Eliminating Pin-Hole Burn Marks in a 32-Cavity Connector Housing Mold
A Tier-1 automotive connector program was scrapping up to 18% of parts to burn marks inside 16-pin blind holes at a 5:1 depth-to-diameter ratio, until vented core pins cleared the trapped gas.
PROJECT OVERVIEW
"A Tier-1 automotive connector supplier ran a 32-cavity housing mold with a 16-pin terminal layout molded in glass-filled PBT. The pin holes are blind cavities at a 5:1 depth-to-diameter ratio, so air trapped at the bottom of each hole could not escape during fill. Trapped gas compressed and carbonized against the core steel, leaving burn marks on the pin-hole walls. At any given time 12–18% of the 32 cavities produced burn-marked parts, holding the program at an 18% defect rate and 6.2% scrap — with an annual volume of 1.8M shots, every percentage point of scrap was a real cost."
PAIN POINTS
- Trapped air in 16-pin blind holes at 5:1 depth-to-diameter ratio burned the cavity steel
- 12–18% of the 32 cavities produced burn-marked parts each cycle
- 18% defect rate and 6.2% scrap, plus full inspection of every batch under IATF 16949 traceability
OUR SOLUTION
- Surface-vented core (SVC) pins in hardened SKH51 — a controlled vent channel along the pin lets gas escape at the moment of fill without flashing
- Ø1.2 mm vented cores ground to ±0.002 mm with the vent geometry EDM'd in-house, heat-treated to HRC 62
- S136 ESR variant offered where resin chemistry also demands corrosion resistance; vent condition added to the 50,000-shot PM schedule with a written report
MEASURED RESULTS
| Defect rate | 18% → 0.3% (98% reduction) |
| Scrap rate | 6.2% → 0.8% |
| Cycle time | Zero loss — venting added no cycle time |
| Throughput | 1.8M shots/year sustained across all 32 cavities, burn-free |
YOUR APPLICATION MAY DIFFER
"Send us your connector part file or pin-hole geometry and we will recommend the venting and steel combination for your resin and shot count — DFM review is free within 24 hours."