative to the surface of the workpiece to gradually heat a selected portion of the workpiece. In some embodiments, the two-dimensional energy distribution of the effective spot is dynamically adapted during the displacement of the effective spot relative to the surface of the workpiece.

[0003] WO-2015 / 135715-A1, the contents of which are incorporated herein by reference, discusses, among other things, how different scan patterns can be used in the context of this technique for laser hardening. The illustrated embodiments include scan patterns having segments that are perpendicular to each other. One illustrated embodiment features a scan pattern that is substantially shaped as a "figure 8".

[0004] It has been found that the technique for heating using an energy beam as proposed in WO-2014 / 037281-A1 and WO-2015 / 135715-A1 can be used for applications other than hardening of workpieces. For example, WO-2016 / 026706-A1 teaches how the technique can be used for additive manufacturing, the contents of which are incorporated herein by reference. WO-2016 / 146646-A1 teaches how the technique can be used for heat treatment of metal sheets, the contents of which are incorporated herein by reference. Further applications include welding of objects, for example, for joining two or more parts of an object, as described in WO-2018 / 054850-A1, the contents of which are incorporated herein by reference.

[0005] It has been found that the technology described in the above-mentioned patent application has significant advantages in terms of flexibility, adaptability, product quality and productivity.

[0006] Determining a suitable scanning pattern and parameters associated therewith, such as scanning rate (that is, the speed at which the spot projected by the laser beam moves along the scanning pattern and along different portions or segments thereof), laser beam power, laser spot size, and the speed of the effective spot along the trajectory or path it follows on the surface of the object being treated, may involve the use of empirical testing (such as trial and error testing), simulations, calculations, or a combination thereof.

[0007] It is often desirable that certain product characteristics remain constant along a trajectory treated by effective spot heat treatment. For example, in the case of laser hardening as discussed in WO-2014 / 037281-A2, a constant hardening depth along the trajectory is often desired. Similar considerations apply to many other applications, such as laser softening, laser welding, etc.

[0008] In many applications such as laser hardening of crankshaft journals and many other applications, the active spot maintains a substantially constant width while moving along its trajectory in order to provide a heat treated portion of the workpiece that has a substantially constant width over its entire extension from its start to its end, for example all the way along the circumference of the crankshaft journal (just to give an example). In the context of heat treatment of sheet metal parts as disclosed in WO-2016 / 146646-A1, another example may be laser softening of a portion of a vehicle pillar to form a softened zone of constant width in the vehicle pillar, for example to form an area that will generally deform in the event of a collision, or an area that the vehicle pillar can be cut through more easily. Summary of the invention

[0009] However, it may sometimes be desirable to provide heat treatment of portions or strips having a width that varies substantially along a trajectory to be followed by the active spots, for example to provide more or less complex patterns of hardened or softened material, welds, consolidation of masses such as molten powder in the context of additive manufacturing, etc.

[0010] In this case, it is generally preferred that the basic characteristics of the heat treatment remain substantially constant along the trajectory, except for the above-mentioned changes in the heated portion or width of the strip along the trajectory. For example, in the case of laser hardening, it is generally desired that the depth of hardening remain constant along the trajectory.

[0011] Calculating the energy necessary to achieve a certain hardening depth may include determining the volume to be heated, the amount by which the temperature will be raised, the specific heat capacity of the material, etc. Thus, for example, to harden a portion having a certain width to a certain depth, the necessary radiant energy per unit length of the trajectory may be determined, thereby providing a basis for determining the speed at which an effective spot produced by a beam having a certain power will shift along the trajectory. Additional aspects to consider include the energy distribution within the effective spot, such as whether a leading portion is selected to have a higher energy density than a trailing portion, just to give an example. Thus, a method may be based on, for example, establishing energy flux (in J / m 2 The selected scan pattern, beam power, speed of the main spot along different parts of the scan pattern (such as along the leading and trailing segments), and speed of the effective spot along the trajectory can be verified by simulation and / or trial and error testing until a suitable combination of parameters has been determined.

[0012] When the portion to be heated has a width that varies along the trajectory, for example by featuring one or more sections with a width that decreases or increases relative to a reference width, a way of ensuring substantially constant properties (for example in terms of hardening depth, softening, weld depth, etc.) exists in operation such that the energy flow (in J / m 2 The width of the scanning pattern is kept substantially constant at different sections or subsections along the trajectory, while the width of the scanning pattern is adapted to correspond to the width of the respective subsection subjected to heat treatment at each specific moment. For example, a variation of more than X% in the width of the portion to be heated may require a corresponding reduction in the width of the effective spot and thus a corresponding variation in the scanning pattern, including a variation in the width of the scanning pattern, so as to take into account the width or diameter of the main laser spot, i.e. the width or diameter of the laser spot projected onto the surface or surfaces being treated at each specific point.

[0013] A first aspect of the invention relates to a method for heating at least a selected portion of an object, comprising the following steps:

[0014] An energy beam is projected onto a surface of the object so as to generate a main spot on the surface, and the beam is repeatedly scanned in two dimensions according to a scanning pattern so as to establish an effective spot (which may also be called a virtual spot, formed by two-dimensional scanning of the main spot) on the surface, the effective spot having a two-dimensional energy distribution, and

[0015] displacing the active spot along a trajectory on the surface of the object to gradually heat selected portions of the object;

[0016] wherein the selected portion has a first width at a first position along the trajectory (such as along a first subportion thereof) and a second width at a second position along the trajectory (such as along a second subportion thereof). That is, the selected portion, such as a band or strip to be heated, substantially has a width that varies along the trajectory, the width being the dimension of the selected portion perpendicular to the trajectory or line followed by the active spot. In some embodiments, the first width is substantially constant throughout the first subportion of the object, and the second width is substantially constant throughout the second subportion of the object, whereby the first and second positions correspond to positions within the respective subportions.

[0017] The beam is scanned according to a scan pattern such that the scan pattern is repeated by the beam at a first frequency corresponding to a first position along a trajectory (such as along a first subsection having the first width) and at a second frequency corresponding to a second position along the trajectory (such as along a second subsection having the second width). The first frequency and the second frequency are both greater than 10 Hz, and the second width is less than 75% of the first width. The second frequency is greater than 60% of the first frequency and less than 140% of the first frequency.

[0018] As explained above, in order to adapt to changes in the width of the portion to be heated, the active spot will be adapted at least by reducing its extension in the direction perpendicular to the track followed by the active spot (i.e. in the width direction). This typically involves adapting the scanning pattern, for example, by reducing or increasing its maximum extension in the width direction (i.e. the direction perpendicular to the track). However, adapting the scanning pattern accordingly typically affects the repetition rate of the scanning pattern: for a given scanning rate, a smaller or shorter scanning pattern can typically be repeated more frequently than a larger or longer scanning pattern.

[0019] However, it has surprisingly been observed that keeping the repetition rate of the scanning pattern substantially constant, such as deviating from a reference frequency by less than 40% (that is, so that the frequency at the portions with narrower width deviates from the frequency at the portions with larger width by less than 40%, and vice versa), may be helpful in order to allow for a substantial maintenance of the performance, for example, in terms of hardening depth, prevention of overheating of the surface, etc. The reasons for this are not entirely clear, but it is believed that this may be related to the fact that a substantially constant repetition rate may have an impact on issues such as temperature fluctuations in the area being heated by the active spot, and / or on deformations of the theoretical scanning pattern when the main spot with its two-dimensional repetitive movement following the scanning pattern is superimposed on the movement of the active spot along the trajectory. Additionally or alternatively, it appears that a very high repetition rate of the scanning pattern may be suboptimal, since this may mean an overly aggressive application of heat, by increasing the number of times or frequency with which a given sub-area receives the laser beam. It appears that this may affect the depth of the heat treatment, and / or lead to overheating of the surface layer. For example, in the case of laser hardening, it has been observed that a significant increase in the frequency of the scanning pattern repetition can lead to melting of the surface layer and even to waves therein, thereby negatively affecting the quality of the product.

[0020] Therefore, and in contrast to the seemingly most attractive approach which involves increasing the repetition rate of the scan pattern as the width of the effective spot decreases (thereby maximizing the use of the scanner's ability to reduce temperature fluctuations within the region being heated, as explained in, for example, WO-2014 / 037281-A2), by keeping the repetition rate substantially constant (such as by deviating by less than 40%, 30%, 25%, 20%, 15%, 10%, 5% or 1% from a given repetition rate such as that set for a wider or narrower sub-portion), the uniformity of the heat treatment can be enhanced along the trajectory despite significant variations in the width of the portion undergoing heat treatment.

[0021] The expressions "first position" and "second position" are used only to distinguish the two positions along the trajectory and are intended to represent any particular order of the two positions along the trajectory. That is, when the effective spot travels along the trajectory, the first position may be reached earlier or later than the second position.

[0022] In some embodiments of the invention, the second width is less than 60% of the first width, such as less than 50% of the first width. Thus, while there is a natural tendency to operate the scanner at or near the highest possible scan rate, by keeping the repetition rate of the scan pattern substantially constant, significant variations in the width of the portion being heated in one sweep of the active spot along the trajectory can be easily accommodated while maintaining the desired characteristics of the resulting product in terms of parameters such as hardening depth, for example.

[0023] In some embodiments of the present invention, the second frequency is greater than 70% of the first frequency, such as greater than 75%, 80%, 85% or 90% of the first frequency. In some embodiments of the present invention, the second frequency is less than 130% of the first frequency, such as less than 125%, 120%, 115% or 110% of the first frequency.

[0024] That is, as explained above, it is preferred that the second frequency is substantially equal to the first frequency, e.g., varies no more than 40%, 30%, 25%, 20%, 15%, 10%, 5% or 1% from the first frequency, although the width varies significantly, e.g., the second width is less than 75%, 60%, 50%, 40% or 30% of the first width. For example, in such a case, the second frequency may be between 60% and 140% of the first frequency, such as between 70% and 130% of the first frequency, including between 80% and 120% of the first frequency, between 85% and 115% of the first frequency, between 90% and 110% of the first frequency, and between 95% and 105%.

[0025] In some embodiments of the present invention, when the effective spot is at a first position along the track, the average speed of the main spot along the scan pattern (based on the length of the scan pattern divided by the time required for the main spot to complete the scan pattern) is significantly higher than the average speed when the effective spot is at a second position along the track. In some of these embodiments, when the effective spot is at the first position along the track, the average speed of the main spot along the scan pattern is at least 10% higher than when the effective spot is at the second position along the track. In some of these embodiments, when the effective spot is at the first position along the track, the average speed of the main spot along the scan pattern is at least 20% higher than when the effective spot is at the second position along the track, such as at least 30%, 50% or 100% higher. In some embodiments, when the effective spot is at the first position along the track, the average speed is X% higher than when the effective spot is at the second position along the track, and X is at least 10, such as at least 20, 30, 40, 50, 75, 100, 200 or more. A significantly higher average speed at the first position than at the second position can be used to keep the repetition rate (repetition frequency) of the scanning pattern substantially the same at the first position and at the second position, despite the fact that the scanning pattern may be significantly longer at the first position due to the larger width of the effective spot required to cover the larger width of the portion to be heated at the first position.

[0026] In some embodiments of the invention, the effective spot is characterized by a first radiant energy flux (in J / m 2 ) onto the surface of the object corresponding to a first position along the trajectory. 2 ) and a second radiant energy flux (in J / m ) onto the surface of the object corresponding to a second position along the trajectory2 The second radiation energy flow rate is not greater than 110% of the first radiation energy flow rate and not less than 90% of the first radiation energy flow rate.

[0027] The radiant energy flux refers to how much energy is applied by the active spot per unit of surface area being treated when swept along the trajectory. It has been found that for uniform heat treatment (e.g., in terms of hardening depth and / or other quality parameters), a uniform radiant energy flux may be preferred. It is preferred that not only the radiant energy flux itself remains substantially constant, such as deviating by less than 10% at the second position compared to the first position, but also the distribution of the radiant energy flux along and across the active spot remains substantially constant. For example, if the leading portion of the active spot represents Y% of the total radiant energy flux of the active spot at the first position, it is preferred that the leading portion also represents approximately Y% of the total radiant energy flux of the active spot at the second position along the trajectory, such as greater than 0.9*Y% and less than 1.1*Y%. It has been found that this contributes to substantially uniform performance in terms of the quality of the heat treatment (e.g., in the case of laser hardening, in terms of hardening depth, etc.).

[0028] In some embodiments of the invention, both the first frequency and the second frequency are greater than 25 Hz, such as greater than 80 Hz, such as greater than 80 Hz and less than 150 Hz, such as greater than 80 Hz and less than 120 Hz. For example, for many surface hardening applications, it has been found that a frequency greater than 80 Hz and less than 120 Hz provides good results.

[0029] In some embodiments of the present invention, the adaptation of the two-dimensional energy distribution of the effective spot comprises adapting the two-dimensional energy distribution by:

[0030] - modifying (i.e. increasing or decreasing) the width of the effective spot by adapting the scanning pattern, and

[0031] - Adapts the average speed at which the main spot moves along the scan pattern.

[0032] In some embodiments of the present invention, the energy beam has a first average power corresponding to a first position along the trajectory (such as along a first sub-portion having a first width) and a second average power corresponding to a second position along the trajectory (such as along a second sub-portion having the second width), the second average power being at least 10% less than the first average power (such as at least 20%, 30%, 40% or 50% less than the first average power). The term "average power" refers to the amount of energy applied by the laser beam during one cycle of the scan pattern divided by the duration of the cycle. However, from the perspective of maximizing the efficient use of the laser power, it is generally preferred to operate the laser at substantially its maximum power output during all or a significant portion of the scan, which has been found to be inappropriate or suboptimal for many applications. For example, if the energy is measured in J / m 2 If the radiant energy flux of the meter is to be kept constant, the reduced width of the scanning pattern corresponding to the narrower sub-portion of the portion undergoing heat treatment while keeping the laser power constant can be compensated for, for example, by increasing the speed at which the effective spot is displaced along the trajectory. However, this increase in speed can have a significant impact on the quality parameters of the heat treatment, for example in the case of laser surface hardening in terms of the hardening depth. For example, in the case of a 50% reduction in the width of the portion being hardened, keeping the beam power and the radiant energy flux constant may require doubling the speed at which the effective spot is displaced along the trajectory, which may be suboptimal. For example, in the case of laser hardening, the hardening depth may actually be insufficient and / or overheating of the surface may occur. Therefore, reducing the average beam power may be a better option, even if this may mean suboptimal use of the available laser power provided by the device.

[0033] In some embodiments of the present invention, the effective spot (12A, 12B) is displaced along the trajectory at a first speed corresponding to a first position along the trajectory and at a second speed corresponding to a second position along the trajectory, the second speed being different from the first speed. For example, the second speed may differ from the first speed by at least 10%, 20%, 30% or more. When transitioning from a subsection having one width to a subsection having another width, changing the speed at which the effective spot moves (i.e., the so-called process speed) can help reduce the need to modify the beam power while keeping the radiant energy flux substantially constant. For example, the speed may be higher in the case corresponding to a narrower subsection to be heated than in the case corresponding to a wider subsection to be heated, so as to at least partially compensate for the reduction in the width of the effective spot, thereby keeping the radiant energy flux and the average beam power substantially constant. As an alternative, the speed may be lower in the case corresponding to the narrower subsection, thereby compensating for the use of a lower average beam power as discussed above, to allow for the use of J / m 2 The radiant energy flux of the meter remains essentially constant.

[0034] In some embodiments of the present invention, the effective spot has a length in a direction parallel to the trajectory that is smaller, for example, at least 10%, 20%, 30%, 40% or 50% smaller, in the case corresponding to the first position than in the case corresponding to the second position. Making the effective spot longer in the case corresponding to the narrower sub-portion to be heat treated than in the case corresponding to the wider sub-portion can help to keep the radiant energy flux substantially constant while increasing the speed of the effective spot along the trajectory, while at the same time keeping each given portion along the trajectory subjected to heat treatment for a sufficient amount of time, for example, to obtain a desired hardening or softening or melting depth. That is, substantially, a higher speed along the trajectory can be compensated by making the effective spot longer in a direction parallel to the trajectory to prevent overheating while keeping the beam power relatively high.

[0035] Another aspect of the present invention relates to a method of heating at least a selected portion of an object, comprising the steps of

[0036] projecting an energy beam onto a surface of the object so as to generate a primary spot on the surface, and repeatedly scanning the beam in two dimensions according to a scanning pattern so as to create an effective (virtual) spot on the surface, the effective spot having a two-dimensional energy distribution, and

[0037] displacing the active spot along a trajectory on the surface of the object to gradually heat selected portions of the object;

[0038] Wherein the selected portion has a first width at a first position along the trajectory and a second width at a second position along the trajectory. That is, the selected portion, such as a band or strip to be heated, has a width that varies substantially along the trajectory, which is the dimension of the selected portion perpendicular to the trajectory or line followed by the active spot. In some embodiments, the first width is substantially constant throughout the first sub-portion of the object, and the second width is substantially constant throughout the second sub-portion of the object, whereby the first and second positions correspond to positions within the respective sub-portions. In some embodiments, the second width is less than 90%, 80%, 70%, 60%, 50% or 40% of the first width. The first position may be positioned before or after the second position in the direction along the trajectory followed by the active spot.

[0039] The beam is scanned according to a scan pattern such that the scan pattern is repeated by the beam at a first frequency corresponding to a first position along a trajectory (such as along a first sub-portion having the first width) and at a second frequency corresponding to a second position along the trajectory (such as along a second sub-portion having the second width). The first frequency and the second frequency are both greater than 10 Hz (such as greater than 50, 80 or 100 Hz). The first and second frequencies may be substantially the same or different; in some embodiments, it is preferred that they are substantially the same, for example, the second frequency differs from the first frequency by no more than 40%, 30%, 25%, 20%, 15%, 10%, 5% or 1%.

[0040] The energy beam has a first average power corresponding to a first position along the trajectory (such as along a first sub-portion having a first width) and a second average power corresponding to a second position along the trajectory (such as along a second sub-portion having a second width), the second average power being less than the first average power (such as at least 10%, 20%, 30%, 40% or 50% less than the first average power). The term "average power" refers to the amount of energy applied by the laser beam during one cycle of the scan pattern divided by the duration of the cycle. However, from the perspective of maximizing the efficient use of the laser power, it is generally preferred to operate the laser at substantially its maximum power output during all or a significant portion of the scan, which has been found to be inappropriate or suboptimal for many applications. For example, if the energy is measured in J / m 2 If the measured radiant energy flux is to be kept constant, the reduced width of the scanning pattern corresponding to the narrower sub-portion of the portion undergoing heat treatment while keeping the laser power constant can be compensated for, for example, by increasing the speed at which the effective spot is displaced along the trajectory. However, this increase in speed can have a significant impact on the quality parameters of the heat treatment, for example in the case of laser surface hardening in terms of the hardening depth. For example, in the case of a 50% reduction in the width of the portion being hardened, keeping the beam power and the radiant energy flux constant may require doubling the speed at which the effective spot is displaced along the trajectory, which may be suboptimal. For example, in the case of laser hardening, the hardening depth may actually be insufficient and / or overheating of the surface may occur. Therefore, reducing the average beam power may be a better option, even if this may mean suboptimal use of the available laser power.

[0041] Another aspect of the present invention relates to a method of heating at least a selected portion of an object, comprising the steps of

[0042] projecting an energy beam onto a surface of the object so as to generate a primary spot on the surface, and repeatedly scanning the beam in two dimensions according to a scanning pattern so as to create an effective (virtual) spot on the surface, the effective spot having a two-dimensional energy distribution, and

[0043] displacing the active spot along a trajectory on the surface of the object to gradually heat selected portions of the object;

[0044] Wherein the selected portion has a first width at a first position along the trajectory and a second width at a second position along the trajectory. That is, the selected portion, such as a band or strip to be heated, has a width that varies substantially along the trajectory, which is the dimension of the selected portion perpendicular to the trajectory or line followed by the active spot. In some embodiments, the first width is substantially constant throughout the first sub-portion of the object, and the second width is substantially constant throughout the second sub-portion of the object, whereby the first and second positions correspond to positions within the respective sub-portions. In some embodiments, the second width is less than 90%, 80%, 70%, 60%, 50% or 40% of the first width. The first position may be positioned before or after the second position in the direction along the trajectory followed by the active spot.

[0045] The beam is scanned according to a scan pattern such that the scan pattern is repeated by the beam at a first frequency corresponding to a first position along a trajectory (such as along a first subsection having the first width) and at a second frequency corresponding to a second position along the trajectory (such as along a second subsection having the second width), and wherein both the first frequency and the second frequency are greater than 10 Hz (such as greater than 50, 80 or 100 Hz). The first and second frequencies may be substantially the same or different; in some embodiments, it is preferred that they are substantially the same, for example, the second frequency differs from the first frequency by no more than 40%, 30%, 25%, 20%, 15%, 10%, 5% or 1%.

[0046] The effective spot is displaced along the trajectory at a first speed corresponding to a first position along the trajectory and at a second speed corresponding to a second position along the trajectory, the second speed being different from the first speed. For example, the second speed may differ from the first speed by at least 10%, 20%, 30% or more, for example, the second speed may be at least 10%, 20% or 30% higher or lower than the first speed. Changing the speed may help reduce the need to modify the beam power when transitioning from a subsection having one width to a subsection having another width while keeping the radiant energy flux substantially constant. For example, the speed may be higher in the case corresponding to a narrower subsection to be heated than in the case corresponding to a wider subsection to be heated so as to at least partially compensate for the reduction in the width of the effective spot, thereby keeping the radiant energy flux and optionally the average beam power substantially constant. As an alternative, the speed may be lower in the case corresponding to the narrower subsection, thereby compensating for the use of a lower average beam power as discussed above to allow for heating in J / m 2 The radiant energy flux of the meter remains essentially constant.

[0047] Another aspect of the present invention relates to a method of heating at least a selected portion of an object, comprising the steps of

[0048] projecting an energy beam onto a surface of the object so as to generate a primary spot on the surface, and repeatedly scanning the beam in two dimensions according to a scanning pattern so as to create an effective (virtual) spot on the surface, the effective spot having a two-dimensional energy distribution, and

[0049] displacing the active spot along a trajectory on the surface of the object to gradually heat selected portions of the object;

[0050] Wherein the selected portion has a first width at a first position along the trajectory and a second width at a second position along the trajectory. That is, the selected portion, such as a band or strip to be heated, has a width that varies substantially along the trajectory, which is the dimension of the selected portion perpendicular to the trajectory or line followed by the active spot. In some embodiments, the first width is substantially constant throughout the first sub-portion of the object, and the second width is substantially constant throughout the second sub-portion of the object, whereby the first and second positions correspond to positions within the respective sub-portions. In some embodiments, the second width is less than 90%, 80%, 70%, 60%, 50% or 40% of the first width. The first position may be positioned before or after the second position in the direction along the trajectory followed by the active spot.

[0051] The beam is scanned according to a scan pattern such that the scan pattern is repeated by the beam at a first frequency corresponding to a first position along a trajectory (such as along a first subsection having the first width) and at a second frequency corresponding to a second position along the trajectory (such as along a second subsection having the second width). The first frequency and the second frequency are both greater than 10 Hz, such as greater than 50, 80 or 100 Hz. The first and second frequencies may be substantially the same or different; in some embodiments, it is preferred that they are substantially the same, for example, the second frequency differs from the first frequency by no more than 40%, 30%, 25%, 20%, 15%, 10%, 5% or 1%.

[0052] The effective spot has a length in a direction parallel to the trajectory that is smaller, for example, at least 10%, 20%, 30%, 40% or 50% smaller, in the case corresponding to the first position than in the case corresponding to the second position. Making the effective spot longer in the case corresponding to the narrower sub-portion to be heat treated than in the case corresponding to the wider sub-portion can help to keep the radiant energy flux substantially constant while increasing the speed of the effective spot along the trajectory, while keeping each given portion along the trajectory subjected to heat treatment for a sufficient amount of time, for example, to obtain a desired hardening or softening or melting depth. That is, substantially, a higher speed along the trajectory can be compensated by making the effective spot longer in a direction parallel to the trajectory to prevent overheating while keeping the beam power relatively high.

[0053] For example, different aspects may be combined by varying the average beam power and the speed of the effective spot along the trajectory, or by varying the average beam power and the length of the effective spot, or by varying the speed of the effective spot along the trajectory and the length of the effective spot, or by varying all three parameters while optionally keeping the repetition rate of the scanning pattern essentially constant.

[0054] In some embodiments of the invention, the effective spot is characterized by a first radiant energy flux (in J / m 2 ) onto the surface of the object corresponding to a first position along the trajectory. 2 ) and a second radiant energy flux (in J / m ) onto the surface of the object corresponding to a second position along the trajectory 2), the second radiant energy flux is not greater than 140% of the first radiant energy flux and not less than 60% of the first radiant energy flux, such as not greater than 130% of the first radiant energy flux and not less than 70% of the first radiant energy flux, such as not greater than 120% of the first radiant energy flux and not less than 80% of the first radiant energy flux, such as not greater than 110% of the first radiant energy flux and not less than 90% of the first radiant energy flux, such as not greater than 105% of the first radiant energy flux and not less than 95% of the first radiant energy flux. The radiant energy flux refers to how much energy is applied by the effective spot to each unit of surface area being treated when sweeping along the trajectory. It has been found that for uniform heat treatment (for example, in terms of hardening depth and / or other quality parameters), a uniform radiant energy flux may be preferred. Preferably, not only the radiant energy flux itself remains substantially constant, such as deviating by less than 40%, 30%, 20%, 10% or 5% at the second position compared to the first position, but also the distribution of the radiant energy flux along and across the effective spot remains substantially constant. For example, if the leading portion of the active spot represents Y% of the total radiant energy flux of the active spot at a first position, it is preferred that the leading portion represents about Y% of the total radiant energy flux of the active spot at a second position along the trajectory, such as greater than 0.9*Y% and less than 1.1*Y%. It has been found that this contributes to substantially uniform performance in terms of the quality of the heat treatment (e.g., in the case of laser hardening, in terms of hardening depth, etc.). By appropriately setting parameters such as average beam power, the speed of the active spot along the trajectory, and the length of the active spot in a direction parallel to the trajectory, it is possible to keep the radiant energy flux substantially constant while also complying with other process requirements, such as, for example, sufficient surface heating (e.g., to avoid remelting or overheating), appropriate treatment depth (such as appropriate hardening depth), etc.

[0055] In some embodiments of the present invention, the first scanning pattern represents a third radiant energy flux, which is defined as the energy supplied by the beam during one sweep along the first scanning pattern divided by the surface area swept by the main spot during the one sweep along the first scanning pattern, and wherein the second scanning pattern (11B) represents a fourth radiant energy flux, which is defined as the energy supplied by the beam during one sweep along the second scanning pattern divided by the surface area swept by the main spot during the one sweep along the second scanning pattern, wherein the third radiant energy flux is substantially the same as the fourth radiant energy flux. In this context, "substantially the same" means that the fourth radiant energy flux differs from the third radiant energy flux by no more than 40%, preferably by no more than 30%, 25%, 20%, 15%, 10%, 5%, 2% or 1%. It has been found that keeping the radiant energy flux corresponding to the scanning pattern substantially constant can maintain quality parameters (e.g., with respect to hardening depth, etc.). Thus, two radiation energy fluxes may be kept substantially constant: one corresponding to the radiation energy per unit surface area applied to each of the different sub-portions due to the movement of the active spot along the respective sub-portions, and the other corresponding to the scan pattern, that is, a radiation energy flux defined by the energy applied by the main spot when sweeping once along the scan pattern divided by the area actually swept by the main spot when moving once along the scan pattern. In the case of complex patterns / energy distributions (such as patterns / energy distributions in which the energy density corresponding to the leading portion is higher than the energy density corresponding to the trailing portion), the identity between the radiation energy fluxes corresponding to the scan patterns should preferably also exist between the different portions of the scan patterns, e.g., the radiation energy flux corresponding to the leading portion of the first scan pattern should preferably be substantially the same as the radiation energy flux corresponding to the leading portion of the second scan pattern, and the radiation energy flux corresponding to the trailing portion of the first scan pattern should preferably be substantially the same as the radiation energy flux corresponding to the trailing portion of the second scan pattern. It has been found that even with variations in the width of the portion being heated (and even with corresponding variations in the width of the scan pattern and the active spot), not only the radiation energy flux in J / m applied to the respective sub-portions of the trajectory is not affected. 2Maintaining the radiant energy flux substantially constant, not only in terms of the radiant energy flux of the meter, but also in terms of the radiant energy flux corresponding to the scan pattern itself (that is, the radiant energy flux corresponding to one sweep of the main spot along the scan pattern) and to various portions thereof (particularly when the energy flux is not constant along the scan pattern, for example, due to different scan speeds and / or different beam power levels corresponding to different portions of the scan pattern), helps to keep the performance of the process substantially constant along the entire portion being heated (for example, in the case of laser hardening, the hardening depth and quality can be kept substantially constant along the entire portion undergoing the heat treatment). It has also been found that another parameter that helps (and may be necessary in some cases) to keep the performance of the process substantially constant along the trajectory is a substantially constant scan frequency, such as a scan frequency that deviates by no more than 20%, 10% or 5% from an average or reference scan frequency.

[0056] Another aspect of the present invention relates to a method of heating at least a selected portion of an object, comprising the steps of

[0057] projecting an energy beam onto a surface of the object so as to generate a primary spot on the surface, and repeatedly scanning the beam in two dimensions according to a scanning pattern so as to create an effective (virtual) spot on the surface, the effective spot having a two-dimensional energy distribution, and

[0058] displacing the active spot along a trajectory on the surface of the object to gradually heat selected portions of the object;

[0059] Wherein the selected portion has a first width in a first sub-portion of the entire selected portion and a second width in a second sub-portion of the entire selected portion; that is, the width remains substantially constant throughout the corresponding sub-portion, such as deviating from the average width by less than 20%, 15%, 10%, 5% or 1%. The first width is greater than the second width (W2). In some embodiments, the (average) second width is less than 90%, 80%, 70%, 60%, 50% or 40% of the (average) first width. The first sub-portion can be positioned before or after the second sub-portion in the direction along the trajectory followed by the effective spot.

[0060] The beam is scanned in a first subsection according to a first scanning pattern and in a second subsection according to a second scanning pattern, wherein the first scanning pattern is repeated by the beam at a first frequency, and wherein the second scanning pattern is repeated by the beam at a second frequency, and wherein both the first frequency and the second frequency are greater than 10 Hz, such as greater than 50, 80 or 100 Hz. The first and second frequencies may be substantially the same or different; in some embodiments, it is preferred that they are substantially the same, for example, the second frequency differs from the first frequency by no more than 40%, 30%, 25%, 20%, 15%, 10%, 5% or 1%.

[0061] The first subsection is subjected to a first radiant energy flux (in J / m 2 ), and the second subsection is subjected to a second radiant energy flux (in J / m 2 The first scan pattern represents a third radiant energy flux, which is defined as the energy supplied by the beam during one sweep along the first scan pattern divided by the surface area swept by the main spot, and the second scan pattern represents a fourth radiant energy flux, which is defined as the energy supplied by the beam during one sweep along the second scan pattern divided by the surface area swept by the main spot. The first radiant energy flux is substantially the same as the second radiant energy flux, and the third radiant energy flux is substantially the same as the fourth radiant energy flux.

[0062] In this context, "substantially the same" means that the second radiant energy flow rate does not differ from the first radiant energy flow rate by more than 40%, preferably by no more than 30%, 25%, 20%, 15%, 10%, 5%, 2% or 1%, and the fourth radiant energy flow rate does not differ from the third radiant energy flow rate by more than 40%, preferably by no more than 30%, 25%, 20%, 15%, 10%, 5%, 2% or 1%.

[0063] It has been found that keeping the radiation energy flux corresponding to the scanning pattern substantially constant maintains quality parameters (e.g., with respect to hardening depth, etc.). Thus, two radiation energy fluxes may be kept substantially constant: one corresponding to the radiation energy per unit surface area applied to each of the different sub-portions due to the movement of the effective spot along the respective sub-portions, and the other corresponding to the scanning pattern, that is, a radiation energy flux defined by the energy applied by the main spot when sweeping once along the scanning pattern divided by the area actually swept by the main spot when moving once along the scanning pattern. In case of complex patterns / energy distributions, such as those in which the energy density corresponding to the leading portion is higher than the energy density corresponding to the trailing portion, the identity between the radiation energy fluxes corresponding to the scanning patterns should preferably also exist between different portions of the scanning patterns, e.g., the radiation energy flux corresponding to the leading portion of a first scanning pattern should preferably be substantially the same as the radiation energy flux corresponding to the leading portion of a second scanning pattern, and the radiation energy flux corresponding to the trailing portion of the first scanning pattern should preferably be substantially the same as the radiation energy flux corresponding to the trailing portion of the second scanning pattern. It has been found that even variations in the width of the portion being heated (and even corresponding variations in the width of the scan pattern and the effective spot) not only affect the heating in J / m applied to the corresponding sub-portion of the track, but also affect the heating in J / m 2Maintaining the radiant energy flux substantially constant, not only in terms of the radiant energy flux of the meter, but also in terms of the radiant energy flux corresponding to the scan pattern itself (that is, the radiant energy flux corresponding to one sweep of the main spot along the scan pattern) and to various portions thereof (particularly when the energy flux is not constant along the scan pattern, for example, due to different scan speeds and / or different beam power levels corresponding to different portions of the scan pattern), helps to keep the performance of the process substantially constant along the entire portion being heated (for example, in the case of laser hardening, the hardening depth and quality can be kept substantially constant along the entire portion undergoing the heat treatment). It has also been found that another parameter that helps (and may be necessary in some cases) to keep the performance of the process substantially constant along the trajectory is a substantially constant scan frequency, such as a scan frequency that deviates by no more than 20%, 10% or 5% from an average or reference scan frequency.

[0064] In some embodiments of the present invention, the energy beam has a first average power corresponding to the first subportion and a second average power corresponding to the second subportion, the second average power being less than the first average power, such as at least 10%, 20%, 30%, 40%, 50% less than the first average power. The term "average power" refers to the amount of energy applied by the laser beam during one cycle of the scan pattern divided by the duration of the cycle. However, from the perspective of maximizing the efficient use of the laser power, it is generally preferred to operate the laser at substantially its maximum power output during all or a significant portion of the scan, which has been shown to be inappropriate or at least suboptimal for many applications. For example, if the power is measured in J / m 2 If the radiant energy flux of the meter is to be kept constant, the reduced width of the scanning pattern corresponding to the narrower sub-portion of the portion undergoing heat treatment while keeping the laser power constant can be compensated, for example, by increasing the speed at which the effective spot is displaced along the trajectory. However, such an increase in speed can have a significant impact on the quality parameters of the heat treatment, for example in the case of laser surface hardening, in terms of the hardening depth. For example, in the case of a 50% reduction in the width of the portion being hardened, keeping the beam power and the radiant energy flux constant may require doubling the speed at which the effective spot is displaced along the trajectory.

[0065] What has been stated in relation to the first aspect of the invention also applies mutatis mutandis to the other aspects of the invention.

[0066] In some embodiments of the invention, the second width is less than 90% of the first width, such as less than 80%, 70%, 60%, 50% of the first width, etc. Significant variations in width may be compensated by adapting process parameters such as average beam power along the scan pattern, speed of the effective spot along the trajectory, extension of the effective spot in a direction parallel to the trajectory, etc., optionally while keeping the repetition rate or frequency of the scan pattern substantially constant, such as within a range of + / - 40%, 30%, 25%, 20%, 15%, 10% or less relative to a reference frequency.

[0067] In some embodiments of the invention, the second frequency is greater than 60% of the first frequency and less than 140% of the first frequency, such as greater than 70% of the first frequency and less than 130% of the first frequency, such as greater than 75% of the first frequency and less than 125% of the first frequency, such as greater than 80% of the first frequency and less than 120% of the first frequency, such as greater than 85% of the first frequency and less than 115% of the first frequency, such as greater than 90% of the first frequency and less than 110% of the first frequency, such as greater than 95% of the first frequency and less than 105% of the first frequency. As explained above, it is generally preferred to keep the frequency constant regardless of changes in the width of the portion to be heated along the trajectory.

[0068] In some embodiments of the invention, the energy beam is a laser beam. Laser beams are generally preferred due to issues such as cost, reliability, and availability of suitable scanning systems. In some embodiments of the invention, the power of the laser beam is higher than 1 kW, such as higher than 3 kW, higher than 4 kW, higher than 5 kW, or higher than 6 kW, at least during a portion of the process.

[0069] Another aspect of the invention relates to a system for heating at least a selected portion of an object, the system comprising:

[0070] means for generating an energy beam and for projecting the energy beam onto a surface of an object, and

[0071] A scanner is provided for scanning an energy beam in at least two dimensions.

[0072] The system is programmed to perform one or more of the above methods.

[0073] It is believed that the teachings of the present document and / or at least some of the advantages involved are particularly applicable to such situations where the thickness of the object undergoing heat treatment along a trajectory or at least along a portion thereof is significantly greater than the depth of the heat treatment (e.g., the hardening depth in the case of laser beam hardening), such as at least 2, 3, 5, 10, 20, 30, 40 or 50 times greater.

[0074] In this document, references to scanning patterns and their shapes refer to the two-dimensional scanning pattern followed by the primary spot when projected onto a plane substantially perpendicular to the beam (e.g., in the xy plane), rather than to the pattern actually followed by the primary spot on the surface of the object; for example, a surface may include sharp bends or bends that will significantly affect the trajectory actually followed by the primary spot in three dimensions. That is, the "scanning pattern" refers to the pattern followed by the beam, rather than the pattern actually followed by the primary spot on the physical surface of the object onto which the beam is projected.

[0075] The displacement of the effective spot relative to the surface of the object may be performed according to a suitable trajectory. That is, the real / primary spot (i.e., the spot produced by the beam at any given moment) is scanned according to a scanning pattern to form an effective spot, and the effective spot is displaced according to a trajectory. Thus, two types of movement are combined or overlapped: the movement of the primary spot according to the scanning pattern (this movement is performed at a speed sometimes referred to as the "scanning speed" or "scan rate"), and the movement of the effective spot according to the trajectory (this movement is performed at a speed sometimes referred to as the "process speed" or "process rate"), which movement may be a simple straight line in some embodiments of the invention, and which movement may be characterized by more or less complex shapes (e.g., including one or more curves) in other embodiments.

[0076] The term "two-dimensional energy distribution" refers to the way in which the energy applied by the energy beam is distributed over the effective spot, for example, during one sweep of the beam along the scan pattern. When the effective spot is projected onto a non-planar portion or region (such as a curved portion or region, such as a portion or region characterized by a bend), the term "two-dimensional energy distribution" refers to how the energy is distributed along and across the surface of the object, that is, the energy distribution along and across the effective spot when projected onto the surface of the object. The effective spot can be considered to have an extension and shape that corresponds to an area where there is a significant amount of energy applied during each sweep of the laser beam along the scan pattern (e.g., corresponding to an area where the energy density is at least 1% of the maximum energy density within the effective spot).

[0077] The method allows relatively fast heating of significant areas of the surface of an object due to the fact that the effective spot can be of considerable size, such as, for example, 4, 10, 15, 20 or 25 times larger than the size (area) of the main spot. Thus, heating a certain zone or area of ​​an object to a desired degree in terms of temperature and duration can be accomplished more quickly than if heating were performed by simply displacing the main spot over the entire area (e.g., following a sinusoidal or zigzag pattern or straight line). The use of an effective spot having a relatively large area allows high productivity while still allowing the relevant portion or portions of the surface to be heated for a relatively significant amount of time, allowing, for example, less aggressive heating without compromising productivity.

[0078] The main spot may have an area that is significantly smaller than the area of ​​the effective spot. For example, in some embodiments of the invention, at least during a portion of the process, the main spot has an area that is less than 4 mm. 2 (such as less than 3 mm 2 The size of the main spot can be modified during the process in order to optimize the way in which each specific part of the object is being heat treated in terms of quality and productivity.

[0079] On the other hand, the use of an effective spot formed by repeatedly scanning a main spot in two dimensions according to a scanning pattern makes it possible to create an effective spot with a selected two-dimensional energy distribution that is substantially independent of the specific optics used (lenses, mirrors, etc.) and has important benefits from different points of view, including the speed at which the thermal treatment is completed (e.g., in cm per minute). 2The effective spot may be customized and adapted to provide enhanced or optimized heating, based on the amount of energy (measured in units of hours or in units terminated per hour) and mass. For example, heat may be distributed so that the leading portion of the effective spot has a higher energy density than the trailing portion, thereby reducing the time required to reach the desired temperature of the surface, while the trailing portion may be used to maintain heating for a sufficient amount of time to reach the desired depth and / or mass, thereby optimizing the speed at which the effective spot can be displaced relative to the surface of the object without sacrificing the quality of the heat treatment. In addition, depending on the characteristics of the object, the two-dimensional energy distribution may be adapted relative to the sides of the effective spot, for example, so as to apply less heat in areas adjacent to the edge of the object or an opening in the object, where cooling due to heat transfer is slower, or so as to apply less heat in areas that are already characterized by relatively high temperatures, for example, due to recent heating that has occurred. In addition, the effective spot may be adapted according to the three-dimensional shape of the object, for example, to adapt the heating for the curvature, width, etc. of the object in the area being heated and for the configuration of the portion of the object to be heated. The shape of the effective spot and / or the two-dimensional energy distribution can be adapted whenever necessary, thereby adapting the process to the specific part of the object to be heated at any given moment. In some embodiments of the invention, the two-dimensional energy distribution can be varied according to the corresponding irradiation location on the object, taking into account, for example, the heat removal capacity of the surrounding area. In some embodiments of the invention, the two-dimensional energy distribution can be varied taking into account the desired properties of the object in different areas of the product (such as different requirements for hardness, rigidity, softness, ductility, etc.).

[0080] In addition, using an effective spot formed by scanning the main spot in two dimensions increases flexibility, for example, in adapting the system for different objects to be produced. For example, the need to replace or adapt the involved optics may be reduced or eliminated. Adaptation may be performed more frequently, at least in part, by adapting only the software controlling the scanning of the main spot, and thus the two-dimensional energy distribution of the effective spot.

[0081] In many prior art systems for heating an object using an energy beam, the area being heated at each moment substantially corresponds to the main spot projected onto the surface by the beam. That is, in many prior art arrangements, the area being heated at each moment has a size substantially corresponding to the size of the main spot, and the width of the track being heated substantially corresponds to the width of the main spot in a direction perpendicular to the direction in which the main spot is being displaced, which in turn is determined by the source of the beam and the means for shaping it, for example, in the case of a laser, by the optics and laser source used. Sometimes, by additionally oscillating the beam (for example, perpendicular to the track), the track becomes wider. Of course, the present invention does not exclude the possibility of using the main spot to perform part of the heating operation in a conventional manner. For example, the main spot may be displaced to perform heating according to the shape or contour of the area to be heated, or to perform heating of certain details of the object being heated, while the above-mentioned effective spot can be used to perform heating of other parts or areas of the object (such as the interior or main part of the area to be heated). The technician will choose the extent to which the effective spot rather than the main spot will be used to perform heating, depending on issues such as productivity and the need to carefully tailor the shape of the area to be heated or a certain part of the object being heated.

[0082] That is, it is not necessary to use the effective spot to perform all the heating that must be performed during the process. However, at least part of the process is performed using the effective spot as described above. For example, it may be preferred that during at least 50%, 70%, 80% or 90% of the time during which the beam is applied to the object, the beam is applied so as to establish the effective spot as explained above, that is, by repeatedly scanning the main spot according to a scanning pattern, the scanning being overlaid on the movement of the effective spot relative to the object (i.e. along the trajectory).

[0083] Heating can be used for any kind of heat treatment purposes, such as surface hardening, welding, curing, etc. The object can be any suitable kind of object in any suitable form, including powder form or the like, which may often be the case in the case of additive manufacturing. For example, the object can be a sheet metal object or any other kind of object. The object can have metal or have any other material. The object does not have to be a single workpiece, but can include several parts, for example, two or more parts that will be welded together by heating performed entirely or partially by a beam. Therefore, the term "object" should not be interpreted narrowly. The surface of the object may include openings or gaps. For example, this may occur when the surface includes parts associated with different objects, where there may be space between the objects. For example, when two parts are to be welded together, it is often the case that one of the parts can be spaced apart from another part corresponding to at least a part of the interface in which the weld is to be established. In some embodiments, the surface is flat, while in other embodiments, the surface is characterized by a three-dimensional shape.

[0084] In the present context, the expression dynamic adaptation is intended to denote the fact that the adaptation may occur dynamically during the displacement of the effective spot along the trajectory. This dynamic adaptation may be achieved using different means, some of which are mentioned below. For example, in some embodiments of the present invention, the scanning system may be operated to achieve dynamic adaptation (e.g., by adapting the operation of a galvano mirror or other scanning device so as to modify the scanning pattern and / or the speed of the main spot along the scanning pattern or along one or more sections or portions thereof), and / or the beam power and / or the size of the main spot may be adapted. Open-loop or closed-loop control may be used to control the dynamic adaptation. The dynamic adaptation may affect the way the energy is distributed within a given area of ​​the effective spot, and / or the actual shape of the effective laser spot, and therefore the shape (including width) of the area being heated at any given moment (ignoring the fact that the main spot is moving, and considering only the effective spot). For example, the length and / or width of the effective spot may be dynamically adapted during the process. Thus, by such dynamic adaptation, the two-dimensional energy distribution may be different relative to different parts of the surface of the object.

[0085] In some embodiments of the invention, the beam is shifted along the scanning pattern without switching the beam on and off and / or while keeping the power of the beam substantially constant. This makes it possible to perform scanning at high speed without taking into account the ability of the device (such as a laser device) to switch between different power levels, such as switching between on and off, and makes it possible to use devices that may not allow very fast switching between power levels. In addition, it provides an efficient use of the available output power, i.e. an efficient use of the capabilities of the device in terms of power. Therefore, an adaptation of the scanning rate and / or the scanning pattern may generally be preferred over an adaptation of the beam power. However, sometimes the beam power must or is preferably adapted, for example to provide an appropriate energy flux (in J / m 2 The effective spot may be moved at an appropriate speed (e.g., in terms of hardening depth) without having to displace the effective spot along the trajectory at an inappropriate speed and / or without (significantly or excessively) increasing the length of the effective spot. For example, it may be preferable not to operate the laser at its maximum power to allow the effective spot to travel at a speed suitable for heating purposes (e.g., in terms of hardening depth) without overheating the surface of the object.

[0086] In some embodiments of the invention, the focus of the beam and / or the size of the main spot is dynamically adapted during a displacement of the main spot along the scanning pattern and / or during a displacement of the effective spot relative to the surface of the object.

[0087] In some embodiments of the present invention, the main spot is displaced on the surface of the object according to the scanning pattern at a first average speed, and the effective spot is displaced relative to the surface of the object at a second average speed, the first average speed being significantly higher than the second average speed, such as at least 5, 10, 50, 100, 200, 500, 1000 or 2000 times the second average speed. Here, the term "first average speed" refers to the length of the scanning pattern projected onto the surface of the object divided by the time required for the main spot to complete one sweep along the scanning pattern, and the term "second average speed" refers to the length of the track followed by the effective spot on the surface divided by the time required for the effective spot to complete the track. The high speed of the main spot along the scanning pattern reduces temperature fluctuations within the effective spot during each sweep of the main spot along the scanning pattern. For example, for many laser surface hardening applications, a typical speed of the active spot along the trajectory may be about 600 mm / min, while commercially available scanners suitable for such processes may displace the main spot projected onto the surface at a speed of about 25,000 mm / s (and the use of such speeds makes it possible to achieve scan patterns and active spots having dimensions of, for example, about 20 mm × 12 mm at scanning frequencies of about 100 Hz sometimes used in laser hardening processes).

[0088] Additionally or alternatively, in some possible embodiments, the size of the effective spot is larger than 4 times the size of the main spot, preferably larger than 10 times the size of the main spot, and more preferably at least 25 times the size of the main spot. In some embodiments of the present invention, the size (i.e., area) of the effective spot (such as the average size of the effective spot during the process or the size of the effective spot during at least one moment of the process, such as the maximum size of the effective spot during the process) is larger than 4, 10, 15, 20, or 25 times the size of the main spot. For example, in some embodiments of the present invention, a 3 mm 2 The main spot size can be used to form a larger than 10 mm 2 (such as greater than 50 or 100 mm 2 The size of the effective spot can be modified dynamically during the process, but a large average size can generally be preferred to increase productivity, and a large maximum size can be used to increase productivity during at least a portion of the process.

[0089] The method may be performed under the control of an electronic control device such as a computer. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] In order to complete the description and to provide a better understanding of the present invention, a set of drawings is provided. The drawings constitute an integral part of the specification and illustrate embodiments of the present invention, which should not be interpreted as limiting the scope of the present invention, but only as examples of how the present invention can be implemented. The drawings include the following legends:

[0091] Figure 1A and Figure 1B is a perspective view schematically illustrating a system and method for heat treatment of an object such as a vehicle pillar according to one possible embodiment of the present invention.

[0092] Figure 2A and Figure 2B is a top view schematically illustrating an embodiment of the present invention.

[0093] FIG. 3A to FIG. 3C Additional or alternative options for adapting the process to variations in the width of a portion to be heat treated, which portion may be used according to different embodiments of the invention, are schematically illustrated.

[0094] Figure 4A and Figure 4B An embodiment of the invention is schematically illustrated which uses scan patterns having different lengths and different widths in directions parallel and perpendicular to the track, respectively.

[0095] Figure 5A and Figure 5B are photographs of tracks that have been laser hardened on a round steel rod using different scanning frequencies. DETAILED DESCRIPTION

[0096] Figure 1A and Figure 1B A system according to one possible embodiment of the invention is shown, in this case for heat treatment of sheet metal objects such as vehicle pillars. The system comprises a laser head comprising a scanner 2 for directing a laser beam 1 onto a workpiece 100. The laser beam may be emitted by a laser source remote from the laser head or in the laser head.

[0097] The laser beam 1 is projected onto the workpiece 100 to generate effective spots 12A, 12B by repeatedly scanning the laser beam (and thus the main spots projected by the laser beam onto the workpiece) in two dimensions according to a scanning pattern. To this end, the laser head comprises a scanner 2, such as a galvanometer scanner having two scanning mirrors 21 and 22, such as Figure 1A and Figure 1B The scanning pattern followed by the main spot projected by the laser beam 1 on the surface of the workpiece 100 at each specific moment is Figure 1A and Figure 1BHowever, any other suitable scanning pattern may be used, including scanning patterns as known from WO-2015 / 135715-A1 cited above, scanning patterns with curved sections, etc.

[0098] Thus, as known from e.g. WO-2016 / 146646-A1, the two-dimensional energy distribution within the active spot 12A, 12B can be customized by selecting the scanning pattern, the speed of the main spot along the scanning pattern and along different parts or sectors thereof, the beam power at each specific part of the scanning pattern, the size of the main spot, etc. This allows a dynamic adaptation of the two-dimensional energy distribution in order to optimize the heat treatment. Thus, as the active spot travels along the trajectory 101 to gradually heat the selected part 102 of the workpiece 100, the two-dimensional energy distribution and the total power of the active spot can be dynamically adapted, e.g. Figure 1A and Figure 1B As schematically illustrated in FIG.

[0099] like Figure 1A and Figure 1B As schematically illustrated in FIG. 1 , the selected portion 102 to be heat treated has a width that varies along the trajectory, and thus the width of the effective spot is variable; it can be observed that the effective spot is Figure 1A How to compare Figure 1B Medium width.

[0100] This concept is Figure 2A and Figure 2B As schematically shown in FIG. Figure 2A and Figure 2B Another embodiment is shown in which effective spots 12A, 12B are also formed by repeatedly scanning the main spot 10 along corresponding scanning patterns 11A, 11B, which correspond to two different sections or sub-sections 102a, 102b of the strip or portion 102 of the workpiece to be heat treated. The effective spot is scanned along the trajectory 101 to gradually heat the two sub-sections 102a, 102b. The first sub-section 102a has a first width W1 (in a direction perpendicular to the trajectory), and the second sub-section 102b has a second width W2 (in a direction perpendicular to the trajectory). In the illustrated embodiment, the second width W2 of the second sub-section is less than 50% of the first width W1 of the first sub-section. Obviously, other embodiments are characterized by other relationships in width between the two sub-sections, sometimes including those in which the width gradually (rather than as in Figure 2A and Figure 2B The transition part that increases or decreases in a step-by-step manner (as in the example of FIG. 1 ).

[0101] exist Figure 2A and Figure 2BIn the case of the embodiment shown in , the scanning pattern is a simple scanning pattern having a rectangular shape. In fact, any suitable scanning pattern may be used, including complex scanning patterns comprising multiple lines and segments (including straight and / or curved segments). In the schematically illustrated embodiment, the main spot 10 repeatedly follows a scanning pattern 11A corresponding to a sub-portion 102a having a first width W1 and a narrower scanning pattern 11B corresponding to a sub-portion 102b having a second width W2, thereby determining the (varying) width of the portion of the object subjected to heat treatment in one sweep of the effective spots 12A, 12B along the trajectory 101. In the illustrated embodiment, both the effective spots 12A and 12B are characterized by such an energy distribution, i.e., wherein the leading portion is characterized by a higher energy density than the trailing portion. As explained in, for example, WO-2014 / 037281-A2 cited above, this approach is sometimes preferred to allow rapid heating to the desired temperature by the leading edge or portion of the effective spot, and then the trailing portion is used to substantially maintain the temperature at the desired level for a certain amount of time. In other embodiments, other energy distributions are used.

[0102] A higher energy density at the leading portion can be established, for example, by keeping the beam power constant while scanning the laser beam at a slower speed along the leading section 11A', 11B' of the respective scan pattern and at a higher speed along the trailing section 11A", 11B". In other embodiments, the beam power can be adapted to achieve the same effect. In other embodiments, a combination of these methods can be used, and / or other parameters can be varied. For example, and although Figure 2A and Figure 2B The schematic diagram shows the use of a single basic scanning pattern layout (i.e., a rectangular layout), but in other embodiments, different scanning patterns can be used for the two sub-portions 102a and 102b having different widths. For example, the scanning pattern used in the second and narrower sub-portion 102b can have a greater length in a direction parallel to the track than the scanning pattern used in the first and wider sub-portion 102a, and the corresponding effective spot can move faster along the track.

[0103] In some embodiments, the repetition rate of the narrower scanning pattern 11B is substantially the same as the repetition rate of the wider scanning pattern 11A: for example, in some embodiments, the frequency of repetition of the narrower scanning pattern 11B in the sub-portion 102b having the narrower width W2 is greater than 80% but less than 120% of the frequency of repetition of the scanning pattern 11A in the sub-portion 102a having the larger width W1. This also means that the average speed of the main spot 10 along the scanning pattern 11A used in the sub-portion 102a having the larger width W1 (greater than twice the width W2 of the second sub-portion) can be significantly higher than the average speed of the main spot 10 along the scanning pattern 11B used in the second sub-portion 102b. In many embodiments, the average beam power can be higher in the sub-portion 102a having the larger width W1 than in the sub-portion 102b having the smaller width W2.

[0104] FIG. 3A to FIG. 3C Schematically illustrating how the adaptation of the process to different widths of the scan pattern may involve changes in operating parameters such as the speed V1 / V2 at which the effective spot moves along the trajectory (i.e., the process speed), the average beam power P1 / P2, and / or the length L1 / L2 of the effective spot. In different embodiments, these parameters may remain substantially constant, and in other embodiments, some or more of them may be varied. For example, the average beam power may be selected to be lower (P2) when the heat treatment is applied to the narrower sub-portion 102b, and higher (P1) when the heat treatment is applied to the wider sub-portion 102a. One reason for this is that when trying to maintain a constant heat treatment rate of J / m 2If the same average beam power is used in the narrower subsections as in the wider subsections (such as in the widest subsection) when the radiant energy flux of the meter is constant, overheating may occur. For example, in the case of laser hardening, undesired melting may occur. Of course, one possibility to avoid overheating may involve shifting the effective spot along the trajectory using a higher speed V2 along the narrower subsection 102b than along the wider subsection 102a, but this may have a negative impact on quality, such as the hardening depth. In some embodiments, the higher speed can be compensated by using such an effective spot, which is characterized by a length L2 in the narrower subsection 102b that is greater than the length L1 of the effective spot in the wider subsection, which length is the extension of the effective spot in a direction parallel to the trajectory. For example, additional segments of the scanning pattern can be added to make the scanning pattern longer and thus distribute the energy over a larger surface, fully or partially compensating for the reduced width of the portion being heated and / or the higher speed at which the effective spot is moved along the trajectory. Thus, a balance can be established between the desire to provide a substantially constant flux of radiant energy corresponding to the different sub-portions undergoing heat treatment, the desire to efficiently utilize the available laser power (preferably operating at a relatively high power level, such as at or close to the maximum power level allowed by the selected equipment), the need to obtain suitable product quality in terms of, for example, surface hardness or softness, depth affected by the treatment, etc., and the desire to operate at high speeds in terms of the number of products heat treated (such as in units / hour, meters / minute, etc.).

[0105] Although it is generally considered preferable to keep the frequency (i.e., the repetition rate of the scanning pattern) substantially constant, in some embodiments the frequency may vary significantly between the wider and narrower sub-portions subjected to heating, although it may generally be preferable for the frequency to be maintained within the range of 80%-120% of the reference frequency.

[0106] Merely as an example of the type of calculations that may be involved when selecting parameters for thermal treatment of a subsection having a second width based on parameters selected for a subsection having a first width ("reference subsection"), the following example is given, assuming a rectangular scan pattern and constant beam power and scan speed (i.e., no leading section with higher energy density is involved):

[0107] Length of the first subsection (in the direction parallel to the track): LSP1 = 50 mm

[0108] Width of the first subsection: W1 = 30 mm

[0109] Length of the second subsection: LSP2 = 70 mm

[0110] Width of the second subsection: W2 = 15 mm

[0111] Beam power applied at the first subsection: P1 = 5000 W

[0112] Beam power applied at the second subsection: P1 = 4000 W

[0113] Diameter of main spot: d=5 mm

[0114] Width of the scanning pattern at the first sub-section: WS1 = W1-d = 25 mm

[0115] Length of the scan pattern at the first subsection (in a direction parallel to the track): LS1 = 8 mm

[0116] The first scanning pattern is repeated at a frequency (repetition rate) of F1 = 100 Hz

[0117] Process speed at the first subsection (speed of the effective spot in a direction parallel to the track): PV1 = 600 mm / min = 10 mm / s

[0118] The parameters applied to the first sub-portion may be considered as reference parameters which have been found to provide a desired product in terms of hardening depth (for the purpose of giving an example only).

[0119] Now, the radiant energy flux EF1 at the first subsection can be calculated as follows:

[0120]

[0121] Now, the radiant energy flux EF2 at the second subsection should be substantially the same as the radiant energy flux at the first subsection: EF2 = EF1 ≈ 16727 kJ / m 2

[0122] Since the power P2 and the dimensions LSP2 and W2 are known, the process speed PV2 at the second subsection can be calculated: PV2 = (LSP2*P2) / [(((LSP2-d)*W2)+((W2-d)*d)+(PI*(d / 2)^2)))*EF2)] ≈ 961 mm / min ≈ 16 mm / s

[0123] However, as explained above, it is also preferred that the radiation energy flux (in J / m 2 The calculation is also the same in the first and second sub-parts: EFS1=EFS2.

[0124] EFS1 corresponds to the amount of energy applied during one sweep of the main spot along the scan pattern divided by the surface area swept by the main spot:

[0125] The amount of energy applied during one sweep of the main spot along the scan pattern is P1 / F1=50 J. The area swept is (((LS1*2)+(WS1*2))*d)+(PI*(d / 2)^2)≈350 mm 2 Therefore, the radiation energy flux EFS1 of the first scanning pattern is ≈143 kJ / m 2 Therefore, the parameters for the scan corresponding to the second subsection will be selected so that EFS2 = EFS1 ≈ 143 kJ / m 2 .

[0126] With the beam power, spot diameter, frequency (repetition rate) and width of the subsection known, the remaining parameter to adjust is the length LS2 of the second scan pattern. The amount of energy applied during one sweep of the main spot along the scan pattern is P2 / F2 = P2 / F1 = 40 J. If the area swept by the main spot during one scan cycle is A m 2 , 40 / A=143006, that is, A≈40 / 143006≈0.000280 m 2 , i.e. 280 mm 2 .

[0127] The swept area is (((LS2*2)+(WS2*2))*d)+(PI*(d / 2)^2) =((2*10+2*LS2)*5)+(PI*(5 / 2)^2)=100+10LS2+(PI*(5 / 2)^2) (mm 2 ). Therefore, LS2=((280-(PI*(d / 2)^2)) / d)-(100)) / 10) mm ≈ 16 mm. That is, the length of the second scanning pattern in the direction parallel to the track will be longer than the length of the first scanning pattern in the direction parallel to the track, and the same applies to the extension of the effective spot along the track. This concept is Figure 4A and Figure 4B Schematically illustrated in FIG. Figure 2A and Figure 2B but wherein the second scanning pattern 12B has a length or extension LS2 that is significantly greater than the length or extension LS1 (in a direction parallel to the track 101) of the first scanning pattern 12A. There is a corresponding difference in the lengths of the corresponding effective spots (ie L2>L1).

[0128] This is just one example of how the length of the second scanning pattern may be determined for a given power level on the basis of the parameters selected for the thermal treatment of the first sub-portion having width W1 and based on the following conditions: Radiant energy flux (in J / m 2The radiant energy flux applied to the heated sub-portion and the radiant energy flux of the scanning pattern (i.e., the energy applied during one scan of the main spot along the scanning pattern divided by the area actually scanned by the main spot) should be kept constant.

[0129] These calculations are based on a simple rectangular scan pattern with constant beam power and scan speed and, therefore, a uniform distribution of energy along the scan pattern. If a more complex pattern / energy distribution is used, such as one with a higher energy density corresponding to the leading portion than to the trailing portion, the calculations may be performed separately for the leading and trailing portions, and the condition that the radiant energy flux should be constant must be met for both the leading and trailing portions.

[0130] Figure 5A and Figure 5B are photographs of tracks that have been hardened on round steel bars. In both cases, the heat treatment was performed using a rectangular scanning pattern with a size of 10 mm × 8 mm, a beam power of 2000 W and a process speed of 200 mm / min. Figure 5A and Figure 5B The difference between the heat treatments is that in Figure 5A In the heat treatment, the frequency (repetition rate) of the scanning pattern is 100 Hz, and in the case corresponding to Figure 5B The frequency (repetition rate) of the scanning pattern was 250 Hz during the heat treatment. It was observed that when a higher frequency (250 Hz) was used, remelting ( Figure 5B ), whereas when a lower frequency (100 Hz) was used, no remelting occurred.

[0131] It should be observed that the different specific scanning patterns discussed above and illustrated in the various figures are by no means intended to represent scanning patterns that are sufficient or optimized for the purposes described. They are merely intended to schematically illustrate the concept of using scanning patterns according to the present invention and adapting them to generate heat in a desired manner according to the specific two-dimensional energy distribution selected at each specific moment. Those skilled in the art will typically use simulation software and trial and error methods to select a suitable scanning pattern.

[0132] In this document, the term "include" and its derivatives (such as "comprises", etc.) should not be understood in an exclusive sense, that is, these terms should not be interpreted to exclude the possibility that the described and defined contents may include additional elements, steps, etc.

[0133] On the other hand, the present invention is obviously not limited to the specific embodiment(s) described herein, but also includes any variation (for example, regarding the choice of materials, dimensions, components, construction, etc.) that may be considered by a person skilled in the art within the general scope of the invention defined in the claims.

Claims

1. A method for heating at least one selected portion of an object, comprising the steps of An energy beam (1) is projected onto a surface of the object (100) to generate a main spot (10) on the surface, and the beam is repeatedly scanned in two dimensions according to a scanning pattern (11A, 11B) to create an effective spot (12A, 12B) on the surface, the effective spot having a two-dimensional energy distribution, and displacing the active spots (12A, 12B) along a trajectory (101) on the surface of the object (100) to gradually heat a selected portion (102) of the object; in, The selected portion (102) has a first width (W1) at a first position along the trajectory (101) and a second width (W2) at a second position along the trajectory (101), the first width (W1) being greater than the second width (W2); wherein the beam (1) is scanned according to the scanning pattern (11A, 11B) such that the scanning pattern is repeated by the beam at a first frequency corresponding to the first position along the trajectory and at a second frequency corresponding to the second position along the trajectory, and wherein both the first frequency and the second frequency are greater than 10 Hz, The effective spot has a length (L1, L2) in a direction parallel to the track, wherein the length (L1, L2) is smaller in a case corresponding to the first position than in a case corresponding to the second position.

2. The method according to claim 1, wherein: The effective spot (12A, 12B) is displaced along the trajectory at a first speed (V1) corresponding to the first position along the trajectory and at a second speed (V2) corresponding to the second position along the trajectory, the second speed (V2) being higher than the first speed (V1).

3. The method according to claim 1 or 2, wherein: The effective spot is characterized by a first radiation energy flux to the surface of the object corresponding to the first position along the trajectory and a second radiation energy flux to the surface of the object corresponding to the second position along the trajectory, the second radiation energy flux is not greater than 140% of the first radiation energy flux and not less than 60% of the first radiation energy flux.

4. The method according to claim 3, wherein: The first scanning pattern (11A) represents a third radiation energy flow rate, which is defined as the energy supplied by the beam during a scan along the first scanning pattern divided by the surface area swept by the main spot during the scan along the first scanning pattern, and wherein the second scanning pattern (11B) represents a fourth radiation energy flow rate, which is defined as the energy supplied by the beam during a scan along the second scanning pattern divided by the surface area swept by the main spot during the scan along the second scanning pattern, wherein the third radiation energy flow rate is substantially the same as the fourth radiation energy flow rate.

5. The method according to claim 4, wherein: The second radiation energy flow is not greater than 120% of the first radiation energy flow and not less than 80% of the first radiation energy flow, and wherein the fourth radiation energy flow differs from the third radiation energy flow by no more than 20%.

6. The method according to claim 5, wherein: The second radiation energy flow is not greater than 110% of the first radiation energy flow and not less than 90% of the first radiation energy flow, and wherein the fourth radiation energy flow differs from the third radiation energy flow by no more than 10%.

7. The method according to claim 6, wherein: The second radiation energy flow is not greater than 105% of the first radiation energy flow and not less than 95% of the first radiation energy flow, and wherein the fourth radiation energy flow differs from the third radiation energy flow by no more than 5%.

8. The method according to claim 1, wherein: The effective spot (12A, 12B) shifts along the trajectory at a first speed (V1) corresponding to the first position along the trajectory and at a second speed (V2) corresponding to the second position along the trajectory, wherein the second speed (V2) is higher than the first speed (V1), and wherein the energy beam (1) has a first average power corresponding to the first position along the trajectory and a second average power corresponding to the second position along the trajectory, and the second average power is substantially the same as the first average beam power.

9. The method according to claim 1 or 2, wherein: The second width (W2) is less than 90% of the first width (W1).

10. The method according to claim 9, wherein: The second width (W2) is less than 75% of the first width (W1).

11. The method according to claim 10, wherein: The second width (W2) is less than 70% of the first width (W1).

12. The method according to claim 11, wherein: The second width (W2) is less than 60% of the first width (W1).

13. The method according to claim 12, wherein: The second width (W2) is less than 50% of the first width (W1).

14. The method according to claim 1 or 2, wherein: The second frequency is greater than 60% of the first frequency and less than 140% of the first frequency.

15. The method according to claim 14, wherein: The second frequency is greater than 70% of the first frequency.

16. The method according to claim 15, wherein: The second frequency is greater than 75% of the first frequency.

17. The method according to claim 16, wherein: The second frequency is greater than 80% of the first frequency.

18. The method according to claim 17, wherein: The second frequency is greater than 85% of the first frequency.

19. The method according to claim 18, wherein: The second frequency is greater than 90% of the first frequency.

20. The method according to claim 15, wherein: The second frequency is less than 130% of the first frequency.

21. The method according to claim 20, wherein: The second frequency is less than 125% of the first frequency.

22. The method according to claim 21, wherein: The second frequency is less than 120% of the first frequency.

23. The method according to claim 22, wherein: The second frequency is less than 115% of the first frequency.

24. The method according to claim 23, wherein: The second frequency is less than 110% of the first frequency.

25. The method according to claim 1 or 2, wherein: The energy beam (1) is a laser beam.

26. A system for heating at least one selected portion (102) of an object (100), the system comprising means for generating an energy beam (1) and for projecting the energy beam onto a surface of the object, and a scanner (2) for scanning the energy beam in at least two dimensions; in, The system is programmed to perform a method according to any one of the preceding claims.

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