DE102017110651B4 - Process for additive manufacturing of workpieces - Google Patents

Abstract

Method for the additive manufacturing of a workpiece (10), with the steps a. Providing a work table (5) in the area of influence of a set of radiation sources, the set of radiation sources comprising at least one radiation source and wherein the work table (5) has at least one lowerable lifting surface (7) in an initial position, b. Placing a layer of powdery raw material (21) on the lifting surface (7), c. Exposing areas of the first material layer which correspond to the desired shape of the workpiece (10) with radiation from the radiation source, so that the powdery raw material (21) in the areas is at least partially heated to at least its melting point, d. Lowering the lifting surface (7) from the starting position, e. Presenting a further layer of powdery raw material (21) on the previously applied layer, f. Exposing areas of the further material layer which correspond to the desired shape of the workpiece (10) with radiation from the radiation source, so that the powdery raw material (21) in the areas is at least partially heated to at least its melting point, g. Repeat steps d. to f. until the workpiece (10) is completed, the lifting surface (7) being in an end position when the workpiece (10) is completed, h. Cooling the finished workpiece on the lifting surface (7), i. Removal of the workpiece (10) from the lifting surface (7), characterized by the further steps: - Construction of at least one cooling body (22) on at least one section of the lifting surface (7) which is not required for the construction of the workpiece (10), by applying areas of the material layers in steps c. and f. with radiation from the radiation source, so that the powdery raw material (21) in the areas is at least partially heated to at least its melting point, the impinged areas corresponding to the desired shape of the heat sink (22) and the heat sink (22) so is built up so that it is in contact with the lifting surface (7), wherein the lifting surface (7) consists of a material with a high thermal conductivity and is tempered with a fluid, the radiation source being an electron beam gun and at least steps c. to g. be carried out at a pressure of at most 10-3 mbar and the heat sinks (22) not directly adjoining the workpiece (10) and before the material layer is applied in step c. with radiation and / or before the material layer is exposed in step f. with radiation, the material layer is preheated and / or pre-sintered.

Description

The present invention relates to a method for additive manufacturing of workpieces. Workpieces that can be manufactured using the method are, for example, turbine blades, but any other desired geometries can also be manufactured.

Devices and methods for the additive production of workpieces are known from the prior art. One also speaks of “generative manufacturing processes” or “3D printing”. In this process, a raw material, usually in powder form, is applied in the form of a layer to a work surface in order to be melted or sintered in sections. Another layer is applied to the layer and proceed as with the first layer. The sections to be melted or sintered are selected in such a way that the three-dimensional workpiece is built up in layers.

The DE 10 2012 216 515 A1 discloses a method for the layer-by-layer production of low-warpage three-dimensional objects with the aid of cooling elements. In a Selective Laser Sintering (SLS) process from polymer powders, not only the objects but also cooling elements are produced at the same time. This is intended to reduce the warpage of the components and the thermal load on the polymer material. The cooling element is a hollow body, preferably arranged in the center of the installation space, from which the powder material can be sucked off at the end of the construction and replaced by a preferably liquid coolant. The components are arranged around the cooling element. Contact between the cooling elements and the building platform is not shown.

Furthermore, the EP 2 910 362 A1 a powder-bed-based additive manufacturing process in which a support structure is built that also serves to dissipate heat. As an improvement on the previously known massive support structures, which are also used for the dissipation of heat from the component into the building platform, a tree structure for such support structures is proposed. In the preferred arrangement, the “branches” of the trees attack the component surface and the “trunk” sits on the construction platform. In this way, the separation points for tools and only small-area contact points with the surface of the component can be easily reached, whereby the smallest possible surface damage is possible.

However, the methods and devices from the prior art have a number of disadvantages. For example, many processes are not economical. This is due to the fact that a vacuum is required, especially when using electron beams for melting or sintering. After completion of a manufacturing process, the workpiece must be removed from the process chamber, which results in the loss of vacuum. The restoration of the vacuum again takes time, during which the manufacturing process of another workpiece cannot yet begin.

Cleaning the process chamber and preparing it for a manufacturing process also takes time. Of course, the manufacturing process cannot be carried out during this time.

The workpieces produced are very hot immediately after production. Many materials, especially metals, are reactive when they are hot and must not come into contact with atmospheric oxygen. Therefore, these materials must cool down to a certain maximum temperature before they can be removed from the evacuated area. During this time, the manufacturing process for another workpiece cannot yet begin. This is particularly relevant because the vacuum required to operate electron beam guns prevents heat conduction by convection, so that cooling takes a considerable amount of time. The cooling times in many processes of the prior art are also very long because the powder arranged around a manufactured workpiece conducts the heat relatively poorly. It usually takes several days to cool down after production.

Radiation sources suitable for additive manufacturing generate high-energy radiation, for example laser or electron radiation, which in most processes is scanned over the applied layers. The speed of melting or sintering depends not only on the time required to bring the raw material to the required temperature, but also on the scanning speed with which the beam can be drawn over the raw material. In addition, workpieces that exceed a certain size can have a correspondingly large cross section, so that focusing a high-energy beam can cause difficulties.

In addition, the use of material for additive manufacturing processes is sometimes immense, since the application quantity required for a layer does not depend on the size of the cross-sectional area of the workpiece to be manufactured, but on the size of the work surface to which the raw material is applied. Once raw material has been used, even if it has not been melted or sintered, it must be processed before it can be reused. Especially with expensive materials like For metals or metal alloys, it is desirable to use as little material as possible.

It is an object of the present invention to provide a method, a device and a production system with which the disadvantages of the methods and devices from the prior art are overcome. In particular, it is the object of this invention to provide methods, devices and systems which are particularly economical with regard to the required production time, downtime, use of materials and energy requirements.

The invention presented herein achieves these objectives.

Procedure

1. a. Bereitstellen eines Arbeitstisches im Einflussbereich eines Satzes von Strahlungsquellen, wobei der Satz Strahlungsquellen wenigstens eine Strahlungsquelle umfasst und wobei der Arbeitstisch wenigstens eine absenkbare Hubfläche in einer Ausgangslage aufweist,
2. b. Vorlegen einer Schicht pulverförmigen Rohmaterials auf der Hubfläche,
3. c. Beaufschlagen von Bereichen der ersten Materialschicht, die der gewünschten Form des Werkstückes entsprechen, mit Strahlung aus der Strahlungsquelle, so dass das Rohmaterial in den Bereichen zumindest teilweise wenigstens auf seinen Schmelzpunkt erhitzt wird,
4. d. Absenken der Hubfläche aus der Ausgangslage, insbesondere um die Dicke der nachfolgend aufzutragenden Schicht,
5. e. Vorlegen einer weiteren Schicht Rohmaterials auf der zuvor beaufschlagten Schicht,
6. f. Beaufschlagen von Bereichen der weiteren Materialschicht, die der gewünschten Form des Werkstückes entsprechen, mit Strahlung aus der Strahlungsquelle, so dass das Pulver in den Bereichen zumindest teilweise wenigstens auf seinen Schmelzpunkt erhitzt wird,
7. g. Wiederholung der Schritte d. bis f. bis zur Fertigstellung des Werkstücks, wobei die Hubfläche sich bei Fertigstellung des Werkstückes in einer Endlage befindet,
8. h. Abkühlen des fertiggestellten Werkstückes auf der Hubfläche,
9. i. Entnahme des Werkstückes von der Hubfläche, gekennzeichnet durch die weiteren Schritte:
   • - Aufbau wenigstens eines Kühlkörpers auf wenigstens einem Abschnitt der Hubfläche, der für den Aufbau des Werkstückes nicht benötigt wird, durch Beaufschlagen von Bereichen der Materialschichten in den Schritten c. und f. mit Strahlung aus der Strahlungsquelle, so dass das Pulver in den Bereichen zumindest teilweise wenigstens auf seinen Schmelzpunkt erhitzt wird, wobei die beaufschlagten Bereiche der gewünschten Form des Kühlkörpers entsprechen und wobei der Kühlkörper so aufgebaut wird, dass er in Kontakt mit der Hubfläche steht,

wobei die Hubfläche aus einem Material mit einer hohen Wärmeleitfähigkeit besteht und mit einem Fluid temperiert wird,
wobei die Strahlungsquelle eine Elektronenstrahlkanone ist und zumindest die Schritte c. bis g. bei einem Druck von höchstens 10^-3 bar durchgeführt werden und wobei die Kühlkörper nicht direkt an das Werkstück grenzen und
wobei vor dem Beaufschlagen der Materialschicht in Schritt c. mit Strahlung und/oder vor dem Beaufschlagen der Materialschicht in Schritt f. mit Strahlung ein Vorwärmen und/oder Vorsintern der Materialschicht erfolgt.The invention relates to a method for additive manufacturing of a workpiece, with the following steps

1. a. Providing a work table in the area of influence of a set of radiation sources, the set of radiation sources comprising at least one radiation source and wherein the work table has at least one lowerable lifting surface in a starting position,
2. b. Placing a layer of powdery raw material on the lifting surface,
3. c. Exposing areas of the first material layer which correspond to the desired shape of the workpiece with radiation from the radiation source, so that the raw material in the areas is at least partially heated to at least its melting point,
4. d. Lowering the lifting surface from the starting position, in particular by the thickness of the layer to be applied subsequently,
5. e. Placing another layer of raw material on top of the previously applied layer,
6. f. exposure of areas of the further material layer which correspond to the desired shape of the workpiece with radiation from the radiation source so that the powder in the areas is at least partially heated to its melting point,
7. G. Repeat steps d. to f. up to the completion of the workpiece, whereby the lifting surface is in an end position when the workpiece is completed,
8. H. Cooling of the finished workpiece on the lifting surface,
9. i. Removal of the workpiece from the lifting surface, characterized by the following steps:
   • - Construction of at least one heat sink on at least one section of the lifting surface that is not required for the construction of the workpiece, by applying areas of the material layers in steps c. and f. with radiation from the radiation source, so that the powder in the areas is at least partially heated to at least its melting point, the impinged areas corresponding to the desired shape of the heat sink and the heat sink being constructed so that it is in contact with the lifting surface stands,

wherein the lifting surface consists of a material with a high thermal conductivity and is tempered with a fluid,
wherein the radiation source is an electron beam gun and at least steps c. to g. be carried out at a pressure of no more than 10 ^-3 bar and where the heat sinks are not directly adjacent to the workpiece and
wherein before the material layer is applied in step c. with radiation and / or before the material layer is exposed in step f. with radiation, the material layer is preheated and / or pre-sintered.

According to the invention, the term “workpiece” relates both to a single workpiece and to a plurality of workpieces. In particular, the method can also be used to produce several workpieces at the same time or together with other workpieces.

The section of the lifting surface not required for the production of the workpiece is determined, for example, by comparing a model, in particular a CAD model, of the workpiece with the lifting surface of the device.

The method of this invention and the apparatus are particularly suitable for the manufacture of large work pieces or a plurality of work pieces. For this, the device offers a structural volume in the process chamber of preferably at least 1 m ³ , in particular even at least 2 m ³ . Accordingly, a lot of time is required for the cooling after production, in particular at least one day or several days (in particular in the case of large workpieces).

The raw material is preferably a metal or a metal alloy. Titanium and titanium alloys, nickel-based alloys, superalloys and steels are particularly preferred. In order to obtain workpieces with a high surface quality, the raw material should have particle sizes which are below 500 µm, in particular below 400 µm, below 300 µm or below 200 µm. The particle sizes of the raw material should but also not be too small, as this worsens the flowability of the powder and increases its surface area, so that setting a vacuum takes all the more time. Smaller particles also slow down the build-up of the workpiece. In a preferred embodiment, the particle size of the raw material is therefore at least 1 μm, in particular at least 10 μm, preferably at least 20 μm and particularly preferably at least 50 μm. The particle size is particularly preferably 50 to 150 μm. According to the invention, “particle size” is preferably understood to mean the average particle size measured according to the principle of dynamic light scattering.

The lifting surface can be lowered from an initial position to an end position. During the process according to the invention, raw material in powder form is applied to the lifting surface. The raw material in powder form is melted or sintered. According to the invention, the condition means that the work table or the lifting surface is in the area of influence of the radiation source, that the work table or the lifting surface is at least so high that a powder layer located on the lifting surface is melted or sintered by the radiation from the radiation source can be.

According to the invention, a “set of radiation sources” means the entirety of the radiation sources used for additive manufacturing within a device. The set of radiation sources can be structurally connected to one another, for example by fastening all radiation sources within a set to a fastening plate or in some other way. Alternatively, the radiation sources can each be attached individually to the device. Suitable radiation sources are electron beam guns and lasers, electron beam guns being according to the invention.

Electron beam guns have the advantage over lasers of higher and flexibly adjustable power densities. This means that higher melting temperatures can be achieved. The electron beam gun is therefore particularly advantageous as a radiation source for raw materials with high thermal conductivity (metals, metal alloys).

In addition, an electron beam gun offers the possibility of using relatively large beam diameters or spot sizes, so that preheating with the radiation source can also be carried out well. In particular, the raw material can be pre-sintered so that powder grains are sintered with one another to a small extent. Pre-sintering prevents the atomization caused by electrostatic charging (“smoke effect”), which is otherwise to be feared when exposed to electron beams. Furthermore, the heat conduction is improved by the pre-sintering, since the powder grains are brought into closer contact with one another.

According to the invention, the radiation source is an electron beam gun. If the set of radiation sources contains more than one radiation source, then preferably all of the radiation sources in the set are electron beam guns. In a preferred embodiment, the set of radiation sources has at least two, at least three or at least four radiation sources. The use of several radiation sources has proven to be advantageous because in this way, even with workpieces with a large cross-sectional area or a plurality of workpieces, uniformly good focusing on the sections to be irradiated is possible and the working speed can be significantly increased.

The method described has the advantage that the dissipation of heat introduced during the method can be significantly increased by constructing at least one cooling body on at least one section of the lifting surface. The thermal conductivity of the heat sink is significantly greater than that of the raw material. According to the invention, the heat sink is constructed in such a way that it is in contact with the lifting surface in order to enable heat to be dissipated via the lifting surface. This means that heat sinks are extremely useful for cooling down even after the workpiece has been completed.

According to the invention, the lifting surface is made of a material with a high thermal conductivity. In this way, the heat dissipation can be further improved. A “high thermal conductivity” is in particular a thermal conductivity at 0 ° C. of at least 13 W / (m * K), more preferably at least 40 W / (m * K), furthermore preferably at least 100 W / (m * K) and very particularly preferably at least 200 W / (m * K). In embodiments preferred according to the invention, the thermal conductivity is even higher, in particular at least 250 W / (m * K) and particularly preferably at least 300 W / (m * K). Suitable materials are metals and metal alloys, in particular steel, copper or copper alloys.

The use of lifting surfaces with high thermal conductivity enables a significant acceleration of the cooling rate and thus of the entire process. Especially when the method is carried out in a vacuum - as is the case according to the invention - the use of such lifting surfaces can improve the cooling of the workpieces, which is otherwise severely restricted due to the lack of convection.

According to the invention, the lifting surface is tempered with a fluid. Tempering can be a Be heating or cooling. The cooling can be accelerated further by cooling the lifting surface with a fluid. Alternatively, the lifting surface can be heated. By heating the lifting surface, the raw material can be preheated before melting or sintering. The fluid for temperature control is liquid or gaseous under standard conditions (DIN 1343: 1990). Liquid fluids are preferred. The fluid is preferably selected from water, thermal oil, inert gas, air and liquid metal (e.g. NaK, Wood's alloy). Water is preferred because of its low cost. The use of gaseous fluid is less advantageous due to the lower heat capacity, but is possible with a lower intended cooling capacity.

In a preferred embodiment of the method, at least two, at least three or at least four heat sinks are built up on the lifting surface. It has proven to be sufficient to construct the heat sink as a hollow body filled with powdery raw material. This greatly improves the heat dissipation without having to melt or sinter the entire volume of the heat sink. The powdery raw material in the heat sink can be reused after the process. In one embodiment, the workpiece is located outside of heat sinks designed as hollow bodies. In a preferred embodiment, the heat sinks are each surrounded by powdery raw material. According to the invention, they do not directly adjoin the workpiece. In particular, they do not form the outer limit of the building volume. The structural volume preferably extends in height between the starting and end positions of the lifting surface and corresponds to the lifting surface in terms of its base area.

The closer the heat sinks are to the workpiece, the more pronounced they support the cooling of the finished workpieces. A distance between a heat sink and at least one workpiece is preferably not more than 30 mm, preferably not more than 25 mm, not more than 20 mm, not more than 15 mm, not more than 10 mm or not more than 5 mm. Due to the targeted construction of the heat sinks during the production of the workpieces, the heat sinks can be constructed with a minimal distance and taking into account the final contour of the workpiece.

The process according to the invention is carried out under vacuum. According to the invention, this corresponds to a pressure of at most 10 ^-3 mbar. According to the invention, at least during steps c. to g. and in particular during steps b. to g. the said pressure.

According to the invention, before the material layer is applied in step c. and / or prior to the application of the material layer in step f., preheating and / or pre-sintering of the material layer. The preheating or pre-sintering can take place using a heat source, which in particular can be identical to the radiation source. Preheating or pre-sintering has the advantage that not all of the heat input takes place in one go when building the workpiece. Otherwise, especially when using electron beam guns, the raw material may be atomized due to electrostatic charging.

In one embodiment, after step g. chilled. This can be done in a separate chamber into which the workpiece was transferred while it was still on the lifting surface. The chamber is referred to herein as the mold chamber.

In one embodiment, the mold chamber is designed to cool a workpiece located therein with a cooling gas. The mold chamber preferably has at least one inlet and / or at least one outlet for the cooling gas. In one embodiment, the mold chamber has at least one means for circulating an amount of cooling gas located in the mold chamber. The means can in particular be a fan or a circulation pump. The device according to the invention makes it possible to close the mold chamber and the process chamber in each case, so that different atmospheres (e.g. vacuum or inert gas) can be set in the two chambers. In particular, in the mold chamber in which a workpiece is cooled, the cooling can be assisted with a cooling gas without a vacuum in the process chamber being impaired. In one embodiment, cooling gas flows through an inlet. In particular, the cooling gas flows out of the mold chamber again through an outlet and / or the cooling gas is circulated in the mold chamber in order to achieve an optimal cooling effect.

In one embodiment, the cooling gas is an inert gas, in particular helium, argon, xenon and / or nitrogen.

The method of this invention is preferably carried out in an apparatus described below.

• - einem Satz von Strahlungsquellen, der wenigstens eine Strahlungsquelle umfasst,
• - einem Arbeitstisch in dem Einflussbereich mit wenigstens einer absenkbaren Hubfläche,
• - wenigstens einem Materialreservoir für ein Rohmaterial in Pulverform,
• - wenigstens einer Prozesskammer,

wobei die Hubfläche zwischen einer Ausgangslage im Einflussbereich der Strahlungsquelle und einer Endlage unterhalb der Ausgangslage bewegbar ist, und sich zwischen Ausgangslage und Endlage ein Bauvolumen für die additive Herstellung von Werkstücken erstreckt.The device is a device for the additive manufacture of workpieces

• - a set of radiation sources which comprises at least one radiation source,
• - a work table in the area of influence with at least one lowerable lifting surface,
• - at least one material reservoir for a raw material in powder form,
• - at least one process chamber,

wherein the lifting surface can be moved between a starting position in the area of influence of the radiation source and an end position below the starting position, and a structural volume for the additive manufacturing of workpieces extends between the starting position and the end position.

In a preferred embodiment, the set of radiation sources is arranged in an upper section of the process chamber, in particular above the work table on which the additive manufacturing of the workpiece takes place.

Unless stated otherwise, “chamber”, as in “process chamber”, only means that a component so designated is a space that can be closed on all sides, so that a controlled atmosphere, such as a vacuum, in particular, can be set. According to the invention, a chamber can assume any external shape. According to the invention, the process chamber is the chamber in which the additive manufacturing of the workpiece takes place. In particular, the area of influence of the radiation source is located in the process chamber.

Interiors of the process chamber can in particular be closed in a vacuum-tight manner. This means that the volume leak rate of the chamber is less than 1 * 10 ^-2 mbar * l / s, in particular less than 5 * 10 ^-3 mbar * l / s. The volume leak rate is preferably measured at 20 ° C. and 1013 hPa ambient pressure. In this way, the desired atmosphere can be set and maintained in the chamber. Vacuum-tight chambers are required for additive manufacturing using electron beam guns, since here - unlike in manufacturing processes such. B. with lasers - a vacuum and not just a protective gas atmosphere must be maintained.

The material reservoir is used to hold the raw material in powder form for the manufacturing process. The material reservoir can contain raw material for carrying out several manufacturing processes. The material reservoir can be arranged in the form of one or more at least partially funnel-shaped chambers in an upper part of the process chamber. In an advantageous embodiment, the device has at least two material reservoirs; these can in particular be arranged on opposite sides of the area of influence of the radiation source. The material reservoir is preferably arranged above the plane in which the melting or sintering process takes place. In this way, the raw material in powder form can flow down into the work area or be distributed there, following the force of gravity. In one embodiment, the material reservoir has an optionally closable opening to the process chamber.

To set a vacuum in the process chamber, the device preferably has at least one vacuum pump, in particular a diffusion pump. In one embodiment, a vacuum pump is associated with the process chamber; H. it is connected to the process chamber in such a way that it can create a vacuum in the process chamber. The device can have several vacuum pumps.

• - Ermitteln des für die Herstellung des Werkstückes nicht benötigten Totvolumens innerhalb des Bauvolumens, der dem Raum zwischen Ausgangslage und Endlage der Hubfläche entspricht,
• - Belegen des Bauvolumens mit einem oder mehreren Füllkörpern, so dass wenigstens ein Teil des Totvolumens belegt ist und ein von Füllkörpern nicht belegtes Bauvolumen verbleibt,

wobei die Hubfläche eine äußere Form aufweist, die es erlaubt, die Hubfläche relativ zu den Füllkörpern durch das Bauvolumen von der Ausgangslage in die Endlage abzusenken.In one embodiment, the method comprises the further steps

• - Determination of the dead volume not required for the production of the workpiece within the construction volume, which corresponds to the space between the starting position and the end position of the lifting surface,
• - Occupying the building volume with one or more fillers, so that at least part of the dead volume is occupied and a building volume that is not occupied by fillers remains,

wherein the lifting surface has an outer shape which allows the lifting surface to be lowered from the starting position into the end position relative to the filler bodies through the structural volume.

The dead volume not required for the production of the workpiece within the structural volume can be determined, for example, by comparing a model, in particular a CAD model, of the workpiece with the structural volume of the device.

The described method has the advantage that by covering the building volume with at least one filler body, the available building volume can be reduced and thus less raw material can be used for the production of a workpiece. It is true that the entire dead volume cannot regularly be covered with fillers, since unirradiated areas always remain after a layer of material has been irradiated. These non-irradiated areas, which consist of powdery material, are smaller compared to conventional methods. This means that less powder has to be discarded or recycled. In addition, the thermal conductivity of the powder is poor and in particular less than the thermal conductivity of the filler body, so that the filler body can greatly accelerate the cooling of the workpieces. According to the invention, the filling bodies can be removed from the device, that is to say connected to the device in a detachable manner. During the process, the filling bodies are at least partially in contact with powdered raw material.

The advantages of the method according to the invention come into play particularly in application devices in the form of powder distribution elements (e.g. doctor blades) which push a powder fraction over the work table and thereby cause the raw material to be presented on the lifting surface. Such powder distribution elements have the advantage that they can also smooth the applied material layer. In order to be able to work with such application devices, the filler bodies preferably end at the level of the work table, in particular with the formation of a flat surface with the work table.

In a preferred embodiment, at least one and in particular all of the filler bodies are made of a material with a high thermal conductivity. In this way, the heat dissipation can be further improved. A “high thermal conductivity” is in particular a thermal conductivity at 0 ° C. of at least 13 W / (m * K), more preferably at least 40 W / (m * K), furthermore preferably at least 100 W / (m * K) and very particularly preferably at least 200 W / (m * K). In embodiments preferred according to the invention, the thermal conductivity is even higher, in particular at least 250 W / (m * K) and particularly preferably at least 300 W / (m * K). Suitable materials are metals and metal alloys, in particular steel, copper or copper alloys. The use of fillers and especially those with high thermal conductivity enable a significant acceleration of the cooling rate and thus of the entire process. Particularly when the method is carried out in a vacuum - as is the case according to the invention - the use of packing elements can improve the cooling of the workpieces, which is otherwise severely restricted due to the lack of convection.

In one embodiment, a filler body can be temperature-controlled with a fluid. The temperature control can be heating or cooling. The cooling can be accelerated further by cooling the filling body with a fluid. Alternatively, the packing can be heated. By heating the filler body, the raw material can be preheated before melting or sintering. The fluid for temperature control is liquid or gaseous under standard conditions (DIN 1343: 1990). Liquid fluids are preferred. The fluid is preferably selected from water, thermal oil, inert gas, air and liquid metal (e.g. NaK, Wood's alloy). Water is preferred because of its low cost. The use of gaseous fluid is less advantageous due to the lower heat capacity, but is possible with a lower intended cooling capacity.

As mentioned above, the entire dead volume is preferably not filled with fillers, since after areas of the material layer have been acted upon, a residual raw material always remains around the irradiated areas. Another reason why the dead volume cannot be completely covered is that many workpieces do not have constant cross-sections, but a filler body cannot be moved in the horizontal direction during production. In order to be able to produce at least those workpieces which have cavities with the advantages of the method of this invention, in a preferred embodiment of the method of this invention at least one filler body is lowered together with or independently of the lifting surface. This is understood to mean a lowering of the filling body in relation to the work table while the additive manufacturing is being carried out. In this way, the cross-sectional area previously occupied by the filler body is free for the next application of material and can be exposed to radiation. The invention encompasses embodiments in which at least one and in particular all of the filler bodies are not lowered in relation to the work table while the additive manufacturing is being carried out.

In one embodiment, the device comprises at least one filling body occupying a partial volume of the structural volume, the lifting surface having an external shape that allows the lifting surface to be lowered relative to the filling bodies through the structural volume from the starting position into the end position.

It is also preferred to use a method of this invention to improve the heat transfer between the manufactured workpiece and the lifting surface.

Figure list

• 1 shows a cross section of a device for carrying out the method according to the invention with a lifting surface in the starting position.
• 2 shows a cross section of a device for performing the method according to the invention with a lifting surface in the end position.

Description of the figures

The embodiments according to the invention described below with reference to the figures merely represent preferred embodiments of the invention and do not restrict the subject matter of protection. Features of the methods and uses of this invention described in the context of the description of the figures also represent preferred features with regard to the methods and uses generally described above.

1 shows a lifting surface 7th who are in a starting position at the height of a work table 5 and is in the area of influence of radiation sources. The lifting area 7th using the lifting device 13 lowered or raised. Placing layers of powdered raw material on the lifting surface 7th takes place by providing raw material from the opening 9 of the material reservoir and subsequent distribution of the raw material over the lifting surface 7th using the application device 16 . In the construction volume that extends between the starting position and the end position, there is a filler body 11 arranged.

2 shows the same device as 1 in a later process step of the process according to the invention. The lifting surface is located here 7th in the final position at the lower end of the construction volume. On the lifting surface 7th are workpieces 10 been made. Between the workpieces 10 are heat sinks 22nd arranged. The heat sinks 22nd are designed as a hollow body. Between the heat sinks 22nd is powdery raw material 21st arranged.

List of reference symbols

5

Work table

7th

Lifting area

9

Opening of the material reservoir

10

workpiece

11

Packing

13

Lifting device

16

Application device

21st

powder

22nd

Heat sink

Claims (8)

A method for the additive manufacturing of a workpiece (10), comprising the steps a. Providing a work table (5) in the area of influence of a set of radiation sources, the set of radiation sources comprising at least one radiation source and wherein the work table (5) has at least one lowerable lifting surface (7) in an initial position, b. Placing a layer of powdery raw material (21) on the lifting surface (7), c. Exposing areas of the first material layer which correspond to the desired shape of the workpiece (10) with radiation from the radiation source, so that the powdery raw material (21) in the areas is at least partially heated to at least its melting point, d. Lowering the lifting surface (7) from the starting position, e. Submitting a further layer of powdery raw material (21) on the previously applied layer, f. Applying radiation from the radiation source to areas of the further material layer which correspond to the desired shape of the workpiece (10), so that the powdery raw material (21) in the areas is at least partially heated to at least its melting point, g. Repeat steps d. to f. until the workpiece (10) is completed, the lifting surface (7) being in an end position when the workpiece (10) is completed, h. Cooling the finished workpiece on the lifting surface (7), i. Removal of the workpiece (10) from the lifting surface (7), characterized by the further steps: - Construction of at least one cooling body (22) on at least one section of the lifting surface (7) which is not required for the construction of the workpiece (10), by applying areas of the material layers in steps c. and f. with radiation from the radiation source, so that the powdery raw material (21) in the areas is at least partially heated to at least its melting point, the impinged areas corresponding to the desired shape of the heat sink (22) and the heat sink (22) so is built up so that it is in contact with the lifting surface (7), wherein the lifting surface (7) consists of a material with a high thermal conductivity and is tempered with a fluid, the radiation source being an electron beam gun and at least steps c. to g. be carried out at a pressure of at most 10 ^-3 mbar and wherein the heat sinks (22) do not directly adjoin the workpiece (10) and wherein before the material layer is applied in step c. with radiation and / or before the material layer is exposed in step f. with radiation, the material layer is preheated and / or pre-sintered. Procedure according to Claim 1 , at least two, at least three or at least four heat sinks (22) being built up. Procedure according to Claim 1 or 2 , the tempering being a heating or cooling. Method according to at least one of the preceding claims, wherein the fluid is liquid or gaseous. Method according to at least one of the preceding claims, wherein the fluid is selected from water, thermal oil, inert gas, air and liquid metal. Method according to at least one of the preceding claims, wherein at least one cooling body (22) is a hollow body which is filled with powdery raw material (21). Method according to at least one of the preceding claims, wherein the set of radiation sources has at least two, at least three or at least four radiation sources. Method according to at least one of the preceding claims, wherein the workpiece (10) is cooled in a chamber separate from the process chamber, preferably using a circulated cooling gas.

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