Cavity pressure
In mold data supporting stable fill.
Cavity pressureGlossary
What Is Process Capability (Cpk)? Injection Molding Explained
Cpk is a statistic describing how well a stable molding process stays inside specification limits.
Glossary
Cpk summarizes how well a stable process fits inside specification limits
Plastic processes drift with moisture, regrind, and temperature so capability needs enough shots.
Capability studies run after process stabilizes, not on first T1 shots alone.
Customer quality plans set Cpk targets. Common discussions start near 1.33 for production features.
SPC charts track drift after capability is demonstrated.
Quality
When Cpk enters molding conversations
Tie capability to features that matter on the drawing.
- Critical fit dimensions with tight tolerances
- Safety features where drift has functional risk
- Automotive or medical style quality plans on RFQ
Go deeper
Where this term connects
Each link is a different angle on the same program, not a duplicate definition.
Scientific molding
Structured process development.
Scientific moldingPPAP
Package that may require Cpk.
PPAPRegrind
Variable that can shift capability.
RegrindVisual 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
Cpk questions
What Cpk is acceptable?
Customer quality plans set targets. 1.33 is a common starting discussion.
Can Cpk be fixed in steel only?
Steel sets nominal. Process control maintains capability.
Does color change reset Cpk?
Major process changes may need new capability studies.
Next step
Define critical features on drawing
Upload CAD with tolerance and capability requirements.