KR101825427B1 - Method for manufacturing vehicle body parts - Google Patents

Abstract

A method for manufacturing an improved vehicle body part capable of coping with various impact performance requirements, comprising the steps of: a) blanking a steel plate having a surface plated layer; b) rolling the blank so as to have at least two regions of different thickness; c) heating the rolled blank to austenite temperature range, followed by hot press forming and cooling, wherein a hole is formed in the blank in a) and the hole position is arranged in the area where the rolling takes place in step b) A manufacturing method of a vehicle body part is introduced.

Description

METHOD FOR MANUFACTURING VEHICLE BODY PARTS [0001]

The present invention relates to a method of manufacturing a vehicle body part by hot stamping.

One of the biggest buzzwords in the automotive industry is light weight and high strength, and hot stamping technology is at the center of these issues. The hot stamping technique is described in detail in British Patent No. 1490535 of Norrbottens Jarnverk A. B. of Sweden.

Hot stamping is characterized in that a steel sheet is heated to a high temperature of Ac3 or higher in a heating furnace, and then subjected to heat treatment at the same time as molding in a press to produce a high-strength part. As the hot stamping material, so-called boron steel containing 0.2% by weight of carbon and using Mn and B as elements for improving the heat treatment performance is used.

Such hot stamping is advantageous in that it is excellent in productivity because the molding and the heat treatment are performed at the same time, and the steel sheet is formed at high temperature, thereby improving the formability and dimensional accuracy and remarkably reducing the problematic springback or delayed fracture have.

Hot stamping is accompanied by a post-forming descaling process when the process uses a non-plated steel sheet at high temperature. An Al-coated steel sheet is proposed to omit the troublesome descaling process. As to the Al-coated steel sheet, US Pat. No. 6,296,805 to Arcelor Mittal can be referred to.

Tailor Welded Blanks (TWB) is a technology that is being applied to the manufacture of vehicle parts for light weight and improved collision safety. TWB is a technology to cut steel sheets of different thicknesses and materials into appropriate sizes and shapes and then weld them with laser to make products of the desired shape.

Tailor Rolled Blank (TRB) technology is a technology that is applied to the manufacture of vehicle body parts to lighten weight and improve safety with TWB. As shown in FIG. 1, the TRB differentially adjusts the thickness of the steel sheet while adjusting the gap between the upper and lower work rolls 1 and 2 during the rolling process of the coil steel sheet 3.

Although the TRB can change the thickness of the blank, it can only change the thickness of the single material in the rolling direction and is uniformly manufactured. Therefore, it is difficult to actually apply it to mass production other than the special parts. Although TWB is applied to vehicle manufacturing, laser welding is required, which is disadvantageous in terms of productivity and economy.

SUMMARY OF THE INVENTION The present invention is based on the recognition of the prior art as described above and aims to provide an improved method of manufacturing a vehicle body part that can cope with increasingly diverging and increasing crash performance demands.

In addition, the present invention aims at hot-stamping a steel sheet having a plated layer on its surface to mold body parts in which a plurality of parts P1 to P4 having different thicknesses are integrally formed as shown in Fig. 2, for example .

The door side body part as shown in Fig. 2 may be manufactured by separately forming respective parts such as a center pillar and a front pillar, and then welding them to each other. TWB is a technique that can be used to fabricate these body parts. These body parts can not be obtained by the TRB which can only change the thickness in the rolling direction.

However, TWB can not be applied to a hot stamping coated steel sheet, for example, an Al-coated steel sheet. This is because when the laser is welded, the strength of the weld is considerably reduced due to the Al plating layer. In US Patent Publication No. 2015-0030382, a method of peeling the plating layer of the welded portion in advance has been proposed, but mass production is not easy.

A technique for manufacturing a body part as shown in Fig. 2 using a hot-stamping plated steel sheet has not been proposed so far. Although the method proposed in U.S. Patent Publication No. 2015-0030382 may be used, mass production is difficult as mentioned above.

The inventors of the present invention have proposed Korean Patent Application No. 2015-0106952 entitled " Hot-formed vehicle steel parts and manufacturing method ". In the invention of this application, the blank is preliminarily heated before rolling for thickness control to oxidize the surface film in advance.

As a result of research and development for this purpose, the present inventors have derived the present invention.

A method for manufacturing a vehicle body part according to the present invention comprises the steps of: a) cutting a steel sheet having a surface plated layer into a blank of a size and shape necessary for hot press forming; b) rolling the blank so as to have at least two regions of different thickness; c) heating the rolled blank to austenite temperature range, followed by hot press forming and cooling, wherein a hole is formed in the blank in a) and the hole position is arranged in the area where the rolling takes place in step b) So as to make it possible for the user to make a request.

Further, the method of manufacturing a vehicle body part according to the present invention comprises the steps of: a) cutting a steel sheet having a surface plated layer by a blank having a predetermined size; b) rolling the blank so as to have at least two regions of different thickness; c) leveling the rolled blank flat; d) secondly cutting the blank in a shape necessary for press forming in consideration of the shape of the body part to be manufactured; And e) heating the rolled blank to austenite temperature range, followed by hot press forming and cooling, wherein a hole is formed in the blank in a) and the hole position is located within the area where rolling is to occur in step b) So as to be disposed.

According to the present invention, in the rolling step of b), the blank can be rolled in different directions in two or more directions, or rolled using a rolling roll having a section with a different diameter in the longitudinal direction.

According to the present invention, in the blanking step of a), when the hole is formed in the blank region where the rolling is performed in the step b), the deformation of the blank which can be generated in the rolling step of b) can be remarkably reduced. Otherwise, the deformation of the blank is difficult to correct even by leveling.

In Korean Patent Application No. 2015-0106952, the present inventors propose a method of forming an oxide layer on a surface by preliminarily preheating a blank before rolling to prevent microcracks on the surface that may occur during the rolling process.

As a result of the experiment, the hot stamping steel sheet, for example, the Al coated steel sheet, did not cause a fine crack on the surface when cold rolling was controlled well. In the process of heating to the austenite temperature range, the plating layer melts and the surface cracking problem can be alleviated. Rather, deformation of the blank due to cold rolling is a problem, but this can be solved by forming a hole in the blank region where rolling is performed according to the present invention.

According to the present invention as described above, it is possible to manufacture a vehicle body part having a plurality of regions having different thicknesses through cold rolling without additional preliminary heating.

In addition, according to the present invention, a body part having two or more regions having different thicknesses can be freely manufactured using a conventionally provided coated steel sheet.

According to the present invention, a body part in which a plurality of parts P1 to P4 having different thicknesses are integrated as shown in Fig. 2 can be manufactured at a time by using a single blank.

Further, according to the present invention, the design and manufacture of the parts are free, so that it is possible to cope with various demands for crash performance.

Fig. 1 is a schematic view for explaining the TRB,
2 is a view showing an example of a steel part that can be manufactured by TWB,
3 is a flow chart of a vehicle body part manufacturing process according to an embodiment of the present invention,
4A to 4D are schematic views showing a blanking and rolling method according to an embodiment of the present invention,
5 is a flowchart of a vehicle body part manufacturing process according to another embodiment of the present invention.
6A to 6D are schematic views showing a blanking and rolling method according to another embodiment of the present invention,
7 is a schematic view showing a rolling method according to another embodiment of the present invention,
8 is a schematic view showing a blank blanked in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same components or parts are denoted by the same reference numerals as much as possible for convenience of description.

A method of manufacturing a vehicle body part according to an embodiment will be described with reference to FIGS. 1 to 4D.

As shown in Fig. 1, according to the embodiment, the vehicle body parts are manufactured by blanking, rolling, leveling, heating, hot press printing and cooling. As the material, an Al-coated steel sheet for hot stamping can be used.

Blanking  Step (S1)

As shown in Fig. 4A, the Al-coated steel sheet is cut into the blank 10 of the size and shape necessary for press forming. Holes (11) are formed in the blank (10) at the time of cutting.

It is preferable that the hole 11 is formed at a portion which is not easily exposed in the body part after press forming or at a portion which is to be removed from the product after press forming anyway.

However, the hole 11 is provided for absorbing the deformation of the blank 10 in the subsequent rolling process, and is disposed in the region where the rolling takes place, at least in the subsequent step. The position of the hole 11 can be set to a position where the thickness is increased by rolling in consideration of the rolling direction, the width, the thickness, and the like and the deformation is generated.

Meanwhile, the blank is stretched by rolling. Naturally, the blanking line needs to be set in consideration of the drawing amount by rolling.

The rolling process (S2)

As shown in Figs. 4B to 4D, the blank 10 is rolled so as to have at least two regions having different thicknesses, preferably at least three regions. The regions having different thicknesses are not arranged along any one direction. Unlike the blanks which can be obtained by TRB, two or more regions with different thicknesses in different directions are arranged.

4B, when the prepared blank 10 has a thickness of 1.4 mm, the rolled sheet is repeatedly rolled in the direction A by the rolling roll R to reduce the thickness of the rolled portion to 1.2 mm. As shown in FIG. 4C, And is repeatedly rolled in the B direction different from the A direction by the rolling roll (R) to reduce the thickness of the rolled portion to 1.0 mm.

By the above rolling, the blank 10 having three regions having different thicknesses as shown in Fig. 4D can be obtained. The changing of the rolling direction is possible, for example, by rotating the blank 10 and entering the rolling roll R, and the holes 11 can be arranged in areas where different rolling directions A and B overlap each other .

Leveling  Step (S3)

The blank 10 is deformed during the rolling process. The amount of deformation can be minimized by the hole 11, but the process of rolling the steel sheet while reciprocating the cylindrical rolling roll R is accompanied by the leveling for leveling the blank 10 after rolling.

Conventional techniques using multiple rollers can be used for leveling.

Heating step (S4)

And austenitizing the blank 10 for hot stamping. More specifically, the Al-coated steel sheet is heated to about 550 ° C to form an oxide layer on the surface, and then heated to austenite temperature range. Electric heating, high frequency induction heating, electric furnace, etc. may be used for heating.

Hot  Press forming and cooling step (S5)

The austenitized blank 10 is press-formed into a product of the desired shape and quenched. A high-strength steel component having a martensite phase is obtained through quenching.

Trimming (S6)

After the hot press forming, a trimming process is performed to remove the excess product existing at the edge of the molded product. The excess may be generated by cutting the blank 10 to a larger size than the product or by stretching the blank 10 by rolling to protect the product.

As shown in FIG. 5, according to another embodiment, the vehicle body parts can be manufactured through primary blanking, rolling, leveling, secondary blanking, heating, hot press printing and cooling.

A method of manufacturing a vehicle body part according to another embodiment will be described with reference to FIGS. 5 to 8. FIG.

Primary Blanking  Step S10:

In the blanking step (S1) of the previous embodiment, the Al-coated steel sheet is cut to a size and shape as close as possible to the final molded product in consideration of the drawing and the forming margin by rolling.

As shown in Fig. 6A, according to the present embodiment, in the primary blanking step S10, the Al-coated steel sheet is simply cut into the blank 20 of a constant size. Naturally, the blanking line can be determined in consideration of the stretching amount in the subsequent rolling step S11 and the amount to be removed in the second blanking step S13.

Holes 21 are formed in the blank 20 as in the previous embodiment.

In the rolling step (S11)

As shown in FIGS. 6B to 6D, the blank 20 is rolled so as to have at least two regions having different thicknesses, preferably at least three regions. The regions having different thicknesses are not arranged along any one direction but arranged in two or more different directions.

6B, when the prepared blank 20 has a thickness of 1.4 mm, the rolled sheet is repeatedly rolled in the direction A 'by the rolling roll R to reduce the thickness of the rolled portion to 1.2 mm, as shown in FIG. 6C , And is repeatedly rolled in the direction B 'different from the direction A' by the rolling roll (R) to reduce the thickness of the rolled portion to 1.0 mm.

By the above rolling, the blank 20 having three regions having different thicknesses as shown in Fig. 6D is obtained. The changing of the rolling direction is possible by, for example, rotating the blank 20 and entering the rolling roll R, and the holes 21 can be arranged in areas where different rolling directions A and B overlap each other .

Referring to Fig. 7, as another method for obtaining the blank 20 shown in Fig. 6D, the blank 20 can be rolled using a rolling roll R 'having a section having a different diameter in the longitudinal direction.

Leveling  Step (S12)

As in the previous embodiment, leveling is performed to planarize the blank 20 in which the deformation has occurred during the rolling step S11.

Secondary Blanking  Step (S13)

As shown in Fig. 8, the leveled blank 20 is cut into the size and shape necessary for press forming. Considering the molding margin, it is cut to the size and shape as close as possible to the final molded product.

After the secondary blanking step (S13), the heating step (S14), the hot press forming and cooling step (S15) and the trimming step (S16) can be carried out in the same manner as in the previous embodiment.

While the invention has been shown and described with respect to the specific embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit of the invention as set forth in the following claims.

10, 20: Blank 11, 21: Hole

Claims (4)

a) cutting a steel sheet having a surface plated layer into a blank of a size and shape necessary for press forming;
b) rolling the blank so as to have at least two regions of different thickness;
c) heating the rolled blank to austenite temperature range, followed by hot press forming and cooling,
a hole is formed in the blank in step a), the hole position being arranged in the area where the rolling takes place in step b)
wherein the blanks are rolled in different directions in two or more directions in step b). a) firstly cutting a steel sheet having a surface plated layer with a blank of a predetermined size;
b) rolling the blank so as to have at least two regions of different thickness;
c) leveling the rolled blank flat;
d) secondly cutting the blank in a shape necessary for press forming in consideration of the shape of the body part to be manufactured;
e) heating the rolled blank to austenite temperature range, followed by hot press forming and cooling,
a hole is formed in the blank in step a), the hole position being arranged in the area where the rolling takes place in step b)
wherein the blanks are rolled in different directions in two or more directions in step b). delete delete

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