Laser beam deflection device for a device for building three-dimensional objects and device for producing three-dimensional objects with such a laser beam deflection device

Abstract

Laser beam deflection device for a device (1) for building three-dimensional objects (10), comprising at least one deflection mirror (15, 16), a motor (19) for controlling the deflection mirror (15, 16) and a housing (17) accommodating at least the deflection mirror (15, 16) and having an inlet and outlet opening for a laser beam (9), wherein the housing has at least one side wall (21) which consists of a solid area (23), ie a non-generatively built area, and a generative area (24) which is formed by a generative construction process, wherein the side wall (21) has a recess for the motor (19), wherein the housing (17) has at least one tempering channel (27) with three sections (28, 29, 30), which runs at least partially in the generative area (24), wherein the tempering channel (27) in the generative area (24) branches into at least two branch channels (31) in section (29), wherein the branch channels (31) lead around the recess for the motor (19).

Description

[0001] The invention relates to a laser beam deflection device for a device for building three-dimensional objects having the features of claim 1 and to a device for producing three-dimensional objects with such a laser beam deflection device.

[0002] Laser beam deflection systems are used in materials processing, rapid prototyping, and other applications. They are used to direct the laser beam emitted by a laser in the desired direction without having to move the entire laser. For example, in rapid prototyping, a laser beam is used to solidify specified areas on the build or work plane. It must therefore be possible to direct the laser beam to any point on the work plane, whereby the work plane is many times larger than the area occupied by the laser beam. It is therefore common practice to rigidly fix the laser and deflect the laser beam using a deflection device. These deflection devices for deflecting the laser beam are also called scan heads. They are housed in a housing that has an inlet and outlet opening for the laser beam.Depending on the design, the housing contains one to three motor-driven deflection mirrors for deflecting the laser beam. A two-dimensional deflection of the laser beam can be achieved with a single mirror, although this mirror must be rotatable about two axes. However, two mirrors are preferred if the laser beam needs to be deflected onto a work plane, as is common in rapid prototyping. Each deflection mirror can be rotated about one axis. This significantly simplifies the control of the deflection mirrors and the design of the motors that drive them.

[0003] Due to the energy transported by the laser beam, the scan head typically heats up during the construction process. This is counteracted by providing cooling channels drilled into the typically metallic housing. A scan head has appropriate connections to enable water cooling or even air cooling of individual device components. For example, it is known to cool the entrance aperture and galvanometer scanner with water, while the deflection mirrors are cooled with air.

[0004] The problem here is that the energy introduced into the scan head housing by the laser beam is not distributed evenly. This results in irregular energy input into the scan head housing, which can lead to heat-induced deformations. Even the slightest deformations and deviations cause a disproportionate misdirection of the laser beam in the working plane.

[0005] DE 100 53 742 A1 discloses a device for sintering, ablating and / or marking by means of electromagnetic focused radiation and methods for operating the device.

[0006] DE 10 2011 101 302 A1 discloses a method for producing a housing with at least one temperature control line and a housing with at least one temperature control line.

[0007] DE 102 29 952 B4 discloses a metallic workpiece and a method for producing the same.

[0008] DE 10 2009 038 255 A1 discloses a method and a device for producing a three-dimensionally shaped object.

[0009] The invention is therefore based on the object of providing a laser beam deflection device in which deformation of the housing and the associated misdirection of the laser beam are avoided.

[0010] This problem is solved by the subject matter of the independent claims.

[0011] The core of the invention is considered to be the formation of the housing in sections using a generative construction process, in particular laser melting or laser sintering. In principle, it is also possible to manufacture the entire housing in this way; however, for economic reasons, it is advantageous to form only the areas particularly affected by the heat input of the laser beam using a generative construction process. This makes it possible to improve the structural design of the critical area in a targeted manner and with minimal overall effort.

[0012] The areas where the deflection mirror(s) are mounted are considered particularly critical. On the one hand, thermal expansion in this area leads to greater misdirection of the laser beam; on the other hand, the laser beam naturally generates a particularly high heat or energy input here.

[0013] When we talk about peripheral housing components arranged on the housing, we are referring in particular to collimator housings, housings of other optical beam-guiding elements, apertures, and the like, which can heat up, for example, due to laser radiation and thus warp slightly. However, other influences are also possible that require particularly high stability in such housings in the peripheral area. Such stability requirements can be met by mechanically designing the housing components in a special way and manufacturing them using a generative construction process. This allows for specific thermal areas to be subjected to targeted cooling, for example, through generatively installed cooling channels.

[0014] The inventive design of this area makes it possible to provide targeted reinforcements, for example in the form of support elements running along the inner wall of the housing, or to ensure improved dimensional stability even at changing temperatures through varying heat input through arbitrarily arranged openings in the housing wall. In particular, the attachment of reinforcements to the inner side of the housing is considerably simplified by the production of at least some of the laser beam deflection device using a generative construction process.

[0015] The housing has at least one temperature control channel, which runs at least partially within the generative region. This makes it possible to shape the temperature control channel more variably than is possible with simple bores. The medium in the temperature control channel can be used both to cool the housing and the interior of the housing, as well as to heat it.

[0016] In particular, those parts of the housing of the laser beam deflection device where the deflection mirror(s) are mounted must be particularly protected against deformation due to temperature changes. A further design therefore provides for the temperature control channel to be designed with a flat surface in some sections. Accordingly, the temperature control channel has a cylindrical structure at the points where the temperature control medium is primarily transported, as this has the smallest surface area relative to the transported volume. Of course, other cross-sectional shapes can also be selected, as long as the surface area of ​​the temperature control channel is not significantly increased. This minimizes the surface area, in fact, allowing the temperature exchange with the housing to be minimized.

[0017] At those points on the housing where a cooling or heating effect is to be achieved, the temperature control channel is designed to be flat, thereby increasing the surface area and thus improving heat exchange with the housing and the housing environment.

[0018] In order to produce such flat, flat-shaped temperature control channels as efficiently as possible, the invention provides for them to be partially or entirely located in the additive manufacturing area. This makes it possible to create delicate or at least complex structures for the temperature control channels, which cannot be produced, for example, by simple drilling.

[0019] By providing a generative area on the laser beam deflection device, it is possible to provide the housing of the laser beam deflection device with twofold protection against thermal deformation. On the one hand, structures that prevent deformation can be created in a simple manner, and on the other hand, existing cooling or temperature control channels can be improved, significantly improving their heat transfer function.

[0020] The flat shape of the tempering channel can be realized in various ways.

[0021] On the one hand, the cooling channel can open from a circular or oval cross-section into a flat cavity, which means that the length and width of the cavity are greater than the height. The cavity can have a cuboid shape, but it can also be designed like a kind of flattened ellipsoid. In the connecting area between the tubular section and the flat section, the cooling channel can taper or narrow conically. Naturally, the cooling channel widens from the tubular section towards the flat section, with the direction being the flow direction of the cooling medium, and it narrows from the flat section to the tubular section.This type of connection between a tubular section and a flat section of the tempering channel naturally applies to all shown designs of both the tubular and the flat section.

[0022] The flat design of the temperature control channel is also achieved by dividing the temperature control channel into several branch channels. The branching can be done in such a way that a tubular section of the temperature control channel opens into the branch channels, but the branch channels can also branch off laterally from the tubular section of the temperature control channel, particularly at right angles.

[0023] The flat section of the tempering channel can be converted back into a tubular section by combining the two channels, as described above, into or with a tubular section of the tempering channel.

[0024] The branch channels are preferably laid out in parallel; they can form a straight line, but they can also be wave-shaped, in the form of a square grid, as is the case with a chain-link fence, or even in a honeycomb shape.

[0025] The reinforcements and / or openings described above can be installed at points on the enclosure wall that are not occupied by a branch duct. This makes it possible to achieve both water cooling and air cooling at the same time. If air cooling is not desired, for example because the temperature control duct is used not only for cooling but also for heating the enclosure, there are no openings in the enclosure or its wall. In this case, only the reinforcements can be combined with the branch ducts. However, the reinforcements can also run over the branch ducts in places, for example if the reinforcements are strip-shaped and run perpendicular to the branch ducts. The reinforcements should not cover the entire surface of a branch duct, as otherwise heat exchange is reduced.

[0026] The housing of the laser beam deflection device comprises at least one non-additively constructed region. Such a region is referred to in the present disclosure as a solid region. Accordingly, a solid region is a pre-machined piece of metal. Instead of metal, any other material that meets the mechanical or other requirements can of course be used. This solid region can be placed in a build chamber to manufacture the laser beam deflection device, so that the additive region is built directly onto and against the solid region. However, the solid region can also be connected to the additive region only after the construction process has been completed. Of course, it is also possible to connect multiple solid regions to one or more additive regions.For example, it is possible for the solid section to form almost the entire housing, with only one or more holes in these sections where additive sections can be inserted. However, the solid section can also represent only a side or end wall of the housing, while other housing walls or parts of housing walls are additively added to the solid section or connected to it after construction. The exact composition of the solid section and the additive section must be determined, particularly depending on economic considerations. The additive sections are usually limited to the necessary minimum, as their production is more expensive and time-consuming than that of solid sections.

[0027] Preferably, the solid area and the generative area are made of the same metal or alloy, since in this case the connection of the areas is particularly easy.

[0028] Particularly advantageously, the laser beam deflection device comprises at least one temperature sensor and a control device that evaluates the sensor data from the temperature sensor, wherein the control device is designed to regulate the temperature control of a temperature control medium in the temperature control channel. In this way, a consistent temperature and thus a consistent shape of the housing can be ensured.

[0029] The control device can influence the temperature by either adjusting the flow temperature of the temperature control medium, i.e., by feeding the temperature control medium into the housing at the required temperature to achieve the desired temperature in the housing. Additionally or alternatively, it is also possible to increase or decrease the flow rate of the temperature control medium to increase or decrease heat exchange. Both measures can be used to vary the temperature control effect of the temperature control medium.

[0030] Instead of a temperature sensor, the control unit can also operate with characteristic curves or parameter sets that are processed depending on predefined events. For example, the flow temperature and / or the flow rate of the temperature control medium can be adjusted depending on the time elapsed since the start of a build process. Typically, the heat output of the laser is constant, so a constant energy input occurs in the laser beam deflection device. Accordingly, the resulting temperature profiles can be determined through preliminary tests, and the temperature control can be adjusted to minimize deformation of the housing.

[0031] In addition, the disclosure also relates to a device for producing three-dimensional objects by solidifying layers, which device has a laser beam deflection device as described. Of course, all embodiments disclosed in connection with the laser beam deflection device alone can also be used in the device for producing three-dimensional objects.

[0032] The device is preferably a laser melting device or a laser sintering device.

[0033] The invention is explained in more detail with reference to advantageous embodiments in the drawing figures. These show Fig. 1 a device for building three-dimensional objects, Fig. 2 an irradiation facility, Fig. 3 a deflecting mirror, Fig. 4 a side wall of the laser beam deflection device in a first embodiment, Fig. 5 a side wall of a laser beam deflection device in a second embodiment, Fig. 6 a side wall of a laser beam deflection device in a third embodiment, Fig. 7 a side wall of a laser beam deflection device in a fourth embodiment, Fig. 8 a section of a temperature control channel in a first embodiment, Fig. 9 a section of a tempering channel in a second embodiment, Fig. 10 a section of a temperature control channel in a third embodiment, Fig. 11 a section of a temperature control channel in a fourth embodiment, Fig. 12 a section of a temperature control channel in a fifth embodiment, Fig. 13 a section of a tempering channel in a sixth embodiment, Fig. 14 shows the flow chart of an operating method for a laser beam deflection device, which does not form part of the invention.

[0034] Fig. 1 shows a device 1 for producing three-dimensional objects. This can be a laser sintering device or a laser melting device. The device 1 comprises a process chamber 2 containing a dosing chamber 3, a build chamber 4, and an overflow chamber 5. Furthermore, a coater 6 is present, which transports the build material 7 from the dosing chamber 3 to the build chamber 4. In the build chamber, the uppermost layer of the build material 7, the so-called working or build plane 8, is solidified at the specified locations by a laser beam 9, so that a three-dimensional object 10 is built. The laser beam 9 is generated by a laser 11, deflected by a laser beam deflection device 12, also called a scan head, and guided through a coupling window 13 into the process chamber 2, where it strikes the working plane 8.By using the laser beam deflection device 12, the laser beam 9 can be directed to predetermined areas of the working plane 8 much more efficiently and quickly than would be possible by rotating or otherwise adjusting the laser 11 itself.

[0035] Fig. Figure 2 shows the path of a laser beam 9 in somewhat greater detail. The laser beam is generated in the laser 11, also called the laser source, and exits it. An intensity control device 14 can be interposed between the laser 11 and the laser beam deflection device 12 to dynamically control the intensity of the laser beam 9. The laser beam 9 then enters the laser beam deflection device 12. There, the laser beam 9 first strikes the Y-deflecting mirror 15 and then the X-deflecting mirror 16. The axes of rotation of the deflection mirrors 15 and 16 are arranged perpendicular to each other. The deflection mirrors 15 and 16 are attached to the housing 17 of the laser beam deflection device 12.

[0036] Fig. Figure 3 shows a deflecting mirror 15 or 16 in more detail. The following refers to deflecting mirror 15 purely as an example, but the explanations naturally also apply to deflecting mirror 16. Fig. Figure 3 shows a mirror arrangement 18 consisting of a galvanometric motor 19, the deflecting mirror 15, and a connecting piece 20 connecting them. Galvanometric motors are used due to their speed; accordingly, the deflecting mirror 15 can be adjusted quickly. The galvanometric motor 19 is attached to a side wall 21 of the housing 17, so that the deflecting mirror 15 is rotatably attached to the side wall 21 via the motor 19. The wall area 22 around the galvanometric motor 19 is particularly important with regard to possible heat-induced deformations. Deformation in this area causes an uncontrolled deviation in the deflection of the deflecting mirror 15, which also deflects the laser beam 9 in a more or less undefined manner.Since even small deviations of the target deflection of the deflection mirror 15 are disproportionately reflected in deviations of the laser beam 9 on the working plane 8, such deviations must be avoided at all costs.

[0037] Fig. 4 shows a design to avoid such deviations. According to Fig. 4, a side wall 21 is divided into a solid area 23 and a generative area 24. The generative area 24 can be connected to the solid area 23, which has a corresponding recess, either after the construction process or, alternatively, the side wall 21 is placed in the construction chamber 4 and the generative area 24 is built directly on the solid area 23. The generative area 24 has reinforcements 25 to strengthen this area. In addition, there are openings 26 in the generative area 24 to enable air exchange and thus cooling of the area.

[0038] Fig. Figure 5 shows an alternative design of the side wall 21, in which the generative area 24 is designed like a chain-link fence. The reinforcements 25 are strip-shaped and have sufficient thickness to support the mirror assembly 18 via the galvanometric motor 19.

[0039] The generative area can be made of the same material as the solid area. However, it can also be made of a material with higher thermal conductivity and / or lower deformability due to heat input.

[0040] An alternative or additional temperature control to prevent deformation of the housing 17 consists in the use of one or more temperature control channels. The exemplary embodiments shown below have in common that the surface of one or more temperature control channels is enlarged in certain sections. Each temperature control channel can have an enlarged surface in one or more sections. The embodiments shown below can also be combined as desired on a single temperature control channel or connected in series. In each case, cross-sections through a side wall are shown below, with cross-sections through side walls to which a galvanometric motor 19 is attached being shown purely as examples. Of course, the temperature control channels can also run through side walls that do not accommodate any devices.

[0041] Fig. 6 shows a side wall 21 consisting of two solid areas and a generative area 24. The temperature control channel 27 consists of three sections 28, 29, 30. Sections 28 and 30 each run in the solid areas 23, while section 29 is arranged in the generative area 24. While sections 28 and 30 of the temperature control channel 27 have a circular cross-section and can be realized, for example, by a simple bore, the temperature control channel 27 in the generative area and in section 29 is divided into branch channels 31. The branch channels 31 run around the recess for the motor 19, so that they can particularly effectively temperature the side wall 21 of the housing 17 in this area, since the branch channels 31 increase the surface area.The cross-sectional area of ​​a branch channel 31 is preferably smaller than the cross-sectional area of ​​the temperature control channel 27, for example in section 28, but the branch channels 31 can also have an approximately identical cross-sectional area to the temperature control channel 27 in section 28 or 30. This results in the flow velocity of the temperature control medium in section 29 being reduced compared to sections 28 and 30, thereby further improving heat exchange. Since the temperature control medium heats up or cools as it passes through the temperature control channel 27, it can also be provided that the cross-sectional area of ​​the temperature control channel 27 changes in one of the sections 28, 29 or 30 or in any other section, thus changing the flow velocity and thus the heat exchange.

[0042] Fig. Figure 7 shows a further embodiment of the branch channels 31. These lead through both the generative area 24 and the motor 19 or its own housing. The housing of the motor 19 is not assigned to the solid area 23 or the generative area 24, but rather is a separate housing. The housing of the motor 19 protrudes, as can be seen from Fig. 3, protrudes from the housing 17, thereby extending the outer surface of the housing 17. On the inside, the solid areas 23, the generative area 24, and the end face of the housing of the motor 19 form a flat surface. The branch channels 31 are continued through the housing of the motor 19.

[0043] In the Fig. 8 - 13 show further embodiments of section 29, with which a surface enlargement can be achieved. The embodiments of the Fig. 8 - 13 may need to be adjusted so that a galvanometric motor 19 can be placed in the middle. As shown in Fig. As shown in Figure 7, the branch channels 31 can be continued in the housing of the motor 19. Otherwise, an adjustment is made by cutting out an opening in the area where the motor 19 is to be arranged.

[0044] Fig. Figure 8 shows sections 28 - 30 of the temperature control channel 27. Sections 28 and 30 are modified in that they no longer open into the branch channels 31 at the front end, but instead bend upwards and downwards and end, with the branch channels 31 branching off in the last and first sections, respectively. The branch channels form a branch channel network. Fig. 9 and Fig. 12 the branch channels are not cross-connected, in the Fig. 8, Fig. 10, Fig. 11 and Fig. 13, however, do. Fig. 8, Fig. 11 and Fig. 13 show a planar cross-connection of sections 28 and 30, each with round or square recesses. This increases the resistance from section 28 to section 30, thereby reducing the flow velocity. Additionally, the surface area of ​​section 29 is enlarged, thereby increasing the heat exchange many times over. Fig. 8, Fig. 10, Fig. 11 and Fig. 13 have a cavity area which is divided by column structures, the cross section of the columns 32 being according to Fig. 8 oval, according to Fig. 10 hexagonal, according to Fig. 11 kite-shaped and according to Fig. 13 is circular. In the Fig. 8, Fig. 10, Fig. 11 and Fig. 13, only a few selected columns 32 have been provided with reference symbols for the sake of clarity. This also applies to the branch channels 31.

[0045] The Fig. 9 and Fig. 12, however, show branch channels 31 connecting the end regions of sections 28 and 30 with straight and corrugated cylindrical tubes, respectively. Fig. 4 - 13 each show only one temperature control channel 27. It is understood that any number of temperature control channels 27 with sections 29 of any desired surface area can be provided on each side wall of the housing 17. The additive region 24 can - as shown - constitute only a small part of a side wall, but the entire housing 17 of the laser beam deflection device 12 can also be constructed additively.

[0046] Fig.14 shows a method for operating a laser beam deflection device 12, which is not part of the invention. In step S1, a heating medium is introduced into the temperature control circuit 27. The heating medium flows through the temperature control channel 27 until a predetermined target temperature (above the initial temperature) of either the housing 17 or the housing environment is reached. Reaching the target temperature can be determined using a temperature sensor; alternatively, the housing can be heated for a predetermined period of time, whereby this period can be determined through preliminary experiments. The period of time may depend on the flow temperature of the heating medium and can be stored as a characteristic curve.

[0047] In the next step S2 a construction process is started.

[0048] The flow temperature of the heat medium is then gradually reduced until it reaches a second target temperature (step S3). The flow temperature can be reduced either depending on the time elapsed since the start of the build process or depending on the previous energy input of the laser. The first approach is suitable if no intensity control device 14 is used and, accordingly, the laser beam delivers a constant energy input or heat input to the laser beam deflection device over time. However, if the intensity of the laser beam varies significantly after leaving the intensity control device 14, the flow temperature can also be adjusted depending on the intensity of the laser beam upon leaving the intensity control device 14.

[0049] Ideally, after the flow temperature has been reduced to a second setpoint, the temperature control can be switched off, so that no more temperature control medium or heating medium needs to be conveyed through the temperature control channel 27. This is possible because, with the method according to the invention, the housing 17 of the laser beam deflection device 12 is no longer designed for a normal temperature such as room temperature, but rather for the operating temperature at maximum heating by the laser beam. With this configuration, the housing only needs to be heated at the beginning of the construction process; thereafter, the heating of the laser beam deflection device 12 is carried out by the laser beam 9 itself. This offers the considerable advantage that only a short-term heating of the laser beam deflection device 12 is required, instead of long-term cooling.Depending on the laser power, cooling may still be necessary, but the cooling performance required is much lower than if the housing 17 of the laser deflection device 12 must be constantly kept at room temperature. LIST OF REFERENCE SYMBOLS 1 device 2 process chambers 3 Dosing chamber 4 Construction chamber 5 Overflow chamber 6 coaters 7 Construction material 8 working level 9 Laser beam 10 three-dimensional object 11 lasers 12 Laser beam deflection device 13 coupling windows 14 Intensity control device 15 Y-deflection mirrors 16 X-deflection mirrors 17 housings 18 Mirror arrangement 19 galvanometric motor 20 connecting piece 21 Side wall 22 Wall area 23 Solid area 24 Generative area 25 Reinforcement 26 Opening 27 Temperature control channel Section 28 Section 29 Section 30 31 branch channel 32 Column

Claims

[1] Laser beam deflection device for a device (1) for building three-dimensional objects (10), comprising at least one deflection mirror (15, 16), a motor (19) for controlling the deflection mirror (15, 16) and a housing (17) accommodating at least the deflection mirror (15, 16) and having an inlet and outlet opening for a laser beam (9), wherein the housing has at least one side wall (21) which consists of a solid area (23), ie a non-generatively built area, and a generative area (24) which is formed by a generative construction process, wherein the side wall (21) has a recess for the motor (19), wherein the housing (17) has at least one tempering channel (27) with three sections (28, 29, 30), which runs at least partially in the generative area (24), wherein the tempering channel (27) in the generative area (24) branches into at least two branch channels (31) in section (29), wherein the branch channels (31) lead around the recess for the motor (19). [2] Laser beam deflection device according to claim 1, characterized by that the tempering channel (27) is formed flat at least in sections. [3] Laser beam deflection device according to claim 2, characterized by that the tempering channel (27) is designed in sections as a flat cavity. [4] Laser beam deflection device according to one of the preceding claims, characterized by that the branch channels (31) are arranged at least partially parallel to one another. [5] Laser beam deflection device according to one of the preceding claims, characterized by that the at least one temperature control channel (27) runs at least partially parallel to the outer and / or inner surface of the housing (17). [6] Laser beam deflection device according to one of the preceding claims, characterized by that the at least one temperature control channel (27) runs along at least one side wall (21) of the housing (17), in particular along a longitudinal wall. [7] Laser beam deflection device according to one of the preceding claims, characterized by that the at least one temperature control channel (27) is designed to receive a temperature control agent in the form of liquid, in particular water or liquid nitrogen, or gas, in particular air. [8] Laser beam deflection device according to one of the preceding claims, characterized by that it has at least two tempering channels (27), wherein the tempering channels (27) are at least partially connected to connecting channels. [9] Laser beam deflection device according to one of the preceding claims, characterized bythat the cross-section of the at least one tempering channel (27) in the housing (17) changes. [10] Laser beam deflection device according to one of the preceding claims, characterized by that the at least one tempering channel (27) continues in the non-generatively constructed area of ​​the housing (17), the solid area (23). [11] Laser beam deflection device according to one of the preceding claims, characterized by that the solid area (23) and the generative area (24) consist of the same metal or alloy. [12] Laser beam deflection device according to one of the preceding claims, characterized by that further components with their own housings are arranged in the housing (17), wherein the at least one temperature control channel (27) leads through at least one own housing. [13] Laser beam deflection device according to one of the preceding claims, characterized byin that it has at least one temperature sensor and a control device evaluating the sensor data of the temperature sensor, wherein the control device is designed to regulate the temperature control of a temperature control medium in the temperature control channel (27). [14] Device for producing three-dimensional objects by solidifying layers, characterized by that it has a laser beam deflection device (12) according to one of the preceding claims.

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