Buyer scales CAD arbitrarily
- Mold steel may double compensate or under compensate
- Assembly fit fails on first samples
Glossary
What Is Shrink Rate? Injection Molding Explained
Shrink rate describes how molded plastic contracts from mold dimensions after cooling.
Glossary
Shrink rate is how far molded plastic moves from cavity size to cooled part size
Mold steel is scaled so dimensions hit nominal after resin solidifies.
Amorphous and semi crystalline families shrink differently with orientation and gate location.
Mold makers apply shrink factors in steel unless the drawing states nominal design intent only.
Glass filler and long flow paths change effective shrink versus isotropic datasheet values.
Glossary
How shrink rate shows up on real programs
Library photos illustrate molding and tooling context for this term.
- Use the term in RFQs with geometry and material context, not in isolation.
- Link to the design guide when the term affects steel or part design.
- Upload CAD when the term changes tooling scope or piece price.
Workflow
Nominal CAD versus shrink compensated steel
Miscommunication here drives T1 dimension fires.
Nominal CAD with mold maker shrink in steel
- Single owner of shrink math on the tooling side
- Critical fits reviewed against steel offsets
Go deeper
Where this term connects
Each link is a different angle on the same program, not a duplicate definition.
Melt flow index
Flow behavior related to packing and shrink.
Melt flow indexCycle time
Cooling affects crystallinity and shrink.
Cycle timeDFM article
Wall and boss design affects shrink sink.
DFM articleCavity
Steel scaled in the cavity half.
CavityVisual reference
Photos from molding and tooling programs
Images are selected from the NetProto Forge media library for this topic.
Injection molded production parts on a tray
Injection molded production parts on a tray
Engineer reviewing a molded part drawing
Engineer reviewing a molded part drawing
Plastic housing components from a steel tool
Plastic housing components from a steel tool
FAQ
Shrink rate questions
Should CAD be scaled for shrink?
Provide nominal design intent unless your quality plan says otherwise.
Does shrink differ by color?
Some programs see lot to lot variation. FAI catches drift.
Can shrink be tuned in process?
Minor dimensional moves are possible but steel is the primary lever.
Next step
Upload nominal CAD for DFM
Let tooling apply shrink in steel with your fit requirements noted.