Method for manufacturing copper extruded materials

Abstract

The present invention provides a method for manufacturing copper extruded materials that can sufficiently reduce the processing load during extrusion, enabling high processing accuracy and stable extrusion, even when the workpiece is a copper material consisting of copper and copper alloys, which have a higher yield stress than other metals. [Solution] A method for producing a copper extruded material made of copper or a copper alloy, comprising inserting a copper material made of copper or a copper alloy into a container portion 21 of a die 20 at room temperature, applying a compressive force from one end of the billet to pass a part or all of the copper material through a forming hole 22 formed such that the cross-sectional area of ​​the die 20 is reduced, characterized in that the arithmetic mean roughness Ra of the inner circumferential surface of the die 20 through which the copper material passes is in the range of 0.03 μm or more and 0.25 μm or less.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a copper extruded material made of copper or a copper alloy.

Background Art

[0002] Conventionally, copper and copper alloys having excellent electrical conductivity and thermal conductivity have been widely used in various fields as materials for conductive members and heat dissipation members. In recent years, with the miniaturization and high functionality of electronic devices, these members have changed to more fine and complex shapes. In particular, the demand for members having a micro-meso scale structure, which refers to the intermediate between macro and micro, has been increasing. Therefore, in the field of metal processing, there is a demand for the development of a processing method for copper and copper alloys that can cope with this change while ensuring mass productivity.

[0003] Here, plastic processing typified by extrusion processing is a processing method with high mass productivity and high yield compared to other processing methods such as cutting processing and 3D printers. Note that extrusion processing is a method of forming a copper material into the shape of an extruded material by inserting a copper material into a container portion of a die, applying a compressive force to the copper material, and extruding the copper material through a forming hole portion of the die formed so that the cross-sectional area decreases.

[0004] In the conventional macro extrusion technology, for example, as shown in Patent Document 1, in order to reduce the load, the copper material was heated before processing and hot working such as extrusion was performed, or devices such as pre-processing the tip of the copper material were made, but in any case, there were problems such as an increase in man-hours and, in the case of hot working, the material was softened and the strength of the product was not ensured.

[0005] In addition, while extrusion processing is an excellent processing method, the correspondence to micro-meso forming has not advanced. In this specification, micro-meso extrusion processing refers to processing in which at least two basic dimensions of the product after extrusion processing are 5 mm or less (micro-meso scale extrusion processing method). Non-patent document 1 reports on the tribology of micro-meso-molding. In micro-meso-scale extrusion, challenges include the decrease in relative accuracy of the product and the large variation in accuracy due to the influence of dimensional effects. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-015057 [Non-patent literature]

[0007] [Non-Patent Document 1] Kuniaki Doda, Takehiko Makino: Plasticity and Processing, Vol. 49, No. 570 (2008), 28-32. [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Incidentally, copper and copper alloys have a higher yield strength than other metals such as aluminum, resulting in higher processing loads during extrusion. This has led to problems such as exceeding the processing machine's upper limit during extrusion, making processing impossible and necessitating changes to the shape, as well as excessive die wear. Furthermore, there was a risk of reduced relative accuracy and greater variability in the product (extruded material) compared to other metals.

[0009] The present invention was made against the background described above, and aims to provide a method for manufacturing copper extruded materials that can sufficiently reduce the processing load during extrusion, even when the workpiece is a copper material consisting of copper and copper alloys, which have a higher yield strength than other metals, and can perform extrusion with high processing accuracy and stability. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, the inventors diligently conducted research and obtained the following findings. When copper material, consisting of copper or a copper alloy, is extruded, as shown in the graph of the relationship between processing distance and processing load in Figure 1, the processing load exhibits peak behavior in the initial stages of processing, and the maximum processing load is recorded at that time.

[0011] The inventors have revealed, through processing tests and studies such as observing changes in the crystalline structure of processed products, that the peak behavior of this processing load is caused by the fact that processing is concentrated near the contact point between the tip of the copper material and the die in the initial stages of processing, and that in such regions, the copper material and the forming hole of the die adhere to each other, thereby hindering smooth material flow and resulting in the peak behavior described above. Furthermore, we discovered that by controlling the surface properties of the die, we can reduce the concentration of processing at the tip of the copper material and create an environment that is less prone to adhesion, thereby reducing the maximum load and improving processing accuracy. Furthermore, we found that by adjusting the surface properties of the die used in extrusion processing to control the friction conditions between the die and the workpiece, the maximum processing load can be reduced, and by optimizing the friction conditions, smooth plastic flow can be promoted, thereby improving processing accuracy.

[0012] The present invention has been made based on the above-mentioned findings, and the method for manufacturing a copper extruded material according to Embodiment 1 of the present invention is a method for manufacturing a copper extruded material made of copper or a copper alloy, in which, at room temperature, a copper material made of copper or a copper alloy is inserted into the container portion of a die, and a compressive force is applied from one end of the copper material to cause part or all of the copper material to pass through a forming hole formed such that the cross-sectional area of ​​the die is reduced, characterized in that the arithmetic mean roughness Ra of the inner circumferential surface of the die through which the copper material passes is in the range of 0.03 μm or more and 0.25 μm or less.

[0013] In the method for manufacturing copper extruded material according to Embodiment 1 of the present invention, the arithmetic mean roughness Ra of the inner circumferential surface of the die through which the copper material passes is set to be in the range of 0.03 μm or more and 0.25 μm or less. As a result, the friction conditions between the die and the workpiece are appropriate, and the maximum processing load can be sufficiently reduced even when extrusion is performed at room temperature, promoting smooth plastic flow. Therefore, even if the workpiece is a copper material made of copper or a copper alloy which has a higher yield strength than other metals, processing accuracy is improved and stable extrusion can be performed.

[0014] The method for manufacturing a copper extruded material according to Embodiment 2 of the present invention is characterized in that, in the method for manufacturing a copper extruded material according to Embodiment 1 of the present invention, the extrusion ratio is 2.0 or more, and at least two basic dimensions of the copper extruded material after extrusion processing are 5 mm or less. According to the method for manufacturing copper extruded material of embodiment 2 of the present invention, at least two basic dimensions of the copper extruded material after extrusion are 5 mm or less, resulting in micro-meso-scale processing, and it becomes possible to efficiently manufacture a component having a micro-meso-scale structure by extrusion processing.

[0015] The method for manufacturing a copper extruded material according to aspect 3 of the present invention is characterized in that, in the method for manufacturing a copper extruded material according to aspect 1 or aspect 2 of the present invention, DLC treatment is applied to the inner circumferential surface of the die. According to the method for manufacturing copper extruded material of embodiment 3 of the present invention, since DLC treatment is applied to the inner circumferential surface of the die, adhesion between the die and the workpiece in the initial stages of processing can be sufficiently suppressed, material flow can be further smoothed, and the life of the mold can be improved.

[0016] The method for manufacturing a copper extruded material according to aspect 4 of the present invention is characterized in that, in the method for manufacturing a copper extruded material according to any one of aspects 1 to 3 of the present invention, the inclination angle of the molding hole is 60° or less. According to the method for manufacturing copper extruded material of embodiment 4 of the present invention, since the inclination angle of the molding hole is 60° or less, the increase in processing load can be further suppressed, processing accuracy can be further improved, and extrusion processing can be performed more stably.

Advantages of the Invention

[0017] According to the present invention, even in the case of a copper material made of copper and copper alloy having a yield stress higher than other metals, it is possible to provide a method for manufacturing a copper extruded material capable of sufficiently reducing the processing load during extrusion processing, performing extrusion processing with high processing accuracy and stability.

Brief Description of the Drawings

[0018] [Figure 1] It is a graph showing the relationship between the processing distance and the processing load during the extrusion processing of the copper material. [Figure 2] It is a partial cross-sectional explanatory view of an extrusion processing apparatus provided with the die shown in FIG. 1. [Figure 3] It is an explanatory view showing an example of a die used in the method for manufacturing a copper extruded material according to an embodiment of the present invention. [Figure 4] It is a schematic explanatory view of a small press apparatus in which an extrusion processing test was carried out in the examples. [Figure 5] It is an explanatory view of the processing form of the extrusion processing test carried out in the examples. [Figure 6] It is a graph showing the relationship between the arithmetic mean roughness Ra of the inner peripheral surface of the die and the maximum load during extrusion processing in the examples.

Modes for Carrying Out the Invention

[0019] Hereinafter, a method for manufacturing a copper extruded material according to an embodiment of the present invention will be described. Hereinafter, based on the accompanying drawings, an example of a method for manufacturing a copper extruded material according to an embodiment of the present invention will be described in detail. In the drawings used in the following description, for the sake of clarity of the features, there are cases where the portions serving as features are shown enlarged for convenience.

[0020] First, an extrusion processing apparatus 10 for carrying out the method for manufacturing a copper extruded material according to the present embodiment will be described with reference to FIGS. 2 and 3. In the extrusion apparatus 10 for manufacturing the copper extruded material according to this embodiment, as shown in Figure 2, it includes a die 20 and a punch 30 that presses one end of the copper material (billet) 1 inserted into the die 20.

[0021] The die 20 comprises a container portion 21 into which the copper material (billet) 1 to be processed is inserted, a forming hole portion 22 formed with a reduced cross-sectional area, a front portion 23 that accommodates the region of the copper material (billet) 1 that has passed through the forming hole portion 22 and been extruded, and a bearing portion 24 disposed between the forming hole portion 22 and the front portion 23.

[0022] In the case of copper material (billet) 1, which is made of copper or a copper alloy, the extrusion load during extrusion is higher compared to other metals such as aluminum, which can lead to a decrease in processing accuracy and premature deterioration of the processing jig. In particular, in micro- and mesoscale extrusion, the specific surface area is large, so the friction conditions between the copper material (billet) 1 and the die 20 have a significant impact on the processing results.

[0023] Therefore, in the initial stages of copper and copper alloy extrusion, we investigated friction conditions that would mitigate the concentration of processing at the tip of the copper material (billet) 1 and prevent adhesion. The problem of high extrusion load during extrusion is due to a high peak in the extrusion load at the beginning of the process. This peak behavior is caused by work hardening at the tip of the copper material (billet) 1 and adhesion with the die 20. In other words, to reduce the maximum load, it is necessary to optimize the friction conditions between the die 20 and the copper material (billet) 1. Therefore, in this embodiment, the friction conditions are optimized by controlling the surface properties of the die 20.

[0024] In this embodiment of the method for manufacturing copper extruded material, the arithmetic mean roughness Ra of the inner surface of the die 20 through which the copper material (billet) 1 passes is set to a range of 0.03 μm or more and 0.25 μm or less. By setting the surface arithmetic mean roughness Ra of the die 20 to 0.25 μm or less, the processing load during extrusion is reduced, and smooth material flow within the die 20 is promoted, improving processing accuracy. In addition, it becomes possible to suppress the deterioration of the processing jig. On the other hand, it is industrially difficult to make the arithmetic mean roughness Ra of the inner surface through which the copper material (billet) 1 of the die 20 passes less than 0.03 μm.

[0025] Here, the lower limit of the arithmetic mean roughness Ra of the inner surface through which the copper material (billet) 1 of the die 20 passes is preferably 0.03 μm or more, and more preferably 0.05 μm or more. On the other hand, the upper limit of the arithmetic mean roughness Ra of the inner surface through which the copper material (billet) 1 of the die 20 passes is preferably 0.25 μm or less, and more preferably 0.20 μm or less. Furthermore, the arithmetic mean roughness Ra of the inner surface through which the copper material (billet) 1 of the die 20 passes can be adjusted by electrical discharge machining and manual polishing.

[0026] Furthermore, in this embodiment, the inclination angle θ of the molding hole portion 22 of the die 20. D It is preferable that the angle is 60° or less. Inclination angle θ of the molded hole 22 D By setting the angle to 60° or less, it becomes possible to further reduce the processing load during extrusion. The inclination angle θ of the molded hole portion 22 D It is more preferable that the angle is 50° or less, and even more preferable that it is 45° or less. On the other hand, the inclination angle θ of the molded hole portion 22 D There is no particular lower limit, but to prevent the length of the molded hole 22 from becoming unnecessarily long, it is preferably 15° or more, and more preferably 20° or more.

[0027] Furthermore, in this embodiment, it is preferable that the inner circumferential surface of the die 20 through which the copper material (billet) 1 passes is treated with DLC. By forming a DLC (diamond-like carbon) film on the inner circumferential surface of the die 20 through which the copper material (billet) 1 passes, and by setting the arithmetic mean roughness Ra of the inner circumferential surface of the die 20 through which the copper material (billet) 1 passes within the range of 0.03 μm to 0.25 μm, adhesion between the die and the workpiece in the initial stages of processing can be further suppressed, and material flow can be made even smoother. Furthermore, there are no particular restrictions on the specific means of the DLC (diamond-like carbon) treatment used to deposit a DLC film on the inner circumferential surface of the die 20 through which the copper material (billet) 1 passes, and existing technologies can be applied as appropriate. In this embodiment, hydrogen-free DLC treatment is performed.

[0028] Furthermore, in this embodiment, there are no particular restrictions on the material of the die 20, and low-carbon steel, stainless steel, alloy tool steel, etc., can be used. Furthermore, as the copper material (billet) 1, for example, an ingot obtained by casting molten metal, or an ingot that has been subjected to splitting, machining, heat treatment, etc. as needed, can be used.

[0029] In this embodiment of the method for manufacturing copper extruded material, as shown in Figure 2, a copper material (billet) 1 made of copper or a copper alloy is inserted into the container portion 21 of a die 20, and a compressive force is applied from one end of the copper material (billet) 1 by a punch 30, causing part or all of the copper material (billet) 1 to pass through the forming hole portion 22 of the die 20, thereby performing an extrusion process on the copper material (billet) 1. In this embodiment, the method for manufacturing copper extruded material is to perform extrusion processing at room temperature (so-called cold extrusion processing).

[0030] Furthermore, in this embodiment, it is preferable that the extrusion ratio is 2.0 or higher, and that at least two basic dimensions of the copper extruded material after extrusion are 5 mm or less. Here, the two basic dimensions of a copper extruded material are, for example, the length of the two intersecting sides if the cross-section of the copper extruded material is rectangular, the diameter if the cross-section of the copper extruded material is circular, and the diameter of the circumscribed circle if the cross-section of the copper extruded material is any other shape.

[0031] In this embodiment of the method for manufacturing copper extruded material, the arithmetic mean roughness Ra of the inner circumferential surface through which the copper material (billet) 1 passes through the die 20 is set to be in the range of 0.03 μm to 0.25 μm. As a result, the friction conditions between the die 20 and the copper material (billet) 1 are appropriate, and the maximum processing load can be sufficiently reduced even when extruding at room temperature, thereby promoting smooth plastic flow. Therefore, even when using a copper material (billet) 1 made of copper or a copper alloy, which has a higher yield strength than other metals, processing accuracy is improved and stable extrusion processing becomes possible.

[0032] In the copper extruded material manufacturing method of this embodiment, if the inner circumferential surface of the die 20 through which the copper material (billet) 1 passes is treated with DLC, adhesion between the die 20 and the copper material (billet) 1 in the initial stages of processing can be sufficiently suppressed, and by facilitating material flow, the life of the die can be improved.

[0033] In the copper extruded material manufacturing method of this embodiment, the inclination angle θ of the molding hole 22 of the die 20 D When the angle is 60° or less, the increase in processing load during extrusion can be further suppressed. Therefore, processing accuracy is further improved, and extrusion can be performed more stably.

[0034] In the method for manufacturing copper extruded material according to this embodiment, when the extrusion ratio is 2.0 or higher and at least two basic dimensions of the copper extruded material after extrusion are 5 mm or less, it is possible to efficiently manufacture components with a micro-mesoscale structure by extrusion.

[0035] Although the method for manufacturing copper extruded material, which is an embodiment of the present invention, has been described above, the present invention is not limited thereto and can be modified as appropriate without departing from the technical spirit of the invention. For example, although this embodiment was described using the extrusion apparatus shown in Figure 2, it is not limited to this, and an extrusion apparatus of other structures may be used. [Examples]

[0036] The results of the verification experiments conducted to confirm the effects of the present invention are described below.

[0037] (Dice) A die with the shape shown in Figure 3 was manufactured by machining using JIS-SKD11. The inner diameter of the container section was 1.71 mm, the inner diameter of the bearing section was 1.09 mm, the inner diameter of the front section was 3.00 mm, and the inclination angle of the forming hole section was θ. D The angle was set to 30°. Furthermore, by combining electrical discharge machining and manual polishing, the arithmetic mean roughness Ra of the inner surface through which the copper material passes the die was adjusted to the value shown in Table 1. Furthermore, as shown in Table 1, a DLC film was deposited on the inner surface of some of the dies by hydrogen-free DLC treatment.

[0038] Here, the arithmetic mean roughness Ra of the inner surface through which the copper material of the die passes was measured as follows. Using a Hitachi High-Tech Science Corporation scanning white light interference microscope (R5500HML-A150-AC), the surface shape of the front portion of the die was measured non-contact in three dimensions (plane) in accordance with ISO 25178. Then, 30 line roughness measurements were taken at approximately 35 μm intervals in a direction parallel to the extrusion direction, which is important during extrusion. The arithmetic mean roughness Ra was obtained by averaging these measurements.

[0039] (Billet) The copper material (billet) to be processed was prepared as follows. A sheet of pure copper (equivalent to C1020) with a homogenized structure was prepared by rolling and heat treatment, and a cylindrical billet made of pure copper with a diameter of 1.7 mm and a length of 6.0 mm was manufactured by machining.

[0040] (Extrusion test) The die prepared as described above was set in the small press device 50 shown in Figure 4, and an extrusion test was conducted. As shown in Figure 5, the extruded material was designed to accommodate the complex shapes required for micro-extrusion. By setting the punch tip diameter to 1.47 mm, which is smaller than the die container diameter, a front-to-back extrusion process was adopted, allowing the front and rear of the billet to be processed simultaneously.

[0041] Here, the small press device 50 shown in Figure 4 comprises a processing section 51 where a die 20 and a punch 30 are arranged, a ball screw 52 and a servo motor 53 for moving the punch 30 up and down, and a load cell 54 for measuring the extrusion load. This small press device 50 has a maximum allowable load of 3.0 kN. In order to perform micro-extrusion processing accurately and safely, it is desirable that the maximum processing load be 75% or less of the maximum allowable load of the press machine. Therefore, in this embodiment, it is preferable that the maximum processing load during extrusion is 2.25 kN or less.

[0042] Then, an extrusion test was conducted under the following conditions. Extrusion temperature: Room temperature (25°C) Extrusion ratio: 2.5 Maximum stroke displacement: 2.0 mm Extrusion speed: 0.10 mm / s Lubricant kinematic viscosity: 429 mm 2 / s

[0043] The extrusion tests described above were conducted, and the maximum processing load during extrusion was measured. The evaluation results are shown in Table 1. Figure 6 shows the relationship between the arithmetic mean roughness Ra of the inner surface through which the copper material passes in the die and the maximum processing load during extrusion.

[0044] Furthermore, the estimated lifespan of the molds (dies and punches) was evaluated based on the measured maximum processing load. Based on the extrusion load (2.25kN) measured in the experiment, the analysis conditions were determined and a simulation (analysis software: deform) was performed, resulting in a maximum surface pressure of 800MPa on the mold. Looking at the fatigue life (SN curve) of SKD11 (alloy tool steel for cold work dies), which is a common material for molds and was also used in this test, it is expected that the fatigue life at a surface pressure of 800MPa will be 100,000 shots. Generally, in industrial cold plastic working, a mold life of several hundred thousand shots is required, so a life of 100,000 shots or more was evaluated as "○" and less than 100,000 shots as "×". The evaluation results are shown in Table 1.

[0045] [Table 1]

[0046] As shown in Table 1 and Figure 6, the maximum processing load during extrusion is proportional to the arithmetic mean roughness Ra of the inner surface through which the copper material passes in the die. In this case, when the arithmetic mean roughness Ra of the inner surface through which the copper material of the die passes was between 0.03 μm and 0.25 μm, the maximum processing load was 2.25 kN or less. Furthermore, when comparing die molds with and without a DLC coating, where the arithmetic mean roughness Ra of the inner circumferential surface through which the copper material passes is similar, it was confirmed that the mold life is further improved when the DLC coating is formed.

[0047] Furthermore, in a comparative example where the arithmetic mean roughness Ra of the inner surface through which the copper material of the die passes was 0.33 μm, the estimated die life from the maximum processing load was 40,000 shots, resulting in a "×" rating. On the other hand, in Example 1-3 of the present invention, where the arithmetic mean roughness Ra of the inner circumferential surface through which the copper material of the die passes is 0.03 μm or more and 0.25 μm or less, the mold life estimated from the maximum processing load exceeded 100,000 shots, and the evaluation was "○".

[0048] Based on the results of the above verification tests, it was confirmed that, according to the present invention, even when the workpiece is a copper material consisting of copper and copper alloys, which have a higher yield stress than other metals, the processing load during extrusion can be sufficiently reduced, and a method for manufacturing copper extruded materials that enables high processing accuracy and stable extrusion can be provided. [Explanation of Symbols]

[0049] 1. Billet (copper material) 10 Extrusion processing apparatus 20 dice 21 Container Section 22 Molding hole 30 punches

Claims

1. A method for producing a copper extruded material, comprising inserting a copper material made of copper or a copper alloy into the container portion of a die at room temperature, applying a compressive force from one end of the copper material to pass part or all of the copper material through a forming hole formed such that the cross-sectional area of ​​the die is reduced, thereby obtaining a copper extruded material made of copper or a copper alloy, A method for manufacturing a copper extruded material, characterized in that the arithmetic mean roughness Ra of the inner surface of the die through which the copper material passes is in the range of 0.03 μm or more and 0.25 μm or less.

2. The method for manufacturing a copper extruded material according to claim 1, characterized in that the extrusion ratio is 2.0 or more, and at least two basic dimensions of the copper extruded material after extrusion processing are 5 mm or less.

3. The method for manufacturing a copper extruded material according to claim 1 or 2, characterized in that the inner surface of the die is subjected to DLC treatment.

4. The method for manufacturing a copper extruded material according to claim 1 or 2, characterized in that the inclination angle of the molding hole is 60° or less.

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