Thanks for pointing out my error. Phil Crosby deserves more than a Ph.D. I didn’t insist on Ph.D as a requirement for any field and I don’t normally attach importance to Qualifications alone. Quality is all about attitude, relevance, consistency and not having any bias. It requires dedication and perseverance and commitment.. Mr. Phil…[Read more]
Thanks for pointing out my typo error. Control charts distinguish clearly what is the difference between assignable cause and common causes. It is an opportunity for me to perfect in my typing also. I have no problems with that as Quality professional.
We need to blame the top management and other relevant people for not allowing the…[Read more]
I didn’t mean to take any credit away from Lean invention. In fact if you look at my initial discussion I wanted to say thanks to the automotive big three industries interest on SPC was sustained to develop into Six-Sigma later and even QMS like ISO-9001 was based on QS-9000 initially. In the same vein, I am willing to accept the cre…[Read more]
Thanks a lot Mr. Andy U for your clear explanation with details for different cases. I will try it out in Minitab and this is what I was looking for. If we can arrive at the process shift for our process on our own, for the sample size, type of chart and control we use, this arbitrary 1.5sigma shift need not be taken into account and we can go by…[Read more]
Point I tried to make is SPC was invented in 1930’s but big way used by 3 big automotives for others to get enlightened to use in small industries also. Otherwise I don’t think ISO would have tried to model their standard in tune with QS-9000’s 20 elements in 1994 version. Then they left it to individual choise in 2000 version, how one use or i…[Read more]
I can agree on what you say. But Shewart’s work was in 1930’s which opened the possibility of mass manufacturing with statistical control made possible. Big 3 automotives are the actual users of SPC for all of us to reach where we are to-day. Forget about 2 or 3 sigma limits or shifts.
But now we have all sophisticated computers, simulations and…[Read more]
We are talking of process shift and I didn’t say we have to recalculate the control limits. Sometimes as long as process is within spec. limits. we are asked to again calculate the short range capability if we want to calculate again the limits to accomodate the new process reality of shift in average. If we take the difference between the…[Read more]
My simple concern of this 1.5sigma shift and sigma table is that it just ignore the Z-table evolved and used by QA professionals all over the world and it is evolved with permanent mathematical correlation irrespective of the sigma process for the last 60 years. 3Sigma limit with specifications tolerance is well established by Walter Shewart to…[Read more]
I strongly feel this 1.5 sigma shift was a goofie to pitch sig-sigma sale stronger by Motorla as it need not be verified by any Scientific panel like in publication of papers. In the case of Walter Shewarts Control chart it is very clear, the control limits are matchable to specifications to 3 Sigma on both sides of the mean and any process can…[Read more]
I have no doubt about the process capability or process in statistical process control means you used all your design, pilot plans in the process to remove all your assignable causes and took out production with Cp or Cpk of atleast 1.33 and above or e1.66 and above to meet the customer’s requirements. That means the process is established before…[Read more]
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