JPH0337442B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field] The present invention relates to a method for forming an overhang in a panel, particularly a steel panel.

[Conventional technology]

Panel stretch molding can increase the section modulus without changing the plate thickness, so it is often used for parts that require both weight reduction and high buckling strength, such as side panels of freight cars and exterior panels of various machines. It is being

[Problem that the invention seeks to solve]

In the stretch molding of such a panel, the amount of molding and the shape of the overhang are restricted because defects in shape such as warping occur in the unprocessed part when the amount of molding exceeds a certain level. When molding exceeds this restriction, it is necessary to perform heat molding or to perform correction after molding, which has been a major obstacle to the application of stretch molding.

The shape defects that occur in conventional panel stretch forming as described above occur when a panel blank held by a blank holder is stretched in one direction with a punch to form a processed part, as shown in Figures 1 and 2. , the existence of residual stress etc. due to the force F ₁ that the processed part a pulls on the unprocessed part b around it,
If the panel was completed as a result of intensive research after realizing the synergistic effect of the springback force _F2 on the processed part a with the springback, heat forming or post-forming correction may be required in the panel stretch forming. The object of this invention is to significantly reduce the amount of warpage of the unprocessed portion and eliminate shape defects.

[Means for solving problems]

After a part of the panel blank 5 is stretched out in one direction with the punch 3 and a processed part 6 is stretch-molded, the processed part 6 that has been stretched for the first time is stretched out in one direction with the punch 4. In the opposite direction, the initial stretch amount
It is characterized by stretch molding with a re-stretching amount of 60 to 80%.

〔Example〕

Embodiments of the present invention will be described based on FIGS. 3 to 10.

In Fig. 3, 1 is the upper blank holder, 2
is a lower blank holder, 3 is an upper punch, and 4 is a lower punch. 5 is a panel blank.

The panel blank 5 is held between the upper and lower blank holders 1 and 2 from above and below, and the upper punch 3 is actuated to form the primary processing section 6 downward. Stretch molding.

Next, as shown in Figure 3B, the lower punch 4
is activated to apply reverse pressure to the primary processing section 6,
Furthermore, as shown in FIG.
That is, reverse re-stretch molding is performed.

Therefore, as panel blank 5, the tensile strength is 70
Kg/mm ^2nd class high tensile strength steel plate, specifically Nippon Steel's steel grade code WT70RE steel plate, thickness 4.0mm, length 1000mm,
Using a plate material with a width of 800 mm, the upper punch 3 is stroked downward by 9 mm using the mold shown in Fig. 4 to stretch-form the first processed part 6. The measurement results were as shown in FIG. Next, the surface of the panel blank 5 when the lower punch 4 is applied to the first processed part 6 of this panel blank 5 and stroked upward by 16 mm to extend the second processed part 6' upward. The strain measurement results were as shown in FIG.

However, in order to measure the above-mentioned surface strain, as shown in FIG. Value h of measured position
The value (h - 4.0) mm obtained by subtracting the plate thickness (4.0 mm) from Δh is the surface strain amount Δh, and the measured surface strain amount is expressed as a contour line.

As is clear from Figures 5 and 6, compared to the case where the processed part is formed by extending in one direction,
In the case of reverse re-stretch molding, the amount of surface strain, that is, the amount of warpage in the unprocessed portion is significantly reduced, and shape defects can be eliminated.

Furthermore, panel blank 5 was made of Nippon Steel's steel type code WT70RE steel plate, with a thickness of 4.0 mm and a length of
A plate material of 3700 mm and a width of 800 mm was used, and the mold shown in Figure 4 was used in the same way as in the previous experimental example, and the upper punch 3 was stroked downward by 9 mm sequentially in the longitudinal direction, with a center spacing of 560 mm between the punches. The results of measuring the surface strain of the panel blank 5 when the first processed portion was stretch-molded were as shown in FIG. Next, apply the lower punch 4 to the first processed portion 6 of this panel blank 5 and punch it upward by 16
The measurement results of the surface strain of the panel blank 5 when the second processed portion 6' was stretched upward with a stroke of mm are as shown in FIG. It is clear that the amount is significantly reduced, and shape defects can be eliminated.

Incidentally, the amount of surface strain was measured by the measuring method shown in FIG. 9, as in the above-mentioned experimental example.

Similarly to the experimental example shown in Figure 6, Nippon Steel's steel grade code WT70RE steel plate was used, with a length of 1000 mm and a width of 800 mm.
using plate materials with thicknesses of 3.2, 4.0, and 6.0 mm, respectively, and the reverse re-stretching rate (%) = lower punch overhang amount (reverse re-stretching amount) / upper punch overhang amount (initial re-stretching amount) The maximum amount of surface strain that occurs in each blank when the forming amount) x 100 is varied (the measurement method is the same as the experimental example above) △h
As shown in FIG. 10, a preferable result was obtained in which the amount of reverse bulge formation was 60 to 80% of the amount of initial bulge formation.

Note that the above-mentioned upper punch overhang amount (initial overhang forming amount) refers to the horizontal center line of the panel blank 5 when it is horizontally installed before overhang forming as a reference line, and the amount of punch 3 above the reference line. Amount of downward protrusion (mm)
Similarly, the lower punch overhang amount (reverse re-stretching amount) is the upward overhang amount (mm) of the punch 4 below the reference line.

〔Effect of the invention〕

In the present invention, by making the amount of reverse re-stretching smaller than the amount of initial stretching, it is possible to significantly reduce the amount of surface strain, that is, the amount of warpage in the unprocessed portion, and eliminate shape defects.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the force exerted by the processed part of the panel on the surrounding unprocessed part, Fig. 2 is an explanatory diagram of the spring back in the processed part of the panel, and Fig. 3 is the process of stretch forming the processed part according to the method of the present invention. Figure 4 is an explanatory diagram of the mold, Figure 5 is an explanatory diagram of the amount of warpage during initial stretch molding of the panel, and Figure 6 is an explanatory diagram of the amount of warpage during reverse re-stretch molding of the panel. , Fig. 7 is an explanatory diagram of the amount of warpage during initial stretch forming of a long material, Fig. 8 is an explanatory diagram of the amount of warpage during reverse stretch forming of a long material, and Fig. 9 is an illustration of the amount of warpage during initial stretch forming of a long material. FIG. 10, which is an explanatory diagram showing the method, is a graph showing the relationship between the reverse overhang ratio and the amount of warpage. 3 and 4 are punches, 5 is a blank, and 6 and 6' are processed parts.

Claims (1)

[Claims] 1 After stretching a part of the panel blank 5 in one direction with the punch 3 to stretch-form the processed part 6, the processed part 6 that has been stretched for the first time is stretched in the first direction with the punch 4. A method for forming an overhang in a panel that causes less warpage, characterized by performing overhang in the opposite direction with a re-stretching amount of 60 to 80% of the initial stretching amount.