WELD LINE IN MOULDING

Weld line ocures in injection molding, it happens when two melt streams join. Melt stream gets divided at cutout (core) in the part and they join at the other end of the cut out.

Normally weld line region is filled at the end of injection stroke or during pressure phase.

Strength of the weld line is weak when partially frozen melt front meet. The orientation at the joint remains perpendicular to direction of flow -a sign of weakness.

Weld line can form by melt stream flowing in same direction or in opposite direction.

It is not possible to eliminate weld line, but it can be made sufficiently stronger or its position can be altered.

MELT STREAM FROM OPPOSITE DIRECTION

weld lines

CHANGING WELD LINE POSITION

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Weld lines on part Weld lines on part Weld lines on part Weld lines on part