Eliminating Ejector Pin Marks on an Automotive Door Panel

A 1,400 g PP door panel came off the mold with circular ejector marks on the A-surface. We fixed it at the tooling level — draft, rib polish and ejector layout — and at the process level — holding pressure and holding time.

PROJECT OVERVIEW

"A Tier-1 automotive interior supplier ran a gray PP door panel, 1,400 g shot weight, gated through a side gate. The A-surface carried visible circular ejector marks — a reject condition for the OEM. Trial data showed the mold needed 40 MPa injection pressure and 18 MPa holding pressure, with a long holding time, to fill the large part. That overpacking gripped the ribs hard enough that ejection required excessive force, and the marks appeared wherever that force concentrated."

Grey PP automotive door panel with a circular ejector pin mark defect highlighted on the A-surface

PAIN POINTS

Circular ejector marks on the grained A-surface — a visible appearance defect that failed OEM inspection at 100% audit
High holding pressure (18 MPa) and long holding time overpacked the rib network, gripping the core and forcing high ejector force
Small draft angles and rough rib flanks increased release friction, so ejection load concentrated on a few large pins

OUR SOLUTION

DFM at the mold-design stage: rib draft raised across the panel and rib flanks polished to a release-grade finish so the part lets go without force
Ejector layout rebuilt — more pins, smaller diameters, positioned on ribs and bosses instead of open A-surface areas; pins ground to ±0.005 mm with matched head-to-shank concentricity
Mold trial with a gate-seal study: holding pressure stepped down and holding time shortened until the part filled and packed without overpacking the ribs

Close-up of a circular ejector pin mark left on a molded surface before the tooling and process fix

Ejector pin mark on the molded surface — the defect class eliminated in this program

Grey PP automotive door panel after the fix — A-surface clean, no ejector pin marks

Same door panel after the mold and process changes — A-surface free of ejector marks

MEASURED RESULTS

Ejector marks	Eliminated — A-surface clean at 100% inspection across the trial and PPAP run
Holding pressure	Reduced from 18 MPa to 13 MPa with a shorter holding time, verified by gate-seal study
Ejector force	Down ~30% — the part releases cleanly after draft and polish changes
Dimensional stability	Panel datums and mounting points held within OEM spec; ISIR/PPAP documents released under IATF 16949 process control

YOUR APPLICATION MAY DIFFER

"For large appearance parts with ejector marks, drag or overpacking, send us the part file and the current molding parameters — we will reply within 24 hours with the draft, ejector layout and process window recommendation."