JPS6365010B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an injection control method for an injection molding machine.

Among the steps in one molding cycle of an injection molding machine, the injection step of filling a mold with molten resin is an extremely important step that affects the quality of the molded product.

Furthermore, various injection process program control devices have been put into practical use for the purpose of improving the quality of molded products and eliminating defects.

The present invention is an injection molding machine that incorporates a proportional electromagnetic flow control valve and a proportional electromagnetic pressure control valve in a hydraulic circuit and is equipped with a device for detecting the position of an injection screw or an injection plunger, in which the injection stroke is divided into several parts. The injection process program control allows the speed or pressure of the injection screw or injection plunger to be set, and the speed or pressure to be electrically switched as the injection progresses, and the dividing position to be set arbitrarily. It is related.

The injection process includes a filling process from the start of injection until the mold is almost filled with resin, a compression process to compress the resin filled in the mold, and a refilling process to compensate for the shrinkage of the compressed and filled molten resin due to cooling. Alternatively, the process can be divided into pressure holding processes to prevent backflow of resin in the product section.

Conventionally, even if it was attempted to accurately divide and control each of these processes using an injection process program control device, it was extremely difficult due to the behavior of the resin and the response delay of the control device, so it was difficult to control speed, pressure, etc. in the control device. Conveniently consider changes as branching points in the process,
Settings such as speed, pressure, control division positions, timer time, etc. were determined through repeated trial and error, and the process was divided into a filling process, a compression process, and a pressure holding process. In particular, when switching from the injection speed control area to the injection pressure control area, rapid changes occur in the speed of the injection screw or the injection plunger, and in the injection cylinder hydraulic pressure.

The above-mentioned rapid change not only adversely affects the quality of the molded product, but also deteriorates the repeatability of the operation of the injection process, making it difficult to produce molded products of constant quality.

The injection process is a series of continuous processes, and it is originally extremely difficult to find the dividing points for each process, so from a control perspective, it is necessary to uniformly divide and control them as speed control areas or pressure control areas. However, this causes the above-mentioned drawbacks.

In order to facilitate understanding of the method of the present invention, an example of a conventional method will be explained with reference to FIG. This figure shows the operation of the screw in the injection process in terms of the relationship among the screw position, time, speed command value, actual speed, pressure command value, and actual hydraulic pressure.

The horizontal axis in the figure represents the position of the screw from _s0 to _s4 on the left side of X-X', and time from _s4 to K on the right side of X-X'. The vertical axis is the injection speed command value (set value)
Vi (i = 1, 2, 3, 4) and actual injection speed (screw speed) Va injection cylinder hydraulic pressure command value (set value) Pi (i = 1, 2, 3, 4) and actual hydraulic pressure
It is Pa. Also, the curve leading to s ₀ -A-B-C-D-E-F shows the injection screw speed (injection speed), and the curve leading to s ₀ -G-H-I-J-K shows the speed inside the injection cylinder. It indicates hydraulic pressure.

The screw, which was at the _s0 position at the start of injection, starts moving under the control of the set value of the speed _V1 at the same time as the start of injection.

When the screw reaches the s ₁ position, the speed command value is V ₂
Thus, the speed becomes the second stage, and at the _s2 position, the speed command value becomes _V3 , which becomes the third stage speed, and at the _s3 position, the speed command value becomes _V4 , which becomes the fourth stage speed. _V4
The speed of the _V3 makes it more decelerating. On the other hand, the injection cylinder hydraulic pressure fluctuates depending on the balance with the load and remains below the set pressure (command value P ₁ ), and immediately drops after passing the _s3 point because the speed set value becomes low. As the s ₄ point approaches, the pressure increases again, and when the resin filling rate in the mold approaches 100%, the hydraulic pressure increases rapidly, and at the s ₄ point, the pressure command value becomes P ₂
The injection stroke shifts from the speed control region to the pressure control region. s After the screw reaches point ₄ , when the previously set time T ₁ has elapsed, the injection pressure set value becomes the set value P ₃ , and when the previously set time T ₂ has elapsed, the injection pressure setting value changes to P ₄ . The setting value is
Controlled by the pressure, the injection process is completed and the injection pressure is released by the injection process end signal.

As mentioned above, in the conventional injection control method, the filling process is performed by speed control, and the compression process and pressure holding process are performed by pressure control of the injection cylinder hydraulic pressure. In this way, if the compression process was changed by switching from the speed control process (filling process) to the pressure control process without directly controlling the compression process, the injection speed just before the filling was completed would be reduced in order to improve the switching accuracy. Even if the screw detection position accuracy is improved, the inertial energy of the injection screw, injection ram, and fluidized resin at the time of filling completion (s ₄ points) cannot be ignored. Immediately after, the hydraulic pressure must be reduced rapidly.

This means that the compression process is controlled in a transient state by switching from speed control to pressure control, which results in a lack of control stability considering the characteristics of the control device as a whole. Further, the repeatability of control of the flow control valve for speed control becomes extremely poor when the flow rate is less than 5% of the rated flow rate, so in order to achieve stable molding, the speed immediately before the completion of filling cannot be set below a certain level.

On the other hand, there are some products, such as thin molded products, in which the injection speed cannot be lowered at the end of the filling process, and in this case, it is not possible to reduce the speed and improve switching accuracy.

The present invention was devised in order to eliminate the drawbacks of the conventional methods as described above, and the problems that arise when the steps are conveniently divided in the transition to the filling step, compression step, and pressure holding step. It is an object of the present invention to provide a new injection control method that can suppress the above-mentioned rapid changes before and after the dividing point of each process and easily mold a molded product of constant quality.

In the injection process of the present invention, the filling process is controlled by injection screw or injection plunger speed (hereinafter referred to as speed) control, the switching point from the filling process to the compression process is performed by the position of the injection screw or injection plunger, and the speed of the compression process is controlled by controlling the injection screw or injection plunger speed. The set value of is desirably lower than the final speed of the filling process, and the set value of the hydraulic pressure inside the injection cylinder (hereinafter referred to as pressure) should be set to a value that approximately matches the pressure at the end of the compression process, and the upper limit of the speed and pressure should be set. The floating control region in which the transition from speed control to pressure control is determined based on the balance with the load is defined as the compression process, and the switching point from the compression process to the pressure holding process is determined by the position of the injection screw or injection plunger. The pressure holding step is carried out by pressure control.

Next, one embodiment of the present invention will be described with reference to FIGS. 2 and 3. The device used was one in which the speed and pressure could be set in four stages using an electromagnetic proportional flow control valve and an electromagnetic proportional pressure control valve. In addition, the same coordinates as in FIG. 1 are used in FIG. 3 to facilitate comparison with the conventional example.

1 is a heating cylinder of the injection molding machine, and 3 is an injection screw (hereinafter referred to as screw), which is connected to an injection ram 5 and is advanced by the pressure oil of the injection cylinder 4, and is driven by an oil motor 6 through a spline shaft. It can rotate. Pressure oil acting on the injection cylinder 4 is controlled by an electromagnetic proportional flow control valve 9 provided in the hydraulic circuit.
The flow rate is adjusted by. The control valve 9 is adapted to adjust its valve opening depending on the magnitude of an electric signal such as a current. Reference numeral 8 denotes an electromagnetic proportional pressure control valve which controls the maximum value of the hydraulic circuit pressure based on the magnitude of electric signals such as current. Reference numeral 10 denotes an electromagnetic switching valve that connects the hydraulic power source 11 to the injection cylinder 4 by an electric signal.

A position detector 7 is composed of an encoder or a potentiometer, and is synchronized with the movement of the screw 3 by means of a rack and pinion.

Reference numeral 12 denotes a position signal processing circuit section which processes the electric signal from the detector 7 into a position signal and generates a screw position signal. A comparison calculation section 13 compares the screw position signal with the set values of the position setters 14, 15, 16, and 17, and generates a timing command signal to the flow rate command section 18 and the timing signal generation section 30.
The timing signal generator 30 includes a timer function that can set the time using the time setter 23.
Based on the signal from the comparison calculation unit 13, the pressure command unit 2
4, generate a timing signal.

Reference numeral 18 denotes a flow rate command section, which controls speed setting devices 19, 20, 2 according to the timing signal from the comparison calculation section 13.
1 or 22, and outputs the set value signal of the speed setting device as a voltage signal to the amplifier 29, and the voltage signal is converted into a control signal of the control valve 9 by the amplifier 29. is converted into a current signal and operates the control valve 9.

24 is a pressure command section, which selects one of the pressure setting devices 25, 26, 27, and 28 according to the timing signal from the timing signal generation section 30, and transmits the setting value signal of the pressure setting device to the amplifier. 29'
The amplifier 29' converts the voltage signal into a current signal to operate the control valve 8.

Next, the control method will be explained. At the beginning of the injection stroke, the screw is in the s ₀ position. The electromagnetic switching valve 10 is operated by an injection signal from an injection molding machine control device (not shown), and the speed is set to V ₁ by the speed setting device 19 in response to signals from the comparison calculation section 13 and the timing signal generation section 30. The pressure is set to P ₁ by the container 25 and injection is started. As the screw 3 moves, the position detector 7 constantly detects its position or the amount of movement, and the position signal processing circuit 1
2, the position signal is sent to the comparison calculation section 13. When the screw 3 reaches the set value _s1 position of the position setter 14, a timing signal is issued from the comparison calculation unit 13, the flow rate command unit 18 selects the speed setter 20, and the set value of the speed becomes _V2 . Furthermore, Sukuriyu 3
moves forward and reaches the set value _s2 position of the position setter 15, a timing signal is issued from the comparison calculation section 13, and the flow rate command section 18 selects the speed setter 21, and the speed set value becomes _V3 . When the screw 3 moves further forward and reaches the set value _s3 of the position setter 16, the comparison calculation unit 13
A timing signal is issued from the flow rate command section 18, and the speed setting device 21 is selected, and the speed setting value becomes _V4.In response to the timing signal from the comparison calculation section 13, the timing signal generation section 30 generates a pressure change timing signal. , the pressure command section 24 selects the pressure setting device 26, and the pressure setting value is switched from P ₁ to P ₂ .

Further, the screw 3 moves forward and when it reaches the _s4 position, which is the setting value of the position setting device 17, the comparison calculation unit 1
A timing signal is issued from the timing signal generating section 30, and the pressure command section 24 selects the pressure setting device 27 based on the pressure change timing signal from the timing signal generating section 30, and the pressure setting value is switched from _P2 to _P3 . On the other hand, the timing signal generator 30 starts measuring time when the screw 3 reaches the _s4 position. When the set time T ₁ hour of the time setting device 23 has elapsed, the timing signal generation section 30 generates a pressure change timing signal, and based on this signal, the pressure command section 24 selects the pressure setting device 28, and the pressure setting value is changed from P ₃ . Switch to P ₄ . The pressure and speed commands are canceled by the injection completion signal from the injection molding machine control device (not shown), and the electromagnetic switching valve 1
The injection process ends when 0 turns OFF.
As mentioned above, in the injection process control method of the present invention, the filling process is performed by speed control while the screw 3 moves from the injection start position s0 to _s3 , and the molten resin enters the mold cavity at _{the s3 position} . The setting value V 4 set in the speed setting device 17 and the setting value P ₂ set in the pressure setting device 20 are set so that the screw 3 is almost filled and the screw 3 is in the s ₃ to s ₄ position, that is, in the compression process period _. And preferably, the set value of V ₄ is lower than the set value of V ₃ , and the set value of P ₂ is slightly higher than the set value of P ₃ , so that the transition from speed control to pressure control is performed as a step-like transient. In order to prevent this from occurring, a floating control state, which is neither speed control nor pressure control, is created based on the balance with the load, and the set pressure of P ₂ and the position of the screw 3 are set at s ₄ . Therefore, the mold cavity is almost 100% filled with molten resin, the end of the compression process is controlled by the screw position, and the pressure holding process is time-controlled.

As explained above, the present invention provides the following effects by performing floating control in the compression process and controlling the end point of the compression process by the screw position.

(1) There is a smooth transition from speed control to pressure control, and the absence of transient conditions improves control stability, making it possible to produce molded products of constant quality.

(2) Since the influence of inertial energy of the screw, ram, resin, etc. can be reduced, the influence of dynamic pressure is reduced, making it easier to determine the injection amount uniquely based on the screw stroke and _P2 setting pressure, and molding conditions It becomes easier to make decisions and improves operability.

(3) Due to the characteristics of floating control, the screw speed is automatically reduced just before the end of the compression process, so the speed reduction that was previously taken to improve the response delay, which is a drawback of the control device, is not as much. This is not necessary, and the speed can be increased in some cases, so it is effective for molded products that cannot be slowed down, such as thin molded products.

(4) Since there is no need to set a low speed, the proportional solenoid flow control valve can be used repeatedly in a stable flow control range, improving control stability and making it possible to produce molded products of constant quality. Become.

(5) The control device can be manufactured at almost the same price as conventional ones.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of an injection control method using a conventional injection process program, Fig. 2 is a block diagram of a device used to implement the injection control method of the present invention, and Fig. 3 is an explanatory diagram of an injection control method of the present invention. FIG. 2 is an explanatory diagram similar to FIG. 1 shown in FIG. DESCRIPTION OF SYMBOLS 1... Heating tube, 3... Screw, 4... Injection cylinder, 5... Injection ram, 6... Oil motor, 7... Position detector, 8... Electromagnetic proportional pressure control valve, 9... Electromagnetic proportional flow control valve, 10... Electromagnetic switching valve, 11... Hydraulic power source, 12... Position signal processing circuit section, 13... Comparison calculation section, 14, 15, 16, 17,... Position setting device, 1
8... Flow rate command section, 19, 20, 21, 22... Speed setting device, 23... Time setting device, 24... Pressure command section,
25, 26, 27, 28...Pressure setting device, 29, 2
9'...Amplifier, 30...Timing signal generator.

Claims (1)

[Claims] 1 In the injection process control of an injection molding machine, the filling process changes the flow rate of the injection cylinder and controls the forward speed of the injection plunger or screw according to a preset program, and the switching point from the filling process to the compression process and the compression process are controlled by changing the flow rate of the injection cylinder. The switching point from the process to the pressure holding process is controlled by the position of the injection screw or plunger, and the injection cylinder hydraulic pressure setting value during the compression process almost matches the injection cylinder hydraulic pressure value at the end of the compression process. Control during the compression process is performed by floating control based on the balance between the speed of the injection screw or plunger, the injection cylinder hydraulic pressure setting value, and the load. During the pressure holding process, the control is performed for a preset time. 1. An injection process control method for an injection molding machine, characterized in that the hydraulic pressure inside the injection cylinder is changed and the holding pressure is controlled according to a preset program.