JPH07100335B2 - Thick product molding method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for molding a thick product of an injection molding machine, and particularly to advancing a screw from a backward limit when filling a molten material into a mold in an injection process. The present invention relates to a molding method for a thick product of an injection molding machine, which is programmable so that the screw is moved forward while being rotated, the screw rotation speed is changed in multiple stages, or the injection speed is changed in multiple stages.

<Prior art> This type of thick-walled product molding method involves rotating the screw at the forward limit of the screw, extruding the molten material into the mold, filling it, and injecting (holding pressure) the short stroke to form the molded product. A method of preventing sink marks and ensuring dimensional accuracy, or by rotating the screw back to the measurement limit and rotating the screw at that position, pushing out the material into the mold by the shortage of the injection amount, then advancing the screw and injecting it. There is a molding method for filling.

<Problems to be solved by the invention> However, in the former method, in the former case, the filling speed of the material resin in the mold by the screw rotation was lower than the injection speed by the forward movement of the screw, and the resin was filled in the mold. The material touches the mold wall surface at low temperature and the fluidity deteriorates. Therefore, weld marks and flow marks are generated. These weld marks and the like improve the fluidity of the material by raising the mold temperature or the screw rotation, which is improved to some extent, but the cooling time becomes longer and the molding cycle is extended, and the screw rotation is increased. If so, the material, especially the resin such as vinyl chloride, which is easily decomposed by heat, is thermally deteriorated due to overheating. Also, it takes time to fill the inside of the mold, and when shifting to pressure holding injection, solidification of the material resin near the gate proceeds,
Since the holding pressure injection does not work sufficiently at the end of the mold cavity, there is a drawback that sink marks are likely to occur.

In the latter case, when moving from screw rotation to injection operation (screw advancing operation), the flow of the material resin filled in the mold stops for a moment and a flow mark is generated at that portion, causing Molding significantly reduces the optical properties of the lens. Also, since the screw rotates in the retracted position,
This effectively shortens the effective screw length, resulting in problems such as lower discharge rate and insufficient material melting. In addition, the material resin injected (extruded) into the mold by the screw rotation enters at a low speed, and when the skin layer becomes hot, the material resin with a high injection speed due to the high temperature screw advancing operation is filled. , The connection with the material resin injected by the previous screw rotation is poor, which causes poor strength of the molded product.

An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional methods and to provide a method for forming a thick product which is homogeneous and has excellent optical characteristics.

<Means for Solving the Problems> In order to achieve the above-mentioned object, in the present invention, when the screw is advanced from the backward limit so as to fill the weighed material into the cavity, the screw is advanced while rotating. The thick-walled product molding method of the injection molding machine is programmable so that the rotation of the screw can be changed in multiple stages. Also, when the screw is advanced from the backward limit to fill the cavity with the measured material, the screw is advanced while rotating the screw, and the thickness of the injection molding machine programmable to change the injection speed during the injection process in multiple stages. The meat product molding method was used.

<Operation> Since the molding method described above is used, a thick product that is homogeneous and has excellent optical characteristics can be molded without the occurrence of weld marks or flow marks.

<Embodiment> Next, one embodiment of the present invention will be described with reference to FIG.
Is inserted, and the injection cylinder 4 advances and retracts by an injection stroke S in the axial direction. It can be rotated by the hydraulic motor 5. Reference numeral 6 is a rotary plate to which a fixed mold 7 is attached. 8 is a moving plate to which a moving die 9 is attached, which is moved forward and backward by a die clamping cylinder 10 so that both die 7 and 9 come into contact with each other during die clamping to form a cavity 11. Reference numeral 12 is a position detecting device for detecting the position of the screw, and while the screw 3 moves the injection stroke S, the position is always detected. 13 to 16 are position setting devices capable of setting an arbitrary position between injection strokes S.
Comparators 17 to 20 compare the detected value detected by 12 and the values set in the position setting devices 13 to 16, respectively, and when the detected value and the set value match, a coincidence signal is issued.
21 to 24 are setters that set the injection speed or screw rotation speed and can be set to any value. Therefore, for example, when the screw 3 passes the position set in the position setting device 13 during the injection stroke S, the screw moving speed (injection speed) set in the setter 21 or the screw rotation speed is set. Reference numeral 25 is a signal switching device for switching the signals from the setters 21 to 24 to act on the electromagnetic flow control valve to be described later, and keeps receiving the signal received earlier until the next signal is received. ing. Reference numerals 26 and 27 are electromagnetic flow rate control valves, the former of which controls the flow rate of the pressure oil acting on the injection cylinder 4 and controls the injection speed of the screw 3. Alternatively, the latter controls the flow rate of the pressure oil acting on the hydraulic motor 5, and controls the rotation speed of the screw 3.
28 is a changeover switch for selecting either the injection speed or the screw rotation.

<Effect> With the above-mentioned configuration, the measured material resin is injected and the screw is rotated at the same time. In addition to injecting the material into the cavity like screw rotation, high-speed material filling by the injection operation is performed. Is done. Furthermore, since the injection speed and screw rotation speed can be controlled in multiple stages, the filling speed in the cavity suitable for the molded product can be obtained.
The weld marks and flow marks that were fried at the beginning are eliminated.

Here, in the above-mentioned embodiment, the example in which the multi-stage control of the screw rotation speed and the injection speed is made selectable by the changeover switch has been described, but both phrase control may be performed at the same time, and the screw rotation speed setting, The setting of the injection speed is not limited to four as in the embodiment, and an arbitrary number can be set. In addition, it is possible to change the position of the screw and control it by time.

<Test> The results of testing by the molding method according to the present invention are shown below.
When a molded product with a product weight of 2000 as shown in Fig. 2 was molded with a molding machine with a mold clamping force of 350 tons and a maximum injection amount of 1000 gr, a thick product with excellent optical properties without weld marks and flow marks was obtained.

Note that the relationship between the injection speed and the screw position and the relationship between the screw rotation speed and the screw position are as shown in FIG. 3, and when the screw advances the injection stroke S, the thick portion (middle) of the product shown in FIG. When filling the part, the screw rotation speed was set to 30% of the maximum rotation speed, and the screw L / D was short, so low heat was used to secure the amount of heat to the material, then the thick wall (large) and thin wall In order to fill the material, the screw rotation speed is increased, the high discharge amount is imaged, and the material is sufficiently distributed in the cavity.

Next, in order to improve the accuracy of the pressure holding position before reaching the pressure holding switching position, the screw rotation speed is reduced and the injection strategy is also lowered to reduce the inertia, and the pressure holding position is set at a predetermined value. Accurately switch from filling to holding pressure.

<Effects of the Present Invention> The present invention has the following effects.

1) The filling rate of the material resin of the die cavity is fast, and the rate can be set freely, so even thick-walled products with complicated shapes have no weld marks or flow marks, and molding defects are eliminated.

2) The material resin in the mold cavity has good resin bonding by injection by screw rotation and filling by injection.
The molded product becomes homogenous, eliminating defects in strength.

3) It is not necessary to increase the screw rotation speed, and it is possible to handle materials that easily decompose such as PVC.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment according to the present invention. FIG. 2 is a view of a product test-molded by the method of the present invention. Fig. 3 is a graph showing the relationship between injection speed, screw rotation and screw position during test molding. 3 ... Screw, 4 ... Injection cylinder, 5 ... Hydraulic motor, 13 to 16
… Position setting device, 17 to 20… Comparator, 21 to 24… Setting device, 25…
Signal switching device, 26, 27 ... Electromagnetic flow control valve, 28 ... Changeover switch

Claims (2)

[Claims] 1. An injection molding which can be programmed so that when the screw is advanced from the backward limit so as to fill the cavity with a measured amount of material, the screw is advanced while being rotated, and the rotation of the screw is changed in multiple stages. Machine thick product molding method. 2. A programmable injection which, while advancing the screw from the backward limit so as to fill the cavity with the metered material, while advancing while rotating the screw, the injection speed during the injection process is changed in multiple stages. Molding method for thick-walled products.