From 4.2% to 0.8% Scrap: Poka-Yoke and SPC in Aerospace Components
A machined-components supplier to a major aerospace OEM was generating 4.2% scrap on tight-tolerance titanium parts — costing $2.1M per year and generating quality escapes that threatened the customer relationship. Twenty-two weeks of A3 problem-solving and poka-yoke engineering reduced the scrap rate to 0.8%.
The Challenge
The company produced machined titanium housings to ±0.001″ tolerances for aircraft engine assemblies. Despite 100% inspection, they had 11 customer escapes in the prior year. The scrap rate of 4.2% was $2.1M in direct material and labor cost. The customer had issued a Level 2 supplier corrective action and was conducting monthly surveillance audits. The business was at risk.
The Diagnosis
A3 structured problem-solving across the top three defect types — which accounted for 84% of all scrap — revealed that two were attributable to setup variation: fixture seating inconsistency invisible to the operator during setup, and a cutting tool wear pattern occurring outside monitored parameters. The third was an inspection method problem: go/no-go gauging with measurement uncertainty too large for the tolerance band.
The Lean Intervention
For fixture seating: a pneumatic detection circuit requiring confirmation of full seating before the spindle could start (poka-yoke, Jidoka principle). For tool wear: SPC on the critical dimension with control limits triggering a tool change before drift reached specification. For gauging: CMM first-article measurement replaced by air gauging at the critical station with automatic sort capability.
The Results
Scrap rate fell from 4.2% to 0.8% over 22 weeks. First-pass yield improved from 78% to 97%. Customer escapes dropped from 11 to 1 in the 12 months following implementation. Annual savings of $2.1M exceeded the engagement investment by 8x. The customer removed the corrective action and designated the plant as a Preferred Supplier.
“KAIZEN's A3 approach forced us to be rigorous. We thought we knew the root cause. We didn't. That discipline is what made the fix permanent.”
— Quality Director, Aerospace Components Manufacturer
Engagement Details
- Client
- Aerospace Components Manufacturer
- Industry
- Aerospace
- Duration
- 22 weeks
Methods Used
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