Rounded corners.
Reduce stress.
Better parts.
Rounded corners in injection molding. All corners — internal and external — should be rounded. Stress concentration, mold flow, and tool life all benefit.
Key principles.
Generous
Internal corners minimum 0.5× wall thickness radius.
Smaller OK
External corners can be smaller (0.25× wall) but rounded.
Stress concentration
Sharp internal corners concentrate stress 3-5×.
Fillets help
Material flows better around radii. Sharp corners cause flow problems.
Sharp corners crack
Mold sharp corners crack and erode. Round corners last.
Same
No cost premium for rounded corners. Same machining or EDM time.
FAQ
Why round corners?
Stress concentration, mold flow, tool life. No cost premium. Always round.
Internal corner radius minimum?
0.5× wall thickness ideal. 0.25× minimum acceptable.
External corner radius?
Can be smaller. 0.25× wall thickness typical.
Sharp corner exception?
Rare — when assembly mating requires square corner. Use chamfer instead.
Specifying on drawing?
Note "all corners R0.5" or specific radii on drawing.
CAD modeling?
Add fillets in CAD model. Standard practice. Avoids manual fillet creation downstream.
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