What Common Defects Does Good Plastic Injection Molding Design Prevent?

Expert plastic injection molding design anticipates and prevents common defects through proper part geometry, mold design, and process optimization.

Sink Marks:

• Cause: Thick sections, insufficient packing
• Prevention: Uniform walls, proper rib ratios (50-60% of wall), adequate pack time, gas-assist for thick parts

Warpage:

• Cause: Non-uniform cooling, differential shrinkage, fiber orientation
• Prevention: Uniform wall thickness, balanced cooling, symmetric design, proper gate location

Short Shots:

• Cause: Insufficient material, inadequate flow, blocked vents
• Prevention: Proper wall thickness, adequate gating, sufficient venting, flow analysis

Weld Lines (Knit Lines):

• Cause: Converging flow fronts
• Prevention: Strategic gate placement, venting at weld locations, mold temperature optimization

Flash:

• Cause: Excessive pressure, worn tooling, inadequate clamp force
• Prevention: Proper process parameters, adequate clamp tonnage, parting line design

Burn Marks (Dieseling):

• Cause: Trapped air compressing and burning
• Prevention: Adequate venting, proper fill speed, vent placement at fill end

Voids:

• Cause: Thick sections, inadequate packing
• Prevention: Core-out thick areas, proper packing pressure/time, sequential valve gating

Jetting:

• Cause: Gate too small, too fast injection
• Prevention: Proper gate sizing, impingement design, fill speed optimization

Flow Lines:

• Cause: Varying flow speeds, temperature variations
• Prevention: Uniform flow path, consistent wall thickness, mold temperature control