JPH01234221A - Improvement in accuracy of mold open amount - Google Patents

Abstract

PURPOSE:To obtain high accuracy of a stopping position without increasing the burden of cost, by making use of a prefill valve of a straight-hydraulic mold clamping system of an injection compression molding machine as a brake valve of a main ram. CONSTITUTION:A directional control valve 11 is excited and a prefill valve 7 is closed under a state where mold register is performed to contrive an improvement in accuracy of mold break stopping position of an injection compression molding method. Mold open is performed by exciting a state SOL 'OP'. Hydraulic oil is sent into a space A, a main ram 5 is moved backward and the hydraulic oil of a space B is discharged into a tank 12 through a space C. Flow path resistance of the space C is made far higher than that of a space D. Therefore, a large volume of the hydraulic oil in the space B becomes a great hindrance for a movement of the main ram 5 according to a mold opening action and when supply of the hydraulic oil into the space A is stopped, the movement of the main ram 5 also stopped immediately. Since necessary hydraulic pressure for the space A is particularly high as compared with an old method, when supply of the hydraulic oil is stopped by closing a directional control valve 10, pressure is lowered immediately, force to open a mold is lost quickly and on the contrary, back pressure to be generated in the space B is little.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for improving mold opening accuracy that can be used in an injection molding machine.

(Prior Art) A compression amount control method in conventional injection compression molding will be explained using a direct pressure mold clamping device shown in FIG. In FIG. 2, the resin plasticized in an injection unit (not shown) is injected into the mold 4 by the same unit, but in normal molding, the mold 4 is held together with enough mold clamping force to overcome this injection pressure. Keep it in good condition.

However, in the case of a thick-walled iI L-' molded product, the resin solidifies as a thin layer on the wall surface when flowing through the mold, so the flow path becomes extremely narrow and the flow resistance becomes extremely large. Therefore, the resin molecules are oriented in the direction of flow, and solidification in this state causes internal stress to occur, causing distortion in the molded product.

In order to prevent this, when injecting the resin into the mold, keep the mold slightly open and inject the resin while increasing the wall thickness, and when the injection is complete, align the mold and place it in the specified position. A method of obtaining a molded article in the form of is conventionally known as injection compression molding. However, this method requires that the mold be opened to a predetermined amount with high precision, but it has been difficult to achieve this precision.

Figure 4 shows the operation diagram of the conventional method.The conventional method is to reduce the mold closing speed from high to low, and to stop the mold by placing a mold closing stop signal at a predetermined position before mold alignment. be.

(Problem to be solved by the invention) However, in the conventional method, as shown in FIG.
The drawback is that the stopping position of the mold cannot be determined with high precision.

In other words, the position where the mold opening speed switches from high speed to low speed is
In the range between points a and b, it changes every time due to variations in the operation within the signal system and hydraulic circuit, and the degree of deceleration also changes over time in the range from slope C to d due to the influence of oil temperature C. Therefore, the position where the speed becomes completely low varies within the range from point e to f.

Therefore, the point j that emits the stop signal of the mold is changed from e to f.
If the stop position is between the two, the stop position will change depending on the speed at which the stop signal is received, for example, the value of g to h. This change greatly exceeds the accuracy of 0, in- order required for the compression allowance, so it is not practical. Therefore, the point j that issues the stop signal should be placed to the right of h (close to the mold matching point k). I need to bring it.

On the other hand, in the case of normal mold closing operation, the mold matching points include:
It can be anywhere to the right of e (to stop it against the mold), so compared to the previous compression molding, the maximum f
The low speed section can be shortened by the stroke of -e. For this reason, the conventional mold stopping method has the disadvantage that stopping accuracy cannot be improved without increasing the time required to open the mold. In addition to the drawbacks that lead to a decrease in productivity, there is also the essential problem of poor stopping accuracy.

The reason for this will be explained below. In Figure 2,
The main ram 5 and the movable mold platen 2 have a large mass, and even if they are moving at a speed of about lz/min, a large force is required to stop them accurately.

In the conventional method, the movement of the main ram 5 and the movable mold platen 2 is attempted to be stopped by closing the oil in spaces C and A with the directional control valve 10, so the compressibility of the oil and the response of the directional control valve 10 are Stopping accuracy cannot be achieved due to variations. In order to prevent this, a method of closing the prefill valve 7 when switching to low mold closing speed or during mold closing low speed may be considered, but in order to obtain the necessary low speed, a large amount of oil needs to be supplied, and the capacity of the hydraulic pump is reduced. In addition to the cost increase due to the increase in the pressure, it was difficult to adopt this method due to the technical difficulty that it would not function to protect the mold unless the pressure in the space B was controlled to an extremely low pressure (~1 kgf/ad).

The present invention has been proposed to solve the above-mentioned conventional problems.

(Means and effects for solving the problem) For this reason, the present invention provides a direct pressure type mold clamping device for injection compression molding, in which the mold is once closed in a normal operation before the start of injection, and after mold alignment, the prefill valve is closed. The system closes the valve and connects the tank line, which has a flow resistance greater than when the valve is open, to the main cylinder, while opening the mold at a low speed only by the amount of compression. It shall be the means and action for that purpose.

(Example) The present invention will be described below with reference to the embodiments shown in the drawings. FIG. 1 shows an operational diagram of the injection compression molding method in the present invention. 1st
In the figure, in order to improve the precision of the mold opening and stopping position, with the molds aligned, the directional switching valve 11 shown in FIG. 2 is energized and the prefill valve 7 is closed. In this state, SQL “OP”
is excited to open the mold. As a result, pressure oil is sent to the space, and when the main ram 5 is retreated, the oil in the space B is transferred to the space C.
The water is discharged into the tank 12 through the process.

A structural feature of the direct pressure type mold clamping device is that the flow path resistance in the space C is significantly larger than that in the space. For this reason, the large volume of oil in space B accompanying the mold opening operation has a small passage through space C, so it plays a large braking role for the movement of the main ram 5, and the supply of oil to the space is limited. When the main ram 5 stops, the movement of the main ram 5 is also immediately stopped.

When using this method, the hydraulic pressure required in space A to open the mold is significantly (70 to 100 kgf/
cot), and therefore, when the directional control valve 10 is closed and the oil supply is stopped, this pressure immediately decreases and the force to open the mold is rapidly lost, and conversely, the back pressure generated in the space B is , is small. Moreover, since this pressure is generated only while the main ram 5 is moving, this force also decreases as the mold opening speed decreases, so that it cannot become a force that prevents the main ram 5 from stopping. For the above reasons, high stopping position accuracy can be obtained.

(Effects of the Invention) Since the present invention is constructed as described in detail above, the cost burden is increased by using the prefill valve originally provided in the direct pressure type mold clamping device as the brake valve of the main ram. Therefore, high stopping position accuracy can be obtained.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the mold clamping operation for carrying out the method of the present invention;
FIG. 3 is a side sectional view of a general direct pressure type mold clamping device, FIG. 3 is an explanatory diagram of variations in mold stop position accuracy according to a conventional method, and FIG. 4 is an explanatory diagram of a conventional mold clamping operation. Explanation of the main parts of the figure 2 - Movable mold platen 3 - Fixed mold platen 4 - Mold 5 - Main ram 6 - Booster ram 7 - Prefill valve 8 - Main cylinder 9 - Prefill valve opening/closing cylinders 10, 11 ... Directional switching valve No. 1 Entai Tomoe Ushi Takui Kata Tsuri Sakuen Fig. 2 Manken Kigen Sosho ff Fig. 13 Injection pressure flat bed type and operation g

Claims (1)

[Claims] In a direct pressure mold clamping device that performs injection compression molding, the mold is closed in a normal manner before injection starts, and after mold alignment, the prefill valve is closed and the flow path resistance is greater than when the valve is open. A method for improving mold opening accuracy, which is characterized in that the tank line is connected to the main cylinder, and the mold is opened at a low speed only by the amount of compression.