JPS6315721A - Sinkage preventive device for injection molder - Google Patents

Abstract

PURPOSE:To prevent a sinkage and obtain a highly accurate molded form, by a method wherein the extruding pin of a mold is retreated previously by a size which copes with the amount of shrinkage of resin and a space, produced by the retreatment of the pin, is filled with molten resin while the resin is extruded into a cavity by the extruding pin after finishing the filling of injection. CONSTITUTION:A pressure sensor 25, provided at the root of an extruding pin 1a arranged at the terminal of a product, detects the filling of molding material and the detecting signal is inputted into an amplifier 27 through a wire 26, thereafter, is inputted into a servo control circuit 29 through the wire 28. In this case, a signal for reading the data program of a memory 30 and driving a servomotor 21 in accordance with the rate of shrinkage of a molded form, is outputted from a servo control circuit 29 into the servomotor 21. The servomotor 21 rotates a screw 22 in accordance with a predetermined said program, drives a ball screw block 20 to a predetermined position, pushes the extruding pins 1,...1a out, forces molten resin in a space 3 into a cavity 2 to compensate the amount of shrinkage of the molded form based on cooling and, thus, faulty molding due to sinkage may be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an injection molding machine that prevents sink marks on a molded product during injection I11 molding.

(Prior Art) Conventionally, as a method of preventing sink marks on molded products, the cutout part of the mold is made into a telescopic shape so that the defining side and the movable side of the mold are driven. There are some that are compressed and injection molded as a whole (Industrial Materials, Vol. 32, No. 111;
(See "Ultra-precision molding of large 11-diameter aspherical plastic lens" described on pages 107 to 113).

In addition, as a pushing device for preventing sink marks in the Ij hinge type of the mold, after injecting synthetic resin into the cavity 50, a pushing member 51 or a pushing member 52 is inserted into the cavity as shown in FIG. Synthetic resin hydraulic cylinder 5
There is a device that is provided with a pushing device 60 that is pushed into the cavity by the operation of step 3 to prevent sink marks at specific locations (see Japanese Patent Laid-Open No. 58-154026).

In addition, when molding a molded product that has thick and thin parts using a mold, pressure is applied to the N-thick part to harden it, thereby preventing the occurrence of sink marks on the surface decoy corresponding to the thick-walled part. It can be prevented. There is a molding method and apparatus (see Japanese Patent Laid-Open No. 18843θ/1983).

(Problems to be Solved by the Invention) In the molding method and apparatus described in -1-, in the telescope type mold, the stationary mold 55 and the movable mold 5B slide as shown in FIG. This is fine if the product is a simple shape such as a circle, but if the product is a large and complex shape such as an automobile part, it becomes extremely difficult to make a mold, and the mold is difficult to manufacture. There is a problem that not only does this lead to higher costs, but also that it is more likely to cause a breakout.

Also, in other devices, after a predetermined period of time has elapsed after injecting molten resin into a cavity, pressure is simply applied by driving a hydraulic cylinder, etc., and the resin is pushed out in the four parts to fill the area where the sink mark is occurring. However, there are problems in that it is difficult to sufficiently adapt to changes in resin shrinkage and is unreliable, and the mold itself becomes locally complicated, resulting in disadvantages in terms of handling and maintenance, and the life of the mold is shortened.

In view of this 11% situation, the present invention has been developed to ensure that the filling of the molten resin injected into the cavity is completed, and to ensure that 11 people are placed in the gap communicating with the cavity by driving an ejector to ensure proper melting. [1] It is an object of the present invention to provide a sink mark prevention device for an injection molding machine that prevents sink marks by extruding resin to compensate for shrinkage due to cooling of a molded product.

(Means for Solving the Problems) In order to achieve the above object, the device of the present invention is equipped with a pressure sensor that detects the pressure exerted on the extrusion pin that ejects the molded product due to the filling of the molten resin injected into the cavity. , The ejector pin advances within the movable mold when the mold is closed; j! A driving means for moving the ejecting pin and an actuator for ejecting the ejecting pin toward the cavity side when the mold is opened are provided. A suitable gap is formed in advance between each extrusion pin and the cavity by the driving means to compensate for the amount of shrinkage due to cooling of the molded product, and the molten resin filled in this gap is forced into the cavity according to predetermined pushing conditions. It is characterized by the provision of a control device for returning the air to the inside.

(Function) With this configuration, the pressure sensor reliably determines the point at which injection and filling is completed, making it possible to fully adapt to changes in resin shrinkage, and to fill the appropriate gap set in advance. The filled molten resin compensates for the amount of shrinkage due to cooling of the molded product, and is returned to the cavity to increase the resin density in the sink area and prevent sink marks.

In addition, the driving means by the ejecting device pushes out the ejecting pins that form the gap between each ejecting pin and the cavity according to predetermined ejecting conditions, and since the tips of the ejecting pins are aligned with the cavity surface, the shape and weight of the molded product can be adjusted. can be kept accurate and dimensional accuracy can be maintained.

(Example) Embodiments of the present invention will be described based on the drawings.

1 and 2 are partial side sectional views of an injection molding machine incorporating the sink mark prevention device of the present invention, and FIG. 1 shows the extrusion pins 1, ′, . A predetermined gap 3 between the cavities 2. ... is formed, and Figure 2 is a diagram showing a state in which the resin filled in the gap 3 is returned into the cavity 2 (however, the control system diagram is omitted).

Here, 4 is a movable plate that can remove the movable mold 5,
Reference numeral 6 denotes a fixed plate which has a through hole 8 in the center so that the fixed mold 7 can be accessed and the nozzle tip of the injection device can abut against the spool opening 7a of the mold 7.

I+ (The cutting side mold 5 has spacer blocks 9 at the four corners,
Core 11 from the top,
The receiver is board +2. Ejector plate I/14 equipped with an ejector pin fixing plate 13 and a guide pin 14a at the bottom
, and a coil spring 15 that urges the extrusion plate unit composed of both plates 13 and 14 toward the base side, and a member 11. A plurality of push-out pins 1, .

An ejecting device 17 that operates these ejecting pins l, . It consists of a drive means lea for advancing and retracting the ejecting pins l, .

The first drive stage +7a has two long extrusion rods 18 and 18 extending through the movable plate 4 and extending along the direction of the moving force of the mold.

Then, connect the link mechanism 19 to the part 18a of this extrusion rod 18, and install the pole screw pro 2o in the center of the link mechanism 18. The threaded portion 22 is rotated by the IJ, and the pole screw block 20 is moved in the 1i11 rear direction (left and right in the figure), thereby moving the push rod 18 forward and backward.

In addition, it is assembled integrally on both sides of this protruding device F1.17 (-J
A high hydraulic cylinder device (71) is installed, and hydraulic pressure is supplied to the cylinder interior;・23.24.
The ejection movement f1 for ejecting the molded product is made by L.

Furthermore, the device of the present invention includes a pressure sensor 25 at the base of the push-out pin 1a arranged at the endmost bundle of products in the cavity 2.
has been set up.

The signal from the pressure sensor 25 is amplified by +1 via an amplifier 27 via a conductor 26, and is further supplied to a servo control circuit 28 via a conductor 28. And the dimensions of the molded product in advance,
A memory device that stores extrusion conditions such as the push stroke of the push pin 1, push time, delay time, etc. according to the shape and shrinkage behavior of the molding material! A control device 40 is provided which outputs a signal from J30 and controls the servo motor 21 by the servo control circuit 29.

The operation of the embodiment of the present invention having the above configuration will be described next.

As shown in FIG. 1, when the mold is closed by closing the movable plate 4, the pole screw block 20 is set at a predetermined position depending on the size and shape of the molded product and the shrinkage rate of the molded material $1.

At this time, each push-out pin 1, 1. ..., Ia forms a gap 3 by a coil spring 15.

The molten resin ejected from the injection device in this state fills not only the cavity 2 but also the gap 3. and,
Product terminal j11! j! installed at the base of the extrusion pin la placed in the j! , the sensor 25 senses the filling of the molding material, and the signal tJ- is inputted to the intensifier 27 through the conductor 2G and into the bottom control circuit 29 through the conductor 12B.

At this time, the data program of the device 30 is output from the control circuit 29 to the servo motor 21 according to the shrinkage rate of the molded product. .

The servo motor 21 operates at a predetermined 1. The screw 22 is rotated according to the above program, and the pole screw block 20 is driven to a predetermined position (l-2 in FIG. 2).

Due to the interlocking of this pole screw block 20, the extrusion rod 18, 18 is moved by the link mechanism 19 to the extrusion play 1□
Push out the j-ts (13, 14, 14a) to the right in Fig. 1, push out the push-out pins l,..., la,
These extrusion pins push the molten resin in the gap 3 into the cavity 2, which is the regular molded product shape, to compensate for the amount of shrinkage due to cooling of the molded product, and to prevent sink defects.

When the molded product is completely solidified, the movable plate 4 is moved to the left in FIG. 2 by the drive of a clamping cylinder (not shown), and the movable mold 5 and the fixed mold 7 are separated. At this point, the molding ridge is fixed to the core 11 of the movable mold.

Hydraulic cylinder device 1 in this state? When hydraulic pressure is supplied from the port 23 of b, the entire ejector 17 is driven to the right, and this force is transmitted from the link mechanism 19 through the ejector rod 18 to the ejector plate unit, and further to the ejector pin 1. The extrusion pin 1 and the tips of the la protrude from the core 11 toward the cavity, allowing the molded product to be released from the mold.

In this embodiment, a servo motor 21. is used as the driving means.
Although the extrusion rod 18 is driven by the pole screw block 20 and the link mechanism 19, other driving methods such as electric, mechanical, hydraulic, pneumatic, etc. may be used.

(Effects of the Invention) As is clear from the above, the pressure sensor accurately determines the completion point of injection of molten resin into the cavity, and the extrusion pin of the mold is The control device is designed to push the ejector pin out to the cavity surface in accordance with the shrinkage change of the resin after completing injection and filling of the molten resin filled into the appropriate cavity by retracting the ejector pin in advance by an amount corresponding to the amount of shrinkage. As a result, injection and compression molding can be easily performed with only the minimum necessary changes to the injection molding machine itself, preventing sink marks and maintaining the correct shape and weight of the molded product, resulting in highly accurate molding. can produce products.

In addition, it is possible to prevent sink marks even in large and complex molded products without increasing the mold cost, and even if the molding pressure is set slightly low, the molten resin in the void can be extruded! (1) Since the molded product is then returned to the inside of the cavity, short shots are prevented, residual stress within the molded product is reduced, and deformation such as warping is prevented.

[Brief explanation of the drawing]

FIG. 1 is a side cross-sectional view of the main part of the device according to the embodiment of the present invention, showing a state with a gap when the mold is closed. FIG. 2 is a side sectional view of the device shown in FIG. Fig. 3 is a schematic sectional view of a conventional sink prevention device, and Fig. 4 is a schematic sectional view showing a telescope type mold structure. .

Claims (2)

[Claims] (1) A pressure sensor is provided to detect the pressure exerted on an extrusion pin for ejecting a molded product due to the filling of molten resin injected into the cavity, and a drive means for moving the extrusion pin back and forth within the movable mold when the mold is closed. and an actuator that causes the ejector pin to protrude toward the cavity side when the mold is opened. A control device is provided that forms an appropriate gap between each extrusion pin and the cavity to compensate for the amount of shrinkage due to cooling of the molded product, and returns the molten resin filled in the gap into the cavity according to predetermined pushing conditions. A sink mark prevention device for an injection molding machine, characterized in that it is provided with a sink mark prevention device. (2) The device according to claim 1, wherein the pressure sensor is provided at the base of the extrusion pin located farthest from the molten resin injection gate.