DE102010029078A1 - Producing an article by layer-wise structures made of powdered metallic or ceramic material, comprises individually preparing material powder layers subsequent to each other on a support, and location-selectively solidifying each layer - Google Patents

Abstract

The method for producing an article by layer-wise structures made of powdered metallic or ceramic material, comprises individually preparing material powder layers subsequent to each other on a support (6), and location-selectively solidifying each layer by melting or optionally sintering the material powder at a predetermined position in according with geometrical description data of the article to be produced and by introducing radiation energy, where the preparation step comprises introducing the material powder on the support and leveling the material powder for producing a powder layer. The method for producing an article by layer-wise structures made of powdered metallic or ceramic material, comprises individually preparing material powder layers subsequent to each other on a support (6), and location-selectively solidifying each layer by melting or optionally sintering the material powder at a predetermined position in according with geometrical description data of the article to be produced and by introducing radiation energy, where the preparation step comprises introducing the material powder on the support and leveling the material powder for producing a powder layer with a determined target layer thickness. The material powder is used for the preparation of the material powder layers and contains upto a minimum portion of powder particle with a grain size that is larger than the target layer thickness. The mass portion of powder particles is larger than 2%, where the powder particles have a grain size larger than the target layer thickness. The mass portion of the powder particles, which have grain size larger than the target layer thickness of the material powder layer, is less than 5%, where the grain size of the largest powder particle is greater than 1.5 times of target layer thickness and less than 5 times of target layer thickness. The leveling step takes place under the use of a stripping tool, which is moved with its lower edge in a horizontal plane over the support to level a concerned material powder layer, where the vertical distance between the support and the lower edge of the stripping tool is adjusted around the measurement of the target layer thickness in an enlarged manner before the stripping tool is moved towards the leveling of a new material powder layer over the support. The stripping tool is moved with its lower edge in an equally remaining horizontal plane over the support during the leveling process. The support is lowered around the measurement of the target layer thickness against the horizontal height plane before the stripping tool is moved towards the leveling of the new material powder layer over the support. A zone-wise elastically flexible evasive stripper is used as the stripping tool for leveling the material powder layers. The material powder is used with grain size of 0 to larger than 90 mm but less than 120 mm containing particle size distribution for the target layer thicknesses of 20-60 mm.

Description

The invention relates to a method for producing an article by layering of powdered, in particular metallic or ceramic material in which successive layers of material powder are prepared individually on a support and each layer by remelting or optionally sintering the material powder at predetermined locations in accordance with Geometriebeschreibungsdaten the preparation of a material powder layer comprises the steps of applying material powder to the carrier and flattening the material powder to produce a powder layer with a certain nominal thickness, wherein for the preparation of the material powder layers material powder is used containing powder particles having a grain size smaller than the target layer thickness.

To the state of the art of such methods and of devices for carrying out such methods, e.g. B. on the DE 199 05 067 A1 , the DE 102 36 907 A1 , the DE 102 08 150 A1 , the DE 101 12591 A1 , the DE 196 49 865 A1 , the DE 102 008 022 495 A1 , the WO 2008/116627 A1 , the EP 1 839 781 A2 , the EP 1 021 997 B1 or the WO 2006/024373 A2 to get expelled.

By the terms selective laser melting, selective powder melting, selective laser sintering, and the like. Like. Recently, powerful methods for the production of objects, even of complicated geometries have become known, these often combined under the term "rapid prototyping" or "rapid tooling" or "rapid manufacturing" methods based essentially on the following principle:
The article to be produced is built up in layers from a fine-grained, powdery raw material in accordance with CAD data or geometric description data derived therefrom by solidifying or fusing the raw material according to a cross-sectional pattern of the article associated with the respective layer by means of locally selective irradiation. The irradiation is normally carried out by means of laser radiation, the control of a beam deflection device deflecting the laser beam being effected by means of a control device on the basis of geometric description data of the object to be produced. The control information is usually derived and provided by a microcomputer according to a corresponding program from CAD data.

The laser beam records on the last-prepared raw material powder layer the cross-sectional pattern of the article associated with that layer to selectively fuse the raw material to the cross-sectional pattern. After such an irradiation step, the preparation of the next material powder layer then usually takes place on the layer which has been finally fused selectively by irradiation and partially. After the formation of a sufficiently smooth powder layer on its surface, an irradiation step is then carried out in the manner explained above. The article thus arises layer by layer, wherein the cross-sectional layers of the article produced in succession are fused together so that they adhere to one another. As powder materials are various metals in question, including z. As steel, titanium, gold, tantalum, cobalt / chromium, aluminum, copper, silver, brass. Also multi-component materials or mixed powder of different materials can be used. In addition, ceramic material powder can be used in selective laser melting. With the method of selective laser melting almost all imaginable forms of objects can be produced, whereby it is predestined for the production of intricately shaped machine elements, prostheses, pieces of jewelry and components with fine wall structures. The layered structure of an object is usually carried out in a protective gas atmosphere or in a vacuum within a process space. In the process space, the carrier is provided, on which the object is built up in layers. A layer preparation device serves to prepare a respective new layer of powdery material on the powder layer which has been recently remelted and solidified by irradiation in portions on the support. Such a layer preparation device usually comprises a powder feed device and a stripping tool, which is moved with its lower, horizontally extending edge in a horizontal plane above the carrier in order to level material powder deposited thereon to form a layer having a respective nominal layer thickness. To produce a respective new material powder layer, the vertical distance between the carrier and the lower edge of the stripping tool is increased in each case by the extent of the nominal layer thickness. This can be z. Example, take place in that the carrier is lowered in each case by this Sollschichtdickenmaß relative to a constant horizontal plane, wherein the lower edge of the Abstreifwerkzeugs is moved when leveling the powder on this horizontal plane on the carrier.

So far, it was assumed that the material powder has a particle size distribution with a maximum grain size, which is smaller than the target layer thickness, so that for the preparation of layers with a nominal layer thickness of z. B. 60 microns often powder with a particle size distribution between 0 and 50 microns was chosen. In the EP 1 021 997 B1 is z. B. a particle size distribution of 0-50 microns for the production of dental prostheses proposed by the method of selective laser sintering.

Correspondingly fine-grained material powder was used for the preparation of even thinner material powder layers. Some materials, such as As gold, show a decreasing grain size a significantly increasing tendency to clumping, so that the powder handling and layer preparation of such materials is difficult.

Object of the present invention is to improve a process for the preparation of objects, in particular by the method of selective laser melting with the features mentioned at the outset that can also be used for lumping material powder.

To achieve this object, a method for producing an article by layering of powdered, in particular metallic or ceramic material is specified in which successive layers of material powder are prepared on a support and each layer by remelting or optionally sintering of the material powder at predetermined locations after Subject to Geometriebeschreibungsdaten of the article to be produced by entry of radiation energy is solidified site-selectively, wherein the preparation of a respective material powder layer comprises the steps of applying material powder on the support and the flattening of the material powder to produce a powder layer having a certain nominal thickness, wherein for the preparation of the material powder layers Material powder is used, which contains powder particles having a particle size which is smaller than the nominal layer thickness, wherein the method erfindun Accordingly, it is characterized in that material powder is used for the preparation of the material powder layers, which also contains powder particles having a particle size which is greater than the nominal layer thickness.

It has been found that the flowability and thus the handling of the material powder used can be substantially improved if a particle size distribution is selected in the material powder, in which also powder particles with particle sizes greater than the nominal layer thickness of the powder layers to be prepared occur. In the case of layer preparation, it may then happen that at certain points the nominal layer thickness is exceeded by particles having a coarser grain size.

So far, the experts had assumed that a very good leveling of the material powder layers to the Sollschichtdickenmaß is essential for the success of the construction process and that this can only be achieved with very fine powder with particle sizes smaller than the target layer thickness. This prejudice was overcome with the present invention. Although in the preparation of the powder layers a layer which is as level as possible is produced with a layer thickness approaching the target layer thickness, the pointwise layer thickness deviations possibly caused by the coarse-grained particles can be tolerated, because they are leveled in the subsequent irradiation step either by the remelting process, provided they are located in a region of the powder layer to be remelted, or in any case do not participate in the remelting process, provided that they lie in an area of the material powder layer which is not to be remelted.

The grain size here is the largest diameter of a powder particle. Since the powder particles usually have spherical shape, this is their ball diameter.

The mass fraction of powder particles having a grain size greater than the target layer thickness should be less than 25%, better still less than 10%. If the mass fraction of the powder particles having a particle size greater than the nominal layer thickness of the material powder layer is less than 5%, the largest powder particles thereof may have a particle size which quite corresponds to a multiple of the nominal layer thickness of the material powder layer. For example, the material powder may contain a small minority of particles with a particle size of 100 or 150 μm in order to form layers with a target layer thickness of 50 μm. According to one embodiment variant of the method, the mass fraction of the powder particles which have a particle size greater than the nominal layer thickness of the material powder layer is less than 5%, the particle size of the largest powder particles being greater than 1.5 times the nominal layer thickness and less than 5 times the nominal layer thickness is.

It has proven to be expedient to select the mass fraction of powder particles which have a particle size greater than the nominal layer thickness of the material powder layer greater than 0.25%, so that a significantly appreciable improvement in the flowability of the otherwise very fine-grained powder is achieved. Very good experiences have been made with the method according to the invention using fine-grained gold powder with a small proportion of gold powder particles coarser grain in the sense explained above. But also powdered material of titanium, platinum, palladium, cobalt / chromium, aluminum, copper, silver, steel, brass, tantalum, bronze and tin were with surprisingly good success according to the method of the present invention for the production of articles, especially too much filigree items, such as jewelry, dental prosthesis, etc. processes, which is the list of suitable material powder materials is not completed. Of course, come as materials, the above materials not only in pure form, but also as alloying ingredients and as components in mixed powders in question.

It may be left to the skilled person in a particular case to test out how large the maximum proportion and the minimum proportion of powder particles with a particle size should be greater than the material powder layer to be prepared and how large the maximum grain size may be, so that the material powder in the layer preparation and at the supply to the relevant process space sufficiently well flowable and manageable and the remelting process or sintering process is well controlled. The powder to be used according to the invention should have a thorough mixing of all the particle sizes present.

The step of leveling the material powder is preferably carried out using a scraper tool which is moved with its lower horizontal edge in a horizontal plane above the support to flatten a respective material powder layer, the vertical distance between the support and the lower edge of the scraper tool respectively is increased by the amount of the target layer thickness, before the stripping tool for leveling a respective new material powder layer is moved over the carrier. In this way, the respective nominal layer thickness is set well defined. The steps of applying powdered material to the carrier and flattening the powdered material may also be combined into a combined step, such as in the sense that the scraper tool advances the powder material toward the carrier. In the stripping process, the stripping tool tends to push the largest powder particles in front of them and, if necessary, push them into the non-remelted areas of the previously prepared powder layer or even advance them beyond the edge of the support. In particular, there will be such an effect of Vorsichherschiebens of the largest particles by stripping in areas of the construction field, under which solidified material of the molded article to be produced in the previous layer is present. In extreme cases, in such areas of the construction field within the freshly prepared powder layer only very few to no particles with a grain size which is substantially larger than the desired layer thickness of the material powder layer before.

Preferably, the stripping tool is moved with its lower edge in a constant horizontal plane during each leveling operation on the carrier. The carrier is then lowered in each case by the extent of the nominal layer thickness with respect to this horizontal height level before the stripping tool is moved over the carrier for flattening a respectively new layer of material powder.

In accordance with a preferred embodiment of the method according to the invention, a stripping element which deflects elastically and yielding in a zone-wise manner is used as a stripping tool to level the material powder layers. Wiper tools made of teflon or / and silicone have proven to be very suitable. With the use of such a stripping element, this possibly occasionally elastically resiliently embedded individually coarsely particulate relatively embedded within the material powder layer to be prepared with the result that eventually coarser particles remain within the prepared material powder layer, but this is quite tolerable for the reasons already mentioned.

In the production of dental prostheses made of various materials, such as titanium or cobalt / chromium material powder of different particle size between 0 and 150 microns was used for material powder layers with nominal layer thicknesses up to 60 microns with good success.

In the production of gold jewelry was used for material powder layers with nominal layer thicknesses up to 30 microns of material powder of different particle size between 0 and 100 microns, the mass fraction of the coarse-grained component was held with particle sizes greater than the nominal layer thickness less than 10%.

The method according to the invention will be explained in more detail below with reference to the figures.

The 1 - 3 show in a rough schematic representation three snapshots of a device for selective laser melting of objects during the implementation of the method according to the invention.

The device has a closed to the outside and flushed with inert gas process chamber housing 2 with a process room 3 on which down from the process room floor 4 and the carrier integrated therein 6 is limited. The carrier 6 is controlled vertically adjustable to adjust the nominal layer thicknesses of the powder layers to be prepared. Above the process chamber housing 2 is the irradiation device with a laser 8th , in particular fiber lasers, and with a galvanometer scanner 10 for controlled XY deflection of the laser beam 12 , The laser beam 12 permeates an optical window 14 , z. B. in the form of an f-theta lens and can on any desired point of the construction field 16 on the carrier 6 be directed. In the process room floor 4 is a powder feed opening 18 provided, through which material powder from below 20 in the process room 3 is introduced. The powder is supplied through the channel 22 coming from a powder reservoir 24 supplied with material powder from above. The material powder 24 If necessary, it will seep into the canal under the effect of gravity, if supported by vibrations 22 and is there by means of a screw conveyor 26 for powder inlet opening 18 in the process room 3 promoted.

In the snapshot according to 1 currently finds the step of irradiating a previously prepared powder layer on the support 6 instead, to another area of the already partially manufactured object 28 to produce by remelting of powder. The current melting process takes place in the area of the impact point 30 of the laser beam 12 instead of. By appropriate deflection of the laser beam 12 through the XY scanner 10 migrates this melting zone over the construction field 16 until the relevant layer of the article to be produced 28 is completed.

2 shows a snapshot, according to which the in 1 indicated irradiation process of the last processing material powder layer is completed. The carrier 6 has been lowered by the amount of the target layer thickness d, so that now room for a next layer of powder material on the support 6 is present. The required powder material is already in the process room 3 above the powder feed opening 18 and can now with a scraping tool 32 , whose horizontal bottom edge 34 on the non-lowerable part of the process room floor 4 rests, to the construction field 16 pushed forward and leveled there to a new layer of powder material, as in the snapshot according to 3 is indicated.

In 3 has the wiper tool 32 already the largest part of the construction field 16 recoated on the support. After completion of the material powder layer, the stripping tool 32 then back to the original position according to 1 and 2 be moved back. For this purpose, it may also be raised in the meantime. Thereafter, the next irradiation step in the in 1 indicated manner. Meanwhile, the screw conveyor can 26 again, the next Pulverration in the process room 3 promote.

That on the basis of 1 - 3 The explained method according to the invention is novel in that a powder is used which contains powder particles having a particle size greater than the nominal layer thickness d of the powder layer to be produced in each case for a relatively small proportion which is effective in terms of improving the flowability of the powder.

A further aspect of the invention, which may be of independent importance independently of the aspect of the particle size distribution in the material powder, is briefly outlined below. In the example according to the 1 - 3 has been only a laser beam 12 considered at the irradiation step. Particular advantages with regard to the speed of the construction process and also with regard to the production of fine outer surfaces of the article to be produced can be achieved simultaneously with several on the construction field 16 directional laser beams are derived, which are derived from one or possibly a plurality of laser radiation sources (not shown) and preferably different spot sizes at the point of impact on the construction field 16 have what z. B. can be achieved by different, in particular fixed focal settings of the individual laser beams. Laser beams with very small spot size at the point of impact on the construction field 16 are preferably for the production of the outer contours, ie the visible after completion of the construction process outer surfaces of the object 28 whereas laser beams with larger spot sizes are used at the place of impact on the construction field 16 for the creation of inner areas of the object 28 can be used. The laser beams can z. B. also differ in the radiation power and, if necessary, when needed in the radiation density or intensity. The Applicant has developed a new selective laser melting apparatus in which a double scanc head can deflect the two laser beams of two laser radiation sources onto a work field, this double scanc head containing two independently controllable scan units. This new and inventive device allows the implementation of very fast construction processes in the production of one or possibly several objects simultaneously on the support 6 , It has also proved to be very advantageous in carrying out the method according to the invention described above.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• DE 19905067 A1 [0002]
• DE 10236907 A1 [0002]
• DE 10208150 A1 [0002]
• DE 10112591 A1 [0002]
• DE 19649865 A1 [0002]
• DE 102008022495 A1 [0002]
• WO 2008/116627 A1 [0002]
• EP 1839781 A2 [0002]
• EP 1021997 B1 [0002, 0005]
• WO 2006/024373 A2 [0002]

Claims (9)

Process for producing an article by layering it from powdery, in particular metallic or ceramic material ( 20 ), in which on a support ( 6 ) successive powder layers are prepared individually and each layer by remelting or possibly sintering of the material powder ( 20 ) at predetermined locations in accordance with geometry description data of the article to be manufactured ( 28 ) is solidified selectively by the input of radiation energy, wherein the preparation of a respective material powder layer comprises the steps of applying material powder to the carrier ( 6 ) and the leveling of the material powder ( 20 ) for producing a powder layer having a specific target layer thickness (d), wherein for the preparation of the material powder layers material powder ( 20 ), which contains powder particles having a particle size which is smaller than the nominal layer thickness (d), characterized in that for the preparation of the material powder layers material powder ( 20 ) is used, which also contains powder particles with a particle size that is greater than the nominal layer thickness to a reduced proportion. A method according to claim 1, characterized in that the mass fraction of powder particles having a particle size greater than the nominal layer thickness (d) is less than 25%, in particular less than 10%. A method according to claim 1 or 2, characterized in that the mass fraction of the powder particles having a grain size greater than the nominal layer thickness (d) of the material powder layer is greater than 0.25%, in particular greater than 2%. The method of claim 1, 2 or 3, characterized in that the mass fraction of the powder particles having a grain size greater than the nominal layer thickness (d) of the material powder layer is less than 5%, wherein the grain size of the largest powder particles is greater than 1.5 -fold target layer thickness and less than 5 times the target layer thickness. Method according to one of the preceding claims, characterized in that material powder is used from one or more of the following materials: gold titanium platinum palladium Cobalt / chromium aluminum copper silver Steel, in particular stainless steel, Brass bronze Tin. Method according to one of the preceding claims, characterized in that the step of leveling the material powder ( 20 ) using a scraper tool ( 32 ), with its lower edge ( 34 ) in a horizontal plane over the carrier ( 6 ) is leveled to level a respective material powder layer, wherein the vertical distance between the carrier ( 6 ) and the lower edge of the stripper tool ( 34 ) is adjusted in each case to the extent of the target layer thickness (d) increased before the stripper tool ( 32 ) for flattening a respective new layer of material powder over the carrier ( 6 ) is moved away. Method according to claim 6, characterized in that the stripping tool ( 32 ) with its lower edge ( 34 ) in a constant horizontal plane during each leveling operation over the carrier ( 6 ) and that the carrier ( 6 ) is lowered in each case by the extent of the nominal layer thickness with respect to this horizontal height plane, before the stripping tool ( 32 ) for flattening a respective new layer of material powder over the carrier ( 6 ) is moved away. Method according to one of the preceding claims, characterized in that for planarization of the material powder layers a zone-wise elastically yielding evasive stripping element as a stripping tool ( 32 ) is used. Method according to one of the preceding claims, characterized in that for nominal layer thicknesses (d) between 20 microns and 60 microns of material powder having a particle size distribution containing grain sizes between 0 and greater than 90 microns but less than 120 microns is used.

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