JPH10244400A - Device for preventing pressure of hydraulic die cushion from raising - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the impact from generating between a die cushion pin and a die cushion pad at the point of time that upper and lower dies attached on a press machine are begun to draw. SOLUTION: A pressure regulating device is installed on a hydraulic die cushion cylinder 2. This pressure regulating device is composed of a pressure regulating piston 3 and a pressure regulating cylinder 4, etc. At the point of time to begin drawing, when a die cushion pad 1a is rapidly energized downward with a die cushion pin 12, the hydraulic pressure inside the hydraulic die cushion cylinder 2 is made instantaneously to raise because a die cushion compression regulating relief valve 8 can be instantaneously responded. Synchronizing to raising of this hydraulic pressure, the pressure regulating piston 3 is lowered resisting the spring force of a spring 5. So, the pressure inside the die cushion cylinder 2 is not raised largely.

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 device used for a press machine. That is, the present invention relates to a device for preventing a sudden rise in pressure of a hydraulic die cushion device.

[0002]

2. Description of the Related Art Conventionally, the hydraulic pressure of a hydraulic die cushion has been controlled or adjusted by a servo valve, a relief valve or the like.

Usually, when drawing by a press machine,
At the point when the slide of the press machine is lowered and the drawing process is started, the die cushion pad is rapidly urged through the die cushion pin and pushed down.

[0004] Under these circumstances, it is not easy to quickly release the pressure oil of the hydraulic die cushion. That is, the so-called responsiveness is hindered by the resistance of various valve parts, the resistance of piping provided to the valves, and the like.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to prevent the hydraulic pressure in a hydraulic die cushion cylinder from increasing significantly at the beginning of press working. In other words, the object of the present invention is to provide a die cushion pin 12 at the time when the upper and lower dies mounted on the press machine start drawing.
The purpose of the present invention is to prevent an impact generated between the die cushion pad 1a and the die cushion pad 1a.

[0006]

A pressure adjusting device is provided in a hydraulic die cushion cylinder. The pressure adjusting device includes a pressure adjusting piston 3, a pressure adjusting cylinder 4, and the like.

[0007] The pressure adjusting piston 3 is incorporated over the hydraulic die cushion cylinder 2 and the pressure adjusting cylinder 4, and is formed by a spring force generating means such as a spring 5 incorporated in the pressure adjusting cylinder 4. It is urged to compress the hydraulic pressure in the cushion cylinder 2.

[0008]

1, a hydraulic die cushion cylinder 2 is fixed to a bed (not shown) of a press machine. A hydraulic die cushion piston 1 is incorporated in the hydraulic die cushion cylinder 2 so as to be vertically movable. A die cushion pad 1a is fixed to the hydraulic die cushion piston 1.

The hydraulic die cushion cylinder 2 is provided with a pressure adjusting device, and the pressure adjusting device comprises a pressure adjusting piston 3, a pressure adjusting cylinder 4, and the like. The pressure adjusting cylinder 4 is fixed to the hydraulic die cushion cylinder 2, and the pressure adjusting piston 3 is incorporated over the hydraulic die cushion cylinder 2 and the pressure adjusting cylinder 4.

The pressure adjusting piston 3 is urged by a spring 5 incorporated in the pressure adjusting cylinder 4 in a direction to compress the oil pressure in the hydraulic die cushion cylinder 2. The step of the pressure adjusting piston 3 hits the bottom of the hydraulic die cushion cylinder 2 and the pressure adjusting piston 3 stops at the upper limit. The step of the pressure adjusting piston 3 constitutes stopper means for the pressure adjusting piston 3.

A screw 6 is screwed into the pressure adjusting cylinder 4 so that the spring force can be adjusted by changing the length of the spring 5. That is, the screw 6 constitutes a spring force adjusting means.
A gas-filled cylinder device 7 may be used instead of the spring 5 (see FIG. 3). The spring 5 or the gas-filled cylinder device constitutes a spring force generating means.

The hydraulic die cushion cylinder 2 is connected to a hydraulic circuit for supplying oil from an oil tank 11 by a hydraulic pump 9. This hydraulic circuit incorporates an initial die cushion pressure adjusting relief valve 10 or a check valve.

A relief valve 8 for adjusting the pressure of the die cushion is connected to the hydraulic die cushion cylinder 2 in order to release a pressure oil equal to or larger than a set value.

The operation will be described below. If the die cushion pad 1a is suddenly urged downward by the die cushion pin 12 at the time of starting the drawing process, the relief valve 8 for adjusting the compression of the die cushion cannot respond instantaneously, so that the pressure inside the hydraulic die cushion cylinder 2 is reduced. The oil pressure tries to rise momentarily. In synchronization with the increase in the hydraulic pressure, the pressure adjusting piston 3 descends against the spring force of the spring 5. Therefore, the pressure in the hydraulic die cushion cylinder 2 does not increase significantly.

In FIG. 2, the parts shown by dotted lines are:
Conventional peak pressure. According to the invention, this peak pressure is very low.

[0016]

As is clear from the above description, according to the present invention, since the peak pressure does not increase, the impact of the press machine and the hydraulic die cushion is small, effective in preventing vibration and noise, and stable. Press processing can be expected.

[Brief description of the drawings]

FIG. 1 is an overall view of a hydraulic die cushion device.

FIG. 2 is an explanatory diagram of a die cushion pressure.

FIG. 3 is an explanatory view of a pressure adjusting device when a gas-filled cylinder device 7 is used.

[Explanation of symbols]

1 is a hydraulic die cushion piston, 1a is a die cushion pad, 2 is a hydraulic die cushion cylinder, 3 is a pressure adjusting piston, 4 is a pressure adjusting cylinder, 5 is a spring, 6 is a screw, 7 is a gas filled cylinder device, 8 Is a relief valve for adjusting die cushion pressure, 9 is a hydraulic pump, 10 is a relief valve for adjusting initial die cushion pressure, 11 is an oil tank, and 12 is a die cushion pin.

Claims (2)

[Claims] A pressure adjusting cylinder (4) is fixed to a hydraulic die cushion cylinder (2), and a pressure adjusting piston (3) extends over the hydraulic die cushion cylinder (2) and the pressure adjusting cylinder (4). The pressure adjusting piston (3) is urged by a spring force generating means in a direction to increase the hydraulic pressure in the hydraulic die cushion cylinder (2), and the hydraulic die cushion cylinder (3) of the pressure adjusting piston (3) is increased. A pressure rise prevention device for a hydraulic die cushion, comprising a stopper means for preventing movement toward 2). 2. A pressure rise preventing device for a hydraulic die cushion according to claim 1, further comprising spring force adjusting means for adjusting a spring force generated by said spring force generating means.