Negative angle-forming die

A negative angle-forming die includes a lower die for mounting a thin metallic plate workpiece onto a supporting portion thereof, and an upper die descendable in a straight direction towards the lower die for forming the workpieces by abutting against the workpiece. A columnar body is arranged in a freely rotating manner on the lower die by a pair of spaced-apart bearings, and has an intruding forming portion formed at an edge portion thereof. A slide cam is formed with an intruding forming portion, and is arranged to oppose the columnar body in a freely sliding manner with respect to the lower die. An automatic returning tool is arranged at the lower die for retracting the columnar body in a rotating manner to an extent with which the workpiece can be taken out from the lower die upon completion of forming. The workpiece that is mounted on the supporting portion of the lower die is formed through the intruding forming portion of the columnar body and the intruding forming portion of the slide cam while the slide cam performs sliding movements, and after completion of forming, the columnar body is retracted in a rotating manner by the automatic returning tool such that the formed workpiece can be taken out from the lower die. The negative angle-forming die includes a locking device for making the columnar body maintain a specified forming posture.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a negative angle-forming die for forming
 metallic thin plates. In this context, a negative angle-forming die is
 used for forming in which a portion of a work is intruded into a lower die
 further than a descending locus in a straight direction of an upper die.
 2. Description of the Background Art
 Negative angle forming wherein a work of metallic thin plate is intruded
 into a lower die than a descending locus of an upper die in a straight
 manner is usually performed by using a slide cam.
 A conventional method for performing intrusion forming of a work of
 metallic thin plate (a workpiece) included the steps of placing the work
 onto a lower die, descending an upper die downward in a vertical
 direction, driving a passive cam of the lower die by an active cam of the
 upper die for processing the work from a lateral direction, and after the
 upper die was raised upon completion of processing, the active cam was
 retracted by a spring.
 In this case, a forming portion of the passive cam that forms the work by
 being slid from outside of the work in a lateral direction is uniformly
 formed to assume a shape that is identical to that of a forming portion of
 the work. However, since the work needs to be taken out from the lower die
 upon completion of processing, the forming portion of the lower die onto
 which the work is mounted is either arranged in that an intruding portion
 of the lower die is provided to be separable for retraction or in that a
 rear portion of the intruding portion is cut off and the work is moved
 forward for enabling the work to be taken out. While it does not become
 problematic in case of a minor degree of intrusion, in case such a degree
 is large or the work is a long and slender frame-like part having a
 grooved section such as a front pillar outer of metallic thin plate used
 in a vehicle, it may happen in case the intruding portion of the lower die
 is divided or cut off that, owing to the narrow groove width of the work,
 no clear shape can be formed by the forming portion of the passive cam and
 moreover, that insufficient strength of the lower die makes it impossible
 to perform intrusion forming at all.
 Further, there are also cases in which torsions or warps are formed in
 products so that correction of products needs to be performed, while
 correction of products is practically impossible in case of parts
 constituting an outer panel portion of a vehicle such as a side panel,
 fender, roof, bonnet, trunk lid, door panel or front pillar outer all of
 which assume three-dimensional curved surfaces and curved lines. In case
 of assembling metallic thin plates for a vehicle, products which assume
 torsions or warps can be hardly combined to other parts, and it could not
 be provided for a structure of metallic thin plates for a vehicle of high
 quality and it could not be maintained for a specified degree of product
 accuracy required for the product of metallic thin plate.
 For solving the above problems, it has been devised for an arrangement as
 follows for converting descending, straight movements of the upper die
 into rotational movements for rotating a columnar body, forming a forming
 portion that is intruded into the lower die further than a straightly
 descending locus of the upper die, and after completion of forming,
 retracting the columnar body in a rotating manner to an extent that a
 formed work can be taken out form the lower die.
 That is, as shown in FIGS. 8 to 11, the negative angle-forming die is
 comprised of a lower die 102 for mounting a work W of metallic thin plate
 onto a supporting portion 101 thereof and an upper die 103 that is
 descended in a straight direction towards the lower die 102 for forming
 the work W by hitting against the work W, wherein there are further
 provided a columnar body 106 arranged in a freely rotating manner on the
 lower die 102 and having a groove 104 that is open to an outer peripheral
 surface and that is carved into an axial direction as well as an intruding
 forming portion 105 formed at an edge portion of the groove 104 closer to
 the supporting portion 101 that is intruded further than a locus of the
 upper die 103, a slide cam 108 formed with an intruding forming portion
 107 being arranged on the upper die 103 in a freely sliding manner as to
 oppose the columnar body 106, and an automatic returning tool 109 arranged
 at the lower die 102 for retracting the columnar body 106 in a rotating
 manner to an extent with which the work W can be taken out from the lower
 die 102 upon completion of forming, wherein the work W that is mounted on
 the supporting portion 101 of the lower die 102 is formed through the
 intruding forming portion 105 of the columnar body 106 and the intruding
 forming portion 107 of the slide cam 108 while the columnar body 106 is
 rotated and the slide cam 108 performs sliding movements, and after
 completion of forming, the columnar body 106 is retracted in a rotating
 manner by the automatic returning tool 109 such that the formed work W can
 be taken out from the lower die 102.
 Operations of such a negative angle-forming die will now be explained.
 As shown in FIG. 8, the upper die 103 is first positioned at a top dead
 center at which time the work W is mounted on to the supporting portion
 101 of the lower die 102. At this time, the columnar body 106 is retracted
 in a rotating manner by the automatic returning tool 109.
 Next, the upper die 103 starts to descend, and as shown in FIG. 9, the
 slide cam 108 is first made to abut against a rotating plate 111 of the
 slide cam 108 without interfering the intruding forming portion 105 of the
 columnar body 106 so as to rotate the columnar body 106 in a rightward
 direction in FIG. 9 to put the columnar body 106 into a forming posture,
 and thereafter, a pad 110 pressurizes the work W.
 When the upper die 103 keeps on descending, the slide cam 108 that is
 energized in a direction outside of the die moves leftward in a lateral
 direction of the drawing by the action of the cam against energizing force
 of a coil spring 112 to assume a condition as shown in FIG. 10, whereby
 intrusion forming of the work W is performed through the intruding forming
 portion 105 of the rotated columnar body 106 and the intruding forming
 portion 107 of the slide cam 108.
 After intrusion forming is completed, the upper die 103 starts rising. The
 slide cam 108, being energized in a direction outside of the die by the
 coil spring 112, is moved rightward in FIG. 11 so that it can be raised
 without interfering the work W.
 On the other hand, accompanying the rising movements of the slide cam 108
 which had been constraining the columnar body 106, the columnar body 106
 rotates leftward in FIG. 11 through the automatic returning tool 109. In
 this manner, when taking the work W out from the lower die 102 after
 intrusion forming, the work W can be taken out without interfering the
 intruding forming portion 105 of the columnar body 106.
 In the above-described negative angle-forming process, a lower surface of
 the slide cam 108 that is energized by the coil spring 112 abuts against
 the rotating plate 111 that is energized by a coil spring 113 of the
 automatic returning tool 109 to rotate the columnar body 106 in a
 rightward direction such that the columnar body 106 assumes a forming
 posture whereupon the pad 110 pressurizes the work W. However, drawbacks
 are presented in that negative angle-forming processes of favorable
 quality cannot be performed in case the work W in the forming posture is
 rotated to some extent in the leftward direction in the drawing since the
 energizing force applied to the work W that is mounted on the pad 110 is
 too large, or in case the energizing force of the coil spring 112 of the
 slide cam 108 and that of the coil spring 113 of the automatic returning
 tool 109 are not balanced, whereby the columnar body 106 is slightly
 rotated such that it cannot maintain a specified forming posture to
 consequently result in a case in which a stepped portion is formed in a
 curved surface of the work W or in which no accurate straight line can be
 formed. Consequently, it becomes difficult to provide products of accuracy
 in units of 1/100 mm, and negative angle forming of favorable quality
 cannot be performed.
 As it can be seen from FIGS. 8 to 11, the columnar body 106 is supported by
 the lower die 102 by directly contacting thereat except for the portion of
 the groove 104 whereby it is required to accurately perform processing of
 the columnar body 106 and a portion of the lower die 102 for supporting
 the columnar body 106 (a hole having a substantially circular section) so
 as to make processing difficult.
 Moreover, the negative angle-forming die assumes a large dimension owing to
 its arrangement in which almost the entire outer periphery of the columnar
 body 106 is supported by the lower die 102 and the rotating plate 111 is
 formed as to extrude from the columnar body 106, whereby the mold becomes
 quite expensive.
 SUMMARY OF THE INVENTION
 The present invention has thus been made in view of these facts and for the
 purpose of providing formings of metallic thin plate of favorable quality
 by maintaining the columnar body in the specified forming posture, and
 although there were cases in which it could not be coped with cases in
 which a columnar body was slightly rotated such that it could not maintain
 a specified forming posture to consequently result in a case in which a
 stepped portion was formed in a curved surface of a work, in which no
 accurate straight line could be formed, or in which it became difficult to
 provide products having accuracy in units of 1/100 mm such that no
 formings of metallic thin plate of favorable quality could be provided,
 the negative angle-forming die of the present invention is comprised with
 a lower die for mounting a work of metallic thin plate onto a supporting
 portion thereof and an upper die that is descended in a straight direction
 towards the lower die for forming the work by hitting against the work,
 wherein there are further provided a columnar body arranged in a freely
 rotating manner on the lower die and having an intruding forming portion
 which is intruded further than a locus of the upper die formed at an edge
 portion closer to the supporting portion, a slide cam formed with an
 intruding forming portion, being arranged as to oppose the columnar body
 in a freely sliding manner with respect to the lower die, and an automatic
 returning tool arranged at the lower die for retracting the columnar body
 in a rotating manner to an extent with which the work can be taken out
 from the lower die upon completion of forming, wherein the work that is
 mounted on the supporting portion of the lower die is formed through the
 intruding forming portion of the columnar body and the intruding forming
 portion of the slide cam while the slide cam performs sliding movements,
 and after completion of forming, the columnar body is retracted in a
 rotating manner by the automatic returning tool such that the formed work
 can be taken out from the lower die, wherein the forming mold is a
 negative angle-forming die comprised with a locking device for making the
 columnar body maintain a specified forming posture.
 The locking device according to the present invention is particularly
 arranged in that the columnar body is locked by an action of a cylinder.
 The locking device according to the present invention is particularly
 arranged in that the columnar body is locked by connection between an
 extruding piece of the columnar body and a locking block formed at a tip
 of a piston rod of an air cylinder.
 Moreover, the locking device according to the present invention is
 particularly arranged in that connecting surfaces of both, the extruding
 piece and the locking block, are formed as tapered surfaces wherein a
 surface opposite to the tapered surface of the locking block is formed as
 a sliding surface for sliding on the lower die.
 In an alternative form of the present invention which aims to assume a
 simple structure in which an entire periphery of the columnar body is not
 supported by the lower die, the negative angle-forming die is comprised
 with a lower die for mounting a work of metallic thin plate onto a
 supporting portion thereof and an upper die that is descended in a
 straight direction towards the lower die for forming the work by hitting
 against the work, wherein there are further provided a columnar body
 arranged in a freely rotating manner on the lower die and having an
 intruding forming portion which is intruded further than a locus of the
 upper die formed at an edge portion closer to the supporting portion, a
 slide cam formed with an intruding forming portion, being arranged as to
 oppose the columnar body in a freely sliding manner with respect to the
 lower die, and an automatic returning tool arranged at the lower die for
 retracting the columnar body in a rotating manner to an extent with which
 the work can be taken out from the lower die upon completion of forming,
 wherein the work that is mounted on the supporting portion of the lower
 die is formed through the intruding forming portion of the columnar body
 and the intruding forming portion of the slide cam while the slide cam
 performs sliding movements, and after completion of forming, the columnar
 body is retracted in a rotating manner by the automatic returning tool
 such that the formed work can be taken out from the lower die, wherein the
 forming die is a negative angle-forming die arranged as to support the
 columnar body by a bearing in a freely rotating manner.
 The negative angle-forming die according to the present invention is
 particularly arranged in that both ends of the columnar body are supported
 by the bearing in a freely rotating manner.
 Moreover, the negative angle-forming die according to the present invention
 is particularly arranged in that a flexible columnar body is supported
 also on a distance between both ends.
 In an alternative form of the present invention in which the columnar body
 does not assume a substantially circular section but a fan-like section
 having a central angle that is as small as possible in order to realize
 down-sizing of the negative angle-forming die that can be distributed at
 low costs, the negative angle-forming die is comprised with a lower die
 for mounting a work of metallic thin plate onto a supporting portion
 thereof and an upper die that is descended in a straight direction towards
 the lower die for forming the work by hitting against the work, wherein
 there are further provided a columnar body arranged in a freely rotating
 manner on the lower die and having an intruding forming portion which is
 intruded further than a locus of the upper die formed at an edge portion
 closer to the supporting portion, a slide cam formed with an intruding
 forming portion, being arranged as to oppose the columnar body in a freely
 sliding manner with respect to the lower die, and an automatic returning
 tool arranged at the lower die for retracting the columnar body in a
 rotating manner to an extent with which the work can be taken out from the
 lower die upon completion of forming, wherein the work that is mounted on
 the supporting portion of the lower die is formed through the intruding
 forming portion of the columnar body and the intruding forming portion of
 the slide cam while the slide cam performs sliding movements, and after
 completion of forming, the columnar body is retracted in a rotating manner
 by the automatic returning tool such that the formed work can be taken out
 from the lower die, wherein the forming die is a negative angle-forming
 die wherein a connecting portion between the columnar body and the lower
 die is formed to be substantially a quarter of the circumference.
 In the present invention, the columnar body is particularly arranged in
 that it abuts against a hitting surface of the lower die.
 Moreover, in the present invention, a negative angle-forming portion of the
 columnar body is disposed on an opposing side with respect to its outer
 peripheral surface.
 Further scope of applicability of the present invention will become
 apparent from the detailed description given hereinafter. However, it
 should be understood that the detailed description and specific examples,
 while indicating preferred embodiments of the invention, are given by way
 of illustration only, since various changes and modifications within the
 spirit and scope of the invention will become apparent to those skilled in
 the art from this detailed description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 The present invention will now be explained in details based on particular
 embodiments as shown in the accompanying drawings.
 FIG. 1 is a sectional view showing a metallic thin plate part for a vehicle
 that is formed by using the negative angle-forming die of the present
 invention, one before and one after processing, wherein a lower portion of
 work W as shown in FIG. 1(b) is an intruding forming portion 1.
 This part assumes three-dimensional curved surfaces and curved lines for
 composing outer panel portions of a vehicle.
 In FIG. 2, a lower die 2 is formed with a supporting portion 3 for the work
 W located on a leftward upper side when facing the drawing, and a columnar
 body 5, which is formed with an intruding forming portion 26 being formed
 at an edge portion on a side of the supporting portion 3 such that it
 intrudes further than a locus of an upper die 4, is provided on the lower
 die 2 in a freely rotating manner. Reference C denotes a center of
 rotation for the columnar body 5. In order to enable taking out of the
 work W from the lower die 2 after forming the work W, an air cylinder 6 is
 provided at the lower die 2 as an automatic returning tool for retracting
 the columnar body in a rotating manner.
 As shown in FIG. 3, a tip portion of a piston rod 7 of the air cylinder 6
 that is connected to the lower die 2 via a pin 27 is connected, by means
 of a pin 10, to a link 9 fixed, via a bolt 8, to an end surface of a
 supporting shaft 12 that is fixedly attached to an outer end of the
 columnar body 5 while being supported by a bearing 11 in a freely rotating
 manner. The automatic returning tool may be, besides an air-pressure
 device as described above, a pushing pin that is energized by a coil
 spring, a hydraulic device, a link mechanism, a cam or any similar
 mechanism.
 As shown in FIG. 2, the lower die 2 is further provided with a slide cam 13
 that is positioned as to oppose the columnar body 5 and which performs
 sliding movements. The slide cam 13 is formed with an intruding forming
 portion 14 at an upper portion of a tip that is closer to the columnar
 body 5, and by guiding the slide cam 13 through a guide post 15 or, as
 shown in FIG. 5, through sliding a lower surface thereof, the slide cam 13
 is energized in a direction to outside of the mold (a direction receding
 from the columnar body 5) by a gas spring 16 that is disposed between the
 slide cam 13 and the lower die 2. The slide cam 13 is terminated at a
 terminating surface 17 of the lower die 2 as shown in FIG. 6. It should be
 noted that the gas spring 16 supports reaction force of energizing force
 actuated by the rod 19 by using a plug 18 that is screwed to the gas
 spring 16.
 The gas spring 16 accumulates in a cylinder 25 thereof high-pressure gas,
 e. g. high-pressure gas of 150 kg/cm.sup.2, depending to various purposes,
 and even though a rod 19 extruding from the cylinder 25 is expanded or
 retracted, a substantially constant output of, e.g. 150 kg/cm.sup.2, can
 be obtained during the entire length of the expanding and retracting
 process of the rod. The substantially constant output can be achieved
 during the entire process of the rod 19 through two tanks that are
 incorporated within the cylinder 25 wherein in case the rod 19 is
 retracted and pressure is applied to one tank, high-pressure gas is made
 to flow out from this tank to flow into the other tank.
 In this manner, the gas spring 16 is capable of performing high output from
 the start of actuation and during the entire process unlike a case with a
 coil spring whereby the slide cam 13 can be reliably returned to ensure
 safety.
 Further, by the use of the gas spring 16, the slide cam 13 is enabled to
 move a distance as long as 150 mm, and processing of a large-sized work
 such as a side panel of metallic thin plate used in a vehicle is also
 enabled.
 A pad 20 is energized in a downward direction by the coil spring 21 and
 suspended at the upper die 4 via a suspending bolt 22 which functions to
 press the work W strongly against the lower 2 such that the work W does
 not move after the columnar body 5 has been positioned to assume a forming
 posture and before intrusion forming is started.
 Further, an active cam 23 is fixedly attached to an upper die substrate 24
 of the upper die 4 at a portion at which it opposes the slide cam 13 of
 the lower die 2.
 In the negative angle-forming die of the present invention, it has been
 provided a locking device for preventing the columnar body 5 from rotating
 not to the slightest degree with the aim to provide formings of metallic
 thin plate of favorable quality at accuracy in units of 1/100 mm.
 As shown in FIG. 2, FIG. 4 and FIG. 7, an extruding piece 31 of a
 substantially triangle shape is made to extrude from a lower portion of
 the columnar body 5, an air cylinder 32 is disposed below, a locking block
 34 is fixedly attached to a tip end of a piston rod 33 of the cylinder,
 and a contacting surface 35 of the extruding piece 31 and a contacting
 surface 36 of the locking block 34 are made to contact. A sliding surface
 37 that is located opposite to the contacting surface 36 of the locking
 block 34 is made to abut against a vertical sliding surface 38 of the
 lower die 2. Further, a rib 39 is formed in proximity of the sliding
 surface 38 of the lower die 2 for satisfactory reinforcement purposes.
 When the work W is mounted on the supporting portion 3 of the lower die 2
 and the upper die 4 is descended, the columnar body 5 is made to assume a
 condition as shown in FIG. 2 through the air cylinder 6, and the columnar
 body 5 assumes a forming posture. The piston rod 33 of the air cylinder 32
 is expanded as shown in FIG. 2, and the tapered contacting surface 36 of
 the locking block 34 of the rod is made to abut against the contacting
 surface 35 of the extruding piece 31 of the columnar body 5, and the
 sliding surface 37 of the locking block 34 is made to abut against the
 sliding surface 38 of the lower die 2 so as to prevent the columnar body 5
 from moving to the slightest degree.
 As shown in FIG. 2, a wedge of the locking block 34 intrudes into a space
 that is formed by the contacting surface 35 of the extruding piece 31 of
 the columnar body 5 and the sliding surface 38 of the lower die 2, and the
 columnar 5 is completely prevented from rotating even to the slightest
 degree. Therefore, it can be prevented that stepped portions are formed in
 curved surfaces of a work W or that curved line become inaccurate, and
 negative angle-forming processes of favorable quality can be performed at
 accuracy of units of 1/100 mm.
 In case a tapering angle .alpha. of the locking block 34 is too small,
 intruding force of the looking block 34 becomes too large so that a large
 extruding force is required at the time of extruding, and in case the
 tapering angle .alpha. is too large, it becomes more difficult to maintain
 the columnar body 5 at its position, so that a proper size for the
 tapering angle .alpha. is selected.
 After positioning the columnar body 5 at a forming posture for the locking
 block 34, the upper die 4 is descended to make the slide cam 13 approach
 the work W.
 The upper die 4 is further descended, and the slide cam 13 is made to abut
 against a lower end portion of the work W by the active cam 23 to assume a
 condition of FIG. 2 at a bottom dead center. The work W is accordingly
 formed by the intruding forming portion 14 of the slide cam 13 and the
 intruding forming portion 26 of the columnar body 5. Even if the intruding
 forming portion 14 of the slide cam 13 should hit against a portion that
 is above the center C of the columnar body 5, the extruding piece 31 that
 is located lower than the center C of the columnar body 5 contacts the
 locking block 34 so that the columnar body 5 can be prevented from moving.
 A tapering fit between the extruding piece 31 and the locking block 34
 provides a fit condition with no space formed between so that the columnar
 body 5 does not move at all. Even if the tapered surface 35 of the
 extruding piece 31, the tapered surface 36 and the sliding surface 37 of
 the locking block 34, and the sliding surface 38 of the lower die 2 should
 be worn during usage, the stroke of the piston rod 33 of the air cylinder
 32 is simply expanded slightly, and the columnar body 5 is not permitted
 to move anyway.
 After completion of forming a negative angle, the upper die 4 is raised,
 the air cylinder 6 actuated, and as shown in FIG. 6, the slide cam 13 is
 retracted upon expansion of the rod 19 of the gas spring 16 such that the
 slide cam 13 is made to abut against the terminating surface 17 of the
 lower die 2, and by actuation of the air cylinder 6, the columnar body 5
 is retracted in a rotating manner to a condition as shown in FIGS. 6 and
 7, whereby the work W can be taken out from the lower die 2 without
 interfering with the columnar body 5. It should be noted that the columnar
 body 5 is rotated into the forming posture around the center C in FIG. 6,
 while it does not happen that it interferes with the locking block 34.
 The negative angle-forming die according to another embodiment assumes an
 even simpler arrangement wherein the columnar body 5 is not supported by
 the lower die 2 over the entire circumference thereof.
 As shown in FIG. 4, instead of supporting the outer periphery of the
 columnar body over the entire circumference thereof as it was
 conventionally the case, a supporting shaft 12 is fixedly attached to both
 ends of the columnar body 5 in an extruding manner and the supporting
 shaft 12 is inwardly fitted to the bearing 11 that is outwardly fitted to
 the lower die 2 to achieve a simple structure. In case the columnar body 5
 becomes as large as 1,200 m and flex may become large, a distance between
 both ends of the columnar body 5 is suitably supported by a plurality of
 supporting bodies (not shown).
 Further, the columnar body 5 of the present negative angle-forming die is
 arranged to assume a fan-like section having a central angle that is as
 small as possible, whereby down-sizing of the negative angle-forming die
 can be achieved to provide the negative angle-forming die at low costs.
 In FIG. 5, the columnar body 5 is formed with an intruding forming portion
 26 that is formed in a concave manner to be located above a center C of
 the columnar body 5 and a transmitting plate 39 is fixedly attached to
 below of the columnar body 5 wherein the transmitting plate is made to
 abut against a hitting surface 40 of the lower die 2. Columnar bodies of
 conventional negative angle-forming dies were supported by the lower die 2
 over the entire outer peripheral surface thereof, whereby the negative
 angle-forming dies became large and costly. The negative angle-forming die
 of the present invention is arranged in that a connecting portion between
 the columnar body 5 and the lower die 2 is made to be a quarter of the
 circumference. In order to decrease the size of the columnar body 5 as
 much as possible, the intruding forming portion 26 of the columnar body 5
 is located above the center C of the columnar body 5 so that the columnar
 body 5 as well as a portion of the lower die 2 which supports the columnar
 body 5 can be made to be a quarter of the circumference (a fan-like
 section which central angle is substantially 90.degree.) Further,
 pressuring force that is applied by the intruding forming portion 14 of
 the slide cam 13 is made to face oblique upward whereby a lower surface of
 the transmitting plate 39 is made to abut against the hitting surface 40
 of the lower die 2 so that it can receive the reaction force of the
 pressing force, and an extruding portion 41 of the slide cam 13 for
 supporting the intruding forming portion 14 is made to abut against an
 upper surface of the transmitting plate 39. With this arrangement,
 pressuring force for forming can be received by the lower die 2 so as to
 perform negative forming process in a clear manner.
 Upon completion of the negative angle-forming process, the upper die 4 is
 raised as shown in FIG. 7, the slide cam 13 is made to retract by the
 energizing force of the gas spring 16, the columnar body 5 is retracted in
 a rotating manner by the action of the air cylinder 6, and the work W can
 be taken out from the lower die 2 without interfering with the columnar
 body 5.
 As explained above, the negative angle-forming die according to the present
 is comprised with a lower die for mounting a work of metallic thin plate
 onto a supporting portion thereof and an upper die that is descended in a
 straight direction towards the lower die for forming the work by hitting
 against the work, wherein there are further provided a columnar body
 arranged in a freely rotating manner on the lower die and having an
 intruding forming portion which is intruding further than a locus of the
 upper die is formed at an edge portion closer to the supporting portion, a
 slide cam formed with an intruding forming portion, being arranged as to
 oppose the columnar body in a freely sliding manner with respect to the
 lower die, and an automatic returning tool arranged at the lower die for
 retracting the columnar body in a rotating manner to an extent with which
 the work can be taken out from the lower die upon completion of forming,
 wherein the work that is mounted on the supporting portion of the lower
 die is formed through the intruding forming portion of the columnar body
 and the intruding forming portion of the slide cam while the slide cam
 performs sliding movements, and after completion of forming, the columnar
 body is retracted in a rotating manner by the automatic returning tool
 such that the formed work can be taken out from the lower die, wherein the
 forming die is a negative angle-forming die comprised with a locking
 device for making the columnar body maintain a specified forming posture.
 With this arrangement, it has been enabled to cope with cases in which a
 columnar body is slightly rotated such that it can not maintain a
 specified forming posture to consequently result in a case in which a
 stepped portion is formed in a curved surface of a work or in which no
 accurate straight line can be formed or in which it becomes difficult to
 provide products having an accuracy in units of 1/100 mm such that no
 formings of metallic thin plate of favorable quality could be provided,
 and to provide formings of metallic thin plate of favorable quality by
 maintaining the columnar body in the specified forming posture.
 The locking device according to the present invention is particularly
 arranged in that the columnar body is locked by an action of a cylinder,
 whereby formings of metallic thin plate of favorable quality can be
 provided.
 The locking device according to the present invention is particularly
 arranged in that the columnar body is locked by connection between an
 extruding piece of the columnar body and a locking block formed at a tip
 of a piston rod of an air cylinder, whereby formings of metallic thin
 plate of favorable quality can be provided.
 The locking device according to the present invention is particularly
 arranged in that connecting surfaces of both, the extruding piece and the
 locking block, are formed as tapered surfaces wherein a surface opposite
 to the tapered surface of the locking block is formed as a sliding surface
 for sliding on the lower die. With this arrangement, formings of metallic
 thin plate of favorable quality can be provided.
 Another negative angle-forming die of the present invention is comprised
 with a lower die for forming a work of metallic thin plate onto a
 supporting portion thereof and an upper die that is descended in a
 straight direction towards the lower die for forming the work by hitting
 against the work, wherein there are further provided a columnar body
 arranged in a freely rotating manner on the lower die and having an
 intruding forming portion which is intruding than a locus of the upper die
 is formed at an edge portion closer to the supporting portion, a slide cam
 formed with an intruding forming portion, being arranged as to oppose the
 columnar body in a freely sliding manner with respect to the lower die,
 and an automatic returning tool arranged at the lower die for retracting
 the columnar body in a rotating manner to an extent with which the work
 can be taken out from the lower die upon completion of forming, wherein
 the work that is mounted on the supporting portion of the lower die is
 formed through the intruding forming portion of the columnar body and the
 intruding forming portion of the slide cam while the slide cam performs
 sliding movements, and after completion of forming, the columnar body is
 retracted in a rotating manner by the automatic returning tool such that
 the formed work can be taken out from the lower die, wherein the forming
 die is a negative angle-forming die arranged as to support the columnar
 body by a bearing in a freely rotating manner. With this arrangement, a
 simple structure is obtained in which an entire periphery of the columnar
 body is not necessary to be supported by the lower die.
 The negative angle-forming die according to the present invention is
 particularly arranged in that both ends of the columnar body are supported
 by the bearing in a freely rotating manner, whereby the negative
 angle-forming die can be made of a simple structure.
 Moreover, the negative angle-forming die according to the present invention
 is particularly arranged in that a flexible columnar body is supported
 also on a distance between both ends, whereby the negative angle-forming
 die can be made of a simple structure.
 Another negative angle-forming die of the present invention is comprised
 with a lower die for mounting a work of metallic thin plate onto a
 supporting portion thereof and an upper die that is descended in a
 straight direction towards the lower die for forming the work by hitting
 against the work, wherein there are further provided a columnar body
 arranged in a freely rotating manner on the lower die and having an
 intruding forming portion which is intruding than a locus of the upper die
 is formed at an edge portion closer to the supporting portion, a slide cam
 formed with an intruding forming portion, being arranged as to oppose the
 columnar body in a freely sliding manner with respect to the lower die,
 and an automatic returning tool arranged at the lower die for retracting
 the columnar body in a rotating manner to an extent with which the work
 can be taken out from the lower die upon completion of forming, wherein
 the work that is mounted on the supporting portion of the lower die is
 formed through the intruding forming portion of the columnar body and the
 intruding forming portion of the slide cam while the slide cam performs
 sliding movements, and after completion of forming, the columnar body is
 retracted in a rotating manner by the automatic returning tool such that
 the formed work can be taken out from the lower die, wherein the forming
 die is a negative angle-forming die wherein a connecting portion between
 the columnar body and the lower die is formed to be substantially a
 quarter of a circumference. With this arrangement, instead of assuming a
 substantially circular section, the columnar body can be formed to assume
 a fan-like section having a central angle that is as small as possible in
 order to realize downsizing of the negative angle-forming die that can be
 distributed at low costs.
 In the present invention, the columnar body is particularly arranged in
 that it abuts against a hitting surface of the lower die, whereby
 downsizing of the negative angle-forming die can be realized that can be
 distributed at low costs.
 Moreover, in the present invention, a negative angle-forming portion of the
 columnar body is disposed on an opposing side with respect to its outer
 peripheral surface, whereby downsizing of the negative angle-forming die
 can be realized that can be distributed at low costs.
 The invention being thus described, it will be obvious that the same may be
 varied in many ways. Such variations are not to be regarded as a departure
 from the spirit and scope of the invention, and all such modifications as
 would be obvious to one skilled in the art are to be included within the
 scope of the following claims.