Method for manufacturing cold forged products

Abstract

The present invention provides a method for manufacturing cold forged products that reduces the number of lubrication steps, thereby shortening processing time, saving energy, and reducing environmental impact. [Solution] The method for manufacturing a cold forged product includes step A of preparing a workpiece, step B of applying a lubrication treatment to the workpiece using a one-component lubricant, and step C of performing cold forging on the workpiece after step B, and further includes step D of applying a surface treatment to the workpiece by laser processing, cutting or rolling before step B.

Description

Technical Field

[0001] The present invention relates to a method for producing a cold forged product. Background Art

[0002] Cold forging is known as one of the forming methods for various parts. Cold forging is a method of forming by applying pressure to a metal material with a die (tool) at room temperature to deform the material, and has many advantages. In order to reduce friction during cold forging to lower the forming load, and to prevent metal-to-metal contact and seizure to the die, a workpiece is subjected to a lubrication treatment prior to cold forging. The lubrication treatment forms a lubricating coating on the surface of the workpiece.

[0003] Patent Document 1 discloses that a so-called bonderite treatment is applied to a workpiece as a lubrication treatment before cold forging. A lubricating coating formed by the bonderite treatment is excellent in lubricity and conformability. Prior Art Documents Patent Documents

[0004] Patent Document 1 Japanese Patent Laid-Open No. 5-7973 Summary of the Invention Problems to be Solved by the Invention

[0005] However, since the bonderite treatment forms a chemical conversion coating as the lubricating coating, it requires many processing steps and a long processing time. Therefore, it is necessary to adopt a batch system for production, which results in an increase in the size of equipment. It also increases energy consumption. Furthermore, it generates a large amount of wastewater and waste, resulting in a large environmental load.

[0006] Embodiments of the present invention have been made in view of the above-mentioned problems, and their purpose is to provide a method for manufacturing cold forged products that can reduce the number of lubrication steps, thereby shortening the processing time and saving energy, as well as reducing the environmental burden. [Means for solving the problem]

[0007] This specification discloses a method for manufacturing cold forged products as described in the following sections.

[0008] [Item 1] Process A involves preparing the workpiece, Step B involves applying a lubrication treatment to the workpiece using a one-component lubricant, After step B, step C is performed to cold forge the workpiece, A method for manufacturing cold forged products, which includes: A method for manufacturing a cold forged product, further comprising step D, which involves performing surface treatment on the workpiece by laser processing, cutting, or rolling, prior to step B.

[0009] The method for manufacturing cold forged products according to an embodiment of the present invention includes a step A ("preparation step") for preparing a workpiece, a step B ("lubrication step") for applying a lubrication treatment to the workpiece, and a step C ("forging step") for performing cold forging on the workpiece after step B. In the manufacturing method according to an embodiment of the present invention, a one-component lubricant is used in the lubrication step (i.e., a "one-component lubrication treatment" is performed), so the number of steps required for treatment can be reduced and the treatment time can be shortened compared to the case where Bonder treatment is applied as the lubrication treatment. Therefore, an in-line system can be adopted for production, and the equipment can be made compact. Energy saving can also be achieved. Furthermore, wastewater and waste can be reduced, thereby reducing the environmental burden. While lubricating films formed by one-component lubrication treatment may have less adhesion compared to lubricating films formed by Bonder treatment, the manufacturing method according to the embodiment of the present invention further includes a step D ("surface treatment step") in which a surface treatment is applied to the workpiece before the lubrication treatment step. Therefore, the adhesion of the lubricating film can be improved by the uneven shape (surface shape including multiple recesses) formed by the surface treatment. Furthermore, in the manufacturing method according to the embodiment of the present invention, the surface treatment is applied by laser processing, cutting, or rolling, making it easier to form recesses as designed, and thus highly effective in improving the adhesion of the lubricating film.

[0010] [Item 2] The method for manufacturing a cold forged product as described in item 1, wherein in step D, the surface treatment is performed by laser processing.

[0011] The surface preparation process (process D) can be suitably performed by laser processing. Laser processing is advantageous because it is a non-contact process and allows for easy modification of the design of uneven surfaces. Furthermore, since laser processing does not cause tool wear, it is advantageous because it allows for processing with the same quality (e.g., the same shape accuracy) over a long period of time.

[0012] [Item 3] The method for manufacturing a cold forged product as described in item 1, wherein in step D, the surface treatment is performed by cutting.

[0013] The surface preparation process (process D) can also be suitably performed by cutting. Cutting is advantageous in that it offers high processing accuracy and a high degree of freedom in shaping the recesses.

[0014] [Item 4] The method for manufacturing a cold forged product as described in item 1, wherein in step D, the surface treatment is performed by rolling.

[0015] The surface preparation process (process D) can also be suitably performed by rolling. Rolling is advantageous in that it offers a high processing speed and a high degree of freedom in shaping the recesses.

[0016] [Item 5] The method for manufacturing a cold forged product according to any one of items 1 to 4, wherein the surface treatment in step D is performed such that the ratio h / d of the depth h to the diameter d of a plurality of recesses formed on the surface of the workpiece is 0.09 or more and 0.2 or less.

[0017] The surface treatment creates multiple recesses on the surface of the workpiece. From the viewpoint of sufficiently improving the adhesion of the lubricating film, it is preferable that the surface treatment is performed such that the ratio of the depth h to the diameter d of the recesses h / d is 0.09 or more and 0.2 or less.

[0018] [Item 6] The method for manufacturing a cold forged product according to any one of items 1 to 5, wherein the surface treatment in step D is performed so that the minimum autocorrelation length Sal on the surface of the workpiece is 29 μm or more.

[0019] From the viewpoint of sufficiently improving the adhesion of the lubricating film, it is preferable that the surface treatment be carried out so that the minimum autocorrelation length Sal of the workpiece surface is 29 μm or more.

[0020] [Item 7] The method for producing a cold forged product according to any one of items 1 to 6, wherein the surface treatment in the step D is performed such that a loaded area ratio Smr2 of a surface of the workpiece is 86% or less.

[0021] From the viewpoint of sufficiently improving the adhesion of the lubricating coating, the surface treatment is preferably performed such that the loaded area ratio Smr2 of the surface of the workpiece is 86% or less.

[0022] [Item 8] The method for producing a cold forged product according to any one of items 1 to 7, wherein the surface treatment in the step D is performed such that an aspect ratio Str of the surface texture of the workpiece is 0.5 or more.

[0023] From the viewpoint of sufficiently improving the adhesion of the lubricating coating, the surface treatment is preferably performed such that the aspect ratio Str of the surface texture of the workpiece is 0.5 or more.

[0024] [Item 9] The method for producing a cold forged product according to any one of items 1 to 8, wherein the surface treatment in the step D is performed such that a kurtosis Sku of the surface of the workpiece is 3.6 or less.

[0025] From the viewpoint of sufficiently improving the adhesion of the lubricating coating, the surface treatment is preferably performed such that the kurtosis Sku of the surface of the workpiece is 3.6 or less.

[0026] [Item 10] The method for producing a cold forged product according to any one of items 1 to 9, wherein the surface treatment in the step D is performed such that a plurality of recesses formed on the surface of the workpiece are arranged in a staggered pattern.

[0027] A plurality of recesses are formed on the surface of the workpiece by the surface treatment. From the viewpoint of forming the plurality of recesses at a high density, the surface treatment is preferably performed such that the plurality of recesses are arranged in a staggered pattern.

[0028] [Item 11] The method for manufacturing a cold forged product according to any one of items 1 to 10, wherein the surface treatment in step D is performed such that the patterns of the plurality of recesses formed on the surface of the workpiece define a plurality of regions that are different from each other.

[0029] Since the degree of deformation in the forging process (process C) may vary depending on the part of the workpiece, the required level of adhesion for the lubricating film may also vary depending on the part of the workpiece. For this reason, the surface treatment may be performed such that multiple regions with different patterns of recesses are defined on the surface of the workpiece. [Effects of the Invention]

[0030] According to embodiments of the present invention, it is possible to provide a method for manufacturing cold forged products that can reduce the number of lubrication steps, thereby shortening processing time, saving energy, and reducing environmental impact. [Brief explanation of the drawing]

[0031] [Figure 1] This is a flowchart showing a method for manufacturing cold forged products according to an embodiment of the present invention. [Figure 2A] This is a diagram illustrating the preparation process S1. [Figure 2B] This is a diagram illustrating the surface preparation process S2. [Figure 2C] This is a magnified plan view showing the vicinity of the surface of the workpiece 10 after the surface preparation process S2 has been performed. [Figure 2D] This is a magnified cross-sectional view showing the vicinity of the surface of the workpiece 10 after the surface preparation process S2 has been performed. [Figure 2E] This is a diagram illustrating the lubrication process S3. [Figure 2F] This is a diagram illustrating the forging process S4. [Figure 2G] This is a diagram illustrating the forging process S4. [Figure 2H] This figure shows the obtained cold-forged product 20. [Figure 3A] This is a plan view showing the cold-forged product 20A of the embodiment. [Figure 3B] This is a perspective view showing the cold-forged product 20A of the example. [Figure 4] This graph shows the results of elemental analysis performed by EDS before and after cold forging for the comparative example. [Figure 5] This graph shows the results of elemental analysis performed by EDS before and after cold forging in the example. [Figure 6A] This graph shows the relationship between the ratio of the depth h to the diameter d of recess 1 (h / d) and the amount of base material detected at the tooth root. [Figure 6B] This graph shows the relationship between the ratio of the depth h to the diameter d of recess 1 (h / d) and the amount of base material detected on the tooth surface. [Figure 7] This graph shows the relationship between the amount of base material detected at the tooth root and the minimum autocorrelation length (Sal). [Figure 8] This graph shows the relationship between the amount of base material detected on the tooth surface and the minimum autocorrelation length (Sal). [Figure 9] This graph shows the relationship between the amount of base material detected at the tooth root and the load area ratio (Smr2). [Figure 10] This graph shows the relationship between the amount of base material detected on the tooth surface and the load area ratio Smr2. [Figure 11] This graph shows the relationship between the amount of base material detected at the tooth root and the aspect ratio Str. [Figure 12] This graph shows the relationship between the amount of base material detected at the tooth root and crustosis Sku. [Figure 13] This is a plan view showing another example of the arrangement of recesses 1. [Figure 14] This is a plan view showing an example where the surface of the workpiece 10 has a first region R1 and a second region R2 in which the patterns of multiple recesses 1 are different from each other. [Modes for carrying out the invention]

[0032] Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the following embodiments.

[0033] The method for manufacturing cold forged products according to embodiments of the present invention will be explained with reference to Figures 1 and 2A to 2H. Figure 1 is a flowchart of the manufacturing method according to embodiments of the present invention. Figures 2A to 2H are diagrams illustrating each step of the manufacturing method according to embodiments of the present invention.

[0034] First, a workpiece 10 is prepared as shown in Figure 2A (preparation step S1). The material of the workpiece 10 is, for example, iron (Fe), but is not limited to this, and can be various metallic materials such as aluminum (Al) or titanium (Ti). The metallic material of the workpiece 10 may be a pure metal or an alloy. An example of an alloy is steel. Steel may be, for example, alloy steel such as SCM material or carbon steel such as S45C.

[0035] Furthermore, although the workpiece 10 is approximately cylindrical in the example shown in Figure 2A, the shape of the workpiece 10 is not limited to this and can be of various shapes. Moreover, the size of the workpiece 10 is not particularly limited. The shape and size of the workpiece 10 are appropriately determined based on the shape and size of the final product, the cold forged product, and the shape and size of the mold (tool) used in the forging process described later.

[0036] Next, as shown in Figure 2B, the workpiece 10 is subjected to surface treatment (surface treatment step S2). This surface treatment is performed by laser processing, cutting, or rolling. Figure 2B shows an example of laser processing. In the case of laser processing, laser light L is irradiated onto the surface of the workpiece 10. Figures 2C and 2D are a magnified plan view and a cross-sectional view of the vicinity of the surface of the workpiece 10 after the surface treatment step S2 has been performed. As shown in Figures 2C and 2D, the surface treatment creates a fine uneven surface shape (a surface shape including multiple recesses 1) on the surface of the workpiece 10.

[0037] Figures 2C and 2D illustrate an example of a recess 1 with a planar shape that is approximately circular. The diameter d, depth h, and pitch p of the recess 1 are not particularly limited and can be set as appropriate. For example, the diameter d of the recess 1 is 30 μm or more and 150 μm or less. For example, the depth h of the recess 1 is 2.7 μm or more and 30 μm or less. For example, the pitch p of the recess 1 is 30 μm or more and 150 μm or less. Note that the planar shape of the recess 1 is not limited to the approximately circular shape illustrated, but may be approximately elliptical or the like.

[0038] For laser processing, for example, a pulsed laser is used. The laser light L may be ultraviolet laser light or infrared laser light. The irradiation conditions of the laser light L (laser output, pulse width, scan speed, and irradiation energy density, etc.) can be appropriately set according to the material of the workpiece 10 and the size of the recess 1 to be formed (diameter d, depth h), etc.

[0039] Next, as shown in Figure 2E, the workpiece 10 is subjected to a lubrication treatment using a one-component lubricant (i.e., "one-component lubrication treatment") (lubrication treatment step S3). The one-component lubrication treatment forms a lubricating film 2 on the surface of the workpiece 10. The one-component lubrication treatment can be performed by applying the one-component lubricant to the surface of the workpiece 10 and then drying it. Various known one-component lubricants can be used as the one-component lubricant. The one-component lubricant may be an aqueous solution containing a lubricating component that exhibits lubrication performance and a binder component that fixes the lubricating component to the surface of the workpiece 10. The lubricating component may be, for example, a metal soap, graphite, molybdenum disulfide, etc. The binder component may be, for example, a water-soluble inorganic salt. The amount of lubricating film 2 attached (film thickness) is not particularly limited, but for example, 3 g / m 2 More than 10g / m 2 The following applies:

[0040] Subsequently, as shown sequentially in Figures 2F and 2G, cold forging is performed on the workpiece 10 (forging process S4). In the illustrated example, cold forging is performed by plastically deforming the workpiece 10 at room temperature using an upper die 3 and a lower die 4 as tools (dies).

[0041] In this way, a cold-forged product 20 as shown in Figure 2H is obtained. The lubricating film 2 present on the surface of the cold-forged product 20 can be removed by subsequent washing with water or the like. Furthermore, the obtained cold-forged product 20 may be subjected to further machining or other processes as needed.

[0042] In the manufacturing method according to the embodiment of the present invention, a one-component lubricant is used in the lubrication treatment step S3 (i.e., a "one-component lubrication treatment" is performed), so the number of steps required for treatment can be reduced and the treatment time can be shortened compared to the case where Bonder treatment is performed as the lubrication treatment. As a result, an in-line system can be adopted for production, and the equipment can be made compact. Energy saving can also be achieved. Furthermore, wastewater and waste can be reduced, thereby reducing the environmental burden. While there is a concern that the lubricating film formed by the one-component lubrication treatment may have insufficient adhesion compared to the lubricating film formed by Bonder treatment, the manufacturing method according to the embodiment of the present invention further includes a step of performing a surface treatment on the workpiece 10 before the lubrication treatment step S3 (surface treatment step S2), so the adhesion of the lubricating film 2 can be improved by the uneven shape (surface shape including multiple recesses 1) formed by the surface treatment. Furthermore, in the manufacturing method according to the embodiment of the present invention, the surface treatment is performed by laser processing, cutting, or rolling, so the recesses 1 can be easily formed as designed, and the effect of improving the adhesion of the lubricating film 2 is high.

[0043] The surface preparation in the surface preparation step S2 can be suitably performed by laser processing. Laser processing is advantageous because it is a non-contact process and allows for easy modification of the design of the uneven shape. Furthermore, since laser processing does not cause tool wear, it is advantageous because it allows for processing with the same quality (e.g., the same shape accuracy) over a long period of time.

[0044] The surface treatment in the surface treatment step S2 can also be suitably performed by cutting. Cutting is advantageous in that it offers high processing accuracy and a high degree of freedom in the shape of the recess 1.

[0045] The surface treatment in the surface treatment step S2 can also be suitably performed by rolling. Rolling is advantageous in that it has a high processing speed and a high degree of freedom in the shape of the recess 1.

[0046] [Verification results of the effect of improving the adhesion of the lubricating coating] Here, we will explain the results of actually prototyping a cold-forged product 20 and verifying its effect on improving the adhesion of the lubricating film 2.

[0047] As an example, a cold-forged product 20A, shown in Figures 3A and 3B, was manufactured. For the manufacture of the cold-forged product 20A, a cylindrical iron workpiece 10 with a diameter of 25 mm and a length of 28 mm was used, and the surface treatment was performed by laser processing. The cold-forged product 20A shown in Figures 3A and 3B has a roughly cylindrical first part 21 and a roughly frustoconical second part 22. The first part 21 and the second part 22 are continuous. The first part 21 has a hole 23 that extends axially inward from its end face 21a (in Figure 3A, a portion of the first part 21 is cut out). The outer circumferential surface of the second part 22 has a plurality of slits 24 that extend axially. Hereinafter, the region 22a of the outer circumferential surface of the second part 22 corresponding to the bottom of the slits 24 will be referred to as the "tooth root," and the region 22b corresponding to the side of the slits 24 will be referred to as the "tooth surface."

[0048] Laser processing was performed by irradiating the workpiece 10 with infrared laser light under the following conditions. The recess 1 formed by laser processing was approximately circular in shape when viewed from above, and the diameter d and depth h of the recess 1 were approximately 100 μm and approximately 10 μm, respectively. Laser oscillator: Trumpf TruPulse2020nano Wavelength: 1064nm Scanner: ARGES Rhino21 ARGnet Focusing spot size: φ610μm Pattern pitch: 100 μm (Pattern arrangement is a square grid) Rated peak output: 10kW Maximum pulse energy: 1.52 mJ

[0049] For the lubrication treatment, FL-E771A manufactured by Nippon Parkerizing Co., Ltd. was used as a one-component lubricant, with a film thickness (adhesion amount) of 8 g / m². 2 It was done in such a way.

[0050] As a comparative example, cold forged products were manufactured in the same manner as in the examples, except that the surface treatment was performed by shot blasting. The conditions for shot blasting were as follows. Projection material: Steel grid Size of projection material: Approximately 100 μm Projection pressure: 0.4 MPa

[0051] Elemental analysis by EDS (energy-dispersive X-ray spectroscopy) was performed on the comparative examples and examples before and after cold forging. EDS analysis was performed using an accessory of a scanning electron microscope (SEM: JEOL JSM-7001F), and analysis results were obtained for an observation area of ​​600 μm × 800 μm. After cold forging, analysis was performed at two locations: the tooth root and the tooth surface (areas 22a and 22b in Figures 3A and 3B).

[0052] The analysis results for the comparative example are shown in Figure 4, and the analysis results for the example are shown in Figure 5. In Figures 4 and 5, the elements that make up the lubricating film (denoted as a, b, c, d, e, f, g, h, and i respectively in the figures) are shown by the "Lubricating Film Components" bar, and the iron material of the workpiece is shown by the "Base Material (Fe)" bar.

[0053] As can be seen from Figures 4 and 5, in both the comparative example and the example, the proportion of lubricating film components decreases after cold forging compared to before cold forging. However, as can be seen from comparing Figures 4 and 5, the degree of decrease in the proportion of lubricating film components is smaller in the example compared to the comparative example. This is thought to be because the adhesion of lubricating film 2 improved.

[0054] Thus, it was confirmed that the manufacturing method according to the embodiment of the present invention improves the adhesion of the lubricating film 2.

[0055] [Examples of preferred embodiments] Examples of preferred embodiments of the manufacturing method according to embodiments of the present invention will be described.

[0056] From the viewpoint of sufficiently improving the adhesion of the lubricating film 2, it is preferable that the surface treatment be carried out in such a way that at least one of the following conditions [1] to [5] is satisfied. [1] The ratio of the depth h to the diameter d of recess 1, h / d, is 0.09 or more and 0.2 or less. [2] The minimum autocorrelation length Sal on the surface of workpiece 10 is 29 μm or more. [3] The surface load area ratio Smr2 of the workpiece 10 is 86% or less. [4] The aspect ratio Str of the surface texture of the workpiece 10 is 0.5 or greater. [5] The kurtosis Sku of the surface of workpiece 10 is 3.6 or less.

[0057] The following explains the results of our verification that the above-mentioned conditions [1] to [5] are preferable.

[0058] Multiple samples were manufactured in the same manner as in the example, with some changes to the laser processing conditions. For these samples, the surface roughness of workpiece 10 was measured after surface treatment and before cold forging, and ESD analysis was performed after cold forging. Then, correlation coefficients were calculated between the various parameters measured as surface roughness and the proportion of base material (iron) obtained by ESD analysis at the tooth root and tooth surface (hereinafter sometimes referred to as "base material detection amount"). The results of the correlation coefficient calculations are shown in Table 1.

[0059] [Table 1]

[0060] Table 1 shows that the correlation coefficients for minimum autocorrelation length (Sal), load area ratio (Smr2), aspect ratio (Str), and crustosis (Sku) are relatively large. Table 2 shows the measured values ​​and base material detection amounts for seven of the samples, samples #1 to #7.

[0061] [Table 2]

[0062] • About the ratio h / d Table 2 also shows the ratio h / d of the depth h to the diameter d of recess 1. Figure 6A shows the relationship between the ratio h / d and the amount of base material detected at the tooth root, and Figure 6B shows the relationship between the ratio h / d and the amount of base material detected at the tooth surface. As can be seen from Table 2, Figure 5 and Figure 6, in samples #2 and #3, the amount of base material detected at both the tooth root and the tooth surface is relatively small, and in sample #5, the amount of base material detected at the tooth root is relatively small. From these findings, it can be said that by performing surface treatment so that the ratio h / d is between 0.09 and 0.2, the adhesion of the lubricating film 2 can be sufficiently improved.

[0063] Regarding minimum autocorrelation length (Sal), load area ratio (Smr2), aspect ratio (Str), and crustosis (Sku): The minimum autocorrelation length Sal represents the horizontal distance in the direction in which the autocorrelation function decays most rapidly to a specific value. As shown in Table 1, there is a relatively large negative correlation between the minimum autocorrelation length Sal before cold forging and the amount of base material detected at the tooth root and tooth surface. This suggests that it is preferable to avoid abrupt changes on the surface of the workpiece 10 before cold forging.

[0064] The load area ratio Smr2 represents the load area ratio that separates the protruding valleys and the core in the load curve. As shown in Table 1, there is a relatively large positive correlation between the load area ratio Smr2 before cold forging and the amount of base material detected at the tooth root and tooth surface. This indicates that a larger volume of valleys is desirable in the load curve of the surface of the workpiece 10 before cold forging.

[0065] The aspect ratio Str is a numerical representation of the strength of the surface directionality. As shown in Table 1, there is a relatively large negative correlation between the aspect ratio Str before cold forging and the amount of base material detected at the tooth root. This indicates that it is preferable for the surface of the workpiece 10 to be isotropic before cold forging.

[0066] The kurtosis Sku represents the sharpness of the surface height distribution. As shown in Table 1, there is a relatively large positive correlation between the kurtosis Sku before cold forging and the amount of base material detected at the tooth root. This suggests that a flatter surface of the workpiece 10 before cold forging is preferable.

[0067] Based on scatter plots obtained from multivariate analysis of numerous parameters shown in Table 1 (parts of which are shown in Figures 7 to 12), preferred ranges for minimum autocorrelation length (Sal), loading area ratio (Smr2), aspect ratio (Str), and crustosis (Sku) were investigated. More specifically, when determining the ranges for these parameters that allow the amount of base material detected at the tooth root to be preferably 40% or less, these ranges were found to be 29 μm or more for minimum autocorrelation length (Sal), 86% or less for loading area ratio (Smr2), 0.5 or more for aspect ratio (Str), and 3.6 or less for crustosis (Sku).

[0068] In this way, by performing surface treatment in such a way as to satisfy at least one of the conditions [1] to [5] described above, the adhesion of the lubricating film 2 can be sufficiently improved.

[0069] Figure 2C shows an example in which multiple recesses 1 are arranged in a matrix (square grid), but the arrangement of recesses 1 is not limited to this example. Figure 13 shows another example of the arrangement of recesses 1. In the example shown in Figure 13, the positions of recesses 1 in the row direction (left-right direction in the figure) are offset between adjacent rows, and multiple recesses 1 are arranged in a staggered pattern. By adopting such a staggered arrangement, multiple recesses 1 can be formed at a higher density.

[0070] Furthermore, the surface treatment may be performed such that multiple regions are defined in which the patterns of the multiple recesses 1 differ from each other. Here, "multiple recesses 1 differ from each other" means that at least one of the size, shape, pitch, and arrangement of the recesses 1 differs between the multiple regions. Figure 14 shows an example of a surface treated in this manner. In the example shown in Figure 14, the surface of the workpiece 10 has a first region R1 and a second region R2 in which the patterns of the multiple recesses 1 differ from each other. The diameter d and pitch p of the recesses 1 formed in the second region R2 are smaller than the diameter d and pitch p of the recesses 1 formed in the first region R1.

[0071] Since the degree of deformation in the forging process S3 may vary depending on the part of the workpiece 10, the required level of adhesion for the lubricating film 2 may also vary depending on the part of the workpiece 10. For this reason, the surface treatment may be performed such that multiple regions with different patterns of multiple recesses 1 are defined.

[0072] As described above, the method for manufacturing a cold forged product 20 according to an embodiment of the present invention is a method for manufacturing a cold forged product 20 that includes a step A of preparing a workpiece 10, a step B of applying a lubrication treatment to the workpiece 10 using a one-component lubricant, and a step C of performing cold forging on the workpiece 10 after step B, further including a step D of applying a surface treatment to the workpiece 10 by laser processing, cutting or rolling before step B.

[0073] The method for manufacturing a cold-forged product 20 according to an embodiment of the present invention includes a step A ("preparation step S1") for preparing a workpiece 10, a step B ("lubrication step S3") for applying a lubrication treatment to the workpiece 10, and a step C ("forging step S4") for performing cold forging on the workpiece 10 after step B. In the manufacturing method according to the embodiment of the present invention, a one-component lubricant is used in the lubrication treatment step S3 (i.e., a "one-component lubrication treatment" is performed), so the number of steps required for treatment can be reduced and the treatment time can be shortened compared to the case where Bonder treatment is applied as the lubrication treatment. Therefore, an in-line system can be adopted for production, and the equipment can be made compact. Energy saving can also be achieved. Furthermore, wastewater and waste can be reduced, thereby reducing the environmental burden. While there are concerns about insufficient adhesion of the lubricating film 2 formed by a one-component lubrication treatment compared to a lubricating film formed by a Bonder treatment, the manufacturing method according to the embodiment of the present invention further includes a step D ("surface treatment step S2") in which a surface treatment is applied to the workpiece 10 before the lubrication treatment step S3. Therefore, the adhesion of the lubricating film 2 can be improved by the uneven shape (surface shape including multiple recesses 1) formed by the surface treatment. Furthermore, in the manufacturing method according to the embodiment of the present invention, the surface treatment is applied by laser processing, cutting, or rolling, making it easier to form the recesses 1 as designed, and thus highly effective in improving the adhesion of the lubricating film 2.

[0074] In one embodiment, the surface treatment in step D is performed by laser processing.

[0075] The surface treatment in the surface treatment process S2 (process D) can be suitably performed by laser processing. Laser processing is advantageous because it is a non-contact process and allows for easy modification of the design of the uneven shape. Furthermore, since laser processing does not cause tool wear, it is advantageous because it allows for processing with the same quality (e.g., the same shape accuracy) over a long period of time.

[0076] In one embodiment, the surface treatment in step D is performed by cutting.

[0077] The surface treatment in the surface treatment process S2 (process D) can also be suitably performed by cutting. Cutting is advantageous in that it offers high processing accuracy and a high degree of freedom in the shape of the recess 1.

[0078] In one embodiment, the surface treatment in step D is performed by rolling.

[0079] The surface treatment in the surface treatment process S2 (process D) can also be suitably performed by rolling. Rolling is advantageous in that it has a high processing speed and a high degree of freedom in the shape of the recess 1.

[0080] In one embodiment, the surface treatment in step D is performed such that the ratio h / d of the depth h to the diameter d of the plurality of recesses 1 formed on the surface of the workpiece 10 is 0.09 or more and 0.2 or less.

[0081] The surface treatment creates multiple recesses 1 on the surface of the workpiece 10. From the viewpoint of sufficiently improving the adhesion of the lubricating film 2, it is preferable that the surface treatment is performed such that the ratio of the depth h to the diameter d of the recesses 1, h / d, is 0.09 or more and 0.2 or less.

[0082] In one embodiment, the surface treatment in step D is performed such that the minimum autocorrelation length Sal on the surface of the workpiece 10 is 29 μm or more.

[0083] From the viewpoint of sufficiently improving the adhesion of the lubricating film 2, it is preferable that the surface treatment be performed such that the minimum autocorrelation length Sal of the surface of the workpiece 10 is 29 μm or more.

[0084] In one embodiment, the surface treatment in step D is performed such that the load area ratio Smr2 on the surface of the workpiece 10 is 86% or less.

[0085] From the viewpoint of sufficiently improving the adhesion of the lubricating film 2, it is preferable that the surface treatment be carried out so that the load area ratio Smr2 on the surface of the workpiece 10 becomes 86% or less.

[0086] In one embodiment, the surface treatment in step D is performed such that the aspect ratio Str of the surface texture of the workpiece 10 is 0.5 or greater.

[0087] From the viewpoint of sufficiently improving the adhesion of the lubricating film 2, it is preferable that the surface treatment be performed so that the aspect ratio Str of the surface properties of the workpiece 10 is 0.5 or more.

[0088] In one embodiment, the surface treatment in step D is performed such that the kurtosis Sku of the surface of the workpiece 10 becomes 3.6 or less.

[0089] From the viewpoint of sufficiently improving the adhesion of the lubricating film 2, it is preferable that the surface treatment be performed so that the kurtosis Sku of the surface of the workpiece 10 becomes 3.6 or less.

[0090] In one embodiment, the surface treatment in step D is performed such that a plurality of recesses 1 formed on the surface of the workpiece 10 are arranged in a staggered pattern.

[0091] The surface treatment creates multiple recesses 1 on the surface of the workpiece 10. From the viewpoint of forming multiple recesses 1 at high density, it is preferable that the surface treatment be performed so that the multiple recesses 1 are arranged in a staggered pattern.

[0092] In one embodiment, the surface treatment in step D is performed such that the patterns of the multiple recesses 1 formed on the surface of the workpiece 10 define multiple regions R1 and R2 that are different from each other.

[0093] Since the degree of deformation in forging process S4 (process C) may vary depending on the part of the workpiece 10, the required level of adhesion for the lubricating film 2 may also vary depending on the part of the workpiece 10. For this reason, the surface treatment may be performed such that multiple regions R1 and R2 are defined on the surface of the workpiece 10, each with a different pattern of recesses 1. [Industrial applicability]

[0094] According to embodiments of the present invention, a method for manufacturing cold forged products can be provided that reduces the number of lubrication steps, thereby shortening processing time, saving energy, and reducing environmental impact. The manufacturing method according to embodiments of the present invention can be suitably used for manufacturing various cold forged products. [Explanation of Symbols]

[0095] 1: Recess, 2: Lubricating film, 3: Upper die, 4: Lower die, 10: Workpiece, 20·20A: Cold forged product, 21: First part, 22: Second part, 22a: Tooth root, 22b: Tooth surface, 23: Hole, 24: Slit, R1: First area, R2: Second area

Claims

1. Process A involves preparing the workpiece, Step B involves applying a lubrication treatment to the workpiece using a one-component lubricant. After step B, step C is performed to cold forge the workpiece, A method for manufacturing cold forged products, which includes: A method for manufacturing a cold forged product, further comprising step D, which involves performing surface treatment on the workpiece by laser processing, cutting, or rolling, prior to step B.

2. The method for manufacturing a cold forged product according to claim 1, wherein in step D, the surface treatment is performed by laser processing.

3. The method for manufacturing a cold forged product according to claim 1, wherein in step D, the surface treatment is performed by cutting.

4. The method for manufacturing a cold forged product according to claim 1, wherein in step D, the surface treatment is performed by rolling.

5. The method for manufacturing a cold forged product according to any one of claims 1 to 4, wherein the surface treatment in step D is performed such that the ratio h / d of the depth h to the diameter d of a plurality of recesses formed on the surface of the workpiece is 0.09 or more and 0.2 or less.

6. The method for manufacturing a cold forged product according to any one of claims 1 to 4, wherein the surface treatment in step D is performed so that the minimum autocorrelation length Sal on the surface of the workpiece is 29 μm or more.

7. The method for manufacturing a cold forged product according to any one of claims 1 to 4, wherein the surface treatment in step D is performed such that the load area ratio Smr2 on the surface of the workpiece is 86% or less.

8. The method for manufacturing a cold forged product according to any one of claims 1 to 4, wherein the surface treatment in step D is performed so that the aspect ratio Str of the surface properties of the workpiece is 0.5 or more.

9. The method for manufacturing a cold forged product according to any one of claims 1 to 4, wherein the surface treatment in step D is performed so that the kurtosis Sku of the surface of the workpiece becomes 3.6 or less.

10. The method for manufacturing a cold forged product according to any one of claims 1 to 4, wherein the surface treatment in step D is performed such that a plurality of recesses formed on the surface of the workpiece are arranged in a staggered pattern.

11. The method for manufacturing a cold forged product according to any one of claims 1 to 4, wherein the surface treatment in step D is performed such that the patterns of the plurality of recesses formed on the surface of the workpiece define a plurality of regions that are different from each other.

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