Two materials.
One part.
Bonded as one.
Overmolding combines two plastics (rigid + soft, or contrasting colors) in single part. Common for soft-grip handles, sealed connectors, multi-material consumer products. Specific design rules apply.
Key principles.
Bond chemistry
Some material pairs bond well (TPE on PP, TPE on ABS); others need mechanical lock. Verify compatibility chart.
For non-bonding
When materials don't chemically bond, use mechanical lock features — undercuts, holes, ribs.
Both layers
Substrate wall ≥ 1.5 mm. Overmold thickness 0.5-2 mm typical. Avoid extreme thickness ratios.
First-shot stays in mold
First-shot substrate must stay in tool when second injection occurs. Design supports this.
Avoid bond face
Gate position affects flow and stress. Don't gate where overmold-substrate bond critical.
Different materials
Different shrinkage rates between substrates. Compensate in mold design.
FAQ
Soft-touch grip applications?
TPE or TPU overmolded on rigid substrate. Toothbrush handles, tool grips, electronics grips. Standard production approach.
Two-shot molding vs insert molding?
Two-shot: same machine, sequential injection, automated. Insert molding: substrate in separately, manually placed. Two-shot more efficient at volume.
Color matching?
Different colors achievable. Specify Pantone for each material. Verify colorfast across operating conditions.
Tool cost?
Two-shot tool 1.5-2× single-shot tool. Insert molding tool similar to single-shot but secondary operation.
Bond strength?
Bond per material pair. TPE on PP excellent. Verify with pull tests during process development.
Cycle time?
Two-shot adds 50-80% to single-shot cycle. Per-part cost optimized at production volumes.
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