Abstract
A laser machining head for machining a workpiece by a laser beam includes: a scanning device for deflecting the laser beam on the workpiece; a housing in which the scanning device is arranged; and at least one overheat protection device configured to protect the housing from overheating, said overheat protection device comprising an energy distribution device for distributing incident radiation energy and/or a heat sink for dissipating heat.
Claims
1. A laser machining head for machining a workpiece by a laser beam, comprising: a scanning device for deflecting the laser beam on the workpiece; a housing in which the scanning device is arranged; and at least one overheat protection device, configured to protect the housing from overheating, wherein the overheat protection device comprises an energy distribution device for distributing incident radiation energy and/or a heat sink for dissipating heat.
2. The laser machining head according to claim 1, wherein: the at least one overheat protection device comprises an active overheat protection device with a cooling channel for conducting a coolant; and the cooling channel is formed in a wall of the housing.
3. The laser machining head according to claim 1, wherein: the overheat protection device is arranged in the housing and/or outside a beam path of the laser beam and/or on an inner surface of the housing and/or on at least one element arranged in the housing; and/or the overheat protection device forms part of the housing and/or is formed so as to be integrated with the housing.
4. The laser machining head according to claim 1, wherein the overheat protection device is arranged at a predetermined critical position in the housing), at which back reflections of the laser beam and/or laser radiation propagating outside of a beam path of the laser beam are incident.
5. The laser machining head according to claim 1, wherein the overheat protection device is arranged next to an optical element arranged in the housing and/or formed on a holder of an optical element arranged in the housing and/or forms a part of a holder of an optical element.
6. The laser machining head according to claim 1, wherein the overheat protection device is arranged in the housing in such a way that back reflections of the laser beam from at least one optical element arranged in the housing, in particular from an aperture stop, an optical element, an F-theta optics, a minor, a beam splitter, and/or a protective glass, hit the overheat protection device.
7. The laser machining head according to claim 1, wherein: the housing includes an entry port for coupling the laser beam into the laser machining head and a collimating optics; and the overheat protection device is arranged between the entry port and the collimating optics.
8. The laser machining head according to claim 1, wherein: the overheat protection device comprises an energy distribution device for distributing incident radiation energy; and the energy distribution device comprises a convex structure.
9. The laser machining head according to claim 8, wherein the convex structure comprises a plurality of periodically arranged and convex partial structures and/or has a partially reflective surface.
10. The laser machining head according to claim 1, wherein: the overheat protection device comprises an energy distribution device for distributing incident radiation energy; and the energy distribution device comprises a dispersion element for attenuating laser pulses and/or laser radiation with a broadband spectrum.
11. The laser machining head according to claim 1, wherein: the overheat protection device comprises a heat sink for dissipating absorbed heat; and the heat sink comprises a cooling element which has both a first surface arranged in the housing for absorbing heat and a second surface arranged on an outside of the housing for dissipating the absorbed heat.
12. The laser machining head according to claim 1, wherein: the overheat protection device comprises a heat sink for dissipating absorbed heat; the heat sink comprises a solid piece of metal attached to the housing and covering a part of the inner surface thereof or forming part of the housing; and the solid piece of metal has a thickness of more than 5 mm, preferably more than 10 mm.
13. The laser machining head according to claim 12, wherein the solid piece of metal consists of copper and/or aluminum and/or copper alloys and/or aluminum alloys and/or a material with a thermal conductivity greater than 50 W/m*K, in particular greater than 100 W/m*K.
14. The laser machining head according to claim 1, wherein at least part of an inner surface of the housing and/or at least part of a surface of an element arranged in the housing is configured to be partially reflective.
15. A laser machining head for machining a workpiece by a laser beam, comprising: a housing defining an optics space; and at least one passive overheat protection device, configured to protect the housing and/or elements arranged in the housing from overheating, wherein the overheat protection device comprises an energy distribution device for distributing incident radiation energy and/or a heat sink for dissipating heat.
16. The laser machining head according to claim 15, further comprising an active overheat protection device with a cooling channel for conducting a coolant, said cooling channel being formed in a wall of the housing.
17. The laser machining head according to claim 15, wherein: the overheat protection device is arranged in the housing and/or outside a beam path of the laser beam and/or on an inner surface of the housing and/or on at least one element arranged in the housing; and/or the overheat protection device forms part of the housing and/or is formed so as to be integrated with the housing.
18. The laser machining head according to claim 15, wherein the overheat protection device is arranged at a predetermined critical position in the housing), at which back reflections of the laser beam and/or laser radiation propagating outside of a beam path of the laser beam are incident.
19. The laser machining head according to claim 15, wherein the overheat protection device is arranged next to an optical element arranged in the housing and/or formed on a holder of an optical element arranged in the housing and/or forms a part of a holder of an optical element.
20. The laser machining head according to claim 15, wherein the overheat protection device is arranged in the housing in such a way that back reflections of the laser beam from at least one optical element arranged in the housing, in particular from an aperture stop, an optical element, an F-theta optics, a mirror, a beam splitter, and/or a protective glass, hit the overheat protection device.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] Exemplary embodiments of the disclosure are shown in the figures and are described in more detail below. In the figures:
[0048] FIG. 1 shows a schematic view of a laser machining head with an overheat protection device;
[0049] FIG. 2 shows a schematic view of another laser machining head with a scanning device and an overheat protection device according to the present invention;
[0050] FIGS. 3A to 3C show exemplary embodiments of an overheat protection device according to the present invention which is configured as an energy distribution device for distributing incident radiation energy;
[0051] FIGS. 4A to 4C show exemplary embodiments for an overheat protection device according to the present invention which is configured as a heat sink for dissipating heat;
[0052] FIGS. 5 to 10 show exemplary embodiments for preferred combinations of the overheat protection devices shown in FIGS. 3A to 3C and in FIGS. 4A to 4C; and
[0053] FIGS. 11 to 13 show exemplary embodiments for preferred combinations of the overheat protection devices shown in FIGS. 3A to 3C and in FIGS. 4A to 4C with a cooling channel.
DETAILED DESCRIPTION OF THE INVENTION
[0054] Unless otherwise noted, the same reference symbols are used for identical elements and elements with the same effect below.
[0055] FIG. 1 shows a schematic representation of a laser machining head 1 for machining a workpiece 10 by means of a laser beam 2. The laser machining head 1 comprises a housing 3 which forms an optics space 3a. Furthermore, the laser machining head 1 comprises an optical fiber 9 for coupling the laser beam 2 into the laser machining head 1, an optics (or optical element) 6, for example collimating optics for a collimating the laser beam 2, and an optics (or optical element) 6, for example a focusing optics 6 for focusing the laser beam 2. The optics 6 and 6 are arranged in the optics space 3a and may each be attached to the housing 3 by means of an optics holder 5, 5, for example. In particular, at least one of the optics holders 5, 5 may be movably attached to the housing 3. The laser beam 2 emerges from the optics chamber 3a through a protective glass 31 and hits the workpiece 10. Even though FIG. 1 shows a linear fixed-optics laser machining head with a linear beam path, the laser machining head 1 may include a scanning device, i. e. it may be a scanner head and/or have an angled beam path.
[0056] Back reflections 21 of the laser beam 2 may occur on the protective glass 31, on the optics 6 and 6 or on their holders 5, 5. In order to protect the housing 3 from overheating due to absorption of the back reflections 21, the laser machining head 1 includes at least one overheat protection device 4 arranged in the optics space 3a, in particular outside the beam path of the (machining) laser beam 2. FIG. 1 shows an overheat protection device 4 arranged or attached on the inside or the inner surface of the housing 3 and an overheat protection device 4 arranged on the holder 5 of the optics 6 or forming part of the holder 5. The at least one overheat protection device 4 may also be integrated into the housing 3 or form part thereof. The at least one overheat protection device 4 is preferably arranged at a point on the housing 3 in the optics chamber 3a at which back reflections 21 of the laser beam 2 occur. Such critical points in the optics space 3a may be determined or specified, for example, by simulations, calculations or based on empirical values. However, it is also possible for the entire housing 3 to form the overheat protection device 4.
[0057] FIG. 2 shows a schematic view of a laser machining head 1 for machining the workpiece 10 by means of a laser beam 2 with a scanning device 80. The scanning device comprises at least one pivotable mirror. In the example shown in FIG. 2, the scanning device 80 comprises two mirrors 8, 8, each pivotable about one axis. The laser beam 2 may be deflected to a plurality of different positions on the workpiece 10 by the scanner mirrors 8 and 8. The laser beam 2 coupled into the laser machining head 1 via the optical fiber 9 passes through the optics 6, for example a collimating optics, the scanning device with the two mirrors 8, 8 and the optics 6, for example a focusing optics, which may in particular be a F-theta optics, and then exits the laser machining head 1 through the protective glass 31.
[0058] In the exemplary embodiment shown in FIG. 2, the housing is formed in a plurality of parts. In particular, the scanner housing 3 may be formed separately. However, the present disclosure is not limited thereto. The scanner housing 3 or the part of the housing in which the scanning device 80 is arranged may also be formed integrally with the rest of the housing 3 of the laser machining head. The scanning device 80 may be arranged in the scanner housing 3. An overheat protection device 4 is arranged in the scanner housing 3 at a predetermined critical point. Especially on flat optical elements, i. e. on optical elements with little curvature, there may be back reflections at high laser power. Back reflections 21 occur in particular on the optics 6, which in this exemplary embodiment is configured as an F-theta lens, and hit the scanner housing 3. In order to protect the scanner housing 3 from being damaged by overheating due to the back reflections 21, the laser machining head 1 includes at least one overheat protection device 4 arranged in the scanner housing 3. The at least one overheat protection device 4 may be integrated in the scanner housing 3 and/or in at least one of the housings 3 or may form part of the same. It is also possible to configure the entire scanner housing 3 as an overheat protection device 4. This is described below with reference to FIG. 4C.
[0059] The overheat protection device 4 according to the present invention may be a passive device, i. e. independent of an external energy and/or coolant supply, and serves to protect the housing or elements arranged in the housing from overheating due to laser radiation propagating outside the beam path, such as such as back reflections. The overheat protection device 4 may be configured as a energy distribution device for distributing incident radiation energy or as a heat sink for dissipating heat generated by incident radiation energy. For this purpose, various embodiments and combinations thereof are possible.
[0060] FIGS. 3A to 3C show exemplary embodiments of a passive overheat protection device according to the present invention configured as an energy distribution device for distributing incident radiation energy, in particular for spatially or temporally distributing incident radiation energy.
[0061] FIG. 3A illustrates an overheat protection device 4 configured as a dispersion element 41 for attenuating laser pulses and/or laser radiation with a broadband spectrum. In order to achieve a change in the energy distribution over time, particularly in the case of laser machining using ultra-short pulses, a dispersion element 41 or a refractive element (e.g. a glass plate) may be arranged at a critical point in the housing 3. This increases the chirp of the pulse, which results in a longer pulse duration and a lower peak intensity or pulse peak intensity of the pulse. Laser radiation or back reflections 21 propagating outside the beam path must pass through the dispersion element 41 before they can hit the critical point. As illustrated in FIG. 3A as an intensity distribution before and after passage through the dispersion element 41, a pulse-like back reflection 21 or pulse-like laser radiation is spread over time by the dispersion element 41 and is thereby weakened.
[0062] The dispersion element 41 may be fixed at a distance from an inner surface of the housing 3 by a suspension 411 in the housing 3, in particular on an inner surface of the housing 3. An optical surface of the dispersion element 41 may extend in parallel to the inner surface of the housing 3. However, the dispersion element 41 may also be fastened to an element arranged in the housing 3 and at a distance therefrom by the suspension 411.
[0063] FIG. 3B shows an overheat protection device 4 which is in the form of a convex structure 42. The convex structure 42 is configured to spatially distribute laser radiation or back reflections 21. Due to the convexity, the incident laser radiation is distributed over a larger surface. The convex structure 42 may be arranged in the housing 3, in particular on the inner surface of the housing 3. The convex structure 42 may be attached to the housing 3, in particular in contact with the housing 3 (see FIG. 3B). Alternatively, the convex structure 42 may be formed integrally with the housing 3. In particular, a scanner housing 3, i. e. a housing for accommodating the scanner mirrors 8 and 8, may have a patterned surface or the convex structure on the inside in order to distribute back reflections over the largest possible area. In addition or as an alternative, internal components such as motor shafts, mirror receptacles, shielding plates for electronics, etc. (not shown) may also be provided with the convex structure 42.
[0064] As shown in FIG. 3B, the convex structure 42 may comprise a plurality of periodically arranged partial structures 42a. In this case, a period of the convex structure 42 may approximately correspond to a diameter of the back reflection 21. The diameter of the back reflection 21 is often of the same order of magnitude as the diameter of the collimated laser beam 2, i. e. the period of the convex structure 42 may be chosen according to the known diameter of the collimated laser beam 2.
[0065] FIG. 3C shows an overheat protection device 4 with a partially reflective surface 44, by which the back reflection 21 is only partially absorbed or reflected back into the optics space 3a of the housing 3. The partially reflective surface 44 may be formed by a coating or by surface treatment. For example, the partially reflective surface 44 may be arranged on the inner surface of the housing 3 or form a part thereof. In particular, a scanner housing 3, i. e. a housing for accommodating the scanner minors 8 and 8, may have the partially reflective surface 44 so that only part of the back reflection is absorbed at the point of incidence, but the rest is reflected away or scattered to other points to be absorbed in the housing. In this way, it can be achieved that energy of the back reflection 21 is no longer deposited at one point in the housing, but is distributed as evenly as possible in the optics space 3a of the housing 3 and/or on the housing 3 and thus does not cause any damage. To this end, it may be advantageous for the partially reflective surface 44 to have a specific structure, for example like the convex structure 42 described above, so that the scattering covers the largest possible solid angle. A period of the structure may roughly correspond to a diameter of the back reflection 21, which is often in the same order of magnitude as the diameter of the collimated laser beam 2. Other internal components (i. e. arranged in the optics space 3a) such as motor shafts, mirror receptacles, shielding plates for electronics, etc, may be provided with the partially reflective surface 44.
[0066] FIGS. 4A to 4C show exemplary embodiments of a passive overheat protection device 4 according to the present invention, which is configured as a heat sink for dissipating heat, in particular heat that stems from the absorption of back reflections or laser radiation propagating outside the beam path.
[0067] FIG. 4A shows an overheat protection device 4 configured as a cooling element 45 for dissipating heat from the housing 3 or the optics space 3a. The cooling element 45 has a first surface arranged in the optics space for absorbing heat and a second surface arranged on an outside of the housing 3 for dissipating the absorbed heat. The second surface may include a plurality of cooling fins 45a. For example, the cooling element 45 is attached to a side of the housing 3 outside the optics space 3a. The cooling element 45 may also be integrated into the housing 3. The first surface of the cooling element 45 may form part of the inner surface of the housing 3. The second surface of the cooling element 45 may form part of an outer surface of the housing 3. The cooling element 45 may be integrated into the housing 3 or may form part thereof.
[0068] FIG. 4B shows an overheat protection device 4 which is in the form of a solid piece of metal 46. The solid piece of metal 46 may be attached in the housing 3, and in particular on the housing 3 within the optics space 3a. The solid piece of metal 46 may cover part of the inner surface of the housing 3. In particular, the solid metal piece 46, for example in the form of solid copper or aluminum pieces, may be deliberately attached at at least one previously known critical point in the optics space 3a, i. e. at which the back reflections 21 are critical.
[0069] Alternatively, the solid piece of metal 46 may be formed integrally with the housing 3 or form part of the housing 3. In particular, as shown in FIG. 4C, a scanner housing 3 may be solid. A material with high thermal conductivity, i. e. a thermal conductivity greater than 50 W/m*K, in particular greater than 100 W/m*K, may be used for this. For example, the scanner housing 3 may consist, at least for the most part, of copper and/or aluminum and/or copper alloy and/or aluminum alloy. In this way, the heat introduced by the back reflection can be distributed and dissipated as quickly as possible. The scanner housing 3 may be a solid piece of metal 46, for example, from which at least part of the optics space 3a is milled. In this case, a thickness or wall thickness of the scanner housing 3 may be more than 5 mm, preferably more than 10 mm.
[0070] The solid piece of metal 46 may have a thickness of more than 5 mm, preferably more than 10 mm. The solid piece of metal 46 may consist of a material with high thermal conductivity, i. e. a thermal conductivity greater than 50 W/m*K, in particular greater than 100 W/m*K. In particular, the solid piece of metal 46 may consist of copper and/or aluminum and/or copper alloy and/or aluminum alloy. As a result, heat introduced into the solid piece of metal 46 by back reflections 21 can be distributed as quickly as possible in the solid piece of metal 46 and dissipated from the solid piece of metal 46.
[0071] While it is not specifically shown, the scanner housing 3 may additionally or alternatively be provided with an active overheat protection device. For example, a cooling channel 43 for cooling by means of a coolant may be formed in a wall of the scanner housing 3. The cooling channel 43 may be provided with a coolant connection for connecting to a coolant circuit.
[0072] FIGS. 5 to 10 show combinations of the above-described embodiments of overheat protection devices.
[0073] However, the combinations shown in FIGS. 5 to 10 are by no means to be regarded as complete. It is hereby expressly pointed out that any combination of the overheat protection devices 4 shown in FIGS. 3A to 3C and in FIGS. 4A to 4C or described in the description of these figures is possible.
[0074] FIG. 5 shows a convex structure 42 with a partially reflective surface 44. The partially reflective surface 44 may be applied to the convex structure 42 by coating or formed thereon by surface treatment. As a result, scattering over the largest possible solid angle may be achieved.
[0075] FIG. 6 shows a combination of the convex structure 42 with the dispersion element 41. The dispersion element 41 overlaps the convex structure 42 (i. e. in a direction perpendicular to an optical surface of the dispersion element 41) and is spaced from the convex structure 42 by the suspension 411. In this way, both a spatial and a temporal distribution of incident radiation energy can be achieved.
[0076] FIG. 7 shows a combination of the partially reflective surface 44 on the convex structure 42 with the dispersion element 41. The partially reflective surface 44 is applied to the convex structure 42. The dispersion element 41 is arranged at a certain distance in front of the convex structure 42 by the suspension 411.
[0077] FIG. 8 shows a combination of the cooling element 45 and the convex structure 42. In this case, the first surface of the cooling element 45 may have the convex structure 42.
[0078] FIG. 9 shows a combination of the cooling element 45 and the dispersion element 41. The cooling element 45 overlaps with the dispersion element 41. In other words, the dispersion element 41 is attached in such a way that back reflections incident on the cooling element 45 must pass through the dispersion element 41. Thus, the dispersion element 41 at least partially shields the cooling element 42. Due to the temporal spread of incident radiation energy due to the dispersion element, the cooling element 45 can dissipate the heat generated to the outside or to the surroundings of the laser machining head more reliably. In particular, intensity peaks that can lead to ablation effects are avoided or at least reduced.
[0079] FIG. 10 shows a combination of the cooling element 45, the dispersion element 41 and the convex structure 42. The cooling element 45 overlaps the convex structure 42. In other words, the dispersion element 41 is attached in such a way that back reflections incident on the convex structure 42 have to pass the dispersion element 41. The dispersion element 41 thus shields the convex structure 42 at least partially. The heat absorbed by the convex structure 42 can be dissipated quickly and efficiently to the outside or to the surroundings of the laser machining head by the cooling element.
[0080] FIGS. 11 to 13 show exemplary embodiments for a combination of an active and at least one passive overheat protection device according to the present invention. The active overheat protection device may include at least one cooling channel 43 through which a cooling medium or coolant, such as a gas or a liquid, flows. The cooling channel 43 may be connected to a coolant circuit via a coolant connection. Ideally, the cooling channel 43 is attached spatially close to the areas on which the back reflections 21 hit. The active overheat protection device may also include a pump or a fan or a controllable valve.
[0081] FIG. 11 shows a combination of a cooling channel 43 and the convex structure 42. The at least one cooling channel 43 is arranged adjacent to the convex structure 42. The at least one cooling channel 43 may be arranged on the housing 3 outside of the optics space 3a. However, the cooling channel 43 may also be arranged within the housing 3 or be integrated into the housing 3 (cf. FIG. 12).
[0082] FIG. 12 shows a combination of a cooling channel 43 and the dispersion element 41. The cooling channel 43 may be arranged in an area of the housing 3 in which back reflections that have passed through the dispersion element 41 are incident. The cooling channel 43 may be arranged within the housing 3 or be integrated into the housing 3. However, the cooling channel 43 may also be arranged outside of the optics space 3a.
[0083] FIG. 13 shows a combination of a cooling channel 43, the dispersion element 41 and the convex structure 42.
[0084] According to the present invention, areas of the housing or areas in the housing or in the optics room which may be affected by back reflections can be provided with overheat protection devices and thus be configured in such a way that they can dissipate the energy introduced without being damaged. In particular in the case of scanner laser machining heads, in which high laser powers are used, or in ablation laser machining processes in which high pulse powers are used, damage due to laser radiation propagating outside the beam path, such as back reflections, can be reduced or even prevented.
LIST OF REFERENCE SYMBOLS
[0085] 1 laser machining head [0086] 2 laser beam [0087] 21 back reflection [0088] 3 housing [0089] 3 scanner housing [0090] 3a optics space [0091] 31 protective glass [0092] 4 overheat protection device [0093] 41 dispersion element [0094] 411 suspension [0095] 42 convex structure [0096] 43 cooling channel [0097] 44 partially reflective surface [0098] 45 cooling element [0099] 45a cooling fin [0100] 46 solid piece of metal [0101] 5 optics holder [0102] 6, 6 optics [0103] 8, 8 scanner mirror [0104] 80 scanning device [0105] 9 optical fiber [0106] 10 workpiece
