Quick answer: Before tooling, create a color-coded wall map and review each deviation from the nominal wall against function, flow, cooling, sink, shrinkage and ejection. The target is not mathematically identical thickness everywhere; it is a controlled thermal and structural path with intentional transitions and a validation plan.
Release Decision Matrix
| Review area | What to inspect | Evidence or disposition |
|---|---|---|
| Nominal wall | Resin, flow length, stiffness and service load | Supplier guidance plus flow and structural review |
| Thick zones | Bosses, pads, corners, ribs and intersections | Core, relocate, transition or accept with risk |
| Thin zones | End of fill, vents, texture and local pressure loss | Gate/flow evidence and minimum functional section |
| Measurement | CTQs, datums, conditioning and inaccessible walls | Defined gauge, sectioning, scan or part-weight control |
Approval Checklist
- Define exact resin, nominal wall, flow length and functional load.
- Map all walls, ribs, bosses, pads, corners and intersections in 3D.
- Explain every thin or thick exception to the nominal section.
- Review transitions, gate access, weld lines, vents and pressure margin.
- Check thick-zone cooling access and cosmetic sink criteria.
- Review draft, ejection support, warm handling and assembly constraint.
- Define CTQ measurement state, datums and methods.
- Mark steel-safe corrections and T1 evidence before release.
Create a Functional Wall Map
Choose a nominal wall from the exact resin, expected flow length, stiffness, impact, appearance and part size. Display meaningful thickness bands on the released CAD, then label intentional exceptions. Do not hide ribs, boss bases or internal pads by reporting only the shell average.
Connect each zone to product function. A sealing lip, flexible hinge and structural enclosure wall may legitimately differ, but their transitions and molding consequences still need review. Record whether a dimension is minimum, nominal or process-sensitive.
Review Transitions and Intersections
Abrupt thick-to-thin changes alter melt velocity, packing and cooling. Use gradual transitions where geometry allows and keep thick intersections away from Class-A surfaces. A rib or boss that looks thin alone can create a large thermal mass where it meets the wall.
Inspect corners in three dimensions. Internal radii and outside form should maintain a deliberate section; adding an inside fillet without adjusting the outside can create a hidden thick corner. Core solid pads and support them with geometry that follows the load path.
Check Flow Length, Gate and Venting
Thin walls require pressure and flow-rate capability, a suitable gate and an escape path for air. Evaluate the longest and most restrictive flow path, not only minimum thickness. Texture, fillers and low mold temperature can reduce practical filling margin.
Locate late-fill ribs, snap tips and thin edges. Consider a gate or wall adjustment before assuming more injection pressure will solve the part. Preserve vents and avoid placing a weld line at a critical loaded feature without evidence.
Treat Cooling and Sink as Design Inputs
Cooling time is strongly affected by the slowest thick region. Identify deep cores, boss clusters and heavy edges that may stay hot after the shell is ready to eject. Review whether the mold can cool those areas with accessible, serviceable circuits.
Sink acceptance is an appearance and dimensional decision. Map visible surfaces and define lighting or boundary samples. Packing can reduce some sink before gate freeze, but it cannot compensate indefinitely for poor section design without adding stress or cycle.
Review Ejection, Warpage and Assembly
A thin or uneven part may release with low hot stiffness and distort under ejector load, robot grip or stacking. Locate ejection support near resistant geometry without marking critical surfaces. Check draft, core grip and release direction together.
Assembly can flatten or constrain a part, but it should not be used to hide uncontrolled molding variation. Define how flatness, gap and fit are measured and whether conditioning or fixture affects the result. Include both free-state and assembled function when needed.
Define What T1 Must Prove
Before steel, list high-risk wall zones and the evidence required: short shots, fill pressure, part weight, surface sink, temperature, section thickness, cavity dimensions or functional tests. Mark steel-safe features and difficult-to-correct areas.
At trial, use the intended resin and controlled process conditions. Compare every relevant cavity after defined conditioning. Update the wall map and drawing when a correction changes product geometry so the approved design does not exist only in tool steel.
Illustrative Wall Review Finding
Illustrative engineering example—not a claimed CKMOLD customer result: A housing has a 2.0 mm nominal wall, but four screw bosses create nearly solid 5 mm intersections under a cosmetic top. The team cores the bosses, adds load-path gussets and reviews gate access to the area. T1 checks top-surface sink, screw torque and flatness rather than relying on wall-color plots alone.
Supporting Review Resources
Questions Before Approval
Does every wall need exactly the same thickness?
No. Functional zones may differ, but transitions and thermal mass should be deliberate and evaluated for molding and performance.
Can packing pressure eliminate sink from a thick boss?
It may reduce sink while the gate remains open, but geometry, cooling and stress limits often make coring or redesign the more robust response.
How should wall thickness be measured?
Use a method suited to access and tolerance, such as gauges, sectioning or scanning, and define part conditioning and measurement location.
When should wall thickness be reviewed?
Review it during product concept and again during DFM before tool release, then validate high-risk zones at T1.
Apply the Wall-Thickness Review Checklist Before Injection Mold Tooling review to your released design. Share the function, exact resin, annual volume, CTQs, cosmetic limits and launch timing through the CKMOLD project form. If CAD is relevant, send it directly to jerry@ckmold.com; the form does not require an upload.