JPS6251417A - precision injection molding machine - Google Patents

Abstract

PURPOSE:To obtain a precision injection molder, which makes the variance in shots small by stabilizing the molding weight, which has the largest effect on the improvement of the dimensional accuracy of a molded part, by a structure wherein a mechanism to decrease the speed to stop an injection screw provided in a control oil hydraulic circuit connected to a retreating side ram in injection. CONSTITUTION:When the time point, at which the necessity of the speed reduction of a screw 2 develops, is reached during the advance of the screw under the condition that the solenoid F of a directional control valve 6 for an advancing side ram in injection is held in excitation so as to supply working fluid in an advancing side ram 5a, the solenoid X of a directional control valve 13 for a retreating side ram in injection is held in excitation. The excitation of the solenoid X causes the working fluid, which has been discharged from a retreating side ram 5b in injection through a check valve 17 to a tank 12 under the state that the direc tional control valve 13 for the retreating side ram in injection has been in its neutral position, is stopped and the working fluid, which is regulated by a flow control valve 16 and a pressure control valve 14, is supplied in the retreating side ram 5b in injection and consequently the advancing speed of the screw 2 is sharply reduced through a piston 4. The reduction of the advancing speed of the screw 2 at this time is determined by the difference between the pressure of the advancing side ram 5a in injection and that of the retreating side ram 5b in injection, both of which are bounded by the piston 4 in an injection ram 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to precision injection molding machines for ultra-precision plastic parts such as optical parts and mechanical parts, particularly molded product dimensions.

This invention relates to a precision injection molding machine suitable for improving accuracy in weight and other measurements.

[Background of the invention]

Regarding the improvement of dimensional stability in conventional injection molding, for example, i. A servo is used for the flow rate control valve of the hydraulic oil for controlling the injection advance of the screw.

ii. Feedback control means is used to control the pressure control valve and flow rate control valve by feeding back the injection oil pressure and cavity internal pressure.

iii. A program control means is used in which the speed and pressure at which the screw advances are programmed in advance and the screw is operated according to the set values.

and so on.

It is a well-known fact that these methods greatly improve the dimensional accuracy of molded products and the accuracy of shot-to-shot quality variations when compared to open-loop control using conventional solenoid valves. For example, special public relations
Publication No. 060 and Plastic VoL 34. Nn
9, pages 17 to 21, "Kronfner Injection Molding Machine and Ultra-Precision Injection Molding Technology", an example of which is as shown in FIG. and connect the injection forward side ram 5a of the injection ram 3 to a hydraulic circuit formed by the direction control valve 6, pressure control valve 7, check valve 8, flow rate control valve 9, pump 10, motor 11 and tank 12. , the injection retreating side ram 5b is connected to the tank 12, and the hydraulic oil whose flow rate and pressure are adjusted by the flow rate control valve 9 and the pressure control valve 7 is transferred to the injection forward side by keeping the solenoid F of the direction control valve 6 energized. When the hydraulic oil is supplied into the ram 5a and at the same time the hydraulic oil in the injection backward ram 5b is discharged to the tank 12, the pressure of the hydraulic oil in the injection forward side ram 5a moves the screw 2 forward via the piston 4. The molten resin collected at the tip fills the cavity of the mold 1.

Therefore, in the above injection method, the acceleration of the screw 2,
It has a feature that deceleration can be controlled by the amount of hydraulic oil supplied or discharged only by the injection forward side ram 5a.

However, in the above injection method, as the injection speed increases, the kinetic energy value possessed by the screw 2 itself becomes relatively large, but no consideration is given to this. Therefore, as the injection speed increases, even if the amount of hydraulic oil supplied to the forward injection ram 5a is reduced or completely cut off, the screw 2 continues to move forward.

Due to this phenomenon, when switching the pressure from the primary injection to the secondary injection or from the secondary injection to the tertiary injection, a deviation occurs from the preset position or the forward stop position of the screw 2 deviates, resulting in melting. The amount of resin filled into the cavity of the mold 1 changes, causing large variations in the dimensions, weight, etc. of the molded product.

On the other hand, in the past, for example, Japanese Patent Publication No. 52-43869, which takes into consideration the relaxation of the rotational inertia force of the screw in order to slightly improve the measurement accuracy, exists.

[Purpose of the invention]

The present invention solves the above-mentioned conventional problems and provides a precision injection molding machine that can stabilize the molding weight and reduce the variation between shots, which is the most effective contributing factor to improving the dimensional accuracy of molded products. .

[Summary of the invention]

The present invention was invented to achieve the above-mentioned object. First, to explain the circumstances leading to the invention, in injection molding, there is a difference between the weight variation of the molded product and the injection speed as the injection speed increases. There is a proportional relationship in which the weight variation of molded products increases as the weight increases. In particular, as there has been a recent tendency to use accumulators and the like to increase the injection rate and increase the injection speed, the weight variation of molded products will increase to the point that it cannot be ignored.

The inventors of the present invention have conducted various studies as to why the weight variation of molded products increases as the injection speed increases, and as a result, they have reached the following conclusion.

That is, conventionally, when determining the weight of a molded product, it is done by setting a measured value and setting a forward stop position of the screw. In this case, the weighing value is determined by moving the screw backwards while rotating until it reaches the set position.

Since it stops at , it is not affected by the injection speed, but
The screw advance stop position deviates significantly from the set position as the injection speed increases. For example 1
If the secondary detection is speed controlled and the secondary injection and tertiary injection are pressure controlled, the secondary switching point and tertiary switching point will be shifted from their set positions, resulting in a situation where program control is not effective. .

This phenomenon is caused by the fact that even if an electric circuit issues an electrical stop command to operate the flow control valve, the speed inertia of the screw at that time is large, so there is a time lag between the operation of the flow control valve and the forward position of the screw. This is thought to be due to the occurrence of misalignment or the fact that, as shown in FIG. 5, since the flow rate is controlled only for the ram on the forward injection side, no force is generated to actively stop the screw.

Therefore, the present invention provides a mechanism that decelerates and stops the injection screw in the control hydraulic circuit connected to the injection retreat side ram, alleviates the forward inertia of the screw that occurs at the switching point, and thereby improves the stability of the molding machine during each operation. It is characterized by the fact that it is made to do so.

[Embodiments of the invention]

FIG. 1, which shows one embodiment of the present invention, will be described below. It should be noted that the same parts as in the prior art are designated by the same reference numerals as in FIG. 5.

As shown in the figure, the injection retreat side ram 5b is connected to the direction control valve 13,
The pressure control valve 14, the check valve 15, the flow rate control valve 16, the pilot check valve 17, and the circuit 18 connecting the directional control valve 13 and the pilot check valve 17 to the injection forward side ram directional control valve 6 are provided. check valve 1
9 and a pump 10a are provided. Furthermore, X.

Y indicates a solenoid of the directional control valve 13, and P and T indicate a pump side port and a tank side port of the directional control valve 13.

Since the injection molding machine according to the present invention has the above-described configuration, the solenoid F of the direction control valve 6 for the injection forward side ram is energized and held, and hydraulic oil is supplied into the injection forward side ram 5a to control the screw 2. When it reaches the point where it is necessary to decelerate the screw 2 while advancing the Solenoid X of directional control valve 13
When energized and held, the injection/retraction side ram directional control valve 1
Check valve 17 from the injection retreat side ram 5a at the neutral position of 3.
The hydraulic oil that was being discharged through the tank 12b is stopped, and the hydraulic oil regulated by the flow rate control valve 16 and the pressure control valve 14 is supplied into the injection retreat side ram 5b, so that the piston 4
The forward speed of the screw 2 is rapidly reduced through this. The deceleration of the forward speed of the screw 2 at this time is determined by the pressure difference between the injection advancing side ram 5a and the injection retreating side ram 5b in the injection ram 3, with the piston 4 serving as a barrier. That is, it is determined by the excitation holding time of the solenoid X of the injection/backward side ram directional control valve 13, the set flow rate value of the flow rate control valve 16, and the set pressure value of the pressure control valve 14.

When the screw 2 reaches a predetermined deceleration as described above and returns to the original neutral position by demagnetizing the solenoid X of the direction control valve 13, the operation is supplied to the injection forward side ram 5a as in the conventional case. Oil pressure shifts to secondary injection and tertiary injection pressure.

Note that it is desirable that the deceleration operation of the screw 2 be completed within as short a time as possible. At this time, the inertia force caused by the advance of the screw 2 is sufficiently alleviated by deceleration, so the screw 2 can be accurately stopped at a preset position, thereby reducing variations in the dimensions and weight of the molded product. It is possible to obtain precise molded products.

Next, a description will be given of FIG. 2 showing another embodiment of the present invention. In this figure, the hydraulic circuit for the injection advancing side ram is shown with the same reference numerals as in FIGS. 1 and 5 because the arrangement of the same parts is changed from that in FIGS. 1 and 5. In the figure, 20 is a direction control valve, 21 is a flow control valve, 22 is a pilot check valve, 23 is a check valve, 24 is a pilot check valve, and the flow control valve 21 uses a single solenoid Z, and the other pilots Check valve 22, 2
4. The check valve 23 has the same structure as in FIG.

Since the injection molding machine according to the present invention has the above-described configuration, the hydraulic oil pumped up from the tank 12 by the pump 10 is supplied to the flow rate control valve 9 and the pressure control valve while the solenoid F of the direction control valve 6 is kept energized. 7 and is supplied into the injection advancing side ram 5a, the screw 2 moves forward via the piston 4 due to the pressure of the hydraulic oil. At this time, the hydraulic oil in the injection retreat side ram 5b is discharged into the tank 12 through the pilot check valve 24 as a first route. In addition, as a second route, the flow control valve 21, pyro・
is discharged into tank 12 through check valve 22. Further, while the solenoid Z of the directional control valve 20 is energized, the pilot check valve 24 is in an open state, and the directional control valve 6 is in an open state.
It is necessary that the pilot check valve 22 be in an open state while the solenoid F is energized.

Next, when it becomes necessary to decelerate the screw 2, the solenoid Z of the direction control valve 20 is kept energized, and the direction of the flow of the pilot pressure oil, indicated by P and P in the figure, is switched and the pilot check valve 24 is activated. When the state is changed from the open state to the closed state, the hydraulic oil in the injection retreat side ram 5b is discharged into the tank 12 through only the flow control valve 21 and the pilot check valve 22. By setting the flow rate of the flow rate control valve 21 at this time to a set amount corresponding to the deceleration of the screw 2, the flow resistance of the hydraulic oil flowing through the flow rate control valve 21 allows injection to be performed as if in the first embodiment. Similar to the case where hydraulic oil is supplied into the retreating side ram 5b, retreating pressure is applied to the piston 4, and the screw 2 can be decelerated.

Next, when decelerating the screw 2, the solenoid Z of the directional control valve 20 is demagnetized to open the pilot check valve 24 and return to the original injection initial state.

Therefore, as shown in Fig. 3, when comparing the performance of the injection molding machines of the present invention and the conventional one, the present invention is four times more effective in cushioning amount and eight times more effective in charge amount than the conventional one. Moreover, the weight variation of molded products can also be reduced. Furthermore, as shown in Fig. 4, when comparing the weight dispersion of the molded products of the present invention and the conventional one, it is found that the present invention has a weight variation of about 172 mm in the normal injection speed range, compared to the conventional one, and in the high speed region using an accumulator. It is also possible to reduce the variation to about 178.

〔Effect of the invention〕

As described above, according to the present invention, the forward inertia force of the screw that occurs when pressure control is transferred from primary injection to secondary injection to tertiary injection during injection of molten resin into a mold cavity is alleviated. Therefore, the operational stability of the injection molding machine can be improved. In particular, even in the case of high-speed injection using an accumulator or the like, it is possible to ensure a level of operational stability equal to or higher than that in a normal injection speed range without using an accumulator or the like.

Furthermore, since the operational stability of the injection molding machine can be improved, the weight variation of molded products can also be reduced.

[Brief explanation of the drawing]

Fig. 1 is a hydraulic circuit diagram of an injection molding machine showing one embodiment of the present invention, Fig. 2 is a hydraulic circuit diagram of an injection molding machine showing another embodiment of the invention, and Fig. 3 is a conventional and the present invention. The amount of cushioning with,
Comparison diagram of charge amount and weight variation frequency of molded products,
FIG. 4 is a comparison diagram of the weight variation of molded products in the normal injection speed range and in the case of high-speed injection between the conventional injection molding machine and the present invention, and FIG. 5 is a hydraulic circuit diagram of the conventional injection molding machine. 1... Mold, 2... Screw, 3... Injection ram,
4... Piston, 5a... Injection forward side ram, 5b.
... Injection retreat side ram, 6.13.20... Direction control valve, 7,14... Pressure control valve, 8.15.19.23.
...Check valve, 9,16.21...Flow control valve, 1
0.13...Pump, 11...Motor, 12...
Tank, 17, 22. 24...Pilot check valve, 18...Pressure oil circuit agent Patent attorney Masami Akimoto Minoru No. 1 (2) Figure 2 Figure 3

Claims (3)

[Claims] 1. A piston connected to the injection screw of a precision injection molding machine is supported so as to be able to reciprocate, and an injection ram is provided that forms an injection forward side ram and an injection backward side ram by sandwiching this piston, and is connected to the injection forward side ram. and a hydraulic circuit for controlling the flow rate and pressure of hydraulic oil into the injection forward ram, and a hydraulic circuit connected to the injection retreat ram to control the forward speed of the piston. Precision injection molding machine. 2. The precision machine according to claim 1, wherein the hydraulic circuit for controlling the forward speed of the piston is configured to supply hydraulic oil into the injection/retreat side ram when decelerating the forward speed of the piston. Injection molding machine. 3. The hydraulic circuit for controlling the forward speed of the piston is configured to control the amount of hydraulic oil discharged from the forward injection/retreat side ram when the forward speed of the piston is reduced. Precision injection molding machine according to item 1.