Thin sheet forming dies

Abstract: It is an object of this invention to use only one die for forming an excessively bent negative angle forming portion when negative angle forming is carried out on formed thin sheets using rotating cams. This is a forming die with a forming portion to achieve a negative angle when the second die is moved in the straight line to abut the first die (5) for forming thin sheets (W) and in the thin sheet forming dies in which a cylindrical rotating cam (4) with a groove formed in the axial direction is rotatably mounted to the first die (5), a negative angle forming portion (16) is formed in the groove edge portion (10) of the rotating cam (4), a slide cam (27) with the negative angle forming portion (28) is mounted to the second die (21) in such a manner to be opposite to the said rotating cam (4), an automatic return device (11-15) for rotating and retracting the rotating cam (4) to enable the removal of the work (W) from the first die (5) after forming is mounted to the first die, it is a thin sheet forming die designed to process an excessively bent negative angle forming portion with one rotating cam (4) equipped with a plurality of cylindrical rotating cam portions (2,3) in varying diameters.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The invention relates to thin sheet forming die as defined in the preamble portion of claim 1. DESCRIPTION OF THE PRIOR ART The negative angle of thin sheets such as sheet metal or plastics is generally formed by the use of a slide cam. Now, the negative angle forming referred to here means forming with a forming portion which comes inwards towards the lower die from the working locus of the upper die when the work loaded on the lower die is formed by descending the upper die in the vertical direction for abutting. In the conventional negative angle forming of thin sheet products, the work is loaded on the lower die and the upper die descends downwards in the vertical direction to drive the driven cam of the lower die by the driving cam of the upper die, and the work is processed from the lateral direction, and when processing completes and the upper die ascends, the driven cam is retracted by springs. In this event, the forming portion of the driven cam which slides and forms the work from the outward lateral direction of. the work is formed in the integrated profile identical to that of the forming portion of the work, but the forming portion of the lower die with the work loaded must be designed to divide and retract the portion forming a negative angle of the lower die, or the rear portion forming the negative angle is deleted and the work is moved forward to enable the removal of the work. When the degree of negative angle is small, no serious problems occur but when the degree of negative angle is great or the product has a slender frame-like cross section with grooves, for example, parts such as front pillar outer of automobile sheet metal parts, due to the narrow groove width of the work, not only the profile is unable to be clearly formed at the forming portion of the driven cam when the portion of the lower die serving as a negative angle is divided or deleted, but also the strength of the lower die lacks and it is impossible to carry out negative angle forming. In negative angle forming using the slide cam, the driven cam is slid in a considerably long straight distance for forming, it is not always easy to repeatedly slide the driven cam exactly to a specified position and it is difficult to produce products with stable quality. In addition, there are cases in which distortion or bend is generated in products and the products must be touched up, but it is practically impossible to touch up products for parts composing the automobile outer plate portions such as side panels, front fenders, roofs, bonnets, trunk lids, door panels, or front pillar outers, because they have three-dimensional curved surfaces and profiles. In the case of automobile sheet metal assembly, if any distortion or bend is generated in products, it is difficult to combine such products with other parts and it is impossible to provide a high-quality automobile sheet metal structure and to maintain a specified product accuracy of thin-plate formed products. When the slide cam is used, a large driven cam and heel must be mounted on the side portion with the work of the lower die loaded, requiring a large lower-die area, increasing the die weight, and resulting in expensive dies. Therefore, in order to solve the above problems, a forming method of thin sheets and the forming dies in which the linear upward and downward motion of a press is converted into rotary motion has already been proposed by the present applicant under Japanese Patent Publication No. Sho 63-41662. Referring now to Figs. 4-9, the forming dies will be described in further detail. FIG. 4 shows right and left schematic perspective views of a complete front pillar outer, an automobile sheet metal part formed by the forming dies. In the figure, the bottom shows the front pillar outer for the right side and the top for the left side. This front pillar outer constitutes part of the front door frame, also part of the front wind shield frame, and in addition part of the frame supporting the roof panel, and comprises the joint part with other many parts, and is a product for which severe product accuracy is required, and if the required accuracy is not satisfied, it is unable to provide a sheet metal car body with good quality. Because the front pillar outer composes the outer plate portion of the automobile, it has three-dimensional curved surfaces and profiles. The portion with the negative angle formed by this forming die is shown with letter F, whose cross section is shown as work W in Fig. 8. That is, after the negative angle is formed, the work W achieves the condition shown in Fig. 8 from the condition shown in Fig. 5. By the way, this press-working process includes drawing which takes place first, then, peripheral trimming to the condition shown in Fig. 5, and this forming process as the succeeding third process. With respect to the lower die 100, a cylindrical rotating can 102 formed with an axial groove 101 is rotatably mounted to the lower die proper 103. The lower die proper 103 is securely fixed to the lower substrate 121 with a bolt 122. The top surface of the lower die proper 103 is formed in a shape that can receive the work W, and a negative angle forming portion 104 is formed at the edge portion of the groove 101 of the rotating cam 102 nearest to the top surface of the lower die 103. An automatic return device 105 which rotates and retracts the rotating cam 102 is embedded in the lower die proper 103 so that the work W can be removed from the lower die proper 103 after forming. In this example, the automatic return device 105 brings a push pin 107 energized by coil spring 106 in contact with the bottom surface of the tip end of the rolling plate 108 securely fixed to the surface opposite to the negative angle forming portion 104 of the groove 101 of the rotating cam 102 with a bolt 151. For the automatic return device 105, pneumatic devices, hydraulic devices, link mechanisms, cams, or other similar mechanisms may be used, and may be mounted not only to the lower die 100 but also between the upper die 109 and the lower die 100. On the other hand, to the upper die 109, a slide cam 110 is mounted to the position opposite to the said rotating cam 102. This slide cam 110 has the negative angle forming portion 112 formed at the bottom end, the slide cam 110 is guided by the guide (not illustrated), and is energized in the outward direction of the die by a coil spring 117 compressedly mounted between the slide cam 110 top surface and the inclined guide 154 bottom surface securely fixed to the top substrate 152 with a bolt 153. The slide cam 110 is stopped by a stopping plate 156 securely affixed to the inclined guide 154 with a bolt 155. A pad 157 is energized downwards by a coil spring 158, is hung from the top substrate 152 with a hang bolt 119, and strongly presses the work W against the lower die proper 103 to prevent the work W from moving before the negative angle is formed on the work W. Next description will be made on the operation of this forming die. First of all, as shown in Fig. 5, the upper die 109 is located at the top dead center, and then, the work W is loaded on the lower die proper 103 of the lower die 100. In this event, the rotating cam 102 is rolled and retracted by the automatic return device 105. Then, the upper die 109 begins descending and as shown in Fig. 6, first of all, the bottom surface of the slide cam 110 comes in contact with the rolling plate 108 to rotate the rotating cam 102 clockwise in Fig. 6 without causing the slide cam 110 to interfere with the negative angle forming portion 104 of the rotating cam 102. As the upper die 109 continues to descend further, the slide cam 110 energized in the outward direction of the die resists against the energizing force of the coil spring 117, moves to the left in the lateral direction by the operation of the can, enters the state shown in Fig. 7, and the negative-angle forming portion 104 of the rolled rotating cam 102 cooperates with the negative-angle forming portion 112 of the slide cam 110 to negative-angle form the work W. After the negative angle is formed, the upper die 109 begins rising. The slide cam 110 is energized in the outward direction of the die by the coil spring 117, moves to the right in Fig. 8, and ascends without interfering with the work W with the negative angle formed. On the other hand, the rotating cam 102 rotates to the right in Fig. 8 by the automatic return device because the slide cam 110 being restrained ascends, enabling the work W to be removed without interfering with the negative angle forming portion 104 of the rotating cam 102 when the negative-angle formed work W is removed from the lower die 103. The formed thin sheet products had the negative angle formed using the rotating cam as described above, but because the rotating cam rotates around the rotation axis to process the work, if the work is nearly linear and is not greatly bent, the negative angle forming portion can enter one of the cylindrical rotating cams in the same diameter and is able to be processed, but if the work is greatly bent, the negative angle forming portion is unable to completely enter one of the cylindrical rotating cams in the sane diameter and is unable to be processed. In particular, automobile sheet metal parts including door panels have many bent portions, and in recent years, there are many negative angle forming portions from the viewpoint of designs in addition to conventional bent portions, and it is demanded to form these negative angle forming portions in one process without undergoing many processes and to improve production efficiency. A prior art thin sheet forming die with the features of the preamble portion of claim 1 is described in US-A-5 347 838. This thin sheet forming die has basically the features of the die shown in Figures 5 to 8 and in addition has a plurality of dedicated rotary cams constituting plural forming portions arranged substantially straight within the range capable of processing with one rotary cam. SUMMARY OF THE INVENTION It is the object of the present invention to provide an improved thin sheet forming die for forming a thin sheet workpiece having a curved portion as seen from a plane and a negative angle in a cross-section thereof which is simplified with respect to its construction while avoiding interference between successive cam portions. The invention provides a thin sheet forming die as defined in claim 1. A preferred embodiment of this thin sheet forming die is defined in the subclaim. The size of the rotating cam diameter is practically unable to be excessively increased from the viewpoint of fabricating dies, and is, for example, about 320 mm, and for the greatly bent work, the bent portions are processed by one rotating cam equipped with a plurality of cylindrical rotating cam portions in different diameters. The diameters are varied at a required position of the rotation axis in accord with the degree of the bend of the work. Special consideration shall be given to the size of diameter of the rotating cam so that the negative angle forming portion of the rotating cam does not become excessively acute. Because the negative angle forming portion becomes excessively acute, the strength lacks, and it is preferable to take care to prevent it from becoming 30° or less. When a plurality of rotating cams are used, their end faces may interfere with one another at the joints of adjoining rotating cams when the rotating cams are rotated, but the dies according to this invention are completely free of such interference because in this invention, one rotating cam is used. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view of one specific embodiment according to this invention; Fig. 2 shows two cross-sectional views of the work taken on line III-III of Fig. 1 before and after negative-angle forming; Fig. 3 is a longitudinal cross-sectional view taken on line III-III of Fig. 1; Fig. 4 shows schematic right and left perspective views of the completed front pillar outer, a sheet metal part of automobiles; Fig. 5 is a longitudinal cross-sectional view when the upper die of the forming dies to form negative angles for the front pillar outer of Fig. 4 is in the top dead center condition; Fig. 6 is a longitudinal cross-sectional view of the upper die of the forming dies of Fig. 5 which descends to come in contact with the lower die; Fig. 7 is a longitudinal cross-sectional view of the upper die of the forming dies of Fig. 5 in the bottom dead center condition; and Fig. 8 is a longitudinal cross-sectional view of the upper die which ascends and is in the top dead center condition after the forming dies of Fig. 5 finish negative-angle forming. EMBODIMENTS Referring now to one specific embodiment shown in FIG. 1-3, this invention will be described in further detail. The work W formed by the forming dies according to this invention is an automobile trunk lid outer as shown in Fig. 1, and the recessed circular arc curved portion of the front edge portion of the trunk lid outer as viewed from the plane is negative-angle formed, and as shown in Fig. 2, it is negative-angle formed to have a cross-section shown below from that shown above. Fig. 1 shows a plan view of the thin sheet forming dies, Fig. 2 the condition of a flange 1 before and after the work W is processed, Fig. 3 a longitudinal cross-sectional view taken on the line III-III of Fig. 1. The processed portion of the work W of the thin sheet forming dies is the rear edge portion of the trunk lid outer and as clear from Fig. 1, it is a protruded form as seen from the plane, and both end portions are considerably displaced forwards. If this is processed with one piece of rotating cam, an extremely large rotating cam is required. Excessively increasing the size is practically impossible in fabricating dies, and is about 320 mm in diameter at maximum. In addition, the flange angle differs at the center portion and both end portions, and there is a case in which the negative-angle forming portion of the rotating cam becomes too acute to maintain the strength. In this invention, the rotating cam is formed into a small-diameter center rotating cam portion at the center portion and large-diameter rotating cam portions at both ends. On both ends of the small-diameter center rotating cam portion 2 of the rotating axis CA in Fig. 1, a rotating cam comprising large-diameter edge portion rotating can portions 3 are arranged. As is clear from Fig. 3, the large-diameter edge portion rotating cam portions 3 are concentric to the small-diameter center rotating cam portion 2, and has a larger diameter than the small-diameter center rotating cam portion 2. For example, the diameter of the large-diameter edge portion rotating cam portions is 290 mm, and that of the small-diameter center portion rotating cam portion is 250 mm. The lower die 5 has a support block 8 fixed to the lower die base 6 with a bolt 7, and rotatably supports the cylindrical large-diameter edge portion rotating cam 3 with a axially formed groove 10 in a horizontal slot groove 9 at the top center of the support block 8. In this embodiment, an air cylinder 11 is equipped as an automatic return device of the rotating cam 4 in Fig. 1. Needless to say, the automatic return device is not limited to an air cylinder but a spring, hydraulic equipment, link mechanism, cam, or any mechanisms similar to these may be used, and can be mounted not only to the lower die but also to the upper die. A connecting member 12 is fixed to the bottom surface of the small-diameter center rotating cam 2, and to the tip end of a piston rod 15 of the air cylinder whose base end is pivotally mounted via the bracket 14 fixed to the support block 8 with a bolt 13, the said connecting member 12 is pivotally mounted, so that the piston rod 14 is contracted to return the small-diameter center rotating cam 2. At the bottom portion of the slot groove 9 of the support block 8, a window slot is provided for allowing the connecting member 12 to rotate. At the edge portion of the groove 10 of the edge portion rotating cam portion 3, a negative angle forming portion 16 is formed, and a rolling plate 17 is fixed to the side opposite to the negative angle forming portion 16 of the groove 10 with a bolt 18. The negative angle forming portion 16 of the large diameter edge portion rotating cam portion 3 is formed into a work support portion 19 in the profile same as the bottom surface of the work W so that the work W is supported, and a work loading portion 20 in the profile same as the bottom surface of the work W is formed slightly outwards in the upper portion linked to the work supporting portion 19 of the edge portion rotating cam portion 3 of the support block 8. The upper die 21 has a support block 23 fixed to the lower surface of the upper die base 22 with a bolt 24, and a wear plate 25 fixed to the lower inclined surface of the support block 23 with a bolt 26, and the slide cam 27 is held by a guide plate (not illustrated) and slid on the lower surface of the wear plate 25. On the top surface of the slide cam 27, the negative angle forming portion 28 is fixed with a bolt, at the opposite position to the groove 10 of the edge portion rotating cam 3 of the slide cam 27. On the top inclined surface of the slide cam 27, a support plate 29 is fixed with a bolt 30, and between this support plate 29 and the support plate 31 fixed to the support block 23, a coil spring 32 is compressedly mounted to energize the slide cam 27 to the outward direction of the die. The said coil spring 32 is mounted in the externally fitted form to the positioning pin 33 screwed into the support plate 31, and the tip end of the said positioning pin 33 allows a stopping plate 34 fixed to the side surface opposite to the support plate 31 to pass through. When the upper die 21 rises, the slide cam 27 moves outwards of the die until the support plate 29 comes in contact with the stopping plate 34 by the energizing force of the coil spring 32. Though it is not illustrated, in order to stably support the work W, the positioning member of the work W is mounted to the lower die 5, and to the upper die 21, as described in the conventional example, a pad for pressurizing the work W is mounted to the lower die 5, but as these would make the illustration complicated and essential points of this invention difficult to understand, the positioning member and the pad are omitted. At the center portion of the work W, the small-diameter center rotating cam portion 2 is shown with an alternate long and two short dashes line, and others are nearly identical to the large-diameter rotating cam portion. Next description will be made on the operation of the thin sheet forming dies. The condition shown in Fig. 3 is the bottom dead center condition and corresponds to Fig. 7 of the conventional example. In this invention, it is not illustrated but as shown in Fig. 5 of the conventional example, the upper die 21 is located at the top dead center, when the work W is loaded to the work support portions 20 of the lower die 5. In this event, the center rotating cam 2 is rolled to retract by the air cylinder 11. Next, as shown in Fig. 6 of the conventional example, in the upper die 21, the inclined surface 41 of the slide cam 27 comes in contact with the rolling plate 17 without allowing the slide cam 27 to interfere with the negative angle forming portion 16 of the small-diameter center rotating cam 2 and large-diameter edge portion rotating cam portion 3, causing the small-diameter center rotating cam 2 and large-diameter edge portion rotating cam portion 3 to rotate counterclockwise (the rolling direction is reversal in the conventional example and this embodiment). As the upper die 21 further continues to descend, the slide cam 27 energized in the outward direction of the dies resists against the energizing force of the coil spring 32 and moves to the right in the lateral direction by the action of the cam, and enters the condition shown in Fig. 7 of the conventional example, that is, the condition shown in Fig. 3, and the negative angle forming portion 16 of the small-diamether center rotating cam portion 2 and large-diameter edge portion rotating cam 3 cooperate with the negative angle forming portion 28 of the slide cam 27 to negative-angle form the work W. After negative-angle forming, the upper die 21 begins to ascend. The slide cam 27 is energized in the outward direction of the dies by the coil spring 32, moves to the left as shown in Fig. 8 of the conventional example, and ascends without interfering with the negative-angle formed work W. On the other hand, when the restrained slide cam 27 ascends and the air cylinder 11 contracts the piston rod 15, the small-diameter center rotating cam portion 2 and the large-diameter edge portion rotating cam portion 3 rotate in the left direction to enable the removal of the work W without interfering with the negative angle forming portion 16 of the small-diameter center rotating cam portion 2 and the large-diameter edge portion rotating cam portion 3, when the negative-angle formed work W is removed from the lower die 5. This invention is a forming die with a forming portion to achieve a negative angle when the second die is moved in the straight line to abut the first die for forming, and in the thin sheet forming dies in which a cylindrical rotating cam with a groove formed in the axial direction is rotatably mounted to the first die, a negative angle forming portion is formed in the groove edge portion of the rotating cam, a slide cam with the negative angle forming portion is mounted to the second die in such a manner to be opposite to the said rotating cam, an automatic return device for rotating and retracting the rotating cam to enable the removal of the work from the first die after forming is mounted to the first die, because it is a thin sheet forming die designed to process an excessively bent negative angle forming portion with one rotating cam equipped with a plurality of integral cylindrical rotating cam portions with different diameters, it becomes possible to form an excessively bent negative angle forming portion with one forming die, to reduce the number of processes, and to improve the processing accuracy. In particular, the thin sheet forming die according to this invention is suited for negative-angle forming the protruded circular are curved portion as seen from the plane. This is because the flange to be formed becomes a shrinkage flange as it is protruded and tends to generate wrinkles at the time of forming, requiring bottom pushing processing. In this invention, because the rotating cams are formed integrally, bottom pushing forming is possible in high accuracy.

Claims: A thin sheet forming die for forming a thin sheet work piece (W) having a curved portion as seen from a plane and a negative angle in a cross section thereof, comprising: a first die (21) movable toward a second die (5) to be abutted to the second die (5); a cylindrical rotating cam (4) rotatably mounted to the second die (5), said cylindrical rotating cam (4) having a groove (10) formed in the axial direction thereof and a negative angle forming portion (16) formed on a groove edge portion of the rotating cam (4); a slide cam (27) with a negative angle forming portion (28) provided on the first die (21) in such a manner to be opposed to said rotating cam (4) and to cooperate with the negative angle forming portion (16) of the rotating cam (4) when the first die (21) moves toward the second die (5) to form the negative angle on the work piece (W) placed on the second die (5); and an automatic return device (11) equipped to the first or the second die (21,5) for rotating the rotating cam (4) to a position in which the work piece (W) can be removed from the second die (5) after forming, characterized in that the rotating cam (4) has a plurality of integral cylindrical cam portions (2,3), laterally adjacent one another, with different diameters for processing the curved portion of the work piece (W) with the negative angle. The thin sheet forming die of claim 1, characterized in that said rotating cam (4) comprises a small-diameter center cam portion (2) and large-diameter edge cam portions (3) concentric to said center cam portion (2).

Inventors: MATSUOKA MITSUO, MATSUOKA, MITSUO
Applicants: UMIX CO LTD, UMIX CO., LTD.
Application year: 1997
Main classification: B21D22
IPC codes: B21D22