JP2021049575A - Press molding method - Google Patents

Abstract

To prevent damage of a mold in O bending process, when forming a cylindrical component having a curved bottom part by UO bending molding.SOLUTION: An upper limb 12a of a pair of vertical wall parts 12 of a U bending molded product 5 is provided with a butting line 12b butting mutually in O bending process, and with an escape line 12c adjoining to the butting line 12b, and retracted from an extension line L of the butting line 12b. The butting line 12b and the escape line 12c are continuous through a corner part 12d with an obtuse angle or a curved part 12f.SELECTED DRAWING: Figure 3

Description

The present invention relates to a press molding method for molding a metal plate into a tubular shape.

UO bending molding is known as a method of press molding a tubular part (see, for example, Patent Document 1 below). In UO bending molding, a metal plate is press-formed (U-bending step) into a U-shaped cross section, and then formed into a tubular shape by the O-bending step shown in FIG. In the O-bending step, first, a metal plate 101 having a U-shaped cross section is set on the lower mold 120 (see FIG. 10 (A)), the upper mold 110 is lowered, and the upper sides of the pair of vertical wall portions 101a are butted against each other. (See FIG. 10 (B)). After that, by further lowering the upper mold 110, each vertical wall portion 101a is buckled and curved outward (see FIG. 10C), and pressed against the molding surface of the upper mold 110 to form a cylinder having a circular cross section. The shaped part 130 is molded (see FIG. 10 (D)).

Further, Patent Document 2 below discloses a method of molding a tubular part having a deformed (non-circular) cross section by UO bending. Specifically, the O-bending process consists of a first O-bending step (intermediate bending step) in which a bent portion is formed on a vertical wall portion of a workpiece having a U-shaped cross section, and a second step in which the ends of the vertical wall portions are abutted against each other. By performing the O-bending step (O-bending step) separately, UO-bending molding of a tubular part having a deformed cross section is possible.

Japanese Unexamined Patent Publication No. 2014-4626 JP-A-2018-161678

For example, when molding a part curved so as to be convex downward along the longitudinal direction, the molding surface of the upper mold in the O-bending process is a vertical wall portion of a molded product having a U-shaped cross section (U-bending molded product). It is designed to have a curved shape along the upper side (see FIG. 3B). When such an upper mold is lowered, theoretically, the U-bent molding surface of the upper mold makes line contact with the entire upper side of the vertical wall portion of the molded product at the same time. However, when the present inventors actually performed an O-bending step on a U-bent molded product that was curved so as to be convex downward along the longitudinal direction, the U-bent molded product among the molded surfaces of the upper mold was obtained. The corners of the vertical wall (the corners at both ends of the upper side of the vertical wall) were scratched. If the mold in the O-bending process is damaged in this way, the life of the mold is shortened, and the scratches on the molded surface are transferred to the subsequent molded product, which may reduce the quality.

Therefore, an object of the present invention is to prevent damage to the mold in the O-bending process when forming a tubular part curved so as to be convex downward along the longitudinal direction by UO bending molding.

For example, if an obtuse-angled corner or curved portion is provided at the upper end of a pair of vertical wall portions of a U-bent molded product, the obtuse-angled corner or curved portion becomes a molding surface of the mold in the O-bending step. Since they come into contact with each other, damage to the mold can be prevented. However, extending the vertical wall portion in the longitudinal direction in order to provide an obtuse-angled corner portion or a curved portion at the end portion of the upper side of the pair of vertical wall portions of the U-bent molded product leads to an increase in cost.

Therefore, the present invention has a U-shaped cross section having an elongated bottom portion curved so as to be convex downward along the longitudinal direction and a pair of vertical wall portions rising upward from both ends in the lateral direction of the bottom portion. The U-bending step of press-molding the U-bending molded product and the O-bending step of pressing the U-bending molded product to abut the ends of the pair of vertical wall portions to form a tubular shape are provided. In a press molding method, on the upper side of a pair of vertical wall portions of the U-bent molded product, a butt line that abuts each other in the O-bending step and a retract that is adjacent to the butt line and recedes from an extension line of the butt line. A line is provided, and the butt line and the withdrawal line are continuously pressed through a corner portion or a curved portion having an blunt angle.

In this way, if the evacuation line recessed from the extension line of the butt line is provided on the upper side of the pair of vertical wall portions of the U-bent molded product, the butt line and the evacuation line are provided without extending the vertical wall portion in the longitudinal direction. It is possible to prevent damage to the O-bending mold by providing an obtuse-angled corner or curved portion between the and.

When the above-mentioned evacuation lines are provided on the upper side of the vertical wall portion of the U-bent molded product, the evacuation lines provided on both vertical wall portions do not abut each other in the O-bending step, so that a molding defect occurs in this portion. May occur. Therefore, if a step of cutting and removing the region including the escape line from the product portion is performed after the O-bending step, the portion where the molding defect has occurred can be separated from the product, so that the occurrence of the defective product can be avoided.

As described above, according to the present invention, when forming a tubular part curved so as to be convex downward along the longitudinal direction by UO bending molding, it is possible to prevent damage to the mold in the O bending process. Therefore, it is possible to extend the life of the mold and improve the quality of the molded product.

(A) is a plan view of a tubular part manufactured by the press molding method according to the embodiment of the present invention (viewed from the direction A in FIG. B), and (B) is a side view (B in FIG. A). (View from the direction) and (C) are the same cross-sectional views (CC cross-sectional view of FIG. B). (A) is a plan view of the drawn product (viewed from the direction A in FIG. B), (B) is a side view (viewed from the direction B in FIG. A), and (C) is a sectional view (C). It is CC cross-sectional view of FIG. B). (A) is a plan view of a U-bent molded product (a view seen from the A direction of FIG. B), (B) is a side view (a view seen from the B direction of FIG. A), and (C) is a sectional view of the same. (C-C cross-sectional view of FIG. B). (A) and (B) are enlarged views of the vicinity of the upper end of the U-bent molded product. (A) to (D) are cross-sectional views showing the procedure of the first O bending step. (A) to (C) are cross-sectional views showing the procedure of the second O bending step. It is a top view of the 2nd O bending molded article. It is an enlarged view of the vicinity of the end portion of the upper side of the U-bent molded article according to another embodiment. It is an enlarged view of the vicinity of the end portion of the upper side of the U-bent molded article according to still another embodiment. (A) to (D) are sectional views of the O bending process in the conventional UO bending molding.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

In this embodiment, the manufacturing method of the tubular part 1 shown in FIG. 1 is shown. The tubular component 1 is used as the left and right trailing arms of the rear suspension of the vehicle. The tubular part 1 has an irregular (non-circular) cross section. In the present embodiment, the cross section of the tubular component 1 is substantially rectangular, and the cross-sectional shape changes in the longitudinal direction. Specifically, as shown in FIG. 1C, the tubular component 1 includes a bottom portion 1b, a pair of side portions 1c rising upward from both ends in the width direction (left-right direction in the figure) of the bottom portion 1b, and a pair. It has a pair of upper portions 1d extending inward in the width direction from the upper end of the side portion 1c. The butt portion 1a in which the ends of the pair of upper portions 1d are butted against each other is joined by the welded portion 1g. A bent portion (hereinafter referred to as “bottom bent portion 1e”) is provided at the boundary between the bottom portion 1b and each side portion 1c, and a bent portion (hereinafter referred to as “bending portion”) is provided at the boundary between each side portion 1c and each upper portion 1d. Shoulder bending portion 1f ") is provided. The bottom portion 1b is curved so as to be convex downward along the longitudinal direction (see FIG. 1 (B)). In the illustrated example, the entire tubular component 1 is curved in both the plan view shown in FIG. 1 (A) and the side view shown in FIG. 1 (B). In the present specification, with the longitudinal direction of the tubular part 1 arranged substantially horizontally, the butt portion 1a side is referred to as the upper side and the bottom portion 1b side is referred to as the lower portion, but these are directions based on the posture at the time of press molding. Yes, it is not intended to limit the usage mode of the tubular part 1.

The tubular part 1 is manufactured through a blanking step, a draw forming step, a trimming step, a U bending step, an O bending step, a welding step, and a cutting step. In the present embodiment, the O-bending step is divided into two stages, a first O-bending step and a second O-bending step.

In the blanking step, a blank material having a predetermined shape is formed by punching a flat metal plate with a die.

In the draw forming step, the draw form 3 shown in FIG. 2 is formed by press forming (drawing) the blank material with a mold. The drawn product 3 has an elongated bottom portion 11, a pair of vertical wall portions 12 rising upward from both ends in the lateral direction of the bottom portion 11, and a pair of flange portions 13 extending outward from the upper ends of the pair of vertical wall portions 12. And have. A bottom bent portion 14 is provided at the boundary between the bottom portion 11 and each vertical wall portion 12. The shape of the lower portion (bottom portion 11 and bottom bent portion 14) of the drawn product 3 is substantially the same as the shape of the lower portion (bottom portion 1b and bottom bent portion 1e) of the tubular part 1 of the finished product.

In the trimming step, the pair of flange portions 13 of the drawn product 3 are cut along a cutting line extending in the longitudinal direction to form a trimmed product. In this embodiment, cutting is performed along the cutting line M shown in FIG. 2 (A). The trimming step may be performed by one press or may be divided into a plurality of presses.

In the U-bending step, the trim product is pressed with a die (not shown) to form the U-bent molded product 5 having a substantially U-shaped cross section shown in FIG. Specifically, the flange portion 13 of the trim product is raised by bending molding and arranged on a substantially extended surface of the vertical wall portion 12. Hereinafter, the vertical wall portion 12 and the flange portion 13 arranged on the extension surface thereof are collectively referred to as a “vertical wall portion 12”.

A butt line 12b and a retreat line 12c are provided on the upper side 12a of both vertical wall portions 12 of the U-bent molded product 5. In the illustrated example, the butt line 12b occupies most of the longitudinal intermediate portion of the upper side 12a, and the escape lines 12c are provided at both ends in the longitudinal direction of the upper side 12a. The butt line 12b is a region that abuts each other in a later O-bending step. The escape line 12c is a region that is provided at a position recessed below the extension line L of the butt line 12b and does not butt against each other in the subsequent O-bending step. As shown in FIGS. 4 (A) and 4 (B), the butt line 12b and the escape line 12c are continuous via an obtuse angled corner portion 12d. In the illustrated example, the escape line 12c forms a straight line, and more specifically, the evacuation line 12c forms a straight line in a direction orthogonal to the press direction.

In the first O-bending step, the first O-bending die 40 shown in FIG. 5 is used. As shown by a chain line in FIG. 3B, a concave groove-shaped molding surface 41a curved substantially parallel to the U-bending molded product 5 is provided on the lower surface of the upper die 41 of the first O bending die 40. In the first O-bending step, first, as shown in FIG. 5A, the bottom portion 11 of the U-bent molded product 5 is set in the recess 42a of the lower mold 42, and then the upper mold 41 is lowered to form the upper mold 41. The upper side 12a of both vertical wall portions 12 of the U-bent molded product 5 is pushed downward on the molding surface 41a. As a result, the pair of vertical wall portions 12 of the U-bent molded product 5 are inclined inward while being guided inward in the width direction by the molding surface 41a of the upper mold 41, and the upper sides 12a of both vertical wall portions 12 become the upper mold 41. It abuts against the provided locking portion 41b (see FIG. 5B). At this time, the upper side 12a of the vertical wall portion 12 slides while being pressed against the molding surface 41a of the upper mold 41, but as shown in FIG. 3B, obtuse-angled corners are formed at both ends of the butt line 12b of the upper side 12a. Since the 12d is provided, it is possible to prevent the molding surface 41a of the upper mold 41 from being damaged by the contact of the corner portion 12d.

After that, when the upper die 41 is further lowered, the vertical wall portion 12 is compressed in the vertical direction to cause buckling, and the intermediate portion of the vertical wall portion 12 bulges outward (see FIG. 5C). When the upper mold 41 is further lowered, the bulging portion of the vertical wall portion 12 is pressed against the molding surface 41a of the upper mold 41, whereby the shoulder bending portion 12e is formed in the intermediate portion of the vertical wall portion 12, and the first O A bent molded product 6 is formed (see FIG. 5 (D)).

In the second O-bending step, the second O-bending die 50 shown in FIG. 6 (A) is used. In the second O bending step, the first O bending molded product 6 is set in the recess 52a of the lower mold 52, and then the upper mold 51 is lowered to lower the upper side 12a of the vertical wall portion 12 of the first O bending molded product 6. Is pushed downward by the upper mold 51, the shoulder bending portion 12e is further bent, and the upper sides 12a of the vertical wall portion 12 abut against each other (see FIG. 6B). After that, when the upper mold 51 is further lowered, the entire vertical wall portion 12 is pressed against the molding surface 51a of the upper mold 51, and the second O-bent molded product 7 is molded (see FIG. 6C).

As shown in FIG. 7, the second O-bent molded product 7 has a butt portion 7a in which the butt lines 12b are butted against each other, but the escape lines 12c provided at both ends in the longitudinal direction do not abut against each other. They face each other through a gap. In the subsequent welding step, the butt portion 7a of the second O-bent molded product 7 is welded to form a welded portion 1 g (see the dotted line). The welded portion 1 g is formed by, for example, arc welding. In the subsequent cutting step, the unnecessary portion of the second O bending molded product 7 is removed. In the present embodiment, the region including the escape line 12c in the second O-bent molded product 7 is cut and removed from the product portion. Specifically, for example, by cutting the second O-bent molded product 7 at a surface V substantially orthogonal to the longitudinal direction, the product portion has a tubular region including the escape line 12c provided at the left end portion in the drawing. Is separated from. Further, in the second O-bent molded product 7, by cutting along the line W along the surface provided with the butt portion 7a, a planar region including the escape line 12c provided at the right end portion in the drawing is formed as a product. Separated from the part. If there is no particular problem as a product, one or both of the escape lines 12c provided at both ends of the butt portion 7a may be left. As a result, the tubular part 1 shown in FIG. 1 is completed.

The present invention is not limited to the above embodiments. Hereinafter, other embodiments of the present invention will be described, but the same points as those of the above-described embodiments will be omitted.

In the embodiment shown in FIG. 8, the butt line 12b and the escape line 12c provided on the upper side 12a of the vertical wall portion 12 of the U-bent molded product 5 are smoothly continuous with each other via the curved portion 12f. The curved portion 12f is formed, for example, by an arc having a radius R1 having a center of curvature O1 below the curved portion 12f. The curved portion 12f is not limited to an arc, but may be an ellipse, a logarithmic curve, or the like. It is considered that the end of the escape line 12c on the opposite side of the butt line 12b does not normally come into contact with the die, but if there is a concern that the end may come into contact with the die due to deformation during pressing or the like, this end A curved portion may also be provided in the portion.

In the embodiment shown in FIG. 9, the escape line 12c itself is formed by a curved line and is smoothly continuous with the butt line 12b. In the illustrated example, the shunt line 12c and the butt line 12b are smoothly continuous with each other via the curved portion 12f which is an extension of the shunt line 12c. The escape line 12c and the curved portion 12f at this time are formed by, for example, an arc having a radius R2 having a center of curvature O2 below the escape line 12c. The escape line 12c and the curved portion 12f are not limited to the arc, but may be an ellipse, a logarithmic curve, or the like. Further, the escape line 12c and the curved portion 12f may have different curves.

In the above embodiment, the case where the escape line 12c is formed by the trimming step is shown, but the present invention is not limited to this, and for example, a part or all of the escape line 12c may be formed by the blanking step. In the above embodiment, as shown in FIG. 2B, the drawn product 3 is curved so as to be convex downward along the longitudinal direction, so that the trimming step is performed in the vicinity of the end portion in the longitudinal direction. The die drawing direction and the surface direction of the flange portion 13 are not orthogonal to each other, and there is a possibility that the relief line 12c cannot be formed accurately. Therefore, if a part or all of the escape line 12c at the end in the longitudinal direction is formed not in the trimming process but in the blanking process, the escape line 12c can be formed with high accuracy. For example, the escape line 12c can be formed in the blanking step, and the butt line 12b can be formed in the trimming step. Alternatively, in the blanking step, a part of the side side 12g shown in FIGS. 4, 8 and 9 and a part of the escape line 12c continuous thereto (if a curved portion is formed between them, the curved portion thereof) is formed. , The butt line 12b, the remaining portion of the escape line 12c, and the corner portion 12d or the curved portion 12f between them may be formed in the trimming step.

Further, the manufacturing process of the tubular part 1 is not limited to the above. For example, the O-bending step may be performed in one step without being divided into two steps (first O-bending step and second O-bending step). Alternatively, the first O bending step may be performed in a plurality of stages. Further, if there is no particular need, any one or more of the draw forming step, the trimming step, and the cutting step may be omitted.

Further, in the above embodiments, the case where the tubular component 1 according to the present invention is a trailing arm of a vehicle is shown, but the present invention is not limited to this. For example, the present invention can be applied to a tubular component such as an intermediate beam connecting the left and right trailing arms, a pillar-to-pillar member, or an impact beam of a door.

1 Cylindrical part 1a Butt part 1g Welded part 3 Stretch-molded product 5 U Bend-molded product 6 First O-bend-molded product 7 Second O-bend-molded product 11 Bottom 12 Vertical wall 12a Top side 12b Butt line 12c Evacuation line 12d Square part 12f Curved part 13 Flange part 40 First O bending die 50 Second O bending die L (butt line) extension line M Cutting line

Claims (2)

A U-shaped U-bent molded product having a U-shaped cross section having an elongated bottom portion curved so as to be convex downward along the longitudinal direction and a pair of vertical wall portions rising upward from both ends in the lateral direction of the bottom portion. It is a press molding method including a U-bending step of press-molding and an O-bending step of pressing the U-bending molded product to abut the ends of the pair of vertical wall portions to form a tubular shape. ,
On the upper side of the pair of vertical wall portions of the U-bent molded product, a butt line that abuts each other in the O-bending step and a retreat line that is adjacent to the butt line and recedes from the extension line of the butt line are provided.
A method in which the butt line and the evacuation line are continuously pressed through an obtuse-angled corner portion or a curved portion. The press molding method according to claim 1, further comprising a step of cutting and removing the region including the escape line from the product portion after the O-bending step.

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