Short shot on the injection molded part

What is this?
The melt is not fully filled after entering the mold cavity, resulting in short shot of the plastic part.

Why do it occur and can it be prevented?
① Improper equipment selection.
Solution: When selecting equipment, the amount of shot size in the machine must be greater than that in the product. Besides, the weight of the injection molded part can only account for 85% of the total amount of shot size in the machine.
② Insufficient feeding.
Solution: If there is a "bridging" phenomenon at the feed inlet, the screw injection stroke can be appropriately increased to increase the feed quantity.
③ Poor raw material fluidity.
Solution:
*Improve the viscous flow defect of the mold gating system.
*Set the gating position reasonably.
*Expand the size of the gate, runner and feed inlet.
*Use a larger nozzle.
*Increase the raw material temperature appropriately.
④ Unreasonable design of the gating system.

Solution: When designing the gating system, it needs to pay attention to the gate balance. In the meanwhile, the weight of the plastic part in each cavity should be proportional to the gate size, so that each cavity can be filled at the same time. Besides, the gate position should be selected in the wall thickness part. At last, it can also adopt a design scheme of balanced layout of the runner.

⑤ Inadequate venting.

Solution: Check whether there is a cold slug well or its position is correct. For molds with deep cavities, venting grooves and venting holes should be added at the short shot. Venting grooves with a depth of 0.02-0.04mm and a width of 5-11mm can be set on the opening mold surface. As for venting holes, they should be set at the final filling of the cavity. In addition, in terms of process operation, by means of increasing the mold temperature, it can reduce the injection speed, the gating system resistance and the mold clamping force.

⑥ Too low mold temperature.
Solution: The mold must be preheated to the temperature required by the process before starting the machine. If the mold temperature cannot be raised, it need to check whether the mold waterline design is reasonable.
⑦ Insufficient injection pressure.

Solution: The injection pressure is close to a positive proportional relationship with the mold filling length. If the injection pressure is too small, the mold filling length is short, so the cavity is not fully filled. In this case, the injection pressure can be increased by slowing down the forward speed of the injection material and appropriately extending the injection time.