METHOD FOR THE MATERIAL-REMOVING LASER MACHINING OF A WORKPIECE

Abstract

A method for the material-removing machining of a workpiece by laser beam pulses. The laser beam pulses are directed to impact points on the surface of a volume to be removed of the workpiece in order to cut away material from the volume to be removed. Cutting away the volume to be removed results in a new contour surface to be produced on the workpiece. An impact angle of the laser beam pulses relative to the contour surface to be produced is set in accordance with a predefined condition during the removal of at least part of the volume to be removed that directly adjoins the contour surface to be produced. According to this condition, the impact angle is the same as a threshold angle (as), or somewhat smaller. The threshold angle corresponds to the impact angle at which an effective laser energy density at the impact point of the laser beam pulses on the contour surface to be produced is equal to a threshold fluence. Material is only removed at an impact point if the effective laser energy density is greater than the threshold fluence. As a result, only those volume elements of the volume to be removed that are adjacent to the desired contour surface to be produced are cut away. By controlling, in an open- or closed-loop manner, the impact angle it is therefore possible to generate with very high precision the desired contour surface on the workpiece.

Claims

1. A method for material removal laser machining of a workpiece under use of a laser processing machine having a laser creating laser beam impulses, having a laser head that directs the laser beam impulses of the laser on the workpiece and having a machine axis arrangement comprising at least one machine axis that is configured to position and/or move the workpiece and the laser head in at least one translatory and/or rotatory degree of freedom relative to each other, comprising the following steps: emitting multiple laser beam impulses by means of the laser head on a surface of a volume to be removed of the workpiece, wherein material is removed from the volume to be removed of the workpiece and thus a contour surface to be created is created on the workpiece, adjusting an impact angle of the laser beam impulses relative to the contour surface to be created at a border location at which the contour surface to be created directly adjoins the volume to be removed such that the impact angle is at most as large as a threshold angle and is at least as large as a minimum angle, wherein the minimum angle is larger than 0 degrees and the threshold angle is equal to the amount of the impact angle at which an effective laser energy density at an impact location of the laser beam impulse on the contour surface to be created of the workpiece corresponds to a threshold fluence, wherein an effective laser energy density that is larger than the threshold fluence effectuates a material removal at the impact location and an effective laser energy density that is smaller than the threshold fluence does not effectuate material removal at the impact location.

2. The method according to claim 1, wherein the impact angle is the angle between a tangent at the border location of the contour surface to be created and a center axis of the laser beam impulses and/or an optical axis of the laser head.

3. The method according to claim 1, wherein the impact angle of the laser beam impulses is adjusted relative to the contour surface to be created at the border location such that it is equal to the threshold angle.

4. The method according to claim 1, wherein the adjusting of the impact angle is executed by positioning and/or orientating the workpiece and the laser head relative to each other.

5. The method according to claim 1, wherein the effective laser energy density of the laser beam impulses is defined as the pulse energy of the laser beam impulses absorbed by the workpiece divided through the cross-section area of the laser beam impulses, wherein the effective laser energy density is always larger than the threshold fluence during the laser machining of the workpiece.

6. The method according to claim 1, wherein the laser beam impulses are directed on impact locations that are arranged within a pulse area.

7. The method according to claim 6, wherein the size and the shape of the pulse area and/or the position of the impact locations within the pulse area are defined depending on one or more parameters of the workpiece and/or the contour surface to be created.

8. The method according to claim 6, wherein the laser beam impulses are emitted from the laser head in a predefined sequence on the impact locations within the pulse area.

9. The method according to claim 6, wherein the outer contour of the pulse area is varied depending on the actual relative position and/or relative orientation of the workpiece relative to the laser head.

10. The method according to claim 1, wherein the impulse duration of the laser beam impulses is in the nanosecond, picosecond or femtosecond range.

11. The method according to claim 1, wherein the methods is used during manufacturing of a tool made from the workpiece.

12. The method according to claim 1, wherein the contour surface to be created is a rake surface or flank adjoining a cutting edge.

13. The method according to claim 2, wherein the impact angle of the laser beam impulses is adjusted relative to the contour surface to be created at the border location such that it is equal to the threshold angle.

14. The method according to claim 13, wherein the adjusting of the impact angle is executed by positioning and/or orientating the workpiece and the laser head relative to each other.

15. The method according to claim 14, wherein the effective laser energy density of the laser beam impulses is defined as the pulse energy of the laser beam impulses absorbed by the workpiece divided through the cross-section area of the laser beam impulses, wherein the effective laser energy density is always larger than the threshold fluence during the laser machining of the workpiece.

16. The method according to claim 15, wherein the laser beam impulses are directed on impact locations that are arranged within a pulse area.

17. The method according to claim 16, wherein the size and the shape of the pulse area and/or the position of the impact locations within the pulse area are defined depending on one or more parameters of the workpiece and/or the contour surface to be created.

18. The method according to claim 17, wherein the laser beam impulses are emitted from the laser head in a predefined sequence on the impact locations within the pulse area.

19. The method according to claim 18, wherein the outer contour of the pulse area is varied depending on the actual relative position and/or relative orientation of the workpiece relative to the laser head.

20. The method according to claim 19, wherein the impulse duration of the laser beam impulses is in the nanosecond, picosecond or femtosecond range.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1 a schematic illustration of an embodiment of a laser processing machine that is configured for carrying out an inventive method,

[0027] FIG. 2 a schematic perspective illustration of a workpiece during the creation of a contour surface,

[0028] FIGS. 3-5 schematic only exemplary illustrations of different embodiments of pulse areas respectively,

[0029] FIGS. 6 and 7 a schematic side view of a workpiece in different conditions during the creation of a contour surface respectively by removal of a volume to be removed from the workpiece,

[0030] FIG. 8 an enlarged basic illustration for explanation of the adjustment of the impact angle of the laser beam impulses relative to the contour surface to be created,

[0031] FIG. 9 another basic sketch for explaining the adjustment of the impact angle relative to the contour surface at a border location in case of a curve extension of the contour surface to be created and

[0032] FIG. 10 a schematic perspective partial illustration of the workpiece in the area of a border between a contour surface to be created and a surface of a volume to be removed for illustration of the effective laser energy density and the laser energy density.

DETAILED DESCRIPTION

[0033] FIG. 1 shows a perspective basic illustration of a laser processing machine 15 that is configured to carry out a method for material removing laser machining of a workpiece 16 according to the invention. The workpiece 16 can have an arbitrary outer shape and is in the embodiments according to FIGS. 1 and 2 cylindrical and preferably circular cylindrical. Also arbitrary other plate-shaped, cuboid-shaped or other shapes and contours of workpieces 16 can be machined.

[0034] The laser processing machine 15 has a pulsed laser 17 that creates a pulsed laser beam and thus laser beam impulses P. The pulsed laser beam is transmitted from the laser 17 to a laser head 18. The laser head 18 is configured to emit the laser beam impulses P relative to its optical axis A in a predefined direction and to focus them in a focus area F.sub.B. During the machining of the workpiece 16 a layer of a volume V of the workpiece 16 to be removed that is actually machined, i.e. the material removal location or the material removal layer, is placed within the focus area F.sub.B.

[0035] The laser head 18 can have focusing means such as optical lenses or the like. Thereby the laser beam impulse P obtains a divergence angle and is focused in the focus area F.sub.B. The divergence angle in the far field is the aperture angle of the laser beam impulse from the focusing means of the laser head 18 up to the focal point of focus within the focus area F.sub.B.

[0036] In addition the laser head 18 has a deflection device that can also be described as laser scanner. The deflection device can comprise one or more movable deflection mirrors and can be configured to adjust the emission direction, i.e. the orientation of a center axis M of a laser beam impulse P relative to the optical axis A.

[0037] A control device 19 of the laser processing machine 15 is configured to control the laser 17 (pulse energy, impulse duration of the laser beam impulses P) and the laser head 18 and particularly the deflection device of the laser head 18 in an open-loop or closed-loop manner.

[0038] The laser processing machine 15 comprises a clamping device 22 adapted to the shape of the workpiece 16 for holding the workpiece 16. In the embodiment shown in FIG. 1 the clamping device 22 is configured to clamp a rod-shaped workpiece 16 on one end. Depending on the shape of the workpiece, suitable clamping devices can be used respectively.

[0039] The laser processing machine 15 has in addition a machine axis arrangement 23. The machine axis arrangement 23 is configured to move, to position and orientate the clamping device 22 and thus the workpiece 16 relative to the laser head 18. The machine axis arrangement 23 is controlled by the control device 19.

[0040] The machine axis arrangement 23 comprises at least one and according to the example multiple machine axes 24, wherein each machine axis 24 is configured to provide a relative movement between the clamping device 22 and the laser head 18 in a translatory or rotatory degree of freedom. Thereby a machine axis 24 can be configured for movement of the laser head 18 or for movement of the clamping device 22 relative to a machine basis or a machine frame. The arrangement of the machine axes 24 as well as the number of machine axes for movement in a translatory or rotatory degree of freedom can vary. For example, six machine axes 24 can be provided for the translatory degrees of freedom X, Y, Z as well as the rotatory degrees of freedom DX, DY, DZ in total. The machine axis arrangement 23 with the machine axes 24 is only highly schematically illustrated in FIG. 1.

[0041] The laser head 18 or its deflection device is controlled by means of the control device 19 in a manner such that the emitted laser beam impulses P are directed in a predefined sequence on impact locations 27 within a pulse area 28. If no relative movement between the laser head 18 and the clamping device 22 is created by the machine axis arrangement 23, the laser beam impulses P would be sequentially directed on the impact locations 27 within the pulse area 28 on the workpiece surface. The shape and contour of the pulse area 28 is adapted to the machining task and can be defined and adjusted based on a geometry of a contour surface 29 to be created and/or a geometry of the workpiece 16, for example. In FIGS. 3-5 different sizes and shapes for pulse areas 28 are illustrated in a simplified manner. Within the pulse area 28 some impact locations are respectively highly schematically illustrated along a pulse path B within the pulse area 28. For example, the impact locations 27 can be arranged on a meandering pulse path B (FIG. 3) or on a pulse path B extending in a spiral form (FIGS. 4 and 5). The contour and size of the pulse area 28 is obtained by the smallest possible circumferential contour around the outermost impact locations that adjoin the circumferential contour of the pulse area 28.

[0042] The circumferential contour or the outer shape of the pulse area 28 can correspond to the cross-section shape of a groove to be created, for example, that is limited by the contour surface 29 to be created (FIG. 2).

Alternatively, the pulse area 28 can also be smaller than the surface of the volume V to be removed and can be moved along the surface of the volume V to be removed by means of the machine axis arrangement 23 in order to remove the material bit by bit in a manner layer by layer.

[0043] The contour surface 29 to be created can limit a chip groove as illustrated in FIG. 2. The contour surface 29 to be created can also be any other arbitrary surface that is created on the workpiece 16. In the embodiments described here the contour surface 29 to be created forms preferably a surface adjoining a cutting edge 30 that can be a rake surface or a flank.

[0044] For manufacturing the contour surface 29 the laser processing machine 15 is operated by means of the control device 19 in a manner as explained in the following.

[0045] Laser beam impulses P are directed on a surface 31 of the volume V to be removed by means of the laser 17 and the laser head 18 in order to form the contour surface 29 by removing the volume V to be removed. Thereby the laser beam impulses P are directed on the impact locations 27 within the pulse area 28 and, as appropriate, the pulse area 28 is moved along the surface 31 of the volume V to be removed. The size of the pulse area 28 can also correspond to the respective size of the surface 31 of the volume V to be removed and can be adapted in shape and dimension, if the shape and dimension of the surface 31 changes during the layer by layer removal. This removal of the volume V to be removed for creating the contour surface 29 is schematically illustrated in FIGS. 6 and 7.

[0046] One location on the workpiece 16 at which the contour surface 29 to be created adjoins the surface 31 of the volume V to be removed is denoted as border location 32. Adjacent to this border location 32 of the contour surface 29 to be created the actual material removal layer is present at the surface 31 of the volume V to be removed. The adjustment of an impact angle α of the laser beam impulses P relative to the contour surface 29 to be created at the border location 32 is of importance. At this border location 32 the impact angle α is controlled by the angle between the center axis M of the laser beam impulses P and the contour surface 29 to be created in an open-loop or closed-loop manner. In general this is illustrated for a convex curved contour surface 29 in FIG. 9. At the border location 32 a tangent T is placed on the contour surface 29 to be created. The tangent T and the center axis M of the laser beam impulses P are located in a common radial plane of the center axis M, wherein this radial plane is orientated orthogonal to the contour surface 29 to be created at the border location 32. Relative to the surface 31 of the volume V to be removed, the center axis M has an angle α that is larger than the adjusted impact angle α. The impact angle α is adjusted depending on the desired geometry of the contour surface 29 to be created at the observed border location 32 complying with the following condition:

[0047] The impact angle α is at most as large as a threshold angle α.sub.S and at least as large as a minimum angle α.sub.min. The minimum angle α.sub.min is remarkably larger than 0 degrees and preferably the amount of the difference α.sub.s−α.sub.min between the threshold angle α.sub.S and the minimum angle α.sub.min is very small. Particularly the minimum angle α.sub.min has at least an amount of 95% of the threshold angle α.sub.S. According to the example, the minimum angle α.sub.min is equal to the threshold angle α.sub.S, such that the impact angle α is defined and adjusted (open-loop or closed-loop controlled) to be equal to the threshold angle α.sub.S.

[0048] The threshold angle α.sub.S is the amount of the impact angle α at which an effective laser energy density E.sub.eff at the impact location 27 of the laser beam impulse P on the contour surface 29 to be created of the workpiece 16 is equal to the threshold fluence F.sub.S. The effective laser energy density E.sub.eff is calculated by the pulse energy of the laser beam impulse P absorbed by the workpiece surface divided through an irradiated area of the impact location 27. If the effective laser energy density E.sub.eff is larger than a threshold fluence F.sub.S, material is removed at the impact location 27. If the effective laser energy density E.sub.eff is smaller than the threshold fluence F.sub.S, no material removal occurs at the impact location 27.

[0049] In other words in that the impact angle α relative to the contour surface 29 to be created is at most as large as the threshold angle α.sub.S or preferably equal to the threshold angle α.sub.S, it is avoided that a material removal occurs on the desired geometry of the contour surface 29 to be created. The material removal only takes place on such volume elements of the volume V to be removed on which the effective laser energy density E.sub.eff is larger than the threshold fluence F.sub.S. This is the case for all volume elements at the volume V to be removed that project obliquely or transverse from the desired geometry of the contour surface 29 to be created, because the impact angle α is adjusted near to or equal to the threshold angle α.sub.S. The control device 19 controls the emission of the laser beam impulses P or the orientation of the center axis M, such that a material removal of the volume V to be removed occurs so-to-speak automatically along the desired geometry of the contour surface 29 to be created.

[0050] This principle is again schematically illustrated based on FIGS. 8 and 10. In the focus area F.sub.B a laser energy density E.sub.L is given as pulse energy of the laser beam impulse divided through a cross-section area X of the laser beam impulse P in the focus area F.sub.B. If the center axis M is orientated orthogonal to the surface 31 of the volume V to be removed, the size of the cross-section area X of the laser beam impulse P in the focus area F.sub.B is approximately as large as a first irradiated surface C.sub.1 on the surface 31 of the volume V to be removed. The effective laser energy density E.sub.eff then corresponds substantially to the laser energy density E.sub.L.

[0051] By predefining the impact angle α at the border location 32 of the contour surface 29 to be created a second irradiated surface C.sub.2 becomes so large at the location at which the surface 31 of the volume V to be removed transitions into the contour surface 29 to be created, such that the effective laser energy density E.sub.eff corresponds to the threshold fluence F.sub.S or is slightly smaller and thus no material removal occurs at the desired geometry of the contour surface 29 to be created. The second irradiated surface C.sub.2 is larger than the cross-section area X of the laser beam impulses P in the focus area and the effective laser energy density E.sub.eff is thus smaller than the laser energy density E.sub.L.

[0052] The invention refers to a method for material removal machining of a workpiece 16 by laser beam impulses P. The laser beam impulses P are directed on impact locations 27 on the surface 31 of a volume V of a workpiece 16 to be removed, in order to remove material from the volume V to be removed. By removing the volume V to be removed, a new contour surface 29 to be created is created on the workpiece 16. An impact angle α of the laser beam impulses P relative to the contour surface 29 to be created is adjusted according to a predefined condition during the removal of at least part of the volume V to be removed that directly adjoins the contour surface 29 to be created. According to this condition, the impact angle α is equal to a threshold angle α.sub.S or slightly smaller. The threshold angle α.sub.S corresponds to the impact angle at which an effective laser energy density E.sub.eff of the laser beam impulses P at the impact location 27 on the contour surface 29 to be created is equal to the threshold fluence F.sub.S. A material removal at the impact location 27 only takes place, if the effective laser energy density E.sub.eff is larger than the threshold fluence F.sub.S. In doing so, it can be achieved that only such volume elements of the volume V to be removed are removed that adjoin the desired contour surface 29 to be created. Thus, the desired contour surface 29 can be created on the workpiece 16 very precisely by open-loop or closed-loop control of the impact angle α.

LIST OF REFERENCE SIGNS

[0053] 15 laser processing machine [0054] 16 workpiece [0055] 17 laser [0056] 18 laser head [0057] 19 control device [0058] 22 clamping device [0059] 23 machine axis arrangement [0060] 24 machine axis [0061] 27 impact location [0062] 28 pulse area [0063] 29 contour surface [0064] 30 cutting edge [0065] 31 surface of the volume to be removed [0066] 32 border location [0067] α impact angle [0068] α.sub.min minimum angle [0069] α.sub.S threshold angle [0070] β angle [0071] A optical axis [0072] B pulse path [0073] F.sub.B focus area [0074] C.sub.1 first irradiated surface [0075] C.sub.2 second irradiated surface [0076] DX rotary degree of freedom around X-axis [0077] DY rotary degree of freedom around Y-axis [0078] DZ rotary degree of freedom around Z-axis [0079] E.sub.L laser energy density [0080] E.sub.eff effective laser energy density [0081] F.sub.S threshold fluence [0082] M center axis of laser beam impulses [0083] P laser beam impulse [0084] T tangent [0085] V volume to be removed [0086] X translatory degree of freedom along X-axis [0087] Y translatory degree of freedom along Y-axis [0088] Z translatory degree of freedom along Z-axis