What causes short shot of plastic mold in injection molding?

Short shot refers to the phenomenon that the cavity of plastic mold is not completely filled due to the insufficient fluidity of plastic, resulting in incomplete plastic products. The main reason is improper injection pressure and speed (including excessive pressure loss caused by resistance), which is mainly affected by the following aspects:


1、 Injection molding machine

(1) Insufficient injection molding capacity – this is caused by the high capacity of the injection molding machine, which may also be caused by insufficient plasticizing capacity or insufficient injection quantity. The insufficient plasticizing capacity can be increased by prolonging heating time, increasing screw speed and increasing back pressure. If the injection volume is not high enough, a larger injection machine can be used to solve the problem.


2、 Improper design of plastic mould

(1) Local short shot caused by flow imbalance in each cavity of a multi cavity mold – when the injection molding capacity of the injection molding machine is sufficient, this defect is mainly caused by the uneven flow in each gate, that is, the uneven distribution of the cavity in the plastic mold.

(2) The flow range of the melt is too long and the flow resistance is too large. The parts that hinder the melt flow include nozzle, gate, runner and the thin wall of the product. By increasing the nozzle diameter / temperature and using the nozzle with small flow resistance, the flow resistance of the nozzle can be reduced.

(3) Poor exhaust. When filling the cavity, air is trapped to produce a reaction force. When the melt is injected into the cavity, the cavity is closed by the melt from the beginning, and the air is trapped in the unfilled local area. Similarly, due to the high filling speed, sometimes the air does not have enough time to discharge from the plastic mold through the parting surface, but is compressed, resulting in some unfilled areas in the cavity, thus shortening the production time of the molded parts.


3、 Improper molding process

(1) Improper injection molding process – low barrel temperature, slow injection speed, short injection time and insufficient back pressure lead to plastic shortage.

(2) Excess supply of plastic – if too much plastic enters the barrel, the injection pressure is lost due to the compression of the particles, which reduces the pressure required to inject the melt from the nozzle, which is necessary for injection molding, resulting in insufficient injection pressure. The solution is to adjust the feed rate, i.e. melting rate, and make it just suitable for molding.

(3) Unstable production cycle: frequent machine shutdown and production inconsistent with normal cycle make some plastics stay in the barrel for a long time, resulting in the reduction of density and viscosity, resulting in short shot.

(4) Improper mold temperature results in lower injection rate and plastic filling.


4、 Choice of plastics

(1) Poor fluidity of plastics – if the plastic material does not have a high fluidity, it solidifies before reaching the furthest end of the cavity or before flowing into the overflow tank, which usually results in insufficient jet flow.

In order to eliminate these defects, the melt / mold temperature and injection pressure / velocity can be increased to make the melt reach the end of the cavity before solidification. In this case, large plastic fluidity is particularly important, so choosing a plastic with good fluidity is also a solution. If the flow coverage is too long and the plastic does not fill the injection molding part correctly, it is recommended to change the gate location to reduce the plastic flow.


5、 Improper product design

In the process of product design, the principle of uniform wall thickness must be followed. If the uniform wall thickness cannot be maintained, please change the plastic mold design in time. Increase the number of flow channels or ribs in areas where feeding is difficult, so as to avoid the defect of insufficient filling due to too thin wall thickness.

In short, there are many reasons for short shot, which restrict and influence each other. In order to reduce and correct this defect, we need to comprehensively consider the relationship between these aspects, constantly practice and accumulate experience, so as to quickly determine the reasons for insufficient filling, so as to reduce the waste of resources and increase the production of products.


About JasonMould Industrial Company Limited

Jasonmould is a China mold maker of plastic molds- injection mold, die casting moulds, plastic blow molding, rotational molding, medical plastic injection molding, two shot plastic injection molding, insert molding, overmolding, metal injection molding, micro injection molding, powder injection molding, ceramic injection molding, liquid injection molding, husky injection molding, household mold, casting mold, die mold tool, custom molds, china moulds, rapid prototyping tooling, plastic prototyping tooling, punch press tooling, die and tooling for mobile/ cell phone parts, automotive parts, vacuum cleaners, rechargeable tools, telephones, copiers, computers, multimedia speakers, and many other electronic products and household appliances. And also a plastic product manufacturer, mold manufacturer China– plastic parts, plastic water tank, plastic balls, plastic containers, plastic buckle, plastic anchor, plastic hanger, plastic spoon, plastic pipe fitting, plastic tumble, plastic tableware, plastic cups, plastic bottles, plastic tray, plastic cosmetic container, plastic case, plastic food container, plastic chairs, plastic caps, plastic cap closure, plastic tubes, plastic water pipes, plastic knobs, plastic tubing, plastic utility boxes, plastic racks and so on.

Person: James Yuan
Company: JasonMould Industrial Company Limited
Add:  LongGang Village,LongXi Town,BoLuo County,HuiZhou City,GuangDong Province, China
Tel: 86-752-6682869
Email: [email protected]

Site: https://www.jasonmolding.com/custom-injection-molding/



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