JPH11104749A - Press forming steel strip and method of manufacturing the same - Google Patents

Abstract

(57) [Summary] [Problem] To dramatically improve productivity and material yield for parts that are nearly columnar, such as a skeleton structure part of an automobile, or parts, such as floors, in which dissimilar materials may be joined in parallel. Plan. SOLUTION: The present invention provides a method of joining steel sheets in a coil state in a tailored blank method for producing a steel strip for press forming in which several kinds of different steel strips are joined. The two or more slit steel strips are joined by a joining method such as laser welding or mash seam welding so as to have a joining line in the longitudinal direction of the steel strip.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel strip to be subjected to press forming and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, in the production of automobile parts and the like,
In order to give the necessary thickness and strength to the necessary parts, steel plates with different thicknesses or strengths are joined by laser etc. to make one steel plate, and then pressed together as a so-called tailored blank, so-called tailored blank The method was adopted. This example is, for example, JP-A-7-290182, JP-A-8-1742
Found at 46 mag. However, this method has a problem that productivity is not improved because the steel sheet is sheared into a small shape and joined to form a single steel sheet. Further, the joining quality is not stable at the welding start end and the end end, and this portion must be cut off, which has a disadvantage that the product yield is poor.

[0003]

On the other hand, the present invention eliminates the above-mentioned drawbacks, and uses a columnar part such as a frame structure of an automobile or a dissimilar material such as a floor in parallel. This is a method for joining steel sheets in a coil state for the purpose of achieving dramatic productivity and improving the yield of a possible part. By doing so, the productivity of joining can be dramatically improved.

[0004]

SUMMARY OF THE INVENTION The gist of the present invention is that two or more steel strips having different tensile strengths and / or sheet thicknesses have a joining line in the longitudinal direction of the steel strip. The joined steel strip for press forming is the invention according to claim 1, and two or more types of steel strips having different tensile strengths and / or sheet thicknesses are welded at their ends while rewinding the steel strip. A method for manufacturing a steel strip for press forming, characterized in that it is joined by a laser welding method, a mash seam welding method, an arc welding method,
A method for producing a steel strip for press forming using either the high frequency induction welding method or the electron beam welding method is defined as the invention according to claim 3.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows that three coiled steel strips A, B, and C having different thicknesses and strengths slit to a predetermined width are unwound, and the coil edges are joined by laser welding to form a joint line in the longitudinal direction of the steel strip. This is an outline of a step of forming a steel strip for press forming which is joined so as to have the same and winding it after joining to form a coil again. The number of steel strips to join
It can be selected according to the required characteristics of the part to be molded, and two or more types can be used. As a welding method at this time, a laser welding method, a mash seam welding method, an arc welding method, a high-frequency welding method, or the like can be adopted. In FIG. 1, after joining, the coil is wound again to form a joined coil. However, after joining, the coil may be cut immediately to a desired length to form a cut plate. It is also possible to join a new steel strip to the coil once joined.

[0006] As a specific example, A: a sheet thickness of 1.0 mm, a tensile strength of 300 MPa,
Width 250mm, B: plate thickness 1.2mm, tensile strength 620M
P, width 190 mm, C: thickness 1.0 mm, tensile strength 3
Prepare a steel strip of A, B, and C3 with a width of 00 MPa and a width of 250 mm, and connect a steel strip of A and C to both ends around B at both ends with a 5 kW laser welding machine at a speed of 5 m / min. And wound up after joining to form a coil-shaped steel strip for press forming. Thereafter, it was rewound and cut at a length of 1000 mm to obtain a steel plate having a width of 690 mm and a length of 1000 mm. The steel sheet was press-formed into a part having the shape shown in FIG.
When a shock crushing load was applied in the longitudinal direction using this part, a peak load of 8 ton was obtained, and a value of 5 ton obtained by the same part formed from a single steel plate having a tensile strength of 300 MPa and a thickness of 1.2 mm was obtained. Higher values were obtained. Further, when the same part was molded using a single steel plate having a tensile strength of 620 MPa and a thickness of 1.2 mm, cracks occurred at the flange portion, and a good molded product was not obtained. If a single steel plate having high strength is used, it is impossible to form a severely formed part such as this molded product.

On the other hand, by arranging a steel sheet having high formability at both edges where the forming is severe as in the method of the present invention, it is possible to form even a severely formed part such as the present molded article. In addition, from the steel strip of A, B, C, length 1000mm
Laser welding was performed under the same conditions as for joining in the coil state, and a joining plate was made in the same manner as the conventional tailored blank manufacturing method, and pressed to obtain the same parts. Cracks occurred and no defect-free parts were obtained. In this method, in order to obtain a molded product having no defect, the joining start and end portions must be cut off and then pressed. When measuring the cut-off margin necessary to avoid defects, it was found that 20 mm had to be cut off from each end. From the above, it can be seen that the method of the present invention is a technique for providing a material capable of forming a part having excellent moldability and excellent strength properties, and is an excellent technique for improving the yield of the material.

[0008]

EXAMPLE Twelve types of slit steel strips having the components shown in Table 1 and having the mechanical properties and dimensions shown in Table 2 were prepared according to a conventional method for manufacturing steel sheets. These steel strips were joined in the combinations shown in Table 3 to form joined coils. Then unwind the joined coil,
The sheet was cut into a predetermined length to obtain a steel sheet. Immediately after the joining, a steel sheet was cut without winding to form a steel sheet. These steel sheets were formed into parts of an automobile body shown in FIGS. For comparison, the same part was manufactured using the highest strength single steel plate and the lowest strength steel plate among the bonded steel plates, and the strength characteristics and weight were measured. The results are shown in Tables 3 to 5. From this table, it can be seen that the use of a steel sheet cut from the steel strip for press forming according to the present invention makes it possible to reduce the weight of parts having a small change in the cross-sectional shape in the longitudinal direction, such as a frame structure member of an automobile and a floor. . In addition, regarding the productivity and yield when forming a press-formed body, 500 members shown in FIG. Table 6 shows a comparison between the required steel sheet production time required for production and the required steel sheet length. From this table, it was confirmed that the method of the present invention can improve the productivity by about 2.6 times and the yield by about 5% as compared with the conventional method.

[0009]

[Table 1]

[0010]

[Table 2]

[0011]

[Table 3]

[0012]

[Table 4]

[0013]

[Table 5]

[0014]

[Table 6]

[0015]

As is apparent from the above description, according to the present invention, when a member having a substantially columnar shape in a frame structure member of an automobile is manufactured by a so-called tailored blank method, a conventional tailored blank for joining a cut plate is used. Compared with the method, the productivity and material yield can be significantly improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a method of the present invention in which a slit steel strip is joined to form a steel strip for press forming.

FIG. 2 is a perspective view of a front side member manufactured from the steel strip for press forming according to the present invention.

FIG. 3 is a perspective view of a pillar manufactured from the steel strip for press forming according to the present invention.

FIG. 4 is a perspective view of a floor manufactured from the steel strip for press forming according to the present invention.

[Explanation of symbols]

 1 Joining wire A steel strip B steel strip C steel strip

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B23K 26/00 310 B23K 26/00 310S

Claims (3)

[Claims] 1. A steel strip for press forming wherein two or more steel strips having different tensile strengths and / or sheet thicknesses are joined so as to have a joining line in the longitudinal direction of the steel strip. 2. A steel strip for press forming, wherein two or more steel strips having different tensile strengths and / or sheet thicknesses are welded to each other at the ends while unwinding the steel strip. Manufacturing method. 3. A method for producing a steel strip for press forming, wherein the welding method according to claim 2 is one of a laser welding method, a mash seam welding method, an arc welding method, a high-frequency induction welding method, and an electron beam welding method.