BACKGROUND OF THE INVENTION
[0001] The present invention relates to a drawing die having a stabilizer, according to
the preamble of claim 1 (see for example
EP-A-0956913).
[0002] A known drawing die is shown in Fig. 5. This drawing die comprises a punch 101 positioned
at a center, a blank holder 103 which is fitted peripherally outside to the punch
101, is supported by a cushion pin 102 and is provided so as to freely move upward
and downward, and a die 104 arranged so as to face the punch 101 and so as to be able
to move upward and downward. Reference numeral 105 denotes an air vent.
[0003] A lower die structure 109 comprising the punch 101 and the blank holder 103 is fixed
to a bolster 106 of a press machine, an upper die structure 110 comprising the die
104 is fixed to a ram 107 of the press machine, and the upper die structure 110 in
operation is moved upward and downward by driving the press machine. Further, the
blank holder 103 which is supported by the cushion pin 102 moves upward and downward
in that the cushion pin 102 is moved upward and downward by a cushion apparatus of
the press machine.
[0004] A description will now be given of a drawing process:
[0005] First, the blank holder 103 is moved upward by the cushion pin 102 to a position
shown by a double-dashed line.
[0006] Next, as shown by a double-dashed line, a thin plate 108 of process material, i.e.
a work piece to be formed, is mounted on the blank holder 103 and the punch 101.
[0007] Thereafter, when moving the upper die structure 110 downward, the die 104 collides
with the thin plate 108 on the blank holder 103 in an entire outer periphery of the
punch 101 so as to pinch the thin plate 108 by the blank holder 103 and the die 104.
[0008] Subsequently, when the upper die structure 110 moves further downward, the thin plate
108 pinched by the blank holder 103 and the die 104 is drawn by the punch 101. Further,
when the upper die structure 110 reaches an illustrated bottom dead center, the thin
plate 108 is finally formed into a work W.
[0009] When the upper die structure 110 moves upward, the blank holder 103 is moved upward
to a state shown by a double-dashed line on the basis of an ascending force of the
cushion pin 102, and the work W is taken off from the punch 101. The upper die structure
110 has the air vent 105 provided in the die 104 so as to prevent a negative pressure
from being generated between the work W and the die 104 when the work W slides downward
by its own weight. Alternatively, the work W is actively moved to the side of the
lower die structure by an extrusion pin (not shown) energized by a spring, the work
W is taken off from the die 104, and the work W picked up from the press machine is
transferred to another press machine in the next step.
[0010] In the drawing process mentioned above, when the die 104 collides with the thin plate
108 mounted on the blank holder 103, the thin plate 108 extending around an entire
surface of an entire outer periphery of the punch 101 (that is, the thin plate 108
on the blank holder 103) and the die 104 are simultaneously brought into contact and
worked by impact. Accordingly, it is necessary to use a high-quality thin plate which
can sustain the impact. Further, the service life of the press die and the press machine
is shortened due to the impact process.
[0011] Even when low quality process material is used, it is required that the finished
product has the same quality as when high quality process material is used, and that
the product cost is reduced.
[0012] In the drawing die, a great impact is generated at the time when the die collides
with the thin plate on the blank holder. In order to prolong the service life of the
drawing die and the press machine, it is desired to make the impact as small as possible.
[0013] If a stabilizer of the drawing die could be standardized, it is more easy to manufacture
and a cost reduction could be achieved.
[0014] Further, at a time of executing the drawing process, a loud noise is generated at
a time when the upper die and the lower die collide.
[0015] Further, when the blank holder finishes the upward movement after the drawing process
is executed, a vibration is frequently generated in the work on the blank holder.
[0016] In view of the above noted problems, the present invention is made in order to make
the impact generated in the drawing die as small as possible. A further aspect is
to provide a drawing die with which it is possible to make a processed product from
a low quality process material with the same quality as when high quality process
material is used, thereby achieving a cost reduction of the product. A still further
aspect is to prolong the service life of the drawing die and of the press machine
and to standardize the stabilizer of the drawing die in order to simplify the manufacture
and to achieve a cost reduction.
[0017] To this end, the present invention provides a drawing die with a stabilizer as defined
in claim 1. Preferred embodiments are defined in the dependent claims.
[0018] The present invention accordingly provides a drawing die comprising a punch, a blank
holder fitted outside the punch and supported by a cushion pin and provided so as
to be able to freely move upward and downward, a die arranged so as to face the punch
and able to move upward and downward, whereby in operation of the die a thin plate
mounted on the blank holder is pinched between the blank holder and the die and is
drawn by the punch by moving the die downward, and a stabilizer unit comprising a
plurality of boxes peripherally arranged around the blank holder between the cushion
pin and the blank holder so as to be freely movable upward and downward by the cushion
pin, a buffer gas spring interposed between each box and the blank holder so as to
define a run-up gap for the blank holder between the boxes and the blank holder, and
a run-up lever rotatably provided in each box and arranged to cooperate with a driver
for driving the run-up lever, said driver being arranged at a position of the die
facing the run-up lever, wherein the run-up lever is adapted to press the blank holder
in operation of the die so as to make the blank holder run up against the operation
of the buffer gas springs before the die collides with the thin plate on the blank
holder.
[0019] In a preferred embodiment the driver is provided with a cam surface with portions
having a changing angle of inclination for changing a driving speed of the run-up
lever.
[0020] In another preferred embodiment an operation starting gap height between the blank
holder and the die is set larger than the run-up gap height for the blank holder between
the boxes and the blank holder in order to make the blank holder run up before it
collides with the boxes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021]
Fig. 1 is a vertical cross sectional view of a main portion of the drawing die in
accordance with the present invention showing a state in which an operation of a run-up
lever is started;
Fig. 2 is a side elevational view of a stabilizer of the drawing die in Fig. 1;
Fig. 3 is a vertical cross sectional view of the main portion of the drawing die in
accordance with the present invention showing a state in which a blank holder runs
up and is brought into contact with a box and a die is joined to a thin plate on the
blank holder;
Fig. 4 is a vertical cross sectional view of the main portion showing a state of a
bottom dead center in which an upper die moves further downward from the state in
Fig. 3, and the drawing process is finished; and
Fig. 5 is a vertical cross sectional view of a conventional drawing die.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] A description of the present invention will be given in detail below on the basis
of a particular embodiment shown in the accompanying drawings.
[0023] In Fig. 1, a lower die structure 1 comprises a punch 2, a blank holder 3 fitted peripherally
outside the punch 2 and provided so as to be freely movable upward and downward by
a cushion pin 4, and a plurality of boxes 5 arranged peripherally outside the punch
2 and around the blank holder 3 and supported by the cushion pin 4 in a manner similar
to the blank holder 3. An upper die structure 6 comprises a die 7 arranged so as to
face the punch 2.
[0024] It is to be noted that the cushion pin (4) can comprise a plurality of pins driven
by a common structure as shown in the drawing or even a plurality of independently
driven cushion pins.
[0025] Conventionally, a sub blank holder constituted by an integrally formed annular ring-like
member fitted outside to the punch 2 has been used However, a drawing die becomes
large by using the sub blank holder and the cost is increased. Therefore, in accordance
with the present invention, the structure is made such that the plurality of standardized
boxes 5 are arranged only at necessary positions below the blank holder 3 around the
periphery of the punch 2. The number of the boxes needed is determined according to
the size of the drawing die, and normally, four to six boxes are arranged around the
periphery. The size of the box can be for example 150 mm x 275 mm x 120 mm height.
[0026] The drawing die of the invention is provided with a stabilizer unit which is attached
to the box 5 and the die 7 and is adapted to make the blank holder 3 collide with
the box 5 after the blank holder 3 is made to run up. An example thereof will be illustrated
and described in the following.
[0027] A buffer gas spring 11 is interposed between each box 5 and the blank holder 3 of
the lower die structure 1 so as to form a gap between the blank holder 3 and each
box 5. Accordingly, the blank holder 3 in the starting position before the processing
stroke is started floats over the box 5, and the gap is set to a run-up gap height
H
1. In this case, the buffer gas spring 11 is fastened in the box 5 by one or more bolt(s)
8.
[0028] The buffer gas spring 11 employs a gas-pressure/hydraulic cylinder, and a operational
stroke and an output of a piston 12 of the buffer gas spring 11 are determined in
correspondence to the drawing die. The buffer gas spring 11 is preferably a standardized
element. Although an output of one cushion pin 4 is normally about 100 ton, one buffer
gas spring 11 has an output of 6 ton and a stroke of about 15 mm.
[0029] A run-up lever 13 is formed approximately in a triangular shape and is rotatably
provided in a bracket 14 so as to be able to press the blank holder 3 in operation
to make the blank holder 3 run up, i.e. to start moving in a downward direction. The
bracket 14 is fixed to the box 5 by one or more bolt(s) 15, and a positioning groove
16 is provided for accurately defining an attaching position of the bracket 14.
[0030] The run-up lever 13 is provided so as to be rotatable around a rotary shaft 17 provided
in the bracket 14 and to press a flange 18 of the blank holder 3. A pressing surface
19 of the run-up lever 13 is provided with a hardened pressing member 20, and a hardened
pressure receiving member 9 is provided at the part of the flange 18 where the pressing
member 20 is brought into contact.
[0031] A first roller 21 is rotatably provided in an upper portion of the run-up lever 13,
and a second roller 22 is provided at a position facing the first roller 21 in the
bracket 14 and so as to be rotatable around a rotary shaft 47.
[0032] A driver 31 is provided at a position of the die 7 between the first roller 21 and
the second roller 22. The driver 31 is attached to the die 7 via a support table 32.
The support table 32 is fastened to the die 7 by one or more bolt(s) 33, and the driver
31 is fastened to the support table 32 by one or more bolt(s) 34. The driver 31 and
the support table 32 may be manufactured as an integral member.
[0033] The driver 31 has a cam surface 35 including a portion with a low speed angle of
inclination α and a portion with a middle speed angle of inclination β that are provided
continuously. The low speed angle of inclination α is such that it creates a small
downward component of movement when a part of the upper die structure 6 is brought
into contact with the first roller 21 at an initial time when the upper die structure
6 moves downward. A connection portion between the portion with the low speed angle
of inclination α and the portion with the middle speed angle of inclination β is formed
to provide a smooth connection in the form of a circular arc. It is possible to control
downward moving speeds of the run-up lever 13 and the blank holder 3 by changing the
low speed angle of inclination α and the middle speed angle of inclination β of the
driver 31.
[0034] Fig. 2 shows a side view of the stabilizer unit of the drawing die in Fig. 1.
[0035] An appropriate number of boxes 5 are arranged in a standardized manner in the lower
portion of the blank holder 3 around the punch 2, and are movable upward and downward
by the cushion pin(s) 4.
[0036] The bracket 14 is firmly fixed to each box 5 by the bolt(s) 15, and side plates 41
are arranged at both outer sides of the bracket 14. Further, the side plates 41 are
fastened to the flange 18 of the blank holder 3 by bolts 42 and 43.
[0037] The rotary shaft 17 is extended through a base end portion of the run-up lever 13,
the base end portion of the run-up lever 13 is received within the bracket 14, and
each end portion of the rotary shaft 17 is inserted through a long hole 44 of each
side plate 41 and is fastened by a bolt 46 via a washer 45.
[0038] The second roller 22 that is provided rotatable around the rotary shaft 47 is received
in the upper portion of the bracket 14. Both ends of the rotary shaft 47 are supported
by the bracket 14, both end surfaces are fixed by stop plates 48, and each stop plate
48 is fastened to the bracket 14 for example by one or more bolt(s) 49.
[0039] The buffer gas spring 11 is fastened to the box 5 by the bolt(s) 8, and a piston
50 of the buffer gas spring 11 is brought into contact with a lower surface of the
flange 18 of the blank holder 3. The flange 18 of the blank holder 3 is lifted up
from the upper surface of the box 5 on the basis of the output of the buffer gas spring
11 to create a run-up gap height H
1 of for example 15 mm.
[0040] Next, a description will be given of an operation of the drawing die of the invention
including the stabilizer unit.
[0041] A thin plate 51 of a process material, i.e. a work piece to be formed in the drawing
die is mounted on the punch 2 and the blank holder 3.
[0042] Fig. 1 shows a state in which the upper die structure 6 moves downward, and the run-up
lever 13 starts being brought into contact with an upper surface of the flange 18
of the blank holder 3 by engagement with the driver 31. An operation starting gap
height H
2 between the blank holder 3 and the die 7 in Fig. 1 is set larger than the run-up
gap height H
1 in order to make the blank holder 3 run up first, and then collide with the box 5.
The run-up gap height H
1, the operation starting gap height H
2, and a relation between the run-up gap height H
1 and the operating starting gap height H
2 (a factor by which the operation starting gap height H
2 is larger than the run-up gap height H
1) are set to values that are sufficient to avoid an impact work, i.e. a simultaneous
contact between the die and the blank holder and a start of drawing on the punch.
[0043] After the blank holder 3 is made to run up by the run-up lever 13 and presses the
piston 50 of the buffer gas spring 11, thereby making the blank holder run up against
the operation of the buffer gas springs before the die collides with the thin plate
on the blank holder, and after the lower surface of the flange 18 of the blank holder
3 is brought into contact with the upper surface of the box 5, the die 7 is brought
into contact with the thin plate 51 on the blank holder 3. The state at this point
is shown in Fig. 3. In the case of H
1 = 15 mm, for example, a relation that H
1 = 0 mm is established when the contact portion of the run-up lever 13 with the flange
18 of the blank holder 3 moves downward by a distance of 15 mm. The die 7 is accordingly
brought into contact with the thin plate 51 on the blank holder 3 that is running
up, i.e. is not in a resting state. Since the die 7 is brought into contact with the
thin plate 51 that is running up and is not coming in static condition, a strong impact
is hardly generated.
[0044] Thereafter, the upper die 6 continuous to move downward and the drawing process is
finished in a state when the die has reached a bottom dead center shown in Fig. 4
where the work W is finally formed. In the case of the present embodiment, the cushion
pin 4 moves downward for example by a distance of 65 mm.
[0045] When the upper die 6 moves upward, the work W is taken out of the punch 2 by the
blank holder 3, and an air vent 52 is provided in the die 7 so as to prevent a negative
pressure from being generated between the work W and the die 7 at a time when the
work W slides down due to its own weight. Alternatively, the work W may be actively
discharged out of the die 7 by an extrusion pin (not shown) energized by a spring.
[0046] If the box 5, the run-up lever 13, the bracket 14, the driver 31 and the like (including
the first roller 21, the second roller 22, the rotary shaft 17, the buffer gas spring
11, and the support table 32) are formed as standardized parts and different parts
are provided essentially only in correspondence to the size, it is possible to easily
modify an existing drawing die to the die having the buffer structure.
[0047] In accordance with the present invention, since the components of the stabilizer
of the drawing die such as the box are provided in a standardized manner, the buffer
structure can be easily provided for any drawing die. Even when low quality process
material is used, it is possible to make the processed product to have the same quality
as when high quality process material is used, and it is possible to achieve a cost
reduction of the product.
[0048] Further, in accordance with the present invention, since the die comes into collision
with the thin plate on the running up blank holder, a noise can be reduced.
[0049] Further, in accordance with the present invention, since the blank holder executes
the drawing process via the stabilizer unit, it moves upward step by step by the stabilizer
unit and it is possible to reduce a vibration of the finished work on the blank holder.
[0050] In accordance with the present invention, it is further possible to make the impact
generated in the drawing die as small as possible and to thus prolong the service
life of the drawing die and the press machine.
[0051] By standardizing the elements of the stabilizer of the drawing die, the same can
be easily manufactures and a cost reduction can be achieved.
[0052] Further, in accordance with the present invention, by providing the cam surface with
portions having a changing angle of inclination, it is possible to control and change
the run-up speed of the blank holder.
[0053] Further, in accordance with the present invention, since the stabilizer unit of the
drawing die is structured such as to be attached to the boxes and the die and collide
with the boxes after making the blank holder run up, it is possible to easily improve
an existing drawing die.
[0054] The present invention is described about the drawing die, however, may be applied
to a forming die.
1. Ziehwerkzeug, mit:
einem Stempel (2),
einem Rohlingshalter (3), der außerhalb des Stempels (2) eingesetzt ist, und durch
einen Abfederungsstift (4) getragen ist und so vorgesehen ist, dass er sich frei aufwärts
und abwärts bewegen kann,
einer Ziehform bzw. Matrize (7), die so angeordnet ist, dass sie dem Stempel (2) gegenüberliegt,
und sich aufwärts und abwärts bewegen kann, wodurch im Betrieb des Ziehwerkzeugs ein
dünnes Blech (51), das an/auf dem Rohlingshalter (3) angebracht ist, zwischen dem
Rohlingshalter (3) und der Ziehform (7) eingespannt und von dem Stempel (2) durch
Abwärtsbewegen der Ziehform (7) gezogen wird, und gekennzeichnet durch
eine Stabilisierungseinheit, umfassend:
mehrere umfangsmäßig um den Rohlingshalter (3) zwischen dem Abfederungsstift (4) und
dem Rohlingshalter (3) so angeordnete Kästen (5), dass sie durch den Abfederungsstift
(4) frei aufwärts- und abwärtsbeweglich sind,
eine Puffer-Gasfeder (11), die zwischen jeden Kasten (5) und den Rohlingshalter (3)
eingefügt ist, so dass sie einen Anlaufspalt für den Rohlingshalter (3) zwischen den
Kästen (5) und dem Rohlingshalter (3) festlegt, und
einen Anlaufhebel (13), der in jedem Kasten (5) drehbar vorgesehen und so angeordnet
ist, dass er mit einem Antriebselement (31) zum Antreiben des Anlaufhebels (13) zusammenwirkt,
wobei das Antriebselement (31) an einer Position der Ziehform (7) angeordnet ist,
die dem Anlaufhebel (13) zugewandt ist, wobei der Anlaufhebel (13) den Rohlingshalter
(3) im Betrieb des Werkzeugs so pressen kann, dass der Rohlingshalter (3) gegen die
Betätigung der Puffer-Gasfedern (11) zum Anlaufen gebracht wird, bevor die Ziehform
(7) mit dem dünnen Blech (51) auf dem Rohlingshalter (3) kollidiert.
2. Ziehwerkzeug nach Anspruch 1, wobei das Antriebselement (31) mit einer Nocken- bzw.
Steuerkurvenfläche mit Abschnitten, die sich ändernde Neigungswinkel zum Ändern einer
Antriebsgeschwindigkeit des Anlaufhebels (13) aufweisen, versehen ist.
3. Ziehwerkzeug nach Anspruch 1 oder 2, wobei eine Arbeitsbeginn-Spalthöhe (H2) zwischen dem Rohlingshalter (3) und der Ziehform (7) größer eingestellt ist als
die Anlauf-Spalthöhe (H1) für den Rohlingshalter (3) zwischen den Kästen (5) und dem Rohlingshalter (3), um
den Rohlingshalter (3) anlaufen zu lassen, bevor er mit den Kästen (5) kollidiert.