EP3837070A1

EP3837070A1 - 3d-metal-printing method and arrangement therefor

Info

Publication number: EP3837070A1
Application number: EP19762302.8A
Authority: EP
Inventors: Kai K.O. Bär; Karl NEULINGER; Lars-Erik RÄNNAR; Andrey KOPTYUG
Original assignee: Value and Intellectual Properties Management GmbH; Additive Innovation And Research Sweden AB; Aim Sweden AB
Current assignee: Value and Intellectual Properties Management GmbH; Additive Innovation And Research Sweden AB; Aim Sweden AB
Priority date: 2018-08-16
Filing date: 2019-08-09
Publication date: 2021-06-23
Also published as: DE102018120015A1; WO2020035109A1; JP7170142B2; US20210178487A1; JP2021535963A; CN112839758A

Abstract

The invention relates to a 3D-metal-printing method for producing a spatial metal product substantially consisting of a metal powder or metal filaments as the starting material, the powder or the filaments being structured layer-by-layer by applying starting material layers to a respectively previously produced layer and selective local heating of predefined points of the layer above a sintering or melting temperature of the powder and sintering or fusing the molten points with the underlying layer and optional tempering of the points, wherein at least the respectively newly applied starting material layer is formed by planar irradiating IR radiation in such a manner that a radiation spot having a surface area of at least 5mm², more specifically of more than 20mm² and even more specifically of more than 100mm², is pre-heated and/or, following the local heating of the predetermined points, is post-treated for thermal stress compensation.

Description

3D metal printing process and arrangement for such

description

The invention relates in particular to an electron beam-based 3D metal printing method for producing a spatial metal product in the

Essentially from a metal powder or metal filaments, the

Metal product layer by layer by applying layers of starting material to a respective previously generated layer and selective local heating of predetermined points of the layer above a sintering or melting temperature and sintering or fusion of the melted points with the underlying layer at the corresponding points and a preliminary Heating of the existing partial metal product and / or a thermal aftertreatment is carried out. It also relates to an arrangement for performing such a method.

In recent years, a large number of processes have been developed for the layered construction of spatial metal products, which are summarized under the terms "additive manufacturing" or "3D printing". These processes are based in part on melting and solidification steps and then exclude a selective local heating previously applied layers of starting material, which is also referred to here as “point-by-point” or “point-by-point scanning” heating. To produce metal products, in particular from relatively high-melting metals, such as titanium, a coordinate control is usually carried out via the Layers of raw material, movable laser beam or electron beam are used.

In practice, laser beam processes (LMB) currently dominate, which, because of the high temperatures required to locally melt the top layer of the product under construction, have to use an energy-rich laser beam. Because of the emerging in the top layer

Depending on the product geometry, softening and thermal tensions sometimes require complex support structures that have to be removed from the finished product in a complex manner. The high temperatures also lead to undesirable “caking” of the starting material powder or the starting material filaments outside the contour of the product to be produced. Detaching such baked powder or filament portions from the finished product also requires effort and often leaves an undesirably uneven product surface. caked

In addition, starting material cannot easily be recovered and used to manufacture further products, so that the use of the starting material in such processes leaves something to be desired.

As a rule, the finished products have to be subjected to a subsequent thermal treatment (tempering, annealing) to relieve tension due to the selective thermal loads that occur in the manufacturing process. Depending on the size and geometry of the product, this takes a considerable amount of time and thus significantly reduces the productivity of the laser-based processes.

Electron beam processes (EBM processes) require a lot of equipment and are currently only economically replaceable for products with relatively small dimensions and are therefore relatively little used. With them

Usually a preheating of the uppermost starting material layer before local melting by means of a “stochastic” scanning of the entire surface with the electron beam, which further increases the outlay in terms of apparatus and control and also considerably extends the manufacturing time of the product. On the other hand, thermal stresses are much less pronounced here, and the measures mentioned above for them

Mastering or eliminating their consequences is largely eliminated. The invention is based on the object of specifying an improved method of the generic type and an arrangement for its implementation, with which high productivity, economical use of materials and moderate energy consumption and thus overall reduced product costs

simultaneous fulfillment of high quality requirements can be achieved.

This object is achieved in its process aspect by a 3D metal printing process with the features of claim 1 and in its device aspect by an arrangement with the features of claim 9. expedient

Developments of the inventive concept are the subject of the dependent

Expectations.

It is a concept of the present invention, a pre-heating before the local, "point-by-point" melting of newly applied material layers and / or a parallel supportive heating during the point-by-point

Melt only to be carried out in the areas (layers) of the metal product that are actually to be processed. According to a relative

independent aspect of the invention, a thermal aftertreatment immediately after local melting is equally area or

made in layers.

Another idea of the invention is to perform the preheating or post-heating not spot-wise as in the established electron beam methods, but rather over a relatively large area (compared to the spot diameter of an electron beam). In particular, the preheating should take place over an area of at least 5 mm ² , more particularly of more than 20 mm ² and even more particularly of more than 100 mm ² . Various contours of the radiation spot can be realized here, but from a practical point of view this will generally be rectangular. With a rectangular radiation spot, a scanning pre-heating or post-heating of the entire surface of the respective starting material layer can be implemented reliably and with relatively little control effort and with a short treatment tent.

Infrared (IR) radiation available at very low cost is used as the energy source, this expressly including the use of near-IR radiation, that is to say those with a radiation density maximum in the wavelength range between 0.8 and 1.5 mhi. In practically significant versions, an aluminum, stainless steel or titanium powder or also refractory metal powder or powder made of alloys with these metals is used as the metal powder. A combination with ceramic or other non-metallic powder is also possible. In principle, the process can also be carried out with filament-shaped starting materials or as granules.

In one embodiment, the IR radiation is sequentially in sections

Sections of the total area of the respective starting material layer are irradiated, the selective local heating via the sintering or

Melting temperature is carried out for predetermined points within a preheated section. The pre-heating or voltage-reducing area after-heating thus “wanders” in particular in preparation and accompanying with the local heating via the sintering or melting temperature over the surface of the particular one to be treated

Starting material layer away.

In a configuration that is preferred from the current perspective, a

stripe-shaped, i.e. the shape of a narrow rectangle

Radiation spot created on the surface of the metal product under construction, which extends over the entire width or length of the product. This strip is then moved across the surface perpendicular to its direction of extension, so that the entire surface of the last starting material layer is successively preheated.

The geometry of the radiation spot, especially the width of a strip-shaped radiation spot, is adjusted by choosing a reflector with a suitable geometry in accordance with the parameters of the IR emitter or NIR emitter used in such a way that the power density achieved meets the process requirements. An important aspect here is that driving over the entire surface with the radiation spot to be preheated is coordinated with the subsequent selective local (selective) heating of the material for sintering and melting. The whole process should be in the interest of a high

Process economics take as little time as possible. However, if the exposure to IR radiation is used for after-heating for the purpose of voltage reduction or annealing or the like, the physical conditions for the effect to be achieved must be primarily observed. As with conventional methods, in a further embodiment the selective local heating of predetermined points for sintering or melting and for annealing by scanning the starting material layer with a

Causes electron beam. It makes sense to synchronize the selective application of the preheated starting material layer with the electron beam to the above-mentioned area-specific and strip-shaped application with the radiation used for preheating. In particular, the electron steel should hit optimally preheated (and not yet somewhat cooled) points of the starting material layer. The control of the electron beam deflection must therefore be linked to the control of the IR irradiation device.

In expedient refinements of the method, the power density of the IR radiation irradiated over a large area or “migrating” on the surface of the uppermost starting material layer is above 1 MW / m ² , and the radiation from at least one halogen radiator, in particular a plurality, is considered to be near IR radiation Halogen lamps, with a lamp temperature of up to 3200 K, in particular in the range from 2900 K to 3200 K, are used.

The preheating according to the invention enables the application of much thicker layers of material than in the previous EBM processes, from the current point of view a thickness of more than 150 mm, more particularly of more than 300 mm and even more particularly of more than 500 mm. The invention ensures that the starting material layers dimensioned in this way are completely warmed and, if necessary, also sufficient heat conduction into an underlying layer for better connection of the successive layers or to their layers

Property improvement contributes.

To what extent high quality products are made from such thick

Having material layers built up with a high level of productivity is what the

Electrode beam-based processes from the possibility of use

powerful electron beam sources and associated deflection and

Depend on focusing devices. In any case, the procedure proposed here creates extensive conditions for this.

In further embodiments of the proposed method, it is provided that depending on the melting temperature and other parameters of the processing metal or the alloy selected preheating temperature, in particular in the range between 600 and 1200 ° C, and

is regulated in particular by a time and / or radiation density control of the area radiation of the IR radiation. For example, a temperature setting in the range between 600 and 800 ° C appears for the processing of titanium alloys and in the range between 1000 and 1200 ° C for nickel-based alloys or so-called super alloys.

For the optimization of the overall process is especially at

electron-beam-based method of maintaining a material-specific predetermined temperature range ("window") of the respective processed layer for a predetermined time is important. The influence of the rather flat IR radiation and the rather punctiform electron beam is therefore preferred on the control side to ensure such a temperature / time window vote.

Overall, the proposed solution enables a significant reduction in process times, both in relation to the layer and in relation to an overall product, in the order of 50% or more.

For the person skilled in the art, advantageous embodiments of the proposed arrangement largely result from the method aspects explained above, so that extensive explanations are largely avoided. However, the following device aspects are pointed out:

While the structure of the overall arrangement largely corresponds to the well-known 3D printer, whose function is based on the sequential local melting of layer-by-layer applied metal powders or filaments, there is a special feature in the design of the device for surface heating of the topmost layer of starting material, in the sense of a Pre-heating before local melting and / or a thermal after-treatment to equalize the tension immediately after melting.

This device has an IR irradiation device for irradiation of IR radiation with a high power density on a predetermined area

at least 5 mm ² , more specifically of more than 20 mm ² , even more particularly of more than 100 mm ² in the area of the work table. From the current perspective, the Further development of the EBM technology including the present invention also a simultaneous preheating much larger

Area areas should be considered, especially if the technology is made applicable to products that are significantly larger than those produced.

The wording “in the area of the work table” is to be understood in a general sense and does not necessarily mean that the IR irradiation device is placed perpendicularly above the work table, nor does it mean that its lateral extension is that of the work table

matches. With a suitable reflector geometry, the IR irradiation device can have a smaller footprint than the work table and can also be positioned diagonally above or even laterally from this.

When using the present invention in the context of the EBM process, which is carried out in a high vacuum, the NIR irradiation device

in particular to place and operate in the vacuum chamber, and it must be positioned such that any interference with the scanning of the product surface by the electron beam is prevented.

In a practically proven embodiment, the special NIR radiation device has at least one rod-shaped (linear)

Halogen emitters, in particular a plurality of halogen emitters, with an associated reflector in such a way that the radiation from the or each infrared emitter is concentrated in the direction of the work table. In other configurations, however, the IR irradiation device can also comprise an array of high-performance NIR laser diodes, and in such an embodiment it is also possible to largely dispense with special reflectors.

In a further embodiment, the plurality of halogen spotlights with an associated reflector are mounted above the work table in a position-controlled manner in at least one axis direction of an XY plane. This

Execution serves to implement a process control in which the preheating is carried out only for a specific Tell surface section of the metal product being created and this area “wanders” over the surface to be processed. As an alternative to this, it can be provided that the plurality of halogen spotlights with an associated reflector are attached in a stationary manner or at most vertically adjustable above the work table.

In a manner known per se, the means for effecting a selective local heating of predetermined points include a previously applied point

Starting material layer associated with an electron beam gun

Deflection devices for beam positioning according to the desired

Product geometry.

The invention provides, at least in certain embodiments, several significant advantages over methods according to the prior art.

In comparison to heat chamber solutions, the heating essentially only enables the last starting material layer immediately before local sintering or melting to heat large workpiece volumes, and is therefore basically energy-saving and reduces the thermal load on the overall device.

Furthermore, the procedure according to the invention reduces the permanent action of relatively high temperatures on areas not sintered or fused according to the program of starting material layers processed in earlier method steps and thus unintentional softening and

Deterioration of the non-sintered powder in those layers, which can significantly improve the efficiency of the recovery of recyclable metal powder after the completion of a product.

Since, according to the invention, larger temperature differences can be set between the "points" of the powder or filament layers to be melted and not to be melted, such undesired softening effects are significantly reduced, if not completely eliminated. In conventional methods, the finished product is often required Such cleaning steps can be largely dispensed with when using the invention, in order to extensively clean from such adhering softening areas, and it is also largely possible to dispense with sieving or other preparation of the starting material returned from the process. Compared to known EBM processes, according to the inventors' knowledge, the invention enables improved drying of the starting material as the basis for a qualitatively improved melting or sintering process, and there also appears to be a positive influence on the conductivity of the metal powder with regard to the to result in subsequent selective exposure to the electron beam, in particular in the sense of accelerating the desired changes compared to electron beam preheating.

With the inventive heating of larger areas of the starting material applied last, according to the inventors' findings, it is also possible to reheat the previously applied and selectively

Link fused or sintered material layer in the sense of annealing or annealing. This offers the possibility of a structural

Quality improvement of the metal product produced.

Especially compared to laser-based processes where the product

Support structures are provided, the invention further provides the advantages of a substantial time and cost saving through the extensive elimination of such support structures and thus also the elimination of the post-processing steps for their removal. Equally serious is the time saved and the resulting productivity advantage due to the elimination or at least the shortening of a total thermal post-processing of the finished product to relieve tension.

Advantages and expediencies of the invention result from the following description of an embodiment with reference to the single figure.

1 shows a sketch of an arrangement 100 for the additive manufacturing of a spatial metal product P (which is still incompletely shown here), which is formed from a metal powder bed 101 by means of layer-wise application of metal powder and scanning local heating of the individual layers

The arrangement comprises a work table 103, on which the

Metal powder bed 101 applied and the metal product P is formed. As symbolized by the arrow A, the work table 103 can be moved vertically around the surface of the metal powder bed 101 despite the progressive To keep the layer job increasing at the same level. A powder application device for feeding metal powder into the actual work area comprises a stamp 105 which can be moved vertically in the direction of arrow B, that is to say in the opposite direction to arrow A, and a powder application doctor 107 which can be moved in the direction of arrow C and on the stamp 105 Metal powder 109 taken up as a supply in individual layers

predetermined thickness in the work area (ie in the figure to the right in the powder bed 101). It is pointed out that the means for the successive application of powder layers to the work table, the metal powder bed 101 formed there are shown only by way of example and symbolically in the figure; The actual execution of this step in the implementation of the invention can take place according to established techniques.

An NIR radiation source 111, which in the example is formed by a single halogen lamp purple and an associated reflector 111b, is positioned above the working area. As symbolized by the arrows D1 and D2, the NIR radiation source 111 can be moved laterally back and forth over the powder bed 101 and serves to preheat the respectively irradiated sections of the powder bed to a temperature below a sintering or melting temperature

Metal powder. Optionally, it is also used for thermal aftertreatment

(Annealing) of a layer locally melted immediately beforehand, which can be done, for example, by “moving back” the NIR radiation source in the direction of arrow D2 if the radiation source is used for preheating In

Direction of the arrow D1 was moved over the surface of the powder bed 101. The NIR radiation source 111 can also comprise a plurality of halogen lamps with a reflector which is then appropriately shaped.

An electron beam tube 113 with associated coordinate controlled

Deflection unit 115 is arranged above the work area. The

Deflection unit 115 directs an electron beam E generated by the electron beam tube 113 to any one, through manufacturing drawings of the

Metal product P with respect to its individual layers predetermined points on the surface of the preheated powder bed 101. With the electron beam, the powder bed 101 preheated by the NIR radiation on its surface is heated above the sintering or melting temperature at the impact points predetermined according to the product geometry. This will make one in those places Sintering with the respective underlying layer and thus the next layer of the metal product P is formed. In the usual way, the metal powder 109 remains in those places where it does not have the sintered or

Melting temperature has been raised in the powder state and falls after that

Removed from the work table from the metal product P or can be washed out of it.

By a power operating current control (not shown) of the

Electron tube 113, the performance of the

Control electron beam E and thus the temperature that can be achieved at the point of impact. Among other things, this enables the precise T-controlled execution of

Sintering or melting steps on the one hand and subsequent ones

Tempering steps of the applied metal layer on the other hand.

The entire arrangement is accommodated in a vacuum chamber 117, which is assigned a vacuum generator 119 for generating a high vacuum in the vacuum chamber during the manufacturing process of a product.

In addition, the embodiment of the invention is also in a variety of

Modifications of the example shown here and aspects of the invention highlighted above are possible.

Claims

Expectations

1. 3D metal printing process for producing a spatial metal product essentially from a metal powder or metal filament as

Raw material,

wherein the powder or the filaments in layers by applying layers of starting material to a respective previously generated layer and selective local heating of predetermined points of the layer via a sintering or

Melting temperature of the powder and sintering or fusion of the melted points with the layer underneath and optional annealing of the points are built up,

wherein at least the newly applied starting material layer by irradiation of IR radiation such that a radiation spot on the surface of the starting material layer with an area of at least 5 mm ² , more specifically of more than 20 mm ² and even more particularly of more than 100mm ² , is formed, preheated and / or at the same time as the selective local

Heating is additionally heated and / or post-treated after the local heating of the specified points for thermal stress compensation.

2. 3D metal printing method according to claim 1, wherein the planar irradiation of IR radiation takes place such that a preheating of the newly applied starting material layer and an additional heating takes place during the selective local heating, in particular a predetermined one

Temperature range is maintained for a predetermined period of time.

3. 3D metal printing method according to claim 1 or 2, wherein the IR radiation is irradiated sequentially in sections in sections of the total area of the respective starting material layer, the sections in particular having the shape of narrow rectangles, the length of at least one lateral dimension of the metal product to be formed equivalent.

4. The method according to any one of the preceding claims, wherein the

The power density of the radially irradiated IR radiation on the starting material layer is above 1 MW / m ² .

5. 3D metal printing method according to one of the preceding claims, wherein as IR radiation, the radiation of at least one halogen lamp, in particular a plurality of halogen lamps, with a lamp temperature in particular in the range from 2900 K to 3200 K, is used.

6. 3D metal printing method according to claim 5, wherein more than one rod-shaped IR emitter, in particular halogen emitter, with an associated reflector is used to generate a narrow rectangular radiation spot.

7. 3D metal printing method according to one of the preceding claims, wherein the selective local heating of predetermined points by scanning the

Starting material layer is effected with an electron beam.

8. 3D metal printing method according to one of the preceding claims, wherein each applied starting material layer has a thickness of at least 150 mm, more particularly of more than 300 mm and even more particularly of more than 500 mm, and is heated in full thickness by the IR radiation.

9. Arrangement for performing the method according to one of the

preceding claims, which comprises:

a work table as a base for the layered construction of the spatial metal product,

a powder application device for the sequential application of

Starting material layers of a metal powder or starting material

Filaments in the area of the work table,

an area heating device for the area heating of each new starting material layer for preheating or thermal aftertreatment, and an IR irradiation device for generating a radiation spot with an area of at least 5 mm ² , more specifically of more than 20 mm ² and even more specifically of more than 100 mm 2 , has, and

Means for effecting selective local heating of predetermined points of the new starting material layer via a sintering or

Melting temperature of the metal powder.

10. The arrangement according to claim 9, wherein the means for causing a selective local heating of predetermined points of a previously applied starting material layer to point an electron beam generator

Have radiation of electron beams on the specified points and the arrangement is arranged in a vacuum chamber charged with high vacuum.

11. The arrangement according to claim 9 or 10, wherein the IR irradiation device has at least one IR emitter, in particular halogen emitter, with an associated and designed reflector such that the radiation of the or each infrared emitter is concentrated in the direction of the work table and on the last starting material -Location the radiation spot is formed with an area of at least 5mm ² , more specifically of more than 20mm ² and even more specifically of more than 100mm ² .

12. The arrangement according to claim 11, wherein the IR emitter or a plurality of IR emitters with an associated reflector is mounted in at least one axial direction of an XY plane above the work table.

13. Arrangement according to claim 11 or 12, wherein the halogen lamp or lamps is / are designed for operation with a lamp temperature in the range from 2900 K to 3200 K.

14. Arrangement according to one of claims 11 to 13, wherein the IR irradiation device is equipped with at least one rod-shaped IR radiator, in particular halogen radiator, the length of which corresponds to at least one dimension of the metal product to be produced, and a device for moving the IR radiator in exactly one axis direction of the XY plane.

15. Arrangement according to one of claims 10 to 14, with a

Heating control device, which is connected via control outputs to the surface heating device and the means for effecting selective local heating and controls them in accordance with a heating control program in such a way that a temperature in the new starting material layer is maintained in a predetermined temperature range for a predetermined period of time.