KR20030085759A - Mold clamping unit - Google Patents

Abstract

PURPOSE: A device for clamping a mold is provided to simplify the structure of the device by reducing the number of parts, and to improve productivity by improving the structure of a piston. CONSTITUTION: A device for clamping a mold is composed of a body(100), a clamp member(200) rotatably installed at the body and clamping the mold, an oil cylinder(300) installed at one end of the clamp member and having small and large oil chambers(320,330), a piston(310) inserted into the inside of the oil cylinder and having an inclined surface, a rod(311) contacted with the inclined surface and the bottom of the clamp member, and a restoring unit. The rod rotates the clamp member when oil is supplied to the oil chambers so the clamp member clamps the mold. The restoring unit releases the locking of the mold when the oil in the large chamber is discharged.

Description

Mold clamping device {MOLD CLAMPING UNIT}

The present invention relates to a mold clamping device, and more particularly to a mold clamping device that can simplify the structure by reducing the number of parts, and can easily machine the piston.

In general, the mold should be fixed to the template of a press, extruder or injection machine (hereinafter referred to as "molding apparatus") so that the mold does not move when forming the material.

One traditional method of securing a mold is for a worker to tighten a plurality of mold fixing bolts and nuts to fix the mold to the mold of the injection machine.

When the mold is fixed to the mold of the molding apparatus by tightening a plurality of mold fixing bolts and nuts, the mold is firmly fixed to the mold of the molding apparatus.

In this case, in order to replace the mold, loosen the bolt and nut fixing the mold to the mold of the molding apparatus, remove the mold fixed to the mold of the molding apparatus, and then attach the bolt and nut to the mold of the molding apparatus. It should be tightened and fixed.

In other words, when fixing the mold by fastening the bolt and nut in this way, the mold and replacement work is cumbersome and takes a long time because the bolt and nut must be fastened and released every time the mold is replaced. Therefore, the production time of the molding apparatus is reduced and the production yield cannot be improved, and this problem is particularly acute in the case of producing small quantities of various kinds.

In order to solve such a problem, a mold fixing device capable of fast and accurately fixing a mold to a template of a molding apparatus has been proposed.

For example, a mold fixing gripping apparatus has been proposed as a domestic patent application No. 1997-2451.

As shown in Fig. 1, the pre-pending mold holding and holding device includes a main body having a T-shaped engaging portion la which is slidably inserted into and fixed to a T-shaped engaging groove 3a formed in the template 3 of the molding apparatus. 1) and the clamp means 7 which is rotatably installed around the shaft 5 in the main body 1 to fix the mold M, and is installed below the proximal end 7a side of the clamp means 7. As shown in FIG. 2, the hydraulic cylinder 9 is divided into a small oil chamber 17 and a large oil chamber 18 by a piston to be described later.

As shown in FIG. 2, in the hydraulic cylinder 9, small oil chambers 17 and large oil chambers 18 of different sizes are respectively partitioned by pistons 20 in their left and right sides. The piston 20 is slidably inserted into the left or right side based on the drawing along the inner circumferential surface of the hydraulic cylinder 9. When oil is supplied to the small oil chamber 17 and the large oil chamber 18 at the same time, the volume of the small oil chamber 17 on the left side of the right oil chamber 18 is moved so that the piston 20 moves to the left side. It is formed smaller than the volume.

When the mold M is fixed by the mold fixing gripping device in the large oil chamber 18, that is, between the cover 14 and the recess 20a formed in the piston 20, the hydraulic cylinder 9 An elastic means 22 is provided to apply an elastic force so that the piston 20 slidably inserted therein is not pushed to the right when the reference is made to the drawing.

The piston 20 has an industrial shape, a small diameter portion 20q fitted into the small oil chamber 17, a large diameter portion 20r fitted into the large oil chamber 18, and the small diameter portion 20q. Tapered inclined surface 20b formed on the outer circumferential surface of one side of the rod portion between the large diameter portion 20r and the groove portion 20a formed on the large diameter portion 20r to accommodate one side of the elastic means 22. Equipped with.

On the inclined surface 20b of the piston 20, a rod 35 for rotating the clamp means 7 is provided.

The lower surface of the rod 35 is in surface contact with the inclined surface 20b formed on the piston 20, and the upper surface thereof has a through hole formed in the hydraulic cylinder 9 as the piston 20 moves to the left side. It protrudes outward through 9a) and pushes the proximal end 7a of the clamp means 7 upward to contact the lower surface of the proximal end 7a of the clamp means 7 so that the clamp means 7 can rotate.

As shown in FIG. 1, a handle 11 is installed at the rear of the hydraulic cylinder 9 so as to carry a mold holding and holding device, and as shown in FIG. 2, left and right covers are provided at the left and right sides thereof. 13 and 14 are respectively sealed by a plurality of fixing bolts 15, and the hydraulic cylinder 9 is fixed to the flanges 1b and 1c formed integrally with the main body 1 by the fixing bolts 28. It is fixed in one piece.

As shown in FIG. 2, the left and right lids 13 and 14 are formed with straight inlets 13a and 14a to supply oil into the respective oil chambers 17 and 18, respectively. The hydraulic hose coupling joint 27 (shown in FIG. 1) coupled to the oil supply hose (not shown) is coupled to the 13a and 14a. The oil supply hose is piped along the longitudinal direction of the mold holding and holding device, and therefore, the inlet port 13a and 14a and the oil supply hose are approximately at right angles, so that the joint 27 is bent at approximately right angles.

The left and right lids 13 and 14 are provided with packing means 30a to prevent leakage of oil injected into the oil chambers 17 and 18 through the space between the left and right lids 13 and 14 and the hydraulic cylinder 9. 30b is provided, and on the outer circumferential surface of the small diameter portion 20q of the piston 20 and the outer circumferential surface of the large diameter portion 20r, oil is leaked between the oil chambers 17 and 18, or the packing means ( 32a, 32b) are provided.

Although not shown in the figure, the main body 1 is provided with elastic means for restoring the clamp means 7 in the clamping release direction when the clamping of the mold M is released. The elastic means is composed of a coil spring and a steel ball installed on the tip of the coil spring in contact with the lower surface of the clamp means (7).

The operation and effects of the pre-pending mold fixing gripping device configured as described above will be described in detail.

First, the handle 11 and the main body 1 are held, and the T-shaped grooves of the template 3 fixed to the molding apparatus by the T-shaped engaging portions la formed integrally with the main body 1 ( The mold M is inserted between the template 3 and the grip portion 7b of the clamp means 7 by inserting it into 3a).

Subsequently, when oil of the same pressure is supplied to both oil chambers 17 and 18 of the hydraulic cylinder 9 through the hydraulic system, the oil larger than the small oil chamber 17 due to the difference between the oil chambers 17 and 18. The piston 10 slides to the left side based on FIG. 2 because a relatively large amount of oil is supplied to the chamber 18 so that the hydraulic pressure on the large oil chamber 18 side is higher than the hydraulic pressure on the small oil chamber 17 side. do.

As the piston 20 moves to the left side, the rod 35, which is in contact with the inclined surface 20b of the piston 20, is along the through hole 9a formed in the hydraulic cylinder 9. Protrudes outwardly to push the proximal end 7a of the clamp means 7 upward.

Accordingly, since the clamp means 7 rotates in one direction about the shaft 5, the grip portion 7b of the clamp means 7 firmly faces one surface of the mold M toward the template 3. Clamp. In this way, when the mold M is fixed by the mold holding gripping apparatus, since the piston 20 receives the elastic force to the left in FIG. 2 by the elastic means 22 installed in the large oil chamber 18, the mold M Should remain firmly gripped.

On the other hand, when the mold M is to be replaced, the oil in the small oil chamber 17 side is not recovered through the hydraulic system, and the oil in the large oil chamber 18 is recovered.

Since the oil in the small oil chamber 17 is not recovered into the oil tank 40, the piston 20 is forced by the pressure difference because the oil pressure in the small oil chamber 17 is higher than the pressure in the large oil chamber 18 side. Move to the right (based on FIG. 2). In other words, the piston 20 moves to the right because the pressure pushing the piston 20 to the right is greater than the elastic force of the elastic means 22 which elastically supports the piston 20 installed in the oil chamber 18 to the left. To move.

Therefore, as the piston 20 moves to the right in FIG. 2, the clamp means 7 rotates about the axis 5 in the opposite direction as the clamping force is caused by the elastic force of the elastic means installed below. 35 is pushed downward by the base end 7a of the clamp means 7 and pushed into the hydraulic cylinder 9. Therefore, the grip portion 7b of the clamp means 7 is released from the mold M to release the clamp state, so that it can be replaced with another product manufacturing mold to be molded.

As described above, the mold holding and gripping apparatus has an advantage that the mold can be replaced accurately and quickly, as compared with the conventional method using the bolt and nut.

However, the previously described mold fixing gripping apparatus described so far has the following disadvantages.

The elastic means 22 on the large diameter portion 20r side of the piston 20 allows the piston 20 to be supported toward the small oil chamber 17 side without being pushed to the large oil chamber 18 side when the hydraulic line breaks down / discharges. However, when the piston 20 slides due to the connection structure between the piston 20 and the rod 35, the rod 35 may rise / fall, but on the contrary, when the rod 35 descends, the piston 20 slides. Since it does not, a separate configuration for supporting the piston 22 to the small oil chamber 17 side, that is, the elastic means 22 is unnecessary.

Therefore, in order to apply the elastic means 22, there is an inconvenience in that the groove portion 20a for installing the elastic means 22 in the large diameter portion 20r needs to be processed, and the assembly work of the elastic means 22 is required. As a result, the production and assembly of parts increases, and manufacturing costs increase.

And the piston 20 consists of the rod part in which the inclination part 20b was formed, and the small diameter part 20q and the large diameter part 20r which are integrally formed in the both sides of this rod part, respectively, Forming the large small diameter portion 20q and the large diameter portion 20r and forming the inclined portion 20b integrally with the rod portion require a high precision work and thus have a disadvantage in that the productivity is low.

In addition, the inlets 13a and 14a are formed in a straight line on the left and right caps 13 and 14, and the joints 27 are bent at approximately right angles to be connected to the oil supply hose so that the joints 27 are caps 13 Protruding to the side of the) 14 not only aesthetically good, but also has the disadvantage that interference may occur by the joint (27).

An object of the present invention is to solve the above problems, and to provide a mold clamping device capable of reducing parts.

In addition, another object of the present invention is to improve the structure of the piston to make processing easy and convenient.

Still another object of the present invention is to prevent the joint for connecting the oil supply hose from protruding to the side of the hydraulic cylinder.

1 is a perspective view of a mold holding gripping apparatus according to the prior art.

Figure 2 is a longitudinal sectional view of the mold holding gripping apparatus according to the prior art.

Figure 3 is a side cross-sectional view of the mold clamping device according to the present invention.

Figure 4 is a front sectional view of the mold clamping device according to the present invention.

5 is a perspective view of a piston applied to the mold clamping device according to the present invention.

Figure 6 is another illustration of a piston applied to the mold clamping device according to the present invention.

7 is a hydraulic circuit diagram applied to a mold clamping device according to the present invention.

<Description of Symbols for Main Parts of Drawings>

3: template, 3a: coupling groove

100: main body, 110: shaft

120: coupling portion, 200: clamp member

220: pressing part, 300; Hydraulic cylinder

310: piston, 311: rod

312: low pressure side small diameter head, 313: high pressure side large diameter head

320,330: Oil chamber, 340, 350: Blind cap

341, 351: oil passing hole, 400: lifting rod

500: restoring means, 510: coil spring

520: ball

A mold clamping device according to the present invention for achieving the above object, the main body is fixed to the template of the molding apparatus; A clamp member installed on the main body so as to be rotatable through a shaft, and the pressing member of one side pressing and fixing the mold; A hydraulic cylinder installed below the other end side of the clamp member and having a small oil chamber and a large oil chamber therein; A piston which is slidably inserted left and right by a pressure difference in the small oil chamber and the large oil chamber inside the hydraulic cylinder, and has an inclined surface on an outer circumferential surface thereof; When the lower surface is in contact with the inclined surface of the piston and the upper side penetrates the hydraulic cylinder to contact the lower surface of the other end side of the clamp member and oil is supplied into the small oil chamber and the large oil chamber partitioned in the hydraulic cylinder. A rod for rotating the clamp member such that one pressing part of the clamp member presses and fixes the mold; And restoring means for pushing the pressing part of the clamp member upward to release the fixed state of the mold when the oil supplied into the large oil chamber of the hydraulic cylinder is discharged.

The piston may include: a rod portion having an inclined surface on an outer circumferential surface thereof and integrally formed with a low pressure side small diameter head disposed on the small oil chamber at one end thereof; And, it may be formed in the other side of the large oil chamber of the rod portion separated by a high pressure side large diameter head pushing the rod portion by hydraulic pressure.

The piston may include a rod part having an inclined surface on an outer circumferential surface thereof; A low pressure side small diameter head installed on the small oil chamber side; And, it may be separated into a high-pressure side large diameter head installed on the large oil chamber side.

First and second blind caps are installed at both sides of the hydraulic cylinder, respectively, and an oil through hole communicating with the small oil chamber and the large oil chamber is formed inside the first and second blind caps. One opening of the hole may be bent to open toward the circumferential surfaces of the first and second blind caps.

The features and advantages of the present invention will become more apparent from the following detailed description based on the accompanying drawings. Prior to this, the terms or words used in the present specification and claims are defined in the technical spirit of the present invention on the basis of the principle that the inventor can appropriately define the concept of the term in order to explain his invention in the best way. It must be interpreted to mean meanings and concepts.

As shown in FIG. 3, the mold clamping device according to the present invention includes a main body 100 fixed to a template 3 of a molding apparatus and a main body 100 rotatably installed via a shaft 110. The clamp member 200 for fixing the mold M, the hydraulic cylinder 300 is installed in the main body 100, the piston 310 (shown in FIG. 4) by the hydraulic pressure linearly reciprocating sliding, and the hydraulic pressure It is installed on the piston 310 inside the cylinder 300 to move up and down in conjunction with the sliding of the piston 310 to push the end of the clamp member 200 so that the clamp member 200 rotates to fix the mold (M). Lifting rod 400 is made.

As shown in FIGS. 3 and 4, the main body 100 has a coupling part 120 formed at a bottom thereof by sliding into a substantially T-shaped coupling groove 3a formed in the template 3 to be fixed to the template 3. It can be fixed to.

As shown in FIG. 4, oil chambers 320 and 330 are formed inside the hydraulic cylinder 300 with the piston 310 interposed therebetween. The piston 310 is installed in the hydraulic cylinder 300 to be slidably left or right when referring to the drawings.

The oil chambers 320 and 330 are the volume of the oil chamber 320 on the left side so that when the oil is supplied to the oil chambers 320 and 330 on both sides at the same time, the piston 310 moves to the left side based on the drawing. It is formed smaller than the volume of the oil chamber 330 on the right side.

The left and right sides of the hydraulic cylinder 300 are respectively opened, and blind caps 340 and 350 may be fastened to the openings by bolts 340a and 350a, respectively. The first and second blind caps 340 and 350 are formed with recesses in which the heads of the bolts 340a and 350a are seated, so that the heads of the bolts 340a and 350a are respectively smaller than the blind caps 340 and 350. Does not protrude

Oil passing holes 341 and 351 through which oil flows in and out are respectively formed in the first and second blind caps 340 and 350, and O-rings 342 and 352 are installed on the outer circumferential surface to prevent leakage of oil. Can be.

The oil passing holes 341 and 351 may be formed so as to start at the sides of the first and second blind caps 340 and 350, respectively, and change directions at approximately right angles.

The oil passing holes 341 and 351 are connected to the oil supply hose not shown through the joint 360, and one opening of the oil passing holes 341 and 351 is the first and second blind caps 340. It is formed on the circumferential surface of the) 350 so that the joint 360 does not protrude to the sides of the first and second blind caps 340 and 350. Although the joint 360 is shown as being connected only to the first blind cap 340 in the figure, the joint is connected to the second blind cap in the same structure.

The piston 310 is to lift the lifting rod 400 while sliding along the bore of the hydraulic cylinder 300, as shown in Figures 4 and 5, the cylindrical rod 311 is provided with an inclined surface 311a on the outer peripheral surface ) And the low pressure side small diameter head 312 integrally formed on one side (the small oil chamber 320 side shown in FIG. 4) of the rod 311, and the large oil chamber 330 (shown in FIG. 4). ) May be separated by a high pressure side large diameter head 313 that is installed to be slidable by hydraulic pressure and pushes the rod 311 to the left side (see FIG. 4). Since the high pressure side large diameter head 313 can push the rod 311 by hydraulic pressure, even if the piston 310 is separated into the rod 311 and the high pressure side large diameter head 313 which the low pressure side small diameter head 312 integrated. The clamp member 200 may operate normally.

As shown in FIG. 5, O-ring mounting grooves 312a and 313a are formed in the outer circumferential surface of each head 312 and 313, and as shown in FIG. 4, the O-rings 314 and 315 are installed to provide an oil chamber ( Oil in the 320, 330 does not leak between the heads 312, 313.

As shown in FIG. 6, the piston 310 may be separated into three types of the rod 311, the low pressure side small diameter head 312, and the high pressure side large diameter head 313.

Although not shown in the drawings, the piston 20 may be divided into both sides with the center of the rod portion 311 as the center.

As shown in FIG. 4, the lifting rod 400 for operating the clamp member 200 by the piston 310 has an inclined surface formed such that its lower surface is in surface contact with the inclined surface 311a formed on the piston 310. The upper surface thereof may protrude upward through the through hole 300a formed in the hydraulic cylinder 300 as the piston 310 moves to the left side (see FIG. 4) to rotate the clamp member 200. It is in contact with the lower surface of the end 210 of the clamp member 200. O-ring 410 for sealing the interior of the hydraulic cylinder 300 may be installed on the outer circumferential surface of the lifting rod 400.

As shown in FIG. 3, the restoring means 500 supporting the clamp member 200 in a counterclockwise direction, that is, in a direction of releasing clamping, may be installed in the main body 100.

Restoring means 500 is a coil spring 510 is inserted into the groove formed in the main body 100 and the clamp member by the elastic force of the coil spring 510 is installed in the upper portion of the coil spring 510 when the hydraulic pressure is released The other pressing portion 220 of the 200, that is, the pressing portion of the mold (M) is pushed upwards is made of a steel ball 520 to release the clamping of the mold (M).

The handle 130 may be formed at one side of the main body 100.

The action of the mold clamping device according to the present invention configured as described above is as follows.

First, the handle 130 and the main body 100 are grasped, and the engaging portion l20 of the main body 100 is inserted into the engaging groove 3a of the template 3 fixed to the molding apparatus. The mold M is disposed between the pressing parts 220 of the 200. In this way, a plurality of mold clamping devices according to the present invention are installed in the mold 3 to be installed in the molding apparatus around the mold M. As shown in FIG.

Next, the oil supply hoses are respectively connected to the joints 360 installed in the oil passing holes 341 and 351 of the first and second blind caps 340 and 350 mounted on the hydraulic cylinder 300. The oil supply hose is piped along the longitudinal direction of the main body 100 so as not to protrude to the side surfaces of the first and second blind caps 340 and 350.

In order to fix the mold M, as shown in FIG. 7, when the power supply is cut off to the power input unit 50 of the solenoid valve 42 and the power is supplied to the pump 52, the solenoid valve 42 is Open, and the pump 52 is operated.

At this time, the oil in the oil tank 40 is supplied to the first and second oil supply hoses (55, 56) through the oil strainer, the check valve 53, the pump 52 and the check valve 54, The oil supplied to the first oil supply hose 55 is supplied to the small oil chamber 320, and the oil supplied to the second oil supply hose 56 is supplied to the large oil chamber 330 through the check valve 58. do.

Oil is supplied to the small oil chamber 320 and the large oil chamber 330 at the same pressure. In this case, a relatively small amount of oil is supplied to the small oil chamber 320 due to the volume difference between the oil chambers 320 and 330. Is supplied, and a large amount of oil is supplied to the large oil chamber 330, so that the pressure on the large oil chamber 330 side is larger than that of the small oil chamber 320 side, and thus is inserted into the hydraulic cylinder 300. The piston 310 is moved to the small oil chamber 320 side.

As shown in FIG. 4, when the operation of the piston 310 is described in detail, the high pressure side large diameter head 313 is pushed to the small oil chamber 320 side by the hydraulic pressure in the large oil chamber 330, and the high pressure side The large diameter head 313 pushes the rod 311 so that the rod 311 slides to the left side, and the lifting rod 400 along the inclined surface 311a of the rod 311 is linked to the sliding of the rod 311. As it rises and protrudes out of the hydraulic cylinder 300 through the through hole 300a, the end portion 210 of the clamp member 200 is pushed upward.

Accordingly, as shown in FIG. 3, the clamp member 200 rotates clockwise about the shaft 110 so that the pressing part 220 presses the upper surface of the mold M toward the template 3 to firmly fix it. Clamp it.

When replacing the mold (M), when power is supplied to the power input unit 50 of the solenoid valve 42, the solenoid valve 42 is connected to the input port T and the output port P connected to the check valve 58. Since it is connected to the input port R, the output port S, and the output port Q of respectively, oil in the large oil chamber 330 is collect | recovered by the oil tank 40. FIG.

At this time, since the oil in the small oil chamber 320 is not recovered into the oil tank 40, as shown in FIG. 4, the low pressure side small diameter formed integrally with the rod 311 by the oil pressure in the small oil chamber 320. The head 312 is pushed by the pressure, the rod 311 pushes the high-pressure side large diameter head 313, the piston 310 is slid to the right.

As the piston 310 moves to the right, the lifting rod 400 descends on the inclined surface 31a, and the clamp member 200 is moved by the shaft 110 by the ball 520 supported by the coil spring 510. ) And the pressing part 220 is rotated counterclockwise (based on FIG. 3) around the mold M to release the clamp state, thereby replacing the mold for manufacturing another product.

Therefore, while the piston 310 is slid by hydraulic pressure, the clamp member 200 is operated to clamp the mold M through the lifting rod 400, and the hydraulic pressure of the piston 310 and the lifting rod 400 is not released. In this state, since the piston 310 does not slide to release the clamping, the elastic means is unnecessary as in the prior art.

Then, the piston 310 is formed by separating the rod 311 and the low pressure side small diameter head 312 assembly and the high pressure side large diameter head 313 in Example 1, and the rod 311 and the low pressure side in Example 2, It is separated into three of the small diameter head 312 and the high pressure side large diameter head 313, and it is easier to manufacture such a separate part than to manufacture a piston of a complete shape as in the prior art.

In addition, oil passing holes 341 and 351 of the first and second blind caps 340 and 350 are formed at substantially right angles, and one end thereof is a circle of the first and second blind caps 340 and 350. Since it opens toward the main surface, the joint 360 for connecting the oil supply hose does not protrude to the sides of the first and second blind caps 340 and 350.

As described above, according to the mold clamping device according to the present invention, since a separate member for supporting the piston by operating the clamp member while the piston slides by hydraulic pressure is not used, the structure of the parts is simplified, assembly process This can increase productivity and reduce costs.

In addition, since the piston is formed separately and manufacturing each single product is easier than manufacturing a piston of a complete shape, precision is not required, and thus productivity can be improved.

In addition, the joint for supplying oil does not protrude to the side but protrudes on the circumferential side of the first and second blind caps, which protrudes along the longitudinal direction of the main body, and the rear of the cap is a free space. There is an effect that the appearance is not bad, and does not interfere with other structures.

While the invention has been described and illustrated in connection with a preferred embodiment for illustrating the principles of the invention, the invention is not limited to the configuration and operation as such is shown and described. Rather, those skilled in the art will appreciate that many modifications and variations of the present invention are possible without departing from the spirit and scope of the appended claims. Accordingly, all such suitable changes and modifications and equivalents should be considered to be within the scope of the present invention.

Claims (4)

A main body fixed to the template of the molding apparatus; A clamp member installed on the main body so as to be rotatable through a shaft, and the pressing member of one side pressing and fixing the mold; A hydraulic cylinder installed below the other end side of the clamp member and having a small oil chamber and a large oil chamber therein; A piston which is slidably inserted left and right by a pressure difference in the small oil chamber and the large oil chamber inside the hydraulic cylinder, and has an inclined surface on an outer circumferential surface thereof; When the lower surface is in contact with the inclined surface of the piston and the upper side penetrates the hydraulic cylinder to contact the lower surface of the other end side of the clamp member and oil is supplied into the small oil chamber and the large oil chamber partitioned in the hydraulic cylinder. A rod for rotating the clamp member such that one pressing part of the clamp member presses and fixes the mold; And, And restoring means for pushing the pressing portion of the clamp member upward to release the fixed state of the mold when the oil supplied into the large oil chamber of the hydraulic cylinder is discharged. According to claim 1, The piston is provided with the inclined surface on the outer circumferential surface and the rod portion formed integrally with the low pressure side small diameter head disposed in the small oil chamber at one end; And, the other side of the rod portion is disposed in the large oil chamber Mold clamping device, characterized in that formed by separating the high-pressure side large diameter head pushing the rod by hydraulic pressure. According to claim 1, The piston, The outer peripheral surface and the inclined surface is provided with a rod portion; A low pressure side small diameter head installed on the small oil chamber side; And a high pressure side large diameter head installed on the large oil chamber side. According to claim 1, wherein the first and second blind caps are respectively installed on both sides of the hydraulic cylinder, the first and second blind caps inside the oil passage hole communicating with the small oil chamber and the large oil chamber, respectively. And an opening of one side of the oil through hole is bent to open toward the circumferential surfaces of the first and second blind caps.