Scratches on a deep molded housing usually indicate controlled or uncontrolled contact during shrinkage and ejection. The mark should be mapped to a mold surface and an event in the cycle before polishing, adding release agent or increasing ejector force.
The scenario below is illustrative engineering guidance. It is not presented as a CKMOLD customer project or measured production result.
Define the Defect Precisely
Record cavity, surface, direction, length, depth, gloss change and cycle timing. Determine whether the line is a drag mark, scuff, burn, weld line, contamination streak or tool-transfer mark. Photograph the part in consistent lighting and mark the corresponding mold region.
Use Mark Direction to Identify the Contact Event
A mark parallel to mold opening often points toward drag during release. A localized arc may be connected to rotation or flex around an undercut. A repeating mark at the same location may indicate a surface defect, burr, texture transition or insufficient clearance. Random marks require a review of handling, robot grippers, bins and packaging as well as the mold.
Inspect Geometry Before Changing Settings
- Measure draft on the actual pull direction, including textured surfaces.
- Check whether shrinkage causes the part to grip a core or local feature.
- Review ribs, bosses and wall transitions that increase local holding force.
- Inspect parting-line mismatch, shutoffs, undercuts and edge conditions.
- Confirm that polishing did not round a sealing or dimensional edge.
Evaluate Ejection as a Load Path
Map ejector-pin, sleeve, blade, stripper and air-assist contact. The system should release the part without excessive local stress or rotation. Compare ejection marks, whitening and part deformation with the scratch location. Cleanliness, lubrication and alignment of the ejector system also matter.
| Evidence | Likely area to investigate | Controlled test |
|---|---|---|
| Mark follows opening direction | Draft, texture, burr or core grip | Blue-check/contact inspection and measured draft review |
| Whitening near ejector | High local ejection stress | Compare release timing, support and ejector balance |
| Mark changes with cooling | Part rigidity or shrink-on-core force | Adjust within the process window and compare deformation |
| Random post-mold scratches | Handling or packaging | Trace parts through robot, conveyor and packing steps |
Change One Cause at a Time
Process changes can test a hypothesis, but they should remain within material and quality limits. More cooling may increase rigidity, while excessive packing may increase core grip. Mold temperature, surface condition and release timing can alter contact. Document each change and compare the same defect criteria.
Illustrative Diagnostic Sequence
A deep housing shows a vertical scuff on one internal wall. The defect repeats in one cavity and aligns with opening direction. Inspection finds adequate nominal draft on the CAD model, but the textured production surface and a local rib reduce effective release margin. Ejection marks show the part rotating toward that wall. The team evaluates a local draft change and ejector-balance improvement, then checks dimensions, texture appearance and release stability across a controlled run. This sequence illustrates evidence-based diagnosis; it does not claim a universal fix.
Validate the Correction
Check all cavities, start-up and steady-state parts, the agreed cosmetic standard, dimensions affected by any steel change, ejection marks and handling. Update maintenance instructions if surface condition or lubrication contributed. A correction is complete only when the part meets the requirement with process margin.
Scratch-Diagnosis Questions
Will polishing generally remove drag marks?
No. Polishing may reduce friction or remove a tool mark, but it cannot correct inadequate draft, an undercut or unbalanced ejection and may change dimensions or appearance.
Can mold release be used as the permanent solution?
It may be a diagnostic aid or approved process input for some materials, but it can affect appearance, painting, bonding and process consistency. The program should review those consequences.
What should be sent for a remote review?
Provide marked part photographs, CAD with pull direction, cavity ID, resin, texture, process record and images of the corresponding mold surface.
To review a recurring scratch, send the defect map and process context through CKMOLD’s engineering contact. For existing tooling, see mold repair and modification; for new designs, use a DFM review before steel release.