JP2001030020A - Forming method of member excellent in impact absorbing characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a member which hardly generates a warp in a side wall part formed in a moving direction of a forming die and excellent in impact absorbing characteristic in draw-bending a metal plate. SOLUTION: A die comprises a lower die 1 having a recessed forming surface 2 and a plate holding surface 3 continuous thereto, an upper die 4 having a projecting forming surface 5 to form a metal plate W in cooperation with the recessed forming surface 2 by being lowered to the lower die 1 side, and a plate holding member 6 to press the metal plate W against the plate holding surface 3. The radius R of curvature of a shoulder part 7 from the recessed forming surface 2 to the plate holding surface 3 is R=1.5t to 3.5t, where (t) is the thickness of the metal plate W. In forming the metal plate W, the metal plate W is restricted by the plate holding member 6 and the plate holding surface 3 when S is between 0.98×ST to 0.99×ST where S is the forming stroke that the upper die 4 is lowered, and ST is the total forming stroke, and a remaining part of ST is formed in this condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding method for improving a shock absorbing property of a shock absorbing member used for, for example, an automobile body, an automobile part and the like.

[0002]

2. Description of the Related Art Along with an increasing demand for improving the collision safety of automobiles, there is an increasing demand for reducing the weight of a vehicle body in order to improve fuel efficiency of automobiles from the viewpoint of protection of the global environment. In order to satisfy such demands, high-strength steel sheets have come to be used as a material for forming a member for absorbing an impact at the time of an automobile collision. As shown in FIG. 4, the shape of the shock absorbing member is such that the side walls 52,
Hat-shaped cross-section structural member 5 having a U-shaped cross-section, comprising:
There are many.

The hat-shaped cross-section structural member 51 is usually
It is formed by draw bending by press forming. As shown in FIG. 1, the draw bending forming includes a lower forming die 2 having a concave forming surface 2 in which a pair of flat portions are arranged to face each other, and a plate pressing surface 3 extending outside the concave forming surface 2. Die) 1 and a convex forming surface 5 which is provided to be able to move up and down with respect to the lower mold 1 and which cooperates with the concave forming surface 2 to form a metal plate W by descending to the lower mold 1 side. A metal mold 10 having an upper die 4 and a plate pressing member 6 for holding the metal plate W in a pressed state between the plate pressing surface 3 and the plate pressing surface 3 is used. The metal plate W is sandwiched in a pressed state, and the lower surface of the convex forming surface 5 of the upper mold 4 is lowered while contacting the lower surface of the convex forming surface 5 with the metal plate W, so that the metal plate W and the concave forming surface 2
Is a method of forming a U-shaped cross section between them. S in the figure is
After the lower surface of the convex molding surface 5 contacts the metal plate W, the upper mold 4
Is the amount of movement for forming, and is called a forming stroke. In addition, the pressing force (plate holding pressure) when the metal plate W is held between the plate holding surface 3 and the plate holding member 6 is equal to the metal plate held between the plate holding surface 3 and the plate holding member 6 during molding. The metal plate W is set so as not to prevent the W from flowing into the forming surface and to prevent the metal plate W from being wrinkled on the plate pressing surface 3.

When a steel plate is used as a metal plate to be formed and is drawn and bent, when the steel plate passes through a shoulder 7 which transitions from the concave forming surface 2 of the lower die 1 to the plate holding surface 3, it is bent and bent.
It undergoes work hardening in response to the bending-back deformation, thereby increasing the yield point or further baking paint (B
Called H processing. ) Further improves the yield point and improves the shock absorption characteristics of the hat-shaped cross-section structural member.

[0005]

When a hat-shaped cross-section structural member is drawn and formed by using a steel plate, as shown in FIG. 2, the hat-shaped cross-section subjected to bending / unbending deformation by an elastic recovery phenomenon after forming. There is a problem that the dimensional accuracy defect (warpage) is likely to occur in the side wall portion 52 of the structural member 51, and this warpage is more remarkable as the strength of the steel sheet is higher.

In order to prevent the warpage of the side wall portion 52, it is basically effective to apply a pulling force to the side wall portion which undergoes bending / unbending deformation during molding. In order to apply a pulling force to the side wall portion, the pressing force during molding is increased, or a concave portion is provided on the plate pressing surface 3, while a convex portion which engages with the concave portion is provided on the plate pressing member 6. A method of increasing the inflow resistance of the steel sheet is adopted.

However, in such a method, although the warpage of the side wall portion 52 is prevented, the thickness of the side wall portion 52 is considerably reduced. However, there is a problem that it is rather lowered.

The hat-shaped cross-section structural member 51 is also formed by V-bending. FIG. 7 shows the V-bending process.
As shown in FIG. 5, a lower die 21 having a V-groove forming surface 22 is lowered to the lower die 21 side to bend the metal plate W along the V-groove forming surface 22 in cooperation with the V-groove forming surface 22. A metal plate W is placed on the V-groove forming surface 22 using a mold 31 having an upper mold 24 having a convex forming surface 25 to be formed.
In this method, the top of the convex molding surface 25 is brought into contact with the metal plate W by lowering the metal plate W, and is further pressed down to bend along the V-groove molding surface 22. When formed by this V-bending, the side wall 52 of the hat-shaped cross-section structural member 51 does not warp and does not have a reduced thickness.
Since it is not deformed, it is not expected that the work hardening and the BH treatment will improve the shock absorbing properties.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a member which is hardly warped on a side wall formed in a moving direction of a forming die in draw bending of a metal plate, and which has excellent shock absorbing characteristics. An object of the present invention is to provide a molding method capable of molding.

[0010]

According to a first aspect of the present invention, there is provided a molding method comprising: a first molding die having a concave molding surface and a plate pressing surface coupled to the outside of the concave molding surface; A second forming die having a convex forming surface for forming a metal plate supplied on the plate pressing surface in cooperation with the concave forming surface by relatively moving to the first forming die side; And a plate pressing member that presses the metal plate against the plate pressing surface at the time of the transfer.The shoulder portion that transitions from the concave forming surface to the plate pressing surface has a curvature radius R where the thickness of the metal plate is t. Using a mold with R = 1.5t to 3.5t, the forming stroke at which the first forming die or the second forming die relatively moves when forming a metal plate is S, and the entire forming required for forming is performed. When the stroke is ST, S is 0.98 × ST
The metal plate is constrained by the plate pressing member and the plate pressing surface when it is between 0.99 × ST and the remaining portion of ST is formed in that state.

[0011] According to the molding method of the present invention, the radius of curvature R of the shoulder portion transitioning from the concave molding surface of the first molding die to the plate pressing surface.
Is drawn and bent using a mold having a thickness of 1.5 to 3.5 t with respect to the thickness t of the metal plate, and when forming, when the total forming stroke required for forming is ST, the forming stroke S Is between 0.98 × ST and 0.99 × ST, the metal plate is constrained by the plate pressing member and the plate pressing surface, and the remaining portion of the ST is formed in that state. In a later stage of molding, elongation strain can be introduced into the side wall portion of the molded member molded in the moving direction of the molding die with almost no change in thickness. For this reason, it is possible to improve the warpage of the side wall portion while preventing the impact absorption characteristics from deteriorating due to the decrease in the plate thickness.

The radius of curvature R of the shoulder is 1.5t to 3.5.
The reason for setting t is to provide appropriate work hardening without reducing the thickness of the metal plate by bending and unbending deformation when the metal plate passes through the shoulder. That is, as is clear from the examples described below, when the radius of curvature R of the shoulder is less than 1.5 t, the yield point due to work hardening due to bending / unbending deformation when the metal plate passes through the shoulder is sufficiently increased. In addition, since the amount of deformation increases, the thickness of the side wall of the molded member decreases, and the shock absorption characteristics deteriorate. On the other hand, if R exceeds 3.5t, bending and bending when the metal plate passes over the shoulder
Since the amount of bending back deformation is small, the rise of the yield point is insufficient,
Shock absorption characteristics are not improved.

The reason why the starting point of the restraint of the metal plate, that is, the switching point from the former stage to the later stage, is that the forming stroke S is between 0.98 × ST and 0.99 × ST will be described later. As is clear from the examples, S is equal to 0.
If it is less than 98ST, the warpage is reduced, but the remaining molding stroke (ST-
Since S) is long, the elongation strain of the side wall portion is increased, the plate thickness is reduced, and the shock absorption characteristics are deteriorated. On the other hand, when S exceeds 0.99ST, the forming stroke (ST-S ) Is short, sufficient extension is not applied to the side wall portion, and the effect of reducing the warp becomes insufficient.

The metal plate to be formed in the present invention is not limited to a steel plate, but may be an Al or Al alloy plate, a Ti or Ti alloy plate, and the higher the strength, the more effective.
Plate thickness 1-3 used as an automobile member as a metal plate
When a steel sheet of about mm is used, the pressing force P by the sheet pressing member of the steel sheet in the pre-forming stage is usually the surface pressure acting on the steel sheet sandwiched between the sheet pressing surface and the sheet pressing member at the end of the forming in the pre-forming step. The pressing force is set to be 10 to 30 kgf / cm ² in order to restrain the steel plate before entering the post-forming stage and prevent the steel plate from flowing into the concave forming surface.
What is necessary is just to set it to 0xP or more.

Also, a first mold of a mold used in the present invention,
The second molds correspond to the lower mold 1 and the upper mold 4 in FIG. 1 respectively, but the arrangement of the lower mold 1 and the upper mold 4 is inverted upside down,
The lower mold 1 may be moved to the upper mold 4 to perform molding.

[0016]

EXAMPLE A steel plate of 590N strength (plate thickness t = 1.6)
0mm, yield point YS = 376N / mm ^Two, Tensile strength TS = 6
03N / mm^Two, Elongation El = 26.5%) in FIG. 1 and FIG.
Using the mold shown in Fig. 7, draw in accordance with the conditions in Table 1.
Manufacture hat-shaped cross-section members by bending and V-bending
Was.

In the drawing bending forming, the total forming stroke ST is 80 mm, and the pressing force F1 at the stage before forming by the plate holding member 6 is 5 tonf (the surface pressure acting on the steel sheet at the end of forming at the stage before forming is 27 kgf / cm ² ). Molded as The molding stroke S is equal to the entire molding stroke ST.
(= 80 mm), when the S / ST in the table is reached, the pressing force is increased to F2, and the steel plate is restrained on the plate holding surface 3 so that the remaining portion of ST (ST-S) is removed. Molded. R in the table is the radius of curvature of the shoulder 7 shown in FIG. 1 or the radius of the tip of the convex molding surface 25 shown in FIG.

After molding, the side wall 5 of the hat-shaped cross section member 51 is formed.
2 was measured. As shown in FIG. 2, the magnitude δ of the warpage is determined by measuring the maximum separation amounts δ1 and δ2 in the side walls 52, 52 from a straight line connecting the R-stops (round ends) of the corners of the hat-shaped sectional member 51, Calculated from δ = (δ1 + δ2) / 2. Further, a tensile test piece was sampled from the side wall portion 52, and the average plate thickness t 'was determined. Further, the yield point was measured by a tensile test, and the difference between the yield point and the steel sheet before forming (Δ
YS).

As shown in FIG. 3, an impact test member 63 is formed by spot welding a flat plate 61 of the same material and thickness to the opening of the hat-shaped cross-sectional structural member 51 and welding end plates 62, 62 to both ends. Was manufactured and subjected to an impact crush test in the following manner to examine the impact absorption characteristics during high-speed deformation. In the impact crush test, one end of the test member 63 was fixed, and 14
A collision object was caused to collide from the axial direction of the test member at m / s, and the absorbed energy when the displacement of the hat-shaped cross-sectional structural member 51 was up to 150 mm was measured. FIG. 3 shows the dimensions (mm) of each part.
Also shown.

The results of these measurements are also shown in Table 1. FIG. 5 is a graph showing the relationship between R / t and absorbed energy for Samples Nos. 2 to 9, and FIG.
FIG. 6 shows a graph in which the relationship between S / ST and the absorbed energy is arranged for.

[0021]

[Table 1]

From the sample Nos. 2 to 9 and FIG. 5, when the radius R of the lower mold shoulder 7 is changed, the thickness t 'after forming is greatly changed, and the invention condition (R / t = 1.5-3) .5) (Nos. 4 to 6) show that the absorbed energy is improved by about 10% as compared with No. 1 formed by V-bending.

Further, from Sample Nos. 14 to 18 and FIG. 6, Sample No. 1 satisfying the steel plate restraint timing of the present invention.
6 and 17, the warpage is small, the absorbed energy is large,
It can be seen that the molding accuracy and the shock absorption characteristics are excellent. On the other hand, when the steel sheet was restrained when the forming stroke S was smaller than 0.98 × ST and the inflow to the forming surface was prevented, the sheet thickness was reduced by 0.10 mm or more, and the absorbed energy was reduced.
Further, when the steel sheet was constrained when S was larger than 0.99 × ST, a large warpage occurred at the time of forming, and it was not possible to manufacture a test member.

No. 1 where F2 / F1 is 3.5 or less.
In Nos. 0 and 11, the steel sheet was not constrained and the steel sheet flowed into the forming surface was recognized, so that large warpage occurred during the forming, and thus the test member could not be manufactured.

[0025]

According to the molding method of the present invention, the radius of curvature of the shoulder of the first mold is set to 1.5 to 3.5 to the thickness t of the metal plate to be molded. The timing for restraining the inflow to the molding surface by restricting the
Since it is performed in the range of 0.99ST (full forming stroke ST), the yield strength due to work hardening can be reduced while preventing a decrease in the thickness of the side wall portion of the formed member that undergoes bending / unbending deformation during forming. In addition, it is possible to obtain a molded member capable of introducing sufficient elongation strain, preventing warpage of the side wall portion, and having excellent shock absorption characteristics.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a mold for performing draw bending.

FIG. 2 is a perspective view of a hat-shaped cross-section structural member in which a side wall has a warp.

FIG. 3 is an overall perspective view of an impact crush test member provided with a hat-shaped cross-section structural member.

FIG. 4 is a perspective view of a hat-shaped cross-section structural member.

FIG. 5 is a graph in which the relationship between R (radius of curvature of shoulder) / t (plate thickness before molding) and absorbed energy in Examples is arranged.

FIG. 6 shows S (forming stroke) / ST in the embodiment.
It is the graph which arranged the relationship between (total molding stroke) and absorbed energy.

FIG. 7 is a sectional view of a mold for performing V-bending.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lower mold | die (1st shaping | molding die in this invention) 2 Concave shaping | molding surface 3 Plate holding surface 4 Upper shaping | molding (2nd shaping | molding die in this invention) 5 Convex shaping | molding surface 6 Sheet pressing member 7 Shoulder W Metal plate

Claims (1)

[Claims] A first molding die having a concave molding surface and a plate pressing surface coupled to the outside of the concave molding surface; and a first molding die having a concave shape formed on the plate pressing surface by relatively moving to the first molding die side. A second molding die having a convex molding surface for molding the supplied metal plate in cooperation with the concave molding surface, and a plate pressing member for pressing the metal plate against the plate pressing surface during molding,
The shoulder portion transitioning from the concave forming surface to the plate holding surface has a curvature radius R = 1.5 when the thickness of the metal plate is t.
The first molding die or the second molding die for molding a metal plate using a mold set to t to 3.5t.
When the molding stroke at which the mold moves relative to each other is S and the entire molding stroke required for molding is ST, S is 0.9
When the metal plate is between 8 × ST and 0.99 × ST, the metal plate is constrained by the plate pressing member and the plate pressing surface, and the remaining portion of ST is formed in that state. Method.