Special Characteristics are special
Just a note while waiting for an airplane to Beijing in Kuala Lumpur. I have been doing alot of work with customers on Special Characteristics lately. One confusing point that requires clarification: what makes a characteristic Special? Is it how important it is? There are several good definitions and it is my opinion several of them work. One such definition is related to control of Variation and if the customer can see value or improvement with this variation minimized. That one is OK, but is this not true of all variation?
I like to suggest it is those characteristics that are at risk of not delivering something important. My example would be:
Is your heart rate important for your survival? Sure it is. Is it special? I think not. Why you might ask? I think it is in control and stable for most of us. Most of us do not get up in the morning and plot a control chart or calculate Cpk on our heart rate. If we are normal (fitting the normal distribution) our heart rate would have a Cpk greater than 2 for sure for what is expected to be normal. However if I were to try to lose 40 pounds by going on a treadmill or walking program, the need to monitor increases due to the increased risk that I just put myself under. A diabetic must monitor and control blood sugar, so that is a special characteristic.
How do I know there may be special characteristics? Design FMEA gives us the best hope of finding them if they exist. When done correctly the DFMEA will give us a clue, but will not be explicit as to where the characteristics are. When should I look for them? Before the design is finished for sure, but also including the manufacturing and assembly peoples input for mitigating the risk by making changes to the Design, Process or both. Error Proofing is our first mitigation obligation, Improved stability and capability the second, and finally special control strategies when risk has not been reduced to an acceptable level. Want to know more? Give us a call at (248) 280-4800 and ask for Michelle.