JP2812171B2 - Hydraulic die cushion device for hydraulic press for punching holes in stepped slender cylindrical forgings - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic die cushion apparatus which is most suitable for a technique which serves both as a knock-out device and a cushion device for a press machine product, in particular, a punching press for a stepped elongated cylindrical forging.

[0002]

2. Description of the Related Art In recent years, there has been a tendency that demands for increasing the degree of molding have been increasing in molding by a press machine. Increasing the degree of molding reduces the weight of the material, improving the yield rate and lowering the material cost, and simplifying the post-process, leading to a reduction in the overall processing energy. Product competitiveness is greatly enhanced. In order to increase the forming degree of the press machine, it is necessary to take measures to enhance the capacity of the machine itself. However, the important point is to apply a forming force that matches structurally the property of the material to plastic deformation. Even if a force greater than the limit that exceeds the durability of the material is forcibly applied, the material breaks or cracks, and only mass production of defective products is performed. Is wise.

[0003] When the material loaded into the die of the press machine is pressed, the die cushion reduces the sudden stress load by the reaction of the pressure supporting the back, thereby fully enhancing the plastic deformation capability of the material. The purpose is to get the most out of the material and to obtain a large degree of molding to the maximum acceptable level. The die cushion moves freely in the hole where the cushion rod or cushion pin penetrates the bolster and the mold,
When knocking out the product from the mold, the tip protrudes into the mold, and when replacing the mold, it sinks to almost the same level as the top of the bolster, facilitating the side-slip mold replacement. When it is in the position, it holds an appropriate pressure, acts on the mold together with the pressure of the press from above, and simultaneously has one surface that actively promotes the deformation of the material clamped between the upper and lower pressures. If this die cushion is used properly, the possibility of completing a high ratio forming process involving deep hole drilling, which was difficult in the past, can be completed in one step, and it can be expected to bring great convenience in manufacturing. is there.

Among them, the problem of drilling deep holes in a molded article is one of the important issues of forging technology. Conventionally, the ratio of the inner diameter to the length of a hole to be drilled (elongation ratio) is limited to about 3 empirically. For products with a higher ratio, it was necessary to resort to drilling by machining. In addition to this, if there is a step in the molded product, it is more difficult with simple normal one-sided press molding, and since a strong pressing force is concentrated near the root of the step, it causes cracks and breaks, This results in increasingly lower limits of slenderness. However, even in this case, if the appropriate cushioning function is supported and the perforation by the forward extrusion of the punch from above and the forming of the extruded material work together, the stepped forged product which could not be obtained at all in the past can be increased. There is a possibility that it can be obtained from the slenderness ratio of the ratio.

[0005] By the way, the most common conventional technology of the die cushion has been a system in which an air cylinder is connected below a cushion rod (pin) to oppose a press pressure from above, but in this case, the stroke of the press advances. At the same time, there is a high possibility that the material may break or crack due to an excessively large clamping stress at the end. As a conventional technique developed for this improvement, for example, in Japanese Patent Application Laid-Open No. 2-38000, a cushion pin is inserted into a pin hole formed in a bolster plate,
A hydraulic cylinder having a piston rod that can be moved up and down below the plate is disposed so that the front end surface of the piston rod can contact the lower end surface of the cushion pin, and the head-side hydraulic chamber of each hydraulic cylinder is provided. It is configured to be connected to a hydraulic servo valve.

Further, in the prior art of Japanese Patent Application Laid-Open No. 63-63333, as shown in FIG. 4, there is a hydraulic cushion cylinder 101 in which an upper outer cushion pad 1 is provided.
An upper oil chamber 104 and a lower oil chamber 105 are formed by the piston 103 coupled to the piston 103. Since the lower oil chamber 105 is in communication with the hydraulic system in which the relief valve 106, the servo valve 107, the oil tank 108, and the like are arranged, the lowering of the cushion pad is received by the hydraulic cushion cylinder, and the oil in the lower oil chamber is relieved. A certain level of cushioning force is obtained by escaping into the oil tank through the valve. It also claims that by detecting the load acting on the cushion pad and activating the servo valve to allow the oil in the room to escape to the tank, the cushion force can be reduced as the stroke increases.

FIG . 5 shows a cushion mechanism and a knockout device.
An example of conventional technology related to a special hydraulic circuit linked with
Yes, cited from Japanese Patent Publication No. 3-29520. this
In the prior art, the lower surface of the bed 203 shown in FIG.
A part cushion device 204 is provided, and as shown in FIG.
Ride 201 equipped with upper cushion device 205
Of the upper and lower cushion devices 204 and 205
It consists of a pneumatic oil conversion mechanism that converts a power source from air pressure to hydraulic pressure.
And the pressure of each cushion device can be adjusted individually
And special oil for knockout
It features a pressure circuit . That is, the invention of the prior art
Focuses on sheet metal presses for thin sheets that perform multiple
The upper cushion device 205
Independently controlled hydraulically operated first piston 20
6, the second piston 207, and the lower cushion device 2
In 04, the third pistons 208 rise in the cylinders respectively.
The ports that are fitted freely and connected to the pneumatic-hydraulic conversion circuit
Increase or decrease the volume of the oil chamber connected to the
It is configured to be.

[0008]

Although the prior art described here is considered to be an effective structure for adjusting the stroke of the press and the adjustment of the cushion pressure, any of the structures described above requires a complicated control circuit. In a severe operating environment that is not always suitable for precision equipment due to repeated shocks and vibrations, complicated maintenance work to maintain the performance becomes a heavy burden You win. Further, once a trouble occurs, it is presumed that there is a great concern that the troublesome productivity of the repair may be impeded due to the complicated structure.

In particular, a stepped slender cylindrical product that has been confused by those skilled in the art in forming a forged product which is an object of the present invention.
(Hereinafter referred to as “stepped work w”) , there is no room for application in the related art, and how to specifically prevent cracks and breaks in the stepped portion due to stress concentration during molding, and How to realize hole punching with slenderness ratio that greatly exceeds the conventional limit, how to handle punched chips that are further removed, it is far from suggesting means to solve as it is The grudge that cannot be a clue remains.

[0010] Among the problems, the largest when forging a stepped work
The difficulty will be described with reference to FIGS. 6 and 7. FIG.
(B) and (C) show that the tip of the punch 9 has a stepped material W from above.
The center of the upper surface of the
It shows the positional relationship of each member at the moment of the attempt.
Fig. (A) shows a normal positional relationship, in which the material
When the step is fitted, just lower the lower end face W1 of the material
Upper end surface of cradle 8 extended on piston rod 3 from
81 is under support. In figure (B), the piston rod
3 supports the stepped material W via the cradle.
Between the step 12 of the mold 1 and the bottom surface W2 of the step of the material.
A gap S1 occurs and the material floats above the normal position in the air
It is in a crooked state. Also, in FIG.
Upper end surface 81 of the cradle on piston rod 3 to be supported
Is too low, and the step bottom surface W of the material is
When the two are in close contact, the lower end surface W1 of the material and the upper end of the cradle 8
This shows a state in which a gap S2 has been formed between the surface 81 and the surface 81. Figure (A)
The upper end surface 35 of the piston rod 31 in the normal position of
When the height protruding from the bolster 2 is H1,
The height in (B) is higher than that in H4.
The same height in H5 is lower than that,
It forms the cause of the gaps S1 and S2. in this way
Attach the same die to the same press machine
At the stop position of the piston rod that supports
If there is a variation, the conditions for the start of the drilling action will vary
Concerns remain.

FIG . 7A shows a forged state in the state of FIG. 6B.
The stepped material W indicates the situation at the beginning.
Since a gap S1 is formed below the step bottom surface W2 of FIG.
Pressing force P of punch 9 and receiving of piston rod
The root of the bottom of the step is plastically deformed by the molding pressure due to the force P2.
The raised bulge W3 appears, elevating the shape of the finished product.
Deterioration is severe. FIG. 7 (B) is FIG. 6 (C)
Shows the situation when forging is performed in the state of
P acts intensively on the base of the stepped bottom surface W2 of the material
From the stepped root of the stepped material W and the tip of the punch 9
As shown by a two-dot chain line, a shearing force appears between
There is no danger of losing material from this part
I can't. After all, the preconditions of the present invention can be summarized as follows: (A) the material W is a stepped cylinder, and the product w
An elongated cylindrical body with a step. (B) A stepped hole is provided in the mold on the bolster, and the stepped
To fit a stepped material into the hole. (C) The punch for punching operates at the center of the upper surface of the stepped material
Time, the position of the upper end surface of the piston rod prop material
If it is not a fixed point, it may lead to defective dimensions and breakage of the product
Is very likely to be The conditions are exhausted.

The prior art piston rod cited above, however,
The stop position of the pad is usually controlled by a solenoid valve.
And a die cushion device accompanying fluid movement.
Position control does not always guarantee high accuracy.
As a result, the above-mentioned issues have not been solved yet.
Is the current situation. The main reason for this is that a rise in the temperature of the hydraulic oil causes a change in viscosity and a change in flow velocity.
That the position varies. Change in flow rate due to change in solenoid valve switching
That vary. Position varies due to change in response of solenoid valve switching signal
That. Such as inevitable fluctuations in the properties of the hydraulic oil passing through the circuit.
Together with the complicated control circuit to determine the position of the operating part
And a large number of control devices are not required for configuration
I can't get it.

An object of the present invention is to provide a hydraulic cushion device which is applied to a press for punching holes in a stepped work and which assures excellent forming ability and excellent quality.

[0014]

According to the present invention, a hydraulic die cushion device for a press for punching a stepped work according to the present invention has an upper end whose diameter is increased to an upper surface 21 of a bolster 2 having a through hole 22 attached to a bed 10. Step 12 and the lower end are connected to the through hole 2
2 and the step 12 and the deep hole 13
a free piston 6 fitted with a mold 1 having a through hole 13 communicating with the free piston 6 fitted up and down only within the upper large-diameter portion 43 within a sealed cylinder 4 fixed to the bed 10. The piston 32 which is vertically moved up and down so as to be detachable from the free piston 6 and is fitted in the lower small-diameter portion 44 in the cylinder 4.
And an upper rod 31 integrally connected to the upper part of the piston 32 and protruding from the cylinder 4 to fit into the deep hole 13a and the through hole 22; and integrally connected to a lower part of the piston 32 and protruding from the cylinder 4. The cylinder 4 is equipped with the piston rod 3 composed of the lower rod 33, and the hydraulic cushion circuit 7 having a control function for the upper and lower ends of the sealing portion of the cylinder 4 and the boundary surface between the large diameter portion and the small diameter portion.
The above problem has been solved by connecting the oil supply / discharge port communicating with the forging and restricting the punch operation start position of the forged product to exactly the same position.

More specifically, the configuration is such that the cylindrical receiving table 8 is mounted on the upper end surface 35 of the piston rod so as to be able to move up and down in the deep hole 13a , and that the piston rod 3 penetrates. The cylinder 4 includes a cap 41 through which the upper rod 31 penetrates, a large-diameter portion 43 above a step 42 provided on the inner surface, a lower small-diameter portion 44 into which the piston 32 integrally connected to the upper rod 31 is fitted , and a piston 32
The lower rod 33 is formed integrally with the upper rod 31 and the large diameter portion 4 of the cylinder.
The free piston 6 which is slidably moved up and down on each surface of the both is fitted into the space 3 and the cap 41 of the cylinder is inserted.
Oil supply chambers A, B, and C are most preferably formed by forming oil supply / discharge ports 46, 47, and 48 connected to the external hydraulic cushion circuit 7 at the step 42 and the bottom 45, respectively.

In addition, oil is supplied from the oil supply / discharge port 46.
With the piston 32 by the oil pressure of the oil chamber A to be formed
When the stepped surface 63 provided on the bottom surface of the free piston 6 to be depressed collides with the step 42 forming the end of the large-diameter portion of the cylinder and stops, the mutual punching out of the stepped material W starts. the positional relationship is established, further feed
The oil pressure in the oil chamber B formed by supplying oil from the oil discharge port 47 is
As a result, the piston 32 is pushed down and its bottom surface 34 is
The piston 32 which is in contact with the upper surface of the
When the position is reached, the upper end surface 35 of the upper rod 31 is replaced.
From the upper surface 21 of the bolster 2 which is the side slip surface of
Position slightly lower than the oil supply port 48
The piston 32 is blocked by the oil pressure of the oil chamber C
Free piston 6 pushed up with Lee piston 6
Upper surface 61 hits the lower surface of cap 41 and stops
When the uppermost position is reached, knock of the molded product from mold 1
It is a preferred embodiment that the outs project strictly at a fixed length .

[0017]

FIG. 3A, FIG. 3B, FIG. 3C, and FIG. 3D are schematic front sectional views showing the operation of the present invention. In each figure, the piston rod 3 is fitted inside the cylinder 4 vertically and the piston 32 is fitted into the large-diameter portion 44 of the cylinder, and the upper and lower rods 31,
A free piston 8 is interposed in the large diameter portion 43 so as to be able to move up and down around the upper rod. In this operation view, the receiving stand 8 is mounted on the piston rod 3 which is the best embodiment. Oil supply / drain ports are opened below the cap 41 of the cylinder chamber, near the step 42, and above the bottom 45, respectively, and are connected to an external hydraulic cushion circuit. An oil chamber formed between the cap 41 of the cylinder and the free piston 6, an oil chamber B formed between the free piston 6 and the piston 32, and an oil chamber C formed between the piston 32 and the cylinder bottom 45 are supplied to each supply. Each volume is increased or decreased according to the press-fitting or discharging of the hydraulic oil from the drain port.

FIG. 2A shows the knockout upper limit state in which the position of the piston rod 3 has reached the maximum. The upper end surface 35 of the upper rod 31 extends through the bolster 2 into the mold 1, and the cradle 8 is moved. The product after molding through the upper surface 14 of the mold
This is the moment when it is pushed upward and released from the mold.
At this time, the operating oil flows out of the oil chambers A and B, and the oil chamber C is filled with the operating oil and presses the piston 32 to push the free piston 6 up to reach the cap.

In FIG. 2B, the hydraulic oil flows into the oil chamber A and pushes the free piston 6 downward, so that the piston 32 is entrained with the movement of the free piston 6, so that the entire piston rod 3 moves downward. , Free piston 6
Is also pushed by the hydraulic pressure and descends in the cylinder 4,
Stepped surface 63 provided on the bottom surface of the piston 6 strikes-out Opposition stepped surface 42 of the cylinder. At this position, the step of the stepped material W is fitted into the step 12 provided on the upper part of the mold 1, and the operation of the press starts.

In FIG. 2C, the press operation starts on the stepped material W set at the position shown in FIG. 1B, and the punch tool descends on the material in the mold, and a molding pressure is applied to the hole. At the same time, it shows the final stage of operation, in which the punch waste P punched by the punch 9 falls in the through hole 37 of the piston rod and is collected. Drilling and forming are parallel
During the operation of the press, a cushioning effect appears in this device,
Hydraulic oil is gradually discharged from the oil chamber C while applying an upward supporting force to the material by the pressure balance maintained between the oil chambers C by the adjusted cushion force, and the piston rod gradually descends as a whole, The cushioning effect that occurs during this time moves together with the stroke of the press, thereby alleviating the stress and enhancing the effective forming process.

The feature of this molding process is that the shaft portion of the material that has protruded due to the punching of the punch is pushed forward in the through hole 13 of the mold, and extends downward while being deformed. Is formed into a stepped work w. Since the cushion force underpinning the cushion force is against the pressing force from above while receding gradually poppy misdirection of one's strength <br/> the molding pressure through the cradle from below is applied, the stepped material Punch
Hole and forming progress, material of perforated part is incorporated into forming volume
The amount of punch waste is reduced to improve the material yield,
In addition, the concentrated load applied to the vicinity of the root of the stepped bottom surface of the stepped material is far buffered, and the action of sufficiently preventing the occurrence of cracks or breakage from this portion works.

FIG. 4D shows that when pressurized oil is fed into the oil chamber B for mold replacement, the piston rod is lowered to the lowest position. The upper end surface 35 of the upper rod is the upper surface 2 of the bolster 2.
The beam always sinks slightly downward, and is positioned at a level that does not hinder the replacement of the mold mounted on the bolster. At this point, the state of each oil chamber is such that the lower end surface 34 of the piston 32 of the piston rod collides with the bottom 45 of the cylinder.
Located in the lower limit lowered to that, regarding the upper surface 61 of the free piston 6 into the oil chamber B is filled hydraulic oil is a cap 41
It rises until it hits and is located at the upper limit. As shown in the figure, the flow of the hydraulic oil is discharged from the oil chamber A, flows into the oil chamber B, and is discharged from the oil chamber C.

[0023]

FIG. 1 is a vertical sectional front view of a cylinder portion according to an embodiment of the present invention, and FIG. 2 is a partially cut perspective view of the same embodiment as a whole. For convenience, the illustration of the mold and the cradle are partially omitted. Is a description of examples based on these figures, when the upper surface 21 of the bolster 2 attached to the bed 10, the position of the upper end face 35 of the piston rod 3 projecting the best in FIG. 1 (H _2), the upper end surface Is a state in which it reaches the inside of the mold 1 and exerts a knockout action. The hydraulic oil flows out of the oil chamber A through the oil supply / discharge port 46, and the upper surface 61 of the free piston 6 is in contact with the lower surface of the cap 41. The lower surface 62 of the free piston 6 and the upper surface 36 of the piston 32 come into contact with each other, and the bottom surface 34 of the piston is pressed upward by the hydraulic oil press-fitted into the oil chamber C from the oil supply / discharge port 48, so that the entire position of the piston rod reaches the upper limit. ing.

When hydraulic oil is pressed into the oil chamber A from the oil supply / discharge port 46 and is discharged from the oil supply / discharge ports 47, 48, the pressure balance changes and the free piston 6 descends.
The piston rod is moved downward together with the piston 32 pushed by the bottom surface 62, upper surface 35 of the piston rod protruding length from the bolster reaches the upper limit position of the die cushion becomes H _1. From this position, the cushion pressure set in advance by the pressure adjusting valve 73 acts , and a cushioning effect appears that cooperates with the depressing pressure of the upper press.

Further, the stroke by the press proceeds
After drilling and forming are completed, the hydraulic circuit shown in FIG.
At the time of construction, the port of the solenoid valve 72 is in the neutral position.
Switch to the left port to allow hydraulic oil to flow into oil chamber C
Therefore, the state shown in FIG.
But the upper limit position is set by the free piston 6.
The solenoid valve 71 is always closed, and then the solenoid valve 71 is closed.
72 switches to the left port to allow hydraulic oil to flow into oil chamber B
As a result, the molding operation starts as shown in FIG.
Points. And the position after completion of the above-mentioned perforation and forming
Switch the solenoid valve 72 to the right port from
When flowing, the position of the piston rod becomes level H ₀ of submerged always slightly than bolster upper surface 21 reaches the lower limit, but here than is the die replacement is performed if necessary, the upper end surface of the piston rod bolster surface There is no danger that it will hinder replacement because it is slightly sinking. The movement distance H (= H ₂ + H ₀ ) of the upper end surface of the piston rod is the stroke of the piston rod, and the distance L until the free piston 6 is locked to the step 42 in the cylinder corresponds to the stroke of the free piston 6. .

In FIG. 2 , the hydraulic cushion circuit 7 includes a set of hydraulic pressure generating sources, two solenoid valves 71 and 72, and one pressure regulating valve 73. If an electromagnetic proportional pressure control valve is applied to the pressure regulating valve 73, an arbitrary hydraulic pressure can be set electrically, so that products of various shapes, that is, various molding processes having different molding ratios are performed by one set of apparatus. There are many advantages in adjusting the cushioning action optimally by adjusting it appropriately.

[0027]

According to the hydraulic die cushion device for a press machine according to the present invention, the basic three positions of the knockout point, the starting point of the cushion action, and the mold changing operation point can be determined by a combination of relatively simple members. By specifying the optimum cushioning effect, it works together with the pressing force of the press applied from above to enable molding processing at a higher ratio than before. Appropriate cushioning is particularly difficult in the past, and forged deep stepped holes, which had to rely on mechanical drilling, improved quality, prevented defective products, and improved efficiency The effects brought to those skilled in the art, such as improvement in material yield, are remarkable regardless of whether they are tangible or intangible.

[Brief description of the drawings]

FIG. 1 is a vertical sectional front view of a cylinder portion according to an embodiment of the present invention.

FIG. 2 is a partially cutaway perspective view of the same embodiment as a whole;

FIGS. 3A, 3B, 3C and 3D are schematic vertical front views showing the operation of the present invention.

FIG. 4 is a flowchart illustrating an example of the related art.

FIG. 5 (A) and (B) show another main part of the prior art vertically.
Shown in cutaway front view.

FIG. 6 The objects of the present invention are described as follows.
Each is shown by a cutaway front view.

FIG. 7 Product defects appearing as a result of the task in FIG.
Each is shown by a cutaway front view.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Mold 2 Bolster 3 Piston rod 4 Cylinder 6 Free piston 7 Hydraulic cushion circuit 8 Cradle 9 Punch 10 Bed 11 Bottom surface (Mold) 12 Step (Mold) 13 Through hole (Mould) 13a Deep hole (Mould) 14 Upper surface (die) 21 Upper surface (bolster) 22 Through hole (bolster) 31 Upper rod 32 Piston 33 Lower rod 34 Piston bottom surface 35 Upper end surface 36 Piston upper surface 37 Through hole (piston rod) 41 Cap 42 Step 43 Large diameter portion 44 Small diameter part 45 Bottom part 46 Oil supply / drain port 47 Oil supply / drain port 48 Oil supply / drain port 61 Upper surface (free piston) 62 Lower surface (free piston) 63 Step surface (free piston) 71 Solenoid valve 72 Solenoid valve 73 Pressure regulating valve P Punch Waste W Stepped material w Stepped slender cylindrical forged product (stepped work)

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ identification code FI B30B 15/32 B30B 15/32 (58) Field surveyed (Int.Cl. ⁶ , DB name) B21J 13/14, 9/04 B21D 24/02 B21K 21/08 B30B 15 / 02,15 / 32

Claims (5)

(57) [Claims] 1. A step 12 having an enlarged upper end and a deep hole 13a having a lower end opened to the through hole 22 and a deep hole 13a formed on the upper surface 21 of the bolster 2 having a through hole 22 attached to the bed 10. The free piston 6 fitted with the mold 1 having the through hole 13 communicating with the hole 13a and fitted so as to be able to move up and down only within the range of the upper large diameter portion 43 in the sealed cylinder 4 fixed to the bed 10 A piston 32 which is removably moved up and down with respect to the free piston 6 and is fitted into a lower small-diameter portion 44 in the cylinder 4; 13a,
The piston rod 3 composed of an upper rod 31 fitted in the through hole 22 and a lower rod 33 integrally connected to the lower part of the piston 32 and protruding from the cylinder 4
Equipped to be connected the upper end of the sealing portion of the cylinder 4, a lower end and a large diameter portion and a small diameter portion supplying and discharging oil port communicating with the hydraulic cushion circuit 7 with each control function to the boundary surface of the punch actuation forgings A hydraulic die cushion device for a hydraulic press for punching holes in a stepped elongated cylindrical forging, characterized in that the starting position is strictly limited to the same position. 2. The cylinder 4 through which the piston rod 3 penetrates, the cap 41 through which the upper rod 31 penetrates, and the large diameter portion 4 above the step 42 provided on the inner surface.
3. The upper rod 31 formed by a lower small diameter portion 44 into which the piston 32 integrally connected to the upper rod 31 is fitted , and a bottom portion 45 through which the lower rod 33 integrally formed with the piston 32 penetrates. The free piston 6 which slidably moves up and down on each surface of the cylinder and the large-diameter portion 43 of the cylinder is inserted into the space, and the cap 41 of the cylinder and the step 4
2. Stepped slender circles characterized by forming oil chambers A, B, and C by forming oil supply / discharge ports 46, 47, 48 connected to the external hydraulic cushion circuit 7 at the bottom 45, respectively.
Hydraulic die cushion device for hydraulic press for punching holes in cylindrical forgings. 3. The oil supply / drain port 4 according to claim 1, wherein
The bottom of the free piston 6 which is pushed down with the piston 32 by the oil pressure of the oil chamber A formed by being supplied with oil from the bottom 6 .
The step surface 63 provided on the surface forms the large diameter end of the cylinder.
That when you stop hitting the step 42 and the luck, it stepped material W
A hydraulic die cushion device for a hydraulic press for punching a stepped elongated cylindrical forged product, characterized in that a mutual positional relationship in which a punching action is started with respect to the forging is established. 4. In any one of claims 1 to 3, supply and discharge
The oil pressure in oil chamber B formed by oil supply from oil port 47
The piston 32 is pushed down and its bottom surface 34 reaches the lowermost position where it contacts the top surface of the cylinder bottom 45.
Can, lateral slipping of the mold upper end surface 35 of the upper rod 31 to exchange
A hydraulic die cushion device for a hydraulic press for punching holes in a stepped elongated cylindrical forging, wherein the hydraulic press is always located at a position slightly lower than the upper surface 21 of the bolster 2 which is a sloped surface. 5. In any one of claims 1 to 4, the supply and discharge
The oil pressure in the oil chamber C formed by oil supply from the oil port 48
The piston 32 is pushed up together with the free piston 6
Upper surface 61 of the free piston 6 and the lower surface of the cap 41 Te
When reaching the uppermost position to stop by hitting, the mold 1
Moldings knockouts stepped elongated cylindrical forgings piercing hydraulic press hydraulic die cushion apparatus for according to claim <br/> Rukoto to protrude by exactly a predetermined length from.