Method and system for optimizing build orientation for manufacturing articles by additive manufacturing - Patent Application 20070122963

Abstract

The present invention relates to a method for manufacturing an article by additive manufacturing, comprising the steps of predicting stress regions in the article, identifying an optimal build orientation for the article, and dispensing a first powder and / or a second powder to form the article, wherein the first and second powders are the same type of powder but have different recycled levels, and the build orientation is optimized to reduce the amount of non-recycled or less recycled powder.

Description

[Technical Field]

[0001] The present invention relates to a method and system for producing articles by additive manufacturing. [Background technology]

[0002] Metal powder-based additive manufacturing (AM) is gaining popularity in the aerospace, medical, electronics and automotive industries due to its ability to build complex components with relative ease.

[0003] In a typical AM process, a CAD model of the article to be manufactured is first created.

[0004] The model may then be refined to improve the quality and accuracy of the final product that is built.

[0005] The model (or data derived from it) is then processed to form instructions that control the AM machine.

[0006] The AM machine then deposits layers of powder onto a build platform based on the instructions it receives, and then selectively melts or otherwise solidifies the powder, typically with a laser or electron beam, to form one or more articles.

[0007] This process is repeated to build the article layer by layer. Summary of the Invention [Problem to be solved by the invention]

[0008] During the build process, unfused powders can undergo degradation. Metal powders, for example, can gradually oxidize, changing their properties and therefore the properties of articles made from them. The tendency of powders to oxidize typically increases with temperature, and temperature exposure can affect other powder properties as well.

[0009] It is common within the industry to reuse or "recycle" unfused powder in other builds, despite the presence of degraded particles. While this is a common approach to reduce costs without significantly compromising product quality and integrity, the presence of degraded particles in areas where the article will be stressed during use remains at risk of premature failure of the article in those areas.

[0010] In light of the above, it is an aim of embodiments of the present invention to provide a more economical route to producing articles by additive manufacturing.

[0011] In particular, it is an object of embodiments of the present invention to provide a method for minimizing the use of powders that are free of contaminant particles or that contain low concentrations of contaminant particles without compromising the integrity or quality of the article.

[0012] It is a further object of embodiments of the present invention to provide users with improved control over how powders containing no or low concentrations of degraded particles are utilized in build operations. [Means for solving the problem]

[0013] According to a first aspect of the present invention, there is provided a method for manufacturing an article by additive manufacturing, comprising the steps of predicting stress regions within the article, identifying an optimal build orientation for the article, and dispensing a first powder and / or a second powder to form the article, wherein the first and second powders are of the same type but have different recycled degrees, and the build orientation is optimized to reduce the amount of unrecycled or less recycled powder.

[0014] The method according to the first aspect of the invention allows for the manufacture of articles at low cost without compromising the quality or integrity of the build.

[0015] In particular, it has been found that optimizing the build orientation ensures that non-recycled or less recycled, more expensive powder is not dispensed, or is dispensed in reduced amounts, in areas of the article where it is not strictly required, i.e., areas that are not expected to be subjected to high levels of stress during use.

[0016] Rather, in these "low stress" regions, more recycled powder can be deposited alone or as part of a larger blend. This more efficient utilization of the more expensive powders provides a more economical manufacturing route for producing one or more articles by additive manufacturing.

[0017] The method can include performing a stress analysis on a model of the article to predict stress regions within the article, hi some embodiments, the stress analysis can include slicing the model to generate two-dimensional cross sections and performing the stress analysis on the two-dimensional cross sections.

[0018] In this way, numerical stress values ​​for each two-dimensional cross section can be obtained, which allows for more accurate prediction of stresses in particular regions and particular layers of the build. The stress analysis can include finite element analysis.

[0019] The method can include rotating the model until an optimized build orientation of the article is obtained, for example, the model can be rotated, for example, by 90°, from a substantially vertical orientation to a substantially horizontal orientation.

[0020] Support structures are typically used to provide mechanical support for overhangs and thin walls of the article being manufactured. In some embodiments, the build orientation can be optimized to minimize the volume of the support structures, further reducing the cost of the build.

[0021] For example, the method can include orienting the build so that the build is substantially self-supporting. In particular, the method can include orienting the build at an angle between 45° and 90° relative to the build platform.

[0022] The first powder may include powder that has never been recycled, and the second powder may include powder that has been recycled one or more times. In the context of the present invention, non-recycled powder is defined as "virgin" powder that has not previously been exposed to the conditions of a build operation, whereas "recycled" powder can be defined as powder that has been exposed to one or more AM build cycles. Because virgin powder does not contain degraded particles, it is likely to be more expensive than recycled powder.

[0023] In some embodiments, the first powder and the second powder may comprise recycled powders, for example, the first powder may have been previously exposed to build conditions only once, and the second powder may have been exposed to two or more build runs.

[0024] The mixing of the first powder and the second powder may occur once the powders are dispensed onto the build platform, or alternatively, the mixing of the first powder and the second powder can occur before the powders are dispensed onto the build platform.

[0025] In some embodiments, the first powder and the second powder can include a metal or a metal alloy. For example, the powder can include titanium metal or a titanium alloy, such as Ti-6Al-4V.

[0026] The ratio of the first powder to the second powder is varied depending on the predicted stress in the region of the article, hi some embodiments, the ratio of the first powder to the second powder is varied depending on the predicted stress in the region and the predicted or analyzed condition of the recycled metal powder.

[0027] In some embodiments, the ratio of first powder to second powder in one layer may be the same or different from the ratio of first powder to second powder in the previous layer.

[0028] According to a second aspect of the present invention, there is provided a system including a processor for controlling operation of an additive manufacturing machine to manufacture an article, the additive manufacturing machine including a first container and a second container capable of selectively dispensing powder to form the article, the first container and the second container containing the same type of powder and recycled to different extents, respectively, and the processor configured to determine an optimized build orientation to reduce the amount of non-recycled powder or the amount of recycled powder to a lesser extent dispensed to manufacture the article.

[0029] The processor can be communicatively coupled to the additive manufacturing machine. The processor can be configured to receive or generate a model of the article. The model can be a 3D model of the article. In particular, the 3D model can be generated using computer-aided design (CAD) software.

[0030] The processor may be configured to perform a stress analysis on the model to predict stress regions in the article and to determine an optimized build orientation based on the results of the stress analysis. In particular, the stress analysis performed by the processor may include finite element analysis (FEA).

[0031] The processor may be configured to determine a build orientation that further minimizes the volume of the support structure.

[0032] In order that the present invention may be more clearly understood, one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0033] [Figure 1]1 illustrates an example of an apparatus for additive manufacturing of an article. [Figure 2] 1 shows a schematic diagram of a model of an article in a first, non-optimized build orientation. [Figure 3] 10 shows a schematic diagram of a model of an article in a second optimized build orientation. DETAILED DESCRIPTION OF THE INVENTION

[0034] Referring to FIG. 1, in one exemplary embodiment of the present invention, an apparatus 10 for manufacturing an article by additive manufacturing is provided.

[0035] The apparatus 10 comprises a laser beam 11 for irradiating selected areas of powder on a build platform 12, a first container 13 for containing a first powder, a second container 14 for containing a second powder, an electronic valve 15 for controlling the flow of powder from the first and second containers 13, 14, a wiper 16 operable to form a layer of powder on the build platform 12, and a build screw 17 for lowering the build platform 12 during a build. In this example, both the first container 13 and the second container 14 contain titanium powder.

[0036] More specifically, the first container 13 contains titanium powder (powder A) that has not been recycled, and the second container 14 contains titanium powder (powder B) that has been recycled at least once. That is, the first and second containers 13, 14 contain the same type of powder, with only the extent to which each powder has been recycled differing.

[0037] 2 depicts a CAD model 20 of an article to be manufactured by additive manufacturing in a first build orientation. The CAD model 20 may be generated on or received from a personal computer or similar device external to the additive manufacturing apparatus 10.

[0038] Prior to the start of any building operations, the CAD model 20 undergoes finite element analysis (FEA), a computerized method for predicting how a product will react under various physical conditions, such as stress. The CAD model 20 may be refined as needed and subjected to another FEA. Thus, FEA allows a user to predict areas of strain and stress within the article, and areas where the article may fail during use.

[0039] As shown in Figure 2, a CAD model 20 of an article has an area of ​​high stress, designated by reference numeral 21. Therefore, to minimize the accumulation of detrimental particles in area 21, where the article is most likely to be damaged during use, it is desirable to deposit a layer containing an increased amount of Powder A in that area. On the other hand, in areas of the article that experience less stress, it is preferable to deposit a layer containing a higher percentage of Powder B. Powder B is less expensive because it contains a higher content of detrimental particles.

[0040] FIG. 2 also shows a CAD model 20 of the article in a non-optimized build orientation, since in addition to the high stress region 21, an increased amount of powder A is deposited in the remainder of the layer (see shaded region X).

[0041] 3, on the other hand, shows a CAD model 20 of the same article in an optimized build orientation in which the article (and areas of high stress) have been rotated from a substantially vertical orientation to a substantially horizontal orientation, which has the effect of reducing the amount of powder A deposited outside the high stress areas (see hatched areas Y).

[0042] Because a reduced amount of more expensive / more costly Powder A is deposited in the orientation shown in FIG. 3, the overall cost of additively manufacturing the article is reduced.

[0043] Once an optimized build orientation is determined that minimizes unnecessary use of Powder A in areas of the article where Powder A is not or is less needed, the CAD model 20 is electronically sliced ​​to obtain a series of 2D layers, defining planar cross sections through the model 20 of the article.

[0044] The numerical stress values ​​obtained from the FEA analysis are reviewed and analyzed layer by layer to identify the highest numerical stress value for each layer, i.e., the worst case scenario.

[0045] Using this information, reference data on the degradation behavior of titanium powder, and the application requirements of the article being manufactured, the user or an algorithm can determine the appropriate mix ratio of Powder A to Powder B for each layer.

[0046] The mixing ratios for each layer are stored on a personal computer or similar device, and a processor then converts the optimized orientation 3D model and the optimized mixing ratio of Powder A and Powder B for a given layer into a set of instructions that can be understood by the AM machine 10.

[0047] The personal computer (or similar device) is communicatively coupled to the AM machine 10 such that the processor can output instructions to the AM machine 10 to manufacture the article in an optimized orientation, as shown in FIG. 3.

[0048] Upon receiving a command from the processor, one or both of the electronic valves 15 are opened to dispense predetermined amounts of powder A and powder B from the first and second containers 13, 14 onto the build platform 12.

[0049] As noted above, the ratio of Powder A to Powder B can be varied depending on the expected stresses in the region of the article, also taking into account the degradation behavior of Powder B.

[0050] This means that layers of the article that are not subject to high levels of stress, such as the layers above and below region 21 (Figure 3), will contain a higher proportion of Powder B, while layers that are expected to be subject to high levels of stress, such as region 21, will contain a higher proportion of Powder A.

[0051] It will be appreciated that in some cases the powder may comprise 100% Powder A or 100% Powder B depending on the stresses expected in a particular area and the application requirements of the article being constructed.

[0052] To ensure that the layer of blended powder has a substantially uniform thickness, a wiper 16 engages with the powder and is then moved back and forth to spread the powder across the build platform 12 until the desired layer thickness is achieved.

[0053] The wiper 16 is then retracted and held out of contact with the powder. It will be appreciated that as the layer of blended powder is formed, some of the blended powder is wiped off the surface of the build platform 12. This powder is collected in collection chambers located on either side of the build platform 12, allowing for the reuse of this unmelted powder.

[0054] A laser beam 11 is then directed at selected areas of the powder corresponding to the desired shape of the article in an optimized build orientation to fuse the powder within the layer and form a solid mass upon cooling.

[0055] Powder is then dispensed from the first container 13 and / or the second container 14 onto the build platform 12 to form layers with uniform layer thickness, and the above process of irradiating selected areas with the laser beam 11 is repeated until the article is formed.

[0056] It will be understood that the ratio of Powder A to Powder B in each subsequent layer may be the same as or different from the previous layer, and this ratio will depend on the predicted stresses in the particular region of the article as determined by FEA analysis. One or more embodiments have been described above by way of example only, and many variations are possible without departing from the scope of protection afforded by the appended claims.

Claims

1. predicting stress areas within the article; identifying an optimal build orientation for said article; and dispensing a first powder and / or a second powder that form the article, The first and second powders are the same type of powder but have different degrees of recycling, and the orientation of the build during the build is optimized to reduce the amount of non-recycled or less recycled powder.

2. 10. The method of claim 1, further comprising the step of performing a stress analysis on a model of the article to predict stress areas in the article during use.

3. The method of claim 2 , further comprising slicing the model to generate two-dimensional cross sections, and performing the stress analysis on the two-dimensional cross sections.

4. 10. A method according to any preceding claim, comprising rotating the model until an optimized build orientation of the article is obtained.

5. 10. The method of any preceding claim, wherein the orientation of the builds is further optimized to minimize a volume of a support structure.

6. The method of claim 5 , wherein the construct is oriented to be substantially self-supporting.

7. 7. The method of claim 6, wherein the build is oriented at an angle between 45° and 90° relative to the build platform.

8. 10. The method of any preceding claim, wherein the first powder comprises a powder that has not been recycled and the second powder comprises a powder that has been recycled one or more times.

9. 8. The method of claim 1, wherein the first powder and the second powder comprise recycled powders.

10. 10. The method of claim 1, wherein mixing of the first powder and the second powder occurs when the powders are dispensed onto a build platform.

11. 11. The method of claim 1, wherein the first metal powder and the second metal powder are mixed together before dispensing the metal powders onto the build platform.

12. 10. The method of any preceding claim, wherein the ratio of the first powder to the second powder is varied depending on expected stresses in regions of the article.

13. 13. The method of claim 12, wherein the ratio of the first powder to the second powder is varied depending on the predicted stress in the region and the predicted or analyzed condition of the recycled metal powder.

14. 14. The method of claim 12 or 13, wherein the ratio of the first metal powder to the second metal powder in one layer is the same as or different from the ratio of the first metal powder to the second metal powder in the previous layer.

15. 1. A system including a processor configured to operate an additive manufacturing machine to manufacture an article, the additive manufacturing machine including a first container and a second container capable of selectively dispensing powder to form the article, the first container and the second container containing the same type of powder and recycled to different extents, respectively, and the processor configured to determine an optimized build orientation to reduce an amount of non-recycled powder or an amount of the lesser recycled powder dispensed to manufacture the article.

16. 16. The system of claim 15, wherein the processor is communicatively coupled to the additive manufacturing machine.

17. 17. The system of claim 15 or 16, wherein the processor is configured to receive or generate a model of the article.

18. 18. The system of any of claims 15 to 17, wherein the processor is configured to perform a stress analysis on the model to predict stress areas in the article and determine an orientation of the optimized build based on the results of the stress analysis.

19. The system of claim 18 , wherein the stress analysis performed by the processor comprises a finite element analysis.

20. 20. A system according to any one of claims 15 to 19, wherein the processor is configured to determine a build orientation that minimizes the volume of the support structure.

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