EP4244005A1

EP4244005A1 - Method and system for the additive manufacturing of a workpiece

Info

Publication number: EP4244005A1
Application number: EP21810006.3A
Authority: EP
Inventors: Thorsten Löwer
Original assignee: Pro Beam GmbH and Co KG
Current assignee: Pro Beam GmbH and Co KG
Priority date: 2020-11-13
Filing date: 2021-11-10
Publication date: 2023-09-20
Also published as: WO2022101246A1; US20240009738A1; DE102020129971A1

Abstract

A method for the additive manufacturing of a workpiece (22) from a powdered material comprises the following steps: a) providing - a device (15, 17) for receiving a powder bed (20) of the powdered material, in particular in a vacuum process chamber (11), and - a beam generator (12), which is designed to direct an energy beam (13) onto laterally different locations of the powder bed (20); b) applying the powdered material in layers to the powder bed (20); c) creating the workpiece (22) layer by layer in the powder bed (20) by selectively fusing the powdered material with the energy beam (13); d) while creating the workpiece (22), creating in addition to the workpiece (22) a cooling structure (30) in the powder bed (20) by selectively fusing the powdered material with the energy beam (13), wherein the cooling structure (30) is designed to dissipate heat.

Description

Process and system for the additive manufacturing of a workpiece

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for additively manufacturing a workpiece from a powdered material.

The invention also relates to a system for carrying out such a method.

2. Description of the Prior Art

Additive manufacturing processes are characterized by the joining of volume elements to form a three-dimensional structure, in particular by a layered structure. Among other things, methods are used in which individual powder particles of a powdery material in a powder bed are selectively connected point by point with an energy beam, thus creating a dimensionally stable workpiece with a 3D structure layer by layer.

The material can be solidified into a workpiece by sintering the powder particles or by completely melting the powder particles and then allowing the material to solidify by means of an energy beam, in particular a laser beam or electron beam. Materials are also known in which chaining reactions, adhesion processes or the like are activated or stimulated by the energy beam. In the following, for the sake of simplicity, all types and degrees of melting/sintering/gluing/activation of the material and thus for each type of connection and each type of powdered material will only be referred to as selective melting, especially since this is also common among experts shortened, only selective melting is spoken of.

In particular, the processing of metal powder by selective electron beam melting (SEBM) allows the production of metallic structures complex geometries while at the same time being able to be manipulated quickly and precisely and with a high degree of automation.

In contrast to laser beam melting, the melting of the material with an electron beam takes place in a vacuum, since the collision of the electrons with air molecules would lead to large energy losses and scattering. Process chambers of electron beam systems are therefore usually evacuated before operation and operated at pressures of 10′ ⁵ to 10′ ² mbar.

During the production of the workpiece, temperatures of over 1000 °C are reached on the material surface due to the energy input of the electron beam and optional additional heating of the powder bed. Therefore, the finished workpiece must be cooled to a certain maximum temperature before it can be removed from the process chamber.

However, the cooling of the workpiece in the process chamber in the vacuum takes several hours to several days, depending on the material, the nature of the powder bed and the construction volume. Because in a vacuum, the heat exchange is very low due to the lack of convection, so that the cooling rates are very low and the cooling times are very long.

Flooding the process chamber with air early to shorten the cooling time is disadvantageous for various reasons. The hot surface of the workpiece reacts with the oxygen contained in the air. The consequences of this can be uncontrolled changes in the structure of the workpiece, e.g. due to oxidation of the metal.

One way to speed up the cooling process is to introduce an inert gas such as helium. The inert gas makes it possible to transport heat away more quickly via convection and to avoid reactions with the metal surface. However, noble gases are generally expensive and increase the process costs.

Alternatively, the problem of long cooling times can be solved by adapting the system and running the cooling and manufacturing processes in parallel. An efficient method and a system for it are disclosed in DE 10 2020 104 381.3. DE 10 2017 110 651 A1 also discloses an electron beam system in which a heat sink is produced in a powder bed during the manufacture of a workpiece using the 3D printing process. The heat sink is preferably contacted with a lifting surface on which the powder bed is arranged.

A method for selective laser sintering (SLS) is known from DE 10 2012 216 515 A1, in which tubular heat sinks are produced in the powder bed during 3D printing, through which a cooling fluid can be conducted.

A similar method is known from DE 10 2013 212 620 A1, which describes in more detail how a functional interface is formed in the lifting surface under the powder bed in order to conduct coolant through the tubular heat sink.

SUMMARY OF THE INVENTION

The object of the invention is therefore to specify a method for additively manufacturing a workpiece which is improved with regard to the long cooling times described. The object of the invention is also to specify a device and a system with which the cooling times in the additive manufacturing of a workpiece can be improved.

This object is achieved according to the invention by a method for additively manufacturing a workpiece from a powdered material, which comprises the following steps: a) providing a device for receiving a powder bed made from the powdered material, in particular in a vacuum process chamber, and a beam generator for this purpose is set up to direct an energy beam to laterally different locations of the powder bed; b) Layered application of the powdered material to the powder bed; c) Layer-by-layer production of the workpiece in the powder bed by selectively connecting the powdery material with the energy beam; wherein d) during the production of the workpiece, in addition to the workpiece, a cooling structure is produced in the powder bed by selectively connecting the powdered material to the energy beam, wherein the cooling structure is set up to dissipate heat, and wherein e) the cooling structure is designed in such a way that between the Cooling structure and the device for receiving a powder bed of powdered material remains and the cooling structure extends at the end of the production of the workpiece up to a top final layer of the powder bed.

As already explained, when processing a powdery material with an energy beam, a certain amount of energy is introduced into the powder bed, which has to be transported away after the material has solidified again. Powder is generally a very poor conductor of heat and stores the heat locally in the powder bed. Additive manufacturing processes are often carried out in a vacuum, which means that the heat transport to the environment is limited to heat radiation.

The method according to the invention solves the described problem of insufficient heat dissipation after the end of the manufacturing process and, as a result, long cooling times, in that an additional cooling structure is produced simultaneously during the additive manufacturing of the workpiece in the powder bed with the energy beam. This means that a cooling structure is solidified in the powder bed, through which the heat can be dissipated in a targeted manner by conduction.

In this way, the lack of heat transport due to a lack of convection and poorly thermally conductive powdered material can be compensated.

The simultaneous manufacture of the cooling structures with the workpiece in the same powder bed made of the same material eliminates the risk of contamination from the subsequent introduction of coolants. Due to the fact that powdered material remains between the cooling structure and the device for receiving a powder bed, the heat can be prevented from being given off to components of the system in the process chamber. The cooling structure is therefore preferably formed only after a certain number of loose powder layers above a construction platform.

Since, according to the invention, the cooling structure extends to the uppermost final layer of the powder bed when the production of the workpiece is completed, the heat can instead be dissipated at the top, in particular only after the production process.

Advantageously, the cooling structure is only indirectly thermally coupled to the construction platform via powder lying in between, i.e. with a lower thermal conductivity, so that the entire system heats up less. This in turn is advantageous for the cooling times, particularly in series production.

The last layer of powder applied in the process is considered to be the final layer.

The structures preferably become thicker towards the top, with the cross-sectional area being greatest in the top layer.

Provision is preferably made for the cooling structure to be specified as a function of a desired heat distribution.

The design of the cooling structure is therefore based on how the heat generated during the additive manufacturing of the workpiece has to be dissipated. Corresponding software modeling of the heat conduction can be used to specify the cooling structure depending on the shape of the workpiece.

Provision is preferably made for the workpiece and/or the powder bed to be cooled after step d), in particular in the vacuum of the vacuum process chamber, in that heat is dissipated via the cooling structure.

This shortens the cooling time after the workpiece has been manufactured. This is particularly important in vacuum process chambers. Provision is preferably made for the workpiece to be separated from the powder bed and the cooling structure after step d) and for the powder bed and the cooling structure, in contrast to the workpiece, to be disposed of systematically.

In contrast to other workpieces, which are produced at the same time as a first workpiece in an additive manufacturing process, the cooling structure is created primarily for the purpose of improving heat conduction. This means that the cooling structure is basically not recycled like a workpiece but is systematically disposed of. For example, the cooling structure is melted down together with a residue of the powder bed that is still in powder form to form raw material and ground again into powder. The workpiece, on the other hand, is exploited, for example through sale. Systematically means that the cooling structures are usually disposed of, with the retention of individual cooling structures, for example for training or advertising purposes, being harmless for this purpose.

Provision is preferably made for the cooling structure to be designed in such a way that powdered material remains between the cooling structure and the workpiece.

This means that the cooling structure is not directly connected to other components in the powder bed, so that at least a certain volume between the fixed structures is filled with powder. Since the cooling structure is not connected to the workpiece to be manufactured, there are no additional post-processing steps on the workpiece that are otherwise required when removing permanently connected structures.

Provision is preferably made for the cooling structure to be designed in multiple parts.

The cooling structure can be designed in several parts and adapted to the shape of the construction container and the workpiece to be produced. Large connected volumes of powder can thus be avoided.

Provision is preferably made for the cooling structure to have a cross-sectional area which is largest in the final layer. In the uppermost layers before the completion of the construction, the transverse area of the cooling structure is made as large as possible in order to form the largest possible heat radiation area. By introducing the largest heat dissipation surface towards the end of the manufacturing process, the heat is only dissipated after the workpiece has been completed and the temperature field is kept constant during construction. After the end of the process, the heat can be transported away more quickly and the cooling process is shortened.

The final layer preferably consists entirely of solidified segments, which are connected downwards to the elongated cooling structures and are separated from one another by powder channels in order to facilitate unpacking of the finished construction container. The segments are designed in such a way that the largest possible area is available for heat radiation. The distance between the segments can vary.

The top layer of the powder bed can be contacted with a cooling plate. The attached body draws additional heat from the cooling structures. The cooling of the cooling plate as well as the cooling of the cooling structure can take place actively or passively. Cooling ribs or fins can be additively manufactured on the cooling structures.

It is preferably provided that the cooling structure comprises one or more branches.

Branches in the structure increase the effect of local heat dissipation. The volume reached by the cooling can thus be distributed as constantly as possible over the installation space and thus enable a more homogeneous temperature field in the installation space. The branches of the cooling structure can be designed in the form of fins or branched.

Provision is preferably made for the cooling structure to be actively cooled.

Basically, the cooling structures always dissipate the heat passively, resulting in better thermal conductivity along the cooling structure compared to the usual loose powder bed. However, active cooling via the cooling structure can also be provided in order to increase the heat dissipation. For example, according to one embodiment, the cooling elements can be hollow. In this process, only the outline of the structure is melted, which then ends up in a hollow, powder-filled mold. After completion of construction, this cavity can be filled with a cooling fluid, for example a coolant, and/or can flow through it, so that the cooling structure is actively cooled. The coolant can then be connected to a heat exchanger, for example.

It is therefore preferably provided that the cooling structure has at least one cavity through which a fluid can be conducted in order to be actively cooled.

The object according to the invention is achieved by a cooling structure for dissipating heat from a powder bed during the additive manufacturing of a workpiece, characterized in that the structure is not connected to the workpiece with the workpiece.

The cooling structure is preferably not connected to a construction platform or a base plate, but is separated from other components of the system by a certain number of loose powder layers. This can prevent the heat from being given off to components of the system in the process chamber.

The cooling structure is preferably not connected to the workpiece. As a result, the workpiece does not have to be reworked in order to remove residues of the cooling structure on the material surface.

Workpieces that are manufactured using the method according to the invention and the system according to the invention can be found, inter alia, in the aerospace industry as turbine blades, impellers and transmission mounts in helicopters; in the automotive industry as turbocharger wheels and wheel spokes; in medical technology as orthopedic implants and prostheses; as a heat exchanger and in tool and mold making.

The powdered material can include all electrically conductive materials suitable for the electron beam process. Preferred examples are metallic or ceramic materials, in particular titanium, copper, nickel, aluminum and alloys thereof, such as Ti-6AI-4V, an alloy of titanium, 6 wt% aluminum and 4 wt% vanadium, Al-SilOMg and titanium aluminides (TiAl).

Further exemplary materials are nickel-based alloys such as NiCr19NbMo, iron and iron alloys, in particular steels such as tool steel and stainless steel, copper and alloys thereof, refractory metals, in particular niobium, molybdenum, tungsten and alloys thereof, precious metals, in particular gold, magnesium and alloys thereof, Cobalt-based alloys such as CoCrMo, high-entropy alloys such as AICo-CrFeNi and CoCrFeNiTi, and shape memory alloys.

The powdery material used preferably has an average grain size D50 of 10 μm to 150 μm.

With regard to the system, the object of the invention is achieved by a system for the additive manufacture of a workpiece from a powdered material, with a) a device for receiving a powder bed made of the powdered material to be processed and b) a beam generator which is set up to emit an energy beam to straighten laterally different locations of the powder bed; wherein c) the plant is designed to carry out one of the methods described above.

Provision is preferably made for the system to have a heat dissipation element which can be brought into contact with the cooling structure after the workpiece has been produced.

This has the advantage that the heat can also be dissipated more quickly, since the heat is then given off to the heat dissipation element as a further heat sink in the chain. The heat dissipation element can in turn conduct the heat to other components of the system. The contacting can be done by lowering onto the cooling structure, such as opening it up, or sliding it on to the side, for example a metal block. The heat dissipation element can comprise a material with high thermal conductivity, in particular greater than 100 Wm' ¹ K' ¹ , such as copper.

Provision is preferably made for the heat dissipation element to have a fluid connection for connection to the cavity of the cooling structure.

As a result, cooling fluid, for example a gas or water, can be conducted through the cooling structure in the powder bed and active cooling can thus be brought about.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. In these show:

FIG. 1 shows a schematic view of a system according to the invention with a powder container;

FIG. 2 shows a side view of the powder bed during additive manufacturing of workpieces and cooling structures

FIG. 3 shows a side view of the powder bed after the production of workpieces and cooling structures has been completed

Figure 4 is a side view of the powder bed after completion of fabrication of work pieces and cooling structures with branches

FIG. 5 shows a side view of the powder bed after completion of the production of workpieces and cooling structures with an increased cross-sectional area in the final layer

FIG. 6 embodiments of the cooling structure FIG. 7 shows a side view of the powder bed after the production of workpieces and cooling structures has been completed, the final layer being contacted by a cooling plate.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows an electron beam system 10 with a process chamber 11 in which an electron beam generator 12 for generating an electron beam 13 is arranged. In the present exemplary embodiment, the electron beam generator 12 with an optional deflection device 14, for example a magnetic optics unit, is arranged above a lifting table 15 with a lifting plate and with a receiving frame, which serves as a spatially limited powder container which receives a powder bed 20 made of a powdery material to be processed.

A powder application device 16 with a squeegee (not shown), which can be moved over the lifting table 15, is arranged above the receiving frame. The powder application device 16 has a container (not shown) for the powdered material 20, from which the material can be applied to the powder bed 21 as the uppermost loose layer 21 by a displacement movement.

The movement of the electron beam 13 relative to the powder bed 20 to laterally different locations in the powder bed 20 can take place by deflecting the electron beam in the deflection device 14 or by laterally displacing the lifting table 15.

Also located in the powder bed 20 is a base plate 17 on which the workpiece 22 is formed layer by layer.

A control unit 23 is connected via one or more signal transmission lines 24 to the essential components of the electron beam system 10, in particular to the electron beam generator 12 and the magneto-optical unit 14, in order to control the entire production process. 2 shows the powder bed 20 during the additive manufacturing process of the workpiece 22. It can also be seen from FIG. The workpieces 22 can be arranged not only next to each other but also one above the other in the powder bed 20 .

The additive manufacturing process begins with the application of layers of powder to the base plate 17. The base plate 17 is located in the construction container over a certain volume of powdered material. The powdered material in the powder bed 20 is then selectively connected, in particular fused, here at specific lateral locations of the powder bed 20 with the electron beam 13 to form a dimensionally stable cross-sectional structure. By repeating this sequence, the workpiece 22 is then created layer by layer as a 3D structure.

In particular, cross sections of support structures can be melted from the first powder layers. The support structures are usually connected to the base plate 17 and the workpiece 22 and stabilize the subsequent workpiece during manufacture. Depending on the selected process, operating parameters and materials, the construction of the workpiece can also start directly on a large number of loose powder layers without support structures.

Simultaneously with the creation of the workpiece 22, however, not only the cross-section of the workpiece 22 is melted, but also the cross-section of one or more cooling structures 30. The cooling structures 30 can start in the same layer of powder as the workpiece 22, in later layers during the build-up or directly on the base plate.

Figure 3 shows the powder bed 20 after construction is complete. To make the display clearer, both the powder and the build container are not visible.

Cooling structures 30 are distributed over the installation space in order to avoid large, poorly thermally conductive powder volumes between the components. The cooling structures 30 are positioned as close as possible to the workpieces 22, but without touching them. In the embodiment of the invention shown in FIG. 3, a cooling structure 30 is essentially rod-shaped, with the diameter of the rod increasing towards the end of construction, ie towards the top in the construction space. The cooling structure 30 reaches its greatest diameter in the final layer. The final layer is the last layer of powder applied and possibly partially fused.

Depending on the workpiece 22 to be manufactured, however, the cooling structures 30 can also be formed one below the other in a construction space in many different forms.

For example, FIG. 4 shows a finished construction with a branched cooling structure 30. In order to make the representation clearer here too, neither the powder nor the construction container are visible.

The individual cooling structure 30 can, for example, have one or more, in particular horizontal, crossbeams on a vertical structure 36, so that branches 32 arise. In addition, the cooling structures 30 can be connected to the vertical structures 36 of other cooling structures 30 . The crossbars can be of different lengths in order to be positioned as close as possible to the contour of the workpieces 22 without making direct contact with them. The length of the vertical structures 36 can also vary.

FIG. 5 shows an exemplary embodiment in which the cooling structures 30 are each terminated by square terminating segments 34 . In FIG. 5 the terminating layer is formed almost completely from the terminating segments 34 of the cooling structures 30 . Each end segment 34 is connected to at least one vertical cooling structure 30 and is directly fused.

The thickness of the finishing segment 34 depends on the geometry of the workpieces 22 and the material and consists of at least one layer of the fused powder, preferably several, in order to obtain a stable plate. The final layer is not melted flat, as this would lead to problems when unpacking. The individual segments 34 are therefore separated by channels of unfused powder. As a The last layer of powder applied is referred to as the final layer. The shape of the end segments 34 is not limited to squares and, as shown in FIG. 3, can also be round or of any shape.

Figure 6 shows a selection of embodiments of the cooling structures 30 that does not restrict the idea of the invention.

FIGS. 6a) and 6b) show a rod-shaped cooling structure 30 with a round cross-section, which becomes larger towards the top and is terminated by a round segment. The round segment can be used as an end segment, or an additional end segment can be attached.

Figures 6c) and 6d) show a cooling structure 30 with a rectangular cross section and branches 32.

The cooling structure 30 shown in FIGS. 6e) and 6f) is designed in the shape of a cone or a truncated cone.

The thickness of the cross section and the length of the individual structures can vary. For example, a cooling structure 30 can also be formed helically around the workpieces 22 .

Also suitable are cooling structures 30 which, like tree roots, combine from different parts of the powder bed 20 to form a thicker strand.

One or more cooling structures 30 can be bounded by end segments 34 .

FIG. 7 shows a side view of the powder bed 20 after the production of workpieces 22 and cooling structures 30 has been completed, with the closing segments 34 being contacted by a cooling plate 38 as a heat dissipation element.

The cooling plate 38 can have passive cooling elements such as cooling fins and/or cooling channels, which are actively cooled by a coolant, in particular a cooling fluid. To The cooling plate 38 can be connected to a coolant circuit by coolant lines.

The cooling plate can be made of a material with high thermal conductivity, in particular greater than 200 Wm" ¹ K" ¹ , such as copper.

After completion of construction, the cooling plate 38 can be introduced into the evacuated process chamber and placed on the closing segments 34 . Alternatively, the cooling plate 38 may already be in the chamber and lowered or slid onto the powder bed 20 after the build is complete.

Alternatively, the cooling plate 38 or the end segments 34 can be additionally cooled with gas that is introduced into the process chamber. Due to the better thermal conductivity compared to vacuum, the heat transport can be improved. The gas is preferably an inert gas in order to avoid reactions with the powdered material. The gas can be in a circuit and cooled outside the plant.

The cooling structures 30 are generated by a control unit before or during construction. The shape and position depends on a model for a desired heat distribution that is as optimal as possible and the associated temperature distribution during and/or after the production of the workpiece 22.

The exact structure of the cooling structure 30 can even be adjusted in real time during the manufacturing process, for example based on continuously measured temperatures. reference sign

10 electron beam system

11 process chamber

12 Electron gun 13 Electron beam

14 Magnetic optics unit

15 lifting table

16 powder application device

17 base plate, build platform 20 powder bed

21 Top powder layer, final layer

22 workpiece

23 control unit

24 signal transmission lines 30 cooling structure

32 branch

34 final segment

36 Vertical structure

38 cooling plate

Claims

PATENT CLAIMS Method for the additive manufacturing of a workpiece (22) from a powdered material, comprising the following steps: a) Providing a device (15, 17) for receiving a powder bed (20) made from the powdered material, in particular in a vacuum process chamber (11 ), and a beam generator (12) which is set up to direct an energy beam (13) onto laterally different locations of the powder bed (20); b) applying the powdered material in layers to the powder bed (20); c) creating the workpiece (22) in layers in the powder bed (20) by selectively connecting the powdery material with the energy beam (13); d) during the production of the workpiece (22), in addition to the workpiece (22), a cooling structure (30) is produced in the powder bed (20) by selectively connecting the powdered material to the energy beam (13), the cooling structure (30) being set up for this purpose is to dissipate heat, characterized in that e) the cooling structure (30) is designed in such a way that powdered material remains between the cooling structure (30) and the device (15, 17) for receiving a powder bed (20) and the cooling structure (30 ) at the end of the production of the workpiece (22) extends to an uppermost final layer of the powder bed (20). Method according to Claim 1, characterized in that the cooling structure (30) is specified as a function of a desired heat distribution. Method according to one of the preceding claims, characterized in that after step d) the workpiece (22) and / or the powder bed (20), in particular in the vacuum of the vacuum process chamber (11), are cooled by the cooling structure (30) heat is dissipated. Method according to one of the preceding claims, characterized in that after step d) the workpiece (22) is separated from the powder bed (20) and the cooling structure (30) and the powder bed (20) and the cooling structure (30) in contrast to the workpiece (22) is systematically disposed of. Method according to one of the preceding claims, characterized in that the cooling structure (30) is designed in such a way that powdery material remains between the cooling structure (30) and the workpiece (22). Method according to one of the preceding claims, characterized in that the cooling structure (30) is designed in several parts. Method according to Claim 6, characterized in that the cooling structure (30) has a cross-sectional area (34) which is largest in the finishing layer. Method according to one of the preceding claims, characterized in that the cooling structure (30) comprises one or more branches (32). Method according to one of the preceding claims, characterized in that the cooling structure (30) is actively cooled. Method according to Claim 9, characterized in that the cooling structure (30) has at least one cavity through which a cooling fluid can be passed for active cooling. System (10) for the additive manufacturing of a workpiece (22) from a powdered material - 19 - a) a device (15, 17) for receiving a powder bed (20) of the powdered material to be processed and b) a beam generator (12) which is set up to project an energy beam (13) onto laterally different locations of the powder bed (20) to judge; characterized in that c) the plant (10) is designed to carry out the method according to any one of claims 1 to 10. Plant according to Claim 11, characterized in that the plant has a heat dissipation element (38) which can be brought into contact with the cooling structure (30) after the production of the workpiece (22). System according to Claim 12 in conjunction with Claim 10, characterized in that the heat dissipation element (38) has a fluid connection for connection to the cavity of the cooling structure (30).