Question

6) Discuss what causes ‘weld lines’ in an injection molded part and why these pose a problem. Sketch examples.

Answer 1

weld lines are the most common defect in injection molding. weld lines is formed when two or more flow path separatly in apposite direction meet during the filling process in a mold cavity.

weld lines can be caused by-

Material flowing around holes,

Inserts in the part

Multiple injection gates

Variable wall thickness

the orientation of the grain in weld line are perpendicular to the flow path.

weld lines are generally undesirable it reduces the sthength in weld line area. the strength of the weld line area can be 10 to 90 % of the pure material used. the exact strength of the weld line based on ability of melt to weld each other at weld line area.