DE102019119113A1 - Process and device for the application of powder for additive manufacturing - Google Patents

Abstract

The invention relates to a method and a device for additive manufacturing of a product (12) from at least one metallic and / or ceramic powder, the powder being fed to an electrostatically chargeable adhesive device (1) which is provided with an electrostatic charge and in a first Process step a powder layer is taken up on the surface and released again in a second process step, the deposition of the powder. According to the invention, the powder layer is delivered and applied directly from the adhesive device (1) to a component table or a surface of the product (12) to be manufactured. The invention also relates to a process product and a printer description file for producing the device.

Description

The invention relates to a method and a device for applying powder for additive manufacturing. The invention relates to a product and a printer description file for producing a device.

Nozzle and squeegee-based application mechanisms for additive, jet-based powder bed processes reach their limits, particularly in multi-material processing, the use of different materials in one product. Nozzle-based systems are again limited in their application rate. There is a conflict of objectives here: If the high resolution of the multi-material component is desired, a correspondingly fine application beam is necessary. Following the contour takes more time as the fineness of this application jet increases. Squeegee-based systems work quickly and enable an even powder application. However, the suitability of doctor-based systems for multi-material applications is severely limited.

Nozzle and doctor blade-based application mechanisms have in common that they are heavily dependent on the powder properties. It can generally be stated here that the more flowable the powder form, the more stable the powder application process is. The nozzle depends to a greater extent on the flowability of the powder. In the case of spattered, non-spherical powders, a stable powder application cannot always be guaranteed despite fluidization measures (e.g. vibration actuators).

A shape of the particles of the powder obtained by means of an atomization process is referred to as spotty. The atomization process belongs to the mechanical processes, like the grinding process. Atomization processes are of particular importance in the production of sinter powders. They cover up to 40% of the global demand for metal powders. Small pieces of molten metal, mixed with air, steam or water, are conveyed through a Venturi nozzle (a smooth-walled piece of pipe with a narrowing of the cross-section, see illustration) at high pressure onto a baffle plate and atomized in the process. The advantage of this method is the controllability of the shape, size and size distribution of the particles. In most cases, this process is used to produce iron and bronze powder through to powders for high-speed steels and superalloys.

With a photoconductor-based application mechanism, a flat powder application that is independent of the powder properties and at the same time precisely contoured powder application can be implemented for both multi-material and mono-material applications.

The current state of the art is largely limited to photoconductor applications for additive processes based on plastics. Kumar and Dutta in the publication Ashok V. Kumar, Anirban Dutta (2003) . Investigation of an electrophotography based rapid prototyping technology. Rapid Prototyping Journal, Vol. 9 (2), 95-103; and in the publication Ashak V. Kumar, Anirban Dutta, James E. Fay (2004) . Electrophotographic printing of part and binder powders. Rapid Prototyping Journal, Vol. 10, 7-13; have already published groundbreaking publications in 2003 and 2004. In their publications they describe the adaptation of the laser printing principle to additive manufacturing. The powder applied is fixed in the same way as toner is applied to paper, i.e. without the plastic powder being melted. This approach of electrophotographic 3D printing was not consistently pursued for several years due to some limitations, such as the limited installation height. Other publications deal with electrophotographic 3D printing, which is not comparable to other additive processes such as laser beam melting or electron beam melting due to the different fixing process of the powder.

The pamphlet WO 2015/091826 A1 from 2014 already suggests the use of a laser for fixation, but here only a plastic powder. The invention describes a self-contained manufacturing head. The fixing unit, the laser, moves here with the production head and is therefore not arranged externally, as in a conventional beam-based system.

In the pamphlet WO 2004/037469 A1 from 2009 the absorption of metal powder by means of a photoconductor is described. The metal powder that is picked up is transported into a sintering mold where it is pressed into a green compact. This method also describes a first approach to material application that also seems suitable for powder bed methods.

Other publications, in particular Laumer, T., Sichel, T., Amend, P., Schmidt, M. (2015) . Simultaneous laser beam melting of multimaterial polymer parts. Journal of Laser Applications Vol. 27 (S2) and Sichel, T., Laumer, T., Amend, P., Roth, S. (2014) . Electrostatic multi-material powder deposition for simultaneous laser beam melting. Erlangen, also deal with the validation of a photoconductor-based multi-material application for plastics, but not for metallic or ceramic powders.

As a result, it can be stated that none of the existing documents from the prior art is a mature approach to describes electrophotographic multi-material application for a jet-based powder bed process with an external fixing unit. In addition, according to the current state of the art, no system is known which provides for a mono-material application by electrostatic pick-up and deposit of the powder. Processing of non-spherical and therefore mostly cheaper powders is also not possible.

It is therefore the object of the present invention, in particular, to offer a method and a device for applying powder for additive manufacturing that works on the basis of electrostatic charging, is suitable for metallic and ceramic powders and requires only a small amount of space.

The object is achieved by a method for additive manufacturing of a product from at least one metallic and / or ceramic powder, the powder preferably coming from a powder feed from an electrostatically chargeable adhesive device, for example one coated with a photo semiconductor and / or designed as a photoconductor roll or photoconductor plate Adhesion device, is supplied, which is provided with an electrostatic charge and in a first process step a powder layer is added to the surface, which powder layer adheres to the surface and is released again in a second process step. According to the invention, the powder layer is delivered and applied directly from the adhesive device to a component table or a surface of the product to be manufactured. The powder layer is then solidified. A hybrid product based on a conventionally manufactured basic product is also to be regarded as a product. According to the present invention, the powder layer is applied to this basic product and the product is further built in this way.

The invention is particularly suitable for processing metallic and ceramic powders in jet-based powder bed processes. Various technical precautions were taken for this purpose, which set the invention apart from the prior art.

The central element of the device according to the invention, also referred to as a coater, is the adhesive device. In the case of a planned multi-material application, a photoconductor is included, for example embodied as a photoconductor roll or photoconductor plate, in the case of a monomaterial application around another electrostatically chargeable element, in particular a roll. The adhesive device is electrostatically charged with a device suitable for this purpose.

Various devices can be used for charging. In order to provide the adhesive device with an electrostatic charge, a separate charging device, for example designed as a roller-shaped element or charging roller, has proven particularly suitable.

With the solution according to the invention, a method for powder application can be carried out in a smaller space. There is no need for transport between the location of the creation of a powder layer and the construction of the product.

It has proven to be advantageous if at least the upper powder layer is sintered after application, for example by laser sintering, with which a sintered area can be precisely determined and specifically influenced. It is also provided that the upper powder layer is not only sintered, but also melted.

Particular advantages result if the sintering or melting takes place under a protective gas atmosphere and the protective gas atmosphere also includes the charging device and the photoconductor. A surprising effect was found here, in that, in addition to improved sintering, the adverse influence of moisture on the process of electrostatic attraction is also reduced and the effectiveness of the process is decisively improved. In particular, a larger amount of powder, but above all larger or heavier particles, can be attracted and transferred even with a lower electrostatic charge.

An advantageous embodiment of the method provides that the adhesive device is cooled. In particular, process-related heat build-up can be counteracted and the reliable function and low wear of the photo semiconductor can be ensured. A process-related development of heat is due to the sintering or melting, which according to the invention takes place in the immediate vicinity of the adhesive device. Depending on the temperatures occurring in the installation space, cooling by means of a cooling device may therefore be necessary when using a photoconductor.

A further process-related heat development can also result from a permanent heat supply to the component table or the surface of the product to be manufactured by means of a heating device. This has proven to be advantageous because less energy has to be entered during the sintering or melting process and the laser beam manages with a lower power.

In the case of the photoconductor, the electrostatic charge can now be extinguished by selective exposure. Various technical solutions can be used for this. Selective exposure using an LED array has proven to be particularly practical. By exposing the photoconductor, e.g. B. the photoconductor roll or the photoconductor plate, this becomes conductive at the point in question and the applied charge can be discharged via the grounding of the roll. An electrostatic charge contour is thus applied to the roller. This charge contour corresponds to the negative of the desired powder application contour.

The powder is then absorbed via the electrostatic force of attraction. The powder is applied to the adhesive device via a suitable powder feed. An advantageous retrofit solution is possible, particularly in systems with a coater filling from above.

The possibility of retrofitting the invention in an existing system also represents a special distinguishing feature from the systems as they are known from the prior art. A compact coater is advantageous here, as not all of the powder has to be carried along for a construction job. Following the powder application, depending on the quality of the layer application, a downstream unit is necessary to ensure the appropriate powder layer thickness.

An advantageous further development of the method provides for partial exposure of the adhesive device comprising the photoconductor at least on its electrostatically activatable surface, preferably designed as a photoconductor roll. This results in a partial reduction in the electrical charge.

The powder can be deposited in different ways. It is possible to wipe the adhesive device with a grounded, differently charged or alternatively charged blade or brush. In the case of powder storage, the photoconductor offers additional options compared to a simple adhesive device without a photoconductor. On the one hand, the photoconductor can be exposed again, which leads to a local loss of the electrostatic charge and thus to powder deposition. Another possibility is the loss of the electrostatic charge of the adhesive device with photoconductor due to the local supply of heat. In this case, the heat radiation of the building platform can be used advantageously.

If necessary, a compression unit, which is connected downstream of the direction of travel of the coater and becomes effective after a powder layer has been deposited, is provided in order to prepare the powder bed in a suitable manner for the melting process. This is because it has proven to be advantageous if the powder is compacted after it has been applied. The density of the later product can be partially determined by the degree of compression. In addition to jet-based powder bed processes, an adaptation of the process for binder jetting, as well as for other processes with a fixing unit independent of the coater, is a very promising option. This is because the subsequent solidification process does not play a role in the application process, so that the invention is suitable for all powder-bed-based processes.

Further process steps have proven to be advantageous. As with a laser printer, the adhesive device must be prepared after an order cycle. In this case, two points must be ensured: On the one hand, the adhesive device must be freed from powder and the remaining charge drained off. To meet both points, the use of a conductive, earthed or alternating current brush roller is expedient. The removal of the powder is thereby combined with a uniform discharge of the adhesive device.

Another aspect of the present invention relates to a device for additive manufacturing of a product from at least one metallic and / or ceramic powder, comprising an adhesion device which can be provided with an electrostatic charge, preferably designed as an adhesion device coated with a photo-semiconductor. As a result, a powder layer adheres to the surface of the adhering device, the powder preferably being fed to the adhering device by a powder feed. According to the invention, the device is designed in such a way that the powder layer is deposited or applied directly from the adhesive device to a component table or a surface of the product to be manufactured.

As a result, the required installation space of the device becomes smaller and no additional transport devices are required between the place where a powder layer is produced and the structure of the product.

In addition, a sintering device is preferably provided which acts on a sintering area and with which at least the upper powder layer is sintered after application, for example by laser sintering or by means of an electron beam. This allows targeted sintering and both heat losses and undesirable effects of heat, e.g. B. on the photoconductor, other parts of the device or the product can be reduced to a minimum. The same applies in the event that melting is provided. In addition, the solidification of the upper powder layer is done by the binder jetting. For this purpose, a binder is applied that glues the particles of the powder together. A green compact obtained in this way must then be post-treated in a sintering furnace. Another material may also have to be diffused in to fill the gaps that have arisen when the binder burns out in the sintering furnace.

It is also advantageous if a protective gas atmosphere is provided which includes at least the adhesive device and the sintering or melting area. This further reduces the disadvantageous effects of heat, such as oxidation of surfaces, and in particular improves the sintering or melting process, since the particles of the powder are also not oxidized, or to a lesser extent. Apart from these expected advantages, it has surprisingly been found that an improvement in the effect of the electrostatic charging of the adhesive device or of the photo semiconductor can also be achieved. The exclusion or reduction of the effects of air humidity is responsible for this.

According to a preferred embodiment of the device according to the invention, a heating device is provided which enables permanent heat supply to the component table or the surface of the product to be manufactured. This means that less energy has to be entered during the sintering or melting process.

An exposure device is required to form powder layers that are not full-area. This is used for the partial exposure of the adhesive device provided with the photoconductor, at least on the electrostatically activatable surface, in particular a photoconductor roller, and thus for the partial reduction of the electrical charge. A compression unit for the applied powder is also provided and serves to partially or layer-wise compression of the powder on the surface of the product.

In the interests of greater resistance, it has proven to be advantageous if the adhesive device has an inorganic coating, in particular for forming the photosemiconductor. This improves the thermal resistance as well as the resistance to abrasive effects of the powder. According to a preferred embodiment, the inorganic coating is designed as a silicon-based coating.

In order to further improve the resistance to abrasive effects of the powder and also to ensure when an organic photoconductor is used, an additional mechanical protective layer is advantageously provided to reduce the abrasion of the adhesive device.

The method according to the invention enables the simple and safe processing of non-spherical and therefore mostly cheaper powders. The approach pursued in the context of the invention thus offers great technical and economic potential.

The object of the present invention is also achieved by a printer description file for producing a device as described above, or a part of that of the device.

A product obtained by a method as described above is also encompassed by the invention.

• 1: eine schematische Darstellung einer Ausführungsform einer Vorrichtung zum Auftrag von Pulver für die additive Fertigung mit Multimaterialauftrag und
• 2: eine schematische Darstellung einer Ausführungsform einer Vorrichtung zum Auftrag von Pulver für die additive Fertigung mit Monomaterialauftrag.

The invention is explained in more detail below on the basis of the description of exemplary embodiments and their representation in the associated drawings. Show it:

• 1 : a schematic representation of an embodiment of a device for applying powder for additive manufacturing with multi-material application and
• 2 : a schematic representation of an embodiment of a device for applying powder for additive manufacturing with monomaterial application.

1 shows a schematic representation of an embodiment of a device 20th for the application of powder for additive manufacturing with multi-material application, whereby the application of one of the intended materials is shown. A detention facility 1 is by means of a charger 2 , preferably designed as a charging roller, electrostatically charged. An exposure device 3 ensures that in certain areas of the photosensitive adhesive device 1 the electrostatic charge is removed.

The powder intended for the later application comes from a powder feed 4th released and passed to an adhesive device 1 whose direction of rotation is indicated by an arrow. In the unexposed areas on the surface of the adhesive device 1 the powder adheres. The temperature of the attachment device 1 is through a cooling device 6th controlled. The layer thickness of the powder is controlled by a layer thickness control 5 controlled.

From the surface of the attachment device 1 the powder gets onto the product 12 . The powder is heated by supplying heat using a heater 8th prepared for sintering and by means of a compression unit 9 condensed. A brush 7th prepares the detention facility 1 for a new exposure by brushing the remains of the powder.

2 shows a schematic representation of an embodiment of a device for applying powder for additive manufacturing with monomaterial application. The individual elements correspond to those from 1 , with an additional blade 10 is provided. The conductive, grounded, or alternating current blade 10 serves to remove the powder as well as a uniform discharge of the adhesive device 1 . Instead of the blade 10 a roller brush can also be provided. With the discharge of the cling device 1 it is thus prepared for a new order cycle.

List of reference symbols

1

Attachment device

2

Charger

3

Exposure device

4th

Powder feed

5

Layer thickness control

6th

Cooling device

7th

brush

8th

Heater

9

Compression unit

10

blade

12

product

20th

Device for multi-material application

30th

Device for mono material application

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• WO 2015/091826 A1 [0007]
• WO 2004/037469 A1 [0008]

Non-patent literature cited

• Kumar and Dutta in the publication Ashok V. Kumar, Anirban Dutta (2003) [0006]
• Rapid Prototyping Journal, Vol. 9 (2), 95-103; and in the publication Ashak V. Kumar, Anirban Dutta, James E. Fay (2004) [0006]
• Laumer, T., Sichel, T., Amend, P., Schmidt, M. (2015) [0009]
• Journal of Laser Applications Vol. 27 (S2) and Sichel, T., Laumer, T., Amend, P., Roth, S. (2014) [0009]

Claims (17)

A method for additive manufacturing of a product (12) from at least one metallic and / or ceramic powder, the powder being fed to an electrostatically chargeable adhesive device (1) which is provided with an electrostatic charge and, in a first method step, takes up a powder layer on the surface and in a second process step, depositing the powder, is released again, characterized in that the powder layer is released and applied directly from the adhesive device (1) to a component table or a surface of the product to be manufactured (12) and subsequently solidified. Procedure according to Claim 1 , wherein at least the upper powder layer is provided with a binding agent for solidification after application, sintered or melted. Procedure according to Claim 2 , wherein the sintering or melting takes place under a protective gas atmosphere. Procedure according to Claim 1 or 2 , wherein the adhesive device (1) is cooled by means of a cooling device (6). Method according to one of the preceding claims, wherein there is a permanent supply of heat to the component table or the surface of the product (12) to be manufactured. Method according to one of the preceding claims, wherein the adhesive device (1) provided with a photoconductor is partially exposed and the electrical charge is thus partially reduced. Method according to one of the preceding claims, wherein after the powder has been deposited, it is compacted. Device for the additive manufacturing of a product from at least one metallic and / or ceramic powder, comprising an adhesion device (1) which can be provided with an electrostatic charge and whereby a powder layer can adhere to the surface of the adhesion device (1) and be released again, characterized in that the device is designed in such a way that the powder layer is deposited or applied directly from the adhesive device (1) onto a component table or a surface of the product to be manufactured (12) and subsequently solidified. Device according to Claim 8 , wherein a sintering device or a melting device is provided which acts on a sintering area or a melting area and with which at least the upper powder layer is sintered or melted after application. Device according to Claim 9 wherein a protective gas atmosphere is provided which includes at least the adhering device (1) and the sintering area or at least the adhering device (1) and the melting area. Device according to one of the Claims 8 to 10 , wherein a heating device (8) is provided which enables permanent heat supply to the component table or the surface of the product (12) to be manufactured. Device according to one of the Claims 8 to 11 An exposure device (3) for partial exposure of the adhesive device (1) provided with a photoconductor and thus for partial reduction of the electrical charge and a compression unit (9) for the applied powder are provided. Device according to one of the Claims 8 to 12 wherein the adhering device (1) has an inorganic coating. Device according to Claim 13 , wherein the inorganic coating is designed as a silicon-based coating. Device according to one of the Claims 8 to 14th , wherein an additional mechanical protective layer is provided to reduce the abrasion of the adhesive device (1). Printer description file for producing a device according to one of the Claims 8 to 15th or part of the device. Product obtained by a method according to one of the Claims 1 to 7th .

Images