METHOD FOR LASER-BASED MACHINING OF A WORKPIECE

Description

[0001] The invention relates to a method for laser-based processing of a workpiece.

[0002] It is known to process workpieces using short, intense laser pulses. The high-power laser radiation heats the material at the workpiece surface. The surface of the workpiece reaches such a high temperature locally that the material vaporizes or sublimates. At high laser power densities, a plasma of electrons and ions from the ablated material is created. This material removal is also known as laser ablation or laser vaporization. The material can be removed, for example, in layers across the entire surface. Furthermore, it is possible to cut a workpiece using continuous or pulsed laser radiation. This is called laser cutting or laser beam cutting. The laser radiation parameters must be adapted to the material being processed and the desired machining operation. These parameters include the wavelength and the average power.If the laser radiation is pulsed, the parameters also include pulse energy and pulse duration.

[0003] For laser processing, the laser beam and workpiece are precisely aligned relative to each other and, if necessary, moved to selectively remove material within predefined areas of the workpiece and to create specific contours on its surface. This includes, among other things, the creation of cutting edges or other edges on workpieces.

[0004] A laser processing machine is equipped with a laser that generates a laser beam. The laser beam extends along a beam axis.

[0005] The beam axis corresponds to a geometric straight line. The laser comprises a laser head that directs the laser beam precisely onto a workpiece and, if necessary, moves it across the workpiece's surface within a predefined contour. The workpiece is arranged in a fixture for alignment and positioning, which, in the case of a machine tool, is also referred to as a clamping device. This fixture is equipped with a fixture base, a workpiece clamping device, and a motion mechanism. The fixture base is stationary and can be part of the machine base of the laser processing machine. The workpiece clamping device receives and securely clamps the workpiece, ensuring that its position relative to the clamping device does not change during processing.The motion device moves the workpiece clamping device relative to the fixture base. Since the laser head of the laser processing machine is typically stationary relative to the fixture base, the motion device also creates a relative movement between the laser head and the workpiece clamping device. This moves a workpiece clamped in the fixture relative to the laser beam generated by the laser head. Thanks to this relative movement, the entire surface of a workpiece can be processed, provided the workpiece surface is not covered by the fixture. During processing, the workpiece surface is aligned with the laser beam at various angles.The laser head can be equipped with a deflection device that uses optical components to deflect the laser beam and guide it at high speed across the surface of the workpiece. This deflection device thus creates an additional relative movement between the laser beam and the workpiece.

[0006] To process a workpiece, the laser beam is typically aligned with its beam axis to the workpiece in such a way that the beam axis is perpendicular to a surface of the workpiece. This is in Figure 1 depicted. Figure 1 Figure 1 shows a workpiece 1 and a laser beam 3 with a beam axis 5. Figures 2 and 3Figure 1 shows the point of impact 2, where the laser beam 3 strikes a flat surface 1a of the workpiece 1. The energy density of the laser beam 3 is greater at its center than at its edge. Consequently, the temperature at the center of the laser beam 3 is higher than at its edge. This results in more material being removed from the workpiece at the point of impact 2 than at its edge. If the laser beam 3 is not moved relative to the workpiece 1, it creates a circular depression 4 on the surface of the workpiece 1. This depression has the shape of a portion of a spherical shell or an ellipsoid. The depression 4 is deeper in the center than at the edge. A cloud or flame 8, which forms on the surface of the workpiece 1 under the influence of the laser beam 3, contains the vaporized or sublimated material of the workpiece, as well as any dust and other particles. Figure 4This shows that the flame 8 has an opening angle γ. When the laser beam 3 is moved relative to the workpiece along a path on the surface 1a of the workpiece 1, a sequence of spatially offset indentations 4 is created, which together form a groove 10. An edge 9 is formed at the transition between the flat surface 1a and the groove 10. The groove 10 has the opening angle γ. If an edge, for example a cutting edge, is to be created on the workpiece 1 using the laser beam 3, or if the workpiece is to be cut, the laser beam 3 is moved back and forth several times along the path relative to the workpiece 1 until the groove 10 has the necessary depth. With each movement, the groove 10 created by the laser beam 3 becomes deeper and wider. This is shown in the Figures 7 and 8 The two figures show that furrow 10 transitions into furrow 10' through additional material removal with the laser beam. Figure 8This clearly shows that the groove 10 becomes not only deeper but also wider due to the opening angle γ of the flame 8. With each movement of the laser beam 3 along the path, the edge 9, which is created at the edge of the flame 8 on the surface 1a of the workpiece 1, shifts laterally. As a result, the edge 9 is not necessarily in the intended position at the end of the laser processing.

[0007] Accordingly, area 7 migrates. Furthermore, in the edge region of the flame 8, dust and sublimated material from the workpiece 1 are deposited on surface 1a. This results in a poor surface quality of the workpiece in the area of ​​edge 9.

[0008] US Patent 2011 / 095005 A1 discloses a laser processing method and a device for surface shaping of a workpiece, in particular for the production of cutting tools with cutting edges and clearance faces. A laser generates pulsed beam pulses which are directed by a deflecting arrangement at an angle onto the surface of the workpiece. The pulses strike adjacent points and form a pulse zone. By means of a controlled relative movement between this pulse zone and the workpiece, an ablation layer of defined thickness is removed with each contour pass.

[0009] The invention is based on the objective of providing a method for laser-based processing of a workpiece, with which a workpiece surface can be produced at a precisely specified position and in which the produced workpiece surface has a high surface quality.

[0010] This problem is solved by a method according to claim 1. The method according to the invention is characterized in that the workpiece and the laser beam are aligned relative to each other such that, during processing, the geometric beam axis of the laser beam, at each point where the beam axis intersects the workpiece surface to be generated, forms an angle α between 1° and 10° with the tangent to the workpiece surface to be generated at that point. This results in the cloud or flame that forms on the surface of the workpiece under the influence of the laser beam also being inclined with its opening angle relative to the surface of the workpiece. Advantageously, the angle α corresponds to the opening angle γ of the flame.By aligning the laser beam axis at an angle α to the tangent of the workpiece surface to be processed, the deposition of vaporized or sublimated material on the workpiece surface is prevented, thus preventing undesirable burning of the workpiece surface. Consequently, the surfaces adjacent to the processed edge exhibit a good surface quality after laser processing.

[0011] A further advantage of the method according to the invention is that the workpiece surface to be produced is created precisely at the predetermined position with the precisely predetermined geometry by targeted material removal using the laser. In contrast to known methods, the workpiece surface produced by material removal does not shift during laser processing.

[0012] During laser processing, the material is not removed layer by layer because the laser is not aligned perpendicular to the workpiece surface being created. Instead, a section of the workpiece is removed to create the surface.

[0013] In an advantageous embodiment of the invention, during laser-based processing, the laser beam and the workpiece are moved relative to each other in such a way that a section of the workpiece is removed. During this material removal, the workpiece surface to be produced is created at the interface with the removed section of the workpiece. If the section to be removed has a small thickness, the removed material from the workpiece vaporizes completely. The material removal occurs along a predetermined path while maintaining the orientation of the beam axis relative to the respective tangent to the workpiece surface to be produced at an angle α. In this way, the workpiece can be cut or an edge can be created. For this purpose, the laser beam is passed along the path multiple times until the desired workpiece surface is completely produced.

[0014] According to the invention, the angle α is determined as a function of the workpiece material, the laser wavelength, and the average laser power. These parameters determine the opening angle γ of the flame that forms on the surface of the workpiece under the influence of the laser beam.

[0015] According to a further advantageous embodiment of the invention, the laser is a pulsed laser. With a pulsed laser, a particularly high energy density can be achieved within the short pulse duration, thereby generating a particularly high surface temperature on the workpiece. Due to thermal conduction, the temperature does not spread significantly within the workpiece during the short pulse duration, since energy transfer by thermal conduction is very slow compared to the pulse duration. Consequently, the energy transferred by the laser beam to the workpiece is concentrated on a very thin layer. Therefore, when using a pulsed laser, the surface of the workpiece reaches a particularly high temperature in a spatially limited area, and the material vaporizes rapidly.

[0016] According to a further advantageous embodiment of the invention, when using a pulsed laser, the angle α is determined not only as a function of the material of the workpiece, the wavelength of the laser and the average power of the laser, but also as a function of the pulse duration and the pulse energy of the pulsed laser.

[0017] According to a further advantageous embodiment of the invention, a flame is generated on the surface of the workpiece using the laser beam. This flame contains sublimated material from the workpiece and has an opening angle γ that depends on the material of the workpiece and the laser beam. The angle α between the beam axis of the laser beam and a tangent to the surface of the workpiece to be generated is adjusted so that it corresponds to the angle γ. This allows for the production of a workpiece surface with particularly high quality.

[0018] According to a further advantageous embodiment of the invention, the laser beam is focused on the workpiece, wherein the focal point of the focused laser beam is located at the point where the beam axis intersects the workpiece surface to be produced.

[0019] According to a further advantageous embodiment of the invention, the workpiece surface to be produced is a flat surface.

[0020] According to a further advantageous embodiment of the invention, the workpiece surface to be produced is a curved surface. The motion device rotates the workpiece, which is held in the workpiece clamping device, about a workpiece rotation axis during the laser-based material removal.

[0021] According to a further advantageous embodiment of the invention, material is removed from the workpiece while the laser beam is aligned relative to the workpiece at a constant angle α. The alignment of the laser beam relative to the workpiece is therefore maintained throughout the entire material removal process. This is suitable, for example, for the production of flat surfaces and when the workpiece has a certain symmetry with respect to the axes of movement of the laser processing device.

[0022] According to a further advantageous embodiment of the invention, the angle α is changed within the angular range 1° ≤ α ≤ 10° when material is removed from the workpiece. The orientation of the laser beam relative to the workpiece thus changes, while the angle α remains within the predetermined angular range. Such an angular change can occur if the laser beam is additionally guided along a laser path in closed or open curves during material removal, if irregularly shaped or non-planar surfaces are produced, or if the workpiece is arranged in a specific orientation relative to the axes of motion of the laser processing device's motion mechanism. Of particular importance here is a workpiece rotation axis around which the workpiece clamping device rotates, and consequently, so does the workpiece itself.

[0023] According to a further advantageous embodiment of the invention, the laser beam is moved relative to the surface of the workpiece, wherein the angle α between the beam axis and the tangent to the workpiece surface to be treated lies within the angular range 1° ≤ α ≤ 10° during the relative movement. The relative movement represents a superposition of a first movement and a second movement. The first movement causes the laser beam to move between a first point A on the surface of the workpiece and a second point B on the surface of the workpiece. In the second movement, the laser beam is moved within a closed or open curve, the extent of which is small compared to the path traveled by the laser beam from point A to point B. The additional loop-shaped second movement increases the area of ​​material removal during the first movement.

[0024] Further advantages and advantageous embodiments of the invention can be found in the following description, the drawing and the claims. drawing

[0025] The drawing shows a known method for laser-based processing of a workpiece and a method for laser-based processing according to the invention. It shows: Figure 1: Perspective view of a workpiece with a laser beam in a known laser processing method; Figure 2: Workpiece according to Figure 1 in another perspective view, Figure 3, workpiece according to Figures 1 and 2 in longitudinal section along the in Figure 2 Plane marked A - A, Figure 4 Workpiece in sectional view according to Figure 3 with a flame containing sublimated material, Figure 5 workpiece according to Figures 1 to 4 , where a depression was created along a path using the laser beam, Figure 6 workpiece according to Figure 5In a front view, Figure 7: workpiece in perspective view, with the laser beam moved multiple times along the path, Figure 8: workpiece according to Figure 7 In a front view, Figure 9 workpiece with laser beam aligned according to the invention, Figure 10 workpiece in longitudinal section during laser-based processing according to Figure 9 Figure 11: second workpiece on which a flat workpiece surface is produced using the method according to the invention; Figure 12: workpiece according to Figure 11 with partially removed material, Figure 13 workpiece according to Figure 11 , wherein the material is completely removed, Figure 14 third workpiece on which a flat workpiece surface is produced by means of the method according to the invention, Figure 15 workpiece according to Figure 14 with partially removed material, Figure 16 workpiece according to Figure 14, wherein the material is completely removed, Figure 17 fourth workpiece on which a curved workpiece surface is produced by means of the method according to the invention, Figure 18 workpiece according to Figure 17 with partially removed material, Figure 19 workpiece according to Figure 17 , wherein the material is completely removed, Figure 20 fifth workpiece on which a curved workpiece surface is produced by means of the method according to the invention, wherein the workpiece is shown in a front view at the beginning of the laser processing, Figure 21 workpiece according to Figure 20 in perspective view, Figure 22 workpiece according to Figure 20 at a first later stage of laser processing, Figure 23 workpiece according to Figure 22 in perspective view, Figure 24 workpiece according to Figure 20 at a second, later point in the laser processing, Figure 25 workpiece according to Figure 24 in perspective view, Figure 26 workpiece according to Figure 20at a third, later point in time during laser processing, Figure 27 workpiece according to Figure 26 In perspective view, Figure 28: Laser processing machine for carrying out the process. Description of the exemplary implementations

[0026] In the Figures 1 to 8 Figure 1 shows a known method for laser-based processing of a workpiece, in which the laser beam 3 is aligned with its beam axis 5 perpendicular to the flat surface 1a of the workpiece 1. This known method is explained in the introductory description above.

[0027] In the Figures 9 and 10The inventive method is illustrated. The workpiece surface 7' to be produced is a flat surface. Therefore, the tangent to this workpiece surface to be produced runs along the surface. In the present embodiment, the workpiece surface 7' to be produced runs perpendicular to the surface 1a of the workpiece. In contrast to the known method according to Figures 1 to 8 In the inventive method according to Figures 9 and 10 the laser beam 3' with its beam axis 5' is not parallel to the surface 7' to be produced and aligned at 90° to the flat surface 1a of the workpiece 1, but at an angle α to the flat workpiece surface 7' to be produced. Figure 10Figure 1 shows the cloud or flame 8' that the laser beam 3' generates upon striking the workpiece 1 and which contains sublimated material from the workpiece 1. The flame 8' has an opening angle γ. Here, angle γ does not correspond to the full opening angle of the conical flame, but only to the opening angle of the conical flame relative to the beam axis 5'. The laser beam is aligned with its beam axis 5' such that angle α corresponds to angle γ. In this way, the left flank of the flame 8' is achieved as shown in Figure 1. Figure 10 parallel to the workpiece surface 7' to be produced. This means that the laser beam 3' can be used to create exactly the surface 7', whereby the edge between the surface 7' and the surface 1a does not shift during laser processing.

[0028] In the Figures 11 to 13A second workpiece 11 is shown, on which a predetermined workpiece surface 17 is produced using the method according to the invention. The workpiece 11 is cylindrical with a circular cross-section. It is in the Figures 11 to 13 The workpiece 11 is shown in cross-section. It has an insert 12 on which a predetermined flat workpiece surface is created by material removal using a laser beam 13 with beam axis 15. For this purpose, part of the insert 12 is removed. The laser beam 13 is aligned with its beam axis 15 to the workpiece 11 such that the beam axis 15 forms an angle α with the tangent 17 to the workpiece surface to be created. Figure 12 The workpiece 11 is shown after part of the insert 12 has been removed using the laser beam 13. Figure 13Figure 1 shows the workpiece at the end of the laser processing. The workpiece surface to be produced is a flat surface. Tangent 17 therefore lies in the plane formed by this surface. Figures 11 to 13 This demonstrates that the angle α remains constant throughout the entire laser processing. In this way, for example, a clearance surface can be created on a cutting tool.

[0029] In the Figures 14 to 16A third workpiece 21 with an insert 22 is shown, on which a predetermined flat workpiece surface is produced using the method according to the invention. Since the workpiece surface to be produced is a flat surface, the tangent 27 to the workpiece surface lies within the workpiece surface. The laser beam 23 is aligned with its beam axis 25 at an angle α to the tangent 27 of the workpiece surface. In accordance with the second workpiece 11, the third workpiece 21 is cylindrical with a circular cross-section. The difference from the second workpiece 11 is that the insert 22 of the third workpiece 21 is inserted into the workpiece with a different orientation.

[0030] In the Figures 17 to 19 A fourth workpiece 31 with an insert 32 is shown, on which a curved workpiece surface is created, the course of which 37 in Figure 17as indicated by a curve. For this purpose, the workpiece 31 is rotated about a longitudinal axis during laser processing. The laser beam 33, with its beam axis 35, is always aligned at an angle α to the tangent 38 of the curved surface. The angle α remains constant during material removal. In this way, for example, a guide phase can be created on a cutting tool.

[0031] In the Figures 20 to 27A fifth workpiece 41 is shown with two inserts 42, 42a, on which a curved workpiece surface is produced. The beam axis 45 of the laser beam 43 forms an angle α with the tangent 48 at the point where the laser beam intersects the surface of the workpiece 41 and the beam axis 45 intersects the workpiece surface. The inserts 42, 42a have the special feature that they are not aligned parallel to the longitudinal axis of the workpiece 41. Therefore, during laser processing with the laser beam 43, the workpiece 41 is rotated about its longitudinal axis. This rotation is necessary, firstly, to produce the curved workpiece surface in a plane perpendicular to the longitudinal axis of the workpiece 41, and secondly, to produce the workpiece surface of the inserts 42, 42a in the axial direction of the workpiece 41. Figures 20 and 21The figures show the workpiece 41 at the beginning of laser processing in two different views. The laser beam 43, with its beam axis 45, is directed at an angle α1 to the tangent 48 at the surface of the insert 42 of the workpiece 41. Figures 22 and 23 The images show workpiece 41 at an advanced stage of laser processing. Figure 23 It can be seen that the laser beam 43 was moved with its beam axis 35 along the insert 42 of the workpiece 41. The beam axis 45 of the laser beam 43 forms an angle α2 with the tangent 48 to the workpiece surface, which differs from α1. Figures 24 and 25 The figures show the workpiece 41 at a later stage of laser processing. The laser beam 43 has moved further along the surface of the insert 42 of the workpiece 41. The beam axis 45 of the laser beam 43 forms an angle α3 with the tangent 48 to the workpiece surface. Figures 26 and 27The figures show the workpiece shortly before the laser processing of the insert 42 of the workpiece 41 is completed. At this point, the laser beam 43 is located at the lower end of the insert 42. The beam axis 45 of the laser beam 43 forms an angle α4 with the tangent 48. The angles α1, α2, α3, and α4 are different, but all angles lie in the range between 1° and 10°. In this case, α1 < α2 < α3 < α4. Figures 20 to 27 show that the angle between the beam axis 45 of the laser beam 43 and the tangent 48 to the workpiece surface 41 can change at the point where laser processing takes place, with the angle always being in the angular range between 1° and 10°.

[0032] In Figure 28A laser processing device 50 for carrying out the method is shown. The laser processing device 50 comprises a workpiece clamping device 54, which receives and clamps a workpiece 55, a motion device 51, which moves the workpiece 55 arranged in the clamping device relative to a device base 56, and a laser 52, which generates a laser beam 53 and moves it with a laser scanning device. In this case, the motion device 51 has three linear axes X, Y, Z and two rotational axes B and C. Reference figures

[0033] 1 Workpiece 1a Flat surface of the workpiece 2 Point of impact of the laser beam 3, 3' Laser beam 4, 4' Indentation 5, 5' Beam axis 7, 7' Created workpiece surface 8, 8' Flame 9 Edge 10, 10' Groove 11 Second workpiece 12 Insert 13 Laser beam 15 Beam axis 17 Tangent to the workpiece surface 21 Second workpiece 22 Insert 23 Laser beam 25 Beam axis 27 Tangent to the workpiece surface 31 Second workpiece 32 Insert 33 Laser beam 35 Beam axis 37 Path of the workpiece surface 38 Tangent 41 Fifth workpiece 42 Insert 42a Insert 43 Laser beam 45 Beam axis 48 Tangent 50 Laser processing device 51 Motion device 52 Laser 53 Laser beam 54 Workpiece clamping device 55 Workpiece 56 Fixture base

Claims

1. Method for laser machining a workpiece, wherein a predetermined workpiece surface (7', 37) is produced on the workpiece (1, 11, 21, 31, 41, 55) by removing material through a laser (52) of a laser machining device (50) which comprises a workpiece fixing device (54) which receives and fixes the workpiece (1, 11, 21, 31, 41, 55) , a moving device (51) which moves the workpiece fixing device (54) relative to a device base (56) including the laser (52), whose laser beam (3', 13, 23, 33, 43, 53) with its geometric beam axis (5', 15, 25, 35, 45), is directed onto the workpiece (1, 11, 21, 31, 41, 55) received in the workpiece fixing device (54), wherein the laser machining device (50) is configured to align the workpiece (1, 11, 21, 31, 41, 55) arranged in the workpiece fixing device (54) relative to the laser beam (3', 13, 23, 33, 43, 53) and to move the laser beam (3', 13, 23, 33, 43, 53) relative to the workpiece (1, 11, 21, 31, 41, 55), with the following steps: aligning the workpiece (1, 11, 21, 31, 41, 55) and the laser beam (3', 13, 23, 33, 43, 53) of the laser (52) relative to one another during the machining so that the beam axis (5', 15, 25, 35, 45) of the laser beam (3', 13, 23, 33, 43, 53 ) encloses an angle α between 1° and 10° with a tangent (17, 27, 38, 48) to the workpiece surface (7', 37) to be produced in a respective point where the beam axis (5', 15, 25, 35, 45) intersects the workpiece surface (7', 37) to be produced; and removing material from the workpiece (1, 11, 21, 31, 41, 55) through the laser beam (3', 13, 23, 33, 43, 53) aligned relative to the workpiece (1, 11, 21, 31, 41, 55) at the angle α, where 1° ≤ α ≤ 10°, characterized in that the angle α is determined as a function of the material of the workpiece (1, 11, 21, 31, 41, 55), the wavelength of the laser (52), and the average power of the laser (52).

2. Method according to claim 1, characterized in that the laser beam (3', 13, 23, 33, 43, 53) and the workpiece (1, 11, 21, 31, 41, 55) are moved relative to one another during the laser machining, so that a portion of the workpiece (1, 11, 21, 31, 41, 55) is removed, wherein the workpiece surface (7', 37) to be produced is formed at the interface with the removed portion.

3. Method according to claim 1 or 2, characterized in that the laser (52) is pulsed.

4. Method according to claim 3, characterized in that the angle α is additionally determined as a function of the pulse duration and the pulse energy.

5. Method according to one of the preceding claims characterized in that the laser beam (3, 13, 23, 33, 43, 53) is focused on the workpiece (1, 11, 21, 31, 41, 55), wherein the focal point of the focused laser beam (3, 13, 23, 33, 43, 53) is located at the point where the beam axis (5', 15, 25, 35, 45) intersects the workpiece surface (7', 37) to be produced.

6. Method according to one of the preceding claims characterized in that the workpiece surface (7') to be produced is a flat surface.

7. Method according to one of claims 1 to 5, characterized in that the workpiece surface (37) to be produced is a cambered surface and the moving device rotates the workpiece (31) received in the workpiece fixing device about a workpiece axis of rotation during the material removal through the laser.

8. Method according to one of the preceding claims, characterized in that the removal of material from the workpiece (1, 11, 21, 31, 41, 55) is performed through the laser beam (3', 13, 23, 33, 43, 53) aligned relative to the workpiece (1, 11, 21, 31, 41, 55) with the angle α held constant.

9. Method according to one of the preceding claims, characterized in that the laser beam (3', 13, 23, 33, 43, 53) is moved relative to the surface of the workpiece (1, 11, 21, 31, 41, 55), wherein the angle α between the beam axis and the tangent to the workpiece surface to be produced is within the angular range of 1° ≤ α ≤ 10° during the relative movement, and wherein the relative movement is a superposition of a first movement and a second movement, wherein the laser beam (3', 13, 23, 33, 43, 53) is moved between a first point A on the surface of the workpiece (1, 11, 21, 31, 41, 55) and a second point B on the surface of the workpiece (1, 11, 21, 31, 41, 55), during the first movement, and wherein the laser beam (3', 13, 23, 33, 43, 53) is moved within a closed or open curve during the second movement, whereby the extent of the curve is small compared to a distance covered by the laser beam (3', 13, 23, 33, 43, 53) between the first point A and the second point B.