JPH048160B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to solve the following problems.

(Industrial Application Field) This invention relates to a hydraulic press for compression molding powder raw materials.

(Prior art) In a conventional hydraulic press for powder molding, in the initial pressurization process, pressure oil from a hydraulic pump device is supplied to the upper hydraulic chamber of the pressurizing cylinder to extract air from the powder raw material ( In the later pressurization process, high pressure is generated using a pressure intensifier or two-stage pressure pump, and the high-pressure hydraulic pressure is supplied to the upper hydraulic chamber of the pressurizing cylinder, and the powder raw material is The powder raw materials were solidified by applying high pressure to the powder. However, in recent years, the capacity of hydraulic pumps has become higher pressure, and as a result, the conventional hydraulic presses mentioned above are
There is a problem in that the pressure applied to the initial powder raw material increases, and as a result, lamination (layers of air) tends to occur in the powder raw material, resulting in poor molding of the powder raw material. When the pressure is increased, if the output of the drive motor is the same, the discharge amount will decrease in inverse proportion to the increase in pressure, and as a result, the drive speed of the upper mold (pressure plate) will decrease and work efficiency will decrease. There were also some problems.

(Problems to be Solved by the Invention) This invention eliminates the above-mentioned conventional problems and uses pressure oil of lower pressure and larger capacity than the pressure oil of the hydraulic pump device in the initial pressurization process of powder raw materials. It is an object of the present invention to provide a hydraulic press that can be pressurized, and can be pressurized with a pressure oil of higher pressure and smaller capacity than the pressure oil of the hydraulic pump device in the later pressurization process.

The configuration of the present invention is as follows.

(Means for Solving the Problems) The present invention takes the measures as described in the claims above, and its effects are as follows.

(Function) The control device controls the operation of each switching valve, and in the initial pressurization stage, pressure oil from the hydraulic pump device is supplied to the small pressure chamber of the pressure conversion cylinder, and pressure oil from the large pressure chamber is supplied to the pressure conversion cylinder. Supplies the upper hydraulic chamber. As a result, pressurized oil having a lower pressure and a larger capacity than the pressure oil of the hydraulic pump device is supplied to the upper hydraulic chamber, whereby the upper mold pressurizes the powder raw material in the mold at a low pressure.
In the latter pressurization stage, the pressure oil from the hydraulic pump device is supplied to the large pressure chamber of the pressure conversion cylinder, and the pressure oil from the small pressure chamber is supplied to the upper hydraulic chamber of the pressure cylinder. As a result, pressurized oil having a higher pressure and a smaller volume than the pressure oil of the hydraulic pump device is supplied to the upper hydraulic chamber, whereby the upper mold pressurizes the powder raw material in the mold at high pressure.

(Example) Below, drawings showing examples of the present application will be described. In FIG. 1, reference numeral 1 denotes a hydraulic press for molding powder raw materials, which includes a press device 2, a hydraulic pump device 3 configured to discharge pressure oil for operating the press device 2, and a hydraulic pump device 3 for discharging pressure oil for operating the press device 2. The pressure oil supply control device 4 is configured to control the supply of pressure oil from the press device 2 to the press device 2. In the press device 2, reference numeral 10 denotes a crown portion, which is integrally provided with a frame (not shown). Reference numeral 11 denotes a pressure cylinder provided in the crown portion 10, and in the drawing, it is composed of a main cylinder 12 and a pair of left and right sub cylinders 13. In the main cylinder 12, 14 is a cylinder body, and 15 is a cylinder body.
1 is a piston, 16 is a piston rod, 17 is an upper hydraulic chamber, and 18 is a lower hydraulic chamber. In the sub-cylinder 13, 19 is a cylinder body, 20 is a plunger exemplified as a piston rod, and 21
is the upper hydraulic chamber. Next, 22 is an upper mold (also referred to as a pressure plate) fixed to the piston rod 16 and the plunger 20, and is disposed above a mold (not shown) which is filled with powder raw material. As is well known, a lower mold (not shown) is disposed below the mold, and a powder raw material supply device (not shown) is disposed on the side of the mold as well known. be.

Next, in the hydraulic pump device 3, 23 is a hydraulic pump, 24 is an electric motor for driving the hydraulic pump 23, 25 is an oil tank, 26 is a filter, 2
Reference numeral 7 denotes a relief valve which sets and maintains the pressure of the pressure oil discharged by the hydraulic pump 23 at a predetermined set pressure P.

Next, in the pressure oil supply control device 4, 28
is a pressure conversion cylinder for converting the pressure of pressure oil discharged from the hydraulic pump device 3. In the pressure conversion cylinder 28, 29 is a cylinder body, 30 is a fitting part protruding into the cylinder body 29, 31 is a piston fitted in the cylinder body 29, and 32 is a fitting part provided on the piston 31. The fitting portion 30 is fitted into the hole. 33 is a pilot cylinder body provided integrally with the cylinder body 29, and 34 is a pilot piston provided integrally with the piston 31, which is fitted into the pilot cylinder body 33. 35 is a small pressure chamber, and the pressure receiving area of the piston 31 is set to S2. 36 is a large pressure chamber, and the pressure receiving area S1 of the piston 31 is set larger than the pressure receiving area S2. 37 is a pilot pressure chamber, and the pressure receiving area S3 of the pilot piston 34 is set to be significantly smaller than the pressure receiving area S2. A back pressure chamber 38 communicates with an oil tank 39.

Next, 40 is a hydraulic circuit that connects the large pressure chamber 36 to the upper hydraulic chamber 17 of the main cylinder 12, and has a switching valve 41 having a solenoid 41a and a check valve 42 interposed therein. 43 connects the large pressure chamber 36 to the upper hydraulic chamber 2 of the sub cylinder 13.
This is a hydraulic circuit connected to 1, in which the switching valve 41 and the flow control valve 44 are interposed. 45 connects the small pressure chamber 35 to the upper hydraulic chamber 17 of the main cylinder 12.
A pilot switching valve 46 is interposed in the hydraulic circuit connected to the hydraulic circuit. 47 is a hydraulic circuit that connects the large pressure chamber 36 to the hydraulic pump device 3, and includes a switching valve 48 having a solenoid 48a and a solenoid 49a.
A switching valve 49 and the switching valve 41 described above are interposed. Reference numeral 50 denotes a hydraulic circuit connecting the small pressure chamber 35 to the hydraulic pump device 3, which includes the switching valve 49, the flow rate control valve 51, and the pilot check valve 52.
has been mediated. 53 is the pilot pressure chamber 3
7 to the hydraulic pump device 3, 54;
A hydraulic circuit connects the lower hydraulic chamber 18 of the main cylinder 12 to the hydraulic pump device 3, and is provided with a switching valve 55 having a solenoid 55a and a pilot check valve 56 for fall prevention. 57
is a hydraulic circuit that connects the upper hydraulic chamber 21 of the sub-cylinder 13 to the hydraulic pump device 3, and the solenoid 58
A switching valve 58 having valves a and 58b is provided.
59 is a surge tank, which is connected to the main cylinder 12 mentioned above.
The hydraulic pressure chamber 17 is connected to the upper hydraulic chamber 17 via a surge valve 60. In addition, the surge tank 59 is connected to the circuit 6.
1 is connected to an oil tank 25. 62 is a pilot switching valve having a solenoid 62a;
It is connected to the circuit 53 mentioned above. 63 is the above circuit 6
A check valve 64 is interposed in the circuit connecting the pressure chamber 1 to the large pressure chamber 36. 65 is the above circuit 4
0, and includes a low pressure switch 65a, a medium pressure switch 65b, and a high pressure switch 65c. 66, 67, 68
are position sensors that detect the lowering of the upper mold 22 to a predetermined position. 69 is each solenoid 4 mentioned above.
1a, 48a, 49a, 55a, 58a, 58
A control device that controls energization to b and 62a.
It is controlled as shown in the figure.

In the above configuration, the electric motor 24 drives the hydraulic pump 23, and the hydraulic pump 23 discharges pressure oil. The pressure of the discharged pressure oil is maintained at the set pressure P of the relief valve 27. First, when all the solenoids are de-energized as shown in section a of FIG. The upper mold 22 is raised by entering the lower hydraulic chamber 18 of the upper mold.

Next, when compressing the powder raw material filled in the mold, the solenoid 58a is energized by an appropriate lowering command as shown in section b of FIG. As a result, as shown in FIG.
3, and pushes down the plunger 20 to lower the upper die 22. In the above case, since the pilot check valve 56 is opened by pilot pressure, the oil in the lower hydraulic chamber 18 of the main cylinder 12 flows into the circuit 54, and the oil that flows out increases the pressure of the hydraulic pump device 3. The sub cylinder 13 passes through the circuit 57 and the switching valve 58 together with the oil.
It flows into the upper hydraulic chamber 21 of. Therefore, the plunger 20 and the upper die 22 are rapidly lowered. In the above case, the upper hydraulic chamber 17 of the main cylinder 12 becomes a negative pressure, and the unpressurized oil in the surge tank 59 flows into the upper hydraulic chamber 17 through the open surge valve 60.

When the upper mold 22 activates the position sensor 66 while the upper mold 22 is lowering, the signal demagnetizes the solenoid 58a and energizes the solenoids 41a, 49a, and 62a as shown in section c of FIG. . As a result, the surge valve 60 closes as shown in FIG. 3, preventing oil from flowing into the upper hydraulic chamber 17 from the surge tank 59, and also preventing pressure oil from leaking when pressure is applied to the upper hydraulic chamber 17. . In addition, the switching valve 49 is switched, and the pressure oil of the hydraulic pump device 3 is transferred to the circuit 50, the switching valve 49, and the flow control valve 5.
1 and the pilot check valve 52 into the small pressure chamber 35 of the pressure conversion cylinder 28, and presses the piston 31. In the above case, since the pilot switching valve 46 is closed by the operation of the switching valve 49, the pressure oil of the hydraulic pump device 3 does not flow into the upper hydraulic chamber 17. Also, the switching valve 41 is switched, and the pressure oil in the large pressure chamber 36 flows into the upper hydraulic chamber 17 of the main cylinder 12 through the circuit 40, the switching valve 41, and the check valve 42, pushing down the piston 15, and the circuit 43 , switching valve 41
The liquid flows into the upper hydraulic chamber 21 of the sub-cylinder 13 through the flow control valve 44 and pushes down the plunger 20. In the above case, the pressure conversion cylinder 28 is
The set pressure P of the pressure oil of the hydraulic pump device 3 is lowered by the ratio of the pressure receiving area S2 of the piston 31 of the small pressure chamber 35 and the pressure receiving area S1 of the piston 31 of the large pressure chamber 36, and the pressure oil of the low pressure is lowered. is sent out from the large pressure chamber 36. That is, the pressure P1 inside the large pressure chamber 36 is P1=
P×S1/(S2−S3), and the above piston 15
A pressure P1 is applied to the plunger 20, and the upper die 22 is pushed down with a low pressure. The maximum oil amount Q1 discharged from the large pressure chamber 36 is the hydraulic pump 2.
If the discharge amount of No. 3 is Q, then Q1=Q×S1/S2, which is faster than pushing down the upper die 22 by the oil discharged from the hydraulic pump 23. However, the actual oil amount is adjusted to an appropriate value by the flow rate control valve 44 within the range of the oil amount Q1.

Next, when the upper mold 22 comes into contact with the powder raw material due to the lowering of the upper mold 22, the pressure in the upper hydraulic chambers 17 and 21 increases due to the resistance, and the upper mold 22 pressurizes the powder raw material. . As a result, when the pressure inside the upper hydraulic chamber 17 reaches a predetermined low pressure P1', the pressure sensor 6
The low pressure switch 65a of No. 5 is activated, and in response to the signal, the solenoids 49a and 41a are demagnetized as shown in section d of FIG.
Excite b. As a result, the switching valve 58 is switched as shown in FIG. 4, and the pressure oil in the upper hydraulic chamber 21 is discharged into the oil tank through the circuit 57 and the switching valve 58. In addition, the switching valve 49 returns to its original position and the supply of pressure oil to the small pressure chamber 35 is stopped.At the same time, the pilot check valve 52 opens and the pilot switching valve 46 returns to its original position. Pressure oil is discharged into the oil tank through circuits 45, 50, switching valve 49, etc. Note that, since pressure oil from the hydraulic pump device 3 is supplied to the lower hydraulic chamber 18 through the circuit 54 and the switching valve 55, the piston 15 is pushed up and the upper die 22 is raised. Moreover, the switching valve 41 returns to its original state and closes.

After the timer setting time T1 has elapsed since the activation of the low pressure switch 65a, the solenoid 58b is again deenergized and the solenoids 49a and 48a are energized, as shown in section e in FIG. This allows the fifth
As shown in the figure, the switching valve 49 switches, and the pressure oil of the hydraulic pump device 3 flows into the small pressure chamber 35 of the pressure conversion cylinder 28 through the circuit 50.
1 is closed, the piston 31 does not move. At the same time, by switching the switching valve 48, the pilot switching valve 46 becomes in communication state, and as a result, the pressure oil of the hydraulic pump device 3 flows into the upper hydraulic chamber 21 of the sub-cylinder 13 through the circuits 47 and 43. It flows into the upper hydraulic chamber 17 of the main cylinder 12 through the circuits 50 and 45, and the set pressure P of the hydraulic pump device 3 flows into the upper hydraulic chambers 17 and 21.
is applied to lower the upper mold 22.

As the upper mold 22 descends, the upper mold 22 presses the powder raw material, and the pressure inside the upper mold hydraulic chambers 17 and 21 rises. Pressure switch 65
b is activated, and the signal demagnetizes the solenoid 49a and energizes the solenoid 58b as shown in section f in FIG. As a result, the switching valve 49 is switched to its original state as shown in FIG.
0 is stopped, and the switching valve 58 is switched to release the pressure oil in the upper hydraulic chambers 17 and 21 into the oil tank through the switching valve 58.

After the timer setting time T1 has elapsed since the operation of the intermediate pressure switch 65b, the solenoid 58b is demagnetized and the solenoid 49a is energized, as shown in section g in FIG. As a result, as shown in FIG. 5 above, the hydraulic pump device 3
Pressure oil with a set pressure P flows in, and the upper mold 22 is lowered again.

Next, as the upper mold 22 descends, the upper mold 22 pressurizes the powder raw material, and the intermediate pressure switch 65b is activated again.After the timer setting time T2 has elapsed, the solenoid is activated as shown in section h in FIG. 55
a, 41a is excited. As a result, the switching valve 55 is switched as shown in FIG.
6 and the switching valve 55 to the oil tank,
All pressure on the pressurizing side is valid. Also, the switching valve 41
is switched, and the pressure oil of the hydraulic pump device 3 is transferred to the circuit 47.
and flows into the large pressure chamber 36 of the pressure conversion cylinder 28 through the switching valves 48 and 41. Further, pressure oil from the hydraulic pump device 3 is always applied to the pilot pressure chamber 37. As a result, the piston 31 and the pilot piston 34 are moved to push out the pressure oil in the small pressure chamber 35 to the circuit 50, but since the pilot check valve 52 is closed, the small pressure chamber 35
The pressure oil in the cylinder 5 flows into the upper hydraulic chamber 17 of the main cylinder 12 through the pilot valve 46 and the circuit 45, pushes down the piston 15, and lowers the upper die 22. The pressure P3 of the pressure oil in the small pressure chamber 35 is:
P3=P×(S1+S3/S2), and the pressure is increased to a value greater than the set pressure P of the hydraulic pump device 3. The increased pressure oil moves the upper mold 22 downward, and the upper mold 22 pressurizes the powder raw material to form an upper hydraulic chamber 17.
When the internal pressure reaches pressure P3' higher than the set pressure, the high pressure switch 65c of the pressure sensor 65 is activated, and the solenoid 55 is activated as shown in section i in FIG.
a, 62a, 49a, 41a, and 48a are demagnetized. As a result, as shown in Fig. 1, the upper hydraulic chamber 1
Pressure oil in 7 and 21 is released into the oil tank, and the surge valve 60 is opened, and the pressure oil in the hydraulic pump device 3 flows into the lower hydraulic chamber 18 through the circuit 53, pushing up the piston 15 and pushing it upward. The mold 22 is raised.

Next, when the upper mold 22 activates the position sensor 67 due to the rise of the upper mold 22, the solenoid 58b is strongly magnetized as shown in section j in FIG. 9, thereby causing switching as shown in FIG. The valve 55 is switched, and as a result, the pressure oil in the upper hydraulic chamber 21, which had been flowing out little by little by the flow control valve 44, is discharged in large quantities into the oil tank through the switching valve 55.
Therefore, the upper mold 22 is quickly raised. after that,
When the upper mold 22 activates the position sensor 68, the solenoid 58b is demagnetized again, and the upper hydraulic chamber 2
The leakage of pressure oil inside 1 is reduced. As a result, the upper mold 22 changes from low speed to high speed to low speed, and can be raised smoothly. With the above steps, a series of powder raw material compression steps is completed.

The piston 31 of the pressure conversion cylinder 28 is
After the above-mentioned pressure increasing action, the pilot piston 34 is moved by the pressure oil flowing into the pilot pressure chamber 37 and returned to the piston 34 to prepare for the next step.

In the above embodiment, the pressure conversion cylinder 28
The ratio of each pressure receiving area S1, S2, S3 is, for example, S1:
S2:S3=50:18:1. Therefore, if the set pressure of the hydraulic pump device 3 is 140Kg/ ^cm2 ,
The maximum value of pressure P1 when the pressure is reduced is 50Kg/cm ² ,
The maximum value of pressure P3 when the pressure is increased is approximately 388 Kg/cm ² . However, in the actual compression process, the operating pressure settings of the pressure switches 65a, 65b, and 65c result in appropriate pressures P1', P2', and
Set to P3′.

FIG. 10 shows a different example of the present application, in which the main cylinder 12m is a single acting cylinder and the sub cylinder 13m is a double acting cylinder.

It should be noted that parts that are functionally the same or equivalent to those in the previous figure are given the same reference numerals as those in the previous figure with the letter "m" added thereto, and redundant explanations are omitted.
(Also, in the following figure, the same idea is given by adding an alphanumeric character "n" and redundant explanation will be omitted.) FIGS. 11 and 12 show another different example of the present application, and the pressurizing cylinder 11n It is composed of only the main cylinder 12n. 56n is a counterbalance valve for preventing the upper mold from falling under its own weight, and is fully opened by the pilot pressure of the pilot valve 58n to eliminate back pressure when the upper mold is lowered. 71
is a switching valve for rapid ascent, and the rapid descent of the upper mold 22n is performed by the fall of the upper mold 22n under its own weight. In Figure 12, the timer setting time T0
This is to create a differential circuit for a while with the pressure oil flowing into the circuit 54n after pressure is applied to the upper hydraulic chamber 17n of the main cylinder 12n.

(Effects of the Invention) As described above, in the present invention, the pressure oil of the hydraulic pump device 3 is supplied to the small pressure chamber 35 of the pressure conversion cylinder 28 and the large pressure chamber 3
The upper hydraulic chamber 17 of the pressurized cylinder 11
Therefore, when compressing powder raw materials, in the initial pressurization process, the upper hydraulic chamber 17 of the pressurizing cylinder 11 is supplied with pressurized oil at a lower pressure and a larger capacity than the pressurized oil of the hydraulic pump device 3. can supply
As a result, even when using the high-pressure hydraulic pump device 3, the initial pressurizing force of the powder raw material can be made much smaller than when pump pressure is directly applied, and there is an advantage that lamination can be prevented from occurring. At the same time, the maximum descending speed of the upper die 22 is significantly faster than when pump pressure is applied directly, and the efficiency of initial pressurization work at low pressure can be significantly improved by increasing the descending speed of the upper die 22. It's also effective.

In addition, in the latter pressurization stage, the pressure oil of the hydraulic pump device 3 is supplied to the large pressure chamber 36 of the pressure conversion cylinder 28, contrary to the above case, and the pressure oil in the small pressure chamber 35 is supplied to the pressure cylinder 11. Since it is designed to be supplied to the upper hydraulic chamber 17, when compression molding powder raw materials, the pressure cylinder 1 is used in the latter pressurization process.
The upper hydraulic chamber 17 of 1 can be supplied with a pressure oil having a higher pressure and a smaller volume than the pressure oil of the hydraulic pump device 3, and as a result, as mentioned above, the pressure of the initial powder raw material is lower than the pump pressure and the pressure oil can be rapidly applied. Even if it is possible,
This method has the revolutionary effect of making it possible to firmly solidify the powder raw material even at a high pressure by applying pressure on the powder raw material in the latter stage very slowly, and improving the quality of the molded product by using two types of pressure means.

Further, in the present invention, the hydraulic pump device 3 is connected to the upper hydraulic chamber 17 of the pressurizing cylinder 11 via a switching valve, and the pressure oil of the hydraulic pump device 3 is connected to the upper hydraulic chamber 17 of the pressurizing cylinder 11 in the middle pressurizing stage. Upper hydraulic chamber 17
When compressing powder raw materials, the process is carried out rapidly at low pressure in the early stage, at medium pressure and fast in the middle stage, and at high pressure in the latter stage at a leisurely pace. It is possible to sequentially compress a single product in various ways, such as by being able to compress the molding of a single product in a variety of ways, which has the effect of making it possible to mold a good molded product with high workability without causing lamination in the powder raw material.

[Brief explanation of drawings]

The drawings show an embodiment of the present application, and Fig. 1 is an explanatory diagram of a hydraulic press, Figs. 2 to 8 are explanatory diagrams of the operation of the hydraulic press, and Fig. 9 is a time chart showing the operation of Fig. 1. , FIG. 10 is an explanatory diagram showing a different example, FIG. 11 is an explanatory diagram showing another different example,
FIG. 2 is a time chart showing the operation of FIG. 11. 1...Hydraulic press, 2...Press device, 3...
Hydraulic pump device, 4... Pressure oil supply control device, 11
...Pressure cylinder, 17...Upper hydraulic chamber, 22...
... Upper mold, 28 ... Pressure conversion cylinder, 31 ... Piston, 35 ... Small pressure chamber, 36 ... Large pressure chamber,
41, 46, 48, 49...Switching valve, 69...Control device.

Claims (1)

[Scope of Claims] 1. A lower mold is disposed below a mold that is filled with powder raw material, and above the mold is an upper mold connected to a lower part of a piston rod of a pressurizing cylinder. a press device equipped with a press device; a hydraulic pump device configured to discharge pressurized oil for operating the pressurized cylinder; and a hydraulic pump device configured to discharge pressurized oil to operate the pressurized cylinder; and a pressure oil supply control device for controlling the supply time and supply pressure. In a hydraulic press for powder molding, which is configured to compress and mold powder raw material in the mold using a mold, the pressure oil supply control device has a piston fitted in its own cylinder body so as to be able to reciprocate, and also controls the piston. A pressure conversion cylinder is provided, in which the pressure receiving area on one side of the piston is larger than that on the other side, and the large pressure chamber on the larger pressure receiving area side of the pressure conversion cylinder is connected to the upper hydraulic chamber of the pressure cylinder and the above hydraulic pressure. a hydraulic circuit connected to the pump device through respective switching valves, and a switching valve that connects the small pressure chamber on the small pressure receiving area side of the pressure conversion cylinder to the upper hydraulic chamber of the pressurizing cylinder and the hydraulic pump device, respectively. It also has a hydraulic circuit connected to each of the above switching valves via a pressurizing cylinder, which supplies pressurized oil from the hydraulic pump device to the small pressure chamber in the initial pressurization stage, and also supplies pressurized oil in the large pressure chamber to the pressurized cylinder. The system is switched to supply the oil to the upper hydraulic chamber, and in the later pressurization stage, the pressure oil from the hydraulic pump device is supplied to the large pressure chamber, and the pressure oil from the small pressure chamber is supplied to the upper hydraulic chamber of the pressurizing cylinder. A hydraulic press for powder molding, characterized in that it is also equipped with a control device for switching control. 2. A lower mold is arranged below the mold which is filled with powder raw material, and an upper mold connected to the lower part of the piston rod of the pressure cylinder is arranged above the mold. a press device, a hydraulic pump device configured to discharge pressurized oil for operating the pressurizing cylinder, and supplying the pressurized oil discharged from the hydraulic pump device to the hydraulic chamber of the pressurizing cylinder and the supply thereof. A pressure oil supply control device for controlling time and supply pressure is provided, and the upper die is lowered by supplying pressure oil to one pressurizing chamber of the pressurizing cylinder,
In a hydraulic press for powder molding, which compresses and molds powdered raw material in the mold using an upper mold and a lower mold, the pressure oil supply control device controls a piston to freely reciprocate within its own cylinder body. The piston is fitted with a pressure conversion cylinder in which one side of the piston has a larger pressure receiving area than the other side, and the large pressure chamber on the larger pressure receiving area side of the pressure conversion cylinder is connected to the upper side of the pressure cylinder. A hydraulic circuit is connected to the hydraulic chamber and the hydraulic pump device through switching valves, and a small pressure chamber on the small pressure receiving area side of the pressure conversion cylinder is connected to the upper hydraulic chamber of the pressurizing cylinder and the hydraulic pump device. and a hydraulic circuit connecting the hydraulic pump device to the upper hydraulic chamber of the pressurizing cylinder via a switching valve, each of the switching valves being connected to each of the switching valves. In the initial pressurization stage, the pressure oil from the hydraulic pump device is supplied to the small pressure chamber, and the pressure oil in the large pressure chamber is switched to the upper hydraulic chamber of the pressurizing cylinder, and in the middle pressurization stage, the hydraulic pump The pressure oil of the device is switched to be supplied to the upper hydraulic chamber of the pressure cylinder, and in the later pressurization stage, the pressure oil of the hydraulic pump device is supplied to the large pressure chamber, and the pressure oil in the small pressure chamber is switched to the upper hydraulic chamber of the pressure cylinder. A hydraulic press for powder molding, characterized in that it is also equipped with a control device that switches and controls the supply to the upper hydraulic chamber.