Scraper unit for additive manufacturing system with powdery starting material

Abstract

The invention relates to a scraper unit for an additive manufacturing system with a powdery starting material. By means of the scraper unit according to the invention, an improved linearity of the scraper and parallelism with respect to the build level are achieved. The scraper is suspended on a crossbeam by means of an adjustable fastening assembly, and the crossbeam in turn is fastened to a guide carriage on one side by means of a locating bearing and on the other side by means of a floating bearing.

Description

[0001] This invention relates to a scraper unit for an additive manufacturing system having a powdered starting material. Improved linearity and parallelism relative to the build-up level are achieved by the scraper unit according to the invention.

[0002] Apparatus and methods for additive manufacturing (also known as additive manufacturing, AM) of workpieces are known in the prior art. "Generative manufacturing methods" or "3D printing" are also mentioned. Here, the raw material can be in powder, filament, or liquid form. Powder methods include, for example, selective laser melting (SLM), selective laser sintering (SLS), or electron beam melting (EBM). Here, the raw material consists of plastic or metal.

[0003] In methods utilizing raw materials in powder form, the material is applied in layers to a lowerable working surface for partial melting or sintering. The working surface is then lowered by one layer thickness. Another layer is then applied to this first layer, and this process is repeated. Here, the portion to be melted or sintered is selected in a layer-by-layer construction manner for a three-dimensional workpiece.

[0004] For component quality, uniform (homogeneous) thickness of each layer is crucial. Specifically, this layer must have equal thickness across the entire plane and be parallel to the build-up layers initially located on the lowerable working surface and subsequently on the respective previously treated layers. Achieving this requires precise powder application, which necessitates a high-precision doctor blade and blade guide. Here, two problems arise with prior art doctor blades, becoming more severe as the doctor blade becomes larger and the temperature in the build-up space increases. One problem is doctor blade deflection, which causes deviations in blade linearity and thus generally results in a thinner powder layer at the center of the movement path. The second problem is thermal expansion.

[0005] If additive manufacturing methods initially started as purely rapid prototyping, providing only design models, often at a reduced scale, the technology has simultaneously evolved to the point where larger functional components can be constructed. In particular, in addition to powder materials initially composed only of polymers, materials made of metals, glass, and ceramics can now be used. Consequently, the demand for construction space has increased, leading to the need for larger scrapers, which in turn introduces the aforementioned problems.

[0006] Furthermore, the processing of metals or ceramics requires relatively higher melting or sintering temperatures than plastics. Therefore, in addition to more powerful lasers, electron beam guns are also used as the radiation unit for these methods, allowing more energy to be input into the powder. The temperatures generated in this way also heat the doctor blade distributing the powder, which has been newly applied to the last layer that has just solidified, to form a new layer. The thermal expansion of the doctor blade during this process generates stress and deformation in the doctor blade between the fastening points.

[0007] In the case of polymer powders, thermal problems occur only to a lesser extent, as temperatures in the preheated powder bed typically only reach around 180°C, whereas in the case of metals such as titanium and titanium alloys, the surface of the preheated powder bed requires temperatures exceeding 1200°C. Therefore, the greatest problems arise in the case of electron beam methods for metal powders, the primary application area of ​​this invention. Specifically, temperatures typically reach around 400°C at the center of the doctor blade, and around 50°C in the edge regions not located above the powder bed. This results in considerable stress in the blade suspension system and the blade itself due to varying degrees of thermal expansion. This leads to deviations in linearity. Background Technology

[0008] For example, EP 2 010 370 B1 describes a powder application device designed to produce simple changes while maintaining parallelism relative to the construction level. Here, a replaceable coating module that can be inserted into a frame-shaped receiving device is used. Two blades are positioned at the edge via a web in the coating module. The blades are set relative to the construction level via the frame-shaped receiving device, into which the coating module is hooked via the web. Therefore, there is a problem that the blade mounted only on the outer side may skew when larger. In the event of thermal deformation, the double suspension has a particularly negative impact on the linearity and parallelism of the blades relative to the construction level, firstly on the blades in the coating module of the frame-shaped receiving device, and then on the frame-shaped receiving device itself.

[0009] Purpose of the invention

[0010] Starting from these problems, one object of the present invention is to provide a scraper unit that overcomes the disadvantages of prior art devices. In particular, an object of the present invention is to provide a device that can apply a particularly uniform powder layer that is parallel to the horizontal orientation of the construction, even at large sizes and high operating temperatures. Summary of the Invention

[0011] This objective is achieved by a scraper unit as described in this invention. Preferred design variations are the target of the appended claims.

[0012] The scraper unit according to the invention is used in an additive manufacturing system having a powdered starting material. The scraper unit includes a scraper and a suspension system, which is mounted in the additive manufacturing system in a horizontally movable manner.

[0013] If a scraper is mentioned in this application, the term includes the actual blade and the combined unit formed with the actual blade; thus, for example, in the case of a double-blade scraper, it refers to the two blades and the means of connecting the two blades.

[0014] The suspension system includes a crossbeam, which is mounted in a positioning bearing on one side and in a floating bearing on the other side. The crossbeam is connected to the guide bracket via the positioning bearing and the floating bearing, respectively.

[0015] The scraper is suspended and secured to a crossbeam along its length by multiple fastening devices. These devices allow for adjustment of the spacing between the scraper and the crossbeam to ensure the scraper is parallel to the build level of the additive manufacturing system. To achieve this, several fastening devices should be installed depending on the scraper's length, ensuring sufficient spacing between them to prevent deflection and allow for precise adjustment of the suspended scraper's linearity. Parallelism relative to the build level can then be established via this entire adjustable fastening system.

[0016] A key feature is the planarity of the applied layer. Here, the maximum achievable position is limited by the grain size of the metal powder used. With the scraper system according to the invention, the target planarity of the powder layer corresponds to a value smaller than the average grain diameter d. 50 Half the deviation. The average powder particle size d of conventional metal powders currently used in electron beam melting methods. 50 The diameter is approximately 50 micrometers. In special cases, smaller diameter powders are also used. Therefore, the accuracy for conventional system operation is within a maximum deviation of 25 micrometers, preferably a maximum of 10 micrometers.

[0017] The scraper can be single-blade, double-blade, or multi-blade. The single-blade, double-blade, or multi-blade is positioned symmetrically beneath a solid block, through which the fastening device extends to a crossbeam. Connection to the block is achieved via horizontal bolts and spacers inserted between the individual blades, occurring within cutouts located in the area of ​​the vertical fastening device. The blades consist of a flexible, thin metal sheet with a comb-like tooth system machined in it, allowing the blades to adapt flexibly to uneven surfaces. A pre-scraper is positioned on the side of the block parallel to the blades. The distance between the lower edge of the pre-scraper and the lower edge of the blade is typically up to 1 mm, generally about 0.5 mm. The pre-scraper minimizes pressure by distributing and smoothing the powder on the blades, facilitating the initial distribution of the powder. The entire block is covered by a roof-like structure, which can be configured flat, curved, or angled.

[0018] Guide brackets are preferably suitable for guides with torsional rigidity in additive manufacturing systems. A torsional rigid guide means that the guide bracket is connected to the additive manufacturing system in a manner that allows torque to be transmitted from the guide bracket to the additive manufacturing system. Therefore, translational movement is only possible in the provided direction above the building level, and not in other spatial directions or rotation.

[0019] The horizontally movable installation of the suspension system in the additive manufacturing system can be achieved via, for example, rails or guide rods. The horizontally movable installation can exist individually or in multiples on each side, particularly in pairs. The horizontally movable installation need not be horizontally oriented and act as a support, but can preferably be vertically oriented. The latter is particularly advantageous in embodiments where the rails and guide brackets have dovetail-like connections and are in the form of double rails, in order to configure the guide brackets with torsional rigidity to connect to the building space of the additive manufacturing system.

[0020] The crossbeam of the scraper unit can be configured as a hollow body. This helps reduce weight while maintaining high rigidity. Here, the hollow body can be open at the ends, meaning it can be tubular, or it can be closed. The crossbeam preferably has a rectangular or elliptical cross-section. This provides greater resistance to torque during installation.

[0021] The locating bearing is preferably surrounded around the crossbeam at least on both sides, and prevents the crossbeam from moving relative to the locating bearing in all three spatial directions.

[0022] A centering pin can be attached to the inner circumference of the positioning bearing, wherein the centering pin engages with a corresponding hole in the crossbeam. This achieves reliable positioning of the crossbeam on the guide bracket. Furthermore, the centering pin contributes to the securing of the crossbeam and, particularly, prevents movement of the crossbeam above the construction level in a direction orthogonal to the crossbeam's direction of movement in a plane parallel to the construction level.

[0023] The floating bearing surrounds the crossbeam using a sliding assembly, allowing the crossbeam to move relative to the bearing along its longitudinal axis, preventing movement in two spatial directions perpendicular to the crossbeam. This compensates for expansion of the scraper and crossbeam due to increased temperature, preventing stresses that could cause deformation within the scraper.

[0024] The scraper preferably has a length from 0.1 to 5 meters, more preferably from 0.2 to 4.5 meters, or from 0.25 to 4 meters, or from 0.3 to 3 meters, or from 0.3 to 2.5 meters. The greater the advantage of the scraper unit according to the invention, the longer the scraper.

[0025] The parallelism deviation ΔP is defined as the difference between the maximum and minimum spacing between the doctor blade and the construction level, preferably from 1 to 50 micrometers, more preferably from 2 to 45 micrometers, or from 3 to 40 micrometers, or from 4 to 35 micrometers, or from 5 to 30 micrometers, or from 10 to 25 micrometers. By definition, the parallelism deviation ΔP detects the doctor blade's tilt and deviation from linearity. The parallelism deviation ΔP is a measure of the quality of the doctor blade adjustment. Therefore, the doctor blade unit according to the invention achieves excellent uniformity of layer thickness, and thus improves component performance. Therefore, for example, smaller layer thicknesses can still be reliably produced, thereby increasing surface quality and resolution.

[0026] The suspension system preferably has 3 to 30, more preferably 3 to 25, or 3 to 20, or 3 to 15, or 3 to 10, or 3 to 5 fastening points per meter of scraper length. This number of fastening points has proven sufficient to reliably set the linearity of the scraper, even with very long scrapers and high operating temperatures.

[0027] The fastening device is preferably a positioning bolt. Here, the bolt must have a sufficiently long thread to provide the necessary adjustment stroke. The bolt can then be easily adjusted using a nut. This occurs during scraper installation. If necessary, the individual bolts can be readjusted to re-establish linearity and parallelism.

[0028] In the case of the scraper unit, in a preferred design variant, the distance between the scraper and the crossbeam can be changed during operation of the additive manufacturing system by means of electromechanical and / or hydraulic actuators acting on the fastening device. In this automated variant of the scraper unit, deviations in linearity and parallelism are measured and monitored via optical and / or mechanical sensors. This information is then used to actuate actuators, such as actuated motors or hydraulic lines with actuators, for example, the actuators correspondingly correct the length of the fastening device to re-establish linearity and parallelism. With this active system, further improvements in layer evenness can be achieved, thereby further improving component performance. In particular, this gives the additive manufacturing system the advantage of being able to operate uninterruptedly without interruption for readjustment. Attached Figure Description

[0029] Figure 1 This is a cross-sectional view of the scraper unit.

[0030] Figure 2 This is a three-dimensional view of the scraper unit as seen from the locating bearing side.

[0031] Figure 3 This is a three-dimensional view of the scraper unit as seen from the floating bearing side.

[0032] Figure 4 It is a three-dimensional cross-sectional view of a scraper unit having a cross-section through a fastening device.

[0033] Figure 5 yes Figure 4 The magnified details show the fastening device and the lower area of ​​the scraper. Detailed Implementation

[0034] The drawings show only one preferred design variation as an example of the invention. Therefore, the examples of the invention should not be construed as limiting.

[0035] Figure 1 This shows a transverse cross-sectional view of the scraper unit according to the present invention, wherein the scraper unit is in Figure 2 as well as Figure 3The diagram again shows the scraper unit in three dimensions. This design variant of the scraper unit shown in the diagram is equipped with a scraper (1) with two blades. The suspension system (2) includes a crossbeam (3), which, in the diagram, is mounted in a positioning bearing (4) on the left side and a floating bearing (5) on the right side. In each case, the positioning bearing (4) and the floating bearing (5) are sequentially connected to a guide bracket (6). In this example, the scraper (1) is fastened to the crossbeam (3) by seven fastening devices (7) in the form of bolts with end threads and associated nuts. The length of the scraper (1) is 2 meters. Therefore, the scraper suspension system has 3.5 fastening devices per meter of scraper length. The resulting parallelism deviation ΔP is 10 micrometers.

[0036] The crossbeam (3) supports its own weight and the mechanical load of the scraper (1). Deflection of the crossbeam (3) is compensated by a fastening device (7), allowing the scraper (1) suspended below the crossbeam (3) to be linearly oriented and parallel to the building plane. As can be seen in Figures 2 and 3, the crossbeam (3) in this example is configured as a tubular hollow body with a rectangular cross-sectional area and rounded edges. For torsional rigidity, the guide bracket (6) in each case is provided with two track receptacles (8), which engage with tracks having a substantially trapezoidal cross-section via a dovetail connection. These tracks are attached to the sides of the building container to the working surface. In this way, deformation-free movement of the scraper unit above the building plane is ensured to level the applied powder.

[0037] like Figure 3 As can be seen, the floating bearing (5) is formed here by means of four sliding components (9) surrounding the crossbeam (3). Therefore, the crossbeam (3) can expand along its longitudinal axis. The crossbeam (3) remains rigid on the locating bearing side, but can expand in the direction of the floating bearing side and slide through the floating bearing (5), thus not introducing constraint forces into the crossbeam (3).

[0038] exist Figure 4 as well as Figure 5 In the diagram, the area near the fastening device (7) is depicted at an enlarged scale in the cross-sectional view. In the example shown, the bolts of the fastening device (7) extend in a guide sleeve inside the crossbeam (3). The bending area defines the maximum actuation stroke for adjusting the blades (10). The two blades (10) are fastened under a solid center block (11), thus being symmetrically centered in the middle. Fastening occurs via horizontal bolts in corresponding cuts in the solid center block (11), with the blades (10) fastened to the bolts by spacer assemblies to separate them from each other. On the sides of the blades (10), two pre-scraper brushes (12) are attached to the outside of the center block (11).

[0039] For example, a laser sensor system can be attached to the guide bracket (6) for active control of the scraper unit (not shown in the diagram), wherein the laser sensor system monitors the linearity and parallelism of the scraper (1). The information obtained in this way can then be used for readjustment, for example, via an electric actuator motor of a drive nut or piezoelectric component.

[0040] Explanation of reference numerals in the attached figures

[0041] 1 scraper

[0042] 2. Suspension System

[0043] 3 crossbeams

[0044] 4 positioning bearings

[0045] 5 floating bearings

[0046] 6 guide brackets

[0047] 7 Fastening devices

[0048] 8-track housing

[0049] 9 sliding components

[0050] 10 blades

[0051] 11 central blocks

[0052] 12 Pre-scraper

Claims

1. A scraper unit for an additive manufacturing system having a powdered starting material, the scraper unit comprising a scraper (1) and a suspension system (2) mounted in the additive manufacturing system in a horizontally movable manner, characterized in that: - The suspension system (2) includes a crossbeam (3), which is mounted in a positioning bearing (4) on one side and in a floating bearing (5) on the other side. - The crossbeam (3) is connected to the guide bracket (6) via the positioning bearing (4) and the floating bearing (5), respectively. - The scraper (1) is suspended and secured to the crossbeam (3) along its length by a plurality of fastening devices (7). The plurality of fastening devices (7) allow for adjustment of the spacing between the scraper (1) and the crossbeam (3) so that the scraper (1) is oriented parallel to the construction level of the additive manufacturing system. The floating bearing (5) surrounds the crossbeam (3) with several sliding components, so that the movement of the crossbeam (3) relative to the floating bearing (5) can be along the longitudinal axis of the crossbeam (3), while preventing movement in two spatial directions perpendicular to the crossbeam (3).

2. The scraper unit as described in claim 1, characterized in that, The scraper (1) may be a single blade, a double blade, or a multi-blade blade.

3. The scraper unit as described in claim 1 or 2, characterized in that, The guide bracket (6) is suitable for use as a guide with torsional rigidity in the additive manufacturing system.

4. The scraper unit as described in claim 1 or 2, characterized in that, The crossbeam (3) is configured as a hollow body.

5. The scraper unit as described in claim 1 or 2, characterized in that, The crossbeam (3) has a rectangular or elliptical cross section.

6. The scraper unit as described in claim 1 or 2, characterized in that, The positioning bearing (4) surrounds the crossbeam (3) at least on both sides and prevents the crossbeam (3) from moving relative to the positioning bearing (4) in all three spatial directions.

7. The scraper unit as described in claim 1 or 2, characterized in that, A centering pin is attached to the inner periphery of the positioning bearing (4), wherein the centering pin is locked into a corresponding hole in the crossbeam (3).

8. The scraper unit as described in claim 1 or 2, characterized in that, The scraper (1) has a length ranging from 0.1 to 5 meters.

9. The scraper unit as described in claim 1 or 2, characterized in that, The scraper (1) has a length ranging from 0.3 to 3 meters.

10. The scraper unit as described in claim 1 or 2, characterized in that, The parallelism deviation ΔP, defined as the difference between the maximum and minimum spacing between the scraper (1) and the construction level, ranges from 1 to 50 micrometers.

11. The scraper unit as described in claim 1 or 2, characterized in that, The parallelism deviation ΔP, defined as the difference between the maximum and minimum spacing between the scraper (1) and the construction level, ranges from 10 to 25 micrometers.

12. The scraper unit as described in claim 1 or 2, characterized in that, The suspension system (2) has 3 to 30 fastening devices (7) per meter of the scraper length.

13. The scraper unit as described in claim 1 or 2, characterized in that, The suspension system (2) has 3 to 10 fastening devices (7) per meter of the scraper length.

14. The scraper unit as described in claim 1 or 2, characterized in that, During operation of the additive manufacturing system, the distance between the scraper (1) and the crossbeam (3) can be changed by means of electromechanical and / or hydraulic actuators acting on the plurality of fastening devices (7).

15. The scraper unit as described in claim 1 or 2, characterized in that, The multiple fastening devices (7) are positioning bolts.

Images