Diaphragm for laser processing head and laser processing head comprising diaphragm

Abstract

The invention relates to a diaphragm for a laser processing head for processing a workpiece by means of a laser beam, comprising a diaphragm opening and a diaphragm body which surrounds the diaphragm opening, the diaphragm being designed such that edge radiation of the laser beam which impinges on the diaphragm body is multiply reflected at the diaphragm, and wherein the edge radiation of the laser beam which impinges on the diaphragm body is multiply reflected at the diaphragm. The diaphragm body is made of a ceramic material. The invention further relates to a laser machining head for machining a workpiece by means of a laser beam, said laser machining head having such a diaphragm.

Description

Technical Field

[0001] The present invention relates to a diaphragm for a laser processing head and a laser processing head including such a diaphragm. In particular, the present invention relates to a diaphragm made of ceramic, which has a shape that reflects a laser beam multiple times thereon. Background Art

[0002] Processing a workpiece with a laser beam (laser material processing) has been used in the manufacturing industry for many years. Laser material processing can include laser welding, laser brazing, and laser cutting. Here, the laser beam emitted from a laser source or from the end of a laser optical fiber is emitted onto the workpiece to be processed by means of a laser processing head. The laser processing head contains various optical elements for beam guiding and beam shaping.

[0003] After the laser beam is emitted from the laser source or from the end of the laser optical fiber, the laser beam diverges into the internal space of the laser processing head. On a cross-sectional surface perpendicular to the beam propagation direction, the laser beam usually has a laser power that is approximately Gaussian or bell-shaped. In this case, a smaller component of the laser power falls in the outer edge or edge range of the laser beam (edge radiation). It is desirable to plan and dimension the laser processing using the laser power in the central range of the laser beam (main radiation). In order to shield or block the edge radiation, a diaphragm can be used in the beam entrance of the laser beam, which is usually arranged in the divergent range of the laser beam. In addition, the components of the laser processing head, such as optical elements (such as lenses) and the inner upper surface of the laser processing head, should also be protected from the edge radiation that is often uncontrolled (especially caused by excessive heating). Therefore, the problem is how to shield and absorb the edge radiation in a controllable manner.

[0004] Recently, this problem has become difficult due to the continuous increase in the laser power of the laser beam or the laser source used. Therefore, the power of the edge radiation to be shielded and absorbed has also climbed and become larger and larger. In addition, the characteristics of the laser beam or the laser source among different manufacturers, especially the distribution of the laser power, may also be significantly different from each other. In particular, the parameters of the laser power falling in the edge range fluctuate very strongly, and in addition, the power in the edge range increases more and more relative to the power in the central range.

[0005] Conventional diaphragms made of metal without a laser beam absorbing coating strongly reflect or scatter the shielded edge radiation and therefore require a complex beam incident geometry so that the shielded edge radiation dissipates in the diaphragm. This complex beam incidence geometry requires a very large number of positions and can generally only be integrated into a laser processing head with a great deal of overhead.

[0006] In contrast, conventional diaphragms made of metals without a laser beam absorbing or anti-reflection coating have the problem that the carrier material and the coating have different coefficients of thermal expansion. In addition, these coatings are unstable from a certain surface temperature onwards. From a certain power of the edge radiation absorbed by this diaphragm, cracks and spalling of the coating due to heat occur, which can subsequently contaminate subsequent optical devices and can lead to total damage of the laser processing head.

[0007] In addition, the carrier material of the diaphragm should be made of stainless steel in order to counteract electrochemical corrosion in a directly water-cooled and coated diaphragm. However, the disadvantage of stainless steel is that its thermal conductivity is relatively small compared to other materials and it cannot conduct heat out of the heat-affected zone quickly enough. This in turn easily causes cracks and spalling due to heat.

[0008] Therefore, the conventional diaphragm design has more and more problems with the current development. Summary of the Invention

[0009] The object of the present invention is to provide a diaphragm for a laser processing head for use at high laser powers, and a laser processing head having such a diaphragm.

[0010] Another object of the present invention is to provide a diaphragm that is suitable for high laser powers during laser material processing, especially for shielding the high-power edge radiation. In particular, the object of the present invention is to provide a durable or robust diaphragm with a simple structure that can absorb and conduct out the high-power edge radiation. In addition, another object of the present invention is to provide a laser processing head having such a diaphragm.

[0011] In addition, another object of the present invention is to provide a laser processing head having a diaphragm with which the edge radiation of the laser beam can be shielded without damaging the laser processing head.

[0012] In particular, the object of the present invention is to provide a diaphragm and a laser processing head having the same diaphragm that can conduct out the high laser power in the edge region of the laser beam without damage with a high heat conduction. In addition, another object of the present invention is to provide a diaphragm and a laser processing head having the same diaphragm that can be directly water-cooled.

[0013] At least one of these objects is solved by the subject matter of the present invention. The subject matter of corresponding further developments is an advantageous embodiment of the present invention.

[0014] The present invention is based on the following recognition that in order to efficiently absorb the edge radiation and the heat energy generated thereby, the material and shape (geometry) of the diaphragm body of the diaphragm must be suitably coordinated with each other. Additionally, water cooling can be used.

[0015] The idea of the present invention is that, contrary to the conventional diaphragm bodies usually composed of metal or coated materials, ceramic materials, especially uncoated ceramic materials, are used for the diaphragm body. Compared with metals (such as stainless steel), such ceramic materials have very high temperature stability and can therefore absorb significantly more power without being damaged. In addition, ceramic materials also have, for example, significantly higher thermal conductivity than stainless steel. Thus, the absorbed heat energy can be efficiently transported to other cooling media, and other components of the laser processing head directly adjacent to the diaphragm body will not overheat. In addition, ceramic materials also have a balanced electrochemical standard potential, such as the electrochemical standard potential of stainless steel. Thus, the diaphragm body can be simply cooled by means of water without the risk of electrochemical corrosion.

[0016] However, generally speaking, the absorption capacity of ceramic materials is small or the reflectivity of ceramic materials is high. Therefore, according to the present invention, the diaphragm body has such a shape that the laser radiation incident on the diaphragm body, that is, the edge radiation (to be blocked), is reflected multiple times, for example, at least three times, especially at least five times, at the diaphragm body or in the diaphragm itself. Thereby, a significant component of the laser radiation incident on the diaphragm body can be prevented from leaving the diaphragm again and from being reflected, for example, in the internal space of the laser processing head. Thus, the edge radiation incident on the diaphragm body is efficiently blocked.

[0017] Reflectivity of ceramic materials Especially if the ceramic material is uncoated, it is often in the lower two-digit range. The disadvantage brought about by the higher reflectivity compared to a metal diaphragm with a coating (such as an absorption coating or an antireflection coating) can be compensated for by the geometric shape (form) of the diaphragm, especially the diaphragm body, in such a way that the laser radiation incident on the diaphragm body, that is, the edge radiation (to be blocked), can only exit the diaphragm again after multiple reflections, or "dissipate" in the diaphragm through multiple reflections, that is, be completely absorbed by the diaphragm body. Through multiple reflections at or inside the diaphragm, the laser power of the edge radiation exiting the diaphragm drops to a range that no longer causes damage to the laser processing head, that is, especially drops to a lower Watt range, for example, less than 50 Watt.

[0018] If, within the scope of the present invention, reference is made to "absorbing radiation by a material or element" or "absorbing a (laser) beam by a material or element", this means that the radiation or beam impinges on the material or on the element and at least a part thereof is absorbed, where the (laser) radiation power or (laser) radiation energy is converted into thermal power or thermal energy, in such a way that the material or the element is heated up or heated. Here, this thermal power or thermal energy is also briefly referred to as "absorbed thermal power" or "absorbed thermal energy". The non-absorbed component of the radiation or the light ray will be reflected again by the material or the element. Within the scope of the present invention, the terms "thermal energy" and "heat" are used as synonyms. "Laser power" means the power of a laser beam or the power of a part thereof, such as marginal radiation or main radiation. The reflectivity (usually denoted by ρ or R) is also referred to as the degree of reflection, the reflection ability or the reflectance, and is the ratio of the reflected intensity of the radiation to the incident intensity of the radiation. Multiple reflections can also be referred to as "multiple reflections" or "multiple reflections". Within the scope of the present invention, marginal radiation denotes a part of the laser beam that should be blocked by a diaphragm, that is, it should impinge on the diaphragm body that defines the diaphragm opening. Main radiation denotes a part of the laser beam that passes through (hindurchtritt) the diaphragm, that is, through the diaphragm opening. The marginal radiation is in the radially outer range of the main radiation with respect to the beam axis.

[0019] According to a first aspect of the present invention, there is provided a diaphragm for a laser beam or for a laser processing head for processing a workpiece by means of a laser beam. The diaphragm includes a diaphragm opening and a diaphragm body. The diaphragm body surrounds the diaphragm opening and / or defines and / or delimits the diaphragm opening. The diaphragm has a shape such that the marginal radiation of the laser beam impinging on the diaphragm body is multiply reflected at the diaphragm. The diaphragm body can in particular have a shape such that the marginal radiation of the laser beam impinging on the diaphragm body is multiply reflected at the diaphragm body. The diaphragm body comprises a ceramic material or consists of a ceramic material.

[0020] The diaphragm body can be arranged to shield and / or block the marginal range of the laser beam, that is, the marginal radiation. The diaphragm opening can be used and / or arranged to allow the central range of the laser beam, that is, the main radiation, to pass through. The diaphragm or the diaphragm body can be arranged to absorb a part of the impinging or reflected marginal radiation during the impingement or reflection of the marginal radiation. Thereby, the diaphragm or the diaphragm body can be heated up.

[0021] According to a second aspect of the present invention, a laser processing head for processing a workpiece by means of a laser beam is provided, wherein the laser processing head includes a diaphragm according to the aspects and embodiments of the present invention.

[0022] Aspects of the present invention may have one or more of the following optional features.

[0023] The following gives the material properties for experimental conditions (25 °C and 101325 kPa).

[0024] The diaphragm or diaphragm body may not be coated, i.e., uncoated. The ceramic material may in particular be an uncoated ceramic material. The diaphragm body may be uncoated in at least one range on which edge radiation impinges and / or is reflected. The diaphragm body may in particular consist of an uncoated ceramic material. The diaphragm or diaphragm body may not have an anti-reflection coating and / or an absorption coating. The upper surface of the diaphragm body on which the edge radiation impinges and / or at which the edge radiation is reflected may in particular be uncoated or not have an anti-reflection coating and / or an absorption coating. This has the advantage that layer peeling does not occur due to heating or thermal loading of the diaphragm or diaphragm body.

[0025] The diaphragm body or ceramic material may have a modulus of elasticity (E-Modul) equal to or greater than 300 GPa, or between 300 GPa and 500 GPa, in particular between 350 GPa and 450 GPa, preferably between 350 GPa and 400 GPa.

[0026] The diaphragm body or ceramic material may have a thermal conductivity at 25 °C equal to or greater than 90 W / (m·K), preferably equal to or greater than 100 W / (m·K), preferably 110 W / (m·K), in particular between 150 W / (m·K) and 250 W / (m·K) or between 150 W / (m·K) and 255 W / (m·K), preferably 200 W / (m·K), 220 W / (m·K), 240 W / (m·K) or 250 W / (m·K). Since the ceramic material has a relatively high thermal conductivity for constructing the diaphragm or diaphragm body, this can ensure efficient and reliable dissipation of the thermal energy generated by absorbing the incident edge radiation.

[0027] The diaphragm body or ceramic material may have a coefficient of thermal expansion equal to or less than 6 1 / (10 6 K), equal to or less than 3 1 / (10 6 K), preferably 2.3 1 / (10 6 K). Since the ceramic material has a small coefficient of thermal expansion for constructing the diaphragm or diaphragm body, high tolerances or stability can be achieved in response to large thermal energies and high temperatures.

[0028] The diaphragm body or the ceramic material can have an absorption degree equal to or greater than 70%, or equal to or greater than 85%, especially for radiation with a wavelength between 1000 nm and 1200 nm. The diaphragm body or the ceramic material can have a reflection degree equal to or greater than 5%, especially equal to or greater than 10% and / or in the range from 5% to 25% (including the boundaries). This reflection degree can be given for radiation with a wavelength between 1000 nm and 1200 nm.

[0029] The diaphragm body or the ceramic material can have an electrochemical standard potential like that of stainless steel and / or between -1.7 V and +1.7 V, between -1 V and +1 V, between 0 V and -0.8 V, preferably between -0.4 V and -0.6 V.

[0030] The ceramic material can comprise or can be a ceramic composite material and / or silicon carbide, especially sintered silicon carbide, pressureless sintered silicon carbide (SSiC), reaction-bonded silicon-infiltrated silicon carbide (SiSiC) or carbon fiber-reinforced silicon carbide, for example The ceramic material, especially in the case of SSiC, can have at least one of the following properties: a density of 3.1 g / cm 3 , an elastic modulus of 400 GPa, and / or a thermal conductivity of 110 W / (m*K) at 25 °C. The ceramic material, especially in the case of SiSiC, can have at least one of the following properties: a density of 2.96 g / cm 3 , an elastic modulus of 350 GPa, a strength (Festigkeit) of 320 MPa, a Weibull modulus between 10 and 25, preferably 16, a specific stiffness of 118 (MPa*m 3 / kg), a coefficient of thermal expansion of 2.3 1 / (10 6 K), a thermal conductivity of 200 W / (m*K) at 25 °C and / or a thermal conductivity of 355 W / (m*K) at 150 K.

[0031] The diaphragm body can have such a shape that the irradiated marginal radiation is reflected at least twice at the diaphragm body, preferably at least four or five times.

[0032] The diaphragm and / or the diaphragm body can be configured rotationally symmetric. The diaphragm body can be configured as a single piece. The diaphragm body can be configured annularly. The axis of symmetry of the diaphragm or the diaphragm body can coincide with the central axis of the diaphragm. The central axis of the diaphragm can coincide with the beam axis of the laser beam and / or the optical axis of the laser processing head. The radial direction of the diaphragm can be in a plane perpendicular to the central axis and / or the axis of symmetry and is defined starting from the central axis and / or the axis of symmetry.

[0033] The diaphragm body can have such a shape that the proportion of the intensity of the component of the incident marginal radiation leaving the diaphragm relative to the intensity of the incident marginal radiation is equal to or less than 20%, preferably equal to or less than 15%, in particular 11%, and particularly preferably equal to or less than 10%. Since the diaphragm body absorbs a certain component of the incident marginal radiation during each reflection, multiple reflections can be used to ensure that a sufficiently large component of the power of the incident marginal radiation is absorbed overall. Therefore, in an uncoated diaphragm body, it is still possible to ensure, through the shape of the diaphragm body, that the incident marginal radiation is sufficiently absorbed by multiple reflections, preferably ensuring that the incident marginal radiation is completely absorbed. "The component of the incident marginal radiation leaving the diaphragm" means such a component of the marginal radiation incident on the diaphragm that is no longer reflected at the diaphragm after multiple reflections at the diaphragm. This component can in particular be reflected back again or injected into the internal space of the laser processing head. Then, this component can irradiate other components of the laser processing head, such as lenses.

[0034] The diaphragm or diaphragm body can have at least one groove or notch. The groove can be configured such that the incident marginal radiation is reflected multiple times until the incident marginal radiation dissipates in the groove. "Dissipates" (Totlaufen) means that the incident marginal radiation is completely absorbed by the diaphragm or diaphragm body after multiple reflections. The groove can also be referred to as a "beam trap" (Strahlfalle).

[0035] The groove can extend annularly around the diaphragm opening and / or be directly adjacent to the diaphragm opening. The diaphragm opening can be defined by the innermost edge or first edge of the diaphragm body in the radial direction starting from the central axis. The groove can be arranged at a position adjacent to the diaphragm opening in the radial direction and / or in the direction of the central axis of the diaphragm.

[0036] The groove can be arranged in the direction of the central axis of the diaphragm and / or be arranged between the first edge and the second edge of the diaphragm body in the beam propagation direction. The second edge can be located at a more external position in the radial direction than the first edge starting from the central axis. The groove can extend in the radial direction.

[0037] In addition, the diaphragm also has a cooling device. The cooling device can be composed of stainless steel or include stainless steel. The cooling device is provided for absorbing and / or discharging the thermal energy or thermal power absorbed by the diaphragm or diaphragm body. The diaphragm body can be provided for discharging or releasing the absorbed thermal energy to the cooling device.

[0038] The cooling device can be constructed as a passive or active cooling device. The cooling device can have cooling fins on the outer side of the bracket for the diaphragm body.

[0039] The cooling device may include at least one channel for guiding a cooling medium, in particular a cooling fluid, preferably water or gas. The first side of the channel, for example the side that is internal in the radial direction, may be defined by a diaphragm body. The diaphragm body and the channel may be arranged adjacent to each other directly. The channel may partially or completely surround the diaphragm body in the circumferential direction. The channel may be part of a circulation loop for the cooling fluid. The cooling device or the channel may in particular be in fluid communication with the cooling system of the laser processing head in a fluid flow-through manner. The cooling system of the laser processing head may provide a circulation loop for the cooling fluid, in particular for water. The diaphragm and the diaphragm body may in particular be water-cooled. Thereby, the diaphragm and the diaphragm body can be directly cooled in a simple manner.

[0040] Furthermore, the diaphragm also has a support for supporting the diaphragm body. The cooling device may be constructed as a single piece together with the support. For example, the cooling fins or channels of the cooling device are constructed as a single piece together with the support. The cooling device, for example the channel for guiding the cooling medium, may in particular be constructed in the support.

[0041] The support may include or consist of stainless steel. The second side of the channel, for example the side that is external in the radial direction, may be defined by the support. The channel may be embedded in or constructed in the support. This means that the channel is defined by the support at least at the second side that is external in the radial direction and at both sides of the channel constructed along the central axis of the diaphragm. If the support consists of stainless steel and the diaphragm body has an electrochemical standard potential that is the same or similar to that of stainless steel, then cooling can be carried out with water without the risk of electrochemical corrosion of the diaphragm.

[0042] The diaphragm may be arranged between the end of the laser optical fiber and the collimating optics in the beam propagation direction of the laser beam, or between the entry port for the laser beam of the laser processing head and the collimating optics. The diaphragm may be arranged in the diverging range of the laser beam in the laser processing head. The diaphragm may be the first optical element in the laser processing head that is traversed by the laser beam.

[0043] The power of the laser beam may be equal to or greater than 10 kW, equal to or greater than 50 kW, preferably equal to or greater than 100 kW.

[0044] The laser head may be set for laser brazing and / or laser cutting and / or laser welding. Description of the Drawings

[0045] Aspects of the present invention will be explained below with the aid of the drawings. Shown here are:

[0046] Figure 1 Schematic diagram of a laser processing head according to an embodiment of the present invention;

[0047] Figure 2A Schematic cross-sectional view of a diaphragm of a laser processing head for processing a workpiece by means of a laser beam according to an embodiment of the present invention;

[0048] Figure 2B Schematic cross-sectional view of a diaphragm of a laser processing head for processing a workpiece by means of a laser beam according to another embodiment of the present invention; Detailed implementation manners

[0049] The same reference numerals are used hereinafter to identify the same or corresponding elements.

[0050] Figure 1 Schematic view showing a laser processing head according to an embodiment of the present invention. The laser processing head 1 is used for processing a workpiece 2 by means of a laser beam 20. The laser processing head 1 can be, for example, a laser cutting head or a laser welding head. The laser beam 20 is transmitted, for example, via a laser optical fiber 3. The laser optical fiber 3 can be connected to a laser source (not shown). The laser processing head 1 has an entry port 12 for the laser beam 20. The laser beam 20 enters the internal space 14 of the laser processing head 1 through the entry port 12. The internal space 14 of the laser processing head 1 is defined by the housing 16 of the laser processing head 1. The power of the laser beam 20 is, for example, 100 kW.

[0051] The laser processing head 1 has a plurality of optical elements arranged in the internal space 14. The optical elements include, for example, a collimating optical device 18 and a focusing optical device 19. The collimating optical device 18 and the focusing optical device 19 each include a lens or a lens group.

[0052] The optical elements 18, 19 are used for beam shaping and beam guiding of the laser beam 20. The laser beam 20 enters the internal space 14 divergently at the entry port 12. The optical elements 18, 19 are particularly used for bunching and focusing the divergent laser beam 20 so that the laser beam 20 exits convergently from the exit port 22 of the laser processing head 1 in order to perform processing on the workpiece 2.

[0053] In the beam propagation direction 13, after the entry port 12, the divergent laser beam 20 impinges on a diaphragm 24 which shields or blocks the marginal radiation of the laser beam 20. Thereby, only a defined component of the laser beam 20, that is, only the main radiation, impinges on the subsequent optical elements in the beam propagation direction 13. Therefore, the diaphragm 24 is arranged in the beam propagation direction 13 of the laser beam 20 between the end of the laser optical fiber 3 and the collimating optical device 18, or is arranged between the entry port 12 of the laser processing head 1 for the laser beam 20 and the collimating optical device 18. The diaphragm 24 is arranged in the divergent range of the laser beam 20.

[0054] The diaphragm 24 is arranged in the laser processing head 1 such that the central axis 201 (see Figure 2A , 2B) coincides with the optical axis of the laser beam 20 and / or the optical axis 11 of the laser processing head 1.

[0055] Figure 2A Schematic cross-sectional view of the diaphragm of a laser processing head for processing a workpiece by means of a laser beam according to an embodiment of the invention. Figure 2B Schematic cross-sectional view of the diaphragm of a laser processing head for processing a workpiece by means of a laser beam according to another embodiment of the invention. In Figure 2A and Figure 2B The diaphragms shown can be, for example, the diaphragm 24 of the laser processing head 1 shown in Figure 1 .

[0056] The diaphragm 24 includes a diaphragm body 202. The diaphragm 24 or the diaphragm body 202 has a central axis 201. The central axis 201 can correspond to the axis of symmetry of the diaphragm 24 or the diaphragm body 202. As shown, the diaphragm 24 can be configured to be substantially rotationally symmetric about the central axis 201. The diaphragm body 202 can likewise be configured to be substantially rotationally symmetric about the central axis 201. In addition, the diaphragm 24 further includes a diaphragm opening 203. The diaphragm body 202 surrounds the diaphragm opening 203 in a plane perpendicular to the central axis 201. Thus, the diaphragm body 202 abuts the diaphragm opening 203. More precisely, the diaphragm opening 203 is defined by a first edge 2021 that is radially innermost of the diaphragm body 202 starting from the central axis 201. As shown, the edge 2021 is configured annularly and lies in a plane perpendicular to the central axis 201. Thus, the diaphragm opening 203 is likewise configured annularly.

[0057] The diaphragm opening 203 is for passing the main radiation of the laser beam, i.e., the central range of the laser beam. The diaphragm body 202 is provided for blocking or shielding the marginal radiation of the laser beam. The diaphragm body 202 has a shape such that the marginal radiation of the laser beam 20 incident on the diaphragm body 202 is multiply reflected at the diaphragm body 202. In Figure 2A , 2B the marginal radiation is illustrated by a single beam 21. When the marginal radiation 21 is incident and each time the marginal radiation 21 is reflected at the diaphragm body 202, the diaphragm body 202 absorbs a component of the incident radiation respectively. In this case, the diaphragm body 202 is heated or gets hot. That is, the radiation energy may be converted into thermal energy.

[0058] The diaphragm body 202 is composed of a ceramic material. The ceramic material can be, for example, silicon carbide, especially pressureless sintered silicon carbide (SSiC) or reaction-bonded silicon-infiltrated silicon carbide (SiSiC). The diaphragm body 202 is uncoated, that is to say, the diaphragm body 202 especially does not have an absorption coating or an antireflection coating for the laser beam 20. The diaphragm body 202 is especially uncoated on at least one upper surface 2022, on which the marginal radiation 21 first irradiates the diaphragm body 202.

[0059] Therefore, there will be no coating material peeling off when the diaphragm 24 gets hot and soiling the internal space of the laser processing head or the optical elements. As shown, the diaphragm body 202 is preferably configured as a single piece composed of a ceramic material.

[0060] In order to reflect the marginal radiation 21 multiply, the diaphragm body 202 has a pre-given shape. Through this pre-given shape, the marginal radiation 21 is Figure 2A reflected five times at the diaphragm body 202 as shown, or Figure 2B reflected four times at the diaphragm body 202 as shown. In Figure 2A , the marginal radiation 21 irradiating the diaphragm body 202 is first reflected on the first side of the diaphragm body 202 with respect to the central axis 201, crosses the diaphragm opening 203, and then is reflected three more times in the groove 213 of the diaphragm body 202 on the second side opposite to the first side with respect to the central axis 201, which will be described in detail later. In Figure 2B , the marginal radiation 21 irradiating the diaphragm body 202 is multiply reflected on one side of the diaphragm body with respect to the central axis 201 of the diaphragm 24, a total of five times.

[0061] Therefore, through the shape of the diaphragm body 202 and through multiple reflections, it can be ensured that the component of the irradiated marginal radiation 21 absorbed by the diaphragm body 202 is sufficient, and this is the case even if the diaphragm body 202 is uncoated. In other words, it can be ensured that the intensity of the component of the irradiated marginal radiation 21 leaving the diaphragm 24 again is as small as possible relative to the intensity of the irradiated marginal radiation 21, for example less than 15%, especially 11%. The component of the marginal radiation 21 leaving the diaphragm 24 again can be, for example, less than 100 watts. Since the component of the marginal radiation 21 leaving the diaphragm 24 again is reflected back again in the internal space of the laser processing head and then partially irradiates other elements of the laser processing head, such as optical elements, through the shape of the diaphragm body 202, it can be ensured that the laser processing head or its elements do not get overheated or out of control.

[0062] The diaphragm body 202 has a groove 2023 that is configured to be annular and is also referred to as a "beam trap". The groove 2023 is configured to multiply reflect the irradiated marginal radiation 21 until the irradiated marginal radiation 21 dissipates in the groove 2023 or exits the groove 2023 again with a significantly reduced intensity. The groove 2023 is arranged adjacent to the edge 2021 of the diaphragm body 202 and the diaphragm opening 203 in the direction of the central axis 201.

[0063] The volume of the groove 2023 extends substantially in the radial direction. As shown, the groove 2023 is arranged between the first edge 2021 and the second edge 2024 of the diaphragm body 202 in the direction of the central axis 201. Here, the second edge 2024 is located more externally in the radial direction than the first edge 2021 starting from the central axis 201.

[0064] In addition, the diaphragm 24 also has a cooling device 204. The cooling device 204 is provided for absorbing and discharging the thermal energy absorbed by the diaphragm body 202. The cooling device 204 is part of a circulation loop for a cooling fluid, such as water, and is connected in a fluid-flow manner to the cooling system 26 of the laser processing head (see Figure 1 ). The cooling system 26 can have, for example, a circulation pump and a heat exchanger for the cooling fluid. The cooling device 204 includes a channel 2041 for guiding water. The first side 2042 that is internal in the radial direction of the channel 2041 is defined by the diaphragm body 202. The diaphragm body 202 and the channel 2041 are arranged adjacent to each other directly. The channel 2041 partially or completely surrounds or encircles the diaphragm body 202 in the circumferential direction. Through the described water cooling, the diaphragm 24 and the diaphragm body 202 can be cooled in a simple and direct manner.

[0065] In addition, the diaphragm 24 also has a bracket 205 for supporting the diaphragm body 202. As shown in Figure 2A and 2B , the bracket 205 includes two parts, namely a first part 205A and a second part 205B. The diaphragm body 202 is inserted or clamped between these two parts 205A, 205B. In addition, in order to fix the diaphragm body 202 and / or to seal the channel 2041, one or more gaskets 206A, 206B can also be provided, as shown in Figure 2A . The bracket 205 is preferably formed of stainless steel. The second side 2043 that is external in the radial direction of the channel is defined by the bracket 204. As shown in Figure 2A , the second side 2043 is defined by the first part 205A of the bracket. As shown in Figure 2BAs shown in, the second side 2043 is defined by the second part 205B of the support. In addition, the side of the channel 2041 constructed in the direction of the central axis 201 is defined by the support 205. As in Figure 2A As shown in, the third upper side 2044 of the channel 2041 is defined by the first part 205A of the support 205, and the fourth lower side 2045 of the channel 2041 is defined by the first part 205A and the second part 205B of the support. As in Figure 2B As shown in, the third upper side 2044 of the channel 2041 is defined by the first part 205A of the support 205, and the fourth lower side 2045 of the channel 2041 is defined by the second part 205B of the support. Thus, the channel 2041 is embedded in the support 204.

[0066] If the support 205 is made of stainless steel and the diaphragm body 202 has an electrochemical standard potential that is the same as or similar to that of stainless steel, then cooling can be carried out with water without the risk of electrochemical corrosion of the diaphragm 24.

[0067] Therefore, the present invention describes a diaphragm for a laser processing head, in which the metallic material of the coated diaphragm body is replaced by an uncoated ceramic material, and in addition, the diaphragm body also has a shape that causes multiple reflections at the diaphragm. Due to the lower coefficient of thermal expansion and the higher thermal conductivity of the ceramic material, the very high power of the edge radiation can be absorbed and dissipated without damaging or destroying the diaphragm. In addition, the diaphragm according to the present invention also allows for simple and direct water cooling without the risk of electrochemical corrosion of the diaphragm.

Claims

1. A diaphragm (24) for a laser beam (20), comprising: an aperture opening (203), and an aperture body (202) surrounding the aperture opening (203), wherein the aperture (24) has such a shape that the edge radiation (21) of the laser beam (20) impinging on the aperture body (202) is multiply reflected at the aperture (24), and Wherein, the aperture body (202) is made of ceramic material.

2. The aperture according to claim 1, wherein: The aperture body (202) is uncoated, and / or Wherein, the aperture body (202) does not have an anti-reflection coating and / or an absorption coating.

3. The aperture according to claim 1, wherein: The ceramic material has an elastic modulus equal to or greater than 300 GPa, preferably 350 or 400 GPa, and / or Wherein, at 25° C., the ceramic material has a thermal conductivity equal to or greater than 90 W / (m*K), preferably 110 W / (m*K) or 140 W / (m*K), or has a thermal conductivity between 150 W / (m*K) and 255 W / (m*K), preferably 200 W / (m*K), 220 W / (m*K), 240 W / (m*K), 250 W / (m*K), and / or Wherein, the ceramic material has a value less than or equal to 3*1 / (10 6 K), preferably 2.3*1 / (10 6 K) coefficient of thermal expansion.

4. The aperture according to claim 1, wherein: The ceramic material is a ceramic composite material and / or comprises silicon carbide, in particular sintered silicon carbide or carbon fiber reinforced silicon carbide.

5. The aperture according to claim 1, wherein: The aperture body (202) has such a shape that the impinging edge radiation (21) is reflected at least twice, preferably at least four times, at the aperture body (202).

6. The aperture according to claim 1, wherein: The aperture body (202) has such a shape that the intensity of the component of the edge radiation (21) leaving the aperture (24) is equal to or less than 20%, preferably equal to or less than 15%, especially 11%, and particularly preferably equal to or less than 10% relative to the intensity of the irradiated edge radiation (21).

7. The aperture according to claim 1, wherein: The aperture body (202) has at least one annularly shaped recess (2023) which is embodied as a beam trap and / or is embodied for causing the irradiated edge radiation (21) to be multiply reflected therein.

8. The aperture according to claim 7, wherein: The aperture opening (203) is defined by a first edge (2021) which is located at the innermost part of the aperture body (202) in the radial direction starting from the central axis (201) of the aperture (24), and the groove (2023) is arranged adjacent to the aperture opening (203) in the radial direction and / or in the direction of the central axis (201) of the aperture (24).

9. The aperture according to claim 7 or 8, wherein: The groove (2023) is arranged between the first edge (2021) and the second edge (2024) of the aperture body (202) in the direction of the central axis (201) of the aperture (24) and / or in the beam propagation direction (13) of the laser beam (20), the second edge being located at a position further outside than the first edge (2021) in the radial direction from the central axis (201), and / or Wherein, the groove (2023) extends in the radial direction.

10. The aperture according to claim 1, wherein: The aperture (24) has a cooling device (204), and the aperture body (202) is configured to discharge thermal energy absorbed during each reflection to the cooling device (204).

11. The aperture according to claim 10, wherein: The cooling device (204) comprises at least one channel (2041) for conducting a cooling fluid, in particular water, and / or Wherein, the cooling device (204) is made of stainless steel.

12. The aperture according to claim 11, wherein: The first side (2042) of the channel (2041) is defined by the aperture body (202), and / or Therein, the aperture body (202) and the channel (2041) are arranged directly adjacent to each other.

13. The aperture according to claim 10, 11 or 12, further comprising a bracket (205A, 205B) for supporting the aperture body (202), wherein: The support is made of stainless steel and / or the cooling device (204) is constructed to be integrated in the support (205A, 205B).

14. A laser processing head (1) for processing a workpiece (2) by means of a laser beam (20), comprising an aperture (24) according to one of the preceding claims, wherein: The aperture (24) is arranged in the region of the divergence of the laser beam (20).

15. The laser processing head (1) according to claim 14, wherein: The power of the laser beam (20) is equal to or greater than 10 kW, preferably equal to or greater than 50 kW or at least 100 kW.

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