JPH0133328B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to an injection control method for a plastic molding machine including an injection molding machine.

[Prior art]

When injecting molten resin into a mold cavity in a plastic molding machine, the most important thing is to minimize stress and to completely transfer the shape of the cavity. However, with conventional technology, when the injection pressure is increased to improve transferability, the stress near the gate increases, and in extreme cases, the stress of the entire molded product increases, which causes warping and reduces the precision of the molded product. I was letting it happen.

Therefore, as shown in Figure 5, the injection oil pressure gradually increases from the start of the injection process at point A, and the filling process ends at point B. Next, the pressure holding process begins, and as time passes during this holding process, the holding pressure increases. A method has been proposed to reduce the amount in stages. According to this method, the stress is certainly alleviated, but since the holding pressure is gradually lowered, the pressure transmission to the end of the flow of the molten resin becomes insufficient, and the transferability deteriorates. On the other hand, the method of gradually increasing the holding pressure improves transferability, but
The drawback was that the stress around the gate was significantly higher.

[Purpose of the invention]

The present invention eliminates these drawbacks, and its purpose is to provide an injection control method that ensures sufficient transferability of the molten resin to the mold cavity and minimizes the stress on the molded product.

[Key points of the invention]

The injection control method of the present invention is characterized in that the injection hydraulic pressure in the pressure holding process following the filling process is pulsed.

[Embodiments of the invention]

The present invention will be explained below with reference to FIG. 1 showing one embodiment. The injection process starts from point A, and at point B, the filling of the molten resin into the mold cavity (not shown) is completed, and thereafter the pressure holding process begins. From the start of this pressure holding process, the injection hydraulic pressure of a screw (not shown) that presses against the molten resin is applied continuously in a pulsed manner. At this time, the peak value of the pulse is approximately 10% higher than the highest oil pressure value during the filling process, and the time continues until the gate section cools down.

FIG. 2 shows another embodiment of the invention. This example is the same as the first embodiment shown in FIG. 1, except that the peak value of the pulse gradually decreases over time.

FIG. 3 also shows another embodiment of the present invention.
The pulse is emitted from point C, after which the pulse is emitted, and the rest is the same as in the first embodiment. Further, as a fourth embodiment of a modification of the third embodiment, the peak value of the pulse may be gradually reduced as time passes, as shown in FIG.

FIG. 4 shows a fifth embodiment, in which an interval time t2 is placed between each pulse, and other aspects are the same as in the first embodiment. Note that the interval time after the second and third shots may be other than t2, and the peak value of the pulse may be made to decrease with time as shown in FIG. Further, although not shown in the drawings, as a sixth embodiment, the peak value of the pulse may be increased or decreased over time.

〔Effect of the invention〕

As explained above, the injection control method of the present invention includes:
The injection oil pressure in the pressure holding process following the filling process was pulsed. For this reason, the pulsed holding pressure that acts over a short period of time effectively transmits pressure instantly to the end of the cavity, while minimizing stress in the pressure transmission path including the gate. Therefore, from thick-walled molded products such as lenses to thin-walled molded products such as laser desks and compact desks, the transferability is excellent and stress is low, etc., and its effects are great.

[Brief explanation of drawings]

Fig. 1 is a diagram of injection oil pressure versus time for the filling process and pressure holding process in one embodiment of the present invention, and Figs. 2 to 4 show the filling process and pressure holding process in other different embodiments of the present invention, respectively. FIG. 5 is a graph of injection oil pressure versus time for the filling process and pressure holding process in a conventional example.

Claims (1)

[Scope of Claims] 1. An injection control method in which the injection hydraulic pressure in the pressure holding process following the filling process is pulsed. 2. The control method according to claim 1, wherein the peak value of the pulse is approximately 10% higher than the maximum injection pressure value in the filling process. 3. The control method according to claim 1, wherein the peak values of the respective pulses are set to the same height. 4. The control method according to claim 1, wherein the peak value of the pulse is lowered over time. 5. The control method according to claim 1, wherein the peak value of the pulse is varied as time passes. 6. The control method according to claim 1, wherein the first pulse is issued after a certain period of time has elapsed after entering the pressure holding step. 7. The control method according to claim 1, characterized in that the pulses are output with an interval between each pulse.