Negative-angle forming die

Abstract: The present application aims with respect to a negative-angle forming die with a lower die half (1) supporting a rotary cam (5) and an upper die half (3) having an intrusion forming portion cooperating with an intrusion forming portion (4) of the rotary cam upon a descend of the upper die half to form a sheet metal product (W) to avoid the problem that slight pivoting movement makes the rotary cam move slightly out of a predetermined forming position, thereby creating an unwanted step in a curved surface of the work or making it impossible to form the work into an accurate contour, particularly if accuracy in the order of 1/100mm is required. The present application aims to maintain the rotary cam at a predetermined forming position during the forming process in that the rotary cam (5) is rotatably supported in the lower die half (1) by supporting shafts (11) respectively projecting from the two axial ends of the rotary cam (5) and in that positioning means (17,19) are provided on the lower die half (1) and on the rotary cam (5) for fixing an axial position of the rotary cam (5).

Description: Background of the Invention The present invention relates to a negative-angle forming die for forming a sheet metal as per the preamble of claim 1. Herein, the negative-angle forming die is used for a formation made at a location more inward of a lower die half than a straight downward stroke line of an upper die half. The forming of a negative angle on a work provided as a sheet metal into a shape having a portion more inward of the lower die half than the straight downward stroke line of the upper die half is generally performed by using a slide cam. According to a prior-art intrusion forming process of the sheet metal work, the work is placed on the lower die half and the upper die half is lowered vertically. At this time a drive cam of the upper die half drives a driven cam of the lower die half, forming the work from a side. After the formation is completed and the upper die half is lifted, then the driving cam is retracted by a spring. In the above arrangement, the driven cam slid onto the work from the side has a forming portion which is formed as a single piece in the same shape the work should have after the formation. The lower die half however, must allow the work to be taken out from the lower die half after the formation, and for this reason, a portion of the lower die half providing the intrusion formation must be made separable for retraction, or a rear portion thereof must be cut off so that the work can be moved forward and taken out. This does not pose a serious problem if the extent of the intrusion is small. However, the problem becomes serious if the extent of the intrusion is large, or if the work is to be formed from a sheet metal into a long frame having a groove-like section such as an automobile front pillar-outer. Since the groove width of the work is often very narrow, the portion of the lower die half corresponding to the groove cannot be divided or cut off, because in this case it becomes impossible for the forming portion of the driven cam to precisely form the desired contour. In addition, strength of the lower die decreases. Thus, it was impossible to perform a clear-shaped intrusion formation. Further, a formed product sometimes has a twist or distortion, which must be corrected. However, for example, many automobile parts that provide the outer skin of the automobile, such as a side panel, fender, roof, bonnet, trunk lid, door panel, front pillar-outer and so on are formed to have a three-dimensional surface contour or line, and therefore it is practically impossible to make a correction after the formation. In assembling the automobile sheet-metal parts, if there is a twist or distortion in the parts, it is difficult to fit the parts together. Without solving this problem, it was impossible to provide a high quality automobile sheet metal structure, and it was impossible to maintain a required level of product accuracy in the formed sheet metal products. In order to solve the above-described problem, an arrangement was proposed, in which the straight downward stroke of the upper die half is converted to a rotary movement of a rotary cam to pivot to form the portion in the lower die half more inward than the straight downward stroke line of the upper die half. In this arrangement, after the forming operation, the rotary cam is pivoted back to a state where the completed work can be taken out of the lower die. This arrangement will now be described in more detail. Specifically, as shown in Fig. 9 to Fig. 12, this negative-angle forming die comprises a lower die half 102 including a supporting portion 101 on which a work W is placed and an upper die half 103 which is adapted to be lowered straightly down onto the lower die half 102 to thereby press and form the work W. The lower die half 102 is provided with a rotary cam 106 supported in an upwardly open axial groove 104. The rotary cam 106 has a portion close to the supporting portion 101 formed with an intrusion forming portion 105 extending inward so as to overlap a stroke line of the upper die half 103. The upper die half 103 is provided with a slide cam 108 substantially opposed to the rotary cam 106 and provided with an intrusion forming portion 107. The lower die half is further provided with an automatic retractor 109 which, after the formation, pivots the rotary cam 106 back to the state that allows the work W to be taken out of the lower die half 102. The work W placed on the supporting portion 101 of the lower die half 102 is formed by cooperation of the intrusion forming portion 105 of the rotary cam 106 and the intrusion forming portion 107 of the slide cam 108. The work W is formed by a rotary movement of the rotary cam 106 and a sliding movement of the slide cam 108. Now, an operation of this negative-angle forming die will be described. First, as shown in Fig. 9, the upper die half 103 is positioned at its upper dead center position. At this stage, the work W is placed on the supporting portion 101 of the lower die half 102. The rotary cam 106 is held at its retracted position by the automatic retractor 109. Next, the upper die half 103 begins to descend and, as shown in Fig. 10, a lower surface of the slide cam 108 makes first contact with a pivoting plate 111 without causing the slide cam 108 to interfere with the intrusion forming portion 105 of the rotary cam 106. Upon further descend the upper die half 103 pivots the rotary cam 106 clockwise as in Figs. 10 and 11, thereby placing the rotary cam 106 at a forming position. Then, a pad 110 presses the work W onto the supporting portion 101. When the upper die half 103 continues to descend, the slide cam 108, which is biased by a coil spring 112 so as to be urged outward of the die half, begins a sliding movement against the urging force from the coil spring 112 in a laterally leftward direction as shown in the sequence of Figs. 10 and 11. In the state shown in Fig. 11 finally the intrusion forming portion 105 of the pivoted rotary cam 106 and the intrusion forming portion 107 of the slide cam 108 slid towards the intrusion forming portion 105 of the pivoted rotary cam 106 perform formation of the work W. After the intrusion formation, the upper die half 103 begins to rise. The slide cam 108, which is urged outwardly of the upper die half by the coil spring 112, moves in a laterally rightward direction as shown in Fig. 12, and the upper die half keeps rising without interfering with the work W after the intrusion formation. On the other hand, the rotary cam 106 is released from being pressed by the slide cam 108 and therefore is pivoted in a counter-clockwise direction as shown in Fig. 12 by the automatic retractor 109. Thus, when the work W is taken out of the lower die half after the intrusion formation, the work W can be removed without interference with the intrusion forming portion 105 of the rotary cam 106. According to the negative-angle forming process described above, the lower surface of the slide cam 108 urged by the coil spring 112 contacts the pivoting plate 111 urged by the coil spring 113 of the automatic retractor 109, rotating the rotary cam 106 in the clockwise direction to the shaping position, and thereafter, the pad 110 presses the work W. With this arrangement the urging force from the pad 110 onto the work W is so strong that the work W under the formation can be slightly pivoted counterclockwise as shown in the figure. In another case, the urge of the coil spring 112 of the slide cam 108 might not be well balanced with the urge of the coil spring 113 of the automatic retractor 109, resulting in a slight pivoting movement of the rotary cam 106 out of the predetermined position for the formation. These situations sometimes make it impossible to form the work into an accurate curve or contour. For example, due to these shortcomings in the prior art dies it is sometimes impossible to provide a product of an accuracy level in the order of 1/100 mm, and it was sometimes impossible to achieve a high quality negative-angle formation. Further, as will be understood from Fig. 9 through Fig. 12, the rotary cam 106 is supported by the lower die half 102 through direct contact of the cam's outer circumference except for the groove portion 104. With this structure, accurate and difficult machining must be made to the rotary cam 106 and the supporting portion (a bore having a generally round section) of the lower die half 102 which supports the rotary cam 106. Further, since most of the outer wall of the rotary cam 106 is used for support by the lower die half 102, the negative angle forming die tends to be large and expensive. Now, in consideration of the background described above, the present invention aims to solve these problems: that slight pivoting movement makes a rotary cam move slightly out of a predetermined forming position, thereby creating an unwanted step in a curved surface of the work or making it impossible to form the work into an accurate curve; that it is difficult to provide a product of accuracy in the order of 1/100 mm; and that it is impossible to provide a formed sheet metal product of a high quality. A negative-angle forming die with the features of the preamble portion of claim 1 is disclosed JP-A-08276218. The present invention aims to maintain the rotary cam at a predetermined forming position and to minimize the unwanted movement of the rotary cam at the time of the intrusion formation, thereby providing a formed sheet metal product of a high quality and accuracy of form. In order to achieve this object, the present invention provides a negative angle forming die comprising the features of claim 1. Preferred embodiments of the negative angle forming die are defined in the dependent claims. Further, in a preferred embodiment the present invention does not rely on the multi-diameter rotary cam in a case in which there is a large variation in the distance of the intrusion forming portion from the axis. Preferably, the present invention provides a negative-angle forming die, wherein the intrusion forming portion varies a pressing side-portion of the rotary cam contacted by the backup portion in accordance with a distance from an axis of pivoting. Brief Description Of The Drawings In the drawing there is Fig. 1 Two sectional views of an automobile sheet-metal part before and after a formation by the negative-angle forming die according to the present invention; Fig. 2 A sectional side view showing a state in which the upper die half forming the sheet-metal part in Fig. 1 has been lowered to a lower dead center; Fig. 3 A conceptual diagram showing support and positioning of a rotary cam according to the present invention; Fig. 4 A front view of a positioning block as an example of positioning means according to the present invention; Fig. 5 A view taken from a direction indicated by arrow V in Fig. 4; Fig. 6 A front view of a receiving block as an example of the positioning means according to the present invention; Fig. 7 A side view of the receiving block shown in Fig. 6; Fig. 8 A plan view of a prior art multi-diameter rotary cam used in a case where a distance from a rotary cam axis varies widely; Fig. 9 A sectional side view of a prior art negative-angle forming die, with an upper die half thereof being at its upper dead center; Fig. 10 A sectional side view of the prior art negative-angle forming die shown in Fig. 9 with the upper die half in its downward stroke, beginning to contact a lower die half thereby making contact with a work; Fig. 11 A sectional side view of the prior art negative-angle forming die shown in Fig. 9 with the upper die half being at its lower dead center; and Fig. 12 A sectional side view of the prior art negative-angle forming die shown in Fig. 9 as after the intrusion forming, with the upper die half lifted to its upper dead center. Embodiment The present invention will now be described in detail, based on an embodiment shown in the attached drawings. Fig. 1 shows sectional views of an automobile sheet-metal part before and after a formation by the negative-angle forming die. A work W shown in Fig. 1(b) has a lower portion shaped by an intrusion forming process. It should be noted here that this part is formed to have a three-dimensional curved surface/contour line to be used as part of an outer skin of the automobile. Referring now to Fig. 2, a lower die half 1 has an upper portion formed with a supporting portion 2 for the work W. The lower die half 1 rotatably supports a rotary cam 5, which has a side close to the supporting portion 2 formed with an intrusion forming portion for forming a recessed portion located inward of a stroke line of an upper die half 3. Code C indicates a center of pivoting movement of the rotary cam 5. In order to take the work W out of the lower die half 1 after the work W has been formed, the lower die half 1 is provided with an unillustrated automatic retractor such as an air cylinder. The rotary cam 5 is supported by a pivot-supporting member 6 fixed to the lower die half by a bolt 7. The upper die half 3 is provided with a slide cam 8 for forming the work W in cooperation with the rotary cam and a pad 9 for pressing the work W onto the supporting portion 2 during the forming process. In order to maintain the rotary cam 5 at a predetermined axial position for providing a high quality formed sheet-metal product, the lower die half 1 and the rotary cam 5 are provided with positioning means for fixing the axial position of the rotary cam 5 as shown in Fig. 3 which is a conceptual diagram of the positioning means. The shaft- or cylinder-like rotary cam 5 has two ends each provided with a supporting shaft 11 extending therefrom. Each of the supporting shafts 11 is fitted into a tubular metal sleeve 12 fixed to a bearing 13. The metal sleeve 12 rotatably supports the rotary cam 5. The supporting shaft 11 has a base plate 14 fixed by a bolt 15 to the axial end of the rotary cam 5. The bearing 13 to which the supporting shaft 11 is fitted is fixed to the lower die half 1 by a bolt 16. The rotary cam 5 is supported at its ends by the bearings 13 as described above. Therefore, as only a small portion of the rotary cam 5 is in direct contact with the lower die half 1, machining of the rotary cam 5 and of the lower die half 1 becomes easy. If the rotary cam is directly contacted with the lower die half in a large portion as in the prior art, accurate machining is required. In order to fix the axial position of the rotary cam 5, an axial positioning block 17 is fixed to the lower die half 1 by bolts 18. The positioning block 17 is opposed by a receiving block 19 fixed on the rotary cam 5 by a bolt 20. The receiving block 19 is fitted to the positioning block 17 for positioning the rotary cam 5 at a predetermined position. With this arrangement, even if the rotary cam 5 receives an axial load during the pressing operation, the rotary cam 5 is prevented from axial movement by the engagement between the receiving block 19 and the positioning block 17. According to this embodiment, the positioning block 17 is formed convex, whereas the receiving block 17 is formed concave in a corresponding shape. The present invention is not limited to this particular shape or contour. For example, the positioning block may be made concave and the receiving block may be made convex. Further, for example, a movement prevention wall may alternatively be provided at a position capable of preventing the rotary cam from unwanted movement during the forming operation. It should be noted here that according to the present embodiment, the positioning block 17 of the lower die half is made convex for ease of use because this arrangement allows dirt, oil and so on to fall off easily. Fig. 4 and Fig. 5 show details of the positioning block 17, whereas Fig. 6 and Fig. 7 show details of the receiving block 19. Since the rotary cam 5 is generally columnar or cylindrical, the positioning block 17 is formed to have an arcuate recess to conform to the columnar or cylindrical outer circumference of the rotary cam 5, whereas the receiving block 19 is formed to correspond and fit to the positioning block 17. The rotary cam 5 is rotatably supported at its end portions by the bearings 13. Differing from the prior art in which the lower die half 1 supports and contacts the rotary cam 5 at a substantial portion of the outer circumference thereof, as shown in Fig. 2, the support in the invention is provided by only a reduced partial contact. The rotary cam 5 includes a rotary cam main body 21 serving as a core portion having an upper portion provided with an intrusion forming portion 4 fixed by a bolt 23, a side portion provided with a pressing side-member 24 fixed by a bolt 25, and a bottom portion provided by a pivoting contact member 26 fixed by a bolt 27. The rotary cam 5 not only has the pivoting contact member 26 contacting the pivoting support member 6 but also has the pressing side-member 24 contacting a backup portion 28 of the lower die half 1. With this arrangement, when the intrusion forming portion 4 of the rotary cam 5 and the intrusion forming portion 22 of the slide cam 8 press and form the work W, the backup portion 28 of the lower die half 1 contacts the pressing side-member 24, thereby preventing the rotary cam 5 from deformation. By providing the backup portion 28, the deformation of the rotary cam 5 can be positively prevented, and it becomes possible to manufacture a high-quality sheet-metal formed product. The slide cam 8 slides on an actuator cam 33 fixed to an upper-die-half base plate 31 by a bolt 32, and further slides on a cam base 35 fixed to the lower die half 1 by a bolt 34. The slide cam 8 holds the intrusion forming portion 22 fixed by a bolt 39 to a bracket 38 fixed to a base portion 36 by a bolt 37. In the base portion 36 of the slide cam 8, a wear plate 41 fixed by a bolt 40 slides on a wear plate 42 fixed to the cam base 35 by a bolt 43. Further, a wear plate 43 fixed to a lower surface of the bracket 38 by a bolt 50 slides on a wear plate 45 fixed by a bolt 44 to the rotary cam main body 21 of the rotary cam 5. When forming a negative angle in a work, a distance of the intrusion forming portion from the pivot axis of the rotary cam generally varies along the axis. This poses no problem as long as the distance of the intrusion forming portion from the axis is small. However, if the distance is large as shown in Fig. 8, a multi-diameter rotary cam 201 having different diameters along the axis is used. The multi-diameter rotary cam 201 has angled edges 202 which often leave a score in the work w. In order to solve this problem, if the distance of the intrusion forming portion from the pivot axis varies widely, no multi-diameter rotary cam is used but the pressing side-member 24 is used to compensate the distance of the intrusion forming portion from the pivot axis. The pressing side-member 24 has a portion gradually varied in accordance with the distance variation between the intrusion forming portion and the rotary axis.

Claims: A negative-angle forming die comprising: a lower die half (1) having a supporting portion (2) for placing a sheet metal work (W) thereon; an upper die half (3) adapted to be lowered straightly downward onto the lower die half (1) for forming the sheet metal work (W); a rotary cam (5) including an intrusion forming portion (4) and being rotatably supported in the lower die half (1) by supporting shafts (11) respectively projecting from the two axial ends of the rotary cam (5); a slide cam (8) including an intrusion forming portion (22) and slidably opposed to the rotary cam (5), said slide cam (8) being adapted to be slid towards the rotary cam (5) by the downward movement of the upper die half (3), wherein the sheet metal work (W) placed on the supporting portion (2) of the lower die half (1) is adapted to be formed by the cooperation of the intrusion forming portions (4;22) of the rotary cam (5) and of the slide cam (8); and an automatic retractor for pivoting the rotary cam (5) back to a position where the sheet metal work (W) can be taken out of the lower die half (1) after a forming operation; characterized in that positioning means (6,17,19) are provided on the lower die half (1) and on the rotary cam (5) so as to be in engagement with each other for fixing an axial position of the rotary cam (5). A negative-angle forming die according to claim 1, wherein said positioning means comprises a positioning block (17) fixed to the lower die half (1) and a receiving block (19) fixed to the rotary cam (5), said receiving block (19) being fitted to said positioning block (17). A negative-angle forming die according to claim 2, wherein said positioning block (17) is formed with a convex or concave surface and said receiving block (19) is formed with a surface in a corresponding shape. A negative-angle forming die according to claim 1, wherein said positioning means comprises a movement prevention wall provided at a position to prevent the axial movement of the rotary cam (1). A negative-angle forming die according to any one of claims 1 to 4, wherein a backup portion (28) is formed in the lower die half (1) for supporting a surface of the rotary cam (5) on a side away from a side receiving the slide cam (8) during the forming process. A negative-angle forming die according to claim 5, wherein a pressing side-portion (24) of the rotary cam (5) contacted by the backup portion (28) of the lower die half (1) varies in accordance with a distance between the intrusion forming portion (4) and an axis of pivoting of the rotary cam (5). A negative-angle forming die according to any one of the preceding claims, wherein an intrusion forming portion is formed in the lower die half (1) at an edge portion near the supporting portion inward of a downward stroke line of the upper die half (3).

Inventors: MATSUOKA MITSUO, MATSUOKA, MITSUO
Applicants: UMIX CO LTD, UMIX CO., LTD.
Application year: 2001
Main classification: B21D5
IPC codes: B21D5, B21D37, B21D22, B21D13