LASER PROCESSING HEAD WITH OVERHEATING PROTECTION DEVICE

Abstract

Laser processing head (1) for processing a workpiece (10) using a laser beam (2), comprising: a scanning device (80) for deflecting the laser beam (2) on the workpiece (10); a housing (3, 3') in which the scanning device (80) is arranged; and at least one overheating protection device (4) designed to protect the housing (3) from overheating, characterized in that the overheating protection device (4) comprises an energy distribution device for distributing incident radiant energy, and the energy distribution device comprises a convex structure (42), and / or the energy distribution device comprises a dispersion element (41) for attenuating laser pulses and / or spectrally broadband laser radiation.

Description

[0001] The present disclosure relates to a laser processing head for processing a workpiece by means of a laser beam with at least one overheating protection device, which, for example, protects the housing of the laser processing head (in particular a scanner housing) and / or components of the laser processing head arranged in the housing from overheating, in particular from overheating due to laser radiation. Technical background

[0002] In a laser processing head for processing a workpiece using a laser beam, the laser beam generated by a laser light source is focused or bundled onto the workpiece to be processed using beam guidance and focusing optics.

[0003] When processing with high laser powers, for example in the multi-kilowatt range, back reflections can occur both at the optics or optical elements and on the workpiece. These reflections can lead to localized, high heating of the housing or other internal components. Often, the back reflections are so strong that they damage or destroy the housing and / or other components of the laser processing head upon contact. This can result in discoloration of the housing surface or even material removal, which can deposit on optical elements such as mirrors or lenses located in the laser beam path, contaminating them. The resulting increased absorption of laser radiation and heating can damage or even destroy the affected optical element.

[0004] This problem is usually addressed by coating the optical elements for the processing wavelengths with an antireflective coating with a high absorption coefficient (e.g., greater than 99.5%) or a low reflection coefficient (e.g., less than 0.5%), so that the reflected laser power is so low that it does not cause damage. This becomes critical when optics, such as an F-theta lens, are composed of multiple lenses and / or protective glass. This quickly results in ten or more interfaces, all of which can contribute to back reflections.

[0005] Apertures are often used to limit the cross-section or diameter of the laser beam or to absorb back reflections. Another approach involves arranging the components of the laser processing head within the housing so that the focus of a back reflection originating from a curved surface lies in the air, meaning it does not strike a surface within the optical chamber and thus cannot damage it due to the high power density. However, this approach is extremely complex and severely restricts the arrangement and design of the laser processing head; for example, it often requires additional installation space.

[0006] However, applying anti-reflective coatings to optical elements also has its limitations, as a certain degree of reflectivity always remains. At higher laser powers, this results in correspondingly higher back reflections, meaning that above a certain laser power, the back reflection can damage the housing and / or the components within it. Furthermore, high-quality anti-reflective coatings are complex and expensive, so there is a strong desire, especially for protective lenses that require frequent replacement, to use the simplest and most cost-effective anti-reflective coatings possible.

[0007] Other known solutions are based on active cooling devices. For example, EP 3 257 616 A discloses a laser processing head with a cooling device for cooling optical components, wherein the cooling device is connected to a gas flow and has at least one throttle for throttling the gas flow. EP 2 162 774 B1 discloses a device for cooling at least one optical component by means of a flowing coolant that flows between the housing and a structural material. However, such active cooling devices require various connections, e.g., a power connection and / or coolant connection, to ensure the coolant flow. Furthermore, active cooling devices consume energy and / or coolant.

[0008] Passive cooling devices in the form of heat sinks or energy distribution devices are also known. Examples include DE 10 2019 122 064 A1, US 2015 / 0 144 607 A1, and DE 20 2018 107 281 U1. These passive cooling devices are also sometimes combined with active cooling devices. Summary of the invention

[0009] It is an object of the present invention to protect the housing and / or components of the laser processing head arranged in the housing from damage caused by laser radiation. In particular, it is an object of the present invention to protect the housing and / or the components of the laser processing head arranged therein from damage caused by laser radiation incident outside the beam path, for example, by back reflections of the laser beam.

[0010] These tasks are solved by the subject matter of the independent claim. Advantageous embodiments and further developments are the subject matter of the corresponding dependent claims.

[0011] The present invention is based on the concept of spatially and / or temporally distributing and / or dissipating the energy introduced or incident into the housing and / or the components arranged therein by laser radiation passing outside the beam path, for example, by back reflections of the laser beam. For this purpose, the laser processing head has at least one (passive or active) overheating protection device, which includes at least one (passive or active) energy distribution device for (spatially and / or temporally) distributing incident radiation energy (and optionally at least one (passive or active) heat sink for dissipating absorbed heat). In this way, the introduced energy cannot cause damage and local overheating is avoided. This is particularly important for laser processing heads used for processing with high laser powers or high laser pulse powers, i.e.,with power outputs of more than 1 kW, especially more than 10 kW, is advantageous.

[0012] According to one aspect of the present invention, a laser processing head for processing a workpiece by means of a laser beam comprises a housing that defines an optical chamber; at least one optical element arranged in the optical chamber, in particular for guiding and / or shaping the laser beam; and at least one overheating protection device configured to protect the housing and / or elements or components arranged in the housing from overheating, wherein the overheating protection device comprises at least one energy distribution device for distributing incident radiation energy (and optionally further at least one heat sink for absorbing and / or dissipating heat, in particular for absorbing and / or dissipating heat generated by absorption of incident radiation energy). The overheating protection device can be an active overheating protection device, e.g.an active device for heat dissipation by means of an supplied coolant, or a passive or self-sufficient overheating protection device, i.e. an overheating protection device without a coolant connection or source and / or external energy supply.

[0013] The laser processing head can be a scanner laser processing head. In this case, the laser processing head can include a scanning device that is configured to direct the laser beam to different positions on the workpiece. The scanning device can be located within the housing. The part of the housing in which the scanning device is located, or which surrounds the scanning device, can be referred to as the scanner housing. Alternatively, the laser processing head can also be a fixed-optics laser processing head.

[0014] According to a further aspect of the present invention, a laser processing head for processing a workpiece by means of a laser beam comprises a scanning device for deflecting the laser beam on the workpiece; a housing (also called a scanner housing) in which the scanning device is arranged; and at least one overheating protection device configured to protect the housing from overheating, wherein the overheating protection device comprises at least one energy distribution device for distributing incident radiation energy (and optionally at least one heat sink for absorbing and / or dissipating heat, in particular for absorbing and / or dissipating heat generated by absorption of incident radiation energy). The overheating protection device can be an active overheating protection device, e.g., an active heat dissipation device by means of a supplied coolant, or a passive or self-contained overheating protection device, i.e.,An overheating protection device without a coolant connection or source and / or external power supply. The scanner housing can be integrated into or formed as a single piece within the housing of the laser processing head, or it can form part of the head. The housing and / or the scanner housing can define an optical chamber in which at least one optical element, in particular for guiding and / or shaping the laser beam, is arranged. The scanning device can be configured to direct the laser beam to different positions on the workpiece, in particular to positions in two mutually perpendicular directions.

[0015] The laser processing head, according to one of these aspects, may include one or more of the following features: The housing of the laser processing head can be modular. The scanner housing can form part of it. The housing of the laser processing head can define an optical compartment in which at least one optical element (in particular for guiding and / or shaping the laser beam) and / or the scanning device is located.

[0016] The scanning device can include at least one pivotable mirror. Preferably, the scanning device includes two mirrors pivotable about different axes. The laser processing head can further include an F-theta lens for focusing the laser beam. The F-theta lens can be arranged in the housing.

[0017] The scanning device, in particular the movable elements of the scanning device that deflect the laser beam, cause back reflections in different directions depending on the position of the scanning device or the position of the movable elements of the scanning device that deflect the laser beam. The scanner laser processing head can further comprise an F-theta lens for focusing the laser beam. Since a surface of the F-theta lens facing the incident beam is relatively flat, back reflections with high energy density occur at the F-theta lens. For these reasons, the overheating protection device according to the invention is particularly advantageous in a scanner laser processing head.

[0018] Laser processing can include laser cutting, laser welding, laser ablation, or laser engraving. In other words, the laser processing head can be a laser cutting head, a laser welding head, a laser ablation head, or a laser engraving head. The laser processing head (or the optical elements it contains) can be specifically designed for laser processing with high laser powers, i.e., more than 1 kW, or more than 10 kW, or even more than 20 kW.

[0019] The laser processing head can be a laser processing head for material processing with a short-pulse laser beam or an ultrashort-pulse laser beam. The overheating protection device according to the invention is particularly advantageous here, since the production of suitable antireflective coatings for ultrashort pulses is even more complex and expensive due to the high spectral bandwidths and high peak intensities (pulse peak intensities).

[0020] The housing defines the optical chamber, i.e., the interior of the laser processing head in which the at least one optical element and / or the scanning device is arranged. The optical chamber can be enclosed or sealed to the outside, in particular dustproof or even hermetically sealed. The at least one optical element arranged in the optical chamber, or the entirety of the optical elements arranged in the optical chamber, can define the beam path of the laser processing head. In other words, the laser beam can be guided along the beam path by the at least one optical element arranged in the optical chamber, or by the entirety of the optical elements arranged in the optical chamber.

[0021] Examples of elements or components arranged in the housing may include, in particular, at least one optical element, a holder for the optical element, an aperture, a motor shaft (e.g., from the scanning device), a mirror mount or mirror holder (e.g., from the scanning device), a shielding plate for electronics, and similar items.

[0022] The optical element can be an optical element for guiding and / or shaping the laser beam. The optical element can be or comprise a lens, a beam splitter, a mirror, a protective glass, an aperture, focusing optics, collimating optics, a movable scanning element, in particular a movable mirror, a scanning device for deflecting the laser beam, and the like. The optical element can be movably arranged within the optical space. For example, the optical element can comprise a lens or lens group that is movable along the beam path or along its optical axis.

[0023] The overheating protection device is designed to protect the housing and / or components located within the housing from (local) overheating, particularly due to laser radiation or absorption of incident laser radiation. Laser radiation can refer specifically to laser radiation occurring outside the (defined) beam path, for example, reflections of the laser beam from components located within the housing and / or from the workpiece. Laser radiation can therefore occur unintentionally.

[0024] At least one overheating protection device can be passive or self-contained. Therefore, no external connections, such as for power supply or for the supply or removal of a coolant or cooling medium, are necessary. The laser processing head thus remains extremely flexible in terms of design and operation.

[0025] The at least one overheating protection device can be or include an active overheating protection device. The active overheating protection device can be a heat sink for dissipating heat. The active overheating protection device can, for example, include a cooling channel for cooling by means of a coolant flowing through the cooling channel. The cooling channel can be formed in the housing, i.e., in a wall of the housing. In particular, the cooling channel can be integrated into the scanner housing. In other words, the at least one overheating protection device can include an active overheating protection device with a cooling channel for guiding a coolant, which is formed in a wall of the housing. The active overheating protection device can further include a coolant connection for connecting the cooling channel to a coolant circuit. The coolant can be a gas, air, liquid, or water.The active overheating protection device may also include a pump or a blower or a controllable valve.

[0026] The overheating protection device comprises an energy distribution device. The energy distribution device is configured to distribute incident radiation energy or intensity, in particular incident radiation energy or intensity from laser radiation, e.g., from reflections of the laser beam. The energy distribution device can be configured to distribute incident radiation energy or intensity spatially and / or temporally. In this way, the energy absorbed by the housing or by an element arranged therein per unit area and time, i.e., the absorbed area power density, can be reduced. The overheating protection device can further comprise a heat sink. The heat sink is configured to absorb and / or dissipate heat, in particular heat generated by the absorption of laser radiation or by the absorption of reflections of the laser beam.The heat sink can be configured to dissipate the heat, for example to the environment of the laser processing head, i.e. to an outside of the laser processing head.

[0027] The overheating protection device can be located in the optical chamber and / or on the inner surface of the housing and / or on at least one element arranged within the housing. The inner surface of the housing can at least partially define or surround the optical chamber. The overheating protection device can, in particular, be located outside the laser beam path within the optical chamber. The overheating protection device can have at least one surface that adjoins the optical chamber or at least partially defines or limits it. The overheating protection device can form part of the housing and / or be integrated with the housing. The overheating protection device can be attached to the housing, in particular within the housing.

[0028] The overheating protection device can be arranged at at least one predetermined critical position within the housing where back reflections of the laser beam and / or laser radiation occur. The critical position can be determined based on empirical data, calculation, and / or simulation. In one embodiment, the overheating protection device can be arranged within the optical chamber such that back reflections of the laser beam from the housing itself (i.e., from the inner surface of the housing) and / or from at least one element arranged within the housing, e.g., an aperture, an optical element, an F-theta optic, a mirror, a beam splitter, and / or a protective glass, strike the overheating protection device. For example, the overheating protection device can be arranged next to or adjacent to the optical element within the optical chamber to intercept back reflections from the optical element.so that back reflections from the optical element reach the overheating protection device. Additionally or alternatively, the overheating protection device can be mounted on a holder for the optical element and / or form part of a holder for the optical element.

[0029] If the laser processing head includes a scanning device, the housing comprises a scanner housing in which the scanning device is arranged. The scanner housing may form part of the housing or be part of the housing. In this case, the overheating protection device may be located in the scanner housing. The scanning device may be a galvo scanner or similar. The scanning device may include at least one mirror pivotable about one or two axes, or two mirrors, each pivotable about one axis. The laser processing head may further include focusing optics, for example, an F-theta lens. The overheating protection device may be located in the housing, particularly in the scanner housing, opposite the focusing optics, so that back reflections from the focusing optics reach the overheating protection device.

[0030] In one embodiment, the laser processing head can include a beam splitter arranged in the laser beam path and configured to allow the laser beam to pass through. The overheating protection device can be positioned in the housing such that a portion of the laser beam reflected by the beam splitter strikes the overheating protection device. The overheating protection device can therefore be located adjacent to the beam splitter in a direction perpendicular to the propagation direction of the laser beam incident on the beam splitter. In other words, the overheating protection device can be positioned so that radiation undesirably reflected by the beam splitter—i.e., radiation that should have passed through the beam splitter—strikes the overheating protection device.The heat generated by absorption can thus be dissipated by the overheating protection device. This prevents the housing from overheating.

[0031] In one embodiment, the laser processing head can include a beam splitter arranged in the laser beam path and configured to reflect the laser beam. The overheating protection device can be positioned such that a portion of the laser beam passing through the beam splitter strikes the overheating protection device. The overheating protection device can therefore be located adjacent to the beam splitter in the housing, in the direction of propagation of the laser beam incident on the beam splitter. In other words, the overheating protection device can be positioned so that radiation that unintentionally passes through the beam splitter—i.e., radiation that should have been reflected by the beam splitter—strikes the overheating protection device. The heat generated by absorption can thus be dissipated by the overheating protection device.This prevents the casing from overheating.

[0032] In one embodiment, the housing can include an entry port for coupling the laser beam into the laser processing head and collimation optics, with the overheating protection device arranged between the entry port and the collimation optics. In this way, the overheating protection device can prevent local overheating of the housing adjacent to the entry port, e.g., due to edge fields of the laser beam or excessive divergence of the coupled laser beam. The collimation optics can be an optical element arranged in the optical space. The collimation optics can comprise or be a lens or a lens group. The entry port can include a fiber coupler for coupling in a fiber-guided laser beam.

[0033] The overheating protection device comprises at least one energy distribution device for distributing incident radiant energy. The energy distribution device comprises a dispersion element and / or a convex surface structure (hereinafter: convex structure). The energy distribution device may include a partially reflective surface.

[0034] The convex structure can be configured to spatially distribute incident radiation energy. The convex structure can have a surface projecting into the optical space and / or be curved and / or domed and / or conical and / or spherical. The convex structure can be composed of a multitude of such surfaces. In other words, the convex structure can comprise periodically arranged and convex substructures. The base of the substructures can be honeycomb-shaped or rib-like. One period of the structure can correspond to a diameter of the incident back reflection and / or a diameter of the collimated laser beam. The convex structure can be formed on the inner surface of the housing and / or on a surface of an element arranged in the optical space. The convex structure increases the surface area onto which laser radiation is incident.This distributes the incident radiation energy spatially and reduces the area power.

[0035] The convex structure may have a partially reflective surface. In this disclosure, "partially reflective" refers to a reflectance in the range of 40% to 95%, particularly 50% to 80%. The partially reflective surface may be produced by surface treatment, e.g., by polishing or oxidation, and / or by a surface coating. The partial reflectivity can enhance the spatial distribution of the incident radiation energy. Thus, the radiation energy can be distributed more evenly, and local peaks can be avoided.

[0036] The dispersion element can be configured to distribute incident radiation energy over time. The dispersion element can be configured to attenuate laser radiation through dispersion, for example, to attenuate laser pulses or pulse-like back reflections or back reflections of laser pulses, or to increase the pulse chirp. In other words, the dispersion element can be configured to increase a pulse duration and / or decrease a pulse peak intensity. The dispersion element can be a refractive element. The dispersion element can be a glass plate. A laser pulse is usually polychromatic or spectrally broadband, meaning that laser pulses can have a large spectral bandwidth and / or high pulse peak intensities. As the laser passes through the dispersion element, the pulse is broadened or attenuated, or the pulse chirp is increased, due to the different speeds of the different wavelengths.

[0037] The dispersion element can be plate-shaped. It can be positioned at a distance from the inner surface of the housing or from one of the elements located within the housing, such that incident laser radiation must first pass through the dispersion element to reach the inner surface or element. The dispersion element, or an optical surface of the dispersion element, can extend parallel to the inner surface of the housing. The dispersion element can be positioned in front of the convex structure (in the direction of incident laser radiation). In other words, the dispersion element can be positioned overlapping the convex structure and spaced apart from it within the optical space. In this way, laser radiation first passes through the dispersion element before reaching the convex structure.

[0038] The partially reflective surface can be configured to spatially distribute incident radiant energy. In this disclosure, "partially reflective" refers to a reflectance in the range of 40% to 95%, particularly 50% to 80%. At least one surface in the optical space can be partially reflective. For example, the inner surface of the housing and / or a surface of an element arranged in the housing, such as a surface of a holder for an optical element and / or a surface of a holder for a movable element, can be partially reflective. For this purpose, the inner surface of the housing and / or the surface of an element arranged in the housing can be provided with a partially reflective coating. Alternatively, the inner surface of the housing and / or the surface of an element arranged in the housing can be made partially reflective by means of a surface treatment.A partially reflective surface on the mounting of a movable optical element, especially a scanner mirror, is particularly advantageous because heat dissipation is especially challenging with a movable optical element. A partially reflective surface is also particularly advantageous on a mirror mounting, since mirrors are often glued in place, and the adhesive softens or detaches when the mirror mounting heats up.

[0039] The overheating protection device may include at least one heat sink for absorbing and / or dissipating heat. The heat sink may comprise a heat sink and / or a solid metal piece.

[0040] The heat sink can comprise a heat sink that has both a first surface located within the optics chamber for heat absorption, particularly through absorption of incident laser radiation, and a second surface located on the outside of the housing or laser processing head for dissipating the absorbed heat, particularly to the surrounding environment. The heat sink can be integrated with the housing or form part of it. In other words, the heat sink can form part of both the inner surface and the outer surface of the housing or laser processing head. The second surface of the heat sink can be provided with cooling fins. This increases the heat-exchanging surface area and improves heat dissipation to the surrounding environment.

[0041] The heat sink can comprise a solid piece of metal. This solid piece of metal can have a thickness greater than 5 mm, preferably greater than 10 mm. The thickness of the solid piece of metal can be a dimension perpendicular to the inner surface of the housing. The solid piece of metal can be attached to the inner surface of the housing and cover a portion of the inner surface. The solid piece of metal can be in surface contact with the inner surface of the housing. Alternatively, the solid piece of metal can be integrated with the housing or form part of the housing. In particular, the solid piece of metal can be a milled housing component. For example, an inner surface of the housing component, which forms part of the inner surface of the housing, can be milled. For example, the solid piece of metal can be a scanner housing. That is, the scanner housing can be solid and thus form the heat sink.

[0042] The solid metal piece can be made of copper and / or aluminum and / or copper alloys and / or aluminum alloys and / or 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.

[0043] The heat sink can include a cooling channel located on or within the housing, particularly in a housing wall, and a coolant connection for linking the cooling channel to a coolant circuit. The coolant can be a fluid, such as liquid, water, air, or gas.

[0044] The at least one overheating protection device can comprise a combination of a passive overheating protection device and an active overheating protection device. The active overheating protection device can preferably be combined with at least one energy distribution device for distributing incident radiant energy and / or with at least one heat sink, in particular with at least one of the passive overheating protection devices described in this disclosure, e.g., with the convex structure and / or the dispersion element and / or the heat sink. The active overheating protection device can be arranged adjacent to and / or near the energy distribution device for distributing incident radiant energy.

[0045] According to the present invention, the aim is no longer to reduce back reflections to such an extent by means of complex antireflective coatings that they cannot cause damage, but rather the impact areas for the back reflections are designed in such a way that they remain undamaged even at higher power levels. This also works for ultrashort pulses, where the high spectral bandwidths and high peak or pulse peak intensities make the production of suitable antireflective coatings even more difficult. Furthermore, the design of a lens for a scanner laser processing head can be simplified, since the formation of back reflections or their location within the scanner housing no longer needs to be considered as critically. Thus, reflections from several interfaces can, for example, converge at a single point on the housing without causing damage. Brief description of the characters

[0046] Examples of the manifestation of the revelation are shown in the figures and are described in more detail below. They show: Fig. Figure 1 shows a schematic representation of a laser processing head with an overheating protection device. Fig. Figure 2 shows a schematic representation of another laser processing head with a scanning device and an overheating protection device according to the present invention; Fig. Figures 3A to 3C show exemplary embodiments of an overheating protection device according to the present invention, which is designed as an energy distribution device for distributing incident radiant energy; Fig. Figures 4A to 4C show exemplary embodiments of an overheating protection device designed as a heat sink for dissipating heat; Fig. Figures 5 to 10 show exemplary embodiments of preferred combinations of the elements described in Fig. 3A to 3C and in Fig. Overheating protection devices shown in 4A to 4C. Fig. Figures 11 to 13 show exemplary embodiments of preferred combinations of the elements described in Fig. 3A to 3C and in Fig. Overheating protection devices shown in 4A to 4C have a cooling channel. Detailed description of the characters

[0047] Unless otherwise noted, the same reference symbols are used for identical and equivalent elements in the following.

[0048] Fig. Figure 1 shows a schematic representation of a laser processing head 1 for processing a workpiece 10 using a laser beam 2. The laser processing head 1 comprises a housing 3, which forms an optical chamber 3a. The laser processing head 1 further comprises an optical fiber 9 for coupling the laser beam 2 into the laser processing head 1, an optic (or optical element) 6', for example, a collimation optic for collimating the laser beam 2, and an optic (or optical element) 6, for example, a focusing optic 6 for focusing the laser beam 2. The optics 6' and 6 are arranged in the optical chamber 3a and can each be attached to the housing 3, for example, by an optic holder 5, 5'. In particular, at least one of the optic holders 5, 5' can be movably attached to the housing 3. The laser beam 2 exits the optics chamber 3a through a protective glass 31 and strikes the workpiece 10. Even if in Fig. Figure 1 shows a linear fixed optics laser processing head with a linear beam path. The laser processing head 1 may include a scanning device, i.e., be a scanner head, and / or have an angled beam path.

[0049] Back reflections 21 of the laser beam 2 can occur at the protective glass 31, at the optics 6 and 6', or at their mounts 5, 5'. To protect the housing 3 from overheating due to absorption of the back reflections 21, the laser processing head 1 has at least one overheating protection device 4, which is arranged in the optics chamber 3a, in particular outside the beam path of the (processing) laser beam 2. Fig. Figure 1 shows an overheating protection device 4 arranged or attached to the inside or inner surface of the housing 3, as well as an overheating protection device 4 arranged on the mount 5 of the optics 6 or forming part of the mount 5. The at least one overheating protection device 4 can also be integrated into the housing 3 or form part of it. Preferably, the at least one overheating protection device 4 is arranged at a location in the optical chamber 3a of the housing 3 where back reflections 21 of the laser beam 2 occur. Such critical locations in the optical chamber 3a can be determined or specified, for example, by simulations, calculations, or based on empirical data. However, it is also possible for the entire housing 3 to constitute the overheating protection device 4.

[0050] Fig. Figure 2 shows a schematic representation of a laser processing head 1 for processing the workpiece 10 using a laser beam 2 with a scanning device 80. The scanning device 80 comprises at least one pivotable mirror. In the Fig. In the example shown, the scanning device 80 comprises two mirrors 8, 8', each pivotable about an axis. The scanner mirrors 8 and 8' allow the laser beam 2 to be deflected to a variety of different positions on the workpiece 10. The laser beam 2, coupled into the laser processing head 1 via the optical fiber 9, passes through the optics 6', for example, a collimation optic, the scanning device 80 with the two mirrors 8, 8', and the optics 6, for example, a focusing optic, which can in particular be an F-theta optic, and then exits the laser processing head 1 through the protective glass 31.

[0051] In the Fig. In the embodiment shown in Figure 2, the housing is formed in multiple parts. In particular, the scanner housing 3' can be formed separately. However, the present disclosure is not limited to this. The scanner housing 3', or the part of the housing in which the scanning device 80 is arranged, can also be formed integrally with the rest of the housing 3 of the laser processing head. The scanning device 80 can be arranged in the scanner housing 3'. An overheating protection device 4 is arranged in the scanner housing 3' at a predetermined critical location. In particular, back reflections with high laser power can occur at flat optical elements, i.e., at optical elements with low curvature. Back reflections 21 occur particularly at the optics 6, which in this embodiment is designed as an F-theta lens, and strike the scanner housing 3'.To protect the scanner housing 3' from damage due to overheating caused by the back reflections 21, the laser processing head 1 has at least one overheating protection device 4 arranged in the scanner housing 3'. The at least one overheating protection device 4 can be integrated into the scanner housing 3' and / or into at least one of the housings 3, or form part of it. It is also possible to design the entire scanner housing 3' as an overheating protection device 4. This is discussed below with reference to... Fig. 4C described.

[0052] The overheating protection device 4 according to the present invention can be a passive device, i.e., independent of an external power 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 back reflections. The overheating protection device 4 is designed as an energy distribution device for distributing incident radiation energy. The overheating protection device 4 can further comprise a heat sink for dissipating heat generated by incident radiation energy. Various embodiments and combinations thereof are possible.

[0053] Fig. Figures 3A to 3C show exemplary embodiments of a passive overheating protection device according to the present invention, which is designed as an energy distribution device for distributing incident radiation energy, in particular for spatially or temporally distributing incident radiation energy.

[0054] Fig. Figure 3A illustrates an overheating protection device 4, which is designed as a dispersion element 41 for attenuating laser pulses and / or broadband laser radiation. To achieve a temporal change in the energy distribution, particularly during laser processing using ultrashort pulses, a dispersion element 41 or a refractive element (e.g., a glass plate) can be attached at a critical point in the housing 3. This increases the "chirp" of the pulse, resulting in a longer pulse duration and a lower peak intensity. Laser radiation or back reflections 21 that propagate outside the beam path must pass through the dispersion element 41 before they can reach the critical point. As shown in Fig. Figure 3A illustrates the intensity distribution before and after passing through the dispersion element 41, showing that a pulse-like back reflection 21 or pulse-like laser radiation is distributed over time by the dispersion element 41 and thereby attenuated.

[0055] The dispersion element 41 can be attached to the housing 3, in particular to an inner surface of the housing 3, at a distance from another inner surface of the housing 3, by means of a suspension 411. An optical surface of the dispersion element 41 can extend parallel to the inner surface of the housing 3. Alternatively, the dispersion element 41 can also be attached to an element arranged in the housing 3 by means of the suspension 411, at a distance from that element.

[0056] Fig. Figure 3B shows an overheating protection device 4, which is designed as 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 area. The convex structure 42 can be arranged in the housing 3, in particular on the inner surface of the housing 3. The convex structure 42 can be attached to the housing 3, in particular in contact with the housing 3 (see Figure 3B). Fig. 3B). Alternatively, the convex structure 42 can be integrated with the housing 3. In particular, a scanner housing 3', i.e., a housing for receiving the scanner mirrors 8 and 8', can have a structured surface or the convex structure on its interior to distribute back reflections over the largest possible area. Additionally or alternatively, internal components such as motor shafts, mirror mounts, shielding plates for electronics, etc. (not shown) can also be provided with the convex structure 42.

[0057] The convex structure 42 can be described as in Fig. Figure 3B shows a plurality of periodically arranged substructures 42a. One period of the convex structure 42 can correspond approximately to one 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 can be chosen according to the known diameter of the collimated laser beam 2.

[0058] Fig. Figure 3C shows an overheating protection device 4 with a partially reflective surface 44, by which the back reflection 21 is only partially absorbed or reflected back into the optical space 3a of the housing 3. The partially reflective surface 44 can be formed by a coating or by surface treatment. For example, the partially reflective surface 44 can be located on or form part of the inner surface of the housing 3. In particular, a scanner housing 3', i.e., a housing for receiving the scanner mirrors 8 and 8', can have the partially reflective surface 44 such that only part of the back reflection is absorbed at the point of impact, while the remainder is reflected away or scattered to be absorbed at other locations in the housing.This ensures that the energy of the back reflection 21 is no longer deposited at a single point in the housing, but is distributed as evenly as possible within the optical space 3a of the housing 3 and / or onto the housing 3 itself, thus preventing damage. For this purpose, it can 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 encompasses the largest possible solid angle. One period of the structure can correspond approximately to the diameter of the back reflection 21, which is often on the same order of magnitude as the diameter of the collimated laser beam 2. Other internal components (i.e., located in the optical space 3a), such as motor shafts, mirror mounts, shielding plates for electronics, etc., can also be provided with the partially reflective surface 44.

[0059] Fig. Figures 4A to 4C show embodiments of a passive overheating protection device 4, which is designed as a heat sink for dissipating heat, in particular heat generated by absorption of back reflections or laser radiation passing outside the beam path.

[0060] In Fig. Figure 4A shows an overheating protection device 4, which is designed as a heat sink 45 for dissipating heat from the housing 3 or the optical chamber 3a. The heat sink 45 has a first surface located in the optical chamber for heat absorption and a second surface located on an outer surface of the housing 3 for dissipating the absorbed heat. The second surface can have a plurality of cooling fins 45a. For example, the heat sink 45 is attached to a side of the housing 3 outside the optical chamber 3a. The heat sink 45 can also be integrated into the housing 3. The first surface of the heat sink 45 can form part of the inner surface of the housing 3. The second surface of the heat sink 45 can form part of an outer surface of the housing 3. The heat sink 45 can be integrated with the housing 3 or form part of it.

[0061] In Fig. Figure 4B shows an overheating protection device 4, which is designed as a solid metal piece 46. The solid metal piece 46 can be attached to the housing 3, and in particular to the housing 3 within the optical chamber 3a. The solid metal piece 46 can 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, can be selectively attached at at least one known critical location in the optical chamber 3a, i.e., where the back reflections 21 are critical.

[0062] Alternatively, the solid metal piece 46 can be integrated with the housing 3 or form part of the housing 3. In particular, as shown in Fig. Figure 4C shows a scanner housing 3' made of solid material. A material with high thermal conductivity, i.e., a thermal conductivity greater than 50 W / m*K, and in particular greater than 100 W / m*K, can be used for this purpose. For example, the scanner housing 3' can consist at least predominantly 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' can, for example, be a solid piece of metal 46 from which at least part of the optical space 3a is milled. In this case, the thickness or wall thickness of the scanner housing 3' can be more than 5 mm, preferably more than 10 mm.

[0063] The solid metal piece 46 can have a thickness of more than 5 mm, preferably more than 10 mm. The solid metal piece 46 can be made of a material with high thermal conductivity, i.e., a thermal conductivity greater than 50 W / m*K, particularly greater than 100 W / m*K. The solid metal piece 46 can, in particular, be made of copper and / or aluminum and / or a copper alloy and / or an aluminum alloy. This allows heat introduced into the solid metal piece 46 by back reflections 21 to be distributed as quickly as possible within the solid metal piece 46 and dissipated from it.

[0064] Although not explicitly shown, the scanner housing 3' can additionally or alternatively be equipped with an active overheating protection device. For example, a cooling channel 43 for cooling by means of a coolant can be formed in a wall of the scanner housing 3'. The cooling channel 43 can be provided with a coolant connection for connection to a coolant circuit.

[0065] Fig. Figures 5 to 10 show combinations of the above-described embodiments of overheating protection devices.

[0066] The in the Fig. The combinations shown in sections 5 to 10 are by no means exhaustive. It is hereby expressly pointed out that any combination of the combinations shown in the sections is possible. Fig. 3A to 3C and in the Fig. Overheating protection devices 4 shown in figures 4A to 4C or described in the figure description of these figures are possible.

[0067] Fig. Figure 5 shows a convex structure 42 with a partially reflective surface 44. The partially reflective surface 44 can be applied to the convex structure 42 by coating or formed on it by surface treatment. This allows scattering to be achieved over the largest possible solid angle.

[0068] Fig. Figure 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. This allows for both a spatial and temporal distribution of incident radiation energy.

[0069] Fig. Figure 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 positioned at a certain distance in front of the convex structure 42 by means of the suspension 411.

[0070] Fig. Figure 8 shows a combination of the heat sink 45 and the convex structure 42. In this case, the first surface of the heat sink 45 can have the convex structure 42.

[0071] Fig. Figure 9 shows a combination of the heat sink 45 and the dispersion element 41. The heat sink 45 overlaps the dispersion element 41. In other words, the dispersion element 41 is positioned such that back reflections incident on the heat sink 45 must pass through the dispersion element 41. The dispersion element 41 thus shields the heat sink 42, at least partially. Due to the temporal distribution of incident radiation energy through the dispersion element, the heat sink 45 can more reliably dissipate the generated heat to the outside or to the surroundings of the laser processing head. In particular, this avoids or at least reduces intensity peaks that can lead to ablation effects.

[0072] Fig. Figure 10 shows a combination of the heat sink 45, the dispersion element 41, and the convex structure 42. The heat sink 45 overlaps the convex structure 42. In other words, the dispersion element 41 is positioned such that back reflections incident on the convex structure 42 must pass through 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 quickly and efficiently dissipated to the outside or to the surroundings of the laser processing head via the heat sink.

[0073] Fig. Figures 11 to 13 show exemplary embodiments of a combination of an active and at least one passive overheating protection device according to the present invention. The active overheating protection device can comprise at least one cooling channel 43 through which a cooling medium or coolant, such as a gas or liquid, flows. The cooling channel 43 can be connected to a coolant circuit via a coolant connection. Ideally, the cooling channel 43 is located close to the areas on which the back reflections 21 strike. The active overheating protection device can further comprise a pump or a fan or a controllable valve.

[0074] Fig. Figure 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 can be arranged outside the optical space 3a on the housing 3. However, the cooling channel 43 can also be arranged inside the housing 3 or be integrated into the housing 3 (see Figure 11). Fig. 12).

[0075] Fig. Figure 12 shows a combination of a cooling channel 43 and the dispersion element 41. The cooling channel 43 can be arranged in a region of the housing 3 where back reflections passing through the dispersion element 41 impinge. The cooling channel 43 can be located inside the housing 3 or integrated into the housing 3. However, the cooling channel 43 can also be located outside the optical space 3a.

[0076] Fig. Figure 13 shows a combination of a cooling channel 43, the dispersion element 41 and the convex structure 42.

[0077] According to the present invention, areas of the housing or areas within the housing or in the optical chamber that may be affected by back reflections can be provided with overheating protection devices and thus be designed to dissipate the input energy without being damaged. Particularly in scanner laser processing heads operating at high laser powers, or in ablative laser processing processes using high pulse powers, damage caused by laser radiation outside the beam path, such as back reflections, can be reduced or even prevented. Reference symbol list 1 laser processing head 2 Laser beam 21 Back reflex 3 cases 3' Scanner housing 3a Optics Room 31 Protective glass 4 Overheating protection device 41 Dispersion element 411 Suspension 42 convex structure 43 Cooling channel 44 partially reflective surface 45 heat sinks 45a Cooling fin 46 solid metal pieces 5 Optics holder 6.6' Optics 8.8' Scanner mirror 80 Scanning device 9 optical fibers 10 workpieces

Claims

[1] Laser processing head (1) for processing a workpiece (10) using a laser beam (2), comprising: a scanning device (80) for deflecting the laser beam (2) on the workpiece (10); a housing (3, 3') in which the scanning device (80) is arranged; and at least one overheating protection device (4) designed to protect the housing (3) from overheating, characterized by , that the overheating protection device (4) comprises an energy distribution device for distributing incident radiant energy, and the energy distribution device comprises a convex structure (42), and / or the energy distribution device comprises a dispersion element (41) for attenuating laser pulses and / or spectrally broadband laser radiation. [2] Laser processing head (1) according to claim 1, wherein the at least one overheating protection device (4) comprises an active overheating protection device with a cooling channel (43) for guiding a coolant, and wherein the cooling channel (43) is formed in a wall of the housing (3, 3'). [3] Laser processing head (1) for processing a workpiece (10) using a laser beam (2), comprising: a housing (3) that defines an optical space (3a); and at least one passive overheating protection device designed to protect the housing (3) and / or elements arranged in the housing (3) from overheating, characterized by that the overheating protection device includes an energy distribution device for distributing incident radiant energy, and the energy distribution device comprises a convex structure (42), and / or the energy distribution device comprises a dispersion element (41) for attenuating laser pulses and / or spectrally broadband laser radiation. [4] Laser processing head (1) according to claim 3, further comprising an active overheating protection device with a cooling channel (43) for guiding a coolant, wherein the cooling channel (43) is formed in a wall of the housing (3, 3'). [5] Laser processing head (1) according to any one of the preceding claims 1 to 4, wherein the overheating protection device (4) is arranged in the housing (3, 3') and / or outside the beam path of the laser beam (2) and / or on the inner surface of the housing (3, 3') and / or on at least one element arranged in the housing (3, 3'); and / or wherein the overheating protection device (4) forms part of the housing (3, 3') and / or is integrated with the housing (3, 3'). [6] Laser processing head (1) according to any one of the preceding claims 1 to 5, wherein the overheating protection device (4) is arranged at a predetermined critical position in the housing (3, 3') where back reflections (21) of the laser beam (2) and / or laser radiation passing outside the beam path occur. [7] Laser processing head (1) according to any one of the preceding claims 1 to 6, wherein the overheating protection device (4) is arranged next to an optical element (6, 6') arranged in the housing (3, 3') and / or is formed on a support (5, 5') of an optical element (6, 6') arranged in the housing (3, 3') and / or forms part of a support (5, 5') of an optical element (6, 6') arranged in the housing (3, 3'). [8] Laser processing head (1) according to any one of the preceding claims 1 to 7, wherein the overheating protection device (4) is arranged in the housing (3, 3') such that back reflections (21) of the laser beam (2) from at least one optical element (6, 6') arranged in the housing (3, 3'), in particular from an aperture, an optical element, an F-theta optic, a mirror, a beam splitter, and / or a protective glass, meet the overheating protection device (4). [9] Laser processing head (1) according to any one of the preceding claims 1 to 8, wherein the housing (3) comprises an entry port for coupling the laser beam (2) into the laser processing head (1) and a collimation optic, and wherein the overheating protection device (4) is arranged between the entry port and the collimation optic. [10] Laser processing head (1) according to one of the preceding claims, wherein the energy distribution device comprises a convex structure (42), and wherein the convex structure (42) comprises a plurality of periodically arranged and convex substructures (42a) and / or has a partially reflective surface (44). [11] Laser processing head (1) according to any one of the preceding claims 1 to 10, wherein the overheating protection device (4) further comprises a heat sink for dissipating absorbed heat, and wherein the heat sink comprises a heat sink (45) which has both a first surface for heat absorption arranged in the housing (3, 3') and a second surface arranged on an outside of the housing (3) for dissipating the absorbed heat. [12] Laser processing head (1) according to any one of the preceding claims 1 to 11, wherein the overheating protection device (4) further comprises a heat sink for dissipating absorbed heat, and wherein the heat sink comprises a solid metal piece (46) that is attached to the inner surface of the housing (3) and covers part of the inner surface, or that forms part of the housing (3), and wherein the solid metal piece (46) has a thickness of more than 5 mm, preferably more than 10 mm. [13] Laser processing head (1) according to claim 12, wherein the solid metal piece (46) consists of copper and / or aluminium and / or copper alloys and / or aluminium alloys and / or a material with a thermal conductivity greater than 50 W / m*K, in particular greater than 100 W / m*K. [14] Laser processing head (1) according to any one of the preceding claims 1 to 13, wherein at least a part of the inner surface of the housing (3) and / or at least a part of a surface of an element arranged in the housing (3) is designed to be partially reflective.

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