Laser processing systems and methods for parts

Abstract

We provide a system for laser processing of parts. [Solution] The system includes a light source L that emits a pulsed laser beam, a first subsystem LDO, particularly a half-wave plate LDO, that adjusts the polarization of the laser beam, at least first and second deflectors, particularly first and second acousto-optic deflectors AOD or first and second electro-optic deflectors having non-parallel axes, particularly vertical axes, a second subsystem LQO, particularly one or two quarter-wave plate LQOs, that adjusts the polarization of the beam leaving the deflectors, a deflector control subsystem, particularly a controllable high-frequency generator, a synchronization subsystem DG, particularly an adjustable delay generator, that synchronizes the laser beam emission light source with the control subsystem, and a first focusing subsystem located after the second subsystem that adjusts the polarization of the beam leaving the deflectors, including a first lens FT.

Description

[Technical Field]

[0001] This invention relates, in particular, to a laser processing system for parts other than those used in watchmaking. The invention also relates to a laser processing method. [Background technology]

[0002] Laser processing is used in microtechnology for manufacturing parts. Femtosecond lasers, in particular, enable precise machining of small parts at very high speeds without thermal damage. However, traditional approaches to focusing and guiding the laser beam make it difficult to manufacture parts with straight sides along the cutting line. The conical shape of the laser beam at the focus, the non-uniform light intensity profile of the laser beam, and the nonlinearity of the ablation depth as a function of light intensity tend to cause the sides to tilt by several degrees.

[0003] To improve this, a widely accepted approach involves manipulating the workpiece and / or laser cutting head using a five-axis machine system. This technique allows the workpiece and / or laser head to be tilted at the focal point on the remaining side of the workpiece to counteract the taper.

[0004] Another popular method is laser processing using a laser beam that is precessed, i.e., tilted and rotated around an axis by optical mechanical means. Focusing this rotating beam generates a specific focal point. The laser beam is tilted slightly in the opposite direction to the machining plane to counteract the taper, and its focal point represents a circular trajectory. This circle forms the base of a cone whose apex lies above the machining plane. Therefore, as the volume of material to be removed increases, the length of the machining path increases.

[0005] In both of the aforementioned cases, the machining feed rate is significantly reduced. In the first method, this reduction in feed rate is due to the limited travel speed of the table or machining head. In the second method, additional time is required for the beam to complete its path around the circular perimeter. Furthermore, the stability of optics-mechanical systems containing optical elements rotating at high speeds of up to 30,000 revolutions per minute or 500 Hz tends to deteriorate rapidly, often accompanied by harmful vibrations.

[0006] In conventional femtosecond laser processing, the femtosecond laser enables material removal by ablation while maintaining a minimum thermal load. To achieve this, the energy supplied with each pulse is kept just above the ablation threshold. The beam is focused on the workpiece, creating a circular focus. This requires overlapping between consecutive pulses to ensure uniform material removal. Assuming a shallow ablation depth, multiple passes along the cut contour are required.

[0007] The superposition between consecutive pulses is typically 50% to 75%. The focus feed rate for this superposition is: vmax = flaser × dfocal × (1 - arec), where The flasher is a laser pulse frequency, dfocal is the focal diameter, arec is the degree of superposition between consecutive pulses. Typically, arec = 0.75, dfocal = 10 μm, and flaser = 1~10 MHz, resulting in a vmax value between 2.5 m / s and 25 m / s. The latter corresponds to the maximum speed of the galvanometric system.

[0008] In laser machining with a precessing beam, as shown in Figure 1, the beam is inclined at an angle α with respect to the normal N of the workpiece S being machined. Regardless of the machining direction, the inclined beam is rotated around the precession axis AP to achieve the desired taper on both sides. The BFI (Best Focus Individual) plane is defined as the instantaneous focal plane of the laser beam. The laser trail within this BFI plane has a circular shape. The beam itself exhibits a cone shape in space around the AP axis, and its apex must always lie on the BFI plane to achieve the desired tapered side.

[0009] The principle of superposition between consecutive pulses is transformed into the superposition between two consecutive precessional circles in precessional machining. The precessional frequency fprec is, vmax = fprec × dfocal × (1 - arec) The maximum machining feed rate is defined according to the following formula. Typical of conventional rotating optical systems, fprec = 500Hz (30,000rpm), arec=0.75, dfocal = 10 μm, From this, we obtain vmax = 0.00125 m / s = 1.25 mm / s. This feed rate is considerably lower than the maximum speed of the galvanometric system estimated above.

[0010] When the diameter of the opening on the laser beam entry side of the workpiece is larger than the diameter of the output side, this is called a positive taper. The taper is considered zero when the two diameters are the same, giving the machined side a linear shape. In this case, the machined geometric shape is a small cylinder in stationary drill mode. Conversely, the taper is negative when the diameter of the input side opening is smaller than the output side of the beam.

[0011] A rotational infinite focus system for precessional laser processing is known from Patent Document 1. The laser beam is shifted parallel to its initial axis by the arrangement of two rotating off-axis lenses. The system is then transformed by a focusing lens at an angle of inclination that can counteract the taper on the side of the hole or cutting path.

[0012] Patent Document 2 discloses a method for scanning a laser beam with up to 5 or 6 axes (5 or 6 axes) having path interpolation between reference points. The 5 or 6 axes are - The three coordinate axes of the focal point (x, y, z), - The angles α and β of the laser beam's inclination relative to the path, and - Angle of linear polarization of the laser beam, Includes. Two quaternary (x, y, α, β) control subsystems for the laser beam, based on four uniaxial galvanometer mirrors or two biaxial galvanometer mirrors, are mentioned as examples. Z-axis control is provided by a focusing lens or workpiece holder.

[0013] Patent Document 3 discloses a system for transforming a laser beam using an inclined mirror that rotates around its own axis of symmetry. To counteract the angular displacement of the beam, a retroreflector reflects the beam off the mirror and then, via a second reflection, returns the beam to a path parallel to the initial beam but offset from it. As a result, the laser beam follows a circle centered around its axis. This circular motion is then converted by a focusing lens into precession that can counteract the taper on the sides of the hole or cutting path.

[0014] A rotating optical machine precession system for performing laser processing with an adjustable lateral taper is known from Patent Document 4. The element that regulates the circular deviation of the laser beam is an inclined plate having parallel surfaces.

[0015] Patent Document 5 states, 1) A first positioning system that imposes a first relative motion of the laser beam axis along the beam path with respect to the workpiece. 2) a processor for determining a second relative movement (dithering) of the laser beam axis having a reduced amplitude compared with the first movement, 3) a second positioning system that imposes the second relative movement, and 4) a laser light source that emits laser beam pulses, A laser processing system including the above is disclosed. The first system is a galvanometric deflector, and the second system is an acousto-optic deflector (AOD). The document aims to protect high-speed machining of conductive tracks with variable cross-sections and variable dimensions for semiconductor chip encapsulation (semiconductor packaging). A relay lens is proposed for directing the beam after the second system (AOD) to the first galvanometric system. These lenses may introduce aberrations and may prevent proper focusing of the laser beam. As a result, machining time may increase, and / or machining accuracy may decrease.

[0016] In Patent Document 6, Patent Document 7, Patent Document 8, Patent Document 9, Patent Document 10, and Patent Document 11, there is respectively disclosed a method for manufacturing a small timepiece stone, which may or may not have a hole, comprising a step of ultrashort pulse laser ablation with a duration shorter than 100 ps. The laser beam is scanned using a 3-axis precession system to cancel and / or control the taper of the machined side surface. [Prior Art Documents] [Patent Documents]

[0017] [Patent Document 1] International Publication No. 2016 / 024069 [Patent Document 2] European Patent Application Publication No. 3700705 Specification [Patent Document 3] European Patent Application Publication No. 3195041 Specification [Patent Document 4] International Publication No. 2012 / 035031 [Patent Document 5] U.S. Patent Application Publication No. 2016 / 0250714 [Patent Document 6] European Patent Application Publication No. 3770697 [Patent Document 7] European Patent Application Publication No. 4004654 [Patent Document 8] Swiss Patent Application Publication No. 716430 [Patent Document 9] European Patent Application Publication No. 3770698 [Patent Document 10] European Patent Application Publication No. 4004653 [Patent Document 11] Swiss Patent Application Publication No. 716431 [Overview of the project] [Problems that the invention aims to solve]

[0018] The object of the present invention is to provide a laser cutting system that can overcome the current limitations associated with using a moving optical system, particularly with respect to the speed of laser cutting by precession, which is limited by the precession speed and its circular trajectory, and with respect to controlling taper and roughness. Closed trajectories, such as circles, ellipses, or polygons, or open trajectories, such as spirals, can be achieved at high speeds. The present invention also aims to overcome some limitations regarding the forces transmitted to the workpiece that arise from optical systems that include multiple refractive elements. The present invention also enables flexible laser cutting that allows for almost instantaneous switching between precession machining mode and conventional machining without precession. [Means for solving the problem]

[0019] The laser processing system according to the present invention is defined in claim 1.

[0020] Various embodiments of the laser processing system according to the present invention are defined in claims 2 to 12.

[0021] The laser processing method according to the present invention is defined in claim 13.

[0022] Embodiments of the method according to the present invention are defined in claims 14 and 15.

[0023] The drawings show, as an example, an embodiment of the laser processing system according to the present invention. [Brief explanation of the drawing]

[0024] [Figure 1] Figure 1 is a schematic diagram illustrating the principle of laser processing with precession. [Figure 2] Figure 2 is a schematic diagram illustrating the operating principle of an acousto-optic deflector. [Figure 3] Figure 3 is a block diagram of an embodiment of the laser processing system according to the present invention. [Figure 4] Figure 4 is a schematic diagram of an embodiment of the laser processing system according to the present invention. [Figure 5] Figure 5 shows the envelope shape of a precessional laser beam without a divergence control system. [Figure 6] Figure 6 shows the envelope shape of a precessional laser beam with a divergence control system in place. [Figure 7] Figure 7 is a table summarizing the parameters that enable the machining method according to the present invention. [Modes for carrying out the invention]

[0025] Embodiments of System 1 will be described below with reference to Figures 3 to 7. The laser processing system may be, in particular, a laser cutting or laser engraving system.

[0026] System 1 is - A laser light source L that emits a pulsed laser beam. - The first subsystem for adjusting the polarization of the laser beam is an LDO, particularly a half-wave plate LDO. - At least first and second deflectors having a vertical axis, non-parallel axis, in particular first and second acousto-optic deflectors (AOD) or first and second electro-optic deflectors, - A second subsystem LQO that adjusts the polarization of the beam emerging from the deflector, particularly one or two quarter-wave plate LQOs that convert the linear polarization of the laser beam to circular polarization. - A controllable high-frequency generator GRP, which can be implemented by either a digital frequency combiner or a voltage-controlled oscillator, controls the energy and emission of the laser pulse by controlling the deflector, particularly by controlling the acoustic excitation of an acousto-optic deflector or the refractive index of an electro-optic deflector, in order to adjust the intensity of the laser beam at the output of the deflector. - A tunable delay generation subsystem DG that allows the GRP to be synchronized with the laser clock to control the change in AOD deflection between two consecutive laser pulses, or a synchronization subsystem DG that synchronizes the laser beam emission source with the control subsystem GRP. - The first focusing subsystem F, which includes the first lens FT and is located after the second subsystem LQO, which adjusts the polarization of the beam leaving the deflector, - A subsystem for simultaneously controlling the divergence and linear deflection of the laser beam at the output of the deflector, and - Beam stabilization subsystem MS, located downstream of the laser light source and / or upstream of the first deflector. Includes.

[0027] Preferably, the system is configured to generate the precession of a laser beam.

[0028] In addition, a subsystem that simultaneously controls the divergence and linear deflection of the laser beam is, - The first telescope RF, the second focusing subsystem RF, and, - (a) The first lens FT, which emits a focal length longer than that of the first lens FT (the distance between the BFI plane and the reference point O upstream of the BFI plane) to the vertex distance of the precessional cone (the distance between the BFG plane and the reference point O upstream of the BFG plane), (b) A predetermined precession ring diameter, The required length to achieve this is the propagation module SPF, Includes.

[0029] Furthermore, a subsystem that simultaneously controls divergence and linear deflection is located between the deflector output and the first focusing subsystem FT.

[0030] In an embodiment of a laser processing system illustrated and described in more detail, the deflector is an acousto-optic deflector (hereinafter referred to as an AOD deflector or AOD).

[0031] In this embodiment, an acousto-optic deflector is used to generate a precessional beam, as will be explained below with reference to Figure 2. High-frequency generator G RF The excitation of the acoustic wave OA within the quartz crystal C by the piezoelectric element PZ, driven by the PZ, generates an in-phase lattice whose propagation speed is the same as the propagation speed of sound in the material. Due to the acousto-optic effect, the refractive index of the material is periodically modulated by regions of compression and expansion caused by the acoustic wave. The incident laser beam B1 is diffracted by the moving lattice. The diffracted beam B2 has a diffraction angle θ with respect to the direction of the incident beam B1. The angle θ is, θ = (λ × f) RF ) / V, It is approximated by the relationship, where, λ is the wavelength of the laser beam. f RF This refers to the frequency of the acoustic wave, and V is the speed of these waves. Therefore, the diffraction angle can be changed by altering the acoustic frequency. However, the maximum angular amplitude is not very large, typically on the order of 1°.

[0032] Preferably, the non-diffraction beam B1 is not used and is blocked by absorber A. Typically, up to 90% of the energy of the incident beam B1 can be converted to beam B2.

[0033] Advantageously, each AOD also includes an acoustic wave absorber (AAC).

[0034] AODs are advantageously paired so that their deflection directions are orthogonal to each other. This allows the beams to be directed in two dimensions, particularly by precession, to form a precessional beam.

[0035] If the deflector is of the AOD type, the amplitude and frequency of the acoustic wave are adjusted according to the desired diffraction angle and laser beam intensity.

[0036] If the deflector is of the EOD type, the amplitude of the deflector drive voltage is varied according to the refraction angle to be achieved.

[0037] To achieve the fastest possible laser processing with femtosecond pulses using a laser driven by precession, it is necessary to ensure proper superposition of precession circles. These circles are generated by the action of an acousto-optic deflector, and the laser processing system also includes a galvanometer system SG (scanner head) that provides the machining feed motion. Thus, the large working area achievable by machining is guaranteed by the SG galvanometer system. The principle requires maximizing the precession speed to fully utilize the maximum scanning speed of the galvanometric system.

[0038] The use of acousto-optic deflectors (AODs) generally increases the address speed within the working plane, and therefore the precession frequency, particularly due to their response time of approximately 1 microsecond (the duration corresponding to the propagation of sound across the beam diameter), in contrast to the millisecond range achievable with mechanical rotating systems. However, specific measures are advantageously employed to improve the effective use of AODs. a) Nonlinear effects caused by high-intensity laser pulses are reduced. b) The variability of the diffraction light intensity, which depends on the diffraction angle and polarization, is compensated for. c) Due to the diffraction angle being limited to approximately 1°, a system is preferably implemented that can convert the angular deflection of the laser beam into linear displacement in a plane perpendicular to the beam, preferably about 10 mm. d) The incident beam is stabilized in light of the small deflection angle and the limited aperture of the AOD, which is typically on the order of 5 mm. e) The control system PC is implemented to control the focus of the precessing beam in order to achieve the desired taper during laser processing.

[0039] In the modified form, the address along the contour, which may be closed or open, is followed by the machining system in an irregular or continuous manner to optimize the lateral roughness and thermal load.

[0040] The use of AODs is limited by laser damage and laser repetition rate. The crystal in the AOD is made of silica, a dielectric with a high damage threshold fluence. With a single pulse of 515 nm and a pulse duration of 500 fs, the damage threshold is approximately 2.5 J / cm² for silica. -2 It is estimated that, however, due to the incubation effect, this threshold becomes approximately 0.6 J / cm² after 100,000 pulses. -2 It decreases to . Since the AOD has a maximum aperture of 7 mm, the maximum energy per pulse is estimated to be 230 mJ. Therefore, the damage threshold beyond 100,000 pulses is approximately 0.6 J / cm -2 Assuming that it can be maintained at a roughly stable level, AOD can be safely used with current industrial lasers with a power of 300W and pulse frequencies in the range of 0.1MHz to 1MHz.

[0041] The maximum usable laser repetition rate is limited by the speed of sound in the AOD crystal and the beam dimensions. For a 7mm beam diameter, the maximum frequency is when the acoustic wave is approximately 5,700ms. -1 Based on the time required to traverse that distance at that speed, it is estimated to be 814 kHz.

[0042] The control subsystem includes a delay generator DG that synchronizes the excitation of acoustic waves in the AOD with the arrival of the laser pulse to generate a diffraction grating, thereby optimizing the intensity of the diffracted light. The subsystem also adjusts the diffraction efficiency based on the acoustic intensity. This control allows for the uniformization of the laser beam intensity along an annular trajectory in a plane perpendicular to the optical axis of the system, particularly when the beam follows a circular path, ensuring homogeneous ablation of the material throughout the machining process. In one embodiment, the control may be based on a lookup table that associates diffraction angle values ​​with specific acoustic frequencies and intensities. In other embodiments, the intensity of the laser pulse at the light source output is adjustable according to the diffraction angle to ensure uniform beam intensity along the path downstream of the AOD.

[0043] In particular, to compensate for deviations caused by thermal fluctuations of the beam at the output of the laser light source L, the MS laser beam stabilization subsystem is advantageously integrated upstream of the AOD. For this reason, the laser beam stabilization subsystem MS may be located between the magnification unit EF and the input of the first acousto-optic deflector (AOD). This subsystem also advantageously reduces pre-machining waiting time due to laser warm-up after power-up.

[0044] After passing through the AOD, the laser beam, following an annular trajectory, is focused by the first focusing subsystem F, specifically by a telecentric F-theta lens, which has the advantage of maintaining the focal dimensions throughout the entire workspace and minimizing aberrations. Because the beam divergence is smaller than the deflection angle of the AOD in the annular trajectory mode, the beam focuses before the apex of the precessional cone. As shown in Figures 5 and 6, the BFG (Best Focus Global) plane is a plane perpendicular to the optical axis where the minimum cross-sectional dimensions of the virtual intersection of the precessional laser beam are formed, very close to the apex of the cone formed by the precessional laser beam. To obtain sides with zero or negative taper, it is essential to machine the material beyond the apex of the precessional cone (downstream of the BFG plane). The BFI plane (meaning "Best Focus Individual") is a plane perpendicular to the optical axis where the laser beam focuses. If the beam is properly collimated, the BFI plane coincides with the focal plane of the lens.

[0045] As shown in Figure 5, premature focusing of the laser beam hinders optimal precessional machining. The width of the cutting groove expands significantly beyond the BFG plane (compared to a beam without precession), requiring higher power pulses and compromising precision. This increases the risk of overheating the material being machined and the risk of degrading the quality of the sidewalls.

[0046] The difference Δ between the BFI and BFG planes is: Δ = BFG - BFI = f / (r / (f × tanα) - 1) It is given by the formula, where, f is the focal length of the focusing subsystem F. r is the radius of the beam circle at the entrance of the focusing subsystem F. α is the angle between the laser beam and the precession axis (optical axis). That is the case.

[0047] - 100mm focal length, - An angle α between 0.1° and 1°, and - Radius r of 10 mm, For typical values, a Δ value between 1 and 20 mm is obtained. This is undesirable because the BFG plane is always located downstream of the BFI plane.

[0048] To rectify this situation, the laser processing system advantageously includes a second focusing subsystem RF, located downstream of the AOD, in particular a slightly focusing telescope of the first. By adjusting the distance between lenses L1 and L2 of the second focusing subsystem RF, the beam can be slightly focused, and beam divergence can be corrected by utilizing the diverging portion beyond the focal point. Soft focus is essential to prevent optical destruction at the intermediate focal point. This is characterized by a long effective focal length. Advantageously, this long distance is also used by the AOD to increase the beam scanning radius. Placing subsystem RF at the output of the AOD places the deflection focus near the center of the positive lens, which leaves the deflection angle required for precession constant or slightly modified. This situation reverses with respect to beam divergence and allows for precise adjustment of the distance between the BFI and BFG planes to form the optimal focus for precessional machining with a controlled taper.

[0049] In Figures 5 and 6, the beam divergence angle is exaggerated for ease of understanding.

[0050] The first focusing subsystem FT, which includes a telecentric F-theta lens in the scanner head, offers two main advantages for achieving linear lateral surfaces in precessional laser processing. The first advantage is that the average incident angle of each laser beam is maintained perpendicular to the surface of the part being machined, both at the center and edges of the machinable region. This is because cos(θ) (which defines the attenuation of the beam energy as a function of the incident angle θ) 4 This prevents the loss of machining homogeneity caused by the law of [unclear]. The second advantage arising from the first is the beam focal shape, which is always maintained as circular even at machining depth. In the case of vertical displacement during machining, this ensures stability of the angle of incidence, thus guaranteeing not only consistency of the lateral inclination but also the quality of the surface.

[0051] Conversely, a scanner head equipped with a standard F-theta lens can cover a larger working area than a telecentric F-theta lens during laser processing. However, the angle of incidence of the light ray changes, being perpendicular to the working plane at the center but gradually tilting towards the edges. Therefore, a standard F-theta lens cannot maintain normal incidence of the laser beam in the case of lateral and vertical shifts, or across the entire working surface. Furthermore, since the shape of the focal point deforms into an ellipse outside the center of the working plane, achieving a constant tilted side through laser beam precession using a non-telecentric lens becomes difficult, if not impossible. In fact, the angle of incidence depends on the position of the machining point on the working plane and the machining depth.

[0052] Figures 3 and 4 schematically illustrate a laser processing system based on controlled taper precession according to one embodiment. The system includes a laser source L that synchronizes the excitation of an acousto-optic deflector AOD via a delay generator DG. The beam emerging from the laser source is magnified by a telescope EF before entering the stabilization subsystem MS. After passing through the stabilization subsystem MS, the polarization of the beam is regulated by a first laser beam polarization adjustment subsystem LDO to maximize the diffraction efficiency of the AOD. The linear polarization of the beam after the AOD is converted to circular polarization by a second subsystem LQO that adjusts the polarization of the beam leaving the acousto-optic deflector. Next, beam divergence is corrected by a subsystem for simultaneous control of laser beam divergence and linear deflection, including a first telescope. A beam propagation module SPF adjusts the divergence of the beam and provides the necessary path length to convert angular deflection to linear deflection before the beam enters the first focusing subsystem F. The first focusing subsystem F includes a galvanometer mirror SG and a first telecentric F-theta focusing lens FT.

[0053] The laser light source L may be associated with a frequency multiplier. Thus, the laser light source L can supply pulses with pulse energies from 1 μJ to 200 mJ, wavelengths from 300 nm to 2,000 nm, beam diameters from 1 to 10 mm, and durations ranging from 10 fs to 10,000 fs, at repetition rates from 100 kHz to 1 MHz.

[0054] Preferably, the EF telescope increases its beam diameter from 3 mm to 5 mm, thereby enabling better utilization of the AOD's full 7 mm aperture.

[0055] A subsystem for simultaneously controlling the divergence and linear deflection of the laser beam includes an RF telescope. The telescope includes, for example, two lenses L1 and L2 with focal lengths of 150 mm and -100 mm, respectively. The two lenses may be positioned approximately 40 mm apart on the motor-driven axis, and this distance can be adjusted via the control subsystem PC.

[0056] The divergence obtained after passing through the RF telescope is 0.1 to 5 milliradians, typically 1 to 2 milliradians. The diameter of the beam without precession is 3 to 18 mm at the entrance of the SG galvanometer system. The diameter of the precession circle may be set to 0.1 to 20 mm. Thus, the outer diameter of the circle is approximately 3 to 38 mm at the entrance of the first F-focusing subsystem, with a typical value of 10 to 20 mm. The total beam propagation distance between the RF telescope output and the input of the SG galvanometric system is approximately 3 to 10 m, typically 5 to 7 m.

[0057] The first F-focusing subsystem is shown in Figure 4. The first F-focusing subsystem is - Scanner head SG, including two galvanometric mirrors, capable of receiving beams typically 20 to 30 mm in diameter, up to 40 mm in diameter, and - Especially the 100mm focal length, telecentric F-theta lens FT, It may include.

[0058] The beam scanning speed may vary between 8 and 14 m / s. The distance between the BFG plane and the BFI plane may be in the range of 10 to 5000 μm, typically between 100 and 500 μm, depending on the beam divergence and the deflection value of the AOD.

[0059] Examples of possible machining parameters are shown in the table of Figure 7.

[0060] Various parameters control the machining taper and side surface roughness in accordance with the method of the present invention or when using the machining system according to the present invention. - Number of passes. As the number of passes increases, the taper becomes more negative up to a certain limit that depends on the ablation threshold. The ablation threshold by laser pulses for a given material depends on the wavelength, pulse duration, pulse energy, and energy intensity on the surface of the material (J / cm -2 ). The latter is determined by a focusing means, typically a lens. - Ring diameter, represented by the laser beam deflected by the AOD. This diameter defines the angle of the precession cone or the angle of attack. The larger the diameter, the more negative the taper at a given focal length of the focusing lens. - Number of laser pulses around the circumference of the ring represented by the laser beam deflected by the AOD. This number ranges from 1 to 10,000, typically between 1 and 1,000. - The focal length of the F-theta lens and the precession cone diameter given by the deflection of the AOD define the angle of incidence on the material to be machined. - The side surface roughness depends on the number of passes and the type of beam path. The roughness decreases as the number of passes increases, and also by unique machining that forms a beam path with maximum uniform focal superposition and no repeating pattern. To achieve this, precession (rotation of the laser beam via the AOD) is performed alternately between clockwise and counterclockwise directions. Discontinuous addressing, for example irregular addressing, of points on the circumference of the precession ring also reduces roughness.

[0061] The taper can be controlled using two separate machining modes. In the first mode, the deflection angle of the laser beam due to AOD is constant because it forms a ring with a constant final diameter. In this first mode, the taper does not change along the machining path of the part, and the control of the laser beam by the scanner head is not synchronized with the deflection angle due to AOD.

[0062] In the second mode, taper values ​​are assigned to each position along the machined contour of the part. The position of the scanner head, which follows the contour of the part, is used to calculate the deflection required by the AOD to form the appropriate precessional cone. For this purpose, the scanner head is synchronized with the AOD. This synchronization is performed by the control subsystem PC.

[0063] In the context of this invention, experiments have shown that the lateral taper range of a 100mm F-theta lens is ±5° at a focal length. By changing the focal length to 50mm, this range was expanded to ±10°.

[0064] The material suitable for laser processing by precession according to the present invention is: - metal, - Metal alloys, - Ceramic, - Glass, - Polymers, and - Especially the form of the mixture, these combinations Includes.

[0065] These materials may be natural or synthetic, crystalline, especially polycrystalline, or amorphous, especially noncrystalline. Examples of polycrystalline and crystalline materials include metallic alloys, semiconductors, ceramics, cermets, sapphires, and rubies. Examples of amorphous materials include mineral glasses and amorphous metallic alloys.

[0066] The wavelength of the laser light source is selected based on the absorption of the material being machined. Typically, metals can be machined well at all practical wavelengths between 2 μm and 300 nm. Wavelengths between 300 nm and 600 nm are preferred for transparent or translucent materials, and for metals, due to the higher precision of the machining.

[0067] Regardless of the embodiment or modification, the AOD may be made of crystalline quartz SiO2. Alternatively, for the AOD, other acousto-optical materials may be used, for example, - Tellurium oxide TeO2, - Potassium niobate KNbO3, - Lithium niobate (LiNbO3), - Lithium tantalate LiTaO3, or - Lead molybdate PbMoO4, This may also be used.

[0068] Regardless of the embodiment or modification, electro-optical deflectors (EODs) can be used as a substitute for AODs. In these deflectors, - Electro-optic effects, particularly the Pockels effect or linear electro-optic effects (proportional to electric field strength), and - Kerr effect or secondary electro-optic effect, It may also be utilized in the configuration of electro-optical deflectors. The advantage of such EODs is the absence of a non-deflected beam, which eliminates the need for a cooling absorber to absorb the non-deflected beam. This allows for the formation of smaller deflectors that do not require water cooling.

[0069] There are two main configurations for constructing an electro-optic deflector. The first configuration utilizes refraction at the plane of a prism. The second configuration utilizes refraction due to the gradient of refractive index perpendicular to the direction of laser beam propagation. In both configurations, the electric field is applied perpendicular to the direction of light propagation.

[0070] Similar to acousto-optic deflectors, electro-optic deflectors exhibit similar deflection characteristics, with deflection frequencies ranging from 1 to 100 MHz and amplitudes ranging from 0.1° to 1°.

[0071] Suitable materials for manufacturing Pockels effect electro-optic deflectors include, for example, - Lithium niobate (LiNbO3), - Lithium tantalate LiTaO3, - Potassium dihydrogen phosphate (KDP) KH2PO4 and its deuterated mutant (DKDP) KD2PO4, - Hydrothermally synthesized potassium triphosphate (HGKTP)K3PO4, - Barium beta-borate (BBO)β-BaB2O4, - Potassium titanium phosphate (KTiOPO4), Includes.

[0072] Regardless of the embodiment or modification, a combination of a table enabling conversion between two non-parallel directions (XY) and a focusing lens, particularly a telecentric lens, integrated into the focusing subsystem F may be used as an alternative to the galvanometric system of the scanner head SG (galvanometric mirror). In this embodiment, the machining path is achieved by the conversion of the XY table rather than scanning the laser beam through the orientation of the galvanometric mirror. This embodiment enables the manufacture of a laser cutting head with improved removal of machining waste and better cutting quality thanks to the integrated compressed gas nozzle system.

[0073] Regardless of the embodiment or modification, the first focusing subsystem may be a scanner head including two SG galvanometric mirrors and a telecentric F-theta lens FT. Regardless of the embodiment or modification, the first focusing subsystem may also include a compressed gas nozzle, in particular a compressed air nozzle, to remove the cut product from the lens's focus.

[0074] Regardless of the embodiment or modification, the machining system may include a conversion table having two, three, four, five, or more axes for moving the machined part relative to the laser beam. Such a table may be used as an alternative to or in addition to a scanner head (having a galvanometric mirror or a two-axis conversion table).

[0075] Regardless of the embodiment or modification, the control subsystem PC allows the deflector and scanner head to synchronize in order to achieve a controlled taper of the side surface according to the position of the machined contour of the part, by adjusting the precession diameter of the laser beam.

[0076] Regardless of the embodiment or modification, the laser beam stabilization module typically includes a motor-driven two-axis mirror, driven by a stepping motor, servo motor, or piezoelectric actuator. These actuators may be controlled by an electronic system in a closed-loop or open-loop configuration to maintain the beam angle and linear position table using the beam position relative to two position sensors, such as a four-segment photodiode or imaging camera, as a counterpoint. These sensors may typically be located behind two partially transparent mirrors, positioned along the beam propagation axis.

[0077] Regardless of the embodiment or modification, when controlling the AOD via a programmable frequency synthesizer, the frequency and amplitude sequences corresponding to beam deflection and laser intensity, respectively, are advantageously stored in a lookup table (LUT) in memory. The clock edge from the laser system is sent to the input of the frequency synthesizer to trigger a transition from one set of LUT values ​​to the next. To ensure that the transient response caused by the change in frequency and amplitude does not interrupt the laser beam, the beam is synchronized between two consecutive laser pulses. This synchronization is ensured by proper adjustment of an adjustable delay generator (DG). The LUT values ​​and delay values ​​are transmitted to the generator by a control computer (PC). The delay generator may be used in master mode or slave mode relative to the scanner head.

[0078] The present invention also relates to a laser processing method, and to the implementation method described below. Such a machining method may be carried out by the laser processing system described above. The laser processing method enables the machining of parts, in particular watch parts or non-watch parts.

[0079] The machining method includes the following steps: - In order to achieve an ablation depth of 1 to 20 μm, preferably 1 to 10 μm, and more preferably 2 to 5 μm, in a single pass, the laser parameters are adjusted, in particular the pulse frequency, energy, and duration of the laser pulse, and the path pattern, based on the material of the part to be machined and the desired roughness of the machined side surface, in the first step E1. - (ii) The distance between the vertex of the precessional cone (or the BFG plane) and a reference point O, such as an FT lens, located upstream of the vertex of the precessional cone. Longer than (i) The distance between the focal point of the laser beam (or BFI plane) and a reference point O, such as an FT lens, upstream of the focal point of the laser beam. To obtain this, the second step E2 adjusts the laser beam divergence control system in the output of the acousto-optic deflector (AOD) based on the material of the machined part and the desired inclination of the machined side, particularly the distance between the RF telescope lenses. - The third step E3 adjusts the feed rate of the laser beam on the machining plane based on the precessional motion velocity of the laser beam obtained by the action of the acousto-optic deflector (AOD). - The fourth step E4 involves laser processing the part using the parameters determined in the first, second, and third steps.

[0080] The above solution makes it possible to reduce the machining or cutting time of parts with straight sides, outside the watchmaking industry, by a factor of 10 compared to existing solutions. According to the present invention, the machining system does not have moving parts, in particular rotating parts, for generating the precession of the laser beam. The precession is actually achieved using a deflector, in particular AOD or EOD. Scanning in a direction perpendicular to the laser beam is achieved using a galvanometer mirror (scanner head). [Explanation of symbols]

[0081] 1 System F First Focusing Subsystem L Laser light source DG Subsystem EF Enlarged Section FT First Lens MS beam stabilization subsystem PC control subsystem RF Second Focusing Subsystem SG Scanner Head AOD acousto-optic deflector EOD electro-optic deflector GRP deflector control subsystem LDO First Subsystem LQO Second Polarization Modulation Subsystem SPF propagation module

Claims

1. A laser processing system (1) for parts, more particularly a laser cutting system (1) for parts, wherein the system (1) is A light source (L) that emits a pulsed laser beam. A first subsystem (LDO) for adjusting the polarization of the laser beam, particularly a half-wave plate (LDO), Non-parallel axes, particularly having vertical axes, at least first and second deflectors, in particular first and second acousto-optic deflectors (AODs) or first and second electro-optic deflectors (EODs), A second polarization adjustment subsystem (LQO) of the beam exiting the deflector, particularly one or two quarter-wave plates (LQO), Deflection control subsystem (GRP), particularly controllable high-frequency generator (GRP), A subsystem (DG), particularly an adjustable delay generator, synchronizes the laser beam emission source (L) with the control subsystem (GRP). A first focusing subsystem (F) is located after the second subsystem, which includes a first lens (FT) and adjusts the polarization of the beam leaving the deflector. (i) a second focusing subsystem (RF), particularly the first telescope (RF), and (ii) a propagation module (SPF), comprising a subsystem for simultaneously controlling the divergence and deflection of the laser beam at the output of the deflector, wherein the subsystem for simultaneously controlling divergence and deflection is positioned between the output of the deflector and the first focusing subsystem (FT), and A beam stabilization subsystem (MS) is located downstream of the laser light source and / or upstream of the first deflector (AOD). Includes, The system is configured to generate the precession of the laser beam. System (1).

2. The system (1) includes a laser beam diameter expanding section (EF), in particular a second telescope (EF), The system (1) according to claim 1.

3. The beam stabilization subsystem (MS) is positioned between the beam expansion unit (EF) and the input of the first deflector (AOD), The system (1) according to claim 2.

4. The first focusing subsystem (F) includes a scanner head (SG) which includes two galvanometer mirrors. The system (1) according to any one of claims 1 to 3.

5. The system (1) adjusts the precession diameter of the laser beam to obtain a controlled taper of the machined side surface corresponding to the position of the machined contour of the part, The deflector (AOD); The scanner head (SG) and, Includes a control subsystem (PC) that is deployed to synchronize, The system (1) according to claim 4.

6. The first focusing lens (FT) is an F-theta-telecentric lens. The system (1) according to any one of claims 1 to 5.

7. The first focusing subsystem (F) is: A compressed gas discharge nozzle, particularly a compressed air nozzle, for removing a machined product from the focal point of the first lens (FT), and A table (T) for moving the component along two axes, three axes, four axes, or five or more axes relative to the first lens (FT), including, The system (1) according to any one of claims 1 to 3.

8. The second focusing subsystem (RF) is configured to form a divergent portion (DP) of the laser beam beyond the intermediate focus (C). The system (1) according to any one of claims 1 to 7.

9. The second focusing subsystem (RF) is the first telescope (RF), which includes lenses having different focal lengths, particularly a first focal length of approximately 150 mm and a second focal length of approximately -100 mm. The system (1) according to any one of claims 1 to 8.

10. The deflector is configured such that the laser beam exhibits an annular shape, particularly a circular shape, in a plane perpendicular to the optical axis (B). The system (1) according to any one of claims 1 to 9.

11. The deflector control subsystem (GRP) controls the energy and generation of the laser pulse by controlling the deflector, particularly by controlling the excitation of the acoustic wave of the acousto-optic deflector (AOD), or by controlling the refractive index of the electro-optic deflector (EOD), in order to adjust the intensity of the laser beam at the output of the deflector. The system (1) according to any one of claims 1 to 10.

12. The synchronization subsystem (DG) enables synchronization, particularly by the laser clock, of the control subsystem (GRP) in order to control the change in the deflection of the deflector between two consecutive laser pulses. The system (1) according to any one of claims 1 to 11.

13. A laser processing method for non-watch parts, particularly a laser cutting method, In order to achieve an ablation depth of 1 to 20 μm, preferably 1 to 10 μm, more preferably 2 to 5 μm, in a single pass, the laser parameters are adjusted, in particular the pulse frequency, the energy and the duration of the laser pulse, based on the material of the part to be machined and the desired roughness of the machined side surface, in a first step (E1). (ii) The distance between the vertex of the precessional cone and the reference point (O), in particular the first lens (FT), upstream of the vertex of the precessional cone, Longer than (i) The distance between the focal point of the laser beam and the reference point (O), in particular the first lens (FT), upstream of the focal point of the laser beam. To obtain the second step (E2), based on the material of the machined part and the desired inclination of the machined side surface, the laser beam divergence control system adjusts the output of the deflector (AOD), particularly the distance between the lenses of the telescope (RF), A third step (E3) involves adjusting the feed rate of the laser beam on the machining plane based on the precessional velocity of the laser beam obtained by the action of the deflector (AOD), A fourth step (E4) is to laser process the part using the parameters determined in the first, second, and third steps. The steps include, method.

14. The method includes the use of the system (1) described in any one of claims 1 to 12. The method according to claim 13.

15. The simultaneous control of the divergence and deflection of the laser beam is performed by: The position of the focal point of the laser beam, and The position of the vertex of the precessing cone, Allows independent adjustment of The method according to claim 13 or 14.

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