JP2636450B2 - Injection molding machine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding machine, and more particularly to control of a holding pressure in a holding pressure stage after filling a cavity with a resin.

2. Related Art An injection molding machine is generally configured to include (a) a mold, (b) a resin injection unit, (c) a hydraulic unit, and (d) a hydraulic unit control device. The mold has a cavity having a shape corresponding to a 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 a hydraulic unit, and injects resin into the cavity at a predetermined pressure. The hydraulic pressure of the hydraulic unit is controlled by a hydraulic unit control device. Molding in such an injection molding machine compensates for the volumetric shrinkage caused by the resin in the cavity by injecting the resin into the cavity and cooling and solidifying the resin in the cavity. Alternatively, it can be divided into a pressure-holding stage in which reflow does not occur and a cooling stage in which the resin in the cavity is further cooled and solidified until it can be taken out of the mold. The set hydraulic pressure of the hydraulic unit in each stage is different, and is set to a height at which resin is injected into the cavity at a predetermined pressure in the resin injection stage, a lower height in the pressure holding stage, and a lower height in the cooling stage. There is no need to apply pressure to and is set to zero.

As described above, the height of the set hydraulic pressure of the hydraulic unit is different at each stage, but the height of the set hydraulic pressure is constant at the resin injection stage and does not cause any trouble. As described on page 157 of the Nikkan Kogyo Shimbun, the fixed hydraulic pressure is constant, the resin in the resin injection unit side decreases as the cavity pressure decreases as the resin solidifies. There is a possibility that the difference between the pressure and the pressure becomes excessive, and the gate seal is broken to cause re-inflow. For this reason, in the injection molding machine described in Japanese Patent Application Laid-Open No. Sho 60-32621, when the set hydraulic pressure of the hydraulic unit is switched between large and small in the pressure-holding stage and the set hydraulic pressure is reduced halfway, re-inflow may occur. There is no such thing. However, at the time of switching, the pressure on the resin injection unit side suddenly drops, becomes too small relative to the pressure in the cavity, and there is a possibility that the resin may flow backward.

On the other hand, in the injection molding machine described in Japanese Patent Application Laid-Open No. Sho 62-174126, the time after the completion of resin injection into the cavity is divided into a plurality of times, and a target pressure at the elapse of the time is set for each divided time. The control is performed such that the set hydraulic pressure of the hydraulic unit decreases according to the gradient connecting the respective target pressures. In this way, the oil pressure is reduced almost continuously during the pressure-holding stage, so that there is no sharp difference between the pressure and the pressure in the cavity. 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 the hydraulic pressure is controlled so that the target pressure is set before injection. Even in such a case, the pressure difference between the resin in the cavity and the resin in the cavity may increase, and there is a possibility that a backflow or a re-flow may occur.

An object of the present invention is to provide an injection molding machine capable of reducing the oil pressure of a hydraulic unit in accordance with the actual pressure in a cavity in a pressure holding stage.

Means for Solving the Problems In order to solve the above problems, the present invention provides the above (a)
In an injection molding machine including a mold, (b) a resin injection unit, (c) a hydraulic unit, and (d) a hydraulic unit control device, a mold is provided with a pressure detector for detecting a pressure in the cavity, and a hydraulic unit is provided. After the resin is injected into the cavity, the set pressure of the hydraulic unit is kept almost constant after the resin is injected into the cavity. A follow-up pressure reducing means is provided for reducing the set hydraulic pressure of the hydraulic unit with a gradient substantially the same as the gradient of the decrease in the detected pressure.

In addition, as the setting conditions, for example, a decrease rate of the pressure in the cavity that exceeds the set value and increases, or that when the pressure in the cavity decreases and the pressure decreases below the set value when the pressure in the cavity decreases, can be adopted. .

In any case, the setting conditions are such that the pressure in the cavity is reduced to some extent, and if the set oil pressure of the hydraulic unit is kept constant any more, it is possible to catch a point slightly earlier than the point at which gate seal destruction will occur. Set. In the dwelling stage, if the pressure in the cavity decreases due to the solidification of the resin injected into the cavity, the pressure difference between the pressure in the cavity and the pressure of the hydraulic unit becomes excessive. Therefore, if the set oil pressure of the hydraulic unit is reduced by following the pressure in the cavity after the pressure in the cavity decreases until the set conditions are satisfied, the set oil pressure of the hydraulic unit is too high or too low with respect to the pressure in the cavity. If not controlled to a height. In addition, since the pressure detector detects the pressure in the cavity, the hydraulic pressure of the hydraulic unit is controlled according to the actual state of the resin in the cavity, and molding conditions such as the temperature and viscosity of the resin and the mold temperature are controlled. Even if it changes every time, a suitable holding pressure is obtained,
The solidification of the resin proceeds without the backflow or re-inflow of the resin due to the destruction of the gate seal.

As described above, according to the injection molding machine of the present invention, the hydraulic pressure of the hydraulic unit in the pressure holding stage can be reduced in accordance with the pressure in the cavity, and even if the molding conditions change for each injection, Therefore, the gate seal can be prevented from being broken, and a high quality molded product can be obtained.

Examples Hereinafter, examples of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a view schematically showing an injection molding machine according to one embodiment of the present invention, in which 10 is a mold. The mold 10 is a first mold 12 and a second mold that can be opened and closed in the horizontal direction in the figure.
The molds 12 and 14 are closed to form a cavity 16 having a shape corresponding to the product to be molded.
The resin supplied from the injection port 18 is injected into the cavity 16 through the spool 20, the runner 22, and the gate 24.
Further, the second mold 14 is provided with a pressure sensor 26 as a pressure detector for detecting the pressure in the cavity 16. The pressure sensor 26 is of a quartz type, and can directly measure the pressure in the cavity 16.

The cavity 16 of the mold 10 has a resin injection unit 30
The resin is injected. The resin injection unit 30 has a cylinder 32 provided to be able to approach and separate from the mold 10,
A screw 34 is rotatably and slidably fitted in the cylinder 32. A hopper 36 is attached to a portion of the cylinder 32 corresponding to the screw portion of the screw 34, and when the screw 34 is rotated by a motor 38, the resin is cut into the cylinder 32 from the hopper 36 and the front side of the cylinder 32. (Mold
10). A heating device (not shown) is provided in the cylinder 32 so as to melt the resin bitten from the hopper 36, and the screw 34 retreats as the molten resin is stored in front of the screw 34. A piston 42 is integrally provided at a rear portion of the screw 34, and constitutes a hydraulic cylinder 44 together with the cylinder 32. A hydraulic chamber 46 formed behind the piston 42 in the forward 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,
As a result, the screw 34 is advanced and the resin is injected into the cavity 16. At this time, the electromagnetic flow control valve
By adjusting the flow rate of 48, the forward speed of the screw 34,
That is, the injection speed can be adjusted. A relief valve 58 is provided between the electromagnetic flow control valve 48 and the pump 50, and is connected to the tank 54. The relief valve 58 is capable of adjusting the relief pressure by adjusting the amount of current supplied to the solenoid, and is capable of adjusting the relief pressure by adjusting the relief pressure.
The height of the oil pressure, that is, the screw 34 cavities the resin
The height of the injection pressure when injecting into 16 can be adjusted. In the present embodiment, the hydraulic cylinder 44, the electromagnetic flow control valve 48, the pump 50, the tank 54, the relief valve 58 and the like constitute a hydraulic unit.

The injection molding machine is controlled by the control device 60. The control device 60 is mainly composed of a microcomputer having a CPU 62, a ROM 64, a RAM 66 and a bus 68 for connecting them, as shown in FIG. An input interface 70 is connected to the bus 68, and the pressure sensor 26 is connected to the amplifier 72 and the A / A
It is connected via a D converter 74, and the pressure in the cavity 16 is converted into a digital voltage value and supplied. bus
An output interface 78 is connected to 68, and a motor 38, an electromagnetic flow control valve 48, a pump motor 56, and a relief valve 58 are connected via drive circuits 80, 82, 84, and 86. As shown in FIG. 3, the RAM 66 is provided with a first cavity pressure memory, a second cavity pressure memory, and a flag for storing the pressure in the cavity 16, together with a working memory. The ROM 64 stores routines required for injection molding, including a routine for setting the resin injection oil pressure of the hydraulic cylinder 44 in the pressure holding stage shown in the flowchart of FIG.

At the time of 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 58
Relief pressure of is set to a size of a predetermined injection speed and injection pressure is obtained, the resin is injected T ₁ times the cavity 16. This time measured by the timer provided in the CPU 62, after time T ₁ has elapsed, the relief pressure of the relief valve 48 is slightly reduced the supply of hydraulic oil to the hydraulic chamber 46 is stopped, from the time the resin injection The resin is refilled into the cavity 16 with a low holding pressure, and the control of the holding pressure stage of waiting for the resin in the gate 24 to solidify is performed. At this time, the actual oil pressure of the hydraulic cylinder 44 is reduced as shown in the graph of FIG. 5 in accordance with the relief pressure of the relief valve 48 set by the execution of the oil pressure setting routine (this is the set oil pressure of the hydraulic unit). .

First, step S1 is pressure V _n in the cavity 16, represented by a voltage value is read (hereinafter, also the same. For. Other steps to be abbreviated as S1) in. Then, the value of the first cavity pressure memory in S2 along with transferred into the second cavity pressure memory, the cavity pressure V _n read in S1 is stored in the first cavity pressure memory. The cavity pressure stored in the second cavity pressure memory is a value read immediately before reading the cavity pressure stored in the first cavity pressure memory, and is represented by V _n-1 . In S3, it is determined whether the flag is ON or not,
This flag is OFF in the initial setting, and when S3 is performed for the first time, the determination is NO and S4 is executed. Cavity pressure V _n In step S4 it is judged whether or not more than the reference value V _A is performed. In the initial stage of the pressure-holding stage, resin injection for compensating for insufficient resin injection into the cavity 16 is performed, and the pressure in the cavity increases as shown by a solid line in FIG. 5, so it is determined whether or not this increase has occurred. Is initially determined to be NO, and one execution of the program ends. Then, after elapse of a predetermined sampling time t, S1 is executed again, and the cavity pressure V _n
Is read.

If the set value or more V _A cavity pressure V _n is increased
After S4 becomes YES and the flag is turned on in S5, S6
This loaded cavity pressure V _n is the determination of whether it is pressure V _n-1 or less within the cavity that has been read last time is performed in. The cavity 16 is filled with the resin without any gap, and the inflow of the resin is stopped.
A determination is made as to whether or not the internal pressure has decreased, but this determination is initially NO, and one execution of the program ends.

Then, if V _n is below V _n-1, decrease rate dV / dt of the cavity pressure is calculated in S7. This calculation is
The value obtained by subtracting V _n from _n-1 is determined by dividing the sampling time t, a determination whether or not the rate of reduction set value ΔD than in S8 is performed. Immediately after turning to pressure drop, the rate of decrease is small and S8 becomes NO, but solidification of the resin progresses,
If the pressure drops significantly and the rate of decrease exceeds the set value ΔD
S9, is executed, it decreases with the relief pressure of the relief valve 58 to follow the pressure V _n cavities. The set value ΔD is slightly lower than the rate of decrease at the time when the gate seal breaks, so that the time at which the gate seal breaks occurs can be captured slightly earlier than the time at which the gate seal breaks if the relief pressure is kept constant. It is set to a small value, and the reduction rate of the hydraulic pressure of the hydraulic cylinder 44 decreases as the relief pressure decreases, which is the same as the reduction rate of the pressure in the cavity. Thereby runner 22
Is maintained at a slightly higher level than the pressure in the cavity 16, and the pressure in the vicinity of the gate 24 between the cavity 16 and the runner 22 is maintained substantially equal, so that the resin solidifies without destruction of the gate seal. Progresses.

Once cavity pressure V _n is below the set value V _B, the gate
It is determined that the resin in the vicinity of 24 has completely solidified and no backflow of resin has occurred even if pressure is not applied by the hydraulic cylinder 44, and the application of pressure is released. That is, S11
The relief pressure of the relief valve 58 is reduced to 0,
The hydraulic oil in 46 is allowed to return to the tank 54. In S11, the flag is turned off, and the execution of the program ends.

As is clear from the above description, in the present embodiment, the portion of the ROM 64 that stores S1 to S11 and the portion of the CPU 62 and the RAM 66 that execute those steps constitute the following pressure reducing means.

This embodiment is merely an example, and various modifications and alterations can be made based on the knowledge of those skilled in the art without departing from the scope of the claims.
The invention can be carried out in an improved manner.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an injection molding machine according to one embodiment of the present invention. FIG. 2 is a block diagram showing a configuration of a control device of the injection molding machine. FIG. 3 is a block diagram showing a configuration of a RAM of a computer which is a main component of the control device. FIG. 4 is a flowchart showing a hydraulic 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 of the hydraulic unit during molding of the injection molding machine. 10: Mold, 16: Cavity 26: Pressure sensor, 30: Resin injection unit 44: Hydraulic cylinder, 48: Electromagnetic flow control valve 50: Pump, 54: Tank 58: Relief valve, 60: Control device

Claims (1)

(57) [Claims] 1. A mold having a cavity having a shape corresponding to a product to be molded, a resin injecting unit for injecting a resin into the cavity of the mold, and operating the resin injecting unit by hydraulic pressure to remove the resin. In an injection molding machine including a hydraulic unit for injecting into the cavity with a predetermined pressure, and a hydraulic unit control device for controlling a hydraulic pressure of the hydraulic unit, a pressure detector for detecting a pressure in the cavity is provided in the mold. Along with the hydraulic unit control device, after injecting the resin into the cavity, in a state where the set hydraulic pressure of the hydraulic unit is kept substantially constant, after the detection pressure of the pressure detector decreases until the set condition is satisfied. Following the decrease in the detected pressure, the set hydraulic pressure of the hydraulic unit is decreased at a gradient substantially the same as the gradient of the decrease in the detected pressure. Injection molding machine, characterized in that a follow-up pressure reducing means.