Really Case :Surface Scratch Resolution for Black High-Gloss Injection Molding Parts
Surface Scratch Analysis on Black High-Gloss Injection Molded Parts
1. Issue Overview
During the production and delivery of black high-gloss (mirror-finish) injection molded parts, the customer reported surface issues including scratches, scuffs, and abnormal gloss.
Part Characteristics: Black high-gloss/mirror finish. Highly sensitive to light reflection, where tiny geometric defects, surface scuffs, or micro-roughness are heavily amplified.
2. Defect Categories
Type A (Fixed Scratches): Continuous or intermittent straight marks appearing in fixed locations on the part.
Type B (Random Scuffs): Localized haze, scuffs, or widespread random fine scratches.
Type C (Pseudo-Scratches / Optical Marks): Non-physical scratches that appear as scratch-like visual lines under reflection (e.g., gas marks, weld lines, cold slug marks).
3. Root Cause Analysis
Mould & Equipment:
Cavity Wear/Damage: Localized scratches, sticking, or galling on the mirror surface duplicate fixed scratches on every shot.
Insufficient Draft Angle: High frictional resistance on mirror surfaces; inadequate draft leads to drag marks during mold opening.
Ejection Issues: Ejector pins protruding above the cavity surface scratch the part during ejection. Uneven ejection causes part tilting and lateral drag marks.
Processing Parameters:
Inadequate Mold Temperature: Low mold temperature causes rapid melt cooling, preventing proper contact with the cavity surface and generating micro-flow lines or stress marks.
Moisture & Contamination: Excessive moisture in raw materials (e.g., ABS, PC/ABS, PMMA) causes thermal degradation (gas marks/silver streaks) misidentified as scratches. Airborne dust in the hopper introduces hard particles that scratch the surface.
Packaging, Handling & Logistics:
Improper Tote Bins: Standard plastic crates or unpadded cartons allow parts to collide and slide against each other.
Lack of Isolation: Parts are not individually packed, lacking protective dividers between them.
Transit Vibration: Box deformation or loose internal packing during transit causes vibration and surface friction.
4. Root Cause Conclusion & Corrective Action Plan
Root Cause:
Follow-up communication confirmed that the surface scratches were caused by a recent change in packaging design.
Corrective Actions:
Custom Blister Trays: Implement dedicated thermoformed blister trays to ensure each part is individually packaged with zero direct contact.
Surface Protection Film: Apply PE electrostatic protective film to all high-gloss surfaces immediately after molding.
Enhanced Outer Cushioning: Add EPE (expanded polyethylene) foam cushioning inside outer cartons to absorb shock and prevent transit vibration.
