JPH09234763A - Method for metering in injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use the method for metering for automation of a molding machine without shartage of injection by a method wherein only the initial metering is performed by no back pressure and metering is performed by adding the amt. of the resin corresponding to the amt. of decrease in density of the resin generated by no back pressure in metering newly the resin after discharging is completed. SOLUTION: When the retained resin in a heating cylinder 3 is discharged by no back pressure and metering of the resin is performed after completion of discharging, only the initial metering is performed under no back pressure and the metering is performed so as to compensate the amt. α of the resin corresponding to the amt. of decrease in density of the metered resin K. In addition, it is performed by retreating an injection screw 3 to a preset stopping position B for increasing metering being more backward than the metering stopping position SM. As no back pressure is applied on a plasticized resin, even when no packing is generated at the apex of a nozzle 2, there exists no possibility of flowing of the metered resin into the mold side and the amt. of the resin corresponding to decrease in density of the metered resin K is compensated with the amt. α of the resin and there exists no possibility of generation of failure of molding caused by shortage of injection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to measurement after discharging stagnant resin in a heating cylinder due to resin change or abnormal accumulation.

[0002]

In injection molding, in order to cope with high-mix low-volume production, mold replacement and resin replacement are frequently performed. Further, with the unmanned molding machine, it has been adopted to automatically discharge the resin that has abnormally stayed due to a trouble during molding.

In the case of resin replacement, the resin used in the previous molding is replaced with a new resin for the next molding, so that the previous resin accumulated in the heating cylinder must be completely discharged. I have to. The accumulated resin is discharged by repeating injection and metering by forward and backward movement of the screw a set number of times while supplying new molding resin for resin replacement with the nozzle of the injection device separated from the mold. There is. When the resin that has abnormally stayed is discharged, the same resin is supplied.

Further, in the usual measurement at the time of molding, back pressure is applied, but the measurement at the time of discharging the stagnant resin is carried out by the plastic resin in the front part of the heating cylinder by the back pressure and the measured resin in a molten state is
No back pressure is applied to prevent leakage from the nozzle and dripping.

In backless pressure measurement, the density of the plasticized resin is lower than that in the case where back pressure is applied.
However, since the resin discharged for the purpose of resin replacement is discarded as it is as a defective material, there is no particular problem even if the density decreases.

After the discharge of the accumulated resin is completed, the nozzle is made to touch the mold and the back pressure is applied as usual to carry out the measurement, whereby a part of the plasticized resin flows into the mold side. And solidify, and the resin amount is small and weighs, resulting in poor molding. In order to prevent this phenomenon at the beginning of weighing,
If the first measurement is performed without back pressure, the density of the plasticized resin will decrease and the injection will always be short, resulting in a defective molded product.

The occurrence of such a defective product is not preferable when a series of molding steps are automatically performed, and even when it is a resin change or a phenomenon after the abnormally retained resin is discharged. On the molding system, a molded product is processed as a defective product, and normal injection molding cannot be performed unless the processing is completed.

The present invention was conceived in view of the above circumstances, and its object is to prevent the injection from being short-circuited even when measuring resin by no negative pressure, and to employ it for automation of a molding machine. Another object of the present invention is to provide a new injection molding weighing method capable of achieving the above.

[0009]

The present invention according to the above-mentioned object is to discharge the stagnant resin in the heating cylinder without back pressure and to newly measure the resin after the discharge is completed. The amount of resin corresponding to the amount of resin density reduction caused by no back pressure is added and measured.

The amount of increase in the resin amount is set by making a trial shot in advance for each molding condition or molded product. This setting can be performed by detecting the backward movement distance of the injection screw, the measuring time, the screw rotation speed, and the like.

In the weighing according to the present invention, even if the density of the resin plasticized by no back pressure is reduced as compared with the case where the back pressure is applied, the amount of reduction is estimated in advance to perform the weighing. Therefore, there is no shortage of the injection filling amount into the mold, and therefore, it is judged as a defective product at the time of molding a new resin after resin replacement or shifting to molding after discharging abnormally retained resin. It is possible to avoid such a situation.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment in which a backward movement distance of an injection screw is detected and a measurement is performed by adding a resin amount corresponding to a density reduction amount.

In the figure, reference numeral 1 denotes a heating cylinder, which is provided with heating means such as a band heater (not shown) on the outer periphery and a nozzle 2 is provided at the tip. An injection screw 3 is provided inside the heating cylinder 1 so as to be rotatable and movable back and forth, and a ring valve 5 is provided between the screw tip and a conical screw head 4. An injection cylinder (not shown) at the rear end of the screw
Plunger 6 is connected.

The injection screw 3 is rotated together with the plunger 6 by a hydraulic motor (not shown) attached to the rear end of the injection cylinder while receiving the supply of granular resin from the supply port 7 at the rear of the heating cylinder. By this rotation, the resin is sent to the front part of the heating cylinder 1 while being plasticized, and the injection screw 3 is moved backward while rotating due to the resin pressure.

Normal metering is completed by moving the injection screw 3 backward from the screw forward most advanced position A to a preset metering stop position (SM) while applying back pressure by the injection cylinder. Since back pressure is applied in this measurement, the decrease in resin density due to melting is prevented, and the resin is measured in proportion to the molded product.

To discharge the stagnant resin or the abnormally stagnant resin at the time of changing the resin, the injection screw 3 is moved back and forth between the most advanced position A of the screw and the metering stop position SM, and injection is repeated several times. Further, since the discharge is performed by separating the nozzle 2 from the mold, the resin leaks and drips from the nozzle 2 in the state where the back pressure is applied as in the case of the measurement, so that the back pressure is not applied to prevent this. .

After the discharge is completed, when the tip of the nozzle 2 is touched by a die (not shown) to measure the resin by applying back pressure, the resin is solidified by cooling from the die side. Before the occurrence of the problem, a part of the measuring resin leaks to the mold side, which causes an inconvenience, and a measuring error corresponding to the amount.

In order to prevent such a situation, if the first measurement is performed without applying back pressure, the resin leakage to the mold side will be eliminated, but the injection will be shorted due to the shortage of the injection filling amount, resulting in a failure. Good products will be generated. This injection short is due to the fact that the density of the molten resin decreases due to weighing without back pressure applied. The volume of resin when the metering stop position (SM) is reached is when the back pressure is applied. Although it is apparently the same, it is substantially small, and when compressed, the amount is reduced to an amount that is less than the amount required to form a molded product.

Therefore, the weighing is performed only in the state where there is no back pressure only at the beginning, and the weighing is performed so as to supplement the resin amount α corresponding to the density decrease of the weighing resin K. In this embodiment, the injection screw 3 is retracted to a preset increased metering stop position B behind the metering stop position SM. With such measurement, back pressure is not applied to the plasticized resin,
Even if no packing occurs at the tip of the nozzle, the measured resin does not flow into the mold side, and the resin amount α compensates the resin amount due to the density decrease of the measured resin K, so that a molding defect due to an injection short circuit occurs. It won't wake up.

After the first metering is completed, the metering is reset to the metering stop position SM, and the injection cylinder side is also set so that the back pressure is applied from the next injection. As a result, the molding continues the injection by the normal measurement until the next resin change or abnormal resin retention occurs.

FIG. 2 shows a flow chart in the case of resin change. According to this flowchart, the process from automatic startup of the molding machine to the start of automatic molding can be performed unattended by adding a resin change process in the middle of the process. it can.

FIG. 3 shows a case where the automatic insert system is used to prevent resin retention when the molding machine is interlocked. In the automatic insert system, when there are no more workpieces, the workpieces cannot be cut out from the workpiece aligner, so that the robot does not insert the workpieces into the mold.

The molding machine waits for an insert completion signal and measures for the next molding. However, if the resin is weighed in the heating cylinder and kept waiting for a long time, the resin is overheated and becomes defective, and if the resin is injected, molding failure occurs. In order to prevent such a situation, the time after the measurement is monitored, and when the time exceeds the set time, it is judged as a retention abnormality and the process is switched to discharge resin and measure new resin.

The removal and measurement of the resin is started after a new work is supplied to the work aligning machine and the work is inserted into the mold by the robot. Then, after the first measurement is performed by the above process, the molding process is switched to the normal measurement again, and the injection molding by the normal measurement is performed unless the work is broken again.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of an essential part of an injection device showing an embodiment of a weighing method according to the present invention.

FIG. 2 is a flowchart of a molding machine automatic start-up system adopting the weighing method of the present invention.

FIG. 3 is a flowchart of an automatic insert molding system that employs the weighing method of the present invention as a resin retention preventing means.

[Explanation of symbols]

 1 Heating cylinder 2 Nozzle 3 Injection screw 4 Screw head

Claims (1)

[Claims] 1. When the accumulated resin in the heating cylinder is discharged with no back pressure, and when the resin is newly measured after the discharge is completed, only the first measurement is performed with no back pressure, and the resin density generated by the no back pressure is measured. A measuring method in injection molding, characterized by adding a resin amount corresponding to the decrease amount and measuring.