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Field guide · Design validation

Validate Injection Molding Part Features Before Tooling

A preliminary ratio should produce a review question, not a false pass/fail verdict.

Classify each flag by consequence

Separate appearance risk, structural performance, fill/pack, cooling, dimensional stability, ejection, assembly and tool-manufacturing concerns. One feature can belong to more than one category.

Resolve conflicts explicitly

A thinner rib may reduce sink risk but lose stiffness. More draft may ease ejection but consume tolerance. A larger boss may support an insert but create a thick section. Record the chosen tradeoff, responsible discipline and evidence required.

Choose evidence proportional to risk

Low-risk changes may need an annotated CAD review. Higher-risk geometry may require structural analysis, filling/packing/warpage simulation, machined or printed assembly prototypes, texture plaques, insert trials or a soft-tool study. Do not claim that a printed prototype validates molded shrinkage or ejection.

Complete the moldmaker handoff

Review parting line, gate, runner or hot-runner interface, vents, cooling, ejection, steel conditions, shutoffs, slides, lifters, draft, texture, tolerances and measurement datums together. A ratio passing in isolation can still conflict with tool access or steel strength.

Plan first-shot evidence

Identify the surfaces and dimensions to inspect, cosmetic lighting and limit samples, assembly torque or pull-out tests, conditioning state, process window and cavity identification. Link those observations back to the feature record rather than changing CAD from undocumented impressions.

Close only with traceability

Close a flag when the CAD revision, rationale, approver, supplier feedback and planned molded-part validation are recorded. Reopen the review if resin, texture, fastener, draw direction, cavity layout or critical appearance requirement changes.

Sources: Protolabs wall-thickness guidance · Protolabs injection-moulding design guide · Protolabs Designing for Mouldability · Covestro strategic-radii guidance.