A side cavity half
- Forms exterior surfaces customers see
- Often receives higher polish or texture spec
- Stays mounted to the stationary platen on many two plate tools
Glossary
What Is the A Side and B Side? Injection Molding Explained
A side and B side are shop names for the stationary cavity half and the moving core half.
Glossary
A side and B side name the two mold halves on the press
Cosmetic assignment and ejection direction start with this convention.
The A side is usually the cavity half on the stationary platen. The B side is usually the core half on the moving platen that opens for ejection.
Shops may flip labels on special tools, so the mold layout drawing beats memory in email threads.
Class A surfaces are often placed on the cavity half when pull direction allows. Ejector pins and robot access usually plan from the B side opening stroke.
Glossary
How a side b side 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.
Assignment
Typical A side versus typical B side roles
Confirm on the tool design print for your program.
B side core half
- Forms ribs, bosses, and interior details
- Carries most ejector pins and stripper actions
- Opens toward the operator or robot pick position
Drawings
What to mark before DFM signoff
These notes prevent reversed cosmetic assumptions.
Preferred pull direction relative to assembly
Visible faces that must stay on cavity half if possible
Parting line location on edges customers see
Side action direction if slides break the simple A B split
Go deeper
Where this term connects
Each link is a different angle on the same program, not a duplicate definition.
Cavity
Exterior half in many two plate layouts.
CavityCore
Interior half and ejection focus.
CoreEjector pin
Push points on the opening half.
Ejector pinDesign guide hub
Parting line and draft tied to A B assignment.
Design guide hubVisual 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
A side and B side questions
Is A side always the cavity?
That is the common convention, but always read the mold designer layout.
Can cosmetics live on the B side?
Yes when geometry demands it. Ejection and witness planning must follow.
Does A B labeling affect quote cost?
Indirectly through cavitation, actions, and polish scope on each half.
Next step
Align parting with DFM
Upload CAD with pull direction and cosmetic faces noted before steel cut.