Toyota’s success was built on Professor Deming’s Quality philosophy. Toyota’s Quality Circles worker teams have produced over 2,000,000 process improvements. However, in their enthusiasm, even Toyota has forgotten some of Deming’s basics.
DEFECTS
Defects relate to the specification. When a product is outside specification, it is called a defect. In 1870, a quality product was defined as one that was not defective. The West hasn’t progressed in the past 153 years.
The specification tells us nothing about what the process is doing. A century ago, Dr Shewhart created a new approach to Quality, based on his control chart. The control chart worked for any process with any data distribution. It allowed a new definition of Quality.
Modern quality means a process is on target with minimum variation. Control charts are central to Quality. They define 2 types of variation: common and assignable causes. Confusion of these is called “tampering”. It increases variation.
TOYOTA GETS IT WRONG
In their enthusiasm for better quality, some Toyota folk decided not to wait for processes to reach control limits. They introduced “upper and lower reaction limits” to take action before control limits are reached. This is tampering. It treats common cause variation as an assignable cause. It increases variation and causes a loss of productivity.
MOTOROLA GETS IT WRONG
Mr Bill Smith is renowned for his process tampering. Smith was a strong advocate of Professor Deming but he ignored his teaching on tampering. Smith tampered with his molding process. It made his process wildly out-of-control. His process mean happened to drift “as much as 1.5 sigma” because of his tampering. This formed the basis of his buddy, self-confessed con man Harry’s Six Sigma Scam.
GM GETS IT WRONG
GM, before it went into bankruptcy, employed hundreds of “experts” in Shainin’s “Pre-control”. Pre-control is a method that like counting defects, totally ignores the process. The method “adjusts the process” based on the specification, ignoring whether a point is outside control limits or not. This is tampering. It makes things worse.
Motorola and many others also use “Pre-control.”
TAMPERING – THE HIDDEN ENEMY
Tampering is the hidden enemy of Quality. A process may appear in-control but may contain excessive variation and loss of productivity, because of full or partial tampering.
SUMMARY
Whether though enthusiasm, ignorance, or following some worthless fad, tampering is a trap for the unwary. It is essential for anyone serious about Quality to have a thorough understanding of tampering. You can experiment with the various tampering modes yourself, with the free Augmented Reality app in the app stores. Search “Deming Funnel”.
by Dr Tony Burns BE (Hon 1) PhD (Chem Eng)