Injection Moulding Defects: A Summary

There are conditions which may result to some injection moulding defects. The following is a summary of what typical defects may occur, however the deviations on the defects would depend on specific circumstances.

         Short mouldings may be due to an inadequate shot capacity or the materials may freeze off before the mould is completely filled.

         Delamination may occur if the materials used are incompatible with the moulding or the skin of the material freezes prematurely, there could also be the possibility of a melt fracture.

         Flashing could occur if the shut-off faces of the mould are mismatched, the mould opens under the pressure of the materials being injected into it, and it could also be that the melt viscosity may be a bit too low.

         Poor weld lines may occur if the converging streams of the materials do not weld properly at the interface or the presence of foreign materials at the interface of the converging streams.

         Ejection difficulties may occur if there is insufficient cooling, there is excess pressure within the cavity of the mould, there is insufficient taper, the surface is poorly finished, the positioning or the area of the ejectors itself are not satisfactory, the cores are misaligned or the spruce may be misaligned.

         Sinking and voiding may occur if there is excessive shrinkage of the moulding itself, the cooling time is incorrectly set, the design of the mould or the product itself is not correctly manufactured, and the gate size is not suited for the grade of the material.

         What causes warpage:

two main reason can occur warpage in plastic parts:

  1. toolcooling temperatures are imbalanced (unreinforced material)

  2. there may also be some variations on the thickness of the productwalls, The solution will be in the  and the ejection system.

How can we prevent warpage?

  1. Design engineer parts and products with uniform wall thickness
  2. The mould heating system should be designed so that it dissipated heat as evenly as possible.


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