mold

Abstract

The present invention provides a mold having a structure that can suppress cracking during additive manufacturing, even when additive manufacturing processes are applied. [Solution] A mold 1 is assembled from a plurality of mold pieces 11 having laser scanning marks or rapidly solidified structures in the cross-sectional structure, wherein the shape of at least one part of the mold, such as a narrow section, a grooved section, a V-shaped section, a U-shaped section, or a notch, is formed by the mold pieces themselves. Preferably, the narrow section, grooved section, V-shaped section, U-shaped section, or notch is a stress concentration point during the additive manufacturing process. More preferably, at least one of the mold pieces is an insert mold, and at least one is a storage mold that houses the insert mold, and the corners 21 of the insert mold and the corners 22 of the storage mold corresponding to the corners are provided with voids 23 formed by chamfering the corners.

Description

Technical Field

[0001] The present invention relates to a mold manufactured by an additive manufacturing process.

Background Art

[0002] Among molds used in forging molds for shaping molten metal into a predetermined shape, presses for shaping a workpiece by pressing it between a pair of upper and lower molds, and forging, as a method for manufacturing a forging mold, a method of cutting out a predetermined shape from a steel material has been generally used as a conventional method. However, in the above conventional method, there is a problem that a large amount of material becomes scrap during the die engraving of the mold, resulting in poor productivity. In contrast, recently, a technique for manufacturing a mold or its parts having a complex shape and structure by applying an additive manufacturing (also referred to as layer manufacturing) process and adding materials one by one based on digital data has been spreading. As a technique for manufacturing a mold by this additive manufacturing process, there is International Publication No. WO2016 / 017155 (Patent Document 1). This Patent Document 1 provides at least one slit groove on the upper surface of a three-dimensional shaped object for the purpose of reducing the warping of the three-dimensional shaped object that may occur due to the stress near the upper surface of the three-dimensional shaped object.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] While many mold structures have been proposed that focus on the molding stress that occurs in specific parts during the molding of a workpiece into a desired shape, Patent Document 1, mentioned above, found that in powder sintering additive manufacturing, unwanted stress occurs in three-dimensional molded objects, and depending on the magnitude of the stress, the three-dimensional molded object may warp. This is an excellent solution that solves a problem specific to additive manufacturing processes. However, when manufacturing molds using additive manufacturing processes, cracks sometimes occur in specific parts of the mold during additive manufacturing. In terms of improving the mold structure, improvements to this problem have still been insufficient. The objective of this invention is to provide a mold having a structure that can suppress cracking during the additive manufacturing process, even when an additive manufacturing process is applied. [Means for solving the problem]

[0005] The inventors of this invention diligently investigated the factors causing cracking when manufacturing molds using additive manufacturing processes. They discovered that in the formation of slits as shown in Patent Document 1, the shape of the slits makes it easy for stress to concentrate, potentially leading to cracking. As a method to prevent cracking during the additive manufacturing process due to stress caused by the melting and solidification of the raw material metal powder, the inventors investigated methods to optimize the composition of the metal powder, as well as methods to improve the structure of the mold. As a result, they discovered that by pre-dividing the areas where stress is expected to occur, it is possible to suppress the occurrence of cracks in the mold due to stress, leading to the present invention. In other words, the present invention is a mold in which a plurality of mold pieces having laser scanning marks or rapidly solidified structures in their cross-sectional structure are assembled, and the shape of at least one part of the narrow section, groove-shaped section, V-shaped section, U-shaped section, or notch section of the mold is formed by the mold pieces themselves. Preferably, the narrow portion, groove-shaped portion, V-shaped portion, U-shaped portion, or notch portion is a mold that is a stress concentration point during the additive manufacturing process. More preferably, in the mold of the present invention, at least one of the mold pieces is an insert mold, at least one is a storage mold that houses the insert mold, and the corners of the insert mold and the corners of the storage mold corresponding to the corners have gaps formed by the chamfering of the corners. [Effects of the Invention]

[0006] According to this invention, even when an additive manufacturing process is applied, a mold can be made that has a structure capable of suppressing cracking during the additive manufacturing process. Furthermore, since multiple mold pieces are used, by adjusting the shape of a specific mold piece, a structure can be made that can reduce the processing stress when the workpiece is formed in the mold. [Brief explanation of the drawing]

[0007] [Figure 1] This is a typical metallographic image of a cross-section of a mold produced by additive manufacturing. [Figure 2] This is a schematic diagram of a typical metallic structure found in the cross-section of a mold produced by additive manufacturing processes. [Figure 3] This is a schematic diagram showing an example of a mold for the present invention. [Modes for carrying out the invention]

[0008] The present invention will be described in detail below. First, this invention applies to molds to which additive manufacturing processes are applied. The “additive manufacturing processes” referred to in this invention include, for example, powder bed methods and directed energy deposition methods. Laser scanning marks or rapid solidification structures, or traces thereof, can be observed in the metal structure of the cross-section of molds produced by these additive manufacturing processes. Figure 1 shows a typical cross-sectional microstructure photograph, and Figure 2 shows a schematic diagram thereof. In Figure 1, you can see the scaly traces of melting and solidification, as well as traces of the interface of the laminated solidification layer or traces of laser scanning. When this is schematicly represented, as shown in Figure 2, traces different from those of ordinary melted materials can be seen, such as the scaly traces of melting and solidification (Figure 2a) and traces of the interface of the laminated solidification layer or traces of laser scanning (Figures 2b,c). In addition, a large number of voids not seen in melted materials may be observed.

[0009] In this invention, multiple mold pieces are assembled (combined) to form a single mold. In this invention, a mold formed by combining multiple mold pieces is sometimes referred to as a "composite mold." The number of mold pieces to be divided varies depending on the size and shape of the composite mold, but it is divided into at least two or more pieces. In conventional composite molds, it was common practice to divide the mold into multiple pieces to reduce molding stress during molding (in use) or to use insert mold pieces in areas where wear is severe due to molding or where defects such as chipping or cracking occur. In contrast, this invention suppresses the generation of stress and prevents the occurrence of cracks caused by stress by dividing the stress-generating areas into two or more mold pieces in advance, in response to the effects of melting, solidification, and layering of the metal powder raw material during the additive manufacturing process. The two or more divided mold pieces are additively manufactured bodies having laser scanning marks or quenched solidification structures in their cross-sectional structure. In this invention, "assembled" of multiple mold pieces means a state in which multiple mold pieces are combined in a predetermined relative positional relationship and can function as a mold (composite mold). The positioning or fixing of the mold pieces may be performed by fitting, press-fitting, clamping, bolts, pins, outer peripheral retaining members, mounting to a storage mold, or a combination thereof. Furthermore, each mold piece may be assembled after additive molding, subjecting it to finishing, heat treatment, or surface treatment as necessary. The molds (composite molds) covered by this invention include forging molds used in hot and cold processes, molds for molding metals and resins, and casting molds. By selecting metal raw materials with the optimal composition for these applications, it is possible to create molds suitable for the desired applications.

[0010] In this invention, the shape of at least one portion of the mold, such as a narrow portion, a groove-shaped portion, a V-shaped portion, a U-shaped portion, or a notch, is formed by combining pieces of the mold. The narrow portion, groove-shaped portion, V-shaped portion, U-shaped portion, or notch is a portion that becomes a stress concentration point during the additive manufacturing process. In this invention, "narrow portion" refers to a portion of the mold that has a locally smaller cross-sectional area or width compared to other parts of the mold. "Groove-shaped portion" refers to a groove-shaped recess formed on the surface of the mold. "V-shaped portion" and "U-shaped portion" refer to portions that form a V-shape or a U-shape in cross-sectional shape or planar shape, respectively. "Notch" refers to a recess or defect formed by cutting off a part of the contour of the mold. Furthermore, in this specification, "stress concentration point" refers to a portion of the mold that tends to experience locally higher stress compared to other parts due to thermal history, shrinkage constraints, or shape during the additive manufacturing process.

[0011] In additive manufacturing processes, the raw material powder is locally melted by a moving high-energy heat source and then rapidly solidifies, resulting in the formation of a steep temperature gradient near the fabricated area. Furthermore, the already solidified areas located directly below or around the newly formed molten pool are reheated during subsequent scanning or layering, so each part of the fabrication process undergoes multiple thermal cycles, including heating, cooling, and possibly remelting. During the cooling process, each part attempts to shrink due to the heat, but this shrinkage is constrained by the surrounding already fabricated areas and nearby high-rigidity areas, resulting in the generation of localized tensile or compressive stresses, which are thought to accumulate as layers are formed. Moreover, when narrow areas are continuous with wide or thick areas, stress tends to increase near the boundary due to the difference in their shrinkage behavior. In other words, because the additive manufacturing process involves sequential melting and solidification, stresses are generated due to thermal expansion and contraction during the manufacturing process, and in some cases, transformation stresses. Furthermore, compressive and tensile stresses are also generated during the layer solidification process, and the combined heat and cooling from these stresses make it easier for cracks to occur in narrow areas, grooves, V-shaped sections, U-shaped sections, or notches, where the cross-sectional area is smaller than in other parts. In addition, stress concentration due to the shape itself is added in the smallest cross-sectional areas, the bottom of V-shaped or U-shaped sections, the roots of notches, or the inner corners, which are presumably prone to becoming the starting points for cracks during manufacturing.

[0012] Therefore, in this invention, by constructing at least a portion of the stress concentration area with multiple mold pieces, local constraints are alleviated and stress concentration is reduced, making it easier to suppress the occurrence of cracks. In other words, by constructing at least a portion of the shape-changing area, where stress tends to increase during the additive manufacturing process, using multiple mold pieces in advance, the effects of constrained shrinkage in that area can be mitigated and stress accumulation and crack formation can be suppressed more easily compared to forming the stress-prone area as a single continuous molded body. In other words, this invention aims to structurally avoid or reduce damage caused by thermal stress and constrained shrinkage, which are unique to additive manufacturing, by making the area where stress concentration is expected to occur a segmented structure.

[0013] A specific example of mold 1 is shown in Figure 3. Note that Figure 3 is a schematic diagram of mold 1 having a V-shaped narrow section, and is assembled from multiple mold pieces 11. In actual use, the integrated mold 1 is used as an insert mold and is fixed in place by a storage mold (not shown). The mold 1 has a star-shaped cavity 3 when viewed from above, and the area indicated by the dashed circle near the tip of the V-shaped narrow section is the area that becomes a stress concentration point 2 during the additive manufacturing process. In this invention, the area where the most stress is concentrated is divided in advance, and the V-shaped narrow section is constructed by multiple mold pieces 11. By constructing a structure in which these stress concentration points are made up of multiple mold pieces, it is possible to suppress the generation of stress and prevent the occurrence of cracks caused by stress.

[0014] Depending on the shape of the mold and cavity, it may be difficult to avoid stress concentration points. In such cases, it is advisable to select a metal raw material with a composition that has high crack resistance for use in the additive manufacturing process. For example, when using a mold for hot working, it is preferable to select an improved alloy of the hot work tool steel JIS-SKD61 having one of the compositions (1) to (5) below, and it is advisable to select the one that is optimal for the desired effect. In all alloy powders, the remainder consists of Fe and impurities, including unavoidable impurities that are inevitably mixed in during manufacturing. The aforementioned impurities can be tolerated up to a maximum of 1.0%, as long as they do not hinder the effects of this invention. Preferably, it is 0.5% or less. (1) Alloy powder capable of forming additively manufactured hot tool steel products with high softening resistance: Additive manufacturing tool steel powder consisting of, in mass%, 0.10%≦C≦0.24%, 0.01%≦Si≦0.50%, 0.01%≦Mn≦0.19%, 0.5%≦Ni≦1.5%, 3.6%≦Cr≦4.4%, Mo or / further W: 2.1%≦(Mo+0.5W)≦3.0%, 0.2%≦V≦1.0%, 0.1%≦Nb≦1.0%, with the remainder being Fe and impurities.

[0015] (2) Tool steel powder capable of producing hot tool steel additively manufactured products with particularly excellent crack resistance during additive manufacturing: Tool steel powder for additive manufacturing consisting of, in mass%, 0.10%≦C≦0.24%, 0.01%≦Si≦0.50%, 0.01%≦Mn≦0.19%, 3.6%≦Cr≦4.4%, Mo or / further W:2.0%≦(Mo+0.5W)≦3.4%, 0.2%≦V≦0.9%, with the remainder being Fe and impurities. (3) Tool steel powder capable of forming a hot work tool steel additive manufacturing product with particularly excellent crack resistance during additive manufacturing: in mass %, 0.10% ≤ C ≤ 0.40%, 0.01% ≤ Si ≤ 0.19%, 0.1% ≤ Mn ≤ 1.0%, 2.0% ≤ Ni ≤ 9.0%, 3.5% < Cr < 4.5%, Mo or / further W: 2.5% ≤ (Mo + 0.5W) < 3.5%, 0.45% ≤ V ≤ 1.0%, 0.3% < Cu < 0.6%, 0.2% ≤ Al ≤ 0.9%, and the balance consists of Fe and impurities, which is tool steel powder for additive manufacturing.

[0016] (4) Tool steel powder capable of forming a hot work tool steel additive manufacturing product with particularly excellent crack resistance during additive manufacturing: in mass %, 0.10% ≤ C ≤ 0.40%, 0.01% ≤ Si ≤ 0.19%, 0.1% ≤ Mn ≤ 1.0%, 0.3 ≤ Ni < 1.0%, 3.5% < Cr < 4.5%, Mo or / further W: 2.5% ≤ (Mo + 0.5W) < 3.5%, 0.45% ≤ V ≤ 1.0%, 0.1% ≤ Cu ≤ 1.0%, and the balance consists of Fe and impurities, which is tool steel powder for additive manufacturing. (5) Tool steel powder capable of forming a hot work tool steel additive manufacturing product with particularly excellent crack resistance during additive manufacturing: in mass %, 0.10 ≤ C ≤ 0.25%, 0.01 ≤ Si ≤ 0.5%, Mn: ≤ 1.5%, 3.0 ≤ Cr ≤ 6.0%, Mo or / further W: 2.0 ≤ (Mo + 0.5W) ≤ 3.5%, 0.3 ≤ V ≤ 0.7%, Ni: ≤ 0.5%, Cu: ≤ 0.25%, and the balance: consists of Fe and impurities, which is tool steel powder for additive manufacturing.

[0017] Also, when the mold of the present invention is used as a mold to which a large compressive load such as forging or pressing is applied, for example, the shape of the mold piece can be adjusted so that the void 23 shown in FIG. 3 can be formed in a portion where the processing stress concentrates during molding or in the vicinity thereof. Specifically, it is preferable to chamfer the corner of the insert mold 21 and provide a rounded portion at the corner 22 of the receiving mold corresponding to the corner portion. By providing the rounded portion, a void portion can be formed between the corner of the insert mold and the corner of the receiving mold. The size of this rounded portion may be appropriately changed according to the size of the mold piece and the size of the compressive load. Such a void can reduce tensile stress, relieve local tensile stress or restraint when used as a mold, and make it easier to prevent mold breakage and the like.

[0018] The mold of the present invention described above can be a mold having a structure capable of suppressing cracks during the additive manufacturing process even when the additive manufacturing process is applied. Furthermore, since a plurality of mold pieces are used, the processing stress when forming a workpiece with a mold can also be reduced by adjusting the shape of a specific mold piece. In addition, the mold of the present invention can also be used for a part of a mold, such as an insert mold. Even when it is used only for an insert mold, it is included in the scope of the mold of the present invention.

Industrial Applicability

[0019] By configuring the stress concentration part by combining a plurality of parts, cracks during the additive manufacturing process can be prevented, so it can also be used for tools other than molds.

Explanation of Signs

[0020] 1 Mold 2 Stress concentration part 3 Cavity 11 Mold piece 21 Corner 22 Corner 23 Void

Claims

1. A mold in which multiple mold pieces having laser scanning marks or rapidly solidified tissue in the cross-sectional tissue are assembled, A mold in which the shape of at least one portion of the narrow part, groove-shaped part, V-shaped part, U-shaped part, or notch of the mold is formed by the mold pieces themselves.

2. The mold according to claim 1, wherein the narrow portion, groove-shaped portion, V-shaped portion, U-shaped portion, or notch portion is a stress concentration portion during the additive molding process.

3. The mold according to claim 1, wherein at least one of the mold pieces is an insert mold, and at least one is a storage mold for housing the insert mold, and the corners of the insert mold and the corners of the storage mold corresponding to the corners have gaps formed by the chamfering of the corners.

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