Instable dimensions of modified plastic injection products--- Mold Failure

- Jun 23, 2018 -

The structural design and manufacturing accuracy of the mold directly affect the dimensional accuracy of the plastic parts. If the rigidity of the mold is insufficient or the molding pressure in the mold cavity is too high during the molding process, deformation of the mold may cause deformation of the plastic parts. stable.


If the gap between the guide pillar and the guide bush of the mold is poor due to poor manufacturing precision or excessive wear, the dimensional accuracy of the molded part of the plastic part will also decrease.


If there are hard fillers or glass fiber reinforced materials in the molding raw material that cause serious wear of the cavity, or when using a single-mold and multi-cavity molding, there is an error between the cavity, gate, runner, etc., and feed port balance and other reasons. Inconsistent mold filling can also cause size fluctuations.


Therefore, when designing the mold, sufficient strength and rigidity of the mold should be designed, and the processing precision should be strictly controlled. The cavity material of the mold should be made of a wear-resistant material, and the surface of the cavity should be heat-treated and cold-hardened. When the dimensional accuracy of the plastic parts is very high, it is better not to adopt a multi-cavity structure. Otherwise, in order to ensure the molding accuracy of the plastic parts, a series of auxiliary devices must be set on the mold to ensure the precision of the molds, resulting in the production of molds. High cost.


When plastic parts have thicker errors, they are often caused by mold failures. If the thickness of the plastic part is thick in the mold under one cavity condition, generally the relative positional deviation of the cavity and the core is caused by the installation error and poor positioning of the mold. At this time, for those plastic parts whose wall thickness is required to be very precise, they cannot be positioned solely by guide posts and guide bushes, and additional positioning devices must be added.


If it is a partial thickness error under a multi-cavity condition, under normal circumstances, the error at the beginning of molding is small, but the error gradually increases after continuous operation. This is mainly caused by the error between the cavity and the core. This phenomenon is most likely to occur especially when hot runner molding is used. In this regard, a dual cooling circuit with a small temperature difference can be set in the mold. If it is a thin-walled round container, a floating core can be used, but the core and cavity must be concentric.