What matters
- Preserve the original condition and collect data before making several changes at once.
- Separate design, tool, material, machine, and process causes.
- A setting that hides the mark may reduce the process window or create a new defect elsewhere.
A first-pass defect map
| Symptom | Mechanisms to investigate | Evidence to collect |
|---|---|---|
| Sink/void | Local mass, packing, gate freeze, shrinkage | Section thickness, pressure, gate seal |
| Warpage | Uneven cooling, shrinkage, orientation | Deflection pattern, temperatures, fill |
| Short shot | Flow resistance, venting, temperature, shot | Fill pattern, pressure, air traps |
| Flash | Clamp/seal condition, pressure, viscosity | Location, mold condition, clamp data |
| Weld line | Flow-front meeting and temperature | Gate layout, fill study, strength |
| Burn mark | Trapped compressed gas or degradation | Vent location, speed, residence time |
| Splay | Moisture, volatiles, shear | Drying log, material handling, gate |
| Dimensional drift | Process/material/temperature change | Time series and cavity identity |
A disciplined troubleshooting sequence
- Define the defect, location, cavity, frequency, and acceptance limit with photos or measured data.
- Confirm what changed: resin lot, regrind, drying, machine, mold maintenance, ambient condition, or setting.
- Check that actual melt, mold, pressure, time, and water conditions match the validated process—not only setpoints.
- Form one mechanism-based hypothesis and change one controlled factor where practical.
- Verify the correction across cavities, startup, steady state, and the required production window.
- Update the control plan, setup sheet, maintenance action, drawing, or design record that prevents recurrence.
Example: a sink mark is not only a pressure problem
Sink often appears opposite a rib, boss, internal fillet, or thick section where the core continues to shrink after the surface has formed. More packing may help if the gate remains open and the region can still receive material. It cannot fully rescue geometry that creates a large isolated mass after the gate freezes.
The durable correction may be to core the feature, reduce the rib or boss mass, move or enlarge the gate, balance cooling, change material, or revise the acceptable surface. Each option has a different effect on cycle, strength, and appearance.
Information that makes a supplier investigation faster
- Part revision, resin grade/lot/color, cavity number, machine and mold identifiers.
- Time since startup, cycle count, process sheet, alarm history, and actual trend data.
- Marked-up photos showing location, scale, orientation, and defect frequency.
- Good and bad samples protected for review, plus measurement method and raw results.
- Recent mold maintenance, material handling, and process changes.
Use this as a design review, not a production release
These guides support early planning. The selected resin supplier, toolmaker, and molder still need to confirm the final geometry, process window, tolerances, safety factors, validation plan, and commercial assumptions for your application.