Cracked latches kept returning to an appliance components supplier: four times in two years, each "fixed" by retraining. A disciplined 8D traced the cracks to one cavity with a missing radius, cut complaints to zero and warranty cost by more than 90%.
Key numbers
The complaint arrived for the fourth time in two years: cracked latches on an appliance component, found by the customer during assembly. Each previous time, the supplier had contained the stock, written a short report citing operator handling and retrained the team. Each time, after a few quiet months, the complaints came back. The customer's quality engineer was now asking whether the supplier understood its own process.
The situation
Complaints were running at around six a month, and warranty and sorting costs had reached roughly $148,000 a year. The relationship with the customer, a major appliance brand, was at risk.
The investigation
This time the supplier ran a disciplined 8D with a cross-functional team: quality, production, tooling and engineering.
- Containment: 100% inspection and sorting of stock at the customer, protecting the line while the investigation ran.
- Problem description: the team used Is/Is Not analysis, asking where, when and on what the cracking occurred, and just as importantly where it did not. Every cracked latch came from one cavity of a four-cavity tool. The other three cavities produced none.
- Root cause: measurement of that cavity found a sharp internal corner where the drawing specified a 0.5 mm radius. The radius had been lost during an earlier tool repair. The sharp corner created a stress concentration that cracked under assembly load.
- Proof: the team switched the suspect cavity off and on. With it off, no cracks; with it on, cracks returned. The cause was confirmed, not assumed.
The structure followed the one-page thinking described in A3 problem solving: facts first, then cause, then countermeasures that address the cause.
What changed
- The radius restored to the cavity insert.
- A corner radius check added to tool maintenance and to first-off inspection, so the same loss could not go undetected again.
- The same check read across to four similar tools, where one more missing radius was found before it caused failures.
Results
Complaints dropped from around six a month to zero within two months of the fix and stayed there. Warranty cost fell from about $148,000 to $9,000 a year, a reduction of more than 90%. The permanent fix took 38 days from the start of the 8D.
Why the earlier fixes failed
Retraining assumed people were the cause. The data said otherwise: a cavity-specific defect cannot be caused by handling that affects all cavities equally. The earlier reports also missed the escape question: why had the tool repair not been checked against the drawing?
Lessons for your operation
- "Operator error" is rarely a root cause. Ask why the process allowed the error.
- Is/Is Not analysis narrows problems quickly. Cavity-specific defects point to the tool.
- Prove the cause by turning it on and off before acting.
- Read across: check similar tools and products for the same weakness.
