KR20110011086A - Vehicle member manufacturing method and side member using the same - Google Patents

Abstract

According to the present invention, TWB is made of a dissimilar thickness boron steel sheet or a boron steel sheet with a steel sheet of dissimilar material, and the tube is formed by tube control. By providing the strength of the material itself and structural stiffness using the closed section at the same time, and provides a vehicle member manufacturing method for manufacturing a vehicle member to induce the absorption direction of the collision energy sequentially and a side member using the same.

Member Production Method, Tube, TWB, Side Member, Hydroforming, Strength

Description

METHOD FOR FABRICATING A MEMBER OF VEHICLE AND SIDE MEMBER PRODUCED BY THE SAME}

The present invention relates to a method for manufacturing a vehicle member and a side member using the same, and more particularly, after fabricating TWB from a dissimilar thickness boron steel sheet or a boron steel sheet with a material of a general steel sheet of dissimilar material, and forming a tube by tube control. Method of manufacturing a member for a vehicle, which manufactures a member formed by hydroforming and secures the strength of the material itself and structural stiffness using the closed cross section through heat treatment, and induces the vehicle member to induce the absorption direction of the collision energy sequentially. The side member using this.

In general, when developing a new car for the first time in a car maker, various safety tests are conducted to verify the safety of the developed vehicle. This establishes a certain standard and checks the completeness according to whether the standard is appropriate.

In particular, safety in a vehicle is the most influential factor in the completeness of the vehicle, as it relates to the life of the rider, and many countries in the world apply the strictest standards to the safety of the vehicle. .

In this safety test, in particular, the vehicle front side member SM, as an example of a vehicle body to prepare for a frontal collision of the vehicle, has the crash box 1 and the stay 3 at the front end thereof, as shown in FIG. The bumper beam 5 is installed, the dash panel 7 is welded and assembled at the center, and the rear end thereof is welded and assembled with the center side member 9.

The front side member SM assembled as described above receives the first collision energy F from the front bumper beam 5 and then transfers the remaining collision energy F to the vehicle body. Function to pass to.

However, the conventional front side member SM is formed of an inner member 11 and an outer member 13 formed by press molding a steel-based steel sheet material, and thus there is a limit to satisfy the rigidity and light weight at the same time.

Accordingly, in recent years, research has been focused on new molding methods and high strength ultra-light weight new materials that can satisfy both rigidity and light weight at the same time.

Tailor Welded Blank (TWB), which manufactures tailored blanks from materials having different materials, thicknesses, and strengths, is an example of a new molding method applied to the front side member SM by such research and development. , TWB) technology or a hydroforming method, which is an integrated molding technology, is applied.

However, in the case of the above-described TWB technology, the front side member (SM) is manufactured by press molding a blank made of a material having a different strength, but rigidity and light weight can be reduced. It is not possible to manufacture it as a member at once, so it must be manufactured separately, like the inner member 11 and the outer member 13, and then assembled by a separate welding process, and a separate reinforcing member for local structural rigidity reinforcement. There are disadvantages such as the need to further configure.

On the other hand, the hydroforming method is focused on securing structural rigidity using a closed section rather than using a high strength steel sheet as an important molding factor in the elongation of the material.

Accordingly, the above-mentioned hydroforming method cannot be applied due to the problem of formability due to the increase in strength of the material itself, and there is still a limit in securing structural rigidity using the closed section.

In particular, in the case of the front side member (SM), the absorption direction of the collision energy is important in order to distribute the collision energy evenly to the vehicle body, so that the front side member (SM) to have the structural rigidity of the closed section through the hydroforming In one case, rather than the sequential absorption of collision energy, the local buckling occurs first, thereby impairing the safety of the vehicle.

Therefore, the present invention has been invented to solve the disadvantages and problems of the prior art through the new molding method and high strength ultra-lightweight new material research and development to satisfy the rigidity and light weight of the body parts at the same time, the problem to be achieved by the present invention TWB is made of dissimilar thickness boron steel plate or boron steel plate with different steel plate material, and it is formed by tube control. It is to provide a vehicle member manufacturing method and a side member using the same to secure the structural rigidity using its own strength and closed cross-section, and to produce a vehicle member to induce the absorption direction of the collision energy in sequence.

Vehicle member manufacturing method of the present invention for realizing the technical problem as described above comprises the steps of preparing a plurality of different blanks from a plurality of different steel sheet material; Arranging the heterogeneous blanks in consideration of collision energy absorption directionality to fabricate a tailored blank by laser welding along each taylor weld line; Manipulating the custom blank with tube control to laser weld along the tube weld line of the connection; Expanding the tube control in a hydroforming mold to produce one member molded product; Heating the member molded product to a high temperature above the transformation point temperature in a press hot forming die; Cooling the heated member molded article by rapid cooling to have a metal structure of high strength; Laser cutting the member molded article having the high strength metal structure along a trim line and a hole processing line.

The dissimilar steel sheet may be a plurality of boron steel sheets having different thicknesses.

The dissimilar steel sheet may be a boron steel sheet and a general steel sheet having different materials.

The boron steel sheet is preferably made of a ferrite metal structure of 30% or more elongation.

Each of the Taylor welding line is formed in a diagonal direction at a predetermined angle so as not to cross the tube welding line when forming the custom blank by tube control.

The rapid cooling is characterized by forming a cooling passage in which the refrigerant circulates in the press die to quench the water at a cooling rate of a predetermined speed or more.

The high strength metal structure is characterized in that the martensite structure.

According to the method for manufacturing a vehicle member according to the present invention as described above, TWB is made of a dissimilar thickness boron steel sheet or a boron steel sheet with a dissimilar thickness of ordinary steel sheet as a material and tubing molded by tube control, and then hydro By forming a member molded product by forming and transforming it into martensite structure through heat treatment, it is effective to manufacture a vehicle member that secures structural strength using the strength of the material itself and the closed section at the same time.

In addition, the front side member produced by the vehicle member manufacturing method described above is applied to a blank made of a boron steel sheet or a regular steel sheet having a different thickness or stiffness from the front so that collision energy is sequentially absorbed to improve crash absorption performance. It works.

In addition, according to the above-described method for manufacturing a member for a vehicle, due to the characteristics of the existing press molding process, it is impossible to manufacture a closed cross-sectional member at one time. There is an effect that can simultaneously solve the disadvantages of the conventional hydroforming method, which could not be applied to a high strength material due to the problem of the castle.

Hereinafter, the preferred configuration and operation of the present invention will be described in detail with reference to the accompanying drawings.

2 is a perspective view of a front side member manufactured by a method for manufacturing a vehicle member according to an embodiment of the present invention, and FIGS. 4 and 5 are process block diagrams and process diagrams of a method for manufacturing a vehicle member according to an embodiment of the present invention.

However, in describing the configuration of the present invention, the same components as those in the prior art will be described with the same reference numerals.

In order to explain the vehicle member manufacturing method according to the present embodiment, as an example of the vehicle member, the vehicle front side member SM will be described as an example, as shown in FIG. 2.

In the manufacturing method according to the present embodiment of the vehicle front side member SM, a boron steel sheet and a general steel sheet are applied as materials.

The boron steel sheet is a steel sheet to which a small amount of boron (B) is added. In the present embodiment, the boron-added steel, commonly known as 22MnB5, is a USIBOR 1500P material coated with Al + Si to prevent oxide film generation. use.

This boron steel sheet, as can be seen in the TTT (Time Temperature Transformation) showing the effect of the addition of boron shown in Figure 3 the effect of delaying the generation of martensite metal structure according to the temperature conditions by the addition of boron There is.

In the boron steel sheet, the boron is segregated in the austenite grain boundary at the temperature condition of 900 ° C. in the atomic state, thereby reducing the free energy of the austenite grain boundary, thereby suppressing the formation of the cornerstone ferrite nucleus, thereby significantly improving the hardenability of the steel.

On the other hand, the boron steel sheet has a tensile strength of about 500 ~ 800MPa in the ferrite structure before heat treatment, the elongation can also be hydroformed to 30% or more, the internal hardness is formed in or out of Hv200. The ferritic boron steel sheet is austenitic at a high temperature of 900 ° C. or higher and rapidly cooled to obtain martensite structure having a high tensile strength of about 1300 to 1600 MPa and an internal hardness of about Hv500.

Boron steel sheet after the heat treatment obtained here is 4 to 5 times higher in strength than the general steel sheet, but the weight can be reduced by up to 40% compared to the conventional, there is an advantage that can achieve the weight reduction and strength improvement of the body parts at the same time.

As shown in FIGS. 4 and 5, the method for manufacturing the vehicle front side member SM according to the present embodiment using the physical properties of the boron steel sheet is a 1.4 t general steel sheet having 1.2 elongation and 1.2 as described above. Heterogeneous blank material preparation step (S1) to prepare a heterogeneous blank (B1, B2, B3) for producing the front side member (SM) from the boron steel sheet 20 of t and 1.8t.

At this time, the boron steel sheet 20 is applied to the ferrite metal structure of the elongation is more than 30%.

Subsequently, in consideration of the collision energy absorption direction of the front side member SM, the normal steel sheet blank B1 of 1.4t and the boron steel sheet blanks B2 and B3 of 1.2t and 1.8t are arranged in order, and then each tailor weld line ( A tailored blank fabrication step (S2) of fabricating a tailored blank 30 is performed by irradiating the laser beam LB along with laser beam TW.

As such, when the custom blank 30 is manufactured, the tube blank tube is welded to the tube control 40, and the tube tube and the welding step are irradiated and laser-joined by irradiating a laser beam LB along the joint weld line W, which is a connecting portion thereof. Proceed to (S3).

At this time, it is important that the welded portion of the tube control 40 is laser welded so as to be highly integrated by the laser beam LB.

Here, in the process of manufacturing the custom blank 30, each Taylor welding line (TW) is a constant so as not to cross each other in the tube welding line (W), when forming the custom blank 30 to the tube control (40). It is important to be formed in the diagonal direction of the angle θ.

As such, the tube control 40 is inserted into the hydroforming mold 15 to perform a hydroforming step (S4) of manufacturing one integral front side member molded product 50 by expansion of the hydraulic pressure.

Here, after the fitting blank 30 is annealed by the tube control 40, the joint portion joined by laser welding transforms the tissue into martensite structure by heat input, but the heat input part is localized so that the martensite structure of the joint part is localized. It is minimized and joined linearly along the tube weld line (W), rather advantageously for hydroforming by expansion.

Subsequently, the front side member molded product 50 expanded by the hydroforming is introduced into the press hot forming mold 17 and the heat treatment step S5 of heating to a high temperature above the transformation point temperature is performed.

That is, the front side member molded product 50 is heated to a high temperature of 900 ° C. or more, which is a transformation point temperature, for a predetermined time through a press hot forming die 17 (hot stamping molding die).

Subsequently, rapid heating of the heated front side member molded product 50 is performed so that the metal structure has a high strength martensite structure.

Here, the rapid cooling is preferably formed by the cooling passage 19 through which the refrigerant circulates inside the press hot forming die 17 and quenching the water at a cooling rate of a predetermined speed or more.

As a result, the heated front side member molded product 50 is austenitic at a high temperature of 900 ° C. or higher in a ferrite (P) structure whose metal structure has a strength of about 500 to 800 MPa before heat treatment, and then rapidly cooled to 1300 to 1600 MPa. It will have a martensite structure with a high degree of strength.

At this time, the rate of rapid cooling is ideally a cooling rate of 57 ℃ / sec or more, in addition to the water cooling quenching method such as oil cooling or forced air cooling may be applied.

Laser cutting step (S7) of cutting the high strength front side member molded article 50 of martensitic metal structure produced through these steps using the laser beam LB along the trim line TL and the hole processing line HL. Proceed).

Thus, by processing the hole (H) for the assembly and positioning of the unnecessary portion (T) and other body parts from the high-strength front side member molded article 50 described above, It is to produce a front side member (SM) for a vehicle having rigidity at the same time.

Therefore, the method for manufacturing a vehicle member as described above is a regular steel sheet blank (B1) having a thickness of 1.4t and a ferrite structure having an elongation of 30% or more, and boron steel sheet blanks (B2, B3) having a thickness of 1,2t and 1.8t in that order. After welding to produce a custom blank (30), and tube tube 40 is formed again, and then produced by the front side member molded product 50 in the hydroforming mold (15), press hot forming mold ( 17; transforming into martensite structure through heat treatment and quenching process in a hot stamping mold) to produce a vehicle front side member (SM) having both high strength of the material itself and structural rigidity using a closed section.

On the other hand, when manufacturing the front side member (SM) by the vehicle member manufacturing method as described above, the collision energy by applying a custom blank 30 made of ordinary steel sheet and boron steel sheet having a different thickness and rigidity from the front By inducing to sequentially absorb, if the structural rigidity of the closed cross-section through the hydroforming to the conventional single material, it is possible to solve the disadvantage of causing the local buckling first rather than the sequential absorption of the collision energy.

As a result, the vehicle front side member SM is improved in its collision performance without additional reinforcement, and can achieve high strength and light weight.

In addition, the vehicle front side member (SM) is formed in a press mold (not shown) due to the characteristics of the existing press molding process, bar members of the closed cross-sectional shape can not be produced at one time, respectively as inner member and outer member The disadvantages of fabricating and assembling each other and the drawbacks of the hydroforming method, which could not be applied to high strength materials due to formability problems, can be solved simultaneously.

While the present invention has been described above with reference to embodiments which are considered to be practical at present, the present invention is not to be understood as being limited to the above embodiments. Rather, the present invention belongs to the above-described embodiments of the present invention. It should be construed as including all modifications that are easily changed by those skilled in the art to be considered equivalent.

1 is an assembled perspective view of a general front side member.

2 is a perspective view of a front side member manufactured by the method for manufacturing a vehicle member according to an embodiment of the present invention.

3 is an isothermal cooling transformation curve (TTT: Time Temperature Transformation) showing the effect of the addition of boron.

4 is a process block diagram of a method for manufacturing a member for a vehicle according to an embodiment of the present invention.

5 is a process chart of the manufacturing method for a vehicle member according to an embodiment of the present invention.

Claims (8)

In the vehicle member manufacturing method, Preparing a plurality of different blanks based on the plurality of different steel sheets; Arranging the heterogeneous blanks in consideration of collision energy absorption directionality to fabricate a tailored blank by laser welding along each taylor weld line; Manipulating the custom blank with tube control to laser weld along the tube weld line of the connection; Expanding the tube control in a hydroforming mold to produce one member molded product; Heating the member molded product to a high temperature above the transformation point temperature in a press hot forming die; Cooling the heated member molded article by rapid cooling to have a metal structure of high strength; And laser cutting the member molded article having the high-strength metal structure along the trim line and the hole processing line. In claim 1, The dissimilar steel sheet is Vehicle member manufacturing method, characterized in that a plurality of boron steel sheet having a different thickness. In claim 1, The dissimilar steel sheet is Vehicle member manufacturing method, characterized in that the material is a boron steel sheet and a general steel sheet. The method of claim 2 or 3, The boron steel sheet is Vehicle member manufacturing method characterized in that the ferrite metal structure of more than 30% elongation. In claim 1, Each taylor weld line is The method of manufacturing a member for a vehicle, characterized in that formed in the oblique direction at a predetermined angle so as not to intersect at the tube weld line when forming the custom blank by tube control. In claim 1, The rapid cooling is And forming a cooling flow path through which the refrigerant circulates in the press die to quench the water at a cooling speed of a predetermined speed or more. In claim 1, The high strength metal structure is Method for producing a member for a vehicle, characterized in that the martensite organization. The side member manufactured by the vehicle member manufacturing method of any one of Claims 1-7.

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