Method for forming an article having a downskin portion by metal additive manufacturing.

Abstract

In metal additive manufacturing, the goal is to minimize the surface roughness of the downskin portion of an article after the additive manufacturing process. [Solution] A method for forming an article having a downskin portion by metal additive manufacturing involves repeating the following steps in the additive manufacturing process in the downskin portion: a first step of forming a metal powder layer 14 over the entire upper surface of the previously added layers 13; a second step of irradiating the region of the metal powder layer that will become the cross-section of the article with a laser beam L to dissolve the metal powder in the metal powder layer and solidifying the molten metal to form a metal layer 14a; and a third step of irradiating the region of the metal powder layer that will not become the cross-section of the article with a laser beam Ld at an intensity that does not dissolve the metal powder to heat it, thereby forming a downskin portion DS.

Description

Technical Field

[0001] The present invention relates to a metal additive manufacturing method, and more particularly, to a method for improving the surface roughness of a downskin portion in a metal additive manufacturing method.

Background Art

[0002] The metal additive manufacturing method, which is a 3D printing method for a metal material, can produce products with more complex shapes than methods such as cutting and casting, and various configurations have been proposed in relation to this method. For example, in Patent Document 1, a Ni-based corrosion-resistant alloy powder for additive manufacturing that has excellent corrosion resistance in a severe corrosion environment (for example, a wet environment containing chlorine or a semiconductor process gas environment) and can reduce the defect rate during additive manufacturing, and a method for manufacturing an additive manufactured product using this powder have been proposed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In metal additive manufacturing, as shown in Figures 3(A) to 3(C), thin metal layers 12a and above, approximately 50 μm thick, are sequentially layered on a base 10 to form an article of the desired shape. Specifically, in the metal layer layering process, as shown in Figure 3(A), metal powder 14 (particle size approximately 5 to 30 μm) is laid in a layer approximately 50 μm thick on the base 10 or on an already layered metal layer 12b. As shown in Figure 3(B), the area that will become the cross-section of the article is scanned with an infrared laser beam through the metal powder layer, causing the metal powder 14 to dissolve. As shown in Figure 3(C), a metal layer 14a approximately 50 μm thick is layered, and this process is repeated to form the article. Various materials such as stainless steel, Inconel, SKD steel, titanium, and aluminum can be used as the metal powder material. Infrared lasers, such as semiconductor lasers, are used, for example, with a beam diameter of 75 μm, an intensity of 400 W, and a scanning speed of 1000 to 1500 m / sec. After the lamination process is complete, the article is removed from its embedded state in metal powder on the base, and the surface of the article is polished as appropriate to achieve the required or desired surface roughness.

[0005] While various shapes can be formed using the metal additive manufacturing method described above, when forming a downskin portion DS, as illustrated in Figures 4(A) and (B), that is, a portion of the shape of an article where there is no material on the underside, for example, a portion where the angle of the downward surface of the shape measured from the stacking direction of the metal layer 12 exceeds 45°, the surface may become rough. More specifically, even in the formation of the downskin portion DS, as shown in Figure 5(A), first, a metal powder layer 14 is laid over the entire surface of the previously stacked layers 13, and then, as shown in Figure 5(B), the region 15 that will become the cross-section of the article is scanned by a beam L from the laser 50 in the metal powder layer 14, and laser light is irradiated into that region, causing the metal powder to melt and form a metal layer 14a, while the powder 14 remains in its original state in the regions that will not become the cross-section of the article. Subsequently, in forming the layer on top of the metal layer 14a, as shown in Figure 5(C), a metal powder layer 16 is laid over the entire surface of the metal layer 14a and the remaining metal powder layer 14. Then, as shown in Figure 5(D), a laser beam L is scanned and irradiated over the metal powder layer 16 in the region 17 that will be the cross-section of the article, causing the metal powder layer 16 to melt and form the metal image layer 16a. At this time, in the down-skin portion, the area of ​​the metal layer 16a is larger than that of the metal layer 14a, so when forming the metal layer 16a, the laser beam L is also irradiated onto the powder layer 16 laid over the area of ​​the metal powder layer 14 that remains in powder form. As a result, as shown in the figure, when the powder layer 16 laid over the layer 14 that remains in powder form melts, a portion of the melted layer 16 penetrates between the powder particles of layer 14, as schematically depicted by reference numeral 20, resulting in a rough surface in the down-skin portion. In practice, even when attempting to fabricate an object so that its surface roughness is typically Ra1μm, the surface roughness of the downskin portion after fabrication ends up being around Ra50μm, making it difficult to achieve a surface roughness of Ra1μm through polishing after the layering process.

[0006] In view of the above circumstances, the main object of the present invention is to minimize the surface roughness of the downskin portion after the additive manufacturing process in the metal additive manufacturing method.

[0007] In this regard, the inventors of the present invention have found that when forming the metal layer of the downskin portion, if a laser beam is irradiated to heat the region where the powder remains undissolved with a laser beam, the spaces between the powder particles become tighter. As a result, when a new powder layer is placed on top of this weakly heated powder layer and the new powder layer melts into a liquid state due to laser beam irradiation, the extent to which the liquid metal penetrates the underlying powder layer can be suppressed, thereby improving the surface roughness of the downskin portion. This finding is utilized in the present invention. [Means for solving the problem]

[0008] According to the present invention, the above problem is solved by a method for forming an article having a downskin portion by metal additive manufacturing, In the lamination process in the downskin portion, The first step is to form a metal powder layer over the entire upper surface of the previously stacked layers, A second step involves irradiating the region of the metal powder layer that will be the cross-section of the article with a laser beam to dissolve the metal powder in the metal powder layer, and solidifying the molten metal to form a metal layer. A third step involves heating the metal powder layer by irradiating a region of the metal powder layer that does not form a cross-section of the article with a laser beam at an intensity that does not cause the metal powder to dissolve. This is achieved by repeatedly forming the downskin portion.

[0009] In the above method, the basic construction method of the metal additive manufacturing method may be the same as in the usual embodiment, and the metal material to be added, the configuration for forming the metal powder layer on the previously added layers, the laser irradiated onto the metal powder, the configuration for forming the beam, and the configuration of the system for scanning the laser beam may be the same as in the usual embodiment. Note that "previously added layers" includes the region where the laser beam has already been irradiated onto the metal powder layer to form the cross-section of the article, resulting in a unified metal layer region and the region where the metal powder remains as is. If the metal powder layer formed in the first step is the bottom layer of the article, then "previously added layers" will be the base that supports the bottom layer of the article.

[0010] In conventional metal additive manufacturing using a laser beam, the laser beam is irradiated only to the region of the metal powder layer that will become the cross-section of the article, and not to the region that will not become the cross-section of the article. However, in the configuration of the present invention described above, the laser beam is irradiated to the region of the metal powder layer that will constitute the downskin portion and will not become the cross-section of the article, so as to heat the metal powder to a degree that it does not melt. With this configuration, as already mentioned, the space between the powder particles in the weakly heated metal powder layer becomes tighter, a new metal powder layer is formed on top of it, and when this new metal powder layer melts into a liquid state due to irradiation with the laser beam, it becomes difficult for it to penetrate the weakly heated metal powder layer below, thus making it possible to further reduce the surface roughness of the downskin portion. Specifically, when heating the metal powder layer with a laser beam, the temperature is set to approximately 1500-2000°C when melting the metal powder in the area that forms the cross-section of the article, while the temperature may be set to approximately 200-500°C in areas that do not form the cross-section of the article.

[0011] In the above configuration, the region where the laser beam is irradiated with an intensity that does not dissolve the metal powder in the metal powder layer in the downskin portion that does not form a cross-section of the article is, more specifically, the region directly above which the cross-section of the article is formed and where the placed metal powder dissolves. In other words, the region directly above which the powder remains in powder form does not need to be irradiated even with a weak laser beam.

[0012] In the implementation, a computer device controlling the system prepares a model of the shape of the article to be formed, a cross-sectional shape in the layering direction is formed in the model, and a scanning trajectory of the laser beam is generated to cover each cross-sectional shape. At that time, if the upper layer of each layer is large, it is identified as a down-skin area, and in that case, an area (preheating area) is identified along the outer circumference of the cross-sectional shape where a weak laser beam is scanned for weak heating. Subsequently, parameters for setting the laser beam intensity between the cross-sectional shape area of ​​the article and the preheating area are adjusted, and control commands to each part of the system are configured based on the fabrication data. [Effects of the Invention]

[0013] Thus, according to the configuration of the present invention described above, it is possible to minimize the surface roughness of the downskin portion after the additive manufacturing process in the metal additive manufacturing method, and it is expected that it will be easier to achieve the desired surface roughness during polishing after the additive manufacturing process.

[0014] Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the present invention. [Brief explanation of the drawing]

[0015] [Figure 1]Figs. 1(A) to (E) are cross-sectional views taken in a direction perpendicular to the lamination direction of the laminate schematically depicting the metal layer lamination process of the downskin part according to the present embodiment. (A) A metal powder layer is formed on the layer up to that point. (B) A laser beam is irradiated onto the cross-sectional area of the article to form a metal layer. (C) A weak laser beam is irradiated onto the area below the downskin part to heat the metal powder layer. (D) A new metal powder layer is formed. (E) A laser beam is irradiated onto the cross-sectional area of the article in the new metal powder to form a metal layer. [Figure 2] Fig. 2(A) is a schematic diagram of the spot shape of the laser beam irradiated onto the metal powder layer that becomes the cross-sectional area of the article according to the present embodiment, and Fig. 2(B) is a schematic diagram of the spot shape of the laser beam irradiated onto the preheated metal powder layer according to the present embodiment. Fig. 2(C) is a cross-sectional view of the laminate schematically showing the area that becomes the cross-section of the article and the area of the preheated metal powder layer in the present embodiment. [Figure 3] Figs. 3(A) to (C) are cross-sectional views taken in a direction perpendicular to the lamination direction of the laminate schematically depicting the processing process of the metal lamination modeling method. [Figure 4] Figs. 4(A) and (B) are schematic diagrams of the downskin part in the shape of the article. [Figure 5] Figs. 5(A) to (D) are cross-sectional views taken in a direction perpendicular to the lamination direction of the laminate schematically depicting the metal layer lamination process of the conventional downskin part.

Explanation of Reference Numerals

[0016] 10... base, 12a, 12b... metal layers, 13... layers laminated up to that point, 14, 16... metal powder layers, 14a, 16a... metal layers, 20... lower surface of the metal layer, 50... laser

Best Mode for Carrying Out the Invention

[0017] The present invention will be described in detail below with reference to the accompanying drawings in several preferred embodiments. In the drawings, the same reference numerals indicate the same parts.

[0018] In the metal layer lamination process by the metal lamination manufacturing method of the present embodiment, for parts other than the downskin part of the article, it may be carried out in a normal manner as exemplified in FIGS. 3(A) to (C). As already mentioned, the metal powder used for forming the metal layer may be powders of various particle sizes of about 5 to 30 μm, such as stainless steel, inconel, SKD series steel materials, titanium, aluminum, etc. In the lamination of the metal layer, a metal powder layer is formed to a thickness of about 50 μm over the entire upper surface of the base 10 or the layer laminated up to that point (including the region that has become a metal layer and the region that remains as a metal powder layer). A process is repeated in which a laser beam is scanned over the region that becomes the cross-section of the article in the metal powder layer, the metal powder layer is irradiated with laser light, and the metal is melted and solidified to form a metal layer. The laser may typically be, for example, a semiconductor infrared laser of about 400 W. The spot diameter of the beam may be, for example, 75 μm, and the scanning speed may be, for example, 1000 to 1500 m / second. The shape of the spot of the beam may be circular or annular as exemplified in FIG. 2(A). When forming a metal layer from the metal powder layer, the temperature of the layer reaches 1500 to 2000 °C. Also, typically, in the scanning of the laser beam, the locus of the spot is adjusted so that the beads of the formed metal overlap by about 20%, for example, about 50 μm, and the formed metal layer has a thickness of about 50 μm.

[0019] On the other hand, in the lamination process of the metal layer forming the downskin part of the article according to the present embodiment, the process of forming the metal powder layer over the entire upper surface of the base 10 or the layer laminated up to that point and scanning the laser beam over the region that becomes the cross-section of the article is carried out in the same manner as above. Further, a preheating process is carried out in which a laser beam with a weak light intensity is irradiated onto the metal powder layer outside the region that becomes the cross-section of the article to heat it to such an extent that the metal powder is not melted.

[0020] More specifically, as shown in Figure 1(A), a metal powder layer 14 is formed over the entire upper surface of the base 10 or the previously stacked layers 13. As shown in Figure 1(B), the region of the metal powder layer 14 that will be the cross-section of the article is scanned by a beam L from the laser 50, and light irradiation is performed to form a metal layer 14a. In this embodiment, the metal powder layer 14 surrounding the metal layer 14a, which is the cross-sectional region of the article, is further scanned with a beam Ld with a light intensity that does not dissolve the metal powder, as shown in Figure 1(C), and heated (preheating treatment). Here, the shape of the beam spot may be a circular or annular shape that is larger and has lower intensity than the beam spot diameter when forming the metal layer 14a, as illustrated in Figure 2(B). Furthermore, regarding beam scanning, the beam path may be adjusted so that the overlapping width in adjacent paths is narrower than when forming the metal layer 14a, that is, so that the distance of beam offset is longer. The temperature of the layer during the preheating process reaches several hundred degrees (200-500°C).

[0021] As described above, when the metal powder layer 14 is subjected to preheating treatment, the spacing between the powder particles becomes tighter and narrower. In this case, when a new layer is laid on top of the previously stacked layers (i.e., the metal layer 14a and the metal powder layer 14), as shown in Figure 1(D), a new metal powder layer 16 is placed on top of it, and as shown in Figure 1(E), the beam L from the laser 50 is irradiated not only on top of the metal layer 14a but also on the portion of the metal powder layer 16 directly above the metal powder layer 14 to melt the metal powder, the degree to which the melted liquid metal penetrates into the metal powder layer 14 can be kept low. As a result, the surface roughness of the metal layer 16a formed from the metal powder layer 16 can be made smaller, and when the article is removed from the base after the completion of the lamination process and the surface is polished, the required or desired surface roughness can be more easily achieved in the downskin portion.

[0022] In the above configuration, the area to which the preheating treatment of the metal powder layer is applied may be the region in the layer directly above it where the metal powder is melted and a metal layer is formed. For example, as shown in Figure 2(C), if the cross-section of an article in a certain layer is region I, and the cross-section of an article in the layer above it extends from region I to a wider region II, the area to which the preheating treatment is performed may be region II.

[0023] When performing additive manufacturing using the metal additive manufacturing method according to this embodiment, as in the usual configuration, a model of the shape of the article to be formed is prepared in the computer device that controls the system, a cross-sectional shape in the layering direction is formed in the model, and a scanning trajectory of the laser beam is generated to cover each cross-sectional shape. At that time, if the upper layer of each layer is large, it is identified as a down-skin area, and in that case, the area to which preheating treatment is applied along the periphery of the cross-sectional shape is identified. Subsequently, parameters for setting the laser beam intensity between the cross-sectional area of ​​the article and the preheating area are adjusted, and control commands to each part of the system are configured based on the manufacturing data. In the actual additive manufacturing process, the formation of the metal powder layer and the scanning and irradiation of the laser beam in the cross-sectional area of ​​the article are repeated according to the settings in the computer device described above. In the layer directly below the layer constituting the down-skin area, scanning and irradiation of a laser beam with a weak light intensity in the outer edge area of ​​the cross-sectional area of ​​the article is further added.

[0024] Thus, according to the method of this embodiment described above, by preheating the outside of the cross-sectional area of ​​the article in the downskin portion, the surface roughness of the downskin portion can be kept as small as possible, making polishing after lamination easier.

[0025] While the above description is made in relation to embodiments of the present invention, many modifications and changes are readily possible for those skilled in the art, and it will be clear that the present invention is not limited to the embodiments illustrated above, but can be applied to various devices without departing from the concept of the present invention.

Claims

[Claim 1] A method for forming an article having a downskin portion by metal additive manufacturing, In the lamination process in the downskin portion, The first step is to form a metal powder layer over the entire upper surface of the previously stacked layers, A second step involves irradiating a region of the metal powder layer that will be the cross-section of the article with a laser beam to dissolve the metal powder in the metal powder layer, and solidifying the molten metal to form a metal layer. A third step involves heating the metal powder layer by irradiating a region of the metal powder layer that does not form a cross-section of the article with a laser beam at an intensity that does not cause the metal powder to dissolve. A method for forming the downskin portion by repeating the process.

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