Erdem Ozdemir 030070307 -1st Week Answers

Error-Proofing

Better Answer – Manufacturing Management

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Error-proofing is another lean manufacturing technique that also supports ISO 9000. Its basic premise is that anything that requires human intervention and judgment to prevent mistakes is a mistake waiting to happen. Dr. Shigeo Shingo introduced this technique to Japan as baka-yoke (fool-proofing). He changed it to poka-yoke because workers inferred from baka-yoke that management perceived them as stupid (Shingo 1986, 45).

Here is an example of poka-yoke. "While the welding operation is in progress, fan-shaped plates, operated by cams, cover in turn all operating buttons except the one needed for the next move. It is impossible for the operator to go wrong" (Ford 1930, 198). Gilbreth's (1911) advice to color-code objects to facilitate proper orientation also is a form of error-proofing. Color-coded wires and matching connection points are an example of this, but keep in mind that some people are color-blind.

Another error-proofing technique is designing keys into parts to pre­vent improper assembly. The large and small prongs on a polarized electri­cal plug, with matching openings in the electrical outlet, are an example. It is impossible to insert the plug backward.

Gages and automatic sorters that prevent the use of substandard parts also are a form of error-proofing. Nonconforming raw materials or compo­nents that enter the constraint can cause downtime, scrap, or rework.⁸ It is therefore very worthwhile to keep such items out of the constraint. Down­stream incorporation of bad parts into good units from the constraint also can be devastating, since post-constraint scrap is irreplaceable.

The concept of error-proofing also applies to workplace safety. The basic principle at Ford's River Rouge plant was, "can't is better than don't." That is, set up the equipment and the job so workers can7 injure themselves instead of telling them, for example, "Don7 monkey with the buzz saw." The System Company (191 la. 114) cites the latter instruction as "one of New England's colloquial proverbs, to which too many four-fingered men call attention " Even Henry Ford's production chief, Charles Sorensen, lost two fingertips when he made wooden patterns for iron casting molds. Interlocks, guards over moving parts, and lockout-tagout are examples of accident-proofi ng.

(Lean enterprise: a synergistic approach to minimizing waste, William A. Levinson, Raymond A. Rerick Pg:77-78)

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It is a basic principle of manufacturing process design that any mistake whose prevention relies on operator vigilance is sure to occur sooner or later. If a job can be done wrong, it eventually will. This is the concept behind error proofing, or poka-yoke. Error-proofing devices and self-check systems support the lean manufacturing principle: "Don't take it (poor quality), don't make it, don't pass it on." Self-check systems can be treated as a special class of error proofing devices that, instead of actually preventing mistakes, catch them before they can cause significant harm. 
(Beyond the Theory of Constraints, William A. Levinson, p 122)