Surface treatment film for press molding dies and press molding dies

Abstract

Provided is a DLC film that suppresses the occurrence of peeling and powdering from a metal plate to be press-molded, prevents the peeled material and powdering from adhering to the surface of a press-molding die, and improves the transportability and dischargeability of the peeled material from the surface of the press-molding die. [Solution] Mr1, which indicates the proportion of protruding peaks on the surface, is 5.6 to 13.6%, Rsk, which indicates the degree of surface distortion, is -7.0 to -3.5, and the correlation between Mr1 and Rsk satisfies 7.5≦Mr1-0.58×Rsk≦16.7. NCRX, which indicates the number of valleys in the surface motif shape, is 200 to 500, Mr2, which indicates the proportion of protruding valleys on the surface, is 81.9 to 88.5%, and Rvk, which indicates the depth of the protruding valleys on the surface, is 0.07 to 0.25 μm, and the correlation between Mr2 and Rvk satisfies 85.5≦Mr2-1.51×ln(Rvk)≦91.2.

Description

Technical Field

[0001] The present invention relates to a surface treatment film for a press molding die, and more particularly to a hard carbon film having a surface property capable of suppressing the generation of powdering and flaking due to the aggregation of powdering during the press molding of a soft material.

Background Art

[0002] In recent years, in the automotive industry, when reducing the weight of automobiles for improving fuel efficiency, multi-materialization using aluminum alloy materials instead of steel materials that have been conventionally widely used as automotive structural materials has attracted attention. This aluminum alloy material is lightweight but a soft material. In addition, in order to avoid the problem of rusting of iron due to deicing agents used in snowy areas, galvanized steel sheets having a rust prevention effect are also widely used.

[0003] In a molding die for press molding these aluminum alloy materials and galvanized steel sheets, in a die formed with a conventional hard film, the surface of the plate material to be pressed is scraped, and powdering scraped from the surface of the material to be pressed is generated. Flaking aggregated with this powdering adheres to the hard film of the die, causing problems such as damage to the hard film due to abrasive wear and a decrease in the accuracy of press products. In addition, there is a problem that the manufacturing cost increases due to the removal maintenance cost of the powdering / flaking adhering to the hard film and the rework cost required to achieve the accuracy of press products.

[0004] In order to solve such problems, a DLC (diamond-like carbon) film, which is a hard carbon film excellent in smoothness and anti-adhesion properties, has come to be used (Patent Documents 1 and 2). In Patent Documents 1 and 2, a method of preventing adhesion by improving the surface property of the hard carbon film, creating an oil pool, and holding lubricating oil therein is proposed. For example, in Patent Document 1, carbon flakes are incorporated in the DLC film and removed to form a concave shape on the film surface. In Patent Document 2, a concave shape is formed on the film surface by projecting the media of a blasting machine.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The technique described in Patent Document 1 forms a DLC film by plasma CVD using hydrocarbons as a raw material, and incorporates carbon flakes into the DLC film to form a concave shape. At this time, sputtering using solid carbon as a raw material is carried out to obtain carbon flakes, and there is a drawback that the equipment limitations are large. In addition, the production of unnecessary substances such as carbon flakes is required, and there is a problem that the manufacturing cost increases.

[0007] The technique described in Patent Document 2 forms dimples by injection processing on the surface of a hard carbon film. In this case, it is necessary to appropriately set many conditions such as the particle size, projection speed, projection pressure, and projection area of the projectile, and there are problems in terms of productivity. In addition, the dimple shapes obtained by these methods have protrusions and edges, and the peeling of the film due to the brittle fracture of the film by the sharp parts, and the attack from the protrusions of the dimples to the object to be formed cause powdering. As a shape requirement for the dents, the conventional specification by roughness Ra or Str is insufficient as a wear countermeasure for adhesion performance suitable for actual machine production.

[0008] In addition, these techniques aim to enhance the retention of the lubricant on the film surface by forming a concave shape. However, from the perspective of environmental issues, the reduction of the amount of lubricant used in press working is progressing, and adhesion countermeasures without using lubricants are required.

[0009] The present invention has been made in view of such problems, and suppresses the occurrence of peeling and powdering from a metal plate to be press-formed during press-forming, prevents the peeled matter and powdering from adhering to the surface of the press-forming die, and increases the conveyance and discharge property of the peeled matter and powdering from the surface of the press-forming die. An object of the present invention is to provide a surface treatment film for a press-forming die and a press-forming die.

Means for Solving the Problems

[0010] The surface treatment film for a press-forming die according to the present invention is a DLC film, In a diamond-like carbon film formed on the forming surface of the die by PVD method, Mr1 indicating the ratio of the protruding peak portions on the surface is in the range of 5.6 to 13.6%, Rsk indicating the surface skewness is in the range of -7.0 to -3.5, and the correlation between Mr1 and Rsk satisfies 7.5 ≦ Mr1 - 0.58 × Rsk ≦ 16.7. NCRX indicating the number of valleys in the surface motif shape is in the range of 200 to 500, Mr2 indicating the ratio of the protruding valley portions on the surface is in the range of 81.9 to 88.5%, Rvk indicating the depth of the protruding valley portions on the surface is in the range of 0.07 to 0.25 μm, and the correlation between Mr2 and Rvk satisfies 85.5 ≦ Mr2 - 1.51 × ln(Rvk) ≦ 91.2. Lr - 100 obtained by subtracting 100 from the developed length ratio due to the unevenness of the surface texture is in the range of 0.035 to 0.09%, θq indicating the surface inclination obtained from RΔq which is the root mean square is in the range of 1.45 to 2.4°, and the correlation between Lr - 100 and θq satisfies 0.80 ≦ θq - 17.6 × (Lr - 100) ≦ 0.95.

[0011] The press-forming die according to the present invention is characterized in that the above-described surface treatment film is formed on the surface.

Effects of the Invention

[0012] According to the present invention, when molding a material to be molded made of a soft material, it is possible to suppress adhesion to the mold forming surface due to peeled-off matter from the material to be molded, avoid maintenance for removing adhered matter on the mold forming surface and the material to be molded, and obtain a DLC film that enables press molding without changing the mold dimensions and without being restricted by the shape.

Brief Description of the Drawings

[0013]

Figure 1

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Figure 12

Embodiments for Carrying Out the Invention

[0014] Next, the present invention will be described in detail. In the present invention, in the surface treatment of forming a DLC film on the press-forming surface of a die for press forming to facilitate press working, when forming a forming target material made of a soft material, it is possible to suppress the generation of exfoliated matter or ground matter from the forming target material and suppress the adhesion of powdering of the exfoliated matter or abrasive matter to the die forming surface. Based on this purpose, the surface properties of the DLC film have been improved.

[0015] As a result, it has been found that in order to suppress the generation of powdering and flaking due to the aggregation of powdering during forming, it is effective to form a DLC film having the surface properties defined in claim 1. For suppressing the generation of powdering, the smoothness of the DLC hard film is important. It is preferable that the DLC hard film has few protrusion shapes and the contact between the soft metal to be pressed and the hard film is a sliding contact in a surface contact. On the other hand, in terms of the transportability of powdering, the number of valleys, the ratio of valleys, and the depth of valleys of the dimples on the hard film are important. Also, in terms of the dischargeability of powdering, the valley angle and the developed length ratio of the dimples on the hard film are important.

[0016] Note that, for example, the DLC film can be formed by using a raw material containing 99.9 mass% or more of carbon and forming ta-C (Tetrahedral Amorphous Carbon) or a-C (Amorphous Carbon) containing no hydrogen on, for example, alloy steel (SKD11 improved steel) as the die base material by the PVD method, particularly the arc ion plating method. This DLC film is polished after film formation. Using an abrasive (such as alumina (Al2O3), silicon carbide (SiC), diamond (C), etc.) with a hardness higher than that of this DLC film and a particle size of 1 to 20 μm to polish the DLC film, dimples are formed on the surface of the DLC film. The target plate for press forming as the soft material is, for example, a galvanized steel sheet (GA sheet) or an aluminum alloy sheet.

[0017] The surface of the DLC film with dimples is measured by a stylus (tip shape: conical, tip diameter: 5 μm) attached to the drive unit of a roughness measuring instrument (e.g., manufactured by Tokyo Seimitsu, product name: HANDYSURF+35), and the measurement results are analyzed by analysis software (e.g., manufactured by Tokyo Seimitsu, product name: ACCTee) to calculate the surface roughness parameters Rsk, Mr1, Mr2, Rvk, NCRX, RΔq, and Lr, which will be described later. θq is calculated from RΔq, and Lr-100 is calculated from Lr. At this time, the measurement can be carried out under the measurement conditions of a cut-off value of 0.8 μm and an evaluation length of 4.0 mm.

[0018] Hereinafter, the suppression of powdering, transportability, and dischargeability will be described. First, the roughness parameters for defining these surface properties will be described. FIG. 1 shows, on the left side, the surface properties of the surface treatment film, that is, the unevenness of the surface of the DLC film, and on the right side, a diagram schematically showing this surface property and defining each roughness parameter. As shown in the left-side figure, the range indicated by Rk in the special roughness curve Rg2 is defined as the core part, the part protruding upward from this core part is the protruding peak part, and the part protruding downward is the protruding valley part. Also, In is the evaluation length.

[0019] The surface property parameters are obtained by various calculation methods from the two-dimensional contour curves (JIS B0601:2001, JIS B0651:2001) extracted from the surface. Note that the following explanations in this paragraph and Figures 1 to 3 are excerpts from the "Surface Roughness Shape Measuring Machine Surfcom Series Parameter Explanation Book (Tokyo Seimitsu Co., Ltd.)". The measurement curve is the locus of the center of the tip sphere of the stylus in the vertical plane when the stylus moves on the target surface, and refers to the contour that appears at the cut surface when the target surface is cut by a plane perpendicular to the measurement target surface. The contour curve refers to a curve representing the contour of a cross-section such as a cross-section curve, roughness curve, or waviness curve obtained by deforming the measurement cross-section curve (discrete data point sequence) in digital form of this measurement curve. The cross-section curve is a curve obtained by applying a low-pass filter with a cut-off value λs to the measurement cross-section curve, and is the one in which the called shape (approximate shape) fitted by the least squares method and the inclination are removed by inclination correction. The roughness curve is a contour curve obtained by blocking the long-wavelength components from the cross-section curve by a wide-band filter with a cut-off value λc.

[0020] Figures 2(a) to (d) are diagrams for obtaining the special roughness curve Rg2. The calculation method of the load curve is, for example, according to ISO 13565 or DIN 4776. The mean line Wcg for the roughness curve is obtained from the cross-section curve P shown in Figure 2(a) by a Gaussian (phase compensation) filter. Next, as shown in Figure 2(b), the upper curve is obtained by connecting the higher one between the cross-section curve P and the mean line Wcg for the roughness curve and removing the valleys. Then, as shown in Figure 2(c), the reference mean curve Wcg2 is calculated by passing the above upper curve through a Gaussian filter. Next, as shown in Figure 2(d), the special roughness curve Rg2 is obtained by subtracting the reference mean curve Wcg2 from the cross-section curve P. This special filter linear expression load curve and parameters are standards compliant with ISO 13565-2 / JIS B0671-2, and are standards for evaluating lubricity by dividing the load curve into a three-layer structure of an initial wear part, a substantial contact part, and an oil sump part. For the special roughness curve Rg2, the load curve is obtained by the evaluation length method and in μm method, and various parameters are calculated.

[0021] "Mr1: Load length ratio of the core part (initial wear load ratio)" Then, take a width of 40% in the direction of the Mr value on the load curve, find the position on the load curve within this 40% width range where the difference in height between both ends is minimized, calculate the least-squares straight line from the data within this 40% width, and use this as the equivalent straight line. Let the intersection of the equivalent straight line and the Mr = 0% line be intersection point a, and let the intersection of the horizontal line extending from this intersection point a and the load curve be intersection point d. Let the Mr value at this intersection point d be Mr1. This Mr value is the load length ratio (initial wear load ratio) of the core part and is defined by JIS B 0671-2.

[0022] 「Mr2: Load length ratio of the core part (oil sump load ratio)」 On the load curve, find the intersection point b of the equivalent curve and the limit line of Mr = 100%. Let the intersection of the horizontal line be and the load curve be point e, and let the Mr value at that time be Mr2. These Mr1 and Mr2 are defined in JIS B0671-2.

[0023] 「Rvk: Depth of the protruding valley part (depth of the oil sump)」 It is equal to the area A2 of the part surrounded by the 100% limit line, the side be, and the load curve. Let the height on the Rmr = 100% limit line forming a right triangle (valley equivalent triangle) with this side be as one side be Rvk. This represents the depth of the oil sump. This Rvk is defined by JIS-B 0671.

[0024] 「Rsk: Skewness of the contour curve (distortion, deviation)」 Rsk is the third-order mean value of Z(x) made dimensionless by the root mean square value Rq and is obtained by the following Equation 1. This is defined by JIS B 0601.

[0025]

Equation

[0026] Figure 3(c) is a graph showing the relationship between P(z) on the horizontal axis and Z / Rq on the vertical axis. This figure shows the case where the part with a large probability density coincides with the average value of Z / Rq. However, when Rsk is a positive value, as shown in Figure 3(d), it is the case where the part with a large probability density is biased downward from the average value, and as shown in Figure 3(e), the contour curve has many protruding convex shapes. In Figure 3(e), the surface roughness of the surface treatment film has many convex shapes, and at the tips of these convex shapes, it is in contact with the product plate to be pressed. On the other hand, when Rsk is a negative value, as shown in Figure 3(a), it is the case where the part with a large probability density is biased upward from the average value, and as shown in Figure 3(b), the contour curve of the surface of the surface treatment film is mainly flat, and the surface property is such that concave shapes appear therein.

[0027] "NCRX: Number of valleys" NCRX is the number of all valleys within the evaluation length before the synthesis of the roughness motif (the minimum unit indicating roughness). Figure 4 is a cross-sectional curve showing the surface property of the surface treatment film, and there is 1 or 2 valleys within the roughness motif. NCRX is defined by JIS B 0631.

[0028] "RΔq: Root mean square slope" Extract a portion of length L from the extraction curve, differentiate this extracted portion to obtain a slope curve, and when obtaining the square values of the values at each point of the curve, the square root of the arithmetic mean value of these many square values is called the root mean square slope. Δq is represented by the following Equation 2.

[0029]

Equation

[0030] According to JIS B 0601:2001 and ISO4287:1997, the slope at each sampling point on the shape curve is calculated by the following Equation 3. ΔX is the interval between adjacent data.

[0031]

Equation

[0032] Figure 5 shows a shape curve at a reference length L, with the direction along the surface of the surface treatment film being x and the direction perpendicular to the surface being Z. When dZ(x) / dx of this shape curve is taken, the inclination is obtained. This is the root mean square inclination angle θq = tan -1 RΔq.

[0033] 「Lr: Development length ratio」 This development length ratio Lr is a parameter defined as Lr in ISO 4287 / 1-1984, but it was abolished in ISO 4287:1997. This development length ratio Lr is a dimensionless number referring to the ratio of the length obtained when the extraction curve is extended to a straight line within the evaluation length to the evaluation length. Lr is given by the following Equation 4.

[0034]

Equation

[0035] In the present invention, by using these roughness parameters to define the surface properties of the DLC film, when molding a material to be molded of a soft material, adhesion of exfoliated matter from the material to be molded to the mold forming surface is suppressed. The above roughness parameters can be analyzed, for example, by inputting necessary data with software such as 「ACCTee」 (manufactured by Tokyo Seimitsu Co., Ltd.).

[0036] The present invention forms gentle dimples by utilizing droplets present on a hard DLC film when polishing a DLC film formed by a PVD method, particularly an arc ion plating method. As a result, the DLC film as the surface treatment film of the press molding die is made to be in surface contact with the soft film that is the press molding target plate during press molding, thereby avoiding point contact. By achieving this surface contact, exfoliated matter generated from the soft material during the forming process adheres to the die surface, condenses, and the generation of powdering is suppressed. Furthermore, it becomes easier to convey and discharge the powdering, thereby suppressing the adhesion and remaining of the powdering on the die surface.

[0037] "Suppression of generation of powdering" For the suppression of the generation of powdering, the smoothness of the hard film is important. There are few protrusion shapes on the hard film, and the contact between the soft metal plate and the hard film is made into surface contact, and the soft metal plate and the hard film slide in this surface contact state. Therefore, it is effective to manage the surface properties so that Mr1, which indicates the ratio of the protrusion shape of the hard DLC film, and Rsk, which indicates the surface skewness, are within an appropriate range.

[0038] Mr1 indicates the initial wear load rate. When the value of Mr1 is large, the ratio of point contact between the soft material and the surface treatment film (hard film) increases, and the powdering due to the scraping off of the product material (press target plate) by the hard film increases. On the other hand, when the value of Mr1 is small, the surface property becomes a flat shape with few convexities, the contact between the soft material (press target plate) and the hard film (surface treatment film) becomes surface contact, and the generation of powdering due to the scraping off of the soft material is suppressed. However, if the value of Mr1 becomes too small, the surface of the surface treatment film approaches a mirror surface, and when Mr1 is 0%, it becomes a completely smooth surface, which causes flaking or adhesion, as described later. Therefore, the Mr1 value is set to 5.6 - 13.6%.

[0039] Rsk represents the bias of the contour curve and the symmetry of concavity and convexity. As shown in Fig. 6(a), when Rsk is a positive value, the contour curve has a shape with many protruding convex shapes, and point contact becomes the mainstream between the soft material (the plate to be pressed) and the hard film (the surface treatment film), increasing the powdering due to the scraping off of the soft material. That is, when the surface treatment film 10 has a smooth surface, the exfoliated matter 12 is crushed between the surface treatment film 10 and the plate 11 to be formed by the surface pressure during pressing, and the exfoliated matter 12 adheres and aggregates with other exfoliated matter 12 to become larger and may adhere to the surface treatment film 10 on the mold surface. Note that Fig. 6 shows a state in which the exfoliated matter 12 from the plate 11 to be pressed is involved between the surface treatment film 10 and the plate 11 to be pressed. Also, although Fig. 6 shows the surface treatment film 10 and the plate 11 to be pressed in a horizontal state, in actual press forming, the relationship as shown in Fig. 6 occurs on the side surface of the mold, so the two face each other in a vertical state.

[0040] On the one hand, when Rsk is a negative value and within the appropriate range, as shown in Fig. 6(b), the surface profile curve of the surface treatment film 10 has a flat portion and a concave portion, and surface contact becomes the main type between the soft material and the hard film, suppressing brittle fracture of the hard film and suppressing the generation of powdering caused by grinding of the soft material by the damaged hard film. That is, when the surface of the surface treatment film 10 has a valley shape with an appropriate depth, the surface pressure applied to the powdering exfoliation 12 is reduced, preventing aggregation of the exfoliation 12 and adhesion to the surface treatment film 10 on the mold surface, and enabling the effect of exfoliation conveyance. However, as shown in Fig. 6(c), when the value of Rsk becomes too small, that is, when the absolute value of Rsk, which is a negative number, becomes too large, the surface of the surface treatment film 10 has many concave shapes, and the contact between the forming target plate 11 and the surface treatment film 10 on the mold surface during press forming becomes close to point contact. For this reason, the powdering exfoliation 12 is deformed and adheres to other powdering exfoliations 12, causing flaking and the generation of large agglomerates. Therefore, the value of Rsk is set to the appropriate range of -7.0 to -3.5. Also, there is a correlation between Mr1 and Rsk, and in order to suppress the generation of powdering, it is necessary for Mr1 and Rsk to satisfy the following formula 5. This formula 5 defines the range of the correlation relationship between Mr1 and Rsk for those for which prevention of powdering generation and the like were possible from the data of the examples and comparative examples described later.

[0041]

Number

[0042] "Conveyability of Powdering" Next, the transportability of the powdering will be described. In terms of the transportability of the powdering, the number of valleys, the ratio of valleys, and the depth of valleys on the hard film are important. Therefore, as parameters of the surface properties, NCRX indicating the number of valleys on the hard film, Mr2 occupying the ratio of the valley shape of the hard film, and Rvk indicating the valley depth on the hard film become effective management items for improving the transportability of the powdering. NCRX indicates the number of valleys in the roughness motif. Since this is the number of recesses in which the valleys transport the powdering, when the number of recesses is large, the diameter of the valleys becomes small and the powdering cannot be transported. On the other hand, when the number of valleys is small, the transportability of the powdering decreases, resulting in adhesion due to aggregation of the powdering. Therefore, the value of NCRX is set to 200 to 500.

[0043] Mr2 indicates the ratio of the valley shape. When the value of Mr2 is small, the number of concave shapes increases, and during press forming, the surface treatment film between the plate to be formed and the mold surface is not in surface contact but is in a state close to point contact. Therefore, this causes peeling of the film from the object to be formed. On the other hand, when the value of Mr2 is large, the number of concave shapes decreases and the surface becomes smooth, but the transportability of the powdering decreases. Therefore, the value of Mr2 is set to 81.9 to 88.5%.

[0044] Rvk indicates the valley depth in the load curve. By having a valley shape, it is possible to suppress the load on the powdering during forming and suppress the expansion of adherents due to aggregation of adjacent powderings. When the valley shape is shallow, the effect of load suppression is small, which becomes a factor for the powdering to aggregate. Therefore, the value of Rvk is set to 0.07 to 0.25 μm.

[0045] Figures 6(d) and 6(e) are diagrams for explaining this load (surface pressure). A peeled-off material 12 is caught between the surface treatment film 10 and the plate 11 to be pressed. During the forming process of the plate material by pressing, surface pressure is applied to the die steel material as a load. When the load is applied, the peeled-off material 12 peeled off as powdering from the plated steel sheet or the soft metal sheet is caught between the surface treatment film 10 and the plate 11 to be pressed. At this time, as shown in Fig. 6(d), when the surface treatment film 10 has a smooth surface, the peeled-off material 12 is crushed and deformed between the surface treatment film 10 and the plate 11 to be formed by the surface pressure during the pressing process. Due to this deformation, the peeled-off material 12 adheres to other powdered peeled-off materials 12, and flaking occurs, easily forming large agglomerates. This agglomerate may adhere to the surface treatment film 10 on the die surface. On the other hand, as shown in Fig. 6(e), when the surface of the surface treatment film 12 has a valley shape with an appropriate depth, the surface pressure applied to the powdered peeled-off material 12 is reduced, preventing the aggregation of the peeled-off material 12 and its adhesion to the surface treatment film 10 on the die surface, and exerting the effect of transporting the peeled-off material.

[0046] Also, there is a correlation between Mr2 and Rvk, and it is necessary to satisfy the following mathematical formula 6.

[0047]

Number

[0048] "Exhaustibility of powdering" Next, the exhaustibility of powdering will be explained. In the exhaustibility of powdering, θq indicating the angle of the valley of the dimple on the hard film and Lr indicating the developed length ratio are important. Therefore, as parameters of the surface properties, θq indicating the angle of the valley of the dimple on the hard film and Lr indicating the developed length ratio are effective control items for improving the exhaustibility of powdering. Lr represents the ratio to the evaluation length when the contour curve including unevenness is extended. The larger the value of Lr, the more unevenness and the larger the surface area. For this reason, Lr - 100 shall be 0.035 to 0.09%.

[0049] θq is calculated using RΔq defined by JIS B 0601 and tan -1 It is calculated by RΔq. When θq becomes smaller and the slope to the valley part becomes smaller, Lr becomes smaller and a smooth surface is formed. Then, the powdering becomes easier to move, but it becomes easier to aggregate accordingly, and the progression to flaking is likely to occur. On the other hand, when θq becomes larger and the slope to the valley part becomes larger, Lr becomes larger, the contact area with the powdering becomes larger, and the sliding resistance becomes larger. Then, adhesion due to seizure occurs, which causes peeling of the hard film (DLC film as a surface treatment film). Therefore, θq is set to 1.45 to 2.4°.

[0050] When Lr - 100 is in the range of 0.035 to 0.09%, there is a correlation between θq and Lr, and both satisfy the following formula 7.

[0051]

Equation

Example

[0052] Hereinafter, embodiments of the present invention will be described together with comparative examples that fall outside the scope of the present invention. FIG. 7 shows a sliding tester for measuring the amount of peeling and aggregation from a material to be formed by simulating an actual machine press test. Test pieces 1a and 1b are supported by support jigs 3 and 4. These test pieces 1a and 1b are in the shape of thick plates, arranged with their longitudinal directions horizontal, and their four corners are rounded in the longitudinal cross-section. Then, these test pieces 1a and 1b are arranged so as to face each other in the horizontal direction, and a drawing material 2 is sandwiched between them. This drawing material 2 is gripped by a chuck 5 and is pulled upward by the upward movement of the chuck 5. The test pieces 1a and 1b receive stress in the direction towards each other via the support jigs 3 and 4, and receive a test load as the pressure for sandwiching the drawing material 2. Hard films (such as DLC films) with various surface properties are formed on the test pieces 1a and 1b. A drawing material 2 simulating a plate to be formed is sandwiched between the hard films of this pair of test pieces 1a and 1b. While applying a load towards each other between the test pieces 1a and 1b, the drawing material 2 is pulled out to measure the adhesion of powdering to the test pieces 1a and 1b due to the peeling from the drawing material 2. The test pieces 1a and 1b have a DLC film (hard film) or the like formed in a range of 6 mm width including a 4 mm flat portion, and a dimple shape is formed by polishing. The drawing test was carried out at room temperature with a test load of 2 tons, a drawing speed of 10 mm / sec, and a drawing distance of 200 mm.

[0053] Figure 8 shows the opposing surface (surface treatment film forming surface) of the test piece 1, and the drawing material 2 is moving in the direction indicated by ⇒ in the figure. Note that for the test pieces 1a and 1b, the upper and lower corner parts of their longitudinal sections are rounded. As described above, the central flat part has a width of 4 mm, and the upper and lower rounded parts each have a width of 1 mm, and they have an opposing surface with a total width of 6 mm. A surface treatment film such as a DLC film is formed in this 6-mm region. And the drawing material 2 slides on the surface of the test piece 1. The surface of the test piece 1 was observed at the initial sliding position 6, the mid-sliding position 7, and the final sliding position 8. This test piece was observed with a microscope (manufactured by Keyence, VHX-7000), and the powdering situation on the surface treatment film was evaluated according to the criteria shown in Figure 9. In Figure 9, the left vertical column is the evaluation criteria regarding the suppression of powdering generation, the middle column is the evaluation criteria regarding the transportability of powdering, and the right column is the evaluation criteria regarding the dischargeability. And based on the presence or absence of scratches on the hard film observed at the initial sliding position 6 in Figure 8 and the peeling of the hard film, the suppression effect of powdering generation from the drawing material 2 was evaluated. When there are no scratches and peeling of these hard films, as shown in Figure 9, it is marked as ○; when a large number of scratches and peeling are observed, it is marked as ×; and the intermediate situation is marked as △. Also, the effect of the transportability of powdering was evaluated from the state of the deposition of adherents on the dents from which the droplets on the hard film observed at the mid-sliding position 7 in Figure 8 were removed, and the effect of the dischargeability of powdering was evaluated from the degree of deposition of adherents on the hard film observed at the final sliding position 8 in Figure 8.

[0054] The parameters of the surface properties of the surface treatment film and the evaluation results of the drawing test are shown in Table 1 and Table 2 below. Table 1 shows the surface parameters of the examples of the present invention and the evaluation results of their powdering, and Table 2 shows the surface parameters of the comparative examples outside the scope of the present invention and the evaluation results of their powdering.

[0055]

Table 1

[0056]

Table 2

[0057] Figure 10 is a graph showing the relationship between Rsk and Mr1 shown in Tables 1 and 2, with Mr1 on the vertical axis and Rsk on the horizontal axis. In the relationship between Rsk and Mr1 of this surface parameter, Mr1 indicating the ratio of protruding peaks on the surface: 5.6 to 13.6%, Rsk indicating the skewness of the surface: -7.0 to -3.5, Correlation between Mr1 and Rsk: 7.5 ≤ Mr1 - 0.58×Rsk ≤ 16.7, Those satisfying any of the following conditions were marked with ○ as examples, and those not satisfying any of the above conditions or not being DLC films were marked with × as comparative examples. However, those that satisfy the conditions of Mr1, Rsk, etc. but deviate from other conditions or are not DLC films were also marked with × as comparative examples. In Figure 10, the horizontal dashed line indicates the positions of M1r = 13.6 and Mr1 = 5.6, and the vertical dashed line indicates the positions of Rsk = -7.0 and Rsk = -3.5. And in Figure 10, the line segments of Mr1 = 0.58×Rsk + 7.5 and Mr1 = 0.58×Rsk + 16.7 are shown as solid lines. The preferred relationship between the surface parameters Mr1 and Rsk is the region (shown shaded) surrounded by the four dashed lines and the two solid lines in Figure 10. Note that there are also × plots within this surrounded region, which are the evaluation results of DLC films that deviate from other conditions or are not DLC films but are CrN films, TiAlN films, or AlCrN films, and are comparative examples.

[0058] Figure 11 is a graph showing the relationship between Rvk and Mr2 shown in Tables 1 and 2, with Mr2 on the vertical axis and Rvk on the horizontal axis. In the relationship between Rvk and Mr2 of this surface parameter, NCRX indicating the number of valleys in the surface motif shape: 200 to 500, Mr2 indicating the ratio of protruding valleys on the surface: 81.9 to 88.5%, Rvk indicating the depth of the protruding valleys on the surface: 0.07 to 0.25 μm, Correlation between Mr2 and Rvk: 85.5 ≤ Mr2 - 1.51×ln(Rvk) ≤ 91.2 Those that satisfy any of the conditions were indicated by ○ as examples, and those that deviated from any of the above conditions or were not DLC films were indicated by × as comparative examples. However, those that satisfied the conditions such as Mr2 and Rvk but deviated from other conditions or were not DLC films were also indicated by × as comparative examples. In FIG. 11, the horizontal dashed line indicates the positions of Mr2 = 88.5 and Mr2 = 81.9, and the vertical dashed line indicates the positions of Rvk = 0.07 and Rvk = 0.25. And in FIG. 11, the line segments of Mr2 = 1.51×ln(Rvk)+85.5 and Mr2 = 1.51×ln(Rvk)+91.2 are shown as solid lines. The preferable relationship between the surface parameters Mr2 and Rvk is the region (shown hatched) surrounded by the four dashed lines and the two solid lines in FIG. 11. Although there are also × plots within this surrounded region, these are the evaluation results of DLC films that deviate from other conditions or are not DLC films but CrN films, TiAlN films, or AlCrN films, and are comparative examples.

[0059] Furthermore, FIG. 12 is a graph showing the relationship between θq and Lr - 100 shown in Tables 1 and 2, with θq on the vertical axis and Lr - 100 on the horizontal axis. In the relationship between the surface parameters θq and Lr - 100, Lr - 100 obtained by subtracting 100 from Lr, which indicates the developed length ratio due to the unevenness of the surface properties: 0.035 to 0.09%, θq indicating the surface slope obtained from RΔq, which is the root mean square: 1.45 to 2.4° The correlation between Lr - 100 and θq: 0.80 ≤ θq - 17.6×(Lr - 100) ≤ 0.95 Those satisfying any of the following conditions were indicated by ○ as examples, and those not satisfying any of the above conditions or not being DLC films were indicated by × as comparative examples. However, those that satisfy the conditions such as Lr-100 and θq but do not satisfy other conditions or are not DLC films were also indicated by × as comparative examples. In FIG. 12, the horizontal broken line indicates the positions of θq = 2.4 and θq = 1.45, and the vertical broken line indicates the positions of Lr-100 = 0.09 and Lr-100 = 0.35. And in FIG. 12, the line segments of θq = 17.6×(Lr-100) + 0.80 and θq = 17.6×(Lr-100) + 0.95 were shown as solid lines. The preferable relationship between the surface parameter θq and (Lr-100) is the region (shown hatched) surrounded by four broken lines and two solid lines in FIG. 12. Note that there are also × plots within this surrounded region, which are the evaluation results of DLC films that do not satisfy other conditions or are not DLC films but CrN films, TiAlN films or AlCrN films, and are comparative examples.

[0060] Those satisfying all the ranges shown hatched in FIGS. 10 to 12 are the surface treatment films of Examples 1 to 14 in Table 1, and all the characteristics of the generation suppression effect of powdering, transportability and dischargeability are excellent. Therefore, the surface treatment film satisfying all the conditions shown in claim 1 of the present application can prevent powdering during press forming, and can prevent adhesion and condensation products caused by peeling etc. from the press target material from adhering to the die surface.

Industrial Applicability

[0061] According to the present invention, the generation of powdering during press forming can be suppressed, and the transportability and dischargeability of the powdering accumulated on the surface of the press forming die are excellent, so that press forming can be performed with high efficiency, the high life of the press forming die and the high precision of the press product can be achieved, and it can greatly contribute to the improvement of the press forming process of the metal plate.

Explanation of Signs

[0062] 1(1a, 1b): Test piece 2: Drawing material 3, 4: Support jig 5: Chuck

Claims

1. In a diamond-like carbon film formed by PVD method on the forming surface of a press forming die, Mr1, which indicates the ratio of the protruding peaks on the surface, is in the range of 5.6 to 13.6%, Rsk, which indicates the surface skewness, is in the range of -7.0 to -3.5, and the correlation between Mr1 and Rsk satisfies 7.5 ≤ Mr1 - 0.58×Rsk ≤ 16.

7. NCRX, which indicates the number of valleys in the surface motif shape, is in the range of 200 to 500, Mr2, which indicates the ratio of the protruding valleys on the surface, is in the range of 81.9 to 88.5%, Rvk, which indicates the depth of the protruding valleys on the surface, is in the range of 0.07 to 0.25 μm, and the correlation between Mr2 and Rvk satisfies 85.5 ≤ Mr2 - 1.51×ln(Rvk) ≤ 91.

2. Lr - 100, obtained by subtracting 100 from the developed length ratio Lr due to the surface unevenness of the surface properties, is in the range of 0.035 to 0.09%, θq, which indicates the surface slope obtained from RΔq, the root mean square, is in the range of 1.45 to 2.4°, and the correlation between Lr - 100 and θq satisfies 0.80 ≤ θq - 17.6×(Lr - 100) ≤ 0.95, a surface treatment film for a press forming die.

2. A press forming die, characterized in that the surface treatment film according to Claim 1 is formed on the surface.

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