JPS5849172B2 - Plastic injection molding control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of controlling molding conditions for plastic index molding.

For plastic extrusion molding, as shown in Figure 1, an extrusion device 3 is used.
, a mold clamping device 4 , a material supply device 5 , and an extrusion molding machine and a hollow mold 2 .

In conventional overflow molding, the overflow pressure and holding pressure are primarily set by opening and closing the hydraulic control valve 6 of the overflow device 3, so changes in resin temperature, mold temperature, oil temperature, and resin loft may cause This results in variations in the cavity pressure and therefore the dimensions,
There were disadvantages in that molded products with uniform weight could not be obtained and the yield was low.

SUMMARY OF THE INVENTION An object of the present invention is to provide a plastic indexing or shaping control method that eliminates the above-mentioned drawbacks of the prior art and improves the dimensional and weight accuracy of molded products as well as the production yield.

First, the principle of the present invention will be explained.

Figure 2 shows the elapsed time t during molding and the cavity internal pressure ps''M output pressure p.

, and the relationship between the holding pressure p1 and the holding pressure p1.

In Figure 2, point A is the point where the resin has begun to fill the cavity, point B is the point where the filling has finished, and point C and D are the process in which holding pressure is applied to prevent sinking of the molded product, and point D. indicates the gate seal point, and the area between D and E indicates that the pressure inside the cavity is decreasing due to the contraction of the large-sized product.

Even if the opening/closing of the hydraulic control valve (6 in Fig. 1) of the ejecting device is set constant, the cavity pressure profile, that is, the curve ABCDE, varies depending on changes in resin temperature, mold temperature, and resin loft, for example, A'B'. It will look like C'D'E' (Figure 3).

This variation in the cavity pressure profile affects the dimensional accuracy of the molded product, and according to research by the present inventors, the integral value over time of the portion of the cavity pressure that affects the dimension ftD Q(t)-p (t) dt ・・・・・・・・・
... It was found that if the holding pressure time is controlled so that (1) becomes a constant value, the dimensions of the molded product will be the same even if the cavity pressure profile is different.

In such a control that changes the holding pressure time so that Q(t) becomes a constant value, the holding pressure is released before the gate seals.

Q(t), which affects the dimensions in this case, is expressed by the following equation with reference to FIG.

Q(t)=j”: t)a t-p(tx) −
(t x - tc) - (2) In equation (2), p(t
x) ・The reason for subtracting (tx - tc) is that when the holding pressure is released at This is based on the experimental fact that it is better to use a value obtained by subtracting the integral value corresponding to tc-σ·X-tx.

Figure 5 is an example showing the relationship between the integral value Q(t) defined by equation (2) and the dimensions of a molded product. This is the result of molding it using resin.

As is clear from FIG. 5, it can be seen that there is a strong correlation between the integral value Q(t) and the dimensions of the precept form.

An embodiment of the present invention will be described below with reference to FIG.

As shown in FIG. 6, the certain type mold 2 is provided with a pressure sensor 9 at the rear of an ejector pin 8 provided in the cavity 7 for detecting the pressure inside the cavity.

The analog signal of the cavity internal pressure is sent to an A/D converter 10.
is converted into a digital signal and input to the microcomputer 11.

The microcomputer 11 calculates the cavity internal pressure integral value Q(t) at time t using the above equation (2).

Cavity internal pressure integral value Q appropriate for each molded product.

is set by the cavity internal pressure integral value setting device 12.

In microcomputer 11, Q(t) and Q. Q(t) is Q.

When it becomes equal to , the microcomputer 11 outputs a holding pressure cut signal to the extrusion molding machine 1.

This output passes through the D/A converter 13 and the amplifier 14 and reaches the holding force cutting device 15, which cuts off the ejection device of a certain type of machine and releases the holding force.

As an example, the cavity dimensions are between outer diameter φ20 and inner diameter φ14.
ms. , a polyacetal resin cylinder or shaped product with a height of 14 mπ has a cavity internal pressure integral value Q(t) of 5000 (kg/
i)・sec4 When a certain shape is controlled, the dimensional variation for each shot is 3σ = 0.005 in height dimension.
The weight variation was within 3 (7=0.005 g), and the yield was greatly improved.

On the other hand, in the conventional molding method, the ejection pressure is 600 kq/Ci. ,
The dimensional variation when the above molded product is shaped under the setting conditions of holding pressure 2001/1, mold temperature 60℃, and resin 215℃ is 3σ
= 0.01g, weight variation 3σ = 0.012g.

As explained in detail above, according to the present invention, the pressure holding time in each shot is controlled so that the value integrated over time of the cavity internal pressure becomes a constant value, so that the dimensions and weight of the shaped product are controlled. Accuracy is improved and molding yield is also improved.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the outline of the plastic protrusion forming device, Fig. 2.3.4 is a diagram showing the relationship between elapsed time and cavity pressure, and Fig. 5 is a diagram showing the relationship between the dimensions of a certain molded product and the cavity pressure. A diagram showing the relationship with the integral value, and FIG. 6 is an explanatory diagram showing one embodiment of the present invention. 7... Cavity.

Claims (1)

[Claims] 1. A plastic indexing molding control method, which is characterized by controlling the pressure holding time in each shot so that the value integrated over time of the cavity internal pressure becomes a constant value in plastic indexing molding.