In automotive spare parts manufacturing—whether producing engine components, wiring harnesses, plastic parts, or machined parts—scrap and NG are critical indicators of process health.
⚙️ Major Processes Where Scrap and NG Occur
🟠 1. Incoming Material Inspection (IQC)
Common Issues:
- Dimensional variation in raw materials
- Surface defects (rust, contamination)
- Incorrect material grade
Impact:
Poor incoming quality leads to defect multiplication across the production line.
🔴 2. Machining Processes (CNC, Turning, Milling)
Typical NG/Scrap:
- Out-of-tolerance dimensions
- Poor surface finish
- Tool marks or chatter
Root Causes:
- Tool wear or breakage
- Improper machine calibration
- Incorrect cutting parameters
👉 This is one of the highest scrap-generating areas in metal component manufacturing.
🔴 3. Casting and Forging
Common Defects:
- Porosity and blowholes
- Cracks or incomplete filling
- Shrinkage defects
Root Causes:
- Improper mold design
- Temperature variation
- Material inconsistency
🔴 4. Injection Molding (Plastic Components)
Common NG:
- Warpage
- Sink marks
- Short shots
Root Causes:
- Incorrect mold temperature
- Poor cooling design
- Material flow imbalance
🔴 5. Heat Treatment
Typical Issues:
- Hardness variation
- Distortion
- Cracks
Root Causes:
- Improper heating/cooling cycles
- Furnace inconsistency
- Incorrect loading pattern
🔴 6. Surface Treatment & Coating
Common NG:
- Poor adhesion
- Uneven coating thickness
- Corrosion spots
Root Causes:
- Inadequate surface cleaning
- Chemical imbalance
- Process contamination
🔴 7. Assembly Line
Frequent Defects:
- Missing or wrong parts
- Improper torque application
- Misalignment
Root Causes:
- Human error
- Lack of poka-yoke systems
- Inadequate work instructions
🟣 8. Testing & Final Inspection
Issues:
- Functional failures
- Leakage in components
- Electrical faults (for electronic parts)
📊 Key Causes of Scrap and NG
Across all processes, major contributing factors include:
- Lack of process control and monitoring
- Inadequate training and skill gaps
- Poor maintenance of machines
- Weak supplier quality management
- Ineffective use of quality tools