JPS6146293B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In injection molding, it is extremely important to prevent sink marks, flow marks, and silver streaks from occurring in molded products in order to maintain the quality of the molded products. Furthermore, in the field of industrial plastic molded products, dimensional accuracy of molded products is increasingly required. To date, many molding factor control devices have been developed for injection molding of high quality and precise dimensions.

The present invention relates to a control device for an injection molding machine, and is an invention of a new control means that has recently been used to control the pressure of molten resin in a mold according to a certain reference pattern. The feature is that the electromagnetic relief valve that controls the injection hydraulic pressure is set to the highest pressure for a certain period of time at the beginning of injecting the molten resin into the mold cavity.In other words, the injection hydraulic pressure remains unchanged until the mold cavity is filled with the molten resin. The pressure is set below the maximum pressure so that it can freely fluctuate, and when the mold cavity begins to be filled with molten resin, that time is detected, and the set pressure of the electromagnetic relief valve is released from the maximum pressure and returns to the standard pattern of molten resin pressure. The control device is adapted to control the pressure of molten resin along the same line. Furthermore, the novelty of the present invention is that the timing at which the molten resin gate-seals the mold is determined by minute changes in the molten resin pressure P with respect to the time T.
The purpose is to detect by DP/DT.

Next, the present invention will be explained according to the drawings.

1 is a heating cylinder, 2 is a screw that rotates and reciprocates within the heating cylinder 1, 3 is a hopper, 4 is an injection cylinder, 5 is a piston, 6 is a mold, and 6a is a mold cavity. 7 is an electromagnetically operated flow control valve (including a servo control valve), 9 is a pump, 10 is a level shift,
11 is a current amplifier, 12 is an arithmetic unit, 13 is an integrator, and 14 is a cavity pressure holding gradient setter. 15 is a function generator. The function generator 15
As shown in Figure 2, resistor r ₁ is connected in series with a circuit in which resistor r ₂ and capacitor c are connected in parallel.
A rectangular input waveform is incompletely integrated to generate a reference pattern signal that approximates a curve of change in molten resin pressure over time in a mold cavity. 16 is an injection speed program setting device, 17 is a cavity pressure setting device, 18 is a differentiator, 19 is a comparator, 20 is an output circuit, 21 is a differentiator, 22 is a comparator, 23 is an output circuit, 24 is a comparator, 25 is an output circuit, 26
and 27 are timers. 28 is a sensor that measures the resin pressure within the mold cavity.

FIG. 3 shows a reference pattern of changes in resin pressure within the mold cavity over time.

Next, the functions and operations of the control device of the present invention will be explained.

First, prior to molding, a molded product is tested and the level shift 10 is set. The level shift 10 is set to be higher than the molten resin pressure that occurs during the initial period when the molten resin is injected into the mold cavity. In FIG. 3, the pressure is P1. The screw 2 rotates to plasticize a certain amount of raw material, the molded product is taken out of the mold, the mold is closed, and injection begins, the switch 29 is turned on and the control circuit is activated. As the screw 2 moves forward within the heating cylinder 1, the molten resin at the tip of the screw flows into the cavity through the gate of the mold. At this time, the cavity is not filled with molten resin, so the molten resin reaches the sensor 28.
It is almost undetectable by the pressure p ₁
Since the input/output signal voltage of the sensor 28 is lower than the reference voltage of the sensor 28, the feedback function of the amplifier 11 outputs the maximum gain to make the signal voltage match the reference voltage, and the set pressure of the electromagnetic relief valve 8 is set to the maximum pressure. Therefore, the injection speed of the flow of the molten resin can be precisely controlled by the electromagnetic flow control valve 7 rather than by pressure control. As molten resin fills the mold cavity, resin pressure begins to rise.

If the switch 30 is switched to the a contact, the differentiator 18 will operate and the resin pressure P will rise rapidly at a point T1.
At this point, a predetermined value of DP/DT is detected, and this signal is transmitted to the comparator 19, and if the signal exceeds the set value, relay R1 is activated. Also, switch 30
If it is switched to the contact point, the signal of the molten resin pressure is directly transmitted to the comparator 19 and activates the relay R1. In the present invention, the mold cavity filling time of the molten resin pressure can be detected by the differentiator 18 or by a predetermined value of the resin pressure.
When the relay R1 is activated, the function generator 15 is activated, and the function generator 15 sets the reference pattern of the rise curve of the molten resin, that is, the curve AB in FIG. 3, according to the time constant curve of integration. The sensor 28 detects the resin pressure in the mold cavity and transmits the detected voltage to the amplifier 11, which compares the voltage with a reference signal generated by the function generator 15 according to the curve AB, and eliminates the difference between the two. Signal to electromagnetic relief valve 8
tell to.

The reason for setting the curve AB shown in Fig. 3 as the reference pattern in the present invention is that if the pressure is increased rapidly to the maximum value of the molten resin pressure, pressure overrun will occur and the dimensional accuracy of the molded product will be affected. Since this would have a negative effect, the molten resin pressure was gradually increased. When the molten resin pressure reaches the cavity pressure set in the cavity pressure setting device 17, the comparator 24 compares the signal from the pressure setting device 17 with the signal from the sensor 28, and the determined signal activates the relay _R2 , which starts the molding machine. Starts the injection holding time timer. At the same time, the timer 26 in this device starts measuring time, and during this time the molten resin pressure changes to the reference pattern BC.
controlled along the lines. When the timer 26 completes timing, the relay R0 is activated and the cavity internal pressure decreases along the reference pattern CD. Depending on the molded product, the CD section may be raised.

The reference pattern CD is performed by operating the cavity pressure holding gradient setter 14 and the integrator 13. On the other hand, the pressure of the molten resin is detected by the sensor 28, and when the gate of the mold is sealed by cooling, the resin pressure drops rapidly. At the inflection point of the resin pressure that occurs at this time, a pulse signal is detected by double differentiation by the differentiator 18 and the differentiator 21. The detected signal is transmitted to the comparator 22 and R3 is activated through the output circuit 23 to complete the injection. timer 27
This prevents the differentiator from detecting the inflection point C at the inflection point C shown in FIG. 3 before gate sealing and completing the injection process.

As described above, the effect of the present invention is that the molten resin pressure is controlled according to the reference pattern by the control device of the present invention, and the quality of the molded product is made constant.

[Brief explanation of the drawing]

FIG. 1 is a block diagram explaining the present invention, FIG. 2 is an electric circuit of the present invention, and FIG. 3 is a reference pattern of molten resin pressure with respect to time.

Claims (1)

[Claims] 1. An electromagnetic relief valve 8 that controls the pressure in the cylinder chamber, an electromagnetic flow control valve 7 that controls the injection speed, and molten resin in the mold are connected to a pipe line that communicates the hydraulic pump and the cylinder chamber that advances the piston of the injection cylinder. In a circuit provided with a resin pressure detection sensor 28 for detecting pressure, an amplifier 11 with a feedback function for setting the pressure of the electromagnetic relief valve 8 is provided, and a level shift 10 and a short circuit are provided as a reference pattern setting device for pressure control. A function generator 15 for incompletely integrating a shape input waveform to generate a reference pattern curve, a pressure holding gradient setting device 14 arranged in series with a cavity pressure setting device 17 and an integrator 13 are provided, and each of these reference pattern setting devices The amplifier 11 compares the output from the resin pressure detection sensor 28 with the output from the resin pressure detection sensor 28, operates the electromagnetic relief valve 8 through feedback control, and generates a signal based on the reference pattern set in the level shift 10 at the initial stage of injection. An injection pressure control device for an injection molding machine, in which the pressure of an electromagnetic relief valve is set to the maximum setting pressure based on the difference in detection signals of the resin pressure sensor 28, and the injection speed is controlled only by the control valve.