WO2018060033A1

WO2018060033A1 - Method for determining a relative powder bed density in a device for the generative production of a three-dimensional object

Info

Publication number: WO2018060033A1
Application number: PCT/EP2017/073829
Authority: WO
Inventors: Stefan Grünberger; Stefan Paternoster
Original assignee: Eos Gmbh Electro Optical Systems
Priority date: 2016-09-28
Filing date: 2017-09-20
Publication date: 2018-04-05
Also published as: DE102016219968A1

Abstract

The method according to the invention serves for determining a relative powder bed density in a device for producing at least one three-dimensional object by applying and selectively solidifying a powdered buildup material layer by layer. The method comprises at least one first test piece and the steps of a) applying a layer of the powdered buildup material within a building zone by means of a coater moving over the building zone, b) optionally compressing the applied layer of the buildup material, c) selectively solidifying the applied layer at points that correspond to a cross section of the at least one first test piece to be produced, by means of a solidifying device, and d) optionally repeating steps a) to c) until the at least one first test piece is completed. The method also comprises the steps of: determining at least one linear dimension perpendicular to a run of the layer of powdered buildup material and assigned to the at least one first test piece, and comparing the at least one linear dimension determined with at least one corresponding linear dimension of at least one second test piece.

Description

A method of determining a relative powder bed density in a device for generatively producing a three-dimensional object

The present invention relates to methods for determining a relative powder bed density in a device for producing a three-dimensional object generatively by layering and selectively consolidating a building material, preferably a powder.

Devices and methods for generatively producing a three-dimensional object are used, for example, in rapid prototyping, rapid tooling or additive manufacturing. An example of such a method is known as "selective laser sintering or laser melting." In this case, a thin layer of a pulverulent constituent material is repeatedly applied and the material in each layer is selectively solidified by selective irradiation from a cross section of the object to be produced with a laser beam.

In this case, the powder bed density prior to solidification plays a major role in terms of the quality of the object to be produced or produced and the process stability. The

DE 102006023484 A1 describes an apparatus and a method for compacting pulverulent building material, wherein the building material is preferably a mixed powder of new and old material.

By the device described in DE 102006023484 AI and the method described by increasing the powder bed density both the refresh rate, i. the proportion of new powder in the mixed powder, can be reduced, as well as made possible to use a powder which is not or only partially suitable for the laser sintering process because of too low melt viscosity.

The powder bed density is quantified therein as follows: A closed hollow thin-walled cuboid laser sintered component is exposed such that the volume enclosed in the exposure has a value resulting from the inner dimensions of the container in the directions xyz, the z-direction extends perpendicular to the powder flow. The thus-built part is freed from the outside of adhering powder residues and weighed. Then the part is cut open and the powder inside is emptied, and the empty part weighed again. The difference of the masses corresponds to the mass of the enclosed powder volume. Since the powder volume is known, the density of the powder bed can be calculated from this. However, the absolute density measurement is often complicated due to numerous imponderables. Accordingly, the object of the present invention is to provide an alternative or improved method or apparatus for determining the powder bed density.

This object is achieved by a method according to claims 1 or 12 or a control unit according to claim 15. Further developments of the invention are specified in the subclaims. In this case, the method can also be developed by the features of the devices set out below or in the subclaims, or vice versa, or the features of the devices can also be used with each other for further development. Features of various advantageous developments and embodiments can furthermore be combined with one another.

The method according to the invention serves to determine a relative powder bed density in a device for producing at least one three-dimensional object by layer-wise application and selective solidification of a pulverulent construction material. The method comprises at least a first specimen and the steps

a) application of a layer of the powdered building material within a construction field by means of a coater passing over the construction field,

b) optionally compacting the applied layer of the building material,

c) selectively solidifying the applied layer at locations corresponding to a cross section of the at least one first specimen to be produced by means of a solidification device and d) optionally repeating steps a) to c) until the at least one first test specimen is completed. Furthermore, the method comprises the steps:

Determining at least one length dimension assigned to the at least one first specimen perpendicular to a layer course of the powdered building material and

Comparing the at least one determined length dimension with at least one corresponding length dimension of at least one second test piece.

The relative determination of the powder bed density makes it possible, for example, to make a more precise statement about the density in comparison to the quantitative determination of the powder bed density. In the case of exactly the same construction conditions of the first and second specimens, the accuracy can be given by the fact that the temperature dependence of the construction process is likewise included in a relative determination of the powder bed density. Preferably, the at least one second specimen is produced by means of a powder-based generative layer construction method, preferably using the same pulverulent build-up material as for producing the at least one first specimen. This facilitates the comparison between the first and the second specimen considerably, since the two

Specimens then - figuratively speaking analogous to a common coordinate system - are based on certain common technical starting conditions, due to which the differences in the comparison of the two specimens are then particularly significant and evaluable. Preferably, a compaction step b) is carried out for the preparation of the first specimen and no compaction step b) is carried out for the preparation of the second specimen. As a result, for example, the efficiency of a compaction method can be compared in direct comparison with uncompacted powder.

Alternatively, different compaction steps b) are carried out to produce the first and the second specimen.

As a result, for example, the efficiencies of two different compression methods can be compared in direct comparison.

Preferably, the first and / or the second test specimen is or are removed from the device before the at least one length dimension is determined, which can considerably simplify the measurability.

The steps a) of powder application and b) of compacting are preferably carried out such that the layer thickness of the first specimen to be consolidated in step c) is the same as the layer thickness of the second specimen to be consolidated in step c). This measure also serves to provide an improved basis for the comparison of the two specimens. Preferably, the step a) of the powder application and the step b) of the compacting of the applied layer occur simultaneously. Preferably, the first and second specimens each a platelet, which by passing through the

Steps a), b) and c) is produced. Preferably

the at least one length dimension to be determined is a dimension of the test specimen perpendicular to the solidified layer.

Alternatively, the first and the second specimens are produced by carrying out steps a), b) and c) 'at least twice, preferably many times

In this case, preferably, the first and the second specimen are each an upwardly open, filled with unverfestigt remained powder cylindrical container, wherein the two specimens have the same geometric inner dimensions. In order to determine the at least one length dimension assigned to a test specimen, a defined pressure is preferably applied in each case to the unconsolidated powder surface of the test specimen. Preferably, the resulting change in height of the powder surface is the at least one length dimension.

As a result, the method can be carried out by machine and is essentially independent of a subjective assessment by an executing person.

Alternatively, each of the first and second specimens is an object having n recesses, where n is a natural number, and wherein each recess comprises a non-solidification region of a given length dimension in which one or more layers have been excluded from solidification, and the length dimensions associated with the specimens are those given length dimensions of the non-solidification areas, taking into account only the non-solidification areas visible after completion of the specimens.

As a result, the relative powder bed density, for example, be assessed visually without much effort of the Abmessens. The powder bed density can thus be assessed with the naked eye.

Preferably, each of the first and second specimens is a three-dimensional object having n non-solidification areas, where n is 1, and wherein at least two, preferably all n, non-solidification areas differ from one another in their predetermined length dimensions perpendicular to the layer course of the powdered building material.

As a result, the optical assessment can be simplified, for example.

Preferably, adhering powder grains are removed after their completion on the test specimens, in particular on the recesses, preferably by blasting. This increases the accuracy of the judgment.

Preferably, at least two, preferably a multiplicity of first test specimens and / or at least two, preferably a plurality of second specimens are produced and / or at least two, preferably a multiplicity of length dimensions are determined on the test specimens and the length dimensions of the first specimen or specimens ( s) and the length dimensions of the or second specimen (s) is compared by means of a suitable index number, the index number preferably being an average value or a frequency distribution of the length dimensions. As a result, the relative powder bed density can be determined even more accurately.

The method according to the invention serves to produce at least one three-dimensional object by layer-wise application and selective solidification of a pulverulent construction material. The method comprises the following steps:

a) applying a layer of the powdery building material within a construction field by means of a moving over the site coater,

b) optionally compacting the applied layer of the building material,

c) selectively solidifying the applied layer at locations corresponding to a cross-section of the at least one object to be manufactured by means of a solidification device and d) optionally repeating steps a) to c) until the at least one object is completed,

wherein the building material is solidified such that at least a first specimen is produced and the following steps are carried out to determine a relative powder bed density:

Determining at least one of the at least one first specimen associated length dimension perpendicular to a layer course of the powdered building material and

Comparing the at least one determined length dimension with at least one corresponding length dimension of at least one second test piece. Preferably, at least one object and at least one first and / or second test specimen are produced.

The programmable control unit according to the invention serves for a device for producing at least one three-dimensional object by layer-wise application and selective solidification of a pulverulent building material. The control unit is designed to control the device such that it carries out all steps a) and c) and optionally b) and / or d) of a method as defined above.

The device according to the invention is used for producing at least one three-dimensional object by layered application and selective solidification of a powdered on aumateri- as. The apparatus comprises a field movable coater for applying a layer of building material within the building field, compacting means for compacting the applied layer of building material, the compacting means optionally being integrally formed with the coater, and a solidification apparatus for selective solidification the applied layer at locations corresponding to a cross section of the at least one object to be fabricated, the device being configured and / or controlled to repeat the steps of application and selective solidification until the at least one object is completed; Furthermore, the above-described control unit according to the invention comprises. Other features and advantages of the invention will become apparent from the description of embodiments with reference to attached drawings, which are not necessarily to be understood as true to scale.

1 shows a schematic representation of an apparatus for producing three-dimensional objects according to an embodiment of the present invention

2 shows a schematic perspective side view of the powder application with the coater and a compaction blade from FIG. 1

Fig. 3 a) -c): a schematic representation of the cross section of three compressor blades which can be used in the example of FIG

4 a), b): a schematic representation of the cross section of platelets according to a first embodiment in a powder bed FIG. 5 a), b): a schematic representation of the cross section of slots according to a second embodiment in a manufactured component

Fig. 6: a) -c) is a schematic representation of the cross-section of a manufactured component with unconsolidated powder inside and applying a compressibility force according to a third embodiment

Fig. 7: General overview of the process steps In the following, a laser sintering or laser melting apparatus 1 for the method according to the invention will be described with reference to FIG. 1 as an exemplary production apparatus according to the invention. For constructing an object 2, it contains a process chamber 3 with a chamber wall 4. As object 2, here both the component to be formed and a test specimen are understood.

In the process chamber 3, an upwardly open container 5 is arranged with a container wall 6. Furthermore, in the container 5 there is arranged a carrier 7 which is movable in the vertical direction V and which carries the object 2 to be formed directly or indirectly. For example, a base plate 8 may be arranged in the container 5 between the object 2 to be formed and the carrier 7. The carrier 7 is adjusted in the vertical direction so that the layer of the object to be consolidated in each case lies in a working plane 9. Furthermore, a reservoir 10 for an electromagnetic radiation solidifiable powdery building material 11 and a movable in a horizontal direction H coater 12 for applying the building material 11 is provided. Preferably, the coater 12 extends transversely to its direction of movement over the entire area to be coated. The building material 11 is preferably a powder. In particular, a metal powder, plastic powder, ceramic powder, sand, filled or mixed powder is used. Preference is given to using a plastic powder, for example a polymer powder such as polyamide, in particular polyamide 12, or polystyrene. The powder can be present as virgin, old or mixed powder. The device further comprises a laser 13. The laser beam 14 generated by the laser 13 is directed by a deflector 15 and by a focusing device 16 on a coupling window 17 and from this into the process chamber 3 passed through and focused at a predetermined point in the working plane 9. By the laser beam 14, the applied layer of the building material is selectively solidified at the locations which correspond to a cross section of the object to be produced.

There is further provided a control unit 18 through which the components of the apparatus are controlled in a coordinated manner for carrying out the building process. A control unit 18 according to the invention is designed as described below.

The laser sintering apparatus 1 may further include a compacting apparatus for compacting powdery building material 11. This may for example be formed as shown in Fig. 2. The coater 12 has two jaws 51, 52 arranged at a distance from each other and at a distance above the working plane, between which a powder reservoir 20 is located. The jaws extend over the entire width of the construction field. At the mutually facing inner sides of the jaws each have a blade 60, 61 is provided, which also extends over the entire field width and which protrudes downwards on the jaw in the direction of the working plane. The underside of the blade has a distance d from the carrier surface or the last solidified layer which corresponds to the layer thickness of the desired layer. At the underside facing the working plane, the blades have inclined surfaces 60c, 61c. The sloping surfaces form an order surface. Due to their shape, the blade 60, 61 can both coat and compact the powder and is therefore referred to below as a compressor blade. 2, the illustrated instantaneous travel direction of the coater 12 is indicated by B.

In operation of the laser sintering or laser melting apparatus 1 with a compaction apparatus as described above, the build-up material 11 is additionally supplied before each coating operation in the coater 12 in an amount sufficient to apply a layer of the powder. Subsequently, the coater 12 moves over the construction field, wherein the compressor blade 60 a layer 21 with the predetermined powder ^¬ layer thickness d applies. This powder layer thickness d corresponds to the above-mentioned preset, predetermined distance between the underside of the blade, in this case the lower edge of the blade 60, 61 and the carrier surface or the last solidified layer. By the inclined in the coating direction B surface 60c is applied to the powder to be distributed, which is located in the front of the compactor blade 60 powder column, a force which is directed into the working plane exerted. Thus, the powder 20 is compressed during the application of the layer. Applying the powder layer and compression can thus take place substantially simultaneously. An applied and compacted powder layer corresponds in height or thickness to the above-mentioned predetermined thickness d, which may for example be 0.10 mm, 0.12 mm or 0.15 mm thick. Subsequently, the cross section of the object 3 in the respective layer is irradiated with the laser beam and thus the powder is solidified. Thereafter, the coater 5 is filled again with powder and is moved in a direction opposite to the direction B shown in FIG. In this case, the second compressor blade 61, which is mirror-symmetrical to the first compressor blade 60, acts as a coater and applies a new powder layer to the last solidified layer or the powder surrounding the solidified region.

As an alternative to the blades of the compression device described above, the compression device may also be designed differently. For example, the blade may be in the form of a flat blade F having a surface 60c 'substantially parallel to the surface of the powder (Figure 3a), a radius blade R having a rounded surface 60c''(Figure 3b) or a roof blade D having two surfaces sloping towards one another 60c '''and60c''''(FIG. 3c). Alternatively, the compacting device can also be designed, for example, as a roller or as a roller. The compression essentially proceeds analogously to what has been described above. It can essentially be done at the same time or after the application. Preferably, application and compression take place simultaneously. However, a different density of the powder bed before solidification can also result from the choice of different powders or different powder material. In the case of the same powder, for example, an old powder may have a lower powder density in comparison with the corresponding new or mixed powder. Investigations have shown that the penetration depth of the energy beam with unconsolidated powder of low compaction is increased compared to unconsolidated powder of higher compaction. The relative increase in powder bed density, for example by means of the blades described above, can thus be determined by the methods described below.

For better illustration, all embodiments and examples presented here are described in such a way that the at least one first specimen PI after the optional compaction of the powder bed has a higher powder bed density than the at least one second specimen P2 after the different compaction step or without the compaction step. Of course, it can also behave the other way round. Correspondingly, the respective first specimens PI, which are generated from a powder with a higher compression in comparison to a respective second specimen P2, in FIGS. 4a), 5a) and 6a), in each case the second specimen P2, which consists of a powder are generated with a lower compression, shown in Figs. 4b), 5b) and 6b). A general overview of the method steps (VS) is shown in FIG. 7.

In a first embodiment of the present method, for example in a laser sintering or laser melting apparatus described above, as shown in FIG. 4a), at least one first specimen PI made of a building material, preferably a powder, is produced as an object to be produced (see also FIG VS1-VS3). For this purpose, at least one powder layer is applied to the construction field (FIG. 7, VS1) and compacted (FIG. 7, VS2), for example by the compression devices described above. Preferably, the application of the powder layer and the compacting of the powder take place simultaneously instead of. The compressed powder layer has a predetermined thickness d to be solidified.

Subsequently, the at least one first specimen PI in the form of a platelet PI ', e.g. of a rectangular plate manufactured by the method described above by selectively solidifying at positions corresponding to the cross section of the plate to be produced (Figure 7, VS3). The construction process preferably takes place under standard conditions known to those skilled in the art. Preferably, only a single

Layer exposed (Figure 7, VS3). The plate PI 'is then, as shown in Fig. 4a), in the midst of unconsolidated powder material and has a perpendicular to the powder flow dimension, the thickness dl on. Preferably, several first specimens, e.g. 2 to 50 simultaneously or sequentially, i. made by repeating the above steps.

Subsequently, at least a second sample P2 is repeated by the process described above in the same or a comparable laser sintering or laser melting apparatus, preferably using the same powder (Figs. 4b, 7, VS1-VS3). Preferably, all construction conditions, such as, for example, building temperature and construction time, correspond to those of the production process of the abovementioned first test specimen. The predetermined powder layer thickness d to be solidified likewise preferably corresponds to the predetermined powder layer thickness d in the production process of the abovementioned first test specimen by appropriate adjustment of the coater and / or the compacting device. Instead of the compression device used above, either a different compression device or no compression device is used. The applied powder layer before solidification, regardless of the optional or different compression step has the same thickness d mentioned above. After preparation of the second specimen P2 in the form of a small plate P2 'by exposure at selective points (FIG. 7, VS3), eg a rectangular plate, this has a length perpendicular to the powder path, the thickness d2 and lies as shown in FIG. 4b ) in the midst of unconsolidated powder material. Preferably, several second test specimens, for example 2 to 50, are produced simultaneously or in succession. The platelets are preferably cleaned after completion, for example by blasting with glass beads or by cleaning with a brush.

The lengths running perpendicular to the course of the layer, the thicknesses of the above-mentioned first and second specimens d1 and d2, are subsequently measured (FIG. 7, VS4), for example with an outside micrometer, preferably after removal of the test specimens from the machine. After determining the measured values, the thicknesses d1 and d2 of the first specimen PI 'and the second specimen P2' are compared with each other (S5). In the case of a plurality of first and / or second test specimens, a suitable index number is selected, which is preferably an average or a frequency distribution of the respective thickness di or d2.

As can be seen from FIGS. 4 a) and b), a small plate PI ', which was manufactured from a previously compacted powder, has a smaller thickness compared with a small plate P2' without a compacting step. The second specimen or bodies P2 can also be produced before or simultaneously with the first specimen PI within a production process. However, the second specimen P2 can also be produced as a reference body independently of the first specimen PI, ie in an earlier manufacturing process. The determination of the thickness di or d2 perpendicular to the course of the layer does not have to take place at the same time as that of the first specimen PI. It can also be done once as a reference value and, for example, noted and used for later produced first or further specimens. Furthermore, the comparison can also be made indirectly, for example by determining a quotient of platelet thickness in relation to the preset powder layer thickness before solidification and subsequent comparison of the quotients.

As mentioned above, a different powder bed density can also be independent of the optional compaction step from the. Choice of a different powder or a different powder material result. Thus, for example, an at least first test specimen PI from a new or mixed powder and an at least second test specimen P2 from a corresponding waste powder can be prepared as explained above.

example 1

Six platelets per manufacturing condition (different blades, different powder material) were prepared in a laser sintering machine according to the above-described method according to the first embodiment. The building temperature was 170 ° C. For this a PA2200 mixed or old powder was used. PA2200 is the trade name of the Applicant's marketed PA12 powder. First, powder blank layers, ie unexposed powder layers, with a total thickness of 6 mm were applied. Each individual powder layer was 0.12 mm thick and was compacted in time with the application of a roof, radius or flat blade. The preset layer thicknesses were the same in each case with and without compression step before solidification with 0.12 mm. Then, in each case, a powder layer to be lighted, which corresponds to the respective

Empty layers was applied. Following was the. each one powder layer selectively exposed in the x and y direction, so that a rectangular plate was prepared. The plates were removed after production from the laser sintering machine and measured in their running perpendicular to the Powder application thicknesses. From the determined values of each production condition (respective blade, respective powder material), the mean value, and the standard deviation - represented in the diagram 1 by a vertical line in each case - was determined.

The results are summarized in Table 1 and partially in Diagram 1. Platelets produced with a higher efficiency compaction step (roof blade> radius blade> flat blade) have a comparatively smaller thickness (roof blade <radius blade <flat blade).

Platelets which were prepared with a relatively fresher powder material have a comparatively clotting ^¬ Gere thickness (mixed powder <waste powder).

Table 1 Blade type Dac kiinge Radius kl. F! Ac klmge

Layering mixed powder 0.215 0.221 0.226

thick [mm] mature powders 0.283 0.321 0.321

Diagram 1

Radius blade roof blade flat blade

In a second embodiment of the present invention, as shown in FIG. 5, a different first and second specimen PI ", P2" are produced by means of the method and building material described above. Identical process steps and devices / materials are therefore not repeated.

In the following, the different powder bed density is based on the use of different compaction devices. However, as mentioned above, a different powder bed density can also depend on the age of the powder material, regardless of a compression step.

For the preparation of the first and second specimens, PI "and P2", the above-described steps of applying build material (Figure 7, VS1), of optional densification

(Figure 7, VS2, VS2 ') and selective solidification (Figure 7, VS3) for each specimen at least three times, preferably multiple times (Figure 7, d)). In this case, one or more powder layers of a predetermined length dimension are selectively excluded from the solidification in the first PI and in the second sample P2. The powder layers are preferably excluded from solidification such that the non-solidification region extends either over the entire width or over the entire length of the specimen (x or y direction). The number of non-solidification areas corresponds to a natural number n, where zero is excluded. Thus, after solidification, a first and a second specimen according to the second embodiment of the present invention with recesses S, s, which, for example, as

Slits can be formed. However, they may also be different, e.g. be formed in the form of grooves. The specimen according to the second embodiment may be formed, for example, as a block in the form of a cube or cuboid.

Depending on the number of powder layers excluded from the consolidation, the non-solidification areas may vary in size. For example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more powder layers may be excluded from solidification in a predetermined range. For example, a powder layer may be 0.12 mm thick so that the dimensions of the non-solidification regions in the x-direction (perpendicular to the powder profile) are 0.12 mm, 0.24 mm, 0.36 mm, 0.48 mm, 0, 60 mm and more. The sequence, number, size and position of the non-solidification areas can be chosen arbitrarily, taking into account the above. It is convenient, however, to choose them equally in the first and second specimens. Adhering powder grains are preferably removed after completion of the sample or sample, in particular by blasting.

After completion of the specimen or bodies, the dimension of the recess (s) running perpendicular to the course of the layer, i. the height h is determined (Figure 7, VS4). In particular, the number of the smallest recesses in the respective specimen is optically determined (FIG. 7, VS4). For example, such that the respective specimen is lifted against the light and the number of visible smallest recesses is determined by eye. The number then represents the code number to be compared (FIG. 7, VS5). Additionally or alternatively, the perpendicular to the layer running height of the recesses can be measured. Preferably, the number of the smallest recesses in combination with the height of the recesses is determined. As shown schematically in FIG. 5, due to the high penetration depth of the energy beam, recesses s in a second test body P2 ", which is produced from powder with lower compression, are melted with rather more than recesses in a first test body PI" with comparatively higher powder density. Consequently, the number of the smallest is also

Recesses in a first specimen PI '', which is made of compacted powder, larger compared to a second sample P2 "made of non-compacted powder. At the same time, the height of the recess in a second specimen made of a powder having a comparatively lower powder bed density is lower as compared with the corresponding recess in a first specimen made of powder having a comparatively higher powder bed density.

Example 2

Each 12 test pieces per compression device (in the z-two layers of six specimens in a range with the same powder bed temperature) were prepared in a laser sintering machine according to the method described above according to the second execution ^¬ form. The building temperature was 170 ° C.

For this a PA2200 powder was used. First, powder blankets, i. unexposed powder layers, applied with a total thickness of 6 mm. Each individual powder layer was 0.12 mm thick and was compacted in time with the application of a roof, radius or flat blade. The layer thicknesses were in each case the same size with and without compression step before solidification with 0.12 mm. Then, the powder layers to be exposed, which were applied according to the respective vacant layers. In each case twelve areas of 3, 4 or 5 powder layers were selected, respectively

0.36 mm, 0.48 mm and 0.60 mm, and not solidified to a predetermined length dimension. The specimens were then removed from the laser sintering machine. Adherent powder grains were removed by blasting. The number of the twelve smallest opened recesses, here in the form of slits, was optically determined by keeping the test piece against the light. The results are summarized in Diagram 2. Test specimens which have been produced with a higher efficiency compaction step (roof blade> radius blade> flat blade) have a comparatively larger number of smallest recesses (roof blade> radius blade> flat blade). For example, the twelve smallest slots can be counted. In the example shown, test specimens which were compacted in the manufacturing process by means of a roof blade, the twelve smallest slots still seven open slots, which before solidifying the height of 0.36 mm and 5 open slots, which before solidification of the height 0.48 mm corresponded. On the other hand, specimens compacted in the manufacturing process by means of a radius blade had as the twelve smallest slits only one open slit which before solidification of the height corresponded to 0.36 mm and eleven open slits which corresponded before solidification of the height 0.48 mm , However, test specimens which were compacted in the manufacturing process by means of a flat blade had as the twelve smallest slits only twelve open slits, which corresponded before solidification of the height 0.48 mm.

Diagram 2

slotted panels

Radius blade Roof blade Flat blade

ΆΟ, Μ ■ 0.48 Hl 0.6

In a third embodiment of the method according to the invention, as is apparent from FIG. 6, a further first PI '' 'and second test body P2' '' are produced by means of the method and building material described above. Identical process steps and devices / materials are therefore not repeated.

To produce the first PI '''and second sample P2''', the above-described steps of applying build material (Fig. 7, VS1), optional densification (Fig. 7, VS2), and selective solidification (Figs , VS3) for each specimen at least twice, preferably many times performed (Figure 7, d)). In this case, a test specimen PI " ¹ , P2""which is hollow inside and filled with unconsolidated powder is produced with a side wall which is open on the upper side and closed by a bottom on the underside. Of the thus prepared specimen is thus a container. Preferably, the specimen is an upwardly open cylinder He may also be shaped differently, for example in the form of an upwardly open cube or cuboid. It is important that no cover layers are applied to the last exposed surface so that the test piece can be removed and measured intact with the powder bed surface. As schematically shown in Fig. 6, the first PI '''and the second sample P2''' are made to have the same inner dimensions, respectively. Consequently, they also have an equal size powder surface AI and A2.

After completion of the specimens PI ' ¹ ', P2 '''in each case a first height of the powder surface is determined relative to the side wall of the respective specimen. Subsequently, a defined, in each case equal, force K is exerted on the powder surface by means of a compression device, for example by means of a compression punch or a compression plate with the surface A (shown schematically in FIG. 6c). This force is perpendicular to the powder surface and pushes it evenly downwards, ie towards the ground. The measurement of the first height and the exertion of the force K is preferably carried out after removal of the specimen from the machine. For example, the compression is carried out in a powder rheometer.

After exerting the force K, in each case a second height of the powder surface relative to the respective side wall is measured, and the height difference Ah between the first and the second measurement result is determined (shown schematically in FIG. 6c, FIG. 7, VS4). The height difference is thus associated with the respective specimen, perpendicular to the course of the layer Length dimension. It corresponds to the distance the compression agent travels through the compression of the powder. The compaction is defined, for example, as a percentage of compressibility, wherein the height difference (x%) is set in relation to the respective height of the powder surface before the application of the force K (100%).

Compared to a first specimen PI ^{1 1 1} , which was produced from a powder with a comparatively higher powder bed density, Ah is larger in a second specimen P2 ''', which was produced from powder of lower powder density (FIG. 7, VS5). , As a "maximum" reference value, for example, a cylinder produced in this way can be produced from and filled with homogenized, uncompacted powder.

Example 3

In each case six specimens per experimental condition (different blades) in the form of an upwardly open cylinder, each with the same size inner dimensions were in a laser sintering machine according to the above-described method according to the third embodiment of the present invention Herge ^¬ presents. The building temperature was 170 ° C.

For this a PA2200 mixing powder (50% new, 50% old powder) was used. First, powder blank layers, ie unexposed powder layers, with a total thickness of 6 mm were applied. Each individual powder layer was 0.12 mm thick and was compacted in time with the application of a roof, radius or flat blade. The layer thicknesses were in each case the same size with and without compression step before solidification with 0.12 mm. Then the powder coatings to be exposed took place. th, which were applied according to the respective vacant layers. , Furthermore, six specimens were prepared from the same but homogenized and uncompacted mixed powder. The specimens were after production 25.2 mm high (external dimension). The height of the powder cylinder was 12.6 mm (inside dimension).

The specimens were then removed from the laser sintering machine. The non-solidified powder inside the sample remained inside. The height of the powder surface relative to the respective specimen was determined as described above. For this purpose, a powder rheometer, for example a Freemann FT 4 powder rheometer, was used with a compression punch. Subsequently, with the stamp a uniform pressure

(Force K) of 0.5; 2; 4; 6; 8th; 10; 12; 14; 16 or 18 kPa applied to the respective powder surface A (normal tension). As described above, the height differences Ah between the respective first and second measurement results were determined and compared with the differences in height of the other specimens. The height differences are expressed here as% in relation to the amount before the exercise of the force K (100%).

The results are summarized in Diagram 3. Test specimens produced with a higher efficiency compaction step (roof blade> radius blade> flat blade> unsealed) have a comparatively smaller height difference (roof blade <radius blade <flat blade <uncompacted). Diagram 3

compression cylinder

A control unit according to the invention is furthermore so pro grammable ^¬ that it so controls laser sintering or laser melting apparatus according to the invention that at least the

Steps of applying powder material, as well as the selective solidification for producing a first inventive ^¬ specimen are executed. Preferably, a He ^¬ invention according to ^"control unit is programmed so that at least the steps of applying powder material, and the se ^¬-selective solidification are carried out for producing a first erfindungsge- MAESSEN specimen. In particular, it ^¬ invention contemporary control unit is programmed so that at least the Steps of applying powder material, the optional compaction and the selective solidification are carried out for producing a first specimen according to the invention and these steps are optionally repeated. Although the present invention based on a Lasersinterbzw. Laser melting device has been described, it is not limited to the laser sintering or laser melting. It can be applied to any methods of generatively producing a three-dimensional object by layering and selectively strengthening a building material. The imagesetter may comprise, for example, one or more gas or solid-state lasers or any other type of laser such as laser diodes, in particular Vertical Cavity Surface Emitting Laser (VCSEL) or Vertical External Cavity Surface Emitting Laser (VECSEL), or a line of these lasers. In general, any device can be used as an imagesetter, with the energy as wave or particle radiation selectively to a

Layer of the building material can be applied. Instead of a laser, for example, another light source, an electron beam or any other energy or radiation source can be used, which is suitable to solidify the building material. Instead of deflecting a beam, it is also possible to use exposure with a movable line imagesetter. Also, selective mask sintering using an extended light source and a mask, or high-speed sintering (HSS), which selectively applies to the build material a material that increases the radiation absorption at the respective sites (absorption sintering) ) or reduced (inhibition sintering), and then exposed nonselectively over a large area or with a movable line exposer, the invention can be applied. Instead of introducing energy, the selective solidification of the applied build-up material can also be done by 3D printing, for example by applying an adhesive. In general, the invention relates to the generative production of an object by means of layered application and selective solidification of a building material, regardless of the manner in which the building material is solidified.

As a building material, various materials may be used, preferably powder, in particular metal powder, plastic powder, ceramic powder, sand, filled or mixed powder.

Claims

1. A method for determining a relative powder bed density in a device for producing at least one three-dimensional object by layered application and selective solidification of a powdered building material,

the method comprising producing at least a first specimen comprising the steps

a) application of a layer of the pulverulent build-up material within a construction field by means of a coater moving over the construction field,

b) optionally compacting the applied layer of the building material,

c) selectively solidifying the applied layer at locations corresponding to a cross section of the at least one first specimen to be produced by means of a solidification device and

d) optionally repeating steps a) to c) until the at least one first test specimen is completed,

the method further comprising the steps of:

Determining at least one length dimension assigned to the at least one first specimen perpendicular to one

Layer course of the powdery building material and

Comparing the at least one determined length dimension with at least one corresponding length dimension of at least one second test specimen.

2. The method of claim 1, wherein the at least one second specimen is produced by means of a powder-based generative layer-building process, preferably using the same powdery building material as for producing the at least one first specimen.

3. The method of claim 1 or 2, wherein for the preparation of the first specimen, a compaction step b) is performed and for the preparation of the second specimen no compaction step b) is performed or wherein for the preparation of the first and the second specimen different compression steps b) performed become.

4. The method according to any one of claims 1 to 3, wherein the first and / or the second specimen is removed before determining the at least one length dimension from the device out or.

5. The method according to any one of claims 1 to 4, wherein the steps a) of the powder application and b) of the compacting are performed such that the in step c) to be consolidated layer thickness of the first specimen is the same as in step c) to be solidified Layer thickness of the second specimen.

6. The method according to any one of claims 1 to 5, wherein the first and the second specimen is each a platelet, which is prepared by performing steps a), b) and c),

and the at least one length dimension to be determined

Dimension of the specimen perpendicular to the solidified layer.

7. The method according to any one of claims 1 to 5, wherein the first and the second specimen by at least twice, preferably many times, performing the steps a), b) and c) are prepared.

8. The method of claim 7, wherein each of the first and second specimens is an open-topped container filled with unsolidified powder, preferably a cylindrical container,

wherein the two specimens have the same geometric inner dimensions and

in order to determine the at least one length dimension assigned to a test specimen, in each case a defined pressure is applied to the unconsolidated powder surface of the test specimen and the at least one length dimension is the resulting change in height of the powder surface.

9. The method of claim 7, wherein each of the first and second specimens is an object having n recesses, where n is a natural number, and

wherein each recess comprises a non-solidification region of a predetermined length dimension in which one or more layers have been excluded from solidification and the length dimensions associated with the specimens are those predetermined length dimensions of the non-solidification regions, preferably taking into account only the non-solidification regions visible after completion of the specimens.

10. The method of claim 9, wherein each of the first and second specimens is a three-dimensional object having n non-solidification areas, where n is 1 and

wherein at least two, preferably all n, non-consolidation regions in their predetermined length dimensions perpendicular to the course of the powdered building material differ from each other.

11. The method according to any one of claims 1 to 10, wherein at least two, preferably a plurality of first specimens and / or at least two, preferably a plurality of second specimens are prepared and / or at least two, preferably a plurality of length dimensions of the Specimens are determined and

the length dimensions of the first specimen (s) and the length dimensions of the second specimen or specimens (s) are compared on the basis of a suitable index number, the index number preferably being an average value or a frequency distribution of the length dimensions.

12. A method for producing at least one three-dimensional object by layered application and selective solidification of a powdered building material, comprising the steps of: a) applying a layer of the pulverulent build material within a construction field by means of a coater moving over the construction field,

b) optionally compacting the applied layer of the building material,

c) selectively solidifying the applied layer at locations corresponding to a cross section of the at least one object to be manufactured by means of a solidification device and

d) optionally repeating steps a) to c) until the at least one object is completed, wherein the building material is solidified such that at least a first specimen is produced and the following steps are carried out to determine a relative powder bed density:

Layer course of the powdery building material and

13. The method according to claim 12, wherein at least one object and at least one first and / or second test specimen are produced.

14. The method according to any one of claims 1 to 13, wherein the comparison of the determined length dimensions is carried out indirectly, preferably by comparing a quotient formed from the first specimen assigned determined Längenab- measurement and at least one layer thickness to be solidified with a corresponding quotient of the at least one second Test specimen and / or object.

A programmable control unit for a device for producing at least one three-dimensional object by layering and selectively solidifying a powdery building material, wherein the control unit is designed to control the device so that it has all steps a) and c) and optionally b) and / or d) carrying out at least one of the processes according to one of claims 1 to 14.

16. An apparatus for producing at least one three-dimensional object by layered application and selective solidification of a powdered building material with

a coater movable over a building field for applying a layer of the building material within the building field, optionally a compacting device for compacting the applied layer of the building material, wherein the compacting device may optionally be formed integrally with the coater, and

a solidifying device for selectively solidifying the applied layer at locations corresponding to a cross-section of the at least one object to be manufactured,

wherein the apparatus is adapted and / or controlled to repeat the steps of applying and selectively solidifying until the at least one object is completed, and

wherein the device further comprises a control unit according to claim 15 and / or is signal-technically connected to such a control unit.