JPH0584728B2 - - Google Patents

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a thick wall molding method for an injection molding machine.

(Prior art) This type of thick-wall molding method rotates the screw near the forward limit of the screw, extrudes molten material into the mold, fills it, and injects the molded material with a short stroke (holding pressure). A method for preventing sink marks and ensuring dimensional accuracy, or by retracting the screw to the measuring limit, rotating the screw at that position, extruding material into the mold by the amount that is insufficient for the injection amount, and then moving the screw forward. There is a molding method that involves injection filling.

(Problems to be Solved by the Invention) However, in the former method, the filling speed of the material resin into the mold due to screw rotation is lower than the injection speed due to advancement of the screw.
The material filled into the mold comes into contact with the low-temperature mold wall, resulting in poor fluidity. Therefore, weld marks and flow marks occur. These weld marks can be improved to some extent by raising the mold temperature or increasing the screw rotation, which improves the fluidity of the material, but it also increases the cooling time, prolonging the molding cycle, and increasing the screw rotation. This has the disadvantage that the material will overheat and cause burns. Furthermore, since injection pressure is applied while the screw is rotating, friction heat is generated in the hydraulic piston.

In the latter case, when moving from the screw rotation to the injection operation (screw forward movement), the flow of the material resin filled in the mold momentarily stops, and flow marks are generated at that part. In addition, since the screw rotates in a retracted position, the screw portion that is involved in the resin is reduced and the effective screw length is substantially shortened, resulting in problems such as a reduction in the discharge amount and insufficient melting of the material.

The present invention eliminates the drawbacks of the conventional method as described above, allows the resin to be filled into the mold continuously without stopping the flow, and fills the cavity before the filling is completed using an injection operation under high pressure. The object of the present invention is to provide a method for molding thick-walled products with uniform appearance and excellent quality at high speed.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above-mentioned object, in the present invention, when advancing the screw from the retraction limit in order to fill the measured material into the cavity, the screw is moved forward while rotating. Thick-wall molding of an injection molding machine, which is characterized in that the screw rotation is stopped and only the injection operation continues when the screw reaches an arbitrary position before holding pressure in the injection process by changing its forward speed in multiple stages. provide a method.

(Function) Since the above-mentioned molding method was used, the resin filling speed is lower than that of the conventional method of filling only by rotating the screw.
Since the filling speed by injection operation is added in multiple stages,
The required cavity filling speed can be obtained without increasing the screw rotation to a high rotation speed, and at the same time, since the screw that is involved in the resin is rotated over a long range, sufficiently melted and kneaded resin is continuously supplied. As a result, the flow marks are eliminated.

In addition, when the screw reaches an arbitrary position before the holding pressure of the injection process, the screw rotation is stopped and only the injection operation is performed, so that the filling of the cavity before the completion of filling, where weld marks are likely to occur, is carried out at high pressure and high pressure. This makes it possible to increase the speed and eliminate weld marks.

(Example) According to the present invention, the relationships between the filling pressure, the screw position, the injection speed (multi-stage speed) and the screw position, and the screw rotation speed and the screw position are as shown in Fig. 1, and the mold clamping force is 220 tons, the maximum injection When a thick-walled product with a product weight of 1300 g as shown in Figure 2 was molded using a molding machine with a capacity of 570 g, a homogeneous product with no weld marks or flow marks and excellent appearance quality was molded.

(Effect of the invention) According to the present invention, the following effects are achieved.

(1) Since the filling speed due to injection operation is added to the resin filling speed due to screw rotation,
The required cavity filling speed can be obtained without increasing the screw rotation to a high rotation speed, and at the same time, since the screw that is involved in the resin is rotated over a long range, sufficiently melted and kneaded resin is continuously supplied. As a result, the flow marks are eliminated.

(2) When the screw reaches an arbitrary position before holding pressure in the injection process, the screw rotation is stopped and only the injection operation is performed, so that filling the cavity before the completion of filling, where weld marks are likely to occur, is carried out under high pressure. , it becomes possible to increase the speed and eliminate weld marks.

(3) As described above, it is possible to mold a thick-walled product with no flow marks or weld marks, and which is homogeneous and has excellent appearance quality.

(4) Since the screw is not rotated during the high filling pressure due to the injection operation before filling is completed, friction heat does not occur in the hydraulic piston part as seen in conventional examples.

(5) There is no need to increase the screw rotation speed, so
The material will not overheat and cause burns.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, and is a diagram showing the relationship between filling pressure and screw position, injection speed and screw position, and screw rotation speed and screw position. FIG. 2 is a diagram showing a thick-walled molded product molded according to the present invention.

Claims (1)

[Claims] 1. When advancing the screw from the retraction limit to fill the measured material into the cavity, the screw is advanced while rotating, and its advancing speed is varied in multiple stages, and the screw is moved to an arbitrary position before holding pressure in the injection process. A thick-wall molding method for an injection molding machine, characterized in that when the screw reaches the target, the screw rotation is stopped and only the injection operation is continued.