JP3394201B2 - Injection method and apparatus for metal injection molding machine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection method and an apparatus for a metal injection molding machine for injection molding a metal material such as a magnesium alloy or an aluminum alloy.

[0002]

2. Description of the Related Art In the conventional injection method of a metal injection molding machine, a molten material is instantly solidified when it is filled in a mold. Therefore, an injection step of high-speed injection and sink or micro shrinkage due to contraction after filling. It comprises a linkage, and a pressure holding step of holding at a higher pressure than the injection step in order to prevent voids and the like due to entrainment of air and gas. The injection device used in this method has an injection cylinder 120 composed of a head side oil chamber 102 and a rod side oil chamber 106 as shown in FIG. 4, and a main direction switching valve 108 is provided during an injection process. Through head side oil chamber 1
The pressure oil from the hydraulic pump 101 is injected into 02, the rod side oil chamber 106 is connected to the tank 117, and the piston rod 128 and the screw 138 connected to the piston rod 128 are advanced at a high speed and injected. When switching from the injection process to the pressure holding process, the position of the screw 138 is detected by a position detector (not shown) attached to the piston rod 128, and when the position of the screw 138 reaches a preset injection pressure holding switching position, The controller of the metal injection molding machine connected to the position detector issues a command to the pressure control valve (not shown) to switch to the pressure holding process.

FIG. 5 shows an injection pressure, a holding pressure and an injection speed with respect to a screw position in a general injection process and a pressure-holding process in a metal injection molding machine. The molten material measured from the injection start position is gold. Since the viscosity of the molten material is small until the mold is almost filled, the flow resistance is small and the injection pressure is very small compared with the holding pressure during the holding process. In addition, the injection speed during the injection process needs to be high because the molten material instantly solidifies when it is filled in the mold. In the pressure-holding process after passing through the injection-holding pressure switching position, the pressure is kept higher than the injection pressure during the injection process in order to prevent sink marks and micro-shrinkage due to contraction after filling, and voids due to entrainment of air and gas. To be done.

[0004]

However, in the conventional injection method of the metal injection molding machine, even if the injection process is switched to the pressure maintaining process at the preset injection pressure maintaining position, the piston moving forward at high speed. The forward speed does not suddenly decrease due to the inertia of the rod, the screw is decelerated by the load of the molten material filled in the mold, and the piston rod connected to the screw is decelerated to switch to the pressure holding process.
Therefore, after passing through the preset injection holding pressure switching position, pressure is applied to the molten material filled in the mold by the piston rod and the screw that advance at high speed due to inertia, so the setting is made as shown in FIG. There was a problem that the pressure became excessively higher than the holding pressure and burr was generated in the molded product.

The present invention has been made in order to solve the above problems, and in a metal injection molding machine, the molten material filled in the mold has an excessive pressure higher than the set holding pressure. An object of the present invention is to provide an injection method and an apparatus thereof that do not add.

[0006]

A two-stage injection cylinder composed of a small-diameter first head-side oil chamber, a large-diameter second head-side oil chamber, and a rod-side oil chamber is used to perform a first-stage injection process. The oil pressure from the pressure oil supply source is supplied to the head side oil chamber via the main direction switching valve, and the second head side oil chamber and the rod side oil chamber are transferred to the tank via the first direction switching valve and the main direction switching valve. The piston rod and screw are advanced at high speed and low pressure by connecting them, and the pressure of the flow path connected to the first head side oil chamber is set by the load of the molten material filled in the mold at the end of the injection process. When the pressure rises to 1, the position of the first direction switching valve is switched by the pressure control valve and the third direction switching valve, the first head side oil chamber and the second head side oil chamber are connected via the first direction switching valve, and the first direction switching valve is connected. Head-side oil chamber and second head-side oil chamber with first directional control valve and main direction By supplying pressure oil through the switching valve and connecting the rod-side oil chamber to the tank through the first directional switching valve and the main directional switching valve, the forward speed of the piston rod and screw is slowed down to a low and high pressure state. Switch to pressure-holding process with.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described based on examples with reference to the drawings. FIG. 1 is a configuration diagram showing an example of an injection device of a metal injection molding machine according to the present invention, and FIG. 2 is a partial sectional view of a two-stage injection cylinder of the injection device.

The injection apparatus of the metal injection molding machine according to the present invention comprises a two-stage injection cylinder 20 as shown in FIGS.
And a hydraulic circuit for operating the injection cylinder 20.

As shown in FIG. 2, the two-stage injection cylinder 20 has a first head side oil formed by a head cover 22 and a small diameter first piston 32 provided on the end surface of the piston rod 28 and a cylinder housing 26. The second head-side oil chamber 4, which is formed by the chamber 2, the first piston 32, the large-diameter second piston 30 provided in the intermediate portion of the piston rod 28, and the cylinder housing 26, the second piston 30, the piston rod. 28, the rod cover 24, the bush 36, and the cylinder housing 26.
And a first piston 32 and a second piston 30.
The outer peripheral surface of the is slidably inscribed on the inner peripheral surface of the cylinder housing 26, and the piston rod 28 is screw 38
(See FIG. 1).

As shown in FIG. 1, the hydraulic circuit includes a second head side oil chamber 4 and a rod side oil chamber 6 of the two-stage injection cylinder 20.
A first directional control valve 10 having a port connected to the main directional control valve 8, a main directional control valve 8 having a port connected to the first directional control valve 10 and the first head side oil chamber 2, and a main directional control valve 8 connected to the main directional control valve 8. The hydraulic pump 1 and the tank 17, the pressure control valve 16 connected to the flow path 7 between the first head side oil chamber 2 and the main direction switching valve 8, and the pilot pressure for switching the positions of the first direction switching valve 10. The pilot pressure circuit is connected to the hydraulic pump 1 and switches to the initial stage of the injection process, and the second directional control valve 12 is connected to the second directional valve 12 to control the pressure at the end of the injection process. The third directional switching valve 14 is switched by the pilot pressure of the valve 16.

Next, the operation of the injection device will be described.
First, in the initial stage of the injection process, the second directional control valve 12 is set to the G position, and the pressure oil from the hydraulic pump 1 is supplied to the second directional control valve 12 so that the first directional control valve 10 becomes the F position and the second head side oil is supplied. The chamber 4 and the rod side oil chamber 6 are connected. Here, the main direction switching valve 8 is set to the D position, the pressure oil from the hydraulic pump 1 is supplied to the first head side oil chamber 2, and the second head side oil chamber 4 and the rod side oil chamber 6 are connected to the first direction switching valve 10. And the piston 38 and the screw 38 connected to the piston rod 28 by connecting to the tank 17 via the main direction switching valve 8.
Moves forward. At the end of the injection process, the pressure in the first head-side oil chamber 2 rises due to the pressure of the molten material filled in the mold cavity, and when it reaches a preset pressure, the pressure control valve 1
6, the third directional switching valve 14 is in the I position, and the pressure oil supplied to the second directional switching valve 12 acts on the first directional switching valve 10 via the third directional switching valve 14 The one-way switching valve 10 is at the E position, the first head side oil chamber 2 and the second head side oil chamber 4 are connected via the first direction switching valve 10, and pressure oil is supplied via the main direction switching valve 8. Then, the rod-side oil chamber 6 is connected to the tank 17 via the first direction switching valve 10 and the main direction switching valve 8 to switch to the pressure holding process.

When the flow rate and pressure of the pressure oil supplied to the injection cylinder 20 via the main direction switching valve 8 during the injection process are constant, when the pressure oil is supplied to the first head side oil chamber 2 during the injection process. The injection speed Vl and the ejection output Fl, and the first head-side oil chamber 2 and the second head-side oil chamber 4 when switching to the pressure holding process.
The relationship between the injection speed V2 and the injection output F2 when the pressure oil is supplied to is expressed by the following mathematical formula 1.

[0013]

## EQU1 ## V2 = {Al / (Al + A2)} × Vl F2 = {(Al + A2) / Al} × Fl In the above formula 1, Al is the pressure receiving area of the first head side oil chamber 2, and A2 is the second It is an effective pressure receiving area of the head side oil chamber 4.

As described above, when switching to the pressure maintaining process, the forward speed of the piston rod 28 and the screw 38 connected to the piston rod 28 is decelerated compared to during the injection process, and measurement is performed in a low speed and high pressure state. Since the molten material can be filled in the mold cavity, as shown in FIG. 3, the molten material filled in the mold does not receive the pressure of the piston rod 28 and the screw 38 that move forward due to inertia, and thus the holding pressure is maintained. It is possible to switch to the process.

In the above description, the hydraulic oil pump is used as the pressure oil supply source in the injection and pressure holding steps, but an accumulator may be used instead, or a hydraulic pump and an accumulator may be used in combination.

Further, although the flow rate and pressure of the pressure oil in the injection process are constant, if another hydraulic circuit is added to change the flow rate and pressure of the pressure oil, more appropriate control becomes possible.

[0017]

Since the present invention is constructed as described above, it has the following effects. That is, when the injection process is switched to the pressure-holding process, the forward speed of the screw is decelerated, and the molten material can be filled in the mold cavity at a low speed and a high pressure. Obtainable.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an example of an injection device of a metal injection molding machine according to the present invention.

FIG. 2 is a partial cross-sectional view of a two-stage injection cylinder of an injection device.

FIG. 3 is a diagram showing an injection pressure, a holding pressure and an injection speed with respect to a screw position of the metal injection molding machine of the present invention.

FIG. 4 is a configuration diagram of an injection device of a conventional metal injection molding machine.

FIG. 5 is a diagram showing an injection pressure, a holding pressure and an injection speed with respect to a screw position of a conventional metal injection molding machine.

[Explanation of symbols]

1 Hydraulic pump (pressure oil supply source) 2 First head side oil chamber 4 2nd head side oil chamber 6 Rod side oil chamber 7 channels 8 main direction switching valve 10 First directional valve 12 Second directional valve 14 3rd directional valve 16 Pressure control valve 17 tanks 20 2-stage injection cylinder 22 head cover 24 Rod cover 26 Shirin Housing 28 Piston rod 30 Second piston 32 1st piston 36 Bush 38 screws

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Bibliography Sho 58-23263 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) B22D 17/32

Claims (3)

(57) [Claims] 1. A two-stage injection cylinder (20) consisting of a first head side oil chamber (2), a second head side oil chamber (4) and a rod side oil chamber (6) is subjected to an injection process. the first head-side oil chamber (2) to supply the pressurized oil, the second head-side oil chamber (4) and the rod-side oil chamber (6) a first directional control valve
Perform injection at a high speed and low pressure by connecting the tank (17) through (10), the first head-side oil chamber by the load of the molten material filled in the mold injection process end (2)
Elevated pressure set pressure the pressure of the connected flow paths (7)
The position of the first directional control valve (10) is controlled by the control valve (16).
When the storage is switched, the first head side oil chamber (2) and the
The second head side oil chamber (4) is connected to the first direction switching valve (10).
Connected via the first head-side oil chamber (2) and the second head-side oil chamber (4) to supply the pressure oil, the rod-side oil chamber (6) a first directional control valve (10 ) Through the tank (1
An injection method for a metal injection molding machine, characterized in that the injection speed is reduced by connecting with 7) , and the pressure holding step is switched to a low pressure and high pressure state. 2. A two-stage injection cylinder (20) comprising a small diameter first head side oil chamber (2), a large diameter second head side oil chamber (4) and a rod side oil chamber (6). A first directional switching valve (10) having a port connecting to the second head side oil chamber (4) and the rod side oil chamber (6), the first directional switching valve (10), and the first head side oil chamber (2). ) And a pressure oil supply source (1) connected to the main direction switching valve (8), and the first head side oil chamber (during the injection process). Pressure oil is supplied to 2), the second head side oil chamber (4) and the rod side oil chamber (6) are connected to the tank (17) via the first directional switching valve (10), and at the end of the injection process. The pressure in the flow path (7) connected to the first head-side oil chamber (2) rises to the set pressure, and the pressure control valve (16) causes the first directional control valve (1).
When the position of (0) is switched, the first head side oil chamber (2) and the second head side oil chamber (4) are connected via the first direction switching valve (10), and the first head side oil chamber ( 2) and a hydraulic circuit for supplying pressure oil to the second head side oil chamber (4) and connecting the rod side oil chamber (6) to the tank (17) via the first direction switching valve (10). An injection device of a metal injection molding machine, which is characterized in that 3. A pilot pressure circuit for switching the position of the first directional control valve (10) is connected to a pressure oil supply source (1) and switched to a second directional control valve (1) at the beginning of the injection process.
It has a 2), wherein connected to the second directional control valve (12) in the injection step final pressure control valve (third directional control valve switched by the pilot pressure of 16) (14), wherein
Item 2. The injection device of the metal injection molding machine according to Item 2 .