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Quality Control Gone Bad #1
(When calibration is a bad thing)
by Tom Waits
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Equipment and instrument calibration is not an acceptable substitute for process feedback.
I once worked with a very intelligent Quality Assurance (QA) engineer. In a discussion where he was espousing the virtues of mandatory periodic equipment calibrations, he made the statement "I never buy tires from a company that doesn't provide alignment services. I always have my car alignment checked when I buy new tires." He was quite certain that this analogy supported his argument that periodic equipment and instrument calibrations were essential.
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The concept argued by the QA engineer is that all things that may require adjustment or calibration have to be checked and adjusted on a periodic basis by qualified technicians using specialized equipment. Belief in this concept is ubiquitous in today's QC systems and is even dictated by many regulatory bodies including the United States FDA.
Back to the car analogy: Let's suppose that I'm taking my car in to get new tires after having gotten 60,000 miles of use. Further, let's say that the tires all wore evenly, that the car drives straight and true and that the car's gas mileage has been constant and is acceptable. Should I have someone check and adjust the wheel alignment?
The purpose of wheel alignment is to insure that the tires track true to the vehicle's path so that the car drives straight, the tires wear evenly, the tires last a long time and the vehicle gets good gas mileage. If these conditions are true, why let someone adjust the alignment? No matter how well trained and no matter how specific their equipment, they are not going to make things any better and they might make things worse. If these conditions are not true, why did I wait until now to do something about it?
A successful process requires timely feedback. Waiting until my tires are worn out to check my alignment is not timely. I should visually inspect my tires as I walk up to the car, not only for wear, but for proper inflation. When I drive, I should be aware of unusual or unacceptable behavior like pulling or drifting. And when I fill up at the gas pump, I should check my gas mileage to verify that nothing's amiss with the engine or drive train.
Time and time again, I've seen manufacturing processes go haywire after mandatory equipment calibrations. I've also seen "validated" processes, using calibrated equipment, drift out of specification. Often this happens with processes that do not have timely feedback and no one realizes that there's a problem until the manufacturing pipeline is full of nonconforming product.
Do not rely on equipment calibrations to insure process integrity. Find timely feedback mechanisms and use them to monitor processes. Use calibrations as diagnostic tools, not as process controls.
Tom Waits founded Reverse Austin, a company that specializes in Digital Shape Sampling and Processing and has worked in the manufacturing, quality control and mechanical design industries in Central Texas for over 30 years. He is an accomplished CNC programmer, computer programmer and mechanical designer.
Tom holds 7 patents, has been involved in 2 successful Medical Device company startups and has experience in areas ranging from oilfield tooling to heart valves.
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