Distortion

Distortion

Distortion is perhaps the prevalent preoblem for the moulding industry today and is normally caused by differences in cooling, shrinkage or orientation from one area

of the part to another.

Distortion concentrated in the corners is often due to poor cooling, parts incorporating a variable wall thickness profile can exhibit distortion due to differential

shrinkage.

As a general rule crystalline materials usually exhibit relatively high shrinkage and are more susceptible to distortion particularly where variable mould surface

temperatures and or variations in wall thickness occur.

Fibre filled compounds often show distortion due to anisotropic shrinkage due to differential fibre orientation effects. Reinforced crystalline grades tend to show

greater distortion than amorphous grades due to higher natural shrinkage of the base polymer.

Possible solution:

                 • Aim for uniform packing of the mould.
            
                 • Experiment with different mould temperatures.

                 • Ensure balanced filling of the mould.

                 • Increase the injection speed.

                 • Ensure uniform and symmetrical cooling of the moulding.

                 • Choose a more free-flowing plastic material.

                 • Consider changing to a material with lower shrinkage.

                 • Reduce differences in wall thickness.

                 • Stiffen up areas showing deflections by adding ribs.

                 • Avoid sharp corners.

                 • Move the gate for more uniform fill.

                 • Seriously consider simulation to identify the problem and help calculate a practical solution.

Fiber filled materials:

                 • Experiment with increasing or decreasing injection rates - fast / slow.

                 • Experiment with increasing or decreasing mould temperature.

                 • Move the gate to change fibre orientation.

                 • Experiment with glass sphere filled materials.