KR101190396B1 - Taylor welded hot stamping method and steel parts using the same - Google Patents

Abstract

The present invention relates to a method for producing a molded article using a steel sheet, and more particularly, to a molded article having different strengths locally by joining materials of different materials and a method of manufacturing the same.

The present invention provides a blank material (material A) having a hardenability and a blank material (material B) which does not have a hardenability; A laser welding step of joining the material A and the material B by laser welding; A heating step of heating the joined material to a molding temperature; A press molding step of forming a molded body by hot forming the heated material into a press mold; Taylor Welded Hot Stamping (Taylor Welded Hot Stamping) forming method comprising a; quenching step of quenching the molded body by cooling the press die in a state in which the press die is closed.

Taylor Welded Blanking (TWB), Hot Stamping, Heterogeneous Strength

Description

Taylor welded hot stamping manufacturing method and molded body having local heterogeneous strength using same {Taylor welded hot stamping method and steel parts using the same}

The present invention relates to a method for producing a molded article using a steel sheet, and more particularly, to a molded article having a locally different strength by joining materials of different materials and a method of manufacturing the same.

Vehicles with various strengths are used. For example, parts that need to absorb energy in a vehicle crash require relatively weak strength, and parts that require shape maintenance to protect occupants need strong strength.

If the part that needs to absorb energy at the time of collision is too high, the impact energy is not properly absorbed and transferred to another part as it is, rather it causes a problem of transmitting excessive shock to the passengers and other parts of the vehicle.

Vehicles are constantly required to be lighter in weight and lower in cost, and accordingly, it is necessary for one part to have different heterogeneous strengths.

Some sections of components require high strength to protect occupants, while others require relatively low strength to absorb impact energy.

Such parts are typically the B-pillar of a passenger car.

1 is an enlarged perspective view of a vehicle body structure and a B pillar portion of an automobile.

The B pillar 1 of the vehicle refers to a portion connecting the roof of the vehicle body with the roof between the front door and the rear door of the passenger vehicle.

A collision reinforcement is coupled to the B-pillar 1, where the lower portion 1b of the collision reinforcement requires relatively low tensile strength, and the upper portion 1a requires high tensile strength. The reason for the difference in strength is that the part that must maintain the shape with high strength during the vehicle crash and the part that must absorb the shock while being crushed are needed at the same time.

In order to secure a stable space for the passenger, the upper portion 1a of the B-pillar 1 has to be maintained in shape, so high strength is required. If the strength of the upper portion 1a of the B-pillar 1 is not secured, when the vehicle is overturned, the roof falls and poses a great threat to the safety of the passengers. However, since the lower portion 1b of the B-pillar 1 must be deformed and absorb impact energy, relatively low strength is required. If the lower portion 1b of the B-pillar 1 also has a high strength, the impact energy is transmitted to other structural members because the collision energy is not absorbed during side impact.

The specific required strength will vary depending on the type or shape of the vehicle, but in the case of the upper portion 1a of the B pillar 1, a tensile strength of about 1500 MPa is required, whereas in the case of the lower portion 1b of the B pillar 1 A tensile strength of about 440 MPa is required.

Conventionally, after forming a part from a material having a low strength, a method of attaching a separate reinforcement to a portion requiring high strength has been used, but a need for manufacturing a single part has been raised to reduce the weight of a vehicle.

In order to solve this problem, the present invention is to provide a manufacturing method capable of manufacturing parts having different strength locally by bonding a material having a hardenability and a material having no hardenability, and then performing a hot stamping process. will be.

It is an object of the present invention to provide a method for producing molded articles having locally different strengths.

Another object of the present invention is to provide a method for producing a molded body that is applied together with a tailored blanking and a hot stamping method.

Another object of the present invention is to provide a molded body having a locally heterogeneous strength and reducing the total weight.

The present invention for solving this object is to provide a blank material (material A) having a hardenability and a blank material (material B) having no hardenability, respectively; A laser welding step of joining the material A and the material B by laser welding; A heating step of heating the joined material to a molding temperature; A press molding step of forming a molded body by hot forming the heated material into a press mold; Taylor Welded Hot Stamping (Taylor Welded Hot Stamping) forming method comprising a; quenching step of quenching the molded body by cooling the press die in a state in which the press die is closed.

After the quenching step, may further include a shot blasting step of removing the oxide scale formed on the material B.

The material A is formed of a boron steel sheet, the material B is preferably formed of a cold rolled steel sheet.

Forming temperature of the heating step is preferably 768 ~ 1000 ℃,

The cooling rate of the cooling step is preferably -20 ℃ / sec ~ -100 ℃ / sec.

The present invention by applying the Taylor welded blanking method and the hot stamping method in parallel, by joining different materials to produce a molded body, there is an effect that can produce a vehicle part having a locally different strength.

In addition, the present invention by reducing the overall weight compared to the method using a conventional reinforcing member by achieving a locally different strength to the differentiation of the material, thereby bringing the effect of providing a molded body to help reduce the weight and improve fuel efficiency of the vehicle. .

Hereinafter, with reference to the accompanying drawings, a description will be made to the Taylor welded hot stamping molding method of the present invention and a molded article having local heterogeneous strength using the same.

Advantages and features of the present invention, and methods for achieving them will be apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, only the present embodiments to make the disclosure of the present invention complete, and common knowledge in the technical field to which the present invention belongs. It is provided to fully inform the person having the scope of the invention, which is defined only by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

In addition, the size of the components constituting the invention in the drawings are exaggerated for clarity of the specification, when any component is described as "exists inside, or is installed in connection with" other components, any of the above configuration An element may be installed in contact with the other component, may be installed at a predetermined distance, and when installed at a distance, a third element for fixing or connecting the component to the other component The description of the means may be omitted.

2 is a process flowchart showing a tailored welded hot stamping molding method according to an embodiment of the present invention, Figure 3 is a flow chart showing a tailored welded hot stamping molding method according to an embodiment of the present invention, Figure 4 is a filler component Fig. 5 is a plan view showing blank materials, and Fig. 5 is a plan view showing a state in which two materials are joined by laser welding, and Fig. 6 is a plan view showing a filler part in which molding is completed.

Referring first to Figure 2, Taylor Welded Hot Stamping (Taylor Welded Hot Stamping) molding method according to an embodiment of the present invention is a blank material (material A) having a hardenability and a blank material (material B) having no hardenability A material preparing step (S-21) to be prepared respectively, a laser welding step (S-22) of joining the material A and the material B by laser welding, and a heating step of heating the joined material to a molding temperature (S- 23), a press molding step (S-24) of forming a molded body by hot forming the heated material into a press mold, and a quenching step of quenching the molded body by cooling the press mold while the press mold is closed ( S-25) and a shot blasting step (S-26) for removing the scale of oxidation formed on the material B.

The shot blasting step S-26 is not a necessary process. If both materials do not generate an oxidation scale, the shot blasting step S-26 may be omitted.

Referring to FIG. 3, in the material preparation step S-21, blank materials are precisely blanked as shown in the left side of the drawing to prepare the material A 30 and the material B. As shown in FIG. At this time, the part requiring high strength is blanked using boron steel, and the part requiring relatively low strength is blanked using general cold rolled steel.

Next, the material A 30 and the material B 40 are aligned with each other, and then bonded together using the laser welder 50. In this case, the material A 30 and the material B 40 may have different thicknesses. This is because a portion requiring high strength requires a relatively thick thickness.

Next, the joined material is heated to the molding temperature in the heating device 60. Since 1500MPa-class parts are difficult to be processed by general press molding, they are heated to a molding temperature capable of securing the formability of the raw material and supplied to the press apparatus 70.

The press apparatus 70 includes a cooling channel therein, and uses a mold in which a mold can be rapidly cooled by a coolant supplied to the cooling channel.

After loading the heated material into the press apparatus 70, the press apparatus 70 is closed and a molded object is formed. At this time, since the molded body is still maintained at a high temperature, unexpected deformation may occur when the press apparatus 70 is immediately opened and the molded body is cooled. Therefore, the quenching step with the molded body constrained with the press apparatus 70 closed Will be performed.

The section requiring high strength is formed of the material A 30, and the section requiring relatively low strength is formed of the material B 40, so that one molded body can have different strength for each section, thereby providing additional reinforcement. It is to have a heterogeneous strength locally with only a single part without using a member.

For example, in the case of manufacturing a filler part of a vehicle, as shown in FIG. 4, the blank material 30 constituting the upper part of the filler is provided using a boron steel sheet having hardenability, and the blank constituting the lower part. The raw material 40 is prepared using a general steel plate.

Boron steel is a steel in which hardenability is improved by adding boron (B) instead of expensive alloy elements nickel (Ni), chromium (Cr), and molybdenum (Mo). Boron steel has excellent toughness and impact resistance, and is particularly used for parts of automobiles and heavy construction equipment because of its high strength, high hardness, and high wear resistance.

Generally, boron steel is manufactured through a steelmaking process, a casting process, a rolling process, a forging process, and a heat treatment process. Here, the steelmaking process is a process of dissolving scrap to obtain a desired molten steel component and temperature. The steelmaking process includes an electric melting step, a LF (Laddle Furnace) refining step, and a degasing step.

Increasing demand for fuel efficiency and weight reduction of vehicles is increasing the required strength of the metal moldings applied to the vehicle. In some sections, high strength of 1500 MPa is required. In the case of such strength, general press molding alone does not produce a desired product shape. This high-strength material is manufactured by heating to a molding temperature using a boron steel material having a hardenability and then quenching to improve strength.

However, since the boron steel is expensive compared to the general cold rolled steel sheet, and as shown in the background art, some parts of the vehicle require different strengths for each section, the present invention uses a boron steel sheet for a portion requiring high strength, and Where cold strength is required in areas where low strength is required, it is to meet the strength standards required by vehicle manufacturers and to reduce the cost of parts.

After blanking the boron steel material having hardenability to the A material 30 and the B material 40 of the general cold rolled steel material having no hardenability, the A material 30 and the B material 40 are TWB (Tailored). Weld Blank: It is bonded by a custom welding foundation method to prepare a bonded blank material as shown in FIG.

In addition, the A material is preferably provided with an Al-Si coating layer, but is not necessarily provided with an Al-Si coating layer. Al-Si coating layer suppresses the generation of oxide scale on the surface of the material during hot stamping process.

The B material of the general cold rolled steel sheet may be provided with an Al-Si coating layer, and when the Al-Si coating layer is not provided, a shot blasting process for removing oxide scale is required. In addition, a GI steel sheet or a GA steel sheet, which is a zinc coating material, may be used as the B material.

The prepared material A and the material B are joined in the laser welding step (S-22).

The method of cutting the material precisely and joining by laser welding is called TWB (Taylor Welded Blanking) method. The TWB method combines steel sheets according to the usage environment before forming a plurality of homogeneous or dissimilar steel sheets. Then, the welding part of a steel plate is welded with a laser welder.

The material joined in the welding step (S-22) is heated to a predetermined molding temperature in the heating step (S-23), and then molded in the press molding step (S-24) in the heated state. At this time, the molding temperature is preferably in the range of 768 ℃ ~ 1000 ℃.

The reason is that the steel is usually heated to the austenite stabilization temperature to obtain a structural state that can secure the strength required by the component after quenching, and when the temperature is above 1000 ° C, the coating layer formed on the surface of the material may evaporate. Because.

Specifically, the heated material is loaded into the press mold in the heated state, and is molded while the press mold is closed. Next, the quenching step (S-25) is passed, the quenching step (S-25) is carried out in a state in which the press mold is closed. In order to prevent the spring back shape of the material and to maintain the desired shape, quenching for hardening is performed with the press mold closed.

At this time, the cooling rate is preferably in the range of -20 ℃ / sec ~ -100 ℃ / sec.

The reason is to facilitate the phase transformation into martensite tissue (martensite). In other words, when the molded body is cooled to a cooling rate of less than -20 ℃ / sec when heated to a high temperature, the structure may have a pearlite or bainite structure may not have sufficient strength have. Therefore, it is preferable to maintain the quenching speed so that the phase transformation of the base iron portion of the molded body can be achieved in a completely martensite structure.

When the quenching process is performed after high temperature molding, in the case of a material having no Al-Si coating layer on the surface, an oxide scale layer is formed on the surface.

In order to remove this, it is preferable to further include a shot blasting step after the quenching step S-25.

When the molded article is manufactured through such a process, a part formed of the A material having hardenability has a high strength, and a part molded of the B material having no hardenability has a relatively low strength.

Such parts having locally dissimilar strength typically include a filler of a vehicle, and the upper part supporting the loop has high strength, and the lower part requiring shock absorption due to a collision can produce a molded article having low strength. The filler parts of the vehicle having heterogeneous strengths thus have an ideal S-shape in which the upper part has a small amount of deformation and the lower part has a deformation.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above embodiments but may be manufactured in various forms, and having ordinary skill in the art to which the present invention pertains. It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without changing the technical spirit or essential features of the present invention. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

1 is an enlarged perspective view of a vehicle body structure and a B-pillar part of the vehicle;

2 is a process flow chart showing a tailored welded hot stamping forming method according to an embodiment of the present invention,

3 is a process chart showing a tailored welded hot stamping forming method according to an embodiment of the present invention,

4 is a plan view showing the blank materials of the filler part,

5 is a plan view showing a state in which two materials are bonded by laser welding;

6 is a plan view showing a filler component is completed molding.

Claims (9)

A material preparation step of providing a blank material (material A) having curability and a blank material (material B) not having curability; A laser welding step of joining the material A and the material B by laser welding; A heating step of heating the joined material to a molding temperature; A press molding step of forming a molded body by hot forming the heated material into a press mold; And And a quenching step of quenching the molded body by cooling the press die in a state in which the press die is closed. Taylor A welded hot stamping molding method characterized in that the material A or material B is provided with an Al-Si coating layer. The method of claim 1, After the quenching step, Taylor welded hot stamping molding method characterized in that it further comprises a shot blasting step of removing the oxide scale formed on the material B. The method of claim 1, Taylor A welded hot stamping molding method characterized in that the material A is formed of a boron steel sheet. The method of claim 1, Taylor welded hot stamping forming method characterized in that the material B is formed of a cold rolled steel sheet. delete The method of claim 1, Taylor Welded hot stamping molding method characterized in that the material A and the material B is different in thickness. The method of claim 1, The forming temperature of the heating step is Taylor welded hot stamping molding method, characterized in that 768 ℃ ~ 1000 ℃. The method of claim 1, Taylor cooling hot stamping molding method characterized in that the cooling rate of the cooling step is -20 ℃ / sec ~ -100 ℃ / sec. A molded article having a heterogeneous strength produced by the method of any one of claims 1 to 4 and 6 to 8.

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