Method for manufacturing hot stamp product

Abstract

To provide a method for manufacturing a hot stamp product, which can easily and effectively suppress or prevent adhesion (agglutination) of an aluminum-plated steel plate to an aluminum-plated mold in a hot stamp step.SOLUTION: This method for manufacturing a hot stamp product, which manufactures a product from an aluminum-plated steel plate in a hot stamp step, manufactures the product after the surface of a mold facing the aluminum-plated steel plate is coated with a non-volatile water soluble agent having no flammability.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a manufacturing method for a hot stamped product in which a product (including a part) is manufactured from a steel sheet by a hot stamping (hot pressing) process, and particularly to a manufacturing method for a hot stamped product in which adhesion (adhesion) of aluminum plating to a hot stamping die can be suppressed or prevented when a product is manufactured from an aluminum-plated steel sheet. [Background technology]

[0002] The hot stamping process is, for example, as shown in Fig. 1. That is, first, a steel sheet material 1 shown in Fig. 1(A) is prepared, then the steel sheet material 1 is carried into a heating furnace 2 as shown in Fig. 1(B) and heated (for example, to 900°C), pressed with a die, and formed and quenched as shown in Fig. 1(C) to obtain a formed product 3, which is then appropriately processed to finally obtain a product 4 as shown in Fig. 1(D). In this case, an aluminum-plated steel sheet is generally used as the steel sheet material 1 to prevent oxidation scale and improve the corrosion resistance of the steel material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-146354 A [Patent Document 2] WO2011 / 158818 [Patent Document 3] WO2013 / 145229 [Patent Document 4] JP 2022-185340 A Summary of the Invention [Problem to be solved by the invention]

[0004] Here, when an aluminum-plated steel sheet is used as the base steel sheet, the steel sheet is heated to the austenite transformation temperature (Ac3 point) or higher, and the heated steel sheet is press-molded and quenched in hot stamping, as shown in FIG. 2(A) in a hot stamping furnace, then conveyed, and quenched in uneven dies 10 and 11 as shown in FIG. 2(B). However, during the molding, the aluminum-plated layer cannot follow the deformation of the material (steel), and the aluminum-plated layer peels off from the steel sheet, and the aluminum plating adheres (adheres) firmly to the surface of the die. FIGS. 3(A) and (B) show the state in which the aluminum plating is actually attached to the die. When the aluminum plating adheres to the die, the adhesion is transferred to the subsequent product, causing a product dent such as a dent mark as shown in FIG. 4(A) or an appearance flaw (galling flaw) such as a scratch mark as shown in FIG. 4(B), resulting in a quality defect of the product. The quality defect of the product is a fatal problem.

[0005] The deposits (aluminum plating) that adhere to the mold are strong and cannot be removed by simple actions such as scratching them with hands or wiping them off with a cloth, but must be removed mechanically, such as by scraping them off with a grinder. However, when scraping them off with a grinder, the surface of the mold is often scraped off along with the aluminum plating that has adhered to it, which causes wear and deterioration of the expensive mold.

[0006] To address this issue, a coating (such as DLC (Diamond-Like Carbon), AlCrN, or AlCrTi) is generally applied to the surface of the mold, but this has little effect in preventing aluminum plating from adhering to the mold, and there is also the problem that the coating layer peels off during molding, as shown in Figure 5. Furthermore, when attempting to remove the adhesions with a grinder or the like, the coating layer is damaged or peels off, so the effect of the coating is extremely short-term.

[0007] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a manufacturing method for a hot stamped product, which is capable of easily and effectively suppressing or preventing adhesion (adhesion) of the aluminum plating of an aluminum-plated steel sheet to a die in a hot stamping process. [Means for solving the problem]

[0008] The present invention relates to a manufacturing method for producing a product from an aluminum-plated steel sheet by a hot stamping process, and the above-mentioned object of the present invention is achieved by manufacturing the product after applying a non-flammable, non-volatile water-soluble agent to a surface of a mold that faces the aluminum-plated steel sheet.

[0009] The above-mentioned object of the present invention is more effectively achieved by the water-soluble drug being a mixture of a high molecular weight polymer, water and a surfactant, or by the mixing ratio of the water-soluble drug being 1 to 25 parts (wt%) of the high molecular weight polymer, 50 to 98 parts (wt%) of the water and 1 to 25 parts (wt%) of the surfactant, or by the application being carried out periodically. Effect of the Invention

[0010] According to the manufacturing method of the hot stamped product of the present invention, by applying a water-soluble agent consisting of a polymer, water, and a surfactant to the surface of a die for hot stamping of an aluminum-plated steel sheet, it is possible to suppress or prevent adhesion (adhesion) of the aluminum plating to the die, thereby improving the quality of the product, eliminating the need for a process for removing adhesions using a grinder or the like, and reducing wear and deterioration of the expensive die. Therefore, the economic merits of product manufacturing are also very large.

[0011] To suppress or prevent adhesion of aluminum plating to a mold, a water-soluble agent can be simply applied to the entire surface of the mold using a sprayer or by hand, which is an extremely simple operation that can produce a significant effect. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic flow diagram showing an example of a hot stamping process. [Diagram 2] 1 is a schematic flow diagram showing the heating and quenching of an aluminum-plated steel sheet. [Diagram 3] FIG. 13 is an image showing an example of aluminum plating adhered to a mold. [Figure 4] FIG. 13 is an image diagram showing an example of transfer of a metal mold deposit onto a product. [Diagram 5] FIG. 13 is an image showing an example of mold coating peeling. [Figure 6] FIG. 1 is a schematic diagram illustrating a concept underlying the present invention. [Figure 7] 1 is a schematic flow chart for explaining the principle of the present invention. [Figure 8] FIG. 1 is an external view of a square-headed drawn die for demonstrating the effects of the present invention. [Figure 9] 1 is an external view of a part illustrating the effect of the present invention. [Figure 10] FIG. 1 is a conceptual diagram for explaining the composition of a water-soluble drug according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The inventors assume that the cause of the adhesion (adhesion) of the aluminum plating to the mold is that aluminum (Al) is hydrophilic and iron (Fe), the material of the mold, is also hydrophilic (see Fig. 6(A)), and therefore the aluminum plating adheres to iron by the action of hydrogen bonds as shown in Fig. 6(B). Based on this assumption, the inventors discovered through many trial and error tests that in order to suppress or prevent the adhesion of the aluminum plating to the mold, it is necessary to prevent the hydrogen bonds shown in Fig. 6(B) from occurring.

[0014] For this reason, the inventors assumed that the hydrogen bonds would be inhibited or prevented if a water-soluble substance was layered on the mold surface, and created and tested a water-soluble agent that is a mixture of a high molecular weight polymer, water, and a surfactant, which is inexpensive and easy to obtain, is non-flammable and non-volatile, has lubricity that provides a low friction coefficient against aluminum plating, and has good retention of a residual film, and found that it produced a remarkable effect. Surfactants include anionic surfactants (negative ions), cationic surfactants (positive ions), zwitterionic surfactants (amphoteric surfactants), and nonionic surfactants (nonionic surfactants), and any of these may be used. Press oil is generally used in cold press molding, but press oil is highly flammable and generates steam, so it is essential that the water-soluble agent according to the present invention is a water-soluble agent that is particularly non-flammable.

[0015] The water-soluble drug according to the present invention is prepared in the following mixing ratio:

[0016] High molecular weight polymer: 1 to 25 parts (weight %) Water: 50~98 parts (weight%) Surfactant: 1 to 25 parts (wt%) The water-soluble agent of the present invention is produced by mixing and stirring in the above-mentioned range. If the ratio is not adjusted within this range, the film quality, film thickness, and lubricating effect will be affected, and the ability to suppress or prevent adhesion (adhesion) of aluminum plating to a mold, as well as weldability and degreasing properties will be impaired.

[0017] In the present invention, as shown in Fig. 7(A), a water-soluble agent is uniformly applied to the entire surface of a mold 30 using a sprayer or the like, and then, as shown in Fig. 7(B), a steel sheet material 20 consisting of a heated high-temperature panel (steel material) 21 and an aluminum plating 22 is transported to the mold 30 in a heating furnace to which the water-soluble agent has been applied. For work efficiency, spraying the water-soluble agent using a sprayer is preferable, but manual application using a brush or the like is also acceptable.

[0018] When the hot steel plate material 20 is transported to the mold 30, the water-soluble agent applied to the surface of the mold 30 evaporates as the hot steel plate material 20 approaches, and the polymer and surfactant remain as residues, forming residue films 40 and 41 as shown in Fig. 7(C). The residue film 40 physically blocks the aluminum plating 22 and the iron material of the mold 30 that would otherwise form hydrogen bonds, thereby suppressing or preventing adhesion of the aluminum plating 22 to the mold 30.

[0019] If the retention of the residue film 40 is good, the quality of the hot stamped product can be maintained for a long period of time, which is economical, so the retention of the residue film 40 related to the water-soluble agent is important. If the retention is poor, the water-soluble agent must be applied frequently. Even if the retention is good, the water-soluble agent must be applied periodically to ensure uniformity of the applied surface, optimize the amount of application, and retain the residue film.

[0020] Fig. 8 shows an example of a square-headed drawn die for evaluating the adhesion of aluminum plating, and a comparison was made between a die coated with the water-soluble agent according to the present invention and a die not coated with the water-soluble agent after 12 hot stamping processes by measuring the adhesion (protrusions) using a three-dimensional measuring machine. As a result, as shown in Fig. 9, the remarkable effect of the present invention was confirmed. That is, in the case where the water-soluble agent was not coated, aluminum plating was already attached to the die by the 12th hot press after coating, whereas in the case where the water-soluble agent was coated, no adhesion of aluminum plating to the die was confirmed even after 12 hot presses were repeated after coating.

[0021] The water-soluble agent according to the present invention, which exerts the above-mentioned effects, suppresses or prevents adhesion of aluminum plating to a mold, but it is necessary to consider the influence on spot weldability. Spot welding (or resistance spot welding) is a method of joining metals together using the electric resistance of the metals, but if the concentration of the high molecular weight polymer is high, the amount of residue carried out from the molded product increases as shown in FIG. 10(A), current conduction inhibition increases, and sputtering is induced, resulting in poor weldability. Therefore, in the present invention, in order to ensure spot weldability, the mixing ratio of water to the high molecular weight polymer is increased to provide a water-soluble agent that does not impair spot weldability and prevents sputtering. In other words, if the concentration of the high molecular weight polymer is low, the amount of residue carried out from the molded product decreases as shown in FIG. 10(B), current conduction inhibition is also small, and sputtering is not induced. Therefore, the balance between the high molecular weight polymer and the spray frequency is important.

[0022] Higher spray frequency increases the retention of the residue film and also increases the cost of using the chemicals. The concentration of the high molecular weight polymer affects weldability and retention of the residue film, with low concentrations deteriorating weldability and retention of the residue film. If a low concentration is used to ensure weldability, retention of the residue film decreases, making it necessary to increase the frequency of spraying. In this way, the balance between spray frequency and chemical concentration is a trade-off between weldability and chemical cost, and there is a criterion for weldability.

[0023] In addition, for example, water repellency in the painting process of a car body is as follows: water repellency → poor degreasing → deterioration of paint adhesion → deterioration of the corrosion resistance of the actual car → corrosion → deterioration of strength → deterioration of safety, which reduces the safety of the car body, so it is necessary to determine the presence or absence of water repellency as a characteristic when applying the agent. By using a water-soluble polymer, the residue attached to the molded product is degreased in the painting process, and the deterioration of the paint film can be suppressed. Compounds such as fluorine and silicon tend to exhibit water repellency as compounds added to the agent, but fluoride compounds and silicon-based compounds with high water repellency are difficult to degrease, so they are not included in the water-soluble agent of the present invention. [Explanation of symbols]

[0024] 1,20 Steel plate material 2 Furnace 3 Molded products 4 Products 10, 11, 30, 31 Mold 40, 41 Residual film

Claims

1. A method for producing a product from an aluminum-plated steel sheet by a hot stamping process, comprising the steps of: applying a non-flammable, non-volatile water-soluble agent to a surface of a die facing the aluminum-plated steel sheet; and then producing the product.

2. The method for producing a hot stamped product according to claim 1, wherein the water-soluble agent is a mixture of a high molecular weight polymer, water and a surfactant.

3. 3. The method for producing a hot stamped product according to claim 2, wherein the mixing ratio of the water-soluble agent is 1 to 25 parts (wt%) of the high molecular weight polymer, 50 to 98 parts (wt%) of the water, and 1 to 25 parts (wt%) of the surfactant.

4. The method for producing a hot stamped product according to any one of claims 1 to 3, wherein the application is carried out periodically.

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