OPTICAL UNIT FOR LASER MACHINING OF A WORKPIECE AND LASER MACHINING DEVICE

Abstract

An optical unit fora laser beam for laser machining of a workpiece is disclosed. With particular application to a laser beam, the optical unit may be applied to a high-power laser beam and comprise an optical element for the optical imaging of the laser beam, and two protective glasses that are transparent for the laser beam, the outer edges of which protective glasses being enclosed in an airtight manner by a holder in such a way that they form an interior space with the holder, the optical element also being arranged in the interior space. A laser machining device is also disclosed.

Claims

1. An optical unit for a laser beam for laser machining of a workpiece, in particular for a high-power laser beam, comprising an optical element (12) for the optical imaging of the laser beam, and two protective glasses (14) that are transparent for the laser beam, the outer edges of which protective glasses are enclosed in an airtight manner by a holder (16) in such a way that with the holder they form an interior space (18), wherein the optical element is arranged in the interior space; characterized in that the optical element (12) contains or is formed from at least one material selected from quartz glass and calcium fluoride; and the protective glasses (14) contain or are formed from at least one material selected from sapphire and zinc sulfide.

2. The optical unit according to claim 1, wherein the optical element (12) has a thermal conductivity of less than or equal to 2 W/(m K); and/or wherein at least one of the protective glasses (14) has a thermal conductivity of greater than or equal to 10 W/(m K).

3. The optical unit according to claim 1, wherein a clean room atmosphere, an inert gas, a vacuum and/or a non-condensing atmosphere is provided in the interior space (18) formed by the protective glasses (14) and the holder (16).

4. The optical unit according to claim 1, wherein the optical element (12) is arranged between the protective glasses (14) and/or in the beam path of the laser beam between the protective glasses (14); and/or wherein the optical element (12) is arranged adjacent to and/or spaced apart from at least one of the protective glasses (14); and/or wherein the optical element and the protective glasses form a sandwich structure; and/or wherein the optical element (12) and/or the protective glasses (14) are fastened or attached to the holder (16).

5. The optical unit according to claim 1, wherein at least one of the protective glasses is designed as a substantially plane-parallel plate; and/or wherein the protective glasses are arranged substantially parallel to one another; and/or wherein the protective glasses and a plane (22) of the optical element (12) which is oriented perpendicular to an optical axis (22) of the optical element and/or to a direction of propagation (122) of the laser beam are arranged substantially parallel to one another are

6. The optical unit according to claim 1, wherein the protective glasses (14) are fastened or attached to the holder (16) with an optical adhesive (26) and/or with a screw connection (28); and/or wherein the optical element (12) is fastened or attached to the holder (16) with an optical adhesive and/or with a screw connection (28).

7. The optical unit according to claim 1, wherein the holder is provided with a cooling means (32), in particular with internal cooling channels.

8. The optical unit according to claim 1, wherein the optical element for the optical imaging of the laser beam is designed in such a way that it is at least partially reflective for the laser beam, is at least partially transmissive for the laser beam, sets a focal length for the laser beam, guides the laser beam, deflects the laser beam and/or shapes the laser beam; and/or wherein at least one of the protective glasses is designed such that the optical properties of the laser beam are substantially not changed.

9. The optical unit according to claim 1, wherein the optical unit and/or the holder are designed in such a way that a thermal expansion of at least one component of the optical unit is tolerated, in particular is tolerated in an airtight manner, wherein the component is selected from one or two of the protective glasses, the optical element, the holder, the optical adhesive, the screw connection, the cooling means, an atmosphere in the interior space and/or a gas in the interior space.

10. The optical unit according to claim 1, wherein at least one first means (34) for monitoring the optical, thermal and/or mechanical properties of at least one of the protective glasses (14) and/or the optical element (12) is provided.

11. A laser machining device, in particular laser machining head, comprising an interface (114) for a laser source (118) for generating a laser beam (121); and an optical unit (10; 20; 30) for a laser beam for laser machining of a workpiece, in particular for a high-power laser beam, comprising an optical element (12) for the optical imaging of the laser beam, and two protective glasses (14) that are transparent for the laser beam, the outer edges of which protective glasses are enclosed in an airtight manner by a holder (16) in such a way that with the holder they form an interior space (18), wherein the optical element is arranged in the interior space; wherein the optical element is arranged in the interior space; characterized in that the optical element (12) contains or is formed from at least one material selected from quartz glass and calcium fluoride; and the protective glasses (14) contain or are formed from at least one material selected from sapphire and zinc sulfide, wherein the optical unit is arranged in the beam path of the laser beam(121).

12. The laser machining device according to claim 11, wherein a cooling device (116) is provided, which is coupled to the cooling means (32), in particular to the cooling channels, of the holder (16); and/or wherein the interface (114) is coupled or provided with a laser source (118) which provides the laser beam (121) with a power greater than or equal to 6 kW, preferably greater than or equal to 10 kW.

13. The laser machining device according to claim 11, further comprising at least one second means (120) for monitoring the optical, thermal and/or mechanical properties of at least one of the protective glasses (14) and/or the optical element (12).

14. A use of an optical unit (10; 20; 30) according to claim 1, for laser machining of a workpiece (112), in particular for high-power laser machining.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0031] All non-mutually exclusive features of embodiments described here can be combined with one another. The same elements of the embodiments are given the same reference signs in the following description. Individual or a plurality of elements of one embodiment can be used in the other embodiments without further mention. Embodiments of the invention are now described in more detail using the following examples with reference to figures, without intending any limitation thereby. In the figures:

[0032] FIG. 1 schematically shows an example of an optical unit 10 for a laser beam for laser machining of a workpiece, according to embodiments of the invention;

[0033] FIG. 2 schematically shows an example of an optical unit 20 for a laser beam for laser machining a workpiece, in a lateral cross-sectional view, according to embodiments of the invention;

[0034] FIGS. 3a and 3b schematically show, by way of example, a detail of the optical unit for a laser beam for laser machining of a workpiece, in a lateral cross-sectional view, according to embodiments of the invention;

[0035] FIGS. 3c and 3d schematically show, by way of example, a detail of the optical unit for a laser beam for laser machining of a workpiece, in a lateral cross-sectional view, according to embodiments of the invention;

[0036] FIG. 4 schematically shows a further example of an optical unit 30 according to embodiments of the invention;

[0037] FIG. 5 schematically shows an example of a laser machining device 100 according to embodiments of the invention; and

[0038] FIG. 6 schematically shows an example of a laser machining device 200 according to embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0039] As used throughout the present disclosure, unless specifically stated otherwise, the term “or” encompasses all possible combinations, except where infeasible. For example, the expression “A or B” shall mean A alone, B alone, or A and B together. If it is stated that a component includes “A, B, or C”, then, unless specifically stated otherwise or infeasible, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C. Expressions such as “at least one of” do not necessarily modify an entirety of the following list and do not necessarily modify each member of the list, such that “at least one of “A, B, and C” should be understood as including not only one of A, only one of B, only one of C, or any combination of A, B, and C.

[0040] The optical unit and/or machining device according to the embodiments of the invention are described below, inter alia, by way of examples with a machining head (also called a laser machining head), without limiting the invention thereto. The optical unit can be provided, for example, in a laser welding head or in a laser cutting head.

[0041] The term “airtight” in the present case includes the terms “gas-tight” and/or “dust-tight”. The term “transparent protective glass” and modifications thereof denote a transparent optical window which, apart from absorption, allows a laser beam that impinges perpendicularly in particular, to pass through substantially optically unchanged. Perpendicular impingement of the laser beam on an element means in embodiments that the laser beam with its direction of propagation and/or optical axis impinges the relevant element, for example protective glass, substantially perpendicularly. The terms “laser beam” and “machining laser beam” are used synonymously. The terms “laser machining device” and “machining device” are also used synonymously. The terms “quartz glass” and “quartz” are used synonymously. The unit W/(m K) of the thermal conductivity used herein is to be understood as W/(m×K).

[0042] Furthermore, where value ranges are described here, the specification of a broad range with narrower alternative or preferred ranges is also considered to disclose ranges that may be formed by any combination of specified lower range limits and specified upper range limits.

[0043] FIG. 1 schematically illustrates an example of an optical unit 10 for a laser beam for laser machining of a workpiece, according to embodiments. FIG. 1 shows a lateral cross-sectional view of the optical unit 10.

[0044] The optical unit 10 has a focusing lens 12 as an optical element for the optical imaging of a laser beam. The focusing lens 12 is only shown schematically in the figures. Furthermore, two protective glasses 14 that are transparent to the laser beam are provided, between which the focusing lens 12 is arranged. The protective glasses 14 have peripheral outer edges 15. The latter are substantially enclosed, in an airtight manner, by a holder 16. The protective glasses 14 form, with the holder, an interior space 17 in which the optical element 12 is arranged.

[0045] In the present example, the focusing lens 12, the protective glasses 14 and the holder 16 are designed to be circularly symmetrical or rotationally symmetrical in a cross-sectional plane (not shown) perpendicular to the plane of the figure. The material of the focusing lens 12 is high-purity quartz glass (fused silica, FS, SiC>2) and has a thermal conductivity of approximately 1.38 W/(m K). The focusing lens 12 is approximately 5.00 cm in diameter. The protective glasses 14 are made of high-purity sapphire (AI2O3) and have a thermal conductivity of approximately 27.2 W/(m K). The protective glasses 14 are approximately 3 mm thick in the present example and have a diameter of approximately 5.00 cm. In other examples, the protective glasses 14 can be approximately 1 to 3 mm thick. The holder 16 is ring-shaped, approximately 6 mm thick, has an inner diameter of approximately 5.00 cm, a height of approximately 2 cm and is made from the aluminium alloy A1Mg4.sMno.7. The protective glasses 14 and the focusing lens 12 are attached to the holder 16, for example with a screw connection.

[0046] The optical imaging takes place with the focusing lens 12 made of quartz glass, while the protective glasses 14 made of sapphire and the holder 16 protect the focusing lens 12 from contamination. The protective glasses 14 do not produce any optical imaging of the laser beam. Forward scattering and birefringence are therefore avoided with the optical unit 10, while the sensitivity of the focusing lens 12 to contamination, moisture and dirt is minimised. Focusing lenses made of quartz and protective glasses made of sapphire are also readily available. The same applies to protective glasses made of zinc sulfide, which can be used as an alternative. Overall, due to the construction of the optical unit 10, its imaging properties, in particular with respect to aberration, the absorption of the laser beam, its sensitivity to dirt, the forward scattering and birefringence of the laser beam caused by the optical unit, as well as its manufacturability and manufacturing costs are optimised.

[0047] FIG. 2 schematically shows an example of an optical unit 20 for a laser beam for laser machining of a workpiece, in a lateral cross-sectional view.

[0048] In contrast to the optical unit 10 of FIG. 1, the optical unit 20 contains a clean room atmosphere in the interior space 17. Both protective glasses 14 are each designed as a substantially plane-parallel plate and are arranged parallel to one another. The protective glasses 14 and a plane 24 of the optical element 20, which is oriented perpendicular to an optical axis 22 of the optical element 20, are arranged parallel to one another. The optical unit is designed in such a way that a laser beam to be focused can, for example, impinge both on the protective glasses 14 and on the optical element 20 substantially perpendicularly. The optical element 20 is arranged adjacent to and spaced apart from the protective glasses 14. The optical element 20 and the protective glasses 14 form a sandwich structure. The aforementioned embodiments of the optical unit 20 thus enable a compact and space-saving configuration of the optical unit.

[0049] FIG. 3a and 3b show, by way of example, a connection point between the holder 16 and one of the protective glasses 14. FIG. 3b shows an enlargement of the circular section A shown in FIG. 3a. The holder 16 has a recess 25 at both ends. In the present example, the protective glasses 14 have a diameter of approximately 5.30 cm, while the holder has an inner diameter of approximately 5.00 cm. As illustrated in FIG. 3a and 3b, the protective glass 14 rests in the recess 25 on the holder 16 and is fastened to the holder 16 at the support point by means of an optical adhesive 26. The protective glass 14 is arranged laterally, i.e. with its peripheral outer edge 15 at a distance from the holder 16, which is identified in FIG. 3b by the double arrow 27.

[0050] A commercially available adhesive which is suitable for laser beam applications and has a modulus of elasticity of less than 500 MPa can be selected as the optical adhesive 26. In the present example, the optical adhesive 26 has a modulus of elasticity of approximately 200 MPa, while the holder 16 made of aluminium has a modulus of elasticity of approximately 70 GPa. For examples in which sapphire or ZnS is used as the material for the protective glasses 14, the modulus of elasticity of sapphire can be approximately 345 GPa and the modulus of elasticity of ZnS can be approximately 88 GPa.

[0051] Due to the elastic properties of the holder 16 and the optical adhesive 26, as well as the spatial configuration of the optical unit 20, the protective glass 14 has a radial play within the holder 16. During irradiation of the optical unit 20 with a laser beam, in particular a high-power laser beam, the thermal expansion of the holder 16, the protective glass 14 and the optical adhesive 26 is tolerated in such a way that the substantially airtight connection between the protective glass 14 and the holder 16 is maintained.

[0052] Similarly, in a further example, the optical element 12 is attached to the holder 16 in a recess or on a projection of the holder 16 with an optical adhesive. The optical element 12 can also be attached to the holder 16 in a substantially airtight manner.

[0053] Alternatively or additionally, in the optical unit of embodiments, at least one protective glass 14 and/or the optical element 12 can be attached to the holder 16 in each case by means of a screw connection and/or a mount 28. The mount 28 for the protective glass 14 and/or the mount 28 for the optical element 12 can be screwed, clamped and/or adhesively bonded into the holder 16. The mount 28 can be easily deformed.

[0054] For example, as shown in FIG. 3c, the protective glass 14 is provided on the inner wall of the holder 16 in the recess 25 and is held in the recess 25 by an inner ring or O-ring as a mount 28. The mount 28 is easily deformable due to its spatial structure and/or its material suitable for laser applications. The mount or the inner ring 28 can be formed, for example, from stainless steel or from an aluminium alloy, for example AlMg4.5Mno.7The side of the protective glass 14 is arranged with its outer edge 15 at a distance 27 from the holder 16 and has a radial play. The inner ring 28 has a thread (not shown) with which it is screwed into an internal thread (not shown) of the holder 16 in a substantially airtight manner. The protective glass 14 lies against or on the deformable inner ring 28. The protective glass 14 is thus attached to the holder 16 in a substantially airtight manner.

[0055] Analogously, in a further example, the optical element 12 is attached between a projection 29 of the holder 16 and an inner ring as a mount 28 on the holder 16, as shown in FIG. 3d. The optical element 12 can also be attached to the holder 16 in a substantially airtight manner.

[0056] In the examples of FIG. 3c and 3d, the mount 28 can, in addition or as an alternative to the screw connection, be clamped into the holder 16 and/or adhesively bonded in with an optical adhesive.

[0057] Thermal expansion of one or both protective glasses 14, the optical element 12, the mount 28 and/or the holder 16 can be tolerated during a screw connection, while their connections, in particular their substantially airtight connections, are maintained.

[0058] As a further example, FIG. 4 shows an optical unit 30 according to embodiments. In contrast to the optical units 10 and 20, the optical unit 30 has a cooling means with cooling channels 32 which are provided in the holder 16. During laser machining, a cooling fluid, for example water or liquid nitrogen, can flow through the cooling channels 32 and thus cool the optical unit 30.

[0059] The optical unit 30 is also provided with a thermal sensor 34, which is connected to one of the protective glasses 14 in a thermally conductive manner. The thermal sensor 34 can be implemented with a Pt100, for example, and serves as the first means for monitoring the thermal properties of the protective glass 14.

[0060] FIG. 5 schematically illustrates an example of a laser machining device 100 according to embodiments of the invention.

[0061] The laser machining device 100 is designed as a laser machining head. The laser machining head 100 has an interface 114 for a laser source for generating a machining laser beam and an outlet opening 115. The optical unit 10 shown in FIG. 1 is arranged between the interface 114 and the outlet opening 115.

[0062] FIG. 6 schematically shows a machining device 200 as an example. The machining device 200 is designed as a machining head which, in contrast to the laser machining head 100 of FIG. 5, is equipped with the optical unit 30 of FIG. 4 instead of the optical unit 10. A laser source 118 is provided at the interface 114, for generating a laser beam 121, which is shown in FIG. 6 with dashed lines as a beam bundle with a direction of propagation 122. In the present example, a transport fibre 119 is provided for coupling the laser source 118. In alternative examples, the machining laser source 118 can be provided directly at the interface 114. In the present examples, the machining laser source 118 has a power of approximately 6 kW and generates the machining laser beam in a spectral range which includes a wavelength of 1070 nm. However, machining laser sources with a power lower than 6 kW, for example approximately 1 kW, or with a power greater than 6 kW can also be used.

[0063] The machining device 200 has a cooling device 116 which is connected to the cooling means, i.e. the cooling channels 32 of the optical unit 30, in a manner that conducts cooling fluid. The machining device is furthermore provided with a second means 120 for monitoring the thermal properties of the protective glass 14, which is arranged in the direction of the interface 114. The second means 120 is in turn connected to the thermal sensor 34, which is in contact with the relevant protective glass 14.

[0064] During operation of the machining device 200, the laser beam 121 is generated with the laser source 118. From the interface 114, the laser beam is directed in the direction of propagation 122 onto the optical unit 30. There the laser beam 121 passes the protective glass 14 arranged in the direction of the interface 114, is focused by the focusing lens 12, passes the protective glass 14 arranged in the direction of the outlet opening 115 and impinges through the outlet opening 115 on the workpiece 112 to be processed.

[0065] The airtight connection of the protective glasses 14 with the holder 16 and the clean room atmosphere in the interior space 18 of the optical unit 30 prevent contamination of the surfaces of the focusing lens 12. When the laser beam 121 passes the focusing lens 12, it is therefore not excessively heated by surface contamination. Damage to the focusing lens 12 and undesired changes in the imaging properties of the focusing lens 12 can therefore also be avoided in long-duration applications.

[0066] During operation of the machining device 200, cooling water is conducted through the cooling channels 32 of the holder 16 by means of the cooling device 116. In this way, the temperature of the holder 16 and thus of the entire optical unit 30 is kept at a desired level. At the same time, the temperature of the protective glass 14 is measured with the thermal sensor 34 and the second means 120 for monitoring the thermal properties of the protective glass. In this way, an undesired rise in the temperature of the protective glass 14 can be detected and a focus shift to be expected as a result can be counteracted, for example by changing the position of the optical unit in the beam path of the laser beam. As an alternative or in addition, an exchange of the optical unit that may be required can thus be displayed. In a modification of this example, the cooling device 116 is provided with a controllable valve for the cooling water and is connected in a data-processing manner by means of a controller to the second means 120 for monitoring the thermal properties of the protective glass 14. In this way, the temperature of the optical unit 30 can be controlled and, in particular, stabilised during the operation of the machining device 200.

[0067] In all examples and embodiments of the machining devices 100 and 200, additional transmissive optical elements (for example lenses) and/or additional reflective optical elements (for example plane mirrors) can be provided in particular in the machining head, for example for deflecting the machining laser beam 121. These additional optical elements can also be designed as optical units according to embodiments of the invention.

[0068] Finally, it should be noted that the description of the invention and the exemplary embodiments are not to be understood as limiting in terms of a particular physical implementation of the invention. All of the features explained and shown in connection with individual embodiments of the invention can be provided in different combinations in the subject matter according to the invention to simultaneously realise their advantageous effects.

[0069] The scope of protection of the present invention is given by the claims and is not limited by the features illustrated in the description or shown in the figures.

[0070] It is particularly obvious to a person skilled in the art that the invention can be used not only for laser machining systems, but also for other devices comprising lasers. Furthermore, the components of the machining device for laser machining of workpieces can be produced so as to be distributed over several physical products.