What Are The Reasons For The Poor Dimensional Accuracy Of Plastic Injection Molding Products?

- Nov 20, 2017-

Plastic injection mold in the process of use, there will be the product size of the poor precision phenomenon, which will lead to the production of waste, affecting the production efficiency of enterprises, then plastic injection molding products, the size of the poor accuracy of what are the reasons?

The main reasons for the poor precision of molding products are as follows: there are problems in the design and manufacturing accuracy of die products; the shrinkage of products caused by forming process conditions is greatly changed; the shrinkage of products caused by molding materials is not balanced; the time variation caused by environmental conditions after molding and so on.

1, the manufacturing accuracy of each part of the mold will directly affect the dimensional accuracy of the product. A fixed mold and a movable mold fitting, the position of the side of the mold structure will cause the product size error. Long term use of mold will be caused by mold cavity pressure, clamping force and other factors causing mold deformation or relaxation, in the design of mold must consider the strength of mold materials and heat treatment.

2. The shrinkage of injection molded parts is caused by the change of the density of the melt from the molding temperature to the ambient temperature. It is not only related to the change of the molding temperature, but also to the constraint of the parts (the core and the location of the insert). Mould designers must consider the influence of process conditions and material behavior shrinkage, especially the design of cooling system, the geometry of runner and gate. We should optimize the gating system to ensure balanced flow, to avoid overvoltage and undervoltage caused by uneven shrinkage; the multi cavity mold cavity layout should be optimized to ensure the thermal equilibrium temperature of water cooling system of the mold, the design optimization of punch and die to ensure uniform mold temperature.

3. Environmental changes caused by the changes in the shape of the products placed in the atmosphere for several days, the size of the shape of the product changes. It is mainly caused by the following reasons: ambient temperature, crystallization after molding, relaxation of residual stress, etc..  The above environmental temperature changes, crystal changes and residual stress caused by dimensional changes are related to time, generally about 10 days after the stability, these changes for high precision dimensional products, must be fully considered in the design.