EP3600729A1

EP3600729A1 - Method for the additive manufacture of workpieces

Info

Publication number: EP3600729A1
Application number: EP18724867.9A
Authority: EP
Inventors: Arno Niebling; Michael Protzmann; Markus Holz; Henrik Franz
Original assignee: ALD Vacuum Technologies GmbH
Current assignee: ALD Vacuum Technologies GmbH
Priority date: 2017-05-16
Filing date: 2018-05-15
Publication date: 2020-02-05
Also published as: DE102017110651B4; DE102017110651A1; WO2018210811A1

Abstract

The present invention relates to a method for the additive manufacture of workpieces. Workpieces that can be manufactured in accordance with the method include, for example, turbine blades, but any other geometries can also be produced. The present invention relates to a device and a method for the additive manufacture of workpieces and use of same. Workpieces that can be manufactured in accordance with the method include, for example, turbine blades, but any other geometries can also be produced. The device for the additive manufacture of workpieces comprises at least one radiation source, at least one lowerable lifting surface, at least one material reservoir for a raw material in powder form and at least one process chamber, wherein the lifting surface can be moved between an initial position in the region of influence of the radiation source and an end position below the initial position, and a construction volume for the additive manufacture of workpieces extends between the initial position and end position, wherein the dead volume within the construction volume not required to manufacture the workpiece is determined when the device is used in a method for additive production.

Description

Method for the additive production of workpieces

The present invention relates to a method for the additive production of workpieces. Workpieces that can be produced by the method are, for example, turbine blades, but any other geometries can also be produced.

Devices and methods for the additive production of workpieces are known from the prior art. It is also called "generative manufacturing process" or "SD printing". In these processes, a raw material, usually in powder form, is applied in the form of a layer to a work surface in order to be partially melted or sintered there. Another layer is applied to the layer and processed as with the first layer. In this case, the sections to be melted or sintered are selected such that the three-dimensional workpiece is built up in layers.

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

Also, the cleaning of the process chamber and their preparation for a manufacturing process takes time. Of course, the manufacturing process can not be carried out during this time.

The produced workpieces are very hot immediately after production. Many materials, especially metals, are reactive when hot and must not come into contact with atmospheric oxygen. Therefore, these materials must be allowed to cool to a certain maximum temperature before removal from the evacuated area before removal. During this time, the manufacturing process of another workpiece can not start yet. This is particularly relevant because the vacuum required for the operation of electron beam guns prevents convective heat conduction, so cooling takes a considerable amount of time. The cooling times are also very long in many prior art processes because the powder around a manufactured workpiece conducts the heat relatively poorly. So the cooling after production usually takes several days. Radiation sources suitable for additive production generate high-energy radiation, for example laser or electron beam 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 jet can be drawn over the raw material. In addition, workpieces that exceed a certain size may have a correspondingly large cross-section, so that the focusing of a high-energy beam can cause difficulties.

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

It is an object of the present invention to provide a method, an apparatus and a manufacturing system which overcomes the disadvantages of the prior art methods and apparatus. In particular, it is the object of this invention to provide methods, devices and systems that are particularly economical in terms of required production time, downtime, material usage and energy requirements.

The invention presented herein solves these problems.

method

The invention relates to a method for the additive production of a workpiece, with the steps a. Providing a work table in the area of influence of a set of radiation sources, wherein the set of radiation sources comprises at least one radiation source and wherein the work table has at least one lowerable lifting surface in a starting position, b. Presenting a layer of powdery raw material on the lifting surface, c. Applying radiation from the radiation source to regions of the first material layer which correspond to the desired shape of the workpiece, so that the raw material in the areas is at least partially heated at least to its melting point, d. Lowering the lifting surface from the starting position, in particular by the thickness of the subsequently applied layer, e. Presenting a further layer of raw material on the previously applied layer, f. Applying portions of the further material layer corresponding to the desired shape of the workpiece with radiation from the radiation source so that the powder in the regions is at least partially heated to at least its melting point, g. Repetition of steps d. to f. until the completion of the workpiece, wherein the lifting surface is at the completion of the workpiece in an end position, h. Cooling the finished workpiece on the lifting surface, i. Removal of the workpiece from the lifting surface, characterized by the further steps

- Construction of at least one heat sink on at least a portion of the lifting surface, which is not required for the construction of the workpiece, by applying portions 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 at least to its melting point, wherein the applied areas correspond to the desired shape of the heat sink.

According to the invention, the term "workpiece" refers both to a single workpiece and to a plurality of workpieces. In particular, the method can also be used to produce a plurality of workpieces simultaneously or together with other workpieces.

Determining the section of the lifting surface not required for the production of the workpiece, 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 workpieces or a plurality of workpieces. For this, the device has a construction volume in the process chamber of preferably at least 1 m ³ , in particular even at least 2 m ³ . Accordingly, cooling down after production takes a long time. in particular at least one day or several days (especially for large workpieces).

The raw material is preferably a metal or a metal alloy. In order to obtain workpieces with high surface quality, the raw material should have particle sizes below 500 μm, in particular below 400 μm, below 300 μm or below 200 μm , The particle size of the raw material should also not be too small, since this deteriorates the flowability of the powder and increases its surface, so that the setting of a vacuum takes more time. Smaller particles also slow down the structure of the workpiece. In a preferred embodiment, therefore, the particle size of the raw material is at least 1 μηι, in particular at least 10 μηι, preferably at least 20 μηι and more preferably at least 50 μηι. More preferably, the particle size is 50 to 150 μηι. According to the invention, "particle size" is to be understood as meaning the average particle size measured on the principle of dynamic light scattering.

The lifting surface can be lowered from a starting position into an end position. On the lifting surface raw material is applied in powder form during the process according to the invention. The raw material in powder form is melted or sintered. According to the invention, the condition that the worktable or the lifting surface is located in the sphere of influence of the radiation source means that the worktable or the lifting surface is arranged at least so high that a powder layer located on the lifting surface is melted or sintered mediated by the radiation of the radiation source can be.

The set of radiation sources can be structurally connected to one another, for example by fixing all radiation sources within a set to a mounting plate or otherwise For example, the radiation sources may be individually attached to the device Suitable radiation sources are electron beam guns and lasers, with electron beam guns being preferred.

Electron beam guns have the advantage over lasers of higher, and flexibly adjustable power densities. This higher melting temperatures can be realized. Thus, the electron beam gun is advantageous especially for raw materials with high thermal conductivity (metals, metal alloys) as a radiation source. 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 presintered, so that powder grains sinter to one another to a small extent. Pre-sintering prevents the electrostatic charge-induced "smoke effect" that is otherwise to be feared upon irradiation with electron radiation, and also improves the heat conduction by pre-sintering because the powder grains are brought into closer contact with each other.

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

The method described has the advantage that the dissipation of heat introduced during the process can be substantially increased by the construction of at least one heat sink on at least one section of the lifting surface. The thermal conductivity of the heat sink is much greater than that of the raw material. In this case, the heat sink is in particular constructed so that it is in contact with the lifting surface to allow the heat dissipation via the lifting surface. Thus, heatsinks are also extremely useful after the workpiece has been completed during cooling.

In a preferred embodiment, 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), further preferably at least 100 W / (m ^* K) and especially preferably at least 200 W / (m ^* K) In preferred embodiments according to the invention, the thermal conductivity is even higher, in particular at least 250 W / (m ^* K) and more 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 allows a significant acceleration of the cooling rate and thus of the entire process. Especially when carrying out the process in vacuo - as it is preferred according to the invention - can Use of such lifting surfaces otherwise greatly improve the cooling of the workpieces due to lack of convection.

In one embodiment, the lifting surface can be tempered with a fluid. The tempering may be heating or cooling. By cooling the lifting surface with a fluid, the cooling can be further accelerated. Alternatively, the lifting surface can be heated. By heating the lifting surface, the raw material can be preheated prior to melting or sintering. The fluid for tempering 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 possible with 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 build the heat sink as filled with powdery raw material hollow body. As a result, a great improvement in heat dissipation is achieved without melting or sintering the entire volume of the heat sink. The powdery raw material contained in the heat sink may be reused subsequent to the process. The workpiece is in one embodiment outside of designed as a hollow body heat sinks. In a preferred embodiment, the heat sinks are each surrounded by powdery raw material. In particular, they do not directly adjoin the workpiece. In particular, they do not form the outer boundary of the construction volume. The volume of construction preferably extends between the starting and end position of the lifting surface in height and corresponds in terms of its base area of the lifting surface.

The closer heat sinks are arranged on the workpiece, the more pronounced they support the cooling of the finished workpieces. In this case, preferably, a distance of a heat sink to at least one workpiece is 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 sink during the manufacture of the workpieces, the heat sink can be constructed with a minimum distance and taking into account the final contour of the workpiece.

The inventive method is preferably carried out under vacuum. This preferably corresponds to a pressure of at most 10 ¹ mbar, preferably at most 10 ² mbar or at most 10 ^{~ 3} mbar. Preferably, at least during steps c. to g. and especially during steps b. to g. said pressure.

In one embodiment, before applying the material layer in step c.

and / or before the application of the material layer in step f. a preheating and / or presintering of the material layer. The preheating or pre-sintering can be carried out using a heat source, which may be identical in particular with the radiation source. The preheating or pre-sintering has the advantage that not the entire heat input takes place in one go during the construction of the workpiece. Otherwise, when using electron guns, sputtering of the raw material due to electrostatic charging may otherwise occur.

In one embodiment, the workpiece produced is following step g. cooled. This can be done in a separate chamber into which the workpiece was possibly still located on the lifting surface befindlich. The chamber is referred to herein as a molding chamber.

In one embodiment, the molding chamber is adapted to cool a workpiece therein with a cooling gas. The molding chamber preferably has at least one inlet and / or at least one outlet for the cooling gas. In one embodiment, the forming chamber has at least one means for circulating an amount of cooling gas in the forming chamber. The means may in particular be a fan or a circulating pump. The device according to the invention makes it possible to close the molding chamber and the process chamber, respectively, so that different atmospheres (for example vacuum or inert gas) can be set in the two chambers. In particular, in the molding chamber in which a workpiece cools, cooling with a cooling gas can be promoted without affecting a vacuum in the process chamber. In this case, in one embodiment, cooling gas flows through an inlet. In particular, the cooling gas flows out of the molding chamber through an outlet and / or the cooling gas is circulated in the molding chamber in order to achieve an optimum 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 performed in a device described below.

The device is a device for the additive production of workpieces with a set of radiation sources comprising 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 between an initial position in the influence of the radiation source and an end position below the initial position is movable, and extends between starting position and end position a volume for the additive production of workpieces.

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 at which the additive production of the workpiece takes place.

Unless stated otherwise, "chamber", as in "process chamber", merely means that such a device is a space that can be closed on all sides, so that a controlled atmosphere, in particular a vacuum, can be set. A chamber can according to the invention take any outer shape. The process chamber according to the invention is that chamber in which the additive production of the workpiece takes place. In particular, the sphere of influence of the radiation source is located in the process chamber.

Interiors of the process chamber are in particular closed vacuum-tight. 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 the additive production using electron beam guns, since - in contrast to manufacturing methods such as lasers - a vacuum and not just a protective gas atmosphere must be maintained.

The material reservoir serves to hold the raw material in powder form for the manufacturing process. In this case, the material reservoir may contain raw material for carrying out a plurality of production runs. 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 on; these can be arranged in particular on opposite sides of the influence range of the radiation source. Preferably, the material reservoir is 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 or be distributed in the work area following gravity. In one embodiment, the material reservoir has an optionally closable opening to the process chamber.

For setting 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, i. it is connected to the process chamber so that it can create a vacuum in the process chamber. The device may comprise a plurality of vacuum pumps.

In an embodiment, the method comprises the further steps

Determining 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,

- Occupy the building volume with one or more packing so that at least a part of the dead volume is occupied and remains unoccupied by packing construction volume, the lifting surface has an outer shape, which allows the lifting surface relative to the packing by the volume of lower the initial position to the end position.

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

The described method has the advantage that by occupying the construction volume with at least one filling body, the available volume of construction can be reduced and thus less raw material can be used for the production of a workpiece. Although the entire dead volume with fillers will not be assignable on a regular basis, since irradiation of a material layer always leaves unirradiated areas. These unirradiated areas, which consist of powdery material, but are smaller compared to conventional methods. As a result, less powder must be discarded or recycled. In addition, the thermal conductivity of the powder is poor and in particular lower than the thermal conductivity of the packing, so that the filler can greatly accelerate the cooling of the workpieces. The fillers are inventively removable from the device, so at best releasably connected to the device. The fillers are at least partially in contact with powdered raw material during the process.

The advantages of the method according to the invention are particularly evident in application devices in the form of powder distribution elements (for example doctor blades) which push a powder fraction over the work table and thereby cause the raw material to be deposited 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 filling bodies preferably end at the level of the work table, in particular forming a flat surface with the work table.

In a preferred embodiment, at least one and in particular all packing is made of a material having 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), further preferably at least 100 W / (m ^* K) and especially preferably at least 200 W / (m ^* K) In preferred embodiments according to the invention, the thermal conductivity is even higher, in particular at least 250 W / (m ^* K) and more 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 enables a significant acceleration of the cooling rate and thus of the entire process otherwise greatly reduced due to lack of convection cooling of the workpieces improve.

In one embodiment, a filler can be tempered with a fluid. The tempering may be heating or cooling. By cooling the filler with a fluid, the cooling can be further accelerated. Alternatively, the filler can be heated. By heating the filler, the raw material can be preheated prior to melting or sintering. The fluid for tempering 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 (eg 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 possible with lower intended cooling capacity. As mentioned above, it is preferable not to fill the entire dead volume with random packings since, after the application of areas of the material layer, a residual amount of raw material always remains around the irradiated areas. Another reason why the dead volume is not completely assignable, is that many workpieces have no consistent cross-sections, but a packing can not be moved during manufacture in the horizontal direction. In order to be able to produce at least those workpieces with the advantages of the method of this invention having cavities, in a preferred embodiment of the method of this invention, at least one packing is lowered together with or independently of the lifting surface. This is understood as meaning a lowering of the filling body in relation to the worktable during the execution of the additive production. In this way, the previously occupied by the filler cross-sectional area for the next application of material is released and can be acted upon with radiation. The invention includes embodiments in which at least one and in particular all random packings are not lowered in relation to the work table during the execution of the additive production.

In one embodiment, the device comprises at least one filling body occupying a partial volume of the construction volume, wherein the lifting surface has an outer shape, which makes it possible to lower the lifting surface relative to the packing by the volume from the starting position to the end position.

Also according to the invention is the use of a method of this invention for improving the heat transfer between the manufactured workpiece and the lifting surface.

Brief description of the figures

Figure 1 shows a cross section of an apparatus for carrying out the method according to the invention with lifting surface in the starting position.

Figure 2 shows a cross section of an apparatus for carrying out the method according to the invention with lifting surface in the end position.

Description of the figures

The embodiments according to the invention described below with reference to the figures represent only preferred embodiments of the invention and do not restrict the subject of protection. Features of the methods and uses of this invention described in the description of the drawings are also preferred in view of the methods and uses generally described above.

Figure 1 shows a lifting surface 7, which is located in a starting position at the height of a work table 5 and in the sphere of influence of radiation sources. The lifting surface 7 is lowered or raised by means of the lifting device 13. The presentation of layers of powdery raw material on the lifting surface 7 takes place by providing raw material from the opening 9 of the material reservoir and subsequent distribution of the raw material via the lifting surface 7 by means of the applicator 16. In the volume, which extends between the starting position and end position, is a packing 1 1 arranged.

FIG. 2 shows the same device as FIG. 1 in a later method step of the method according to the invention. In this case, the lifting surface 7 is in the end position at the lower end of the construction volume. On the lifting surface 7 workpieces 10 have been made. Between the workpieces 10 heatsink 22 are arranged. The heat sink 22 are designed as a hollow body. Between the heat sinks 22 powdered raw material 21 is arranged. LIST OF REFERENCES

5 work table

7 lifting area

9 Opening of the material reservoir

10 workpiece

1 1 packing

13 lifting device

16 application device

21 powders

22 heat sink

Claims

claims

1 . Method for the additive production of a workpiece (10), comprising the steps a. Providing a work table (5) in the area of influence of a set of radiation sources, wherein the set of radiation sources comprises at least one radiation source and wherein the work table (5) has at least one lowerable lifting surface (7) in a starting position, b. Presenting a layer of powdery raw material (21) on the lifting surface (7), c. Irradiating portions of the first material layer corresponding to the desired shape of the workpiece (10) with radiation from the radiation source such that the raw material (21) in the regions is at least partially heated to at least its melting point, i. Lowering the lifting surface (7) from the initial position, e. Submitting another layer of raw material (21) on the previously acted upon

Layer, f. Subjecting regions of the further material layer corresponding to the desired shape of the workpiece (10) to radiation from the radiation source so that the powder (21) in the regions is at least partially heated to at least its melting point, g. Repetition of steps d. to f. until the completion of the workpiece (10), wherein the lifting surface (7) is in an end position upon completion of the workpiece (10), h. Cooling of 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 heat sink (22) on at least a portion of the lifting surface (7), which is not required for the construction of the workpiece (10), by applying portions of the material layers in the steps c. and f. with radiation from the radiation source, so that the powder (21) in the areas at least partially is heated to at least its melting point, wherein the applied areas of the desired shape of the heat sink (22) correspond.

2. The method of claim 1, wherein at least two, at least three or at least four heat sinks are constructed (22).

3. The method of claim 1 or 2, wherein the lifting surface (7) consists of a material having a high thermal conductivity and / or is tempered with a fluid.

4. The method of claim 3, wherein the tempering is heating or cooling.

5. The method of claim 3 or 4, wherein the fluid is liquid or gaseous.

6. The method according to at least one of claims 3 to 4, wherein the fluid is selected from water, thermal oil, inert gas, air and liquid metal.

7. The method according to at least one of the preceding claims, wherein at least one heat sink (22) is a hollow body which is filled with powdery raw material (21).

8. The method according to at least one of the preceding claims, wherein the set of radiation sources comprises at least two, at least three or at least four radiation sources.

9. The method according to at least one of the preceding claims, wherein at least the steps c. to g. be carried out at a pressure of at most 10 ³ bar.

10. The method according to at least one of the preceding claims, wherein the radiation source is an electron beam gun.

1 1. Method according to at least one of the preceding claims, wherein the workpiece (10) cools in a separate chamber from the process chamber, preferably using a circulated cooling gas.

12. Use of a method according to at least one of the preceding claims for improving the heat transfer between the manufactured workpiece (10) and lifting surface (7).