Warpage in Reinforced PA6: Causes and Six Practical Fixes

Three main causes

One, fibre orientation. Low shrinkage along flow versus high across it is the dominant reason for warpage in reinforced compounds.

Two, uneven crystallisation. Mould temperature variation or wall thickness differences create different crystallinity across the part, and post-crystallisation then causes dimensional drift — the feature that separates PA from PC.

Three, unbalanced cooling. Unequal cooling between the moving and fixed halves bows the part toward the hotter side.

Six fixes, cheapest first

1. Raise and balance mould temperature to 80-100 °C, keeping the difference between halves within 5 °C.

2. Optimise holding: extend hold to gate freeze-off and use a profiled hold curve to compensate shrinkage.

3. Adjust injection speed: slower reduces orientation, but watch for short shots and fibre show.

4. Move the gate or add gates to shift the orientation pattern favourably.

5. Uniform wall thickness — the most effective route and unfortunately the latest one available.

6. Compound change: replace part of the glass with mineral fillers such as glass beads or talc to cut anisotropy.

Verification

Run mould-flow analysis before production to predict warpage, and check short shots to confirm orientation. Simple checks: measure flatness on a granite plate with feeler gauges, or re-measure after three days to reveal post-crystallisation distortion.