Analysis and Solutions of Injection Molding Shrinkage Causes

The thermoplastic resin used for injection molding is injected into the cavity of the mold in a state of heating and liquefaction, and its heat is taken away by contacting the surface of the mold, and then cooled and solidified.

At this time, the volume in the liquid state is reduced by the volume contraction during solidification. This phenomenon is called "molding shrinkage". It is called "shrinkage" in English.

Mold shrinkage is a very important physical phenomenon when manufacturing plastic injection molded products. Only an accurate understanding of this physical phenomenon can produce injection-molded products of the desired size and shape.

Additionally, during the design and fabrication of injection molds, mold shrinkage must be taken into account when determining cavity dimensions and dimensional tolerances.

The range of molding shrinkage depends largely on the kind of thermoplastic resin. That is, the type of resin determines the shrinkage rate. However, in addition to the type of resin, the following factors must also be considered.

1. Cavity surface temperature

2. Thickness of molded product

3. Molding conditions (holding pressure)

4. Gate shape

5. Gate size

6. Resin temperature

7. Packing Type

8. Resin flow direction

9. Material particle pre-drying

10. Exhaust port exhaust efficiency

In the actual mold design, it is necessary to comprehensively investigate these factors, determine the molding shrinkage rate, and then deduce the manufacturing size of the cavity through the specified technical calculation formula.

The most reliable shrinkage rate data can be obtained by analyzing the original data obtained during the trial production of its own molding process. During the trial production of injection molding, it is very important to collect the above data as accurately as possible and compare it with the dimensional data. The cumulative amount of these data determines technical capabilities.

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