Surface treatment film for press molding dies and press molding dies

Abstract

The present invention aims to provide a surface treatment film for a press-molding die, which can prevent material peeled off from a metal plate such as a zinc-plated steel plate or an aluminum plate from aggregating and becoming coarse on the surface of the press-molding die when the metal plate is press-molded, thereby preventing scratches and defects from occurring in the press-molded sheet, and a press die using the same. [Solution] A press-molded sheet such as a zinc-plated steel sheet is press-molded using a mold on which a surface treatment film such as DLC is formed. The surface free energy of this surface treatment film is calculated by separately calculating its dispersion component d and hydrogen bond component h, and the dispersion component d is 32.1 mJ / m 2 more than 40.4 mJ / m 2 Below, the hydrogen bond component h is 1.1 mJ / m 2 More than 7.5 mJ / m 2 Make it so that it is as follows.

Description

[Technical Field]

[0001] The present invention relates to a surface treatment film for a press-forming die that can prevent the aggregation of flaked material from a zinc-plated steel sheet, an aluminum sheet, etc., on the press-forming die during press-forming of a sheet such as a zinc-plated steel sheet, an aluminum sheet, etc. The present invention also relates to a press-forming die on which the surface treatment film is formed, and a method for evaluating the surface treatment film. In particular, the present invention relates to press forming of galvanized steel sheets. [Background technology]

[0002] In press-forming dies, during press forming, material peeling off from the surface of the galvanized steel sheet or aluminum sheet that is the sheet to be formed adheres to the surface of the die and agglomerates, and these agglomerates further promote peeling from the surface of the sheet to be formed, resulting in defects on the surface of the sheet product to be formed.

[0003] Specifically, peeling of the plating layer from the sheet to be molded reduces the rust prevention performance of the product, causes seizure, and deteriorates the molded product. Furthermore, the surface of these molded products must be reworked, which is a problem that requires unnecessary time and effort.

[0004] On the other hand, when exfoliated materials aggregate on the surface of a mold, the surface shape of the mold changes, degrading the precision of the molded product. Furthermore, as these aggregates peel off, the surface treatment film of the mold peels off, resulting in the problem of a shortened mold life. To prevent adhesion of the aggregates to the mold surface and the resulting peeling of the mold surface treatment film, maintenance is required to remove the aggregates from the mold surface, which results in reduced productivity and increased product costs.

[0005] To prevent these problems, one method is to use press oil to suppress peeling of the plating on press-molded products, which suppresses the aggregation of peeled material from the surface of the press-molded product and thereby improves the life of the mold.

[0006] However, due to recent demands such as the SDGs, lubrication-free molding is being promoted, and the need to use environmentally friendly press oils is increasing. However, these environmentally friendly press oils have the problem that, compared to conventional press oils, they are more likely to cause flaked material to aggregate on the die surface. Therefore, neither lubrication-free molding nor the selection of a suitable press oil is an effective means of preventing the aggregation of flaked material.

[0007] Under these circumstances, Patent Document 1 discloses a coated tool used in cutting aluminum materials, which includes a base material and an amorphous carbon surface treatment material formed on the base material by surface treatment. It is disclosed that this coated tool has a surface free energy difference between the workpiece material and the surface treatment material that is equal to or greater than a predetermined value in order to perform cutting without adhesion.

[0008] Patent Document 2 discloses a molding die used to mold synthetic resin or other molded products, in which the base surface of the molding die is formed into an uneven surface that has been blasted to a maximum height (Sz) of 0.1 to 10.0 μm. It also discloses that the molding surface can have excellent releasability for synthetic resins or other materials because the contact area between the molding surface with these fine irregularities formed thereon is small and the synthetic resin can be made to have excellent releasability for synthetic resins or other materials.

[0009] Non-Patent Document 1 discloses that the durability of a coating film for a press die used in press-forming high-tensile steel sheets was evaluated because the coating film for the die is subjected to high surface pressure and sliding loads due to the application of a press load. In the method for evaluating the durability of a coating film for a press die described in Non-Patent Document 1, the adhesion of the film and its influence on sliding damage were investigated by observing the cross section of the coating film.

[0010] Non-Patent Document 2 states that the important factors in preventing seizure during cold plastic working are the appearance of new surfaces and sliding distance, and in order to quantitatively evaluate the effects of these factors, an ironing-type friction tester was prototyped to evaluate the effects of the above factors on seizure resistance. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-239781 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-209876 [Patent Document 3] WO2020 / 183708 A1 [Non-patent literature]

[0012] [Non-Patent Document 1] Paper titled "Durability Evaluation of Coating Films for Press Dies," author: Soichiro Nishino http: / / www.amada-f.or.jp / r_report2 / kkr / 26 / AF-2010019.pdf [Non-patent document 2] Transactions of the Japan Society of Mechanical Engineers (C), Vol. 48, No. 433 (1982-1989), Paper entitled "Evaluation of Seizure Resistance Using an Ironing-Type Friction Tester" Author: Nozomi Kawai et al. https: / / www.jstage.jst.go.jp / article / kikaic1979 / 48 / 433 / 48_433_1473 / _pdf / -char / ja Summary of the Invention [Problem to be solved by the invention]

[0013] However, the above-mentioned prior art techniques do not address the problem of condensation of flaked deposits from unformed sheets on the surface of a surface treatment coating of a mold. It is believed that in cutting processes, the greater the difference in surface free energy between the surface treatment coating of a cutting tool and the workpiece, the less likely the workpiece is to adhere to the surface treatment coating (see, for example, Patent Document 1). It is also believed that blasting the molding surface of a molding die to form fine irregularities on the surface reduces the surface free energy, thereby improving the mold release properties of molded products such as synthetic resins (see, for example, Patent Document 2). However, these prior art techniques relate to cutting processes or the molding of synthetic resins, and do not suggest methods for reducing or preventing the condensation of flaked deposits from press-formed products when press-forming sheets such as galvanized steel sheets or aluminum sheets. Patent Documents 1 and 2 attempt to evaluate the condensation of flaked deposits solely based on the difference in surface free energy, but this does not provide a highly accurate evaluation. Patent Document 3 attempts to evaluate powder adhesion from polar components or hydrogen bond components using surface free energy, but when it comes to the aggregation of peeled material from a zinc-plated steel sheet or aluminum sheet onto a surface treatment film for a press molding die, aggregation occurs in films with a small polar component, so the evaluation method of Patent Document 3 cannot be applied.

[0014] The present invention has been made in view of the above problems, and has an object to provide a surface treatment film for a press-molding die that can prevent material peeled off from a metal sheet such as a zinc-plated steel sheet or an aluminum sheet from aggregating and coarsening on the surface of the press-molding die when the metal sheet is press-molded, thereby preventing scratches and defects from occurring in the press-molded sheet, and a method for evaluating the press-molding die and the surface treatment film. In particular, an object of the present invention relates to a surface treatment coating for a mold that can be prevented from peeling off from a zinc-plated steel sheet and coagulating and adhering to the mold surface when the zinc-plated steel sheet is press-formed. [Means for solving the problem]

[0015] The surface treatment film of the press molding die according to the present invention is Press forming galvanized steel sheets Mujun Slippery The surface treatment film formed on the surface of the mold for molding with a PVD arc ion plating process, This surface treatment film is The dispersion component of the surface free energy is d, and the hydrogen bond component is in minutes When the value of the equation is h, The value calculated using the Owens-Wendt theory is d is 32.1 mJ / m 2 more than 40.4 mJ / m 2 is as follows: h is 1.1 mJ / m 2 More than 7.5 mJ / m 2 is It is characterized by:

[0016] In the surface treatment film of the press molding die, preferably, The value calculated using the Owens-Wendt theory is d is 34.3 mJ / m 2 more than 36.9 mJ / m 2 is as follows: h is 4.2 mJ / m 2 More than 7.5 mJ / m 2 The following is the result.

[0018] The present invention Related Other surface treatment films for press molding dies are In a surface treatment film formed by arc ion plating treatment of PVD treatment on the surface of a press molding die that uses press oil, This surface treatment film is When the dispersion component d in the surface free energy is d and the hydrogen bonding component h is h, d is 35.3 mJ / m 2 or more, 39.0 mJ / m 2 is as follows: h is 3.7 mJ / m 2 More than 15.1 mJ / m 2 is It is characterized by:

[0019] The press molding die using the press oil is, for example, It is used for press molding of aluminum plates.

[0020] The press molding die according to the present invention comprises: The above-mentioned surface treatment film is formed on the surface.

[0021] Furthermore, the present invention Related The evaluation method for the surface treatment film is as follows: A method for evaluating a surface treatment film to be formed on the surface of a press molding die, comprising: A droplet is dropped onto the surface treatment film or the press oil present on the surface treatment film, and the contact angle of the droplet is measured. Kaelble-Uy theory or the dispersion component and hydrogen bond component of the surface free energy calculated in the case of the Owens-Wendt theory from the formula of the Wu theory and the contact angle; or Kaelble-Uy theory Or, calculate the dispersion component and polar component of the surface free energy calculated by Wu theory, The method is characterized in that the aggregation and adhesion suppression performance of the surface treatment film to be formed on the press molding die is evaluated based on a predetermined relationship between the dispersive component and hydrogen bond component or the dispersive component and polar component and the suppression effect of the aggregation and adhesion of the surface treatment film during press molding. [Effects of the Invention]

[0022] According to the present invention, by appropriately defining the dispersion component d and the hydrogen bonding component h that constitute the surface free energy of the surface treatment film, it is possible to suppress the aggregation and adhesion of the surface treatment film on the surface of the press mold due to peeling from the workpiece during press molding. This prevents changes in the mold shape and product defects in the workpiece, without requiring maintenance to remove the aggregation, thereby improving the mold life and productivity. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 2 is a schematic diagram showing a wetting angle. [Figure 2] This is a sliding tester that tests the amount of coagulated deposits during press molding. [Figure 3] 1(a) to 1(c) are diagrams showing the shape of a test piece for a sliding tester. [Figure 4] FIG. 1 is a diagram (partially a photograph substituting a drawing) showing the criteria for determining the effect of inhibiting aggregation and adhesion. [Figure 5] FIG. 1 is a diagram (partially a photograph substituting a drawing) showing the effect of suppressing aggregation and adhesion in non-lubricated pressing. [Figure 6] FIG. 1 is a graph showing the relationship between the range of the dispersion component d and the hydrogen bonding component h of the surface free energy and the aggregation and adhesion suppression effect in non-lubricated pressing. [Figure 7] FIG. 1 is a diagram (partially a photograph substituting a drawing) showing the effect of suppressing coagulation and adhesion in pressing using a press oil. [Figure 8] FIG. 1 is a graph showing the relationship between the range of the dispersion component d and the hydrogen bond component h of the surface free energy and the aggregation and adhesion suppression effect in pressing using a press oil. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present invention will be described. In order to suppress adhesion and cohesion of material peeled off from a workpiece sheet during press molding, when the material adheres to and coheses with a surface treatment coating on a press mold, the present invention uses the Owens-Wendt theory to define the surface free energy. According to the Owens-Wendt theory, the surface free energy is composed of a dispersion component d and a hydrogen bond component h. The present invention was completed based on the discovery that adhesion and cohesion can be suppressed by separately defining the surface energy of the dispersion component d and the surface free energy of the hydrogen bond component h, i.e., by defining a range appropriate for suppressing adhesion and cohesion of the dispersion component d and a range appropriate for suppressing adhesion and cohesion of the hydrogen bond component h. The appropriate ranges for the dispersion component d and the hydrogen bond component h are as described in the Summary of the Invention.

[0025] The reason for defining the dispersion component d and the hydrogen bond component h in this way is as follows. The surface free energy is calculated using the Owens-Wendt theory, which expresses the polar component as the hydrogen bond component. Kaelble-Uy theoryAlternatively, the dispersion component and polar component calculated by Wu theory can also be used for evaluation. In the case of galvanized steel sheets in non-lubricated press forming, as shown in Figures 5 and 6 described below, the aggregation and adhesion suppression effect is observed when the dispersion component d is 32.1 to 40.4 mJ / mm 2 , the hydrogen bond component h is 1.1 to 7.6 mJ / mm 2 If the range is exceeded, zinc particles will aggregate on the surface treatment film of the mold. Therefore, the dispersion component d should be set to 32.1 to 40.4 mJ / mm 2 , hydrogen bond component h 1.1 to 7.6 mJ / mm 2 The maximum value for industrially usable coatings (DLC (Diamond-Like Carbon), Ti-based coatings) is 40.4 mJ / mm 2 , the hydrogen bond component h is 7.5 mJ / mm 2 Therefore, this was set as the upper limit. The most desirable range of the coating is when the dispersion component d is 34.3 to 36.9 mJ / mm 2 The hydrogen bond component h is 4.2 to 7.5 mJ / mm 2 The range is.

[0026] As shown in Figures 7 and 8, when a press solvent is used on an aluminum plate, the coating has a lower hydrogen bonding component h than the aluminum plate, and the peeled material aggregates. The range in which the effect of suppressing aggregation and adhesion to the aluminum plate is apparent is when the dispersion component d is 35.3 to 39.0 mJ / mm 2 , the hydrogen bond component h is 3.7 to 15.1 mJ / mm 2 The range is.

[0027] Let's go into more detail. Surface free energy is equivalent to the surface tension of a liquid, and is the molecular energy possessed by the surface of a solid. While intermolecular forces act between a molecule in the bulk of a solid and surrounding molecules, molecules on the surface of a solid also act between themselves and molecules in the atmosphere. From an energetic perspective, bulk molecules are attracted to surrounding molecules by intermolecular forces, but this interaction lowers their energy. On the other hand, surface molecules have fewer partners in the atmosphere with which to interact, so their energy is higher. This excess energy possessed by surface molecules is surface free energy (Asumi Giken Co., Ltd., document titled "Contact Angle Meter / Surface Tension Meter").

[0028] Like surface tension, surface free energy is composed of the sum of the components of intermolecular forces possessed by a solid. One theoretical formula for surface free energy is Owens and Wendt. If the surface energy is γ, the surface free energy due to the dispersion component d is γ(d), and the surface free energy due to the hydrogen bond component h is γ(h), the surface free energy γ is expressed as the following formula 1.

[0029]

number

[0030] Figure 1 is a diagram showing the effect of surface tension. When a drop of liquid is dropped onto a solid surface and the liquid wets the solid, at a certain point the liquid stops spreading and the drop comes to rest. Three forces act at the end points of the drop: the surface tension of the solid (interfacial tension between gas and solid) γ(SV), the surface tension of the liquid (interfacial tension between gas and liquid) γ(LV), and the interfacial tension between the liquid and solid γ(SL). Each of these three forces acting at the end points acts in a direction that reduces the area of ​​the surface or interface. The contact angle θ, which indicates the state of wetting, is determined by the balance of these three forces, as shown in Equation 2 below.

[0031]

number

[0032] On the other hand, when a liquid wets a solid and the solid and liquid are separated at their interface, the interface between the liquid and solid has interfacial free energy γ(SL), and the energy required to separate this interface is called the work of adhesion or work of adhesion, which is represented as W(SL), and is expressed by the following equation 3.

[0033]

number

[0034] From the above formulas 2 and 3, the Young-Dupre formula of the following formula 4 can be obtained.

[0035]

number

[0036] In the Owens and Wendt equation, the following equation 5 is proposed.

[0037]

number

[0038] According to Equation 1, the surface free energy γ(SV) of the solid and the surface free energy γ(LV) of the liquid are expressed by the following Equations 6 and 7.

[0039]

number

[0040]

number

[0041] From the above formula 4 and formula 5, the following formula 8 is obtained.

[0042]

number

[0043] To find the two unknown components of the surface free energy of a solid from Equation 8, two types of liquids with known surface free energies are used to calculate the two types of surface free energies of the solid from the detected contact angles. That is, the surface free energy of Liquid 1, whose components are known, is defined as γ(LV1) [γ(LV1) = γ(LV1,d) + γ(LV1,h)], and the contact angle between Liquid 1 and the solid is defined as θ1. Also, the surface free energy of Liquid 2, whose components are known, is defined as γ(LV2) [γ(LV2) = γ(LV2,d) + γ(LV2,h)], and the contact angle between Liquid 2 and the solid is defined as θ2. Then, Equation 7 above yields the following Equations 9 and 10 for Liquid 1 and Liquid 2.

[0044]

number

[0045]

number

[0046] From these equations 9 and 10, a two-dimensional linear equation is derived with two unknown components (γ(SV,d), γ(SV,h)) in the surface free energy of the solid. By solving this equation, the dispersion component γ(SV,d) and the hydrogen bond component γ(SV,h) of the surface free energy can be obtained.

[0047] Examples of liquids with known surface free energies include water and dioctyl methyl ether. The dispersion component d and hydrogen bonding component h of a solid's surface free energy can be calculated by placing droplets of water and dioctyl methyl ether on a test specimen, measuring the two contact angles, and then applying them to Equations 9 and 10. In practice, software for calculating surface free energy is available. By inputting the contact angles of water and dioctyl methyl ether, the surface free energy of the solid can be calculated using the Owens-Wendt theory. Examples of such software include "FAMAS" from Asumi Giken or Kyowa Interface Chemistry. Using this software, the dispersion and hydrogen bonding components of the surface free energy can be easily calculated by inputting the contact angles based on the Owens-Wendt theory, Kaelble and Uy theory, or Wu theory. Ultimately, by dropping two types of liquid onto a solid surface and detecting the contact angle, the dispersion component and hydrogen bond component of the solid's surface free energy can be calculated based on the Owens-Wendt theory, the Kaelble and Uy theory, or the Wu theory using software such as FAMAS. While the present invention evaluates surface free energy based on the Owens-Wendt theory, it is also possible to evaluate it using other theoretical formulas, such as the Kaelble and Uy theory or the Wu theory. Asami Giken's software is listed in "How to Use Surface Free Energy Calculation Software" (https: / / www.contact-angle.jp / contact / fac / column20210407 / ).

[0048] The present inventors discovered that, when evaluating adhesion to the surface of a press-molding die, the magnitude of the surface free energy between the die surface treatment film and the zinc-plated steel or aluminum sheet alone is insufficient to evaluate the aggregation and coarsening of exfoliated material from the workpiece (hereinafter, the molded sheet). After extensive research and development into conditions for suppressing the aggregation of exfoliated material, they discovered that the aggregation of exfoliated material can be evaluated based on the ratio of components in the surface free energy of a solid. This led to the completion of the present invention. The surface free energy of a solid is expressed as the sum of a dispersive component and a polar component (the hydrogen-bonding component in Owens-Wendt theory), and it is known that the closer the ratio of these dispersive and polar components between a solid and a liquid, the more easily the solid will wet. Based on this, the present inventors calculated the dispersive and hydrogen-bonding components of the surface free energy of a surface treatment film and a molded sheet using the same liquid using Owens-Wendt theory, and discovered that adhesion of exfoliated material can be suppressed by selecting a surface treatment film with a different ratio of dispersive and hydrogen-bonding components. The effect of suppressing the aggregation of this peeled material was verified by a pull-out test between the surface treatment film and the molded plate, and the relationship between the component ratios of the dispersion component and the hydrogen bond component of the surface free energy that can suppress aggregation was determined.

[0049] This surface treatment film is formed by arc ion plating, a PVD treatment. Typical surface treatment films include DLC (Diamond-Like Carbon) films, TiAlN-based films, and AlCrN-based films. The base material for press molding dies is alloy tool steel (SKD11 improved steel manufactured by Nippon Koshuha Steel Co., Ltd.).

[0050] This component ratio will be explained in detail below. First, referring to Figure 2, a sliding tester for measuring the amount of peeling and cohesion from the molding target material, simulating a press test, will be described. Figure 2 is a schematic diagram of this sliding tester. Test pieces 1a and 1b are supported by support jigs 3 and 4. These test pieces 1a and 1b are thick plates with their longitudinal direction horizontal and their four corners rounded in vertical cross section. These test pieces 1a and 1b are arranged facing each other in the horizontal direction, with a drawn material 2 sandwiched between them. This drawn material 2 is gripped by a chuck 5 and pulled upward by the upward movement of the chuck 5. Test pieces 1a and 1b are subjected to stress in a direction toward each other via the support jigs 3 and 4, and a test load is applied as pressure to clamp the drawn material 2.

[0051] Figure 3 shows the dimensions and shapes of test specimens 1a and 1b. As shown in Figure 3(a), the longitudinal cross sections of test specimens 1a and 1b are squares with rounded corners, and the vertical dimension of the flat portions of the opposing surfaces is 4.00 mm and the horizontal dimension is 30.00 mm, resulting in a sliding surface area of ​​4.00 × 30.00 mm. Test specimens 1a and 1b are made of alloy tool steel (SKD11 improved steel manufactured by Nippon Koshuha Steel Co., Ltd.) with a hardness of 60 HRC. A mold surface treatment film was formed on the surfaces of test specimens 1a and 1b, but the surface treatment film was polished over a 6.00 mm wide region including the 4.00 mm wide portion of the flat portion.

[0052] As the pulled material 2 is pulled upward, it rubs against the test pieces 1a and 1b, causing aggregates that peel off from the pulled material 2 to adhere to the surfaces of the test pieces 1a and 1b. The aggregation-inhibiting effect is evaluated based on the amount of this peeled aggregates.

[0053] Table 1 below shows the pull-out test conditions, and Table 2 shows the method for measuring surface free energy. The pull-out distance was set to 20 to 200 mm in order to grasp the amount of initial peeled material. The drawn material was tested in two modes: unlubricated and with press oil. The unlubricated test was conducted on a GA steel plate (hot-dip galvanized steel plate), and when press oil was used, tests were conducted on an A5052 aluminum plate using three types of press oils manufactured by Nippon Kogyoyu Co., Ltd. The press oil was applied solidly to the drawn material with a sponge.

[0054] [Table 1]

[0055] [Table 2]

[0056] The surface free energy of the test piece is calculated from the contact angle measured by the θ / 2 method after applying a drop of liquid to the test piece that has been washed with alcohol and dried using the equipment in Table 2. However, in the case of aluminum plate test pieces, in order to understand the change in surface free energy due to press oil, the test piece is coated with a solid coat of press oil before applying a drop of liquid, and the surface free energy is calculated from the contact angle.

[0057] The test pieces were surface-treated by forming a coating using the PVD AIP (arc ion plating) method, and the amount of cohesive adhesion was investigated for three cases: one with no polishing treatment on the sliding surface, one with buffing treatment after surface treatment, and one with shot peening treatment.

[0058] The test specimens were made of SKD11 modified steel, tempered to 60HRC, and polished to a mirror finish with a smooth surface of Rz 0.7μm or less. Then, using an arc ion plating device, coatings were formed on this substrate through the following processes: evacuation, heating, etching, and deposition. Impurities on the specimen surface were evaporated through the evacuation and heating processes. In the etching process, impurities were removed by metal bombardment using a commercially available Ti target. In the deposition process, a specific coating was formed directly or via an intermediate layer using commercially available targets tailored to the coating composition. The deposition time was controlled to achieve thicknesses of approximately 1-3μm for DLC, 8-12μm for TiAlN, and 2-4μm for AlCrN. After heating, the specimen's actual temperature was maintained below 450°C during deposition. After deposition, the specimens were polished in three ways: unpolished, buffed, shot peened, or buffed and shot peened. The Rz after DLC buffing was 0.71-0.83 μm, the Rz after buffing and shot peening was 0.54 μm, the Rz after TiAlN buffing was 0.45 μm, the Rz after AlCrN buffing was 0.83 μm, and the Rz after shot peening was 0.99 μm. Buffing was performed as follows depending on the film type. TiAlN and AlCrN were polished with a #1000 abrasive disk and then finish polished with diamond paste with a 4-6 μm grain size. DLC was finish polished with diamond paste with a 1-3 μm grain size. Shot peening was performed to modify the surface by projecting fine particle shots. Note that the vacuum level and gas type of the arc ion plating equipment were general conditions, and the voltage, current value, pressure, etc. were set appropriately depending on the type of film formation equipment and cathode.

[0059] Figure 4 shows the criteria for visual and sensory evaluation of the amount of cohesive adhesion. The surface of the test piece after the sliding test was observed, and as shown in the upper diagram of Figure 4, if no adhesion was observed visually, the cohesive adhesion suppression effect was rated as ○, if a thin layer of peeled material was attached, the cohesive adhesion suppression effect was rated as △, and if a thick layer of peeled material was attached, the cohesive adhesion suppression effect was rated as ×.

[0060] Next, we will explain the results of investigating the adhesion and agglomeration in tests simulating unlubricated press forming. GA steel sheet (zinc-plated steel sheet) was selected as the target sheet for unlubricated press forming, and a pull-out test was conducted on this GA steel sheet. Figure 5 is a photograph showing the sliding surface of the test piece after this pull-out test. The test piece was an alloy tool steel (SKD11) surface coated with a DLC (diamond-like carbon), TiAlN, or AlCrN film, which simulates the surface treatment film of a forming mold.

[0061] Test Nos. 1 to 3 show the surface free energy of the DLC film. Test No. 1 is unpolished, No. 2 is buffed, and No. 3 is shot peened. The surface free energy of Test No. 1 is calculated based on the Owens-Wendt theory, where the dispersion component is 40 mJ / m 2 , the hydrogen bond component is 3.4 mJ / m 2 On the other hand, the surface free energy of No. 2 has a dispersion component of 34.3 mJ / m 2 , the hydrogen bond component is 7.5 mJ / m 2 The surface free energy of No. 3 is 36.9 mJ / m 2 , the hydrogen bond component is 4.2 mJ / m 2 Thus, it was found that compared to the unpolished case, the dispersed component decreased and the hydrogen bond component increased in the buffed and shot peened cases. On the other hand, Test No. 4 shows the effect of suppressing cohesion adhesion of the TiAlN-based film, and Nos. 5 and 6 show the effect of suppressing cohesion adhesion of the AlCrN-based film, but the surface free energy of the hydrogen bond component of these TiAlN-based and AlCrN-based films is 1.0 mJ / m 2 and 1.1 mJ / m 2 As such, it can be seen that the DLC film has a higher hydrogen bonding component than the TiAlN-based film and the AlCrN-based film. Test No. 7, where no surface treatment film was formed, had a surface free energy of 11.6 mJ / m 2 is extremely high.

[0062] The adhered agglomerates that peeled off from the GA steel sheets on these surface treatment films were as shown in the photographs in Figure 5. The agglomerate adhesion suppression effect was evaluated as follows: ○ for Test Nos. 2 and 3, △ for Test Nos. 1 and 5, and × for Test Nos. 4, 6, and 7. As shown in Figure 5, no correlation was observed between the surface free energy (d+h) and the agglomerate adhesion suppression effect of the surface treatment film on the surface.

[0063] Figure 6 is a scatter plot of the surface free energy of the test specimens with each surface treatment film and the GA steel sheet, with the dispersion component calculated using the Owens-Wendt theory on the horizontal axis and the hydrogen bond component on the vertical axis.

[0064] Tables 3 and 4 below quantitatively express the effect of suppressing cohesion and adhesion in the non-lubricated press working shown in FIG. 6, together with the surface free energy. Table 4 is calculated not only by the dispersion component d and the hydrogen bond component h obtained by the Owens-Wendt theory, but also by Kaelble-Uy theory The values ​​of the dispersion component d and polar component p calculated by Wu theory are also listed.

[0065] Figure 6 plots the dispersion component d and hydrogen bond component h of the Owens-Wendt theory from Table 4, and displays the dispersion component d and hydrogen bond component h two-dimensionally for Tests No. 1 to No. 7 shown in Figure 5. The area surrounded by the solid line in Figure 6 is the area in Figure 5 where the coagulation and adhesion suppression effect is marked ○, and the area surrounded by the dashed line is the area in Figure 5 where the coagulation and adhesion suppression effect is marked △ (including the area marked ○). Tests Nos. 4, 6, and 7 fall outside the area surrounded by the dashed line.

[0066] [Table 3]

[0067] [Table 4]

[0068] The dispersion component d of the GA steel sheet calculated by the Owens-Wendt theory is 34.6 mJ / m2 , the hydrogen bond component h is 0 mJ / m 2 Test No. 4, which has a component ratio (dispersion component, hydrogen bond component) relatively close to that of the GA steel sheet, has a dispersion component d of 35.4 mJ / m 2 and the hydrogen bond component h is 1.0 mJ / m 2 On the other hand, Test Nos. 1 to 3 and 5, which have different component ratios, have an effect of suppressing coagulation and adhesion. The most effective coagulation suppression is when the dispersion component is 34.3 mJ / m 2 More than 36.9mJ / m 2 or less, and the hydrogen bond component is 4.2 mJ / m 2 More than 7.5mJ / m 2 The surface treatment film satisfies the following ranges.

[0069] Test No. 7, which was not subjected to surface treatment, had a hydrogen bond component h of 11.6 mJ / m 2 Although the component ratios are different from those of the drawn material, the zinc plating does not have any effect in suppressing cohesion. This shows that although the component ratios of the surface free energy are different, the metals have a high affinity with each other, and zinc adheres easily.

[0070] In Figure 6, the area surrounded by a solid line is the area defined in claim 2, and the area surrounded by a dashed line is the area defined in claim 1. As such, in claim 1, the area where the coagulation adhesion suppression effect is marked with either ○ or △, and in claim 2, the area where the coagulation adhesion suppression effect is marked with only ○, thereby demonstrating the effects of claims 1 and 2 of the present application. That is, as mentioned above, no correlation was observed between the surface free energy (d + h) and the coagulation adhesion suppression effect of a surface treatment film. However, as shown in Figure 6, by dividing the surface free energy into a dispersion component d and a hydrogen bonding component h and examining the relationship between each and the coagulation adhesion suppression effect, it is found that there is a clear correlation between the coagulation adhesion suppression effect and the dispersion component d and the hydrogen bonding component h, and that the coagulation adhesion suppression effect can be evaluated using the two factors of the dispersion component and the hydrogen bonding component h.

[0071] Next, we will explain the results of an investigation into adhered aggregates in a test simulating press forming using press oil. Aluminum plates were selected as the target sheets for forming using press oil, and pull-out tests were conducted on these aluminum plates. Figure 7 is a photograph showing the sliding surface of the test piece after this pull-out test. The test pieces were alloy tool steel (SKD11) with a DLC (Diamond-Like Carbon) film or TiAlN film formed on the surface to simulate the surface treatment film of a forming mold.

[0072] Test Nos. 8, 9, 11 to 13 are cases where a DLC film was formed as the surface treatment film, and Test No. 10 is a case where a TiAlN-based film was formed. Test Nos. 8, 10, 11, and 13 were buffed, and Test Nos. 9 and 12 were not polished.

[0073] Comparing Tests No. 8 and 9 with Tests No. 11 and 12, it is clear that the hydrogen bond component of the surface free energy is lower for press oil G3144 and higher for press oil EM3239, indicating that the hydrogen bond component is affected by the press oil. In particular, as in Test No. 12, applying EM7230 without polishing the film significantly increases the hydrogen bond component.

[0074] As shown in Tests 8, 11, and 13 in Figure 7, the higher the hydrogen bond component h, the better the coagulation and adhesion inhibitory effect of the aluminum plate. Furthermore, as shown in Tests 8 and 9, polishing increases the hydrogen bond component h, demonstrating a superior coagulation and adhesion inhibitory effect. A comparison of Tests 8 and 9, in which the same press oil was used (G3144), reveals that buffing increases the hydrogen bond component h, enhancing the coagulation and adhesion inhibitory effect. Furthermore, a comparison of Tests 11 and 12, in which the same press oil was used (EM7230), reveals that, when the press oil was EM7230, there was no difference in the hydrogen bond component h value with or without buffing, but buffing improved the coagulation and adhesion inhibitory effect. Furthermore, a comparison of Tests 8, 11, and 13 shows that when buffing was performed, the hydrogen bond component h value increased in the following order: G3144, G6231F, EM7230 press oil, i.e., Tests 8, 13, and 11, indicating a high coagulation and adhesion suppression effect in all cases. A comparison of Tests 8 and 10 shows that when buffing was performed with G3144 press oil, the hydrogen bond component h was higher and the coagulation and adhesion suppression effect was higher for the DLC film in Test 8 than for the TiAlN-based film in Tests 10. Thus, the hydrogen bond component h and the coagulation and adhesion suppression effect differ depending on whether or not polishing was performed, the type of press oil used, and the type of surface treatment film. Therefore, by adjusting these factors, the coagulation and adhesion suppression effect can be enhanced by adjusting the hydrogen bond component h and dispersion component d so that they fall within the region indicated by the solid line in Figure 8 below.

[0075] Figure 8 is a two-dimensional diagram showing the range of the dispersion component d and the hydrogen bond component h relative to the aggregation and adhesion inhibitory effect, with the horizontal axis representing the dispersion component d and the vertical axis representing the hydrogen bond component h. In Figure 8, the solid line indicates the range in which the aggregation and adhesion inhibitory effect is high (circles in Figure 7), and the dashed line indicates the range in which the aggregation and adhesion inhibitory effect exists.

[0076] Tables 5 and 6 below quantitatively express the aggregation and adhesion suppression effect in press processing using the press oil shown in Figure 8, along with the surface free energy. Table 6 not only includes the dispersion component d and the hydrogen bond component h calculated by the Owens-Wendt theory, but also the Kaelble-Uy theory The values ​​of the dispersion component d and polar component p calculated by Wu theory are also listed.

[0077] [Table 5]

[0078] [Table 6]

[0079] The dispersion component d of the aluminum plate calculated by the Owens-Wendt theory is 27.1 mJ / m 2 , the hydrogen bond component h is 2.6 mJ / m 2 Test Nos. 9 and 10, which have a surface free energy of the hydrogen bonding component lower than the hydrogen bonding component h of this drawn aluminum plate (A5052), have no condensation adhesion inhibitory effect, while surface treatment films with a hydrogen bonding component higher than this aluminum plate exhibit an aggregation inhibitory effect. Surface treatment films with a dispersion component d in the range of 35.3 to 39.0 and a hydrogen bonding component h in the range of 3.7 to 15.1 have the greatest aggregation adhesion inhibitory effect.

[0080] The results of the pull-out tests shown in Figures 7 and 8 show that a large difference in surface free energy between the drawn material and the surface treatment film does not necessarily result in a high coagulation adhesion suppression effect. Furthermore, the surface roughness Rz does not indicate that a mirror finish is as effective in suppressing coagulation adhesion. In other words, it is clear that there is no correlation between the surface treatment film on the press workpiece and the press mold and their surface free energy difference or surface roughness Rz.

[0081] Furthermore, because the surface free energy varies depending on the type of press oil, by selecting an appropriate press oil, the dispersing component d and hydrogen bonding component h of the surface treatment film can be adjusted to ranges that achieve the aforementioned effect of inhibiting cohesion and adhesion, thereby inhibiting cohesion and coarsening of the formed plate on the mold surface due to plating peeling. [Industrial Applicability]

[0082] According to the present invention, the generation of agglomerated deposits during press forming can be suppressed, thereby enabling press forming to be performed with high efficiency, thereby extending the life of the press forming die and increasing the precision of the pressed product, thereby making a significant contribution to the improvement of the press forming process of metal sheets. [Explanation of symbols]

[0083] 1(1a, 1b): Test piece 2: Drawn material 3, 4: Support jig 5: Zipper

Claims

1. A surface treatment film formed by arc ion plating, a PVD treatment, on the surface of a die for non-lubricated press forming used to press-form zinc-plated steel sheets, This surface treatment film is When the dispersion component of the surface free energy is d and the hydrogen bond component is h, the value calculated by the Owens-Wendt theory is: d is 32.1 mJ / m 2 more than 40.4 mJ / m 2 is as follows: h is 1.1 mJ / m 2 More than 7.5 mJ / m 2 is A surface treatment film for a press molding die.

2. As a value calculated by the Owens-Wendt theory, d is 34.3 mJ / m 2 more than 36.9 mJ / m 2 is as follows: h is 4.2 mJ / m 2 More than 7.5 mJ / m 2 is The surface treatment film of the press molding die according to claim 1.

3. A press molding die having the surface treatment film according to claim 1 or 2 formed on its surface.

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