KR20110062428A - Partial-strengthening hot-stamping method for improving impact resistance of vehicle parts - Google Patents

Abstract

PURPOSE: A partial-strengthening hot-stamping method for improving impact resistance of vehicle components is provided to minimize damage to passengers by producing components with high-strength and low-strength. CONSTITUTION: A partial-strengthening hot-stamping method for improving impact resistance of vehicle components is as follows. A martensite structure(7) is constituted by heating, pressing, and quenching a blank. A ferrite/perlite structure(8) is constituted by heating a part of the blank with temperature which is less than austenitizing temperature.

Description

Local Reinforced Hot Stamping Method for Improving Collision Performance of Automotive Parts {PARTIAL-STRENGTHENING HOT-STAMPING METHOD FOR IMPROVING IMPACT RESISTANCE OF VEHICLE PARTS}

The present invention relates to a method for manufacturing a major collision component of the vehicle body for improving the collision performance of the vehicle. More specifically, the present invention is applied to the production of the main collision parts, such as the front side member, the center pillar, the roof side member, the rear side member, the cross member of the automobile, for absorbing the collision energy due to the collision and for protecting the main portion It is to increase the occupant protection function in case of collision by having the intrusion prevention function at the same time.

Figure 1 shows a hot stamping process for producing a conventional ultra high strength crash parts. Conventional hot stamping processes have four steps: blanking, heating, conveying, flashing and quenching. After blanking the boron heat-treated hardened steel with or without an aluminum coating layer appropriately to the size of the part, the blank 1 is heated in the furnace 2 above the austenizing temperature (820 ° C., Ac3). Thereafter, the blank 1 heated using the transfer robot 5 is subjected to a process of forming and quenching the press 3 in the press 3. The mold absorbs the heat transferred from the blank by the cooling water passage 4 in the mold to enable rapid cooling. Pressed and quenched materials are used as the high-impact collision parts of 1500MPa class and are applied to the main collision parts of automobiles.

As shown in the left side of FIG. 2, the existing hot stamping part is a martensite structure 7 having the same parts as the whole after heat treatment, and has a high elongation (1500 MPa to 2000 MPa) and a low elongation (about 8%). (7). However, a component having a low elongation as an ultra high strength component may be insufficient in absorbing collision energy. In addition, only the component is significantly higher than the strength of the peripheral parts to be combined (490 ~ 780 MPa), and in some cases, the corresponding parts may penetrate the peripheral parts.

The present invention has been made to solve the problems of the prior art as described above, to provide a method for producing a collision part and at the same time to provide a collision part to achieve the two objects of securing the body rigidity and shock absorption of the invention The purpose.

In order to solve the above problems, the present invention, in the hot stamping method comprising the step of heating the blank above the austenizing temperature (AC3 or more), pressing and quenching to form a martensite structure, the heating of the blank At least a portion of the blank in the step is a locally hardened hot stamping method that is heated to below the austenizing temperature (below AC1) to finally form the ferrite / perlite structure.

Here, the method of heating a portion of the blank below the austenizing temperature, a method of heating the portion to be heated above the austenizing temperature through induction heating or gas burner.

In addition, the method of heating a part of the blank below the austenizing temperature, by inserting into the heating furnace using a heat insulator in a part to be heated below the austenizing temperature, the temperature of the part where the heat is blocked by the heat insulator is austeni The method may be applied to bring the temperature below the gong temperature.

On the other hand, in order to solve the above problems, the present invention, in the hot stamping method comprising the step of heating the blank to the austenizing temperature (AC3 or more), pressing and quenching, at least in the quenching step A locally hardened hot stamping method in which a portion is cooled slowly than the remainder so that the strength of the portion is lower than that of the remainder.

The method of slowly cooling a part of the workpiece in the quenching step comprises: forming the pressing die into at least a split mold divided into a heating mold and a cooling mold, and cooling the workpiece to be cooled in a pressed state on the heating mold side. Alternatively, a hot stamping method may be applied in which the heating mold is cooled in a state where the void is kept at a predetermined distance from the workpiece immediately after pressing.

In addition, in order to solve the above problems, the present invention is a vehicle collision part manufactured by any one of the above methods, partly having a high strength portion, partly having a low strength portion, the high strength portion is the main part side of the vehicle It is a collision part for a vehicle fixed to the vehicle and mounted on the vehicle so that the low intensity part faces the anticipated collision direction.

According to the above invention, it is possible to produce a collision part having a locally high strength, locally low strength, to achieve the effect of securing the body rigidity and shock absorption at the same time to minimize the damage of passengers in the event of a crash accident.

Hereinafter, a localized hot stamping method according to the present invention and a concrete embodiment of a crash part manufactured according to the method will be described.

The impingement part has a high strength part 7, partly a low strength part 8, as shown on the right side of FIG. 2, thereby providing a high strength martensite structure 7 and a low strength within the same part. It is manufactured to have a ferrite / perlite structure (8). Therefore, in the event of collision, the ferrite / perlite tissue portion 8 of low intensity induces the absorption of collision energy, and the high strength martensite tissue portion 7 has the function of supporting / protecting the main portion so that no further intrusion occurs. These local reinforced hot stamping parts can simultaneously achieve collision energy absorption and major part intrusion prevention at the time of collision, thereby enhancing the occupant's protection function. To this end, it is possible to use a method of producing a part having a different strength in the same part by different heating methods or cooling methods when forming the material.

There are two ways to fabricate localized hot stamping parts. The first is to produce parts with different strengths within the same part, by locally varying the heating temperature of the material. The second method is to locally control the cooling rate of the material heated to the same temperature to produce parts with different strengths in the same part.

The material used is heat-hardened boron steel 6 and its component system is as shown in FIG. Specific embodiments of each manufacturing method of the present invention are as follows.

[Differential heating method]

The first is a method of locally controlling the strength of the final part by locally changing the heating temperature of the material as shown in FIG. As can be seen in Figure 4, when the material is locally heated to 770 ° C (Ac1; temperature at which transformation to austenite begins) and quenched, the strength of the part is about 780 MPa. However, when the material is locally heated above 820 ° C. (Ac 3, the temperature at which transformation to austenite is completed), the strength of the part is about 1500 MPa. Thus, by locally varying the heating temperature of the raw material, it is possible to produce locally reinforced hot stamping parts having different strengths in the same part.

≪ Example 1 >

As a specific embodiment, FIG. 5 illustrates a method of locally heating the boron steel material 1 using the induction coil 11. The heating section 9 is heated above the Ac 3 temperature (820 ° C.), the non-heating section 10 is heated below the Ac 1 temperature (770 ° C.) and cooled by the cooling water passage 4 during molding in the press 3. Quench. In this case, the high strength portion 7 and the low strength portion 8 can be obtained in the same component.

<Example 2>

As another local heating method, as shown in FIG. 6, the heating unit 9 is heated by directly applying the flame 13 directly to the surface of the material 1 using the gas burner 12. After heating above Ac3 temperature (820 degreeC) and heating the non-heating part 10 below Ac1 temperature (770 degreeC), it is quenched by the cooling according to the cooling water path 4 in the press 3 during molding. Through this method, the desired portion can be obtained by the high strength martensite (7) structure, and the rest can be obtained by the low strength ferrite / perlite structure (8).

<Example 3>

Finally, a portion of the material 1 is inserted into the heating furnace 2 in a state in which a part of the material 1 is covered with the heat insulating material 14 to heat only a part of the material, that is, a portion exposed to the outside in a rotary or series mobile heating furnace. Only by heating, the heating section 9 is heated above the Ac 3 temperature (820 ° C.) and the non-heating section 10 is heated below the Ac 1 temperature (770 ° C.), and then in the press 3 the cooling water passage 4 during molding. Quench through cooling according to In the same part, a high-strength martensite (7) structure and a low-strength ferrite / perlite (8) structure can be obtained.

[Differential cooling method]

Second, as shown in Figure 8, by locally adjusting the cooling rate of the material is heated to the Ac3 temperature (820 ℃) or more, the method of controlling the strength of the final part. As can be seen in Figure 8, when locally quenched (15) the material heated above the Ac3 temperature as a whole 30 ° C / sec or more, the locally quenched site has a high strength of 1500MPa. On the other hand, when the material is locally cooled 16 at a rate of 12 ° C./sec or less, the portion has a strength of 780 MPa. Therefore, localized cooling rates can lead to different strengths in a single part.

&Lt; Example 1 >

As a specific embodiment, as shown in Figure 9, by dividing the mold to produce a heating mold 17 and a cooling mold 18 to differentially control the cooling rate of a single part. The heating die 17 is inserted into the cartridge heater to maintain a high temperature (400 ℃ or more), the cooling die 18 to form a cooling water flow path (4) to maintain the temperature of the mold at room temperature. The blank 9, the whole of which is heated above the Ac3 temperature (820 占 폚), is placed in a divided mold, and molding and local cooling rate control are performed. At this time, in the case of the part in contact with the heating mold, the cooling rate is low (20 ° C./sec or less), and finally, the material 8 having low strength can be obtained. On the other hand, in the case where the part is in contact with the cooling die, the cooling rate is high (about 30 ° C./sec), and finally, a high strength material 7 can be obtained. Therefore, parts having different strengths can be obtained in the same part by using divided molds.

<Example 2>

If necessary, when a lower tensile strength is required, as shown in FIG. 10, when the high temperature mold 17 is molded and the molding is completed, the mold is immediately separated from the raw material at intervals of 2 to 8 mm. In this case, voids (2 to 8 mm) are formed to further reduce the cooling rate (10 ° C./sec or less) and obtain a lower strength (780 MPa or less) grade material locally.

[Crash Parts with Local Reinforced Hot Stamping Method]

11 shows a rear floor side member 22 fabricated in this manner. Locally-reinforced hot stamping parts manufactured by the method as described above have a high-strength section 21 and a low-strength tool section 20 simultaneously in the same part.

As shown in FIG. 12, in the case of the rearside member manufactured by the above method, a portion having a maximum strength of 1500 MPa and a portion having a minimum strength of 780 MPa exist simultaneously in the part. The rear side member is a representative part of the rear body to protect against rear collision. Immediately after the rear collision, the low steel tool section 20 serves to absorb the collision energy as much as possible. Since the high-strength section 21 so that the vehicle body is no longer deformed, it serves to prevent the intrusion of various members into the fuel cylinder installed under the high-strength section.

13 shows the acceleration / acceleration of the neck of the initial driver's seat. In the case of using a new collision part manufactured by the method described above, the collision energy absorption is made more in the low intensity section 22. Accordingly, as shown in FIG. 13, it can be seen from the collision analysis that the highest acceleration decreases from the prior art 62.4G (G: gravity acceleration) to 59.4G of the present invention. This serves to reduce the driver's neck injury in a collision.

In addition, as shown in FIG. 14, when comparing the amount of sliding of the rear suspension after the collision, it was found that the maximum 28 mm was improved. This protects the fuel tank in the event of a rear collision and prevents fuel leakage. Therefore, it can be seen that when using the collision parts using the present invention, the effects of collision energy absorption and the main part intrusion prevention.

1 is a hot stamping method for manufacturing a conventional collision parts;

2 is a schematic view of a conventional hot stamping part and a locally hardened hot stamping part according to the present invention;

3 is a table showing the component system of the material used for local hardening hot stamping;

Figure 4 is a chart showing the difference in tensile strength with the difference in heating temperature in the hot stamping method;

5 is a view showing a local strengthening method through induction local heating;

6 is a view showing a local strengthening method through gas burner local heating;

7 is a view showing a local strengthening method through heating after local thermal insulation treatment;

8 is a chart showing the difference in tensile strength according to the difference in cooling rate in the hot stamping method;

9 is a view showing a local strengthening method through the cooling rate control through a heating mold;

10 is a view showing a local strengthening method through the heating mold application and surface contact control of FIG.

11 is a view showing a collision part manufactured according to an embodiment of the present invention and a mounting state of the part;

12 is a view showing the intensity distribution and the structure state in the longitudinal direction of the conventional collision parts of the present invention.

13 is a view showing the acceleration of the neck region obtained through the collision test after the conventional mounting of the collision component of the present invention; And

14 is a view showing the amount of push by position obtained through the crash test after the mounting of the crash parts of the prior art and the present invention.

<Description of the symbols for the main parts of the drawings>

1: blank

2: heating furnace

3: press

4: with coolant in the mold

5: transfer robot

6: Boron heat treated hardened steel before heat treatment

7: martensite structure after heat treatment

8: ferrite / perlite structure after heat treatment

9: heating part

10: non-heating part

11: induction coil

12: gas burner nozzle

13: flame

14: heat insulation

15: quench curve (30 ° C / sec)

16: slow cooling curve (6 ° C / sec)

17: heating mold

18: cooling mold

19: cartridge heater for heating

20: energy absorption area (780 MPa class)

21: intrusion prevention zone (1500MPa ~ 2000MPa class)

22: rear floor side member

Claims (7)

A hot stamping method comprising the step of heating a blank above an austenizing temperature (above AC3), pressing and quenching to form a martensite structure, At least a portion of the blank in the heating step of the blank to heat below the austenizing temperature (below AC1) to finally form a ferrite / perlite structure. The method according to claim 1, The method of heating a portion of the blank below the austenizing temperature, the localized hot stamping method of heating a portion to be heated above the austenizing temperature through induction heating or gas burner. The method according to claim 1, In the method of heating a part of the blank below the austenizing temperature, the temperature of the part at which the heat is blocked by the heat insulating material is charged into the heating furnace by using a heat insulating material in a part to be heated below the austenizing temperature. Locally strengthened hot stamping method to bring the temperature below. In the hot stamping method comprising the step of heating and quenching the blank after the austenizing temperature or more (AC3 or more), Cooling at least a portion of the workpiece more slowly than the remaining portion in the quenching step, so that the strength of the portion is formed to be lower than the strength of the remaining portion. The method according to claim 4, The method of slowly cooling a part of the workpiece in the quenching step comprises: forming the pressing die into at least a split mold divided into a heating mold and a cooling mold, and cooling the workpiece to be cooled in a pressed state on the heating mold side. Hot stamping method. The method according to claim 4, The method of slowly cooling a part of the workpiece in the quenching step comprises: forming the pressing die into at least a split mold divided into a heating mold and a cooling mold, and heating the mold immediately after pressing the workpiece to be slowly cooled from the heating mold side. Hot stamping method to allow the air gap to be cooled at a predetermined distance away from the workpiece. A crash part for a vehicle manufactured by the hot stamping method of any one of claims 1 to 6, The crash part has a high strength part, partly a low strength part, and the crash part for a vehicle is mounted on the vehicle such that the high strength part is fixed to the main part side of the vehicle and the low strength part faces the anticipated collision direction.

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