JPH03197115A - Injection molding machine - Google Patents

Abstract

PURPOSE:To prevent a gate seal from getting broken securely even the molding conditions are varied in every injection shot and manufacture molded product of high quality by lowering the sensing pressure of a pressure sensor until satisfying the set conditions, and then lowering the set hydraulic pressure of a hydraulic pressure unit following the lowering of sensed pressure and almost same deterioration gradient of said sensed pressure. CONSTITUTION:The flow rate of an electromagnetic flow control meter 48 and the relief pressure of a relief valve 58 are set to the rate and pressure for obtaining the given injection speed and injection pressure, and resin is injected into a cavity 16 for time T1. Said time is measured by a timer installed in a CPU, and the feeding of hydraulic oil to a liquid pressure chamber 46 is discontinued after the time T1 is passed, while the relief pressure of the relief valve 48 is slightly lower and replenishment of resin to the cavity 16 is carried out with the dwelling force lower than what was at the time of injection, and the control of dwelling stage waiting for the solidification of resin in a gate 24 is carried out. At that time, actual hydraulic pressure of a hydraulic cylinder 44 is lowered according to the relief pressure of the relief valve 48 (the set hydraulic pressure of the hydraulic unit) set by applying the hydraulic pressure setting routine.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an injection molding machine, and in particular to control of holding force in the holding pressure stage after filling a cavity with resin.

Prior art injection molding machines are generally configured to include (a) a mold, (b) a resin injection unit, (C) a hydraulic unit, and (d) a hydraulic unit controller. The mold has a cavity shaped to correspond to the product to be molded, and a resin is injected into the mold by a resin injection unit. The resin injection unit is operated by hydraulic pressure supplied from the hydraulic unit and injects resin into the cavity at a predetermined pressure, and the hydraulic pressure of the hydraulic unit is controlled by a hydraulic unit control device. Molding with this type of injection molding machine involves the resin injection stage in which resin is injected into the cavity, and the volumetric shrinkage that occurs when the resin in the cavity cools and solidifies. At the same time, the resin at the gate solidifies and the resin backflows. Alternatively, it can be divided into a pressure holding stage in which the resin in the cavity waits until no re-inflow occurs, and a cooling stage in which the resin in the cavity waits for it to further cool down and solidify to a state where it can be removed from the mold. The height of the hydraulic pressure set in the hydraulic unit at each stage is different; at the resin injection stage, the height is set to inject resin into the cavity at a predetermined pressure, at a lower pressure stage, it is set to a lower height, and at the cooling stage, the height There is no need to apply pressure to , and it is assumed to be O.

In this way, the height of the hydraulic pressure setting of the hydraulic unit differs for each stage, but in the resin injection stage the height of the hydraulic pressure setting is constant and there is no problem, while in the holding pressure stage, "Introduction to Plastic Molding Processing" ( As stated on page 157 of Nikkan Kogyo Shimbun (first edition), if the height of the set oil pressure is constant,
As the pressure inside the cavity decreases as the resin solidifies, the difference between the pressure of the resin on the resin injection unit side and the resin pressure on the resin injection unit side becomes excessive, which may break the gate seal and cause re-inflow. Therefore, in the injection molding machine described in Japanese Patent Application Laid-Open No. 60-32621, the set hydraulic pressure of the hydraulic unit is switched to two levels, large and small, during the pressure holding stage, and the set hydraulic pressure is lowered midway through, thereby causing re-inflow. There is no such thing. However, at the time of switching, the pressure on the resin injection unit side decreases rapidly and becomes too low compared to the pressure inside the cavity, which may cause a backflow of resin.

On the other hand, in the injection molding machine described in JP-A No. 62-174126, the time required for gate sealing is divided into multiple parts after the resin injection into the cavity is completed, and for each divided time, the target value at the time of elapsed time is set. The pressure is set, and control is performed so that the set hydraulic pressure of the hydraulic unit is reduced according to a gradient connecting each target pressure. In this way, the hydraulic pressure is reduced almost continuously during the pressure holding stage, and there is no sudden difference between the pressure inside the cavity and the backflow or re-inflow of the resin. obtain.

Problems to be Solved by the Invention However, the actual molding conditions, such as the temperature and viscosity of the resin or the temperature of the mold, are not always constant, and it is difficult to control the hydraulic pressure to achieve the target pressure set before injection. Even if the resin is used, the pressure difference between the resin and the resin in the cavity may become large, and there is a risk that backflow or re-inflow may occur.

An object of the present invention is to provide an injection molding machine that can reduce the hydraulic pressure of a hydraulic unit in accordance with the actual pressure inside the cavity during the pressure holding stage.

Means for Solving the Problems In order to solve the above problems, the present invention includes the above-mentioned (a) mold, Q) resin injection unit), (C) hydraulic unit, and (d) hydraulic unit control device. In the injection molding machine, the mold is provided with a pressure detector that detects the pressure inside the cavity, and the hydraulic unit control device is provided with a pressure detector that detects the pressure detected by the pressure detector after the pressure detected by the pressure detector decreases to meet the set conditions.
The present invention is characterized in that a follow-up pressure reducing means is provided which follows the decrease in the detected pressure and lowers the set hydraulic pressure of the hydraulic unit at a slope substantially the same as the slope of the decrease in the detected pressure.

The setting condition may be, for example, that the rate of decrease in the cavity pressure exceeds the set value, or that the pressure decreases beyond the set value when the cavity pressure decreases. .

In any case, the setting conditions are such that it is possible to detect a point slightly earlier than the point in time when the pressure inside the cavity has decreased to a certain extent and if the set hydraulic pressure of the hydraulic unit is kept constant beyond that point, gate seal failure will occur. Set. If the hydraulic unit's set hydraulic pressure is lowered to follow the cavity internal pressure after the cavity pressure has decreased until this setting condition is met, the hydraulic unit's set hydraulic pressure will not be too high or low relative to the cavity internal pressure. Height controlled. In addition, since the pressure detector detects the pressure inside the cavity, the hydraulic pressure of the hydraulic unit is controlled according to the actual state of the resin inside the cavity, and molding conditions such as resin temperature and viscosity or mold temperature are controlled. Even if the pressure changes each time, a holding force of a suitable height can be obtained, and the solidification of the resin will proceed without causing backflow or re-inflow of the resin due to destruction of the gate seal.

Effects of the Invention As described above, according to the injection molding machine of the present invention, the hydraulic pressure of the hydraulic unit during the pressure holding stage can be lowered in accordance with the pressure inside the cavity, and even if the molding conditions change for each injection, the oil pressure of the hydraulic unit can be reduced reliably. can prevent damage to the gate seal,
High quality molded products can be obtained.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a diagram schematically showing an injection molding machine which is an embodiment of the present invention, and in the figure, 10 is a mold. Mold 10
has a first mold 12 and a second mold 14 that can be opened and closed in the left and right directions in the figure, and when the molds 12 and 14 are closed, a cavity 16 having a shape corresponding to the product to be molded is formed.
form.

The resin supplied from the injection port 18 is supplied to the cavity 16 from the spool 20. Injected through runner 22 and gate 24. Further, the second mold 14 is provided with a pressure sensor 26 as a pressure detector for detecting the pressure inside the cavity 16. This pressure sensor 26 is of a crystal type and can directly measure the pressure inside the cavity 16.

A resin is injected into the cavity 16 of the mold 10 by a resin injection unit 30. Resin injection unit 30
is a cylinder 3 provided so as to be able to approach and separate from the mold 1o.
2, and a screw 34 is rotatably and slidably fitted into the cylinder 32. A hopper 36 is attached to a portion of the cylinder 32 that corresponds to the threaded part of the screw 34. When the screw 34 is rotated by a motor 38, the resin is bitten into the cylinder 32 through the hopper 36, and the resin is removed from the cylinder 32. It is sent to the front side (the mold 10 side).

The cylinder 32 is provided with a heating device (not shown), and the hopper 36
The screw 34 is designed to melt the resin that has bitten in, and as the molten resin is accumulated on the front side of the screw 34, the screw 34 retreats. A piston 42 is integrally provided at the rear of the screw 34, and forms a hydraulic cylinder 44 together with the cylinder 32. A hydraulic chamber 46 formed on the rear side of the piston 42 in the forward movement direction of the screw 34 is connected to a pump 50 via an electromagnetic flow control valve 48, and a chamber 52 provided on the other side is connected to a tank 54. The pump 50 is driven by a pump motor 56 to supply hydraulic oil to the hydraulic chamber 46, which causes the screw 34 to advance and resin to be injected into the cavity 16.
At this time, by adjusting the flow rate of the electromagnetic flow control valve 48, the forward speed of the screw 34, that is, the injection speed can be adjusted. In addition, the electromagnetic flow control valve 48 and the pump 5
A relief valve 58 is provided between the tank 54 and the tank 54 . This relief valve 58 can adjust the relief pressure by adjusting the amount of current supplied to the solenoid, and by adjusting the relief pressure, the height of the oil pressure in the hydraulic chamber 46, that is, when the screw 34 injects resin into the cavity 16. In this embodiment, the hydraulic cylinder 44. can adjust the height of the injection pressure of the hydraulic cylinder 44. Electromagnetic flow control valve 4
8. Pump 50. The tank 54, the relief valve 58, etc. constitute a hydraulic unit.

This injection molding machine is controlled by a control device 60.

The control device 60 includes a CPU 62°RO as shown in FIG.
M64. It is mainly a microcomputer that has a RAM 66 and a bus 68 that connects them.

An input interface 70 is connected to the bus 68, and the pressure sensor 26 is connected via an amplifier 72 and an A/D converter 74, and the pressure inside the cavity 16 is converted into a digital voltage value and supplied. . An output interface 78 is also connected to the bus 68, and a drive circuit 80.
．． 82, 84, 86 to the motor 38. Electromagnetic flow control valve 48. Pump motor 56. A relief valve 58 is connected. As shown in FIG. 3, the RAM 66 includes a first cavity pressure memory that stores the pressure inside the cavity 16;
A second cavity pressure memory and a flag are provided along with a working memory. Further, the ROM 64 stores routines necessary for injection molding, including a resin injection oil pressure setting routine for the hydraulic cylinder 44 in the pressure holding stage shown in the flowchart of FIG.

During molding in the injection molding machine configured as described above, first, the flow rate of the electromagnetic flow control valve 48 and the relief valve 5 are controlled.
The relief pressure 8 is set to a level that allows a predetermined injection speed and injection pressure to be obtained, and the resin is injected into the cavity 16 for a time T. This time is measured by a timer provided in the CPU 62, and after T8 time has elapsed, the supply of hydraulic oil to the hydraulic pressure chamber 46 is stopped and the relief pressure of the relief valve 48 is slightly lowered to be lower than when resin is injected. The resin is replenished into the cavity 16 by the holding force, and
A pressure holding stage control is executed to wait for the resin in the gate 24 to solidify. At this time, the actual oil pressure of the hydraulic cylinder 44 is reduced as shown in the graph of FIG. 5 according to the relief pressure of the relief valve 48 (this is the set oil pressure of the hydraulic unit) set by executing the oil pressure setting routine. .

First, step Sl (hereinafter abbreviated as Sl).

The same applies to the other steps.) The pressure (7) in the cavity 16 expressed as a voltage value is read. Next, in S2, the value of the first cavity pressure memory is transferred to the second cavity pressure memory, and the cavity pressure V7 read in S1 is stored in the first cavity pressure memory.

The cavity pressure stored in the second cavity pressure memory is the value read immediately before reading the cavity pressure stored in the first cavity pressure memory, and this value is set as V n-1
Expressed as In S3, it is determined whether the flag is ON or not, but this flag is OFF in the initial setting.
When S3 is performed for the first time, the determination is No and S4 is executed. In S4, the pressure inside the cavity is V.

A determination is made as to whether or not is equal to or greater than the reference value 71.

At the beginning of the pressure holding stage, resin is injected to compensate for the insufficient injection of resin into the cavity 16, and the pressure inside the cavity increases as shown by the solid line in FIG. 5, so it is determined whether or not this increase has occurred. is performed, but the determination is initially NO, and one execution of the program ends. Then, after the predetermined sampling time has elapsed, the s
1 is executed and the cavity pressure 7 is read.

If the cavity pressure ■7 rises and becomes equal to or higher than the set value 74, S4 becomes YES, and after the flag is turned ON in s5, the cavity pressure ■7 read this time is changed to the previously read cavity pressure in S6. A determination is made as to whether or not it has become VR-1 or lower. A determination is made as to whether or not the cavity 16 has been filled with resin without any gaps, the flow of resin has stopped, and the pressure inside the cavity 16 has decreased as it solidifies. If the answer is NO, one execution of the program ends.

When (7) becomes less than V, the rate of decrease in cavity pressure dV/dt is calculated at sl. In this calculation, the value obtained by subtracting ■1 from V is the sampling time t
In step S8, it is determined whether the rate of decline is equal to or greater than the set value of 60. Immediately after the pressure starts to decrease, the rate of decrease is small and S8 becomes NO. However, as the solidification of the resin progresses and the pressure decreases significantly and the rate of decrease reaches the set value of 60 or more, S9 is executed and the relief valve 58 is closed. The relief pressure is lowered to follow the cavity internal pressure V7. The set value ΔD is set slightly earlier than the rate of decline at which gate seal failure would occur, so that it is possible to detect a point that is slightly earlier than the point at which gate seal failure would occur if the relief pressure was kept constant. It is set to a small value, and as the relief pressure decreases, the hydraulic cylinder 44
The oil pressure decreases at the same rate of decrease as the cavity pressure. As a result, the pressure in the runner 22 is kept slightly higher than the pressure in the cavity 16 and is lowered, and the pressure in the vicinity of the gate 24 between the cavity 16 and the runner 22 is kept approximately equal, which prevents failure of the gate seal. The solidification of the resin progresses without any problems.

When the cavity internal pressure v7 becomes equal to or lower than the set value vl, it is determined that the resin near the gate 24 has completely solidified and no backflow of resin will occur even if no pressure is applied by the hydraulic cylinder 44, and the application of pressure is stopped. It will be canceled. That is, the relief pressure of the relief valve 5 is set to 0 at Sll, and the hydraulic oil in the hydraulic chamber 46 is allowed to return to the tank 54. In Sll, the flag is also set to O.
It becomes FF and execution of the program ends.

As is clear from the above explanation, in this example,
The part that stores S1 to Sll of the ROM64 and the CP
The portions of U62 and RAM66 that execute these steps constitute follow-up pressure reduction means.

This embodiment is literally an illustration, and the present invention can be implemented with various modifications and improvements based on the knowledge of those skilled in the art without departing from the scope of the claims.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an injection molding machine according to an embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of a control device for the injection molding machine. FIG. 3 is a block diagram showing the configuration of a RAM of a computer that constitutes the main body of the control device. FIG. 4 is a flowchart showing the oil pressure setting routine stored in the ROM of the computer. FIG. 5 is a graph showing changes in the pressure in the cavity and the pressure in the hydraulic unit during molding with the injection molding machine. lO: Mold 16: Cavity 26: Pressure sensor 30: Resin injection unit 44: Hydraulic cylinder 48: Electromagnetic flow control valve 50: Bump 54
:tank

Claims (1)

[Scope of Claims] A mold having a cavity having a shape corresponding to a product to be molded; a resin injection unit for injecting resin into the cavity of the mold; and a resin injection unit that is hydraulically actuated to In an injection molding machine, the injection molding machine includes a hydraulic unit that injects water into the cavity at a predetermined pressure, and a hydraulic unit control device that controls the hydraulic pressure of the hydraulic unit. At the same time, the hydraulic unit control device is configured to control the hydraulic unit to follow the decrease in the detected pressure after the detected pressure of the pressure detector has decreased until it satisfies the set condition, and to control the hydraulic unit at a gradient substantially the same as the decreasing gradient of the detected pressure. An injection molding machine characterized by being provided with follow-up pressure reducing means for lowering the set oil pressure.