How do Weld Lines and Flow Marks occur? What are the solutions?

Date：2025-07-29   Views：1009

Primary Causes: 

• Low feedstock temperature

• Low mold temperature

• Low barrel temperature

Other Causes: 

Improper mold design, such as long runners (resulting in lower feedstock temperature after traveling through a long runner), improper gate location (e.g., not allowing feedstock to flow from thicker wall sections to thinner wall sections), improper vent locations, etc.

Mechanism:

Flow marks: Occur when low-temperature injection material flows over the mold surface under high pressure.

Weld lines: Occur when separate injection material flows meet again.

Solutions:

Temperature-related: 

Increase barrel temperature, nozzle temperature, and mold temperature.

Mold Design-related:

Enlarge the gate, add vent channels or overflow ports near the weld line location; optimize mold structure to avoid flow separation, thereby preventing injection material from solidifying before fully filling the mold.