[5 Case studies] CQI

Case Study

Problem Description

Methodology Used

Key Steps Applied

Key Results

1. Paint Defects in Body Shop

Frequent fisheyes (bubbles) on car doors.

5 Whys

1. Why? → Contaminated paint.

2. Why? → Dirty air filters.

3. Why? → No PM schedule.

4. Why? → Missing SOP.

5. Why? → Inadequate training.

Result: Implemented filter checks + training. Defects reduced by 90%.

2. Engine Mount Failures

Customer returns due to cracked mounts.

8D Problem-Solving

1. D1: Formed cross-functional team.

2. D4: Root cause → Poor rubber curing.

3. D6: Corrective action → Revised curing time/temp.

4. D7: Updated PFMEA.

Result: Warranty claims dropped by 75%.

3. ABS Sensor False Alerts

High field failures in ABS sensors.

FMEA (PFMEA)

1. Identified failure mode: Moisture ingress.

2. RPN=432 (Severity=9, Occurrence=6, Detection=8).

3. Added sealant + ingress testing.

Result: RPN reduced to 56, field failures down 60%.

4. Transmission Leaks

12% leak rate in final inspection.

Six Sigma (DMAIC)

1. Measure: Leaks at gasket joint.

2. Analyze: Torque variation (MSA proved gauge imprecise).

3. Improve: Automated torque wrench + training.

4. Control: SPC charts for torque.

Result: Leaks reduced to 0.8%, saving $500K/year.

5. Assembly Line Bottleneck

20% idle time at wheel station.

Kaizen/PDCA

1. Plan: Time-motion study.

2. Do: Relocated tools + kanban racks.

3. Check: Cycle time ↓ 30%.

4. Act: Standardized across shifts.

Result: Productivity ↑ 25%, eliminated overtime costs.

Tool

Strengths

Limitations

Best for Automotive Use Cases

5 Whys

Fast, simple, no data needed.

Superficial if stopping too early.

Quick shopfloor fixes (e.g., contamination, misalignments).

8D

Structured, customer-focused.

Time-intensive for small issues.

Warranty claims, supplier defects (IATF 16949 must).

FMEA

Proactive risk prevention.

Subjective scoring (SOD).

Design/process risks (e.g., sensor failures, weld cracks).

Six Sigma (DMAIC)

Data-driven, high ROI.

Requires statistical expertise.

Chronic defects (leaks, noise/vibration).

Kaizen/PDCA

Engages frontline teams.

Small-scale impact.

Lean waste reduction (motion, waiting, inventory).