The Andon That Nobody Pulls
At Meridian Stamping, a 24/7 press-welding line produces seat frames for two automotive customers. The line has an andon cord, but operators say pulling it triggers a supervisor visit and a 20-minute production meeting after the shift. Uptime bonuses for supervisors are tied to line output, and the plant's largest customer has imposed a 50 ppm defect target. Last month, customer audits found 420 ppm, mostly weld porosity and missing welds. Defects are found at final inspection, 90 minutes downstream, and 38% of suspect parts are reworked. The quality manager wants to add another final inspector. Operators claim weld tips wear out and the fixture shifts when changeovers are rushed; maintenance logs show 6 hours of unplanned downtime per week, but no record of andon calls. The plant manager says stopping the line is too expensive because the line generates $18,000 of contribution per hour when running. You are asked to advise.
1. What immediate actions would you take in the first 48 hours, and what would you not do yet? Explain the jidoka logic.
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First 48 hours. Protect the customer first: quarantine suspect WIP and finished goods, verify traceability, and sort against the weld criteria. Establish a visible andon response standard: team leader responds within two minutes, records the reason and downtime, and escalates if the same defect recurs. Stop the line for repeated missing welds or porosity until the condition is contained. Check weld-tip wear and fixture position after every changeover; add first-piece verification before running production. Start a simple defect log at the station, not 90 minutes downstream.
Do not yet. Do not add another final inspector as the primary countermeasure. Inspection catches defects after they are made; it does not build quality at the source. Do not launch a broad culture programme before the response system works.
Jidoka logic. Jidoka means stop at the first abnormality, make it visible, and separate human work from machine work so the process cannot pass defects forward. The andon is only jidoka if pulling it produces a fast, skilled response and a countermeasure. At Meridian, the cord currently produces a meeting, so operators have learned not to use it.
2. Analyze the root causes of the 420 ppm defect rate using the case evidence. Include the role of metrics and leadership.
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Technical branch. Missing welds and porosity are consistent with weld-tip wear and fixture shift. Why? There is no evidence of a tip-wear counter or daily replacement standard, and changeovers are rushed, so the fixture is not verified. Maintenance is reactive; 6 hours of unplanned downtime per week suggests equipment problems are being tolerated rather than eliminated.
Detection branch. Defects are found 90 minutes downstream, so the process runs for 90 minutes after a bad condition appears. The 38% rework rate creates a hidden factory and masks the true defect rate. No andon-call record means the abnormality data needed for problem solving is missing.
System and leadership branch. Supervisors' uptime bonuses are tied to output, which directly discourages stopping the line. Operators have learned that pulling the cord creates a post-shift meeting rather than help. The plant manager justifies running because the line generates $18,000 per hour, but that figure ignores the cost of escapes, sorting, rework, and customer risk. The 50 ppm target is not achievable by inspection alone; it requires stopping at the source and fixing the wear and fixture conditions.
3. Design a quality-at-source control plan for the weld line. What metrics would show it is working, and how would you handle the plant manager's cost objection?
Read the worked answer
Control plan.
- First-piece approval after every changeover, with fixture-position check and weld-tip condition recorded.
- Weld-tip wear counter and scheduled replacement; daily PM checklist owned by the operator.
- In-station error-proofing where feasible: missing-weld sensor or weld-monitoring signal that stops the line.
- Standard work for changeover, including fixture verification and tip change.
- Andon with a two-minute response standard, defect reason recorded, and stop-and-fix for repeated defects.
Metrics. Andon pulls per shift, response time, first-pass yield at the station, defects per million at final inspection, rework rate, unplanned downtime, and customer escapes. These show whether defects are being caught earlier, not merely inspected more.
Cost objection. Do not argue that stopping is free. Compare a 10-minute stop, about $3,000 of contribution at $18,000 per hour, with the cost of one escape: sorting, rework, expediting, warranty, and customer disruption. The current 420 ppm and 38% rework indicate the line is already paying for poor quality. Propose a one-shift pilot with stop-and-fix and measure both output and defects. If stops are frequent, fix reliability before expanding the protocol.