In the 1960s and 70s, manufacturing companies around the world took efforts to improve quality through defect prevention.
Prior to this, quality was seen as a function of appraisal, sorting, reworking and disposition. When something was produced, if it met the specifications, it was sent to market. If it failed to meet the requirements it was sorted out, reworked and then sent to market. This added expense to “quality” and led to the belief that “you can have too much quality”.
To avoid those extra costs, product that didn’t meet the specifications was deemed “good enough” and it was also sold in the market place. This good enough attitude led to a multiplicity of recalls, field service and dissatisfied customers.
Quality experts, like Phil Crosby, Dr. W Edwards Deming and Dr. Shigeo Shingo knew there was a better way, and that way was to prevent mistakes, errors and nonconforming product from being produced at all.
Shingo’s work, in particular, is very interesting. He invented a methodology called poka-yoke (Japanese for “mistake proofing”), in which various means of preventing errors or stopping errors very early in the work process were followed. He advocated three methods:
- The contact method identifies product defects by testing the product's shape, size, color, or other physical attributes. (Think of a work activity that can be completed only if steps in the process come together in a specific arrangement. A printer cable will plug into your computer in one way only. Or a credit card that must be swiped in a specific way to be read.If contact is not made properly, the process does not progress.)
- The constant number method alerts the person doing the work if a certain number of objects or movements are not made. (Think of an egg carton that has specific space for a specific number of eggs. Or a surgical instruments tray that has outlined impressions for all tools, clamps and materials guaranteeing that at a glance, a missing component will be determined. Either method helps ensure that mistakes are seen immediately and corrected.)
- The sequence method determines whether the prescribed steps of the process have been followed. (Think of a computer template that requires all data fields be completed before moving to the next step. Missing information as a problem would be eliminated. Or depressing the brake on a car before the engine can start will eliminate a vehicle accidentally jumping forward when started.)
In the days following Shingo’s methodology, we have also learned to use “artificial intelligence” to help us eliminate errors. The spell-check on your computer is an example of this, as are computer monitoring and controls on a mechanical system.
While Shingo’s methods found easy application in high-volume manufacturing processes, they also have application in continuous-flow and service work processes. It requires some imagination, but it can be done. The benefit of defect prevention or correcting a defect early in the process will greatly lower costs (no rework or lost sales), improve productivity and lead to higher customer satisfaction.