[0002] There is a known method for stamping a box from a parent sheet on a single-action
press (
RF invention patent No. 2527820, publ. on 10.09.2014, Bull. No. 25), including the placement of a workpiece in a
die for extension, pressing of the workpiece flange by the hold-down's working surface
to the pressing surface of the counter die and extension of the box by pulling the
workpiece flange into the clearance between the punch and counter die, forming a box
wall using the punch and the counter die, whose outlines in plan view correspond to
the box wall outline in plan view with account of the wall thickness, after extension
there are one or several holes in the box bottom, characterized in that a sheet workpiece
is made preliminarily with holes punched in the areas corresponding to the unsafe
cross-sections during extension and located opposite to the angular chamfers of the
minimum curvature radius of the box wall in plan view.The disadvantage of this method
is the low quality of produced parts, because the box part has technological holes.Moreover,
there is a known method for multi-operation extension of a box part from a parent
sheet on single-action presses or a multiple-point automatic press (
RF invention patent No. 2545863, publ. on 27.12.2014, Bull. No. 36). The dies for implementation of each operation
in this extension method comprise the following main working parts: punch, counter
die and hold-down. The punch is fastened on the die's fixed lower plate, and the counter
die - on the movable upper plate. Inside the counter die there is an ejector of stamped
semi-finished product, acting from a pusher by means of a die or press device. The
hold down rests via the pushers onto the press bed or the die buffer, which provides
the required force for pressing of the parent sheet flange and pushing-in of the inclined
wall of the previous semi-finished product into the counter die for extension of the
subsequent semi-finished product.A disadvantage of this method is the limited technological
capabilities related to need for new jigging in each machining step, which also needs
replacement during change of the manufactured part. In the prior art a device is known
for adjustment of bed load and a press machine, containing a device for adjustment
of bed load (
RF invention patent No. 2401742, publ. on 10.04.2010, Bull. No. 10), containing a bed under the press slide. The
adjustment device comprises a hydraulic cylinder, forming the die bed, a hydraulic
control valve connected with this cylinder, a hydraulic source, an opening speed adjustment
unit, a unit for determination of die bed lowering speed, a signal correction unit.The
shortcomings of the described device include restricted technological capabilities,
related to the fact that local forces of the hold-down in its different points are
constant but may vary in time. Moreover, special equipment is required for control
of local forces.The said methods are implemented using the standard elements, namely
mechanical and gas springs, arranged in the die between the hold-down and the die
block part (lower or upper plate), and/or damping devices built into the press.There
is a known design of a damping device with a pneumatic spring (
RF useful model patent No. 81541, publ. on 20.03.2009, Bull. No. 8), comprising a reservoir containing a stem with
a piston, the following successively installed on the stem: guide with cover, first
sealing element, back-up ring, second sealing element which together with the stem
form a cavity with lubricating fluid. The stem guide and the back-up ring have radial
channels connected with the cavity; the first channel serves as an oil supply line,
the second serves for air discharge from the cavity and has a return valve, additionally,
the pneumatic spring comprises a unit for cavity filling with lubricating fluid.The
disadvantage of this design is the constancy of the algorithm for control of local
force transfer upon press impact on the hold-down, related to the fact that local
forces are transferred according to linear law depending on cylinder stem motion.The
suggested technical object is aimed at increasing the technological capabilities of
the sheet stamping process and accuracy of manufactured parts, as well as the possibility
of its use on universal equipment.The technical effect is achieved by the installation
of a differentiated hold-down device into the die; the device ensures the following
during workpiece forming: adjustment of metal flow and movement from the periphery
into the deformation zone by way of local force control. A differentiated hold-down
device, characterized in that the hold-down is made of sectors, fastened on a plate,
and each hold-down sector is equipped with a hydraulic device for force transfer under
a specified algorithm. The differentiated hold-down device comprises a hydraulic device
for force transfer under a specified algorithm, comprises a housing, a stem with a
piston, the housing comprises rings with an internal surface of variable cross-section,
which together with the piston's peripheral surface form a clearance that may change
during the piston movement in relation to the housing. Additionally, the differentiated
hold-down device may comprise a hydraulic device for force transfer under a specified
algorithm, which consists of a housing, a stem with piston, the stem is hollow and
has radial holes, while the piston is provided with a movable ring configured to close
the piston hole, the housing comprises an axle of variable cross-section, one end
whereof is made in the form of a piston placed in the stem cavity, wherein the movable
ring together with the axle of variable cross-section form a clearance that may change
during movement of the hollow stem with the piston and ring in relation to the axle.The
essence of the declared technical solution is shown in figures. Fig.1 shows the die
of sheet stamping with a differentiated hold-down device; Fig.2 - the die of sheet
stamping with a differentiated hold-down device, section A-A; Fig.3 - the hydraulic
device for force transfer under a specified algorithm according to the first embodiment;
Fig.4 - the hydraulic device for force transfer under a specified algorithm according
to the second embodiment; Fig.5 - the die of sheet stamping with a differentiated
hold-down device at the beginning of the shaping process; Fig.6-the hydraulic device
for force transfer under a specified algorithm according to the first embodiment at
the beginning of the shaping process; Fig.7 - the hydraulic device for force transfer
under a specified algorithm according to the second embodiment at the beginning of
the shaping process; Fig.8 - the die of sheet stamping with a differentiated hold-down
device in the shaping process; Fig.9 - the hydraulic device for force transfer under
a specified algorithm according to the first embodiment in the shaping process; Fig.10
- the hydraulic device for force transfer under a specified algorithm according to
the second embodiment in the shaping process; Fig.11 - the die of sheet stamping with
a differentiated hold-down device at the end of the shaping process; Fig.12 - the
hydraulic device for force transfer under a specified algorithm according to the first
embodiment at the end of the shaping process; Fig.13 - the hydraulic device for force
transfer under a specified algorithm according to the second embodiment at the end
of the shaping process; Fig.14 - the change of force value at δ = 0.03 mm; Fig.15
- the change of force value at δ = 0.04 mm; Fig.16 - the change of force value at
δ = 0.05 mm; Fig.17 - the change of force value at δ = 0.25 mm; Fig.18 - the graphical
dependence of change in local forces on clearance of the hydraulic device for force
transfer under a specified algorithm, built according to the first embodiment; Fig.19
-the graphical dependence of change in local forces on clearance of the hydraulic
device for force transfer under a specified algorithm, built according to the second
embodiment.The claimed method for control of local forces in the die of sheet stamping
is implemented using the following components: upper plate 1 and lower plate 2, whereon
punch 3 and counter die 4 are rigidly installed. Additionally, a differentiated hold-down
device 5 is installed on upper plate 1; this device comprises several hydraulic devices
6 for force transfer under a specified algorithm and hold-down 7. Hydraulic device
6 for force transfer under a specified algorithm comprises housing 8, stem 9, one
end whereof is fastened on upper plate 1, while the other is in the form of piston
10. Inside housing 8 there are rings 11 with internal surface of variable cross-section
12. Clearance δ is provided between the peripheral surface of piston 10 and the internal
surface of variable cross-section 12 of rings 11. Cover 13 is installed on the housing
butt surface. Inside housing 8 there is spring ring 14, restricting the travel of
air piston 15 with sealing rings 16, which is installed between housing 8 and stem
9. Spring 17 is installed between air piston 15 and cover 13. It is possible to manufacture
device 6 for load transfer under a specified algorithm, which comprises hollow stem
18 with radial holes 19, capable of moving along the axle of variable cross-section
20, one end whereof is made in the form of piston 21 with seals 22, while the other
end is fixed in housing 8 by means of threaded joint 23. Stem 18 has piston 24 with
holes 25 along its perimeter and sealing rings 26. Ring 27 is installed on one of
the butts of piston 24. Ring 27 together with holes 25 and spring ring 28, installed
in piston 24, forms a return valve. Besides, ring 27 together with axle 20 forms clearance
Δ. Hold-down 7 consists of separate sectors 29, rigidly fastened on common steel plate
30, to which housings 8 of hydraulic devices 6 for force transfer under a specified
algorithm are fastened. Wherein, housings 8 are located opposite the corresponding
sectors 29.Let us consider the application of the method to control local forces in
dies of sheet stamping and the operation of the differentiated hold-down device according
to the example of shaping of a box-section part. The standard sheet stamping technology
provides for the use of gas or mechanical springs, wherein local forces are transferred
to the rigid hold-down. Value of hold-down force is selected on the basis of assurance
of metal flow in places of dislocation of the maximum internal stresses at the initial
shaping moment and applies to the entire surface of hold-down contact with the part.
As the springs are compressed according to the slide, the force increases and does
not depend on the value required for the optimal shaping process. Wherein defects
may occur such as excessive thinning up to rupture, or thickening up to wrinkling.In
the suggested method, local forces in the shaping process are controlled as follows.
At the initial stage a calculation is performed in order to determine the optimal
local forces of the hold-down in different workpiece areas and in different moments
of the shaping process. The obtained data is used to determine the necessary quantity
and mutual location of sectors for hold-down 29, which are fastened on elastic plate
30, thus forming hold-down 7. Devices 6 for force transfer under a specified algorithm
are fastened to each sector 29. Hold-down 7 and devices 6 form differentiated hold-down
device 5 that allows for control of local forces in the die. Stamping is performed
by moving upper plate 1 together with punch 3 and differentiated hold-down device
5 in relation to lower plate 2, whereon counter die 4 is fastened. At the initial
time moment, a differentiated hold-down device 5 squeezes the workpiece with the design
forces provided by devices 6 for force transfer under a specified algorithm. Wherein
the force value on each of sectors 29 is different and corresponds to the optimal
value for the shaping process at the given time moment and in the given zone of hold-down
7. Change of force for each device 6 for force transfer under a specified algorithm
is determined according to the value of clearances δ or Δ. In the next time moment
the punch comes to the workpiece surface and starts deforming it. Wherein changes
of local forces in the sectors of hold-down 29 are necessary to ensure the optimal
shaping process. Further deforming of the workpiece also causes redistribution of
local forces in the sectors of hold-down 29, which continues until completion of the
shaping process and is ensured through control by device 6.Two embodiments are suggested
for implementation of hydraulic device 6 for force transfer under a specified algorithm
and, accordingly, two embodiments of operation of the differentiated hold-down device.
Both embodiments are described below.Operation of hydraulic device 6 for force transfer
under a specified algorithm according to the first embodiment is as follows. At the
initial moment, stem 9 and piston 10 are in the upper position, wherein pressure in
the cavity under the piston is equal to atmospheric pressure. When stem 9 moves downwards
under the action of die's upper plate 1, fastened on the press slide, pressure in
the cavity under the stem piston increases. Pressure value in this case is determined
by motion speed of stem 9 and clearance δ between the inner surface of variable cross-section
12 of rings 11 and the peripheral surface of piston 10. Motion speed of stem 9 depends
on motion speed of the press slide and may vary up to zero. Rings 11, installed inside
housing 8, are made with internal surfaces of variable cross-section 12. When the
peripheral surface of piston 10 passes in relation to rings 11, clearance δ between
them changes. Change of clearance δ allows for adjusting the speed of working fluid
overflow from the cavity under piston 10 into the cavity above the piston and, respectively,
controls the pressure in the cavity under piston 10, which via housing 8 is transferred
to the sectors of hold-down 29. Shape of the internal surfaces of rings 11 is determined
by calculation so as to ensure the optimal shaping process for the given hold-down
sector and, together with the peripheral surface of piston 10, assigns an algorithm
for control of force transfer from the press slide via the upper plate to a specific
sector of hold-down 29. The number of rings 11 depends on control algorithm complexity.
The working fluid in the cavity above the piston moves air piston 15, by compressing
spring 17. Shape of the internal surfaces of rings 11 is determined by calculation
so as to ensure the optimal shaping process for the given hold-down sector and, together
with the peripheral surface of piston 10, assigns an algorithm for control of force
transfer from the press slide via the upper plate to a specific sector of hold-down
29. When stem 9 moves backwards, the working fluid above the cavity of piston 10 under
the weight of housing 8 and hold-down 7, as well as the accumulated energy of spring
17 flows from the cavity above the piston into the cavity under the piston. Ring 14
is configured to restrict the travel of air piston 15. Sealing rings 16 prevent the
ingress of working fluid into the air chamber formed by air piston 15, cover 13 and
internal walls of housing 8.Operation of hydraulic device 6 for force transfer under
a specified algorithm according to the second embodiment is as follows. At the initial
moment, hollow stem 18 and piston 24 are in the upper position, wherein pressure in
the cavity under the piston is equal to atmospheric pressure. When stem 18 moves downwards
under the action of die's upper plate 1, fastened on the press slide, pressure in
the cavity under the stem piston increases and presses ring 27 to the butt surface
of hollow piston 18, which closes holes 25. The hole of ring 27 and the outer surface
of axle 20 form variable clearance Δ, through which the working fluid flows over to
the cavity formed by axle 20 and the internal surface of hollow stem 18. Then the
working fluid flows through radial holes 19 into the cavity above piston 24. The value
of pressure under piston 24 in this case is determined according to the motion speed
of stem 18 and clearance Δ between the hole of ring 27 and the outer surface of axle
20. Motion speed of stem 18 depends on motion speed of the press slide and may vary
up to zero. Axle 20, having a variable cross-section, is fastened to the bottom of
housing 8 by thread 23. When piston 24 with ring 27 moves in relation to axle 20,
the value of clearance Δ changes. Change of clearance Δ allows for adjusting the speed
of working fluid overflow from the cavity under piston 24 into the cavity above the
piston and, respectively, controls the pressure in the cavity under piston 24, which
via housing 8 is transferred to the sectors of hold-down 29. Shape of the surface
of axle 20 is determined by calculation so as to ensure the optimal shaping process
for the given sector of hold-down 29 and, together with the hole of ring 29, assigns
an algorithm for control of force transfer from the press slide via upper plate 1
to a specific sector of hold-down 29. Sealing rings 26, arranged on piston 24, prevent
working fluid ingress into the cavity above the piston, bypassing clearance Δ. The
working fluid in the cavity above the piston moves air piston 15, by compressing spring
17. When stem 18 moves backwards, the working fluid above the cavity of piston 10
under the weight of housing 8 and hold-down 7, as well as the accumulated energy of
spring 17 moves ring 27 up to the extreme position, limited by ring 28, and flows
through holes 25 from the cavity above the piston into the cavity under the piston.
Ring 14 is configured to restrict the travel of air piston 15. Sealing rings 16 prevent
the ingress of working fluid into the air chamber formed by air piston 15, cover 13
and internal walls of housing 8. Sealing rings 22 prevent working fluid ingress into
the intracavity of stem 18.The experimental results have showed a considerable change
in local forces upon clearance change. Several experiments have been carried out with
the following input values:hydraulic device 6 for force transfer under a specified
algorithm built according to the first embodiment;diameter of piston 10 is equal to
49 mm;clearance values 0.03, 0.04, 0.05 and 0.25 mm;viscosity of working fluid ISO
VG-10 (Mobil Velocite 6);press model K3732.With the clearance of δ = 0.03 mm, the
force value was 23.4 tons, δ = 0.04 mm - 2.08 tons, δ = 0.05 mm - 1.28 tons and δ
= 0.25 mm - 0.33 tons.The results of the experiment using hydraulic device 6 for force
transfer under a specified algorithm, built according to the second embodiment with
the diameter of internal hole in ring 27 equal to 5 mm, are as follows: with clearance
Δ = 0.3 mm the force was 23.4 tons, Δ = 0.38 mm - 2.08 tons, Δ = 0.47 mm - 1.28 tons
and Δ = 2.04 mm - 0.33 tons.Fig. 18 and Fig. 19 show graphical dependences of change
in local forces on clearance of hydraulic device 6 for force transfer under a specified
algorithm, built according to the first and second embodiments respectively. Analysis
of the graphical dependences showed that the rational use region for the device, manufactured
according to the first embodiment, is in the force range from 0.5 tons to 2.5 tons,
and for the device according to the second embodiment - from 2 tons to 11 tons. Thus,
we may conclude that these device may complement the operation of each other and be
used in the differentiated hold-down device depending on the specified conditions
of the shaping process.The positive result from the suggested technical solution is
as follows. Control of local forces of workpiece pressing to the counter die positively
affects the shaping process, extends the technological capabilities, allowing for
manufacturing parts of hard-to-deform materials, as well as increases the accuracy
of part manufacture. Compactness of the differentiated hold-down device and the possibility
to use a relatively simple and reliable control member, that can be made for the given
part, allows for its installation in the standard dies used in universal equipment.
