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• Warpage / Distortion - plastic injection troubleshooter


• Description:
A dimensional deformation of the moulding resulting from frozen-in stress, or because the part was taken too hot from the mould. Basically it is due to pressure differences between areas.

• Causes:
part
· wrong part design
· part too heavy
machine
· insufficient cooling time
· too high injection pressure
mould
· wrong gate location:
  different shrinkage in different flow directions
· too big undercuts
· inadequate ejector pins
· cavity too hot
material
· orientation of fillers
· wrong material choice


• Actions:
1st
equalize temperature of both mould halves
2nd
observe mould for uniform part ejection
3rd
check handling of parts after ejection from mould
4th
check part weight: take care with some resin
5th
increase injection hold time
6th
increase cooling time
7th
increase or reduce injection pressure
8th
increase mould close time
9th
increase or reduce mould temperature
10th
set differential mould temperatures to counteract warpage due to part geometry
11th
check gate locations and total number of gates to reduce orientation
12th
additional gates may be required to overcome overpacking or underpacking on large parts
13th
increase gate dimensions
14th
change gate location if glass-filled, notice fibre orientation
15th
redesign part to equalize wall variation in moulded part - heavy and thin walls in same part create differential shrinkage stresses
16th
use shrink fixtures and jigs for uniform cooling of the part


contact: jmfalcao@moldplast.com