JP3255174B2 - Method of preventing plunger bottoming of die cushion pin pressure equalizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing the bottom of a plunger of a hydraulic cylinder of a die cushion pin equalizing device used for drawing.

[0002]

2. Description of the Related Art In a press apparatus, a die cushion is provided below a lower die in order to prevent wrinkles from occurring during drawing press working.

That is, FIG. 8 shows a press machine provided with a die cushion, 1 is a crown, 2 is an upright, 3 is a bed, 4 is a slide, 5 is an upper mold, 6 is a lower mold,
7 is a bolster, 8 is a moving bolster, 9 is a die cushion pin, 10 is a pressure equalizer plate, 11 is a hydraulic cylinder for equalizing, 12 is a die cushion pad, 13 is a die cushion leg, 14 is a die cushion air cylinder, Reference numeral 15 denotes a die cushion rod, and reference numeral 16 denotes a damper filled with oil.

[0004] That is, in FIG.
A bolster 7 is installed on the upper side via a moving bolster 8.
2 are accommodated. The die cushion pad 12 is supported by a die cushion cylinder 14 provided on a die cushion leg 13. A compressed air source is connected to the die cushion cylinder 14 via an air pressure adjusting unit (not shown).

[0005] A lower die 6 is mounted on the bolster 7, and a plurality of die cushion pins 9 inserted in a plurality of pin holes are provided in the bolster 7. The plurality of die cushion pins 9 support a die pad (not shown) in the lower die 6.

A plurality of pressure equalizing hydraulic cylinders 11 are provided on the pressure equalizing device plate 10 in correspondence with the positions of the plurality of cushion pins 9, and these pressure equalizing cylinders 11 are arranged as shown in FIG. As shown in FIG.
Abuts against the lower end of the cushion pin 9 and the flange portion 17 of the plunger 18 is accommodated in the cylinder oil chamber. That is, the flange portion 17 of the plunger 18 functions as a stopper above the cylinder 11.

Each cylinder oil chamber of the equalizing hydraulic cylinder 11 is connected to a hydraulic source (not shown) via an oil passage 19. At this time, the oil adjusted to a pressure enough to absorb the length error of each cushion pin is supplied to the oil passage 19.
And is enclosed in each cylinder oil chamber.

[0008] Therefore, when performing the draw forming, if the press machine is driven after selecting the die cushion pin corresponding to the die, the slide 4 and the upper die 5 are moved down to use the die. When a pressure is applied to the cushion pin 9, the hydraulic pressure supplied to each pressure equalizing hydraulic cylinder 11 is prevented from flowing out, so that the pressure is applied to the die cushion pad via the cushion pin 9 and the hydraulic cylinder 11. The power is transmitted to the die cushion cylinder 14 and is absorbed by the die cushion cylinder 14. At the same time, the unevenness of the pressing force due to the length error of each die cushion pin 9 and the error at the time of mounting is absorbed by the cushion pressure of the equalizing hydraulic cylinder 11.

By the way, in the die cushion pin pressure equalizing device composed of the plurality of pressure equalizing hydraulic cylinders 11 and the like, when the displacement of the die cushion pin is larger than the maximum displacement, the pressure of the die cushion pin pressure equalizer is increased. The plunger of the pressure equalizing hydraulic cylinder 11 is bottomed on the bottom of the cylinder oil chamber as shown on the right side of FIG. 9, causing a problem that the pressure equalizing function of the pressure equalizing device itself is lost. .

When such bottoming occurs, conventionally, the following measures have been usually taken.

(1) Use more die cushion pins.

(2) The air pressure of the die cushion cylinder 14 (die cushion air pressure) is reduced to the limit at which molding is possible.

(3) Decrease the number of continuous strokes (the number of slide strokes per minute, spm).

[0014]

However, the method (1) has difficulty in implementation in consideration of the correspondence with the mold.

In addition, the method (2) cannot be carried out because molding defects easily occur.

Further, the above method (3) has a problem that the production amount per hour is reduced, so that the producer cannot easily accept the method.

Here, in the conventional die cushion pin pressure equalizing apparatus, the operating conditions (pressure equalizing hydraulic cylinder 11) are used.
Without accurately considering the diameter of the plunger 18, the number of pins used, the speed at the time of pin touching-the speed at which the mold touches the die cushion pin, the total oil amount of the pressure equalizing device, and the die cushion air pressure). Therefore, there has been a problem that an excessive peak pressure is generated in the pressure equalizing device and a fatigue crack fracture occurs in the flange portion 17 of the plunger of the unused pressure equalizing hydraulic cylinder 11. It is considered that the cause is that the peak hydraulic pressure generated when the mold touches the die cushion pin is excessive.

Considering such circumstances, the above (1)-
It is preferable that the condition (3) is not changed and the peak oil pressure does not change.

The present invention has been made in view of such circumstances, and does not cause excessive peak oil pressure in the die cushion pressure equalizing apparatus, and does not reduce the productivity and machining accuracy. It is an object of the present invention to provide a method of preventing a bottom of a plunger of a die cushion pin pressure equalizing device from being suitably prevented.

[0020]

According to the present invention,
A plurality of die cushion pins are provided in a bolster of a press machine so as to be vertically movable, and a pressure equalizing hydraulic cylinder supported by a die cushion is provided below each of the plurality of die cushion pins. In a die cushion pin pressure equalizing device in which cylinders are connected to each other to apply a hydraulic pressure, a relational expression between a hydraulic pressure of the pressure equalizing device and a total absorption stroke is obtained by using a preload hydraulic pressure as a parameter. From the formula, a preload hydraulic pressure is determined such that the total absorption stroke corresponding to the stable hydraulic pressure according to the capacity of the die cushion does not cause bottoming of the plunger, and a preload hydraulic pressure higher than the preload hydraulic pressure is set in the press machine.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the accompanying drawings.

FIG. 2 shows a hydraulic pressure waveform of the die cushion pin pressure equalizing device shown in FIGS.
Is the preload hydraulic pressure, Pmax is the peak hydraulic pressure at the time of pin touch (when the die touches the die cushion pin), PD
Is a stable hydraulic pressure according to the capacity of the die cushion, and the present inventors raise the preload hydraulic pressure P0 of the hydraulic pressure waveform as compared with the related art, so that even under the condition that there is a die cushion pin displacement greater than the maximum displacement, It has been found through experiments that the plunger of the pressure equalizing hydraulic cylinder 11 of the die cushion pin pressure equalizing device can be prevented from bottoming out. In such an experiment, an experimental facility as shown in FIG. 3 was configured. That is, in FIG. 3, the diameter is 60 mm and the length is 675.
Approximately 30 to 40 mm die cushion pins 9 are arranged, and the slide 4 on which the mold 5 is mounted is driven by microinching to pressurize the die cushion. The relative stroke with respect to the cushion pin is measured by the dial gauge 20, and the oil pressure in the oil passage 19 of the die cushion pin pressure equalizer at this time is measured by the oil pressure gauge 21. In addition,
11 is a pressure equalizing hydraulic cylinder, 22 is a pressure head,
23 is a check valve, and 24 is a recorder.

Then, the total absorption stroke δ is calculated according to the following equation (1).

Total absorption stroke δ = (reading of dial gauge) × (number of pressurized pins) (1) FIG. 4 shows the die cushion capacity, the number of pins, and the die cushion pin average when the preload hydraulic pressure P0 is 25 kg / cm 2. FIG. 5 shows the values of the hydraulic pressure and the absorption stroke of the pressurizing device. FIG. 5 shows the values when the preload hydraulic pressure P0 is 75 kg / cm2. FIG. 6 shows the preload hydraulic pressure P0 of 25 kg / cm2. 6 is a plot of the relationship between the die cushion pin total absorption stroke δ and the oil pressure P of the die cushion pin pressure equalizer at 75 kg / cm 2 and 75 kg / cm 2.

When these measurement points are approximated by straight lines, when the preload hydraulic pressure P0 is 25 kg / cm2, P =
1.14δ + 25 is obtained and the preload hydraulic pressure P0
Was 75 kg / cm 2, the relationship P = 1.14δ + 75 was obtained.

That is, FIG. 6 shows the relationship between the total absorption stroke and the pressure equalizing device oil pressure when the preload oil pressure P0 is P01 and P02 as shown in FIG. In FIG. 1, PD indicates the stable oil pressure value in FIG. As can be seen from FIG.
When the pressure is increased from 01 to P02, the total absorption stroke at the stable pressure PD is reduced from L2 to L1 by (L2-L1), thereby preventing the plunger of the pressure equalizing hydraulic cylinder 11 from bottoming out. It will be appreciated that it is possible. That is, in this method, the preload hydraulic pressure is increased by an appropriate amount as compared with the conventional method, so that the stable pressure PD is increased.
In this case, the total absorption stroke of the pressure equalizing device is shortened, thereby preventing the bottoming.

Here, FIG. 7 shows the relationship between the preload hydraulic pressure P0 and the primary peak pressure Pmax when the total oil amount of the pressure equalizing device is 6.1 l and the pin touch speed is 0.757 m / sec. The measured values show a case where the number of pins used is 20 and the air pressure is 2.0 kg / cm2, and a case where the number of pins used is 40 and the air pressure is 6.2 kg / cm2. As can be seen from FIG. 7, the primary peak pressure Pmax is almost plotted parallel to the horizontal axis, and the primary peak pressure is not affected by the preload pressure.

Therefore, even if the preload pressure is increased by the above-described method, the primary peak pressure of concern does not increase, so that the increase in the preload pressure causes the above-mentioned unused equalizing hydraulic cylinder 11 to be used. No fatigue crack failure occurs at the stopper of the plunger.

[0029]

As described above, according to the present invention,
A very simple method, such as increasing the preload oil pressure of the supply oil pressure of the die cushion pin pressure equalizer, without causing excessive peak oil pressure in the die cushion pressure equalizer and reducing productivity and machining accuracy Therefore, the plunger of the pressure equalizing hydraulic cylinder of the pressure equalizing device can be properly prevented from bottoming out.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the total absorption stroke and the oil pressure of a pressure equalizing device using two preload pressures as parameters.

FIG. 2 is a graph showing a hydraulic pressure waveform of the pressure equalizing device.

FIG. 3 is a view showing experimental equipment.

FIG. 4 is a view showing experimental results.

FIG. 5 is a view showing another experimental result.

FIG. 6 is a graph of an experimental result showing a relationship between a total absorption stroke and a hydraulic pressure of a pressure equalizing device using two preload pressures as parameters.

FIG. 7 is a graph showing a relationship between a primary peak pressure and a preload pressure.

FIG. 8 is a view showing a press machine provided with a die cushion and a die cushion pin pressure equalizing device.

FIG. 9 is a diagram showing bottoming of a pressure equalizing cylinder and the like.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Crown 2 ... Upright 3 ... Bed 4 ... Slide 5 ... Upper die 6 ... Lower die 7 ... Bolster 8 ... Moving bolster 9 ... Die cushion pin 10 ... Pressure equalizer plate 11 ... Pressure equalizing hydraulic cylinder 12 ... Die cushion Pad 13 ... Die cushion leg 14 ... Die cushion air cylinder 15 ... Die cushion rod 16 ... Damper 17 ... Flange part of plunger 18 ... Plunger 19 ... Oil passage 20 ... Dial gauge 21 ... Hydraulic gauge

Continuation of the front page (56) References JP 3-9297 (JP, U) JP 634753 (JP, Y2) JP 527215 (JP, Y2) (58) Fields surveyed (Int) .Cl. ⁷ , DB name) B21D 24/02

Claims (1)

(57) [Claims] A plurality of die cushion pins are provided in a bolster of a press machine so as to be vertically movable, and a pressure equalizing hydraulic cylinder supported by a die cushion is provided below each of the plurality of die cushion pins. In a die cushion pin pressure equalizing device that connects hydraulic pressure equalizing hydraulic cylinders to each other to apply hydraulic pressure, the relational expression between the hydraulic pressure of the pressure equalizing device and the total absorption stroke is obtained using the preload hydraulic pressure as a parameter. From this relational formula, a preload hydraulic pressure that gives a total absorption stroke corresponding to the stable hydraulic pressure according to the die cushion capacity that does not cause bottoming of the plunger is calculated from this relational expression, and a preload hydraulic pressure higher than the preload hydraulic pressure is set to the press machine. A method of preventing a plunger from being attached to a bottom of a die cushion pin pressure equalizing device.