Method of manufacturing sintered component

Abstract

To improve the accuracy of a sintered component.SOLUTION: A method of manufacturing a sintered component 1 according to the present invention includes: a forming step of forming a protrusion T in an end face of a green compact P;and a re-compression step of giving a shape of an undercut 30 by a metal die (lower punch 300) in forming an undercut 30 by pushing out the protrusion T toward a side of a sintered body S. This facilitates control of a pushout amount (dimension / shape) of a convex portion 21 to make up the undercut 30 and improves the accuracy of the sintered component 1.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a method for producing a sintered part having an undercut. [Background technology]

[0002] Conventionally, in the molding process of powder metallurgy, unevenness on the side (unevenness in a direction perpendicular to the direction of removal from the die) that makes it impossible to remove a part from a die is called an undercut, and parts with undercuts cannot be shaped with a die. In the field of injection molding, there is a method called "slide" (see Patent Document 1), in which the die is divided at the undercut and slid in a direction different from the removal direction to remove the part, but this cannot be used in powder metallurgy using metal powder as the raw material due to problems with die strength and moldability. For this reason, in the powder metallurgy method in which metal powder is used as the raw material and press compressed from above and below, a method of forming an undercut by recompression such as caulking has become common. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-52384 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the method of forming the undercut portion by re-compression, it is difficult to control the extrusion amount (dimensions and shape) of the convex portion that constitutes the undercut portion, making it difficult to obtain a highly accurate sintered part. An object of the present invention is to improve the precision of sintered parts. [Means for solving the problem]

[0005] In order to solve the above problems, the manufacturing method of a sintered part according to the first invention includes a molding step of compressing and molding a raw material including a metal powder to form a green compact, a sintering step of sintering the green compact to form a sintered body, and a recompressing step of recompressing the sintered body, wherein the molding step forms a protrusion on an end face of the green compact, and in the recompressing step, the protrusion is pushed out towards the side face of the sintered body to form an undercut portion, and the shape of the undercut portion is imparted by a mold. In the manufacturing method of the sintered part according to the first aspect of the present invention, when the protruding parts are pushed out toward the side faces of the sintered body in the recompression step to form the undercut parts, the shape of the undercut parts is given by a die. This makes it easy to control the amount of extrusion (dimensions and shape) of the protruding parts that form the undercut parts, and makes it possible to improve the precision of the sintered part. Here, the green compact corresponds to the green compact P described later. The sintered body corresponds to the sintered body S described later. The protruding portion corresponds to the protruding portion T described later. The undercut portion corresponds to the undercut portion 30 described later. The die corresponds to the lower punch 300 (particularly the upper portion 310) described later.

[0006] The method for producing a sintered part according to the second aspect of the present invention is the method for producing a sintered part according to the first aspect of the present invention, characterized in that the elongation of the sintered body is 10% or more. In other words, if the elongation of the sintered body is less than 10%, it becomes difficult to extrude the protruding parts and to impart the shape of the undercut parts using a die. Therefore, in the manufacturing method of the sintered part according to the second invention, by making the elongation of the sintered body 10% or more, it becomes easy to extrude the protruding parts and to impart the shape of the undercut parts using a die.

[0007] The method for producing a sintered part according to a third aspect of the present invention is the method for producing a sintered part according to the first or second aspect of the present invention, characterized in that the hardness (Rockwell hardness) of the sintered body is within the range of 20 to 40 HRB. That is, if the hardness of the sintered body is less than 20 HRB, the strength of the undercut portion is insufficient. On the other hand, if the hardness of the sintered body is more than 40 HRB, there is a risk of cracks occurring in the undercut portion when the protruding portion is extruded. Therefore, in the manufacturing method of the sintered part according to the third invention, by setting the hardness of the sintered body within the range of 20 to 40 HRB, it is possible to prevent the occurrence of cracks in the undercut portion while ensuring the strength of the undercut portion. Effect of the Invention

[0008] According to the method for producing a sintered part of the present invention, it is possible to improve the precision of the sintered part. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view of a sintered part 1. [Diagram 2] FIG. 2 is a side view of the sintered part 1. [Diagram 3] 2 is a flowchart of a manufacturing process of the sintered part 1. [Figure 4] FIG. 2 is a cross-sectional view of a powder compact (sintered compact S). [Diagram 5] FIG. 1 is a diagram showing the procedure of a recompression process. [Figure 6] 13 is a diagram showing the relationship between the inclination angle θ1 of a protrusion T and the inclination angle θ2 of a mold. FIG. [Figure 7] 2A to 2C are diagrams illustrating a method for forming the protrusions 21. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, a sintered part 1 produced by the production method according to the present invention will be described. Fig. 1 is a perspective view of the sintered part 1. Fig. 2 is a side view of the sintered part 1. The sintered part 1 is made of a sintered body and has a porous structure. In particular, the sintered part 1 has an undercut portion 30. Here, the "undercut portion" refers to a portion having a shape (convex or concave shape) that makes it impossible to release (take out) a molded product from a mold in a molding process by simply opening the mold. In this embodiment, an example will be described in which a male fixing part into which a female fixing part (not shown) is fitted is applied as the sintered part 1. 1 and 2, the sintered part 1 includes a base portion 10 and a fitting portion 20 that protrudes upward from the upper surface of the base portion 10. The base portion 10 and the fitting portion 20 are integrally formed. The base portion 10 is formed in a substantially disk shape. The fitting portion 20 is formed in a hexagonal column shape having three long sides and three short sides in a plan view. In this case, the long sides and short sides of the fitting portion 20 are arranged alternately. The base portion 10 and the fitting portion 20 are arranged coaxially with each other. The outer diameter of the base portion 10 is larger than the outer diameter of the fitting portion 20 in a plan view. Three protrusions 21 are provided on the side surface of the fitting portion 20. Specifically, a protrusion 21 is provided on the side surface of each short side of the fitting portion 20. Each protrusion 21 extends along the short side. Each protrusion 21 protrudes outward from the side surface of the fitting portion 20 (in a direction perpendicular to the direction in which the central axis of the sintered part 1 extends (=the direction in which the die is removed)). Each protrusion 21 is provided at the upper end of the side surface of the fitting portion 20. As a result, in the sintered part 1, a concave shape is formed between each protrusion 21 and the base part 10, which becomes an undercut portion 30. That is, in the sintered part 1, three undercut portions 30 are formed on the side surface. The female fixing part has a mating portion into which the mating portion 20 is inserted. When mating the sintered part 1 (male fixing part) with the female fixing part, the mating portion 20 of the sintered part 1 is inserted into the mating portion of the female fixing part, and each of the convex portions 21 of the sintered part 1 is mated with a concave portion provided in the mating portion of the female fixing part, thereby mating the sintered part 1 with the female fixing part.

[0011] (Manufacturing method of sintered part 1) Next, a method for producing the sintered part 1 will be described. Fig. 3 is a flow chart of the manufacturing process of the sintered part 1. Fig. 4 is a cross-sectional view of the green compact (sintered compact S). Fig. 5 is a diagram showing the procedure of the recompression process. Fig. 6 is a diagram showing the relationship between the inclination angle θ1 of the protrusion T and the inclination angle θ2 of the die. Fig. 7 is a diagram explaining a method of forming the protrusion 21. As shown in FIG. 3, in the manufacture of the sintered part 1, first, raw material powder (raw material) is produced. The raw material powder contains metal powder. In particular, the raw material powder is produced by stirring and mixing a plurality of types of powder (metal powder, solid lubricant, etc.). As the raw material powder, it is possible to use iron-based, copper-based, SUS-based, and other metal powders. In particular, in this embodiment, the composition of the raw material powder is selected so that the sintered body S described later has an elongation of 10% or more and a hardness within the range of 100 to 300 Hv (0.2). For example, the raw material powder may contain, in weight ratio relative to the total weight of the raw material powder, less than 0.03 wt % C, 9 to 13 wt % Ni, 18 to 20 wt % Cr, 1.5 wt % or less Si, with the remainder being Fe and unavoidable impurities (equivalent to SUS304L). Furthermore, the raw material powder can have a composition (corresponding to SUS316L) that contains, in weight ratio relative to the total weight of the raw material powder, less than 0.03 wt % C, 12 to 15 wt % Ni, 2 to 3 wt % Mo, 16 to 18 wt % Cr, and 1.5 wt % or less Si, with the remainder being Fe and unavoidable impurities.

[0012] Next, a molding step is performed. In the molding step, the raw material powder is compression molded to form a green compact P. Specifically, the raw material powder thus produced is placed in a metal mold. The raw material powder placed in the metal mold is then press molded at a pressure within a range of 400 to 1200 MPa to form a green compact P. In this embodiment, a protrusion T is formed on an end face of the powder compact P (sintered body S) by the molding process. Then, in a re-compression process described later, the protrusion T is pushed out toward the side surface of the sintered body S to form a convex portion 21. The shape of the protrusion T is given by the mold. That is, as shown in Fig. 4, a protrusion T that protrudes toward the mold removal direction is formed on the end face of the fitting portion 20 (the end face in the mold removal direction). At this time, three protrusions T are formed on the end face of the fitting portion 20. Each protrusion T is formed along each short side of the fitting portion 20. Each protrusion T extends along the short side. Here, each protrusion T is formed by transferring a concave shape provided on the end face of the die, but since the compression ratio of the raw material powder is lower than that of the surrounding area, the density is lower than that of the surrounding area, and the amount of voids is increased compared to that of the surrounding area. For this reason, in this embodiment, the volume of each protrusion T is set to be larger than the volume of each convex portion 21. In particular, the volume of each protrusion T is set to be within a range of 130 to 300% of the volume of each convex portion 21. That is, if the volume of each protrusion T is less than 130% of the volume of each convex portion 21, the amount of extrusion to the side surface of the sintered body S in the recompression process may be insufficient, and each convex portion 21 may not be formed. On the other hand, if the volume of each protrusion T exceeds 300% of the volume of each convex portion 21, the amount of extrusion to the side surface of the sintered body S in the recompression process may be excessive, and each convex portion 21 may be deformed. Therefore, by setting the volume of each protrusion T to be within a range of 130 to 300% of the volume of each protrusion 21, the precision of each protrusion 21 can be improved.

[0013] Next, a sintering step is carried out. In the sintering step, the green compact P is sintered to form a sintered body S. Specifically, the green compact P is sintered under predetermined atmosphere and temperature conditions to form the sintered body S. In this embodiment, sintering is performed in hydrogen gas (100%). This suppresses hardening of the surface of the sintered body S compared to when sintering is performed in an inert gas (nitrogen gas, etc.), and makes it possible to suppress the occurrence of cracks when the protruding portion T is pushed out in the recompression step described below. The sintering temperature is appropriately selected within the range of 700 to 1300°C depending on the composition of the raw material powder. In this embodiment, the elongation of the sintered body S is 10% or more. In other words, if the elongation of the sintered body S is less than 10%, it becomes difficult to extrude the protruding portion T in the recompression process described below, and it becomes difficult to impart the shape of the undercut portion 30 by a die. Therefore, by making the elongation of the sintered body S 10% or more, it becomes easier to extrude the protruding portion T and easier to impart the shape of the undercut portion 30 by a die. Moreover, the hardness (Rockwell hardness) of the sintered body S is within the range of 20 to 40 HRB. That is, if the hardness of the sintered body S is less than 20 HRB, the strength of the undercut portion 30 is insufficient. On the other hand, if the hardness of the sintered body S exceeds 40 HRB, there is a risk that cracks will occur in the undercut portion 30 when the protruding portion T is extruded. Therefore, by setting the hardness of the sintered body S within the range of 20 to 40 HRB, it is possible to prevent the occurrence of cracks in the undercut portion 30 while ensuring the strength of the undercut portion 30.

[0014] Next, a recompression step is performed. In the recompression step, the sintered body S is placed in a metal mold, and sizing (recompression) is performed on the sintered body S placed in the metal mold to form the sintered part 1. By applying sizing to the sintered body S, the dimensional accuracy is improved, and the surface roughness is also improved. Particularly in this embodiment, the re-compression process causes the protrusions T formed on the end faces of the sintered compact S to be pushed out to the side faces, forming the convex portions 21 (undercut portions 30) on the side faces of the sintered part 1. At this time, when the protrusions T are pushed out to the side faces, the shape of the convex portions 21 (undercut portions 30) is imparted to the protrusions T by a die. As shown in Fig. 5, in the recompression step, sizing is performed on the sintered body S using dies consisting of an inner die (core) 100, an outer die 200, a lower punch 300, and an upper punch (not shown). The inner die 100 and the outer die 200 are fixed in position. The lower punch 300 can be moved in the vertical direction relative to the inner die 100 and the outer die 200. The upper punch can be moved in the vertical direction relative to the inner die 100 and the outer die 200. An inclined surface 101 for pushing out (pressing) the protrusion T is formed on the upper surface of the inner die 100. In the recompression process, the protrusion T is pushed out toward the side surface of the fitting portion 20 by pressing the protrusion T with the inclined surface 101, and a convex portion 21 is formed on the side surface of the fitting portion 20. Here, as shown in FIG. 6, in this embodiment, the inner side surface of each protrusion T is an inclined surface t that slopes downward toward the inside. This makes it easy to push out each protrusion T to the outside (the side surface of the fitting portion 20). The inclination angle θ1 of the inclined surface t is within a range of 30 to 90°. Moreover, the inclination angle θ2 of the inclined surface 101 is within a range of 0 to 45°. Here, the inclination angle θ1 and the inclination angle θ2 are angles with respect to the horizontal plane. A convex shape 301 for forming the convex portion 21 (undercut portion 30) is provided on the inner side surface of the lower punch 300. Then, in the re-compression process, the convex shape 301 provided on the side surface of the lower punch 300 is transferred to the side surface of the fitting portion 20 of the sintered body S, thereby forming the convex portion 21 (undercut portion 30) on the side surface of the fitting portion 20.

[0015] 5(a), in the recompression step, first, the sintered body S is placed on the upper surface of the inner die 100. At this time, the sintered body S is placed on the upper surface of the inner die 100 with the upper end surface of the sintered body S (the end surface on which the three protrusions T are formed) facing downward. In addition, the lower punch 300 is placed on the side of the fitting portion 20 of the sintered body S. Next, as shown in FIG. 5(b), the sintered body S is pressed downward by the upper punch. As a result, the inclined surface 101 provided on the upper surface of the inner die 100 presses the protruding portion T provided on the end surface of the fitting portion 20, and the protruding portion T is plastically deformed and extruded to the side surface of the fitting portion 20. At this time, the movement of the material extruded to the side surface of the fitting portion 20 is restricted by the convex shape 301 provided on the side surface of the lower punch 300, and the convex shape 301 is transferred to the side surface of the fitting portion 20 to form the convex portion 21 (undercut portion 30). As a result, as shown in FIG. 7, it is possible to form the convex portion 21 (undercut portion 30) on the side surface of the fitting portion 20, and it is also possible to control the dimensions, shape, etc. of the convex portion 21 (undercut portion 30) with high precision. In particular, in this embodiment, the three protrusions T provided on the end face of the fitting portion 20 are pressed simultaneously, and three convex portions 21 are simultaneously formed on the side face of the fitting portion 20. This makes it possible to suppress the occurrence of distortion in the sintered part 1. The volume of each of the convex portions 21 is within a range of 30 to 70% of the volume of each of the protrusions T. Next, as shown in FIG. 5(c), the pressing by the upper punch is terminated, and the sintered part 1 is removed. At this time, in this embodiment, the lower punch 300 is divided into an upper part 310 having a convex shape 301 and a lower part 320. The upper part 310 can be moved outward (in a direction perpendicular to the direction of removal of the die) relative to the lower part 320. As a result, by moving the lower punch 300 upward relative to the inner die 100 and the outer die 200, the upper part 310 can be moved outward relative to the lower part 320, and the convex shape 301 provided on the side of the upper part 310 can be removed from within the undercut part 30 formed on the side of the fitting part 20. Here, the density of the sintered part 1 is 6.2 to 7.2 g / cm 3 It is preferable that the range is within the range.

[0016] Next, the sintered part 1 is subjected to a shot blasting process. In the shot blasting process, a predetermined blasting material (small metal or ceramic balls, particles, etc.) is blasted against the surface of the sintered part 1. This makes it possible to remove burrs that occur at the corners of the undercut parts 30 (particularly the protrusions 21) during the recompression process. It also makes it possible to densify the surface of the sintered part 1, thereby improving its strength and hardness. It also makes it possible to fill the surface pores of the sintered part 1, thereby improving its corrosion resistance. It also makes it possible to improve the surface properties of the sintered part 1 (improving surface roughness). The sintered part 1 may be subjected to a cleaning process to remove metal chips, sizing lubricant, etc., generated during processing. The sintered part 1 may also be subjected to a process such as impregnation with a lubricant depending on the application.

[0017] (Function of the manufacturing method of sintered part 1) The manufacturing method of the sintered part 1 includes a molding step of compressing and molding a raw material including metal powder to form a green compact P, a sintering step of sintering the green compact P to form a sintered body S, and a recompressing step of recompressing the sintered body S. In particular, a protrusion T is formed on the end face of the green compact P by the molding step, and in the recompressing step, the protrusion T is pushed out toward the side face of the sintered body S to form an undercut portion 30, and the shape of the undercut portion 30 is imparted by a die (lower punch 300). That is, in the manufacturing method of the sintered part 1, when the protruding parts T are pushed out toward the side faces of the sintered compact S in the re-compressing step to form the undercut parts 30, the shape of the undercut parts 30 is imparted by a die. This makes it easy to control the amount of extrusion (dimensions and shape) of the convex parts 21 that constitute the undercut parts 30, and makes it possible to improve the precision of the sintered part 1. Furthermore, in the manufacturing method of the sintered part 1, the elongation of the sintered body S is set to 10% or more. In other words, if the elongation of the sintered body S is less than 10%, it becomes difficult to extrude the protrusions T and to impart the shape of the undercut portions 30 with a die. Therefore, by setting the elongation of the sintered body S to 10% or more, it becomes easier to extrude the protrusions T and to impart the shape of the undercut portions 30 with a die. Furthermore, in the manufacturing method of the sintered part 1, the hardness (Rockwell hardness) of the sintered body S is within the range of 20 to 40 HRB. That is, if the hardness of the sintered body S is less than 20 HRB, the strength of the undercut portion 30 is insufficient. On the other hand, if the hardness of the sintered body S exceeds 40 HRB, there is a risk that cracks will occur in the undercut portion 30 when the protruding portion T is extruded. Therefore, by setting the hardness of the sintered body S within the range of 20 to 40 HRB, it is possible to prevent the occurrence of cracks in the undercut portion 30 while ensuring the strength of the undercut portion 30. [Explanation of symbols]

[0018] 1 Sintered parts 10 Base 20 Fitting part 21 Convex 30 Undercut section P powder compact S sintered body T protrusion

Claims

1. a molding step of compressing and molding a raw material containing metal powder to form a green compact; a sintering step of sintering the green compact to form a sintered body; A recompression step of recompressing the sintered body, A protrusion is formed on an end surface of the powder compact by the molding step, A method for manufacturing a sintered part, characterized in that in the re-compression process, when the protrusion is pushed out toward the side surface of the sintered body to form an undercut portion, the shape of the undercut portion is imparted by a mold.

2. 2. The method for producing a sintered part according to claim 1, wherein the elongation of the sintered body is 10% or more.

3. 3. The method for producing a sintered part according to claim 1, wherein the hardness of the sintered body is within a range of 20 to 40 HRB.

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