Manufacturing method of hot-stamped product

Abstract

The present invention relates to a manufacturing method of a hot-stamped product, manufacturing the product (including parts) from a steel sheet through a hot stamping (hot-press) process, and it is possible to inhibit or prevent an adhesion (agglutination) of aluminum plating to a hot-stamping mold when manufacturing the product from the aluminum plating steel sheet in particular.

Description

BACKGROUND OF THE INVENTION1. Technical Field of the Invention

[0001] The present invention relates to a manufacturing method of a hot-stamped product, for manufacturing the product (including parts) from a steel sheet through a hot stamping (hot-press) process, and particularly to the manufacturing method of the hot-stamped product that is possible to inhibit or prevent adhesion (agglutination) of aluminum plating to a hot-stamping mold when manufacturing the product from the aluminum plating steel sheet.2. Description of the Prior Art

[0002] The hot stamping process is a process, for example, shown in FIGS. 1A to 1D. That is, first, a steel sheet material 1 as shown in FIG. 1A is prepared, and the steel sheet material 1 is carried into a heating furnace 2 as shown in FIG. 1B and is heated (for example at 900° C.) and is press-worked by a mold. A processed product is further molded and quenched as shown in FIG. 1C, and the molded product 3 is processed as appropriate to finally obtain the product 4 as shown in FIG. 1D. In this case, the aluminum plating steel sheets are generally used as the steel sheet material 1 for the prevention of oxidation scale and the improvement of corrosion resistance of the steel sheet.

[0003] Now, in case of using the aluminum plating sheet as the steel sheet material, in the hot stamping that has press-forming and quenching the heated steel sheet with heating the steel sheet greater than or equal to austenitic transformation temperature (Ac three point), the steel sheet is carried after heating it in the heating furnace for hot-stamping shown in FIG. 2A, and is then quenched and molded by concave and convex molds 10 and 11 as shown in FIG. 2B. However, an aluminum plating layer cannot follow to the modification of the material (steel) at the molding time. In this way, the aluminum plating layer peels from the steel sheet, and the aluminum plating adheres (agglutination) on the surface of the mold. FIGS. 3A and 3B show the situations on which the aluminum plating truly adhesives on the mold. The adhesion is transcribed to the subsequent product if the aluminum plating adheres on the mold, in this way, a quality defect of the product is caused by generating product depressions, such as dent, shown in FIG. 4A or appearance cracks (galling) like scratch shown in FIG. 4B. The quality defect of the product is a fatal problem.

[0004] The adhesive material (the aluminum plating) is rigid and cannot absolutely be removed by an easy work such as rubbing by hands or wiping off with cloth. Thus, it is necessary to remove the adhesive material with a machine operation such as scraping off by a grinder. However, in case scraping off by the grinder, the surface of the mold is also often scrape off with the adherent aluminum plating, thereby causing the abrasion or degradation of the expensive mold.

[0005] As the countermeasure to the above problems, the coating (for example, DLC (Diamond-Like Carbon), AlCrN, AlCrTi) is generally applied on the surface of the mold. However, the inhibitory effect of the aluminum plating adhesion to the mold is small, moreover, there is a problem in that the coating layer peels off during molding, as shown in FIG. 5. Furthermore, when attempting to remove the adhesive material by using the grinder or the like, the coating layer may be damaged or peeled off. Consequently, the effectiveness of the coating is extremely short-lived.SUMMARY OF THE INVENTION

[0006] The present invention has been made in view of the above described problems, and an object of the present invention is to provide a manufacturing method of a hot-stamped product, for manufacturing the product (including the parts) from the steel sheet through a hot stamping (hot-press) process, and it is possible to inhibit or prevent an adhesion (agglutination) of aluminum plating to a hot-stamping mold.

[0007] In accordance with the present invention, there is provided an method for manufacturing a hot-stamped product from an aluminum plating steel sheet, and an object of the present invention is achieved by providing a method for manufacturing a product after applying the water-soluble agent, which is non-flammability and non-volatility, to the surface of the mold opposing to the aluminum plating steel sheet.

[0008] In accordance with the present invention, there is further provided the manufacturing method of the hot-stamped product, wherein the water-soluble agent is a mixture of macromolecular polymer, water and surfactant; wherein the mixing ratio of the macromolecular polymer is 1 to 25 part by weight (weight %) to the water-soluble agent, the mixing ratio of the water is 50 to 98 part by weight (weight %), and the mixing ratio of the surfactant is 1 to 25 part by weight (weight %); and wherein the application to the surface of the mold is regularly performed.

[0009] That is, the present invention is the manufacturing method of the hot-stamped product, for making from aluminum plating steel sheet to the product by the hot-stamping process, comprising steps of: preparing the water-soluble agent having no flammability and non-volatility, where the mixing ratio of the macromolecular polymer is 1 to 25 part by weight (weight %), the mixing ratio of the water is 50 to 98 part by weight (weight %) and the mixing ratio of the surfactant is 1 to 25 part by weight (weight %); applying the water-soluble agent to the surface of the mold opposite to the aluminum plating steel sheet; and manufacturing the product after application of the water-soluble agent, thereby to apply the water-soluble agent to the surface of the mold so as to inhibit or prevent the adhesion of the aluminum plating.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In the accompanying drawings:

[0011] FIGS. 1A to 1D are a schematic flow chart showing one example of a hot-stamping process;

[0012] FIGS. 2a and 2B are a schematic flow chart showing an aspect of a heating and a quenching of an aluminum plating steel sheet;

[0013] FIGS. 3A and 3B are image views showing an example of an adhesion of the aluminum plating to the mold;

[0014] FIGS. 4A and 4B are image views showing one example of a product transcription of an adhesive material of the mold;

[0015] FIG. 5 is an image view showing a peeling example of the mold coating;

[0016] FIGS. 6A and 6B are schematic views showing a concept of an assumption of the present invention;

[0017] FIGS. 7A to 7C are a schematic flow chart for explaining a principle of the present invention;

[0018] FIG. 8 is an external view of a square head drawing mold for proving the effect of the present invention;

[0019] FIG. 9 is an external view of parts showing the effect of the present invention; and

[0020] FIGS. 10A and 10B are a conceptual scheme for explaining the composition of the water-soluble agent of the present invention.DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Inventors of the present invention assume that the causing factor of the previously described adhesion (the agglutination) to the mold of the aluminum plating is that the aluminum plating adheres to iron (Fe) by an action of hydrogen bond as shown in FIG. 6B, because aluminum (Al) has hydrophilicity, and the iron (Fe), which is a material of the mold, has also the hydrophilicity (refer to FIG. 6A). On the basis of this assumption, in order to inhibit or prevent the adhesion to the mold of the aluminum plating, the inventors discovered from many experimentation tests that the hydrogen bond should not be generated as shown in FIG. 6B.

[0022] In this connection, the inventors supposed to inhibit or prevent the above hydrogen bond if a water-soluble material was coated on the surface of the mold, and produced a water-soluble agent which is mixture of easily-obtained macromolecular polymer, water and surfactant as the water-soluble material. The water-soluble agent has non-flammability and non-volatility and further has lubricity that is a low frictional coefficient to the aluminum plating, and retention of a residue film is excellent. Then, the inventors many times tested the produced water-soluble agent in the hot-stamping process and found that it has a notable effect as a result of the tests. Although the surfactants are such as anionic surfactant (anion), cationic surfactant (cation), amphoteric surfactant (ampho-ion), non-ionic surfactant (non-ion) and so on, any of them is / are optionally selected. Press forming oil is generally used in a cold press molding, however it is essential that the water-soluble agent according to the present invention is particularly non-flammable so the press forming oil has strongly flammability and generates soot.

[0023] The water-soluble agent according to the present invention is produced by the below mixing ratios.

[0024] Macromolecular polymer: 1 to 25 part by weight (weight %)

[0025] Water: 50 to 98 part by weight (weight %)

[0026] Surfactant: 1 to 25 part by weight (weight %)

[0027] By mixing and stirring within the ratio of above range, the water-soluble agent according to the present invention is prepared. So it affects a film property, a film thickness, or a lubricant effect if not preparing within the above range, inhibitory or resistance, weldability, and degreasing power of the adhesion (the agglutination) to the mold are impaired.

[0028] In the present invention, a highly-heated panel (steel material) 21 and a steel sheet material 20 made of an aluminum plating 22 shown in FIG. 7B are carried to a mold 30 after uniformly applying the water-soluble agent to the whole surface of the mold 30 by a sprayer and so on as shown in FIG. 7A. With regard to the application of the water-soluble agent, spraying by the sprayer is preferable on an efficiently performance, however, manually spraying by a paintbrush of hand work and so on is also capable.

[0029] When the high-temperature steel sheet material 20 is carried to the mold 30, only the water in the water-soluble agent applied to the surface of the mold 30 evaporates as the high-temperature steel sheet material 20 approaches, and the macromolecular polymer and the surfactant remains as the residue and forms residue films 40 and 41 as shown in FIG. 7C. The residue film 40 physically intercepts the aluminum plating 22 and an iron material of the mold 30, which are bonded by hydrogen bonding, so it is possible to inhibit or prevent the adhere to the mold 30 of the aluminum plating 22.

[0030] The retention of the residue film 40 according to the water-soluble agent is important, since a quality of the hot-stamped product can be kept and is economical for a long time if the retention of the residue film 40 is good. If the retention is no good or bad, the application of the water-soluble agent must be quite often done. Even if the retention is good, the application of the water-soluble agent is regularly necessary in order to retain the uniformity of the applying surface, the optimization of the application quantity and the retention of the residue film.

[0031] FIG. 8 shows an example of the square head drawing mold for evaluating the adhesion of the aluminum plating in comparison with a mold being applied the water-soluble agent of the present invention and a mold not being applied the water-soluble agent thereof. They are respectively measured with the measurement of the adhesion (convex) by a three-dimensional (3D) measuring apparatus after the hot-stamping process is performed twelve times. As a result, the notable effect of the present invention is identified as shown in FIG. 9. That is, the aluminum plating already adheres to the mold on twelve times of the hot-press after applying in case of no application of the water-soluble agent. While, in case of there is the application of the water-soluble agent, no adhesion of the aluminum plating to the mold is not entirely confirmed even if repeating the hot-press twelve times after the application.

[0032] The water-soluble agent of the present invention, which has above effective, inhibits or prevents the adhesion of the aluminum plating to the mold, as well as, has necessary to allow for an effect to a spot weldability. The spot welding (or the resistance spot welding) means a method for joining metal to metal each other by using the electric power resistance which metal has. However, if the macromolecular polymer has a high concentration, the residue on the molding becomes larger as shown in FIG. 10A, an electric conduction blocking becomes larger, and the weldability becomes worst by spattering. In this connection, in the present invention, the water-soluble agent is the agent not to injure the spot weldability by raising up the mixing content of the water to the macromolecular polymer in order to secure the spot weldability and thus to prevent the generation of the sputter. That is, if the macromolecular polymer has a low concentration, the residue on the molding becomes smaller as shown in FIG. 10B, the electric conduction blocking also becomes smaller, and the weldability becomes no sputtering. Therefore, the balance between the macromolecular polymer and a spray frequency is important.

[0033] The retention of the residue film is improved when the spray frequency is high, while the cost for using the agent also increases. The concentration of the macromolecular polymer is influenced by the weldability, the retention of the residue film, and the weldability and the retention of the residue film are respectively getting worse if the concentration is low. Consequently, the retention of the residue film is lower in case the concentration of the macromolecular polymer is low for an insurance of the weldability, it becomes necessary to increase the spray frequency. In this way, the balance between the spray frequency and the agent concentration has a relation of the trade-off between the weldability and the agent cost, and there is a criteria for the weldability.

[0034] Moreover, for example, the water repellency in the vehicle body painting process is “water repellent”→“poor degreasing”→“deterioration of the paint film adhesion”→“decrease of the corrosion resistance of the actual vehicle”→“corrosion”→“strength decrease”→“safety decrease”, and thus the water repellency reduces the safety of the vehicle body. Accordingly, with the application of the agent, it is necessary to determine the presence or absence of the water repellency as a characteristic. By using the water-soluble macromolecular polymer, the residue attached to the molded product is degreased during the coating process, and therefore it is possible to suppress the deterioration influence of the coating properties. Although the compounds such as fluorine, silicon (e), as the material adding to the agent, have an inclination indicating the water-repellent. The materials, such as fluorine compound, or silicone compounds, having the high water-repellent do not contain as the water-soluble agent according to the present invention since it is difficult to degrease.

[0035] According to the manufacturing method of a hot-stamped product of the present invention, it is possible to inhibit or prevent the adhesion (the agglutination) of the aluminum plating to the mold and thus improve the quality of the product by applying the water-soluble agent being the mixture of the macromolecular polymer, the water and the surfactant to the surface of the mold of the aluminum plating steel-sheet hot-stamping, and to reduce the abrasion or the degradation of the high-expensive mold without the step of removing the adhesion by the grinder and so on. Therefore, the economic benefits of product manufacturing are also significant. The great effect can be obtained by the extremely easy work, so the inhibition or prevention of the aluminum plating application to the mold can be only performed to apply the water-soluble agent to the whole surface of the mold.

Claims

1. A manufacturing method of a hot-stamped product, for making from aluminum plating steel sheet to a product by a hot-stamping process, comprising steps of:preparing water-soluble agent having no flammability and non-volatility, where a mixing ratio of macromolecular polymer is 1 to 25 part by weight (weight %), a mixing ratio of water is 50 to 98 part by weight (weight %) and a mixing ratio of surfactant is 1 to 25 part by weight (weight %);applying said water-soluble agent to a surface of a mold opposite to said aluminum plating steel sheet; andmanufacturing said product after application of said water-soluble agent,thereby to apply said water-soluble agent to said surface of said mold so as to inhibit or prevent adhesion of aluminum plating.

2. The method according to claim 1, wherein said application of said water-soluble agent is regularly performed.

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