Method for manufacturing die-casting die

Abstract

To provide a method for manufacturing a die for die-casting, which effectively strengthens a specific portion of the die for die-casting, i.e., a portion where heat check, erosion or the like is liable to occur, and extends the life of the whole die.SOLUTION: In the method for manufacturing the die-casting die, a treatment region on the surface of the die-casting die is determined, pits are formed in the treatment region by a mechanical method, a fibrous metal structure is formed in the treatment region by shot peening, and a hardened layer is formed in the treatment region by nitriding treatment. Further, in the method for producing the die for die casting, a treatment region on the surface of the die for die casting is determined, pits are formed in the treatment region by a mechanical method, a hardened layer is formed in the treatment region by laser heat treatment, a fibrous metallic structure is formed in the treatment region by shot peening, and the hardened layer is formed in the treatment region by nitriding treatment.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a die-casting mold, and more particularly to a method for manufacturing a die-casting mold that effectively strengthens specific parts of the die-casting mold, i.e., parts that are prone to heat checking, melting, etc., thereby extending the life of the entire mold. [Background technology]

[0002] Die casting is highly productive and can provide high-quality castings, so the majority of aluminum castings are currently produced by die casting. Furthermore, many aluminum die-cast products are automotive parts, and in recent years, the trend toward higher performance, lighter weight, and the shift to electric vehicles has led to demand for higher quality, lighter weight, and larger parts with integrated structures. While products are becoming higher quality, lighter, and larger, high productivity is also required, placing a greater strain on die-casting molds. Therefore, higher quality and longer life are required for die-casting molds, and higher performance steel materials and a variety of surface treatments have been proposed and put into practical use.

[0003] Furthermore, during use, molds such as die-casting molds often suffer damage such as cracks and melting due to thermal loads and chemical reactions. However, uniform deterioration or damage to the mold surface is rare, and melting and cracking, which affect the mold's lifespan, rarely occur uniformly across the entire mold surface. Damage to a specific portion of the mold, such as the area directly hit by molten metal from the gate, often results in the end of the mold's lifespan. Therefore, if it is possible to predict that a specific portion of the mold is prone to melting or cracking, that portion can be strengthened specifically to extend the mold's lifespan. Furthermore, if damage to that specific portion can be reduced while also improving the flow of the mold, defects occurring in that specific portion of the product can also be improved.

[0004] Therefore, mold surface treatments have been considered as a method for preventing or suppressing mold damage. For example, mold surface treatments include nitriding, PVD (Physical Vapor Deposition), CVD (Chemical Vapor Deposition), and shot peening. A combined nitriding and shot peening treatment has also been proposed. Patent Document 1 discloses a method for suppressing damage by imparting roughness to the mold surface and compressive stress using shot blasting or shot peening. Also, mold surface roughening has been performed using chemical etching, or by coating the surface with a refractory metal compound and imparting roughness using an electric discharge machine. Furthermore, Patent Document 2 discloses a method for improving mold life by combining nitriding and shot peening to create a nitride layer and compressive stress. Patent Document 3 also describes mechanical dents in addition to shot peening and chemical etching as roughening treatments for runner sections. Furthermore, Non-Patent Document 1 discloses laser hardening as a method for locally strengthening molds. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Hideo Kubo, "Practical Surface Technology", 1982, Vol. 29, No. 4, p. 170 [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-148362 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-235318 [Patent Document 3] Japanese Patent Publication No. 2022-063174 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the past, even though the melting damage and cracks that affect the lifespan of a mold rarely occur uniformly over the entire surface of the mold, even if it was predicted that a specific part of the mold would be susceptible to damage, such as a part directly hit by molten metal from the gate, it was technically difficult to strengthen that specific part in advance.

[0008] Furthermore, shot blasting or shot peening has limitations on the size of the irregularities that can be produced, and they may not be sufficient to strengthen the mold or improve melt flow. Chemical etching or large-particle shot blasting requires masking to treat only specific areas of the mold, which requires time and effort. This masking process is time-consuming and difficult to perform manually, and the resulting irregularities have a short lifespan, making improvements to these techniques desirable. While mechanically indenting irregularities is described in Patent Document 3, this is done on the runner section. In the case of irregularity treatment on the runner section, the traces of the irregularity treatment are not directly transferred to the product, so the pit formation area is not necessarily precise. Even if the pits are formed outside the specified area, this does not directly affect product quality. Furthermore, variations in pit depth, size, or density do not directly affect product quality. On the other hand, when applying texture to the product formation area, i.e., the cavity, if pits are formed outside the designated pit formation area or if there is variation in the size or density of the pits, it often leads to product defects. In such cases, the mold must be repaired or a new mold must be created. For this reason, texture processing using mechanical dents on the cavity has not been practiced in practice until now. Furthermore, laser hardening alone increases hardness, but generates tensile residual stress, so it is not necessarily sufficiently effective in extending the mold's lifespan.

[0009] Therefore, an object of the present invention is to solve the problems of the prior art and to provide a method for manufacturing a die-casting die that effectively strengthens specific parts of the die-casting die, i.e., parts that are prone to heat checks and melting damage, particularly parts of the cavity that are related to quality and are prone to heat checks and melting damage, thereby extending the life of the die as a whole. [Means for solving the problem]

[0010] As a result of intensive research to solve the above problems, the inventors have discovered a treatment method that can achieve high durability in a shorter time and at lower cost than conventional methods for areas of a mold that are prone to damage or areas where it is desired to improve the flow of molten metal, and have found that the above-mentioned object can be achieved, thereby completing the present invention.

[0011] That is, the manufacturing method of the die-casting mold of the present invention includes the following steps: Determine the areas to be treated on the surface of the die-casting mold, forming pits at the treated area by a mechanical method; A fibrous metal structure is generated at the treated portion by shot peening, The method is characterized in that a hardened layer is formed at the treated portion by nitriding.

[0012] Further, the manufacturing method of the die-casting mold of the present invention includes the steps of: Determine the areas to be treated on the surface of the die-casting mold, forming pits at the treated area by a mechanical method; generating a hardened layer at the treated area by laser heat treatment; A fibrous metal structure is generated at the treated portion by shot peening, The method is characterized in that a hardened layer is formed at the treated portion by nitriding.

[0013] Furthermore, in the method for manufacturing a die-casting die of the present invention, a method for determining the treatment area on the surface of the die-casting die (hereinafter, the treatment area is also referred to as a "pit formation area" because it is an area where pits are formed) is (1) Identifying the shape of the die-casting mold using data on the mold surface shape based on 3D CAD data of the die-casting mold, and determining the treatment area on the die-casting mold surface based on the 3D CAD data; (2) Identifying the shape of the die-casting mold using data on the mold surface shape obtained by a 3D scanner, and determining the treatment area on the die-casting mold surface based on the data from the 3D scanner; (3) determining the treatment area on the surface of the die-casting mold by teaching the robot; The above methods (1) to (3) are preferred.

[0014] Furthermore, the manufacturing method of the die-casting mold of the present invention includes the steps of: the mechanical technique is a mechanical impact technique, The diameter of the formed pits is 400 μm to 800 μm, the depth of the pits is 50 μm to 200 μm, and the opening area of ​​the pits with respect to the treated area is 40 to 80%; It is preferable that the pits are formed in a state where they are aligned linearly.

[0015] Furthermore, the method for manufacturing a die-casting mold of the present invention includes the steps of: In the shot peening, The shot material is one selected from the group consisting of spherical glass beads having a diameter of 20 μm to 150 μm, zircon, stainless steel, and steel; It is preferable that the shot pressure is 0.3 MPa to 0.6 MPa and the injection distance is 50 mm to 300 mm.

[0016] In addition, in the method for manufacturing a die-casting die of the present invention, the nitriding treatment is preferably a nitriding treatment that does not produce a white layer.

[0017] Furthermore, in the method for manufacturing a die-casting die of the present invention, it is preferable that the hardened layer formed by the laser heat treatment (laser irradiation) is deeper than the hardened layer formed by the nitriding treatment. [Effects of the Invention]

[0018] According to the present invention, a method for manufacturing a die-casting mold can be provided that effectively strengthens specific parts of the die-casting mold, i.e., parts that are prone to heat checking, melting, etc., thereby extending the life of the entire mold. [Brief explanation of the drawings]

[0019] [Figure 1] Schematic cross-sectional view of a recess made by the mechanical indentation method ((a) is a plan view, (b) is a cross-sectional view). [Figure 2] FIG. 2 is a plan view showing an example of pits and pit-forming areas in the present invention. [Figure 3] 1 is a schematic diagram of a surface layer of a die-casting mold according to the present invention. [Figure 4] This is a photograph showing an example of pits formed in a die-casting mold due to mechanical impact. [Figure 5] 5 is an enlarged photograph of the pit in FIG. 4. [Figure 6] FIG. [Figure 7] FIG. 2 is a view showing the tip of a forming punch. [Figure 8] 1 is a photograph showing the metal structure of a cross section near the surface of a heat-treated SKD61 material when shot peening is performed. [Figure 9] 1 is an SEM photograph showing the metal structure of a cross section near the surface of heat-treated SKD61 material when shot peening is performed. [Figure 10] 10 is a photograph showing a cross section of the surface of a sample of Example 3. [Figure 11] 10 is a photograph showing an enlarged image of a pit portion on the surface of a sample of Example 3. [Figure 12] This is a metallographic image of a cross section near the surface of a sample of Example 4, in which pits were formed by mechanical impacts on heat-treated SKD61 material in the same manner as in Example 3, and then shot peening was performed, followed by nitriding treatment. [Figure 13] 10 is an enlarged image of the vicinity of the surface of the sample of Example 4. [Figure 14]10 is a photograph showing a cross-sectional image of a sample that has been subjected to laser treatment after pit formation, shot peening, and then nitriding treatment. [Figure 15] 10 is an enlarged image of the vicinity of the surface of the sample of Example 6. DETAILED DESCRIPTION OF THE INVENTION

[0020] The die-casting die manufacturing method of the present invention will be specifically described below. The method for manufacturing a die-casting mold of the present invention comprises determining a treatment area on the surface of the die-casting mold, forming pits in the treatment area by a mechanical means, generating a fibrous metal structure in the treatment area by shot peening, and generating a hardened layer in the treatment area by nitriding, and is a method for manufacturing a die-casting mold having a nitride layer including pits and a fibrous metal structure on the mold surface.The method for manufacturing a die-casting mold of the present invention comprises determining a treatment area on the surface of the die-casting mold, forming pits in the treatment area by a mechanical means, generating a hardened layer in the treatment area by laser heat treatment, generating a fibrous metal structure in the treatment area by shot peening, and generating a hardened layer in the treatment area by nitriding, and is a method for manufacturing a die-casting mold having a nitride layer including pits and a fibrous metal structure and a hardened layer formed by laser heat treatment. For areas of a die-casting mold that require reinforcement, the shape of the die-casting mold is identified using (1) 3D CAD data or (2) mold surface shape data obtained by a 3D scanner. The treatment area (pit formation area) on the die-casting mold surface is determined based on the (1) 3D CAD or (2) 3D scanner data (drawings). A robot is then operated, and the treatment area is mechanically textured using a tool attached to the robot. If 3D CAD or 3D scanner data is unavailable or unavailable, the treatment area (pit formation area) on the die-casting mold surface can be determined by (3) teaching the robot, and the robot is then operated. Manual texture processing is also possible, but manual texture processing is undesirable due to variations in pit size and density and lack of stability. Furthermore, after texture processing, the treatment area is subjected to intense shot peening to improve the metal structure of the mold surface, strengthen the material itself, and impart compressive stress. Furthermore, the treatment area is subjected to nitriding to harden the mold surface and impart compressive stress. After the mechanical roughening treatment, the treated area is subjected to laser heat treatment (laser hardening), followed by shot peening and nitriding. By performing the laser heat treatment, a deeper hardened layer can be obtained.This improves the strength of areas of the die-casting mold where melting or cracking is expected, thereby extending the life of the die-casting mold. It also improves the flow of molten metal in specific areas of the die-casting mold and prevents cracking, thereby extending the life of the mold.

[0021] Specifically, for areas of the die-casting mold that are prone to damage or areas where melt flow needs to be improved, 3D CAD data (drawings) of the die-casting mold or shape data collected with a 3D scanner are used. Based on this data, a mechanical denting device installed on a 6-axis robot precisely creates pits in the required areas (treatment areas), improving melt flow and imparting compressive stress. Furthermore, shot peening is used to improve the metal structure and impart compressive stress. Nitriding is then performed, hardening the mold surface with a nitride layer and imparting compressive stress.

[0022] In the present invention, 3D CAD stands for three-dimensional "Computer Aided Design." Examples include high-end CAD, mid-range CAD, and low-end CAD. Any CAD can be used as long as it achieves the effects of the present invention. However, the operating program used by the robot must be compatible with the 3D CAD. Using 3D CAD allows the shape and structure of the design to be grasped as three-dimensional data, enabling the robot to accurately specify pit formation areas for the processing areas on the surface of the die-casting mold.

[0023] In the present invention, a 3D scanner measures the surface of an object as points, generates three-dimensional data, and reproduces the shape and characteristics of the object as a three-dimensional model. Examples include optical scanners such as patterned light projection and stereo camera structured light scanners, laser scanners such as time-of-flight and triangulation scanners, and X-ray / CT scanners. Any type of scanner can be used as long as the effects of the present invention are achieved. However, the data format must be convertible to 3D CAD compatible with the operating program used by the robot. By using a 3D scanner and converting it into 3D CAD data, the surface shape of the design object can be grasped as a three-dimensional model (data), and the robot can be accurately instructed on the pit formation areas for the treatment areas on the surface of the die-casting mold.

[0024] Furthermore, in the present invention, the procedure for performing unevenness processing by a robot using 3D CAD data is as follows. (1) Determine the areas of the mold that need to be strengthened by taking into consideration the mold shape, casting method, and past examples of mold damage. (2) Identify the pit formation area on the 3D CAD. (3) Link the 3D CAD data with the robot's operating program. (4) The robot's operating range is specified in the robot's operation program. (5) The robot is activated, and the pit formation area is roughened using a denting device attached to the robot arm. Furthermore, the processing conditions required for uneven processing, such as the robot's scanning speed and the pressure settings of the denting device, must be understood in advance using test pieces, etc. Furthermore, when using a 3D scanner, the data from the 3D scanner must be converted into 3D CAD data. Furthermore, if 3D CAD data and a 3D scanner cannot be used, the pit formation area must be taught to the robot on the mold.

[0025] Furthermore, in the present invention, the improvement of the metal structure by the fibrous metal structure is 20 μm to 30 μm from the surface of the die-casting mold, and the hardening depth by the nitriding treatment is approximately 100 μm or less in the case of nitriding treatment that does not produce the so-called ``white layer''.If a deeper hardened layer is required, laser hardening (laser heat treatment) is performed after pit formation, followed by shot peening, and then nitriding treatment, which will further increase the effect of suppressing crack generation.

[0026] In addition, in the present invention, the mechanical method for forming pits is not particularly limited as long as the effects of the present invention can be obtained, but examples include an electric drill, and an electric or air-powered vibration-type mechanical tool, and among these, a mechanical indentation method using an air-powered vibration tool is preferred.

[0027] Furthermore, in the present invention, from the viewpoint of suppressing a sudden temperature rise in the die-casting mold when molten metal is poured in and improving the flow of the metal, it is preferable that the pits formed by the mechanical indentation method have an opening diameter of 400 μm to 800 μm, a depth of 50 μm to 200 μm, and the opening area of ​​pit 51 accounts for 40% to 80% of the area of ​​the treated portion 52. Furthermore, it is preferable that pits 51 are formed in a regular linear array, which can improve the stability of the treatment effect.

[0028] FIG. 1 is a cross-sectional schematic diagram of a recess formed by a mechanical denting technique ((a) is a plan view, and (b) is a cross-sectional view). As shown in FIG. 1, mechanical denting can create pits 51 (pit irregularities) with raised edges. FIG. 1 is a schematic diagram of a case where pit irregularities are formed by mechanical denting using a conical punch with a 60° tip angle. In this case, the material in the recess rises almost evenly around the pit edges due to plastic deformation, and the height of the raised pit 51a with raised edges of pit 51 is 5 to 20 μm. However, this raised portion is smoothed by shot peening in a subsequent process. FIG. 2 is a plan view showing an example of pits and pit-formed regions according to the present invention. The pit-formed region 52 of a die-casting mold 5 is the region formed by connecting the outermost pits 51 as shown in FIG. 2 (the region 52 surrounded by the curved line in FIG. 2).

[0029] Furthermore, in the present invention, since pit formation may require precision down to the millimeter, robotic operation using the shape data of the die-casting mold is desirable. Furthermore, robotic operation is more appropriate in terms of the stability of the formed pit shape. In robotic operation, the pit formation area 52 obtained from 3D CAD data or the like is instructed to the robot operation program, and the unevenness is processed in the precise pit formation area 52 using a tool attached to the robot arm. The unevenness processing is performed using the tool's operating conditions and the robot arm's scanning speed, which are appropriately set in advance. This robotic operation enables uneven processing that ensures stable pit depth and density within an accurate range.

[0030] In the present invention, the shot peening treatment can be carried out using an air-type shot peening machine, and the shot material used can be one selected from the group consisting of spherical glass beads, zircon, stainless steel, and steel, each having a diameter of 20 μm to 150 μm. It is preferable that the shot pressure (air pressure) is 0.3 MPa to 0.6 MPa and the blast distance is 50 mm to 300 mm. Furthermore, the blast time is 1 cm. 2 A hit of 10 to 30 seconds is desirable.

[0031] Furthermore, while there are various types of shot peening machines, when using an air-type, a so-called direct pressure shot peening machine is preferable. By using a direct pressure shot peening machine, fine pits are formed on the entire treated surface, including the inner surfaces of pits caused by mechanical impacts, further improving the melt flow effect. Furthermore, at the same time, the metal structure on the surface of the die-casting mold becomes a fibrous structure, increasing strength and hardness, and even generating a nanostructure, significantly improving strength at high temperatures.

[0032] Furthermore, in normal shot peening treatment, measures such as masking are required to distinguish treated areas from untreated areas. However, under the shot peening treatment conditions of the present invention, the irregularities on the mold surface are approximately 20 μm or less and the dimensional change at the corners is approximately 50 μm or less, so measures such as masking are not necessary unless particularly strict dimensional control is required.

[0033] Furthermore, in the present invention, the nitriding method is preferably a nitriding method that does not produce a so-called white layer. Nitriding hardens the mold surface layer and imparts compressive stress, but if a white layer is produced, this white layer is hard and brittle, and is therefore prone to cracking due to the thermal cycle of die-casting, which may adversely affect the life of the die-casting mold. Therefore, the nitriding method is preferably a nitriding method that involves holding the mold in a nitrogen gas atmosphere at 500 to 530°C for 3 to 8 hours, resulting in a nitrided layer of 20 to 100 μm, and does not produce a white layer.

[0034] Furthermore, in the present invention, if laser heat treatment (laser hardening) is not performed, the improvement of the metal structure by shot peening is within a range of 20 μm to 30 μm from the surface, and the hardening depth by nitriding treatment is 100 μm or less under conditions that do not produce a white layer. Therefore, if greater durability is required than the effects of pit formation, shot peening, and nitriding treatment, a deeper hardened layer can be obtained by performing laser heat treatment (laser hardening) after shot peening.

[0035] Furthermore, in the present invention, laser heat treatment (laser hardening) can increase the hardness of the material to approximately 200 μm by controlling the irradiation energy, the scanning speed of the laser beam, etc. In this case, the improvement of the metal structure by shot peening is in the range of 10 μm to 20 μm from the surface, but the hardening depth by nitriding is the same as when laser heat treatment (laser hardening) is not performed.

[0036] Figure 3 is a schematic diagram of the surface layer of a die-casting mold of the present invention. A fibrous metal structure is formed near the mold surface, and a hardened layer is formed by nitriding to a depth of 20 μm to 100 μm from the mold surface, in a shape that follows the mold surface shape. Furthermore, when laser heat treatment (laser hardening) is performed, a hardened layer is formed by the laser treatment to a depth of 100 μm to 200 μm from the convex parts of the pits. The depth of the hardened layer by this laser treatment is a nearly constant depth from the mold surface (flat surface) before the pits were formed, resulting in a deep hardened layer in the convex parts of the pits and a shallow hardened layer in the concave parts.

[0037] In the present invention, examples of the mold (die-casting mold) include die-casting molds used for casting aluminum alloys, magnesium alloys, etc. The steel material for such molds is not particularly limited as long as the effects of the present invention can be obtained, and examples thereof include JIS G 4404 SKD61.

[0038] Furthermore, in the present invention, steps that can be used in ordinary mold manufacturing methods can be added within the scope that does not impair the effects of the present invention. For example, the mold manufacturing method of the present invention may include a discharge coating or oxidation treatment step.

[0039] In the present invention, the treatment area on the surface of a die-casting mold is determined, pits are formed in the treatment area by mechanical means, a fibrous metal structure is generated in the treatment area by shot peening, and a hardened layer is generated in the treatment area by nitriding treatment, so that the surface of a specific part of the mold can be used as a die-casting mold material composed of pits, a fibrous metal structure, and a nitrided layer.

[0040] In addition, in the present invention, the treatment area on the surface of the die-casting mold is determined, pits are formed in the treatment area by mechanical means, a hardened layer is generated in the treatment area by laser heat treatment, a fibrous metal structure is generated in the treatment area by shot peening, and a hardened layer is generated in the treatment area by nitriding treatment, so that the surface of a specific part of the mold can be used as a die-casting mold material composed of pits, a fibrous metal structure, a nitrided layer, and a hardened layer generated by heat treatment.

[0041] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples. [Example]

[0042] Example 1 Figure 4 is a photograph showing an example of a pit formed in a die-casting die by mechanical impact, Figure 5 is an enlarged photograph of the pit in Figure 4, Figure 6 is a diagram showing a forming punch, and Figure 7 is a diagram showing the tip of the forming punch. The forming punch is made of KH03 material, has a tip angle of 60°, and a tip radius of 0.5 mm. The pit formation area was determined based on 3D CAD data for the die-casting die, and a vibration-type machine tool (air-type) was attached to a 6-axis robot, and the pit was formed using the forming punch shown in Figure 6 at an air pressure of 0.6 MPa.

[0043] Example 2 Figure 8 is a photograph showing the cross-sectional metal structure near the surface of heat-treated SKD61 material after shot peening, and Figure 9 is an SEM photograph showing the cross-sectional metal structure near the surface of heat-treated SKD61 material after shot peening. The shot peening machine used was an air-type direct pressure peening machine, and the shot material was spherical zircon with a center particle size of 120 μm. The air pressure was 0.6 MPa, the shot distance was 100 mm, and the shot time was 10 seconds. It can be seen that the crystalline structure of the metal surface has been stretched thinly and fibrous by shot peening. The SEM image in Figure 9 suggests that the metal structure has been strongly processed into extremely fine fibers, resulting in nanocrystallization. Nanocrystals have high strength and hardness, with little loss of strength at high temperatures, making them less susceptible to cracking due to the thermal cycle during die casting.

[0044] Example 3 FIG. 10 is a photograph showing a cross section of the surface of a sample of Example 3, and FIG. 11 is a photograph showing an enlarged image of a pit on the surface of the sample of Example 3. Pits were formed by mechanical impact in the same manner as in Example 1 on a heat-treated SKD61 material, and shot peening was then performed in the same manner as in Example 2. As shown in FIG. 10, regular irregularities (pits) were formed. Furthermore, as shown in FIG. 11, a fibrous structure similar to that in FIG. 8 can be seen on the surface of the material.

[0045] Example 4 Figure 12 shows a cross-sectional metallographic image of the near-surface region of a sample of Example 4, in which mechanically pitted SKD61 heat-treated material was subjected to shot peening and subsequent nitriding, as in Example 3. Figure 13 shows a magnified image of the near-surface region of the sample of Example 4. The nitriding treatment was performed at 530°C for 8 hours, under conditions that did not produce a white layer. A layer that appears slightly darker due to etching extends approximately 80 μm from the surface. The dark color due to etching in the surface region is due to the high nitrogen atom concentration in the surface region resulting from the nitriding treatment, as well as the fibrous metal structure, which results in many crystal interfaces and a high dislocation density. This layer, which can be identified by etching, corresponds to the hardening due to nitriding, as described below (Example 5). In the magnified image of the near-surface region of Figure 13, a fibrous metal structure can be observed in the surface region, as in Figure 11.

[0046] Example 5 The results of measuring the hardness of the cross section of the test piece treated in Example 4 are shown in Table 1 below. The hardness measurements were performed using a Mitutoyo HM-210A micro Vickers hardness tester at a load of 0.1 MPa. The base material hardness was approximately Hv:500, but the surface had a hardness of approximately Hv:1000 due to the nitriding treatment. Both the convex and concave portions had been hardened by the nitriding treatment to a depth of 50 to 60 μm from the surface. Note that in Tables 1 and 2 below, it was not possible to measure the surface of the concave portions due to their shape. The depths in the tables are the distances from the surfaces of the convex and concave portions, respectively.

[0047] [Table 1]

[0048] Example 6 Figure 14 is a photograph showing a cross-section of a sample that was subjected to laser treatment after pit formation, followed by shot peening and then nitriding, and Figure 15 is an enlarged image of the surface vicinity of the sample of Example 6. A nitride layer can be seen, with a thickness that follows the surface irregularities. Also, as shown in Figure 3, linear boundaries of the layer affected by the laser treatment can be seen at a depth of approximately 170 μm from the convex portions and 90 μm from the concave portions. The laser treatment was performed using a semiconductor laser with a rated output of 800 W, an input voltage of 5 V, an irradiation distance of 113 mm, a scanning speed of 6 mm / sec, and continuous oscillation.

[0049] Example 7 The results of measuring the hardness of the cross section of the sample shown in Example 6 are shown in Table 2 below. The surface had a hardness of approximately Hv: 1000, which is almost the same as the value in Table 1 for Example 5. On the other hand, in the case of Example 6, the nitriding depth was approximately 50 to 60 μm in both the convex and concave portions, whereas in Table 2, a hardened layer of 100 μm or more was observed in the convex portions, and hardening had occurred to a depth of approximately 80 μm even in the concave portions.

[0050] [Table 2] [Explanation of symbols]

[0051] 5. Die-casting molds 51 Pit 51a A protrusion on the edge of the pit 52 Area of ​​the treated area (pit formation area)

Claims

1. Determine the areas to be treated on the surface of the die-casting mold, forming pits at the treated area by a mechanical method; A fibrous metal structure is generated at the treated portion by shot peening, A method for manufacturing a die-casting mold, characterized in that a hardened layer is formed in the treated area by nitriding.

2. Determine the areas to be treated on the surface of the die-casting mold, forming pits at the treated area by a mechanical method; generating a hardened layer at the treated area by laser heat treatment; A fibrous metal structure is generated at the treated portion by shot peening, A method for manufacturing a die-casting mold, characterized in that a hardened layer is formed in the treated area by nitriding.

3. The method for determining the treatment portion of the die-casting die surface comprises: (1) Identifying the shape of the die-casting mold using data on the mold surface shape based on 3D CAD data of the die-casting mold, and determining the treatment area on the die-casting mold surface based on the 3D CAD data; (2) Identifying the shape of the die-casting mold using data of the mold surface shape obtained by a 3D scanner, and determining the treatment area on the die-casting mold surface based on the data from the 3D scanner; (3) determining the treatment area on the surface of the die-casting mold by teaching the robot; The method for manufacturing a die-casting mold according to claim 1 or claim 2, which is the method (1) to (3) above.

4. the mechanical technique is a mechanical impact technique, the diameter of the formed pit is 400 μm to 800 μm, the depth of the pit is 50 μm to 200 μm, and the opening area of ​​the pit with respect to the treated portion is 40 to 80%; 4. The method for manufacturing a die casting mold according to claim 3, wherein the pits are formed in a linear alignment.

5. In the shot peening, the shot material is one selected from the group consisting of spherical glass beads having a diameter of 20 μm to 150 μm, zircon, stainless steel, and steel; 5. The method for manufacturing a die-casting mold according to claim 4, wherein the shot pressure is 0.3 MPa to 0.6 MPa and the injection distance is 50 mm to 300 mm.

6. 6. The method for manufacturing a die-casting mold according to claim 5, wherein the nitriding treatment is a nitriding treatment that does not produce a white layer.

7. 3. The method for manufacturing a die-casting die according to claim 2, wherein the hardened layer formed by the laser heat treatment (laser irradiation) is deeper than the hardened layer formed by the nitriding treatment.

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