Cracks and fractures in injection-molded parts are symptoms, not a single diagnosis. A useful investigation compares the failed part with its specification and records the material, mold, molding history, assembly and service conditions before any corrective change is approved.
Capture a reproducible failure record
- Identify the part revision, resin grade, color, material lot, mold and cavity, machine, process revision and production date.
- Record where the crack starts, when it appears, how the part was assembled, and whether the affected parts share a lot, cavity or shipment.
- Retain failed and unaffected samples with their labels. Photograph the location and note any exposure to cleaners, lubricants, temperature, load or storage conditions.
- Separate confirmed observations from possible causes. Do not describe a suspected mechanism as proven until the evidence supports it.
Review possible causes by evidence
| Lĩnh vực | Evidence to compare | Questions for the project team |
|---|---|---|
| Material and lot | Approved grade, lot records, storage and preparation records, approved substitutions | Does the failed part differ from an unaffected lot or material revision? |
| Part and mold design | Crack location, section changes, assembly features, gate and weld-line location, ejection contact | Does the location align with a geometric stress concentration or a feature that needs review? |
| Molding history | Machine and cavity, setup records, process changes, startup and maintenance history, sample measurements | Did the failure begin after a documented change, or appear across more than one cavity? |
| Assembly and service environment | Fasteners, fixtures, mating parts, cleaning agents, temperature and applied loads | Can the assembly or exposure reproduce the failure under an agreed test method? |
Autodesk’s Moldflow troubleshooting reference lists residual stress, weld-line weakness and differential shrinkage as possible cracking factors. These are investigation leads, not a universal diagnosis or a process recipe; each proposed change should be reviewed against the part, material and mold specification: Autodesk cracking troubleshooting.
Validate changes with a controlled plan
Agree on the failure definition, sample selection, test conditions and acceptance criteria before changing material, geometry or process conditions. Record the original baseline, the variable changed, the result and any side effects. Where the part has a critical function, use the project’s formal engineering and change-approval process.
For related buyer checks, see the resin-selection guide và những injection molding tolerance guide.
Các câu hỏi thường gặp
Can a crack identify the molding cause by itself?
No. A crack location can guide investigation, but the material, design, process, assembly and service history must be compared before a cause is assigned.
Should a supplier change the temperature or injection speed first?
Not without a documented diagnosis and material-specific process review. Any change should have a defined test, acceptance criteria and side-effect check.
What should a buyer send with a crack complaint?
Send the part revision, affected lot and cavity if known, retained samples, photographs, failure timing, assembly details and any known service exposure. Include the expected requirement and the observed result.