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84 The PCB Magazine • June 2015 by Steve Williams STEVE wIllIaMS cOnSulTInG llc Point of View Best Practices 101, Part 8: Poka-Yoke Column One day, Shigeo Shingo was explaining baka- yoke, or foolproofing devices, created and imple- mented by workers on the Arakawa Body Com- pany factory floor. A young woman started to cry. "Why are you crying?" Shingo asked. "Because I am not a fool," she answered. "I am truly sorry." Shigeo responded, and at that exact moment he changed the name from baka-yoke to poka-yoke: mistake-proofing devices. — from The Kaizen/Kaikuku Life Poka-Yoke Literally translated as mistake-proofing, poka-yoke is commonly pronounced a number of ways, but the Japanese pronounce it poh- kah yo-kay. So what is poka-yoke? It is a meth- od that uses fixtures, tooling, sensors or other devices to eliminate, or design out, the errors within a process. Cost of Quality Poka-yoke is important because of its pur- pose: to reduce the cost of quality, or more ac- curately stated, the cost of poor quality. The cost of quality is comprised of all the costs that relate to poor quality. As I have discussed be- fore, the Four "Rs" are the major components of the cost of quality: repairs, rework, rejects, and returns. Each of these components can be reduced, if not eliminated, by implementing an effective poka-yoke solution. Defects and Process Variation What causes defects? The answer is pro - cess variation, which begs the question, what causes process variation? Here are the 'big five' reasons for process variation: 1. Poor procedures 2. Equipment 3. Non-conforming material 4. Tooling, fixtures, jigs, etc. 5. Human mistakes Except for human mistakes, these condi - tions can be predicted and addressed with corrective action to eliminate the cause of de- fects. Poka-yoke detects process variation and shuts down the process before it produces an error. Poka-yoke will catch the errors before a defective part is manufactured 100% of the time. Poka-yoke focuses on the process, not on after-the-fact finger pointing. Types of Poka-Yoke Systems There are two basic systems for poka-yok - ing a process: the control system and the warn- ing system. Control System: This takes the human element totally out of the equation. This is Figure 1: Pcb offset tooling poka-yoke.

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