JPH0470967B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an injection molding method and a mold for carrying out the method.

(Prior art and its problems) The molding process in the injection molding method for thermoplastic synthetic resins consists of the following steps: injection filling of molten resin, holding pressure in anticipation of post-shrinkage (holding pressure), cooling solidification, and mold release. has been done. In the injection filling process, the molten resin injected from the injection nozzle of the injection molding machine flows into the cavity through the sprue, runner, and gate, so the gate that serves as the injection port into the cavity must have low flow resistance. is preferred. On the other hand, after the cavity is filled with molten resin, the pressure generated at the injection nozzle port is applied to the molten resin in the cavity through the sprue, runner, and gate to maintain pressure. Since the resin is cooled and solidified, even if the flow resistance increases, the amount of molten resin supplied from the gate into the cavity is very small, so it is not a big problem.On the contrary, reducing the size of the gate is This is preferable because it can simplify the post-finishing of the gate of the molded product after it has been released from the mold, and it can also make the marks less noticeable and improve the quality of the molded product.

In other words, there should be an optimal gate size for each of the injection filling process and the holding pressure/cooling solidification process.

However, conventionally, as shown in Fig. 6, the size of the gate of the injection mold is fixed as a compromise between the above two contradictory requirements, and molten resin is exclusively injected from the injection nozzle opening. The resin filling speed and pressure inside the cavity were controlled by controlling the speed and pressure. Therefore, control is complicated and requires a high-grade control device, which increases equipment costs. Since the gate of the molded product cannot be made smaller, there is an unavoidable problem that there is a limit to the simplification of post-finishing and the improvement of the quality of the molded product.

(Objective of the Invention) The present invention was made to solve the above-mentioned conventional problems, and by providing an optimal gate size for the injection filling process and the pressure holding/cooling solidification process,
In addition to making injection molding machine control easier and more reliable, it also simplifies post-finishing of molded products, and
The purpose is to improve the quality of molded products.

(Structure of the Invention) The mold with a variable gate of the present invention is provided with a gate piece movable in a direction to change the size of the gate at the gate position of the injection mold. An operating mechanism for operating from outside the mold is attached to the mold, and the operating mechanism is operated in conjunction with the operation of the molding machine to move the gate piece, and the size of the gate is adjusted to match the injection filling process and holding pressure.・It is characterized by being optimized to correspond to the cooling solidification process.

(Example) Hereinafter, an example of an apparatus for carrying out the method of the present invention will be described with reference to FIGS. 1 to 4.

In the figure, 1 is a fixed mold mounted on a fixed platen 2 via a mold mounting plate 3, 4 is a movable mold mounted on a movable platen 5 via a mold mounting plate 6, and these are fixed when the mold is closed. The mold 1 and the movable mold 4 constitute a cavity 7.

8 is a sprue provided on the fixed mold 1 side so that molten resin can flow from an injection nozzle of a plasticizing device (not shown); 9 is a cold slug provided on the movable mold 4 side as an extension of the outlet of the sprue 8 Well. 10 is a runner provided on the movable mold 4 side;
1 is located at the end of the runner 10 and has a cavity 7
This is the gate that serves as the resin injection port.

12 is a protruding pin facing inside cavity 7,
Reference numeral 13 denotes a protruding pin facing into the cold slug well 9, both of which are attached to a protruding plate 14, and are movable in the mold opening/closing direction by a cylinder or the like (not shown).

The present invention provides a movable mold 4 of such an injection mold with a piston rod 16 and a piston 17 each having a gate piece 15 forming a gate 11 at the tip thereof.
The movable mold 4 is fitted into the movable mold 4 so as to be movable in the mold opening/closing direction.
The oil passages 20 and 21 are connected to a hydraulic power source via switching valves (not shown). The runner 10 and the cold slug well 9 are formed at the tip of the piston rod 16, and a projecting pin 13 forming the bottom surface of the cold slug well 9 is movably fitted into the piston rod 16.

According to the above configuration, when pressure oil is supplied to the rod retraction side oil chambers 18 of the hydraulic cylinders 16 to 19 by operating the switching valve, the piston rod 16 is retracted to the retraction end position as shown in FIG. Gate 1 between the gate piece 15 at the tip of the rod and the fixed mold 1
1 is the optimum size a for the injection filling process. Conversely, when pressure oil is supplied to the rod forward movement side oil chambers 19 of the hydraulic cylinders 16 to 19, as shown in FIG.
The piston rod 16 advances to the forward end position,
The gate 11 has a size b that is optimal for the pressure holding/cooling solidification process.

Gate 1 of injection filling process and holding pressure/cooling solidification process
If it is desired to reverse the size of 1, the order of operation of the switching valves, which are operated in conjunction with the operation of the molding machine, may be reversed.

In addition, when controlling the size of the gate 11 according to the resin pressure inside the cavity 7 during the pressure holding process, as shown in FIG. 1, the pressure sensor 22 is connected to a controller 23 that controls the switching valve, and during the pressure holding process, the controller 23 switches the resin pressure in the cavity 7 inputted from the pressure sensor 22 to a certain pattern. The size of the gate 11 may be adjusted by controlling a flow rate or pressure control valve such as a servo valve that is equivalent to a valve.

In the above embodiment, the gate piece 15 constituting the gate 11 is moved and operated by the hydraulic cylinders 16 to 19 in the direction of changing the size of the gate 11, but the point is that the gate piece 15 Any operating mechanism may be used as long as it can be moved and operated from outside the mold in conjunction with the mold. FIG. 5 shows an example of a mechanical operating mechanism, which includes a rod 24 having the same structure as the piston rod 16 and piston 17.
The movable mold 4 is provided with a cam follower 25 and a tiltable adjustment lever 28 having a cam 26 at one end and a gear 27 at the other end, which can come into contact with the back surface of the cam follower 25. gear 27
A pinion 29 that meshes with the cam mechanism 29 is integrally provided on the outside of the drive mold 4 so that it can be driven by a motor 30.
6, the size of the gate 11 is adjusted by advancing the gate piece 15, which is biased with a retreating force by resin pressure.

(Effects of the Invention) As described above, the present invention makes the gate that functions as a throttle at the cavity entrance variable, and adjusts the gate size in the injection filling process and the holding pressure/cooling solidification process in conjunction with the operation of the molding machine. By switching to the optimal one, flow resistance is reduced in the injection filling process, and holding pressure and pressure are reduced.
In the cooling solidification process, the molten resin can be reliably contained within the cavity, making control easier and more reliable than in the past. Since the gate of the molded product taken out from the mold can be made smaller than before, post-finishing can be easily performed, and the quality of the molded product can be improved by making the gate so small that the marks are not noticeable.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, and FIG.
3 are enlarged views of essential parts for explaining the operation, FIG. 4 is a sectional view to which a control system is added, and FIG. 5 is a sectional view showing another embodiment of the present invention. FIG. 6 is a sectional view showing a conventional example. 1... Fixed mold, 4... Movable mold, 7... Cavity, 8... Sprue, 9... Cold slug well, 10... Runner, 11... Gate, 15
...Gate piece, 16...Piston rod, 17...
...Piston, 18, 19...Oil chamber, 20, 21...
...Oil passage, 22...Pressure sensor, 23...Controller, 24...Rod, 25...Cam follower,
26...cam, 27...gear, 28...adjustment lever, 29...pinion, 30...motor.

Claims (1)

[Claims] 1. An operation in which a gate piece movable in a direction to change the size of the gate is provided at the gate position of an injection mold, and the gate piece is operated from outside the mold in conjunction with the gate piece. A mechanism is attached to the mold, and the operating mechanism is operated in conjunction with the operation of the molding machine to move the gate piece, and the size of the gate is adjusted to correspond to the injection filling process and the holding pressure/cooling solidification process. An injection molding method characterized by being optimized. 2. A pressure sensor for detecting the resin pressure in the cavity by attaching a piston rod and a piston having a gate piece forming the gate at the tip to the movable mold of the injection mold so as to be movable in the mold opening/closing direction, and facing the cavity. A mold with a variable gate, characterized in that the size of the gate can be adjusted by controlling a piston rod drive mechanism using a signal from the pressure sensor.