TWI540005B - Press forming method and producing method of pressed part - Google Patents

Description

Stamping forming method and manufacturing method of stamping member

The present invention relates to a press forming method and a method of producing a part of a pressing member for press forming a composite sheet.

For example, in the automotive field, there is a tailor-welded sheet in which two or more types of sheets are overlapped, such as weight reduction or high strength of a member for the purpose of optimizing an applicable material, simplification of a manufacturing process of a press member, and reduction in the number of molds. Stamping forming technology. The tailor-welded sheet is subjected to butt welding or spot welding such as laser welding before press forming (for example, refer to Patent Documents 1 to 3).

[Advanced technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2001-001062

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2007-075881

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2007-029966

In laser welding, since the strength of the joint which is continuously welded is high, forming defects such as breakage are less likely to occur, but the equipment cost is high. Moreover, since the cycle for obtaining the welding plate is long, it has problems in terms of cost and productivity. Moreover, in order to obtain good welding quality, the joint portion is also required to have high docking precision.

On the other hand, in spot welding, although it is advantageous in terms of cost and productivity, the strength of the joint portion is not sufficient, and there is a possibility that cracking may occur in the vicinity of the joint portion due to stress concentration at the time of press forming.

An object of the present invention is to press-form a welded plate material in which a plurality of welded plates are combined so that molding defects do not occur, and an increase in cost and a decrease in productivity can be suppressed.

In order to solve the above problems, the present invention provides a press forming method in which a plurality of welded plates are partially overlapped, and the plurality of welded plates are directly subjected to press forming of the plurality of welded plates in a non-joined state.

In the above press forming method, it is preferable to press-form the at least one plate thickness or material different from the other plurality of the plurality of welded plates.

Further, in the overlapping portion in which the plurality of welded plates are overlapped, it is preferable to maintain the non-joined state at least in the field of deformation in which deformation is caused by press forming.

Further, after the press forming, the overlapping portion in which the plurality of welded plates are overlapped is preferably joined.

Further, the overlapping portion after the press forming is configured to have a minimum width or more for bonding, and the pre-pressing is set. The overlapping portion is preferred.

Further, the present invention provides a method for producing a press member, which is produced by press forming using the above-described press forming method.

According to the present invention, since the press forming is directly performed without joining the plurality of welded plates, it is possible to prevent the occurrence of molding failure as in the prior art. Moreover, since new equipment and processes are not required, it is possible to suppress an increase in cost and a decrease in productivity.

Hereinafter, embodiments of the present invention will be described in accordance with the drawings.

"Pressing Forming Method"

Fig. 1 is a view showing a press forming method. In the figure, (a) shows the conventional method, and (b) shows the method of the present embodiment.

In the prior art, different composite plates of different thicknesses and materials are pre-joined by laser welding (continuous welding) and spot welding, from which press processing is performed.

On the other hand, in the present embodiment, the plurality of welded plates having different thicknesses and materials are partially overlapped (overlapped), and these are directly subjected to press working in a non-joined state. Further, the non-joined state refers to a field of deformation in which at least deformation (compression, tensile) can be caused by press forming in the overlapping portion. Therefore, outside the field of deformation, that is, by means of molds and The field in which the crease-resistant platen is restrained or the detached portion or the like which is removed by the decorating process or the like may be pre-joined (temporarily fixed).

Further, after the press working, the overlapping portions where the welded plates are overlapped are joined. This joining is preferably performed by spot welding, for example, from the viewpoint of productivity and cost, but arc welding, brazing, clamping, rivet joining, bolt joining, bonding agents, and the like are also applicable. Moreover, this joining process may be carried out in the press process, for example, at the lowest point of the stroke (bottom dead center).

"effect"

In the prior art, the plurality of welded plates are joined by laser welding or spot welding before the press forming. First, when the plurality of welded plates are joined by laser welding, the equipment cost becomes high. Moreover, since the cycle is also long, it also causes a decline in productivity. On the other hand, when the plurality of welded plates are joined by spot welding, the strength of the joint portion is insufficient as compared with the laser welding, and the stress is concentrated at the time of press forming to cause breakage in the vicinity of the joint portion.

In this regard, in the present embodiment, the plurality of welded plates are directly press-formed in an unjoined non-joined state. In other words, since the overlapping portion of the welding plates is maintained in an unconstrained state, it is possible to prevent molding failure such as breakage when spot welding is performed before press forming. This is because the relative displacement of the welding plates to each other can be tolerated when subjected to an external force generated by press forming.

After the press forming, the overlapping portions of the bonding plates are joined by spot welding or the like. So, the case of spot welding is applied because laser welding is not required. The equipment used, so that the existing equipment can be used, and the increase in the cost of equipment introduction can be suppressed. Further, since the joining is performed only before the press forming or the joining after the press forming, a new process is not required, and even in the case of spot welding with a short cycle, the decrease in productivity can be suppressed.

After the press forming, since the overlap portion is smaller than that before the press forming, it is necessary to set the reduction portion to set the overlap portion before press forming. In other words, in order to perform spot welding, the minimum width required for the minimum is required. Therefore, the overlapping portion after press forming is such that the minimum width is required, and the overlapping portion before press forming is set.

"Embodiment 1"

In Example 1-1, a cylindrical shape was press-formed from two welded sheets which were a combination of mild steels. In the molding simulation, a general-purpose dynamic cation method software LS-DYNA ver. 971 (manufactured by Livermore Software Technology Corporation) was used.

Fig. 2 is a view showing the analysis result of Example 1-1. Fig. 2(a) shows the result of crack determination and the thickness reduction rate when the two welding plates are continuously welded (laser welded) before press forming, and Fig. 2(b) shows two before the press forming. The crack determination result and the plate thickness reduction rate in the case of spot welding of the welded plate are shown in Fig. 2(c) as the crack determination result and the plate thickness reduction rate when the joint is not joined before press forming. The plate thickness reduction rate is a reduction in the thickness of 0 to 20% from the shade of white and black.

Here, mild steels A and B having the same thickness and the same material are used. The welding plate A is a plate thickness of 0.7 mm and a tensile strength of 270 MPa, and the welding plate B is a plate thickness of 1.2 mm and a tensile strength of 270 MPa. The size of the welded plates on both sides is 200 mm × 200 mm. Stamping forming conditions are 150mm The cylinder is formed to constrain the outer circumference of the welded sheet across the entire circumference.

As shown in Fig. 2(a), when the steel sheet which has been continuously welded in advance is subjected to press working, when the height of the cylinder reaches 15.7 mm, a part of the peripheral edge of the upper surface of the cylinder is broken. The reason for the occurrence of cracking is that the thickness reduction rate of the entire soft steel A having a thinner plate thickness is higher than that of the mild steel B.

As shown in Fig. 2(b), when the welding material which has been spot-welded in advance is subjected to press working, when the height of the cylinder reaches 8.9 mm, the spot-welded portion located at the center of the upper surface of the cylinder is broken. The nugget diameter of the spot welding is 4 √t (t: plate thickness), the overlap portion is 12 mm, and the interval between the spot weld portions is 40 mm, and spot welding is performed at a total of five places. The part where the rupture occurs is in the soft steel A having a thin plate thickness, and the portion where the plate thickness reduction rate is high is concentrated in the spot welding portion.

As shown in Fig. 2(c), if the welded plate material is directly subjected to press working without being joined, even if the height of the cylinder reaches 18.7 mm, the crack does not occur, and the molding failure such as (a) or (b) can be prevented. The overlap before the press forming was 40 mm. Further, in the overlapping portion, since spot welding is performed after press forming, the overlapping portion before press forming is set so that only the width for spot welding remains in the overlapping portion after press forming.

In Example 1-2, the hat shape was press-formed from two welded sheets which were a combination of mild steels. In the forming simulation, use the general dynamic positivity Solution software LS-DYNA ver.971.

Fig. 3 is a view showing the analysis result of Example 1-2. Fig. 3(a) shows the result of crack determination and the thickness reduction rate when two welded sheets are continuously welded (laser welded) before press forming, and Fig. 3(b) shows two before press forming. The crack determination result and the plate thickness reduction rate in the case of spot welding of the welded plate, and Fig. 3(c) show the crack determination result and the plate thickness reduction rate when the joint is not joined before press forming. The plate thickness reduction rate is a reduction in the thickness of 0 to 20% from the shade of white and black.

Here, mild steels A and B having the same thickness and the same material are used. The welding plate A is a plate thickness of 0.7 mm and a tensile strength of 270 MPa, and the welding plate B is a plate thickness of 1.2 mm and a tensile strength of 270 MPa. The size of the welded plate which overlaps both sides is 100 mm × 200 mm. The press forming condition is a hat-shaped mold forming, and the both ends of the welded plate are restrained.

As shown in Fig. 3(a), when the welding plate which has been continuously welded in advance is subjected to press working, when the height of the hat reaches 15.8 mm, a part of the upper corner is broken. The reason for the occurrence of cracking is that the thickness reduction rate of the entire soft steel A having a thinner plate thickness is higher than that of the mild steel B.

As shown in Fig. 3(b), when the welding plate which has been spot-welded in advance is subjected to press working, the spot welding portion is broken when the height of the cap reaches 9.0 mm. The nugget diameter of the spot welding is 4 √t (t: plate thickness), the overlap portion is 12 mm, and the interval between the spot weld portions is 40 mm, and spot welding is performed at a total of three places. The part where the rupture occurs is in the soft steel A having a thin plate thickness, and the portion where the plate thickness reduction rate is high is concentrated in the spot welding portion.

As shown in Fig. 3(c), when the welded plate material is directly subjected to press working without joining, the height of the cap does not occur even if it reaches a break of 26.6 mm, and the molding failure such as (a) or (b) can be prevented. The overlap before the press forming was 60 mm. Further, in the overlapping portion, since spot welding is performed after press forming, the overlapping portion before press forming is set so that only the width for spot welding remains in the overlapping portion after press forming.

<<Example 2》

In Example 2-1, a cylindrical shape was press-formed from two welded sheets of a combination of mild steel and high tensile steel (high tensile strength). In the forming simulation, the general-purpose dynamic positivity software LS-DYNA ver.971 is used.

Fig. 4 is a view showing the analysis result of the embodiment 2-1. Fig. 4(a) shows the result of crack determination and the thickness reduction rate in the case where the welded plate material is continuously welded (laser welded) before press forming, and Fig. 4(b) shows the spot welding of the welded plate before press forming. In the case of the rupture discrimination result and the plate thickness reduction rate, Fig. 4(c) is a rupture discrimination result and a plate thickness reduction rate when the film is not joined before press forming. The plate thickness reduction rate is a reduction in the thickness of 0 to 20% from the shade of white and black.

Here, mild steel A and high tensile steel C having different thicknesses and materials are also used. The welding plate A is a plate thickness of 0.7 mm, a tensile strength of 270 MPa, and a welding plate C having a plate thickness of 1.2 mm and a tensile strength of 440 MPa. The size of the welded plate which overlaps both sides is 200 mm × 200 mm. Stamping forming conditions are 150mm The cylinder is formed to constrain the outer circumference of the welded sheet across the entire circumference.

As shown in Fig. 4(a), for continuous welding that has been previously performed When the welded plate is subjected to press working, when the height of the cylinder reaches 15.7 mm, a part of the periphery of the upper surface of the cylinder is broken. The portion where the crack occurs is a soft steel A having a thin plate thickness and a low tensile strength, and the overall plate thickness reduction rate is higher than that of the high tensile steel C.

As shown in Fig. 4(b), when the welded sheet material which has been spot-welded in advance is subjected to press working, when the height of the cylinder reaches 8.9 mm, the spot welded portion located at the center of the upper surface of the cylinder is broken. The nugget diameter of the spot welding is 4 √t (t: plate thickness), the overlap portion is 12 mm, and the interval between the spot weld portions is 40 mm, and spot welding is performed at a total of five places. The part where the rupture occurs is the soft steel A having a thin plate thickness and a low tensile strength, and the portion where the plate thickness reduction rate is high is concentrated in the spot welding portion.

As shown in Fig. 4(c), if the welded plate material is directly subjected to press working under non-joining, the cylinder height does not occur even if it reaches a crack of 20.8 mm, and the molding failure as in (a) or (b) can be prevented. The overlap before the press forming was 40 mm. Further, in the overlapping portion, since spot welding is performed after press forming, the overlapping portion before press forming is set so that only the width for spot welding remains in the overlapping portion after press forming.

In Example 2-2, the hat shape was press-formed from two welded sheets which were a combination of mild steel and high tensile steel (high tensile strength). In the forming simulation, the general-purpose dynamic positivity software LS-DYNA ver.971 is used.

Fig. 5 is a view showing the analysis result of the embodiment 2-2. Fig. 5(a) is a rupture discrimination result and a plate thickness reduction rate in the case where two welded plates are continuously welded (laser welded) before press forming, and Fig. 5(b) shows two welds before press forming. Crack determination of the case where the sheet is spot welded The thickness and the plate thickness reduction rate are shown in Fig. 5(c) as the crack determination result and the plate thickness reduction rate when the film is not joined before press forming. The plate thickness reduction rate is a reduction in the thickness of 0 to 20% from the shade of white and black.

Here, mild steel A and high tensile steel C having different thicknesses and materials are also used. The welding plate A is a plate thickness of 0.7 mm, a tensile strength of 270 MPa, and a welding plate C having a plate thickness of 1.2 mm and a tensile strength of 440 MPa. The size of the welded plate which overlaps both sides is 100 mm × 200 mm. The press forming condition is a hat-shaped mold forming, and the both ends of the welded plate are restrained.

As shown in Fig. 5(a), when the welding plate which has been continuously welded in advance is subjected to press working, when the height of the cap reaches 14.3 mm, cracking occurs at the upper corner. The portion where the crack occurs is in the soft steel A having a thin plate thickness, and the overall plate thickness reduction rate is higher than that of the high tensile steel C.

As shown in Fig. 5(b), when the welding material which has been spot-welded in advance is subjected to press working, when the height of the hat reaches 8.9 mm, the spot welding portion is broken. The nugget diameter of the spot welding is 4 √t (t: plate thickness), the overlap portion is 12 mm, and the interval between the spot weld portions is 40 mm, and spot welding is performed at a total of three places. The part where the rupture occurs is in the soft steel A having a thin plate thickness, and the portion where the plate thickness reduction rate is high is concentrated in the spot welding portion.

As shown in Fig. 5(c), when the welded plate material is directly subjected to press working without being joined, the height of the cap does not occur even if it reaches a break of 26.6 mm, and the molding failure such as (a) or (b) can be prevented. The overlap before the press forming was 60 mm. Further, in the overlapping portion, since spot welding is performed after press forming, the overlapping portion before press forming is set so that only the width for spot welding remains in the overlapping portion after press forming.

As described above, it can be confirmed that the press forming can be directly performed without joining the plurality of welded plates, and molding failure such as breakage during spot welding before press forming can be prevented.

Further, as is apparent from the graphs of the reduction ratios of the thicknesses as shown in FIGS. 2 to 5, the distribution of the reduction in the thickness of the sheet is also advantageous in terms of maintaining rigidity (strength) because the spots are less likely to adhere.

[Fig. 1] A view showing a press forming method.

[Fig. 2] A diagram showing the analysis result of Example 1-1.

[Fig. 3] A diagram showing the results of analysis of Example 1-2.

[Fig. 4] A diagram showing the analysis result of the embodiment 2-1.

[Fig. 5] A diagram showing the results of analysis of Example 2-2.

Claims (6)

A press forming method in which a plurality of welded plates are partially overlapped, and the plurality of welded plates are directly press-formed on the plurality of welded plates in a non-joined state, and at least overlapped portions of the plurality of welded plates are overlapped In the field of deformation that is deformed by press forming, it is maintained in a non-joined state. The press forming method according to claim 1, wherein the at least one sheet thickness or material is press-formed with the other different plurality of welded sheets. The press forming method according to the second aspect of the invention, wherein the overlapping portion in which the plurality of welded plates are overlapped is maintained in a non-joined state at least in the field of deformation in which deformation is caused by press forming. The press forming method according to any one of claims 1 to 3, wherein after the press forming, the overlapping portions in which the plurality of welded plates are overlapped are joined. In the press forming method according to the fourth aspect of the invention, the overlapping portion after the press forming is such that a minimum width or more is required for joining, and the overlapping portion before the press forming is set. A method of manufacturing a stamped member, which is manufactured by press forming using a method as claimed in any one of claims 1 to 5.