Three main reasons for dimensional changes of injection molded parts during processing

No matter what kind of plastic is, it has a certain shrinkage rate. If it is not controlled properly, it will directly lead to the change of the size of the injection molded parts. If the change is too large, it will directly lead to the unqualified quality of the injection molding products. This is a period that many injection molding factories do not want to see, and the three major factors affecting the dimensional change of injection molding parts.


1. Wrong selection of injection molding materials

The shrinkage of injection molding materials has little effect on the dimensional accuracy of plastic parts. If the precision of molding equipment and mold is very low, but the shrinkage rate of molding material is very small, it is very easy to ensure the dimensional accuracy of plastic parts. In general, the smaller the shrinkage of molding material is, the more difficult it is to ensure the dimensional accuracy of plastic parts. Therefore, in the selection of molding resin, it is necessary to fully consider the influence of shrinkage rate of raw materials on the dimensional accuracy of plastic parts. For the selected raw materials, the variation range of shrinkage rate must not be greater than the requirements of dimensional accuracy of plastic parts.

It should be noted that the difference of shrinkage rate of various resins is relatively small, and the analysis is based on the degree of crystallization of resins. Generally, the shrinkage of crystalline and semi crystalline resins is higher than that of non crystalline resins, so the range of shrinkage changes is small, and the shrinkage fluctuation of corresponding plastic parts after molding is also large; For the crystalline resin, the crystallinity is low, the molecular volume is reduced, and the shrinkage of the plastic part is small. The size of the resin spherulite also has an effect on the shrinkage rate. The spherulite is large, the gap of the molecular building is large, and the shrinkage ratio of the plastic part is large, so the impact strength of the plastic part is low.

2. Injection mold failure

The structural design and manufacturing accuracy of the mold indirectly affect the dimensional accuracy of the plastic part. In the molding process, if the rigidity of the mold is lacking or the molding pressure in the mold cavity is very low, the mold will deform, which will cause the plastic part forming size to be unstable.

If the fit clearance between the guide pillar and the guide sleeve block of the mould is out of tolerance due to less manufacturing accuracy or excessive wear and tear, the forming dimensional accuracy of the plastic part will also be reduced.

The first mock exam is that if the rigid filler or glass fiber reinforced material is used to form the raw material, the cavity will be slightly worn, or if the cavity is formed by one mold, the error between the cavity and the gate, the flow path and the improper balance of the feeding port will result in the filling process.

3. Injection molding equipment failure

If the plasticizing capacity of molding equipment is not enough, the feeding system is not stable, the screw speed is not stable, the stop function is abnormal, the check valve of hydraulic system is out of order, the thermocouple of temperature control system is burnt out, and the heater is open circuit, etc., the molding size of plastic parts will not be stable. If these faults are found out, targeted measures can be taken to eliminate them, including the failure of injection mold.

In the process of injection molding, any small problem will affect the quality of injection molding products, and even directly affect the size change.


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]


Share this post