EXPENSIVE INJECTION MOLDING DEFECTS!

EXPENSIVE INJECTION MOLDING DEFECTS!

How to eliminate and avoid the most frequent defects in plastics injection molding

kunststofftechnische Software GmbH

kunststofftechnische Software GmbH

1. DIESEL EFFECT

Burn marks at the end of the flow path

REASON

Air cannot escape from the mold and is compressed at the end of the flow path. The compression causes the air to heat up to such an extent that burn marks result.

Elimination of the defect via the material

Use materials or additives that set free less gas

Elimination of the defect via the process parameters

Reduce the injection speed, if possible reduce the clamping force

Elimination of the defect via the mold

Add venting channels and check for depositions

Avoid defects

Identify the missing venting numerically with CADMOULD beforehand.

2. SINK MARKS

Recesses or depressions on the surface

REASON

Nonuniform shrinkage

Elimination of the defect via the material

Use a material with less shrinkage

Elimination of the defect via the process parameters

Higher packing pressure, longer packing pressure time, lower mold temperature, lower injection speed, later switchover time

Elimination of the defect via the mold

Move the injection point to shorten the flow paths or avoid the weld line, employ cascade filling, add venting channels

Avoid defects

Sink marks can be determined with CADMOULD beforehand.

kunststofftechnische Software GmbH

3. JETTING

A strand of melt emerges from the gate, generally in the shape of a snake

REASON

As the melt does not adhere sufficiently to the wall, no uniform flow front develops, leading to a jet of melt instead

Elimination of the defect via the process parameters

Reduce the injection speed, increase the melt temperature, increase the mold temperature

Elimination of the defect via the mold

Move the runner, optimize the gate and runner.

Source: Bakelite AG

4. INCOMPLETE FILLING

The mold is not completely filled

at the end of the flow path or at

thin areas

REASON

Thin areas or points at the end of the flow path cannot be filled on account of the melt freezing prematurely or insufficient venting. It is also possible that the shot volume or residual melt cushion is too small.

Elimination of the defect via the material

Set a later switchover time, check the shot volume and residual melt cushion, increase the injection pressure or injection speed

Elimination of the defect via the mold

Add venting, increase wall thicknesses, insert flow aids, balance the runner system

Avoid defects

CADMOULD shows you the unfilled areas so that you can adjust the parameters prior to starting on mold construction.

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