This can be not conclusive but…
I have a publication from Ford Motor Argentina, “Control Continuo de Proceso” (Process Continous Control), probably a translation or adaptation from an original version in English by Ford Motor Co. It looks very much like the SPC handbook from Ford, Chrysler, GM, which is probably based mainly in this work from Ford. This is my translation to English from the version in Spanish I have in fron of me now. The bold and underline is mine:
On page 23, under the title “Interpret for Process Capability”, it says:
“4.a. Calculation of the Process Standard Deviation
As the short term process variability is reflected in the subgroup ranges, the estimation of the short term process capability is based on the average range Rbar. Calculate:
sigma hat = Rbar/d2″
Then the caclulation of ZU, ZL and Cpk follow.
No mention is done to the long term variation, Pp and Ppk (which are included in the SPC handbook from AIAG) are not mentioned either.
But I am sure noone will refer to a “short term variability” and “short term process capability” if there were not other things known as “long term variability” and “long term process capability”.
So my conclusion is that the copncepts short term variation, long term variation, short term process capability, long term process capability, and therefore Ppk or an equivalent form as an equivalent of “Cpk for long term process capability” already existed by the time of this publication.
This publication is dated 1983.
Also, in my previous job, we used a PDCA system to make improvement projects in teams. I had a direct participation putting in place this system (I will not say “I was the responsible for..” because I was, but was not the only one) It was a local company (big for a local one, but small compared to the multinationals) and we had never heard of six sigma.
The main phase was “plan”, and it icluded to looking at compny objectives, measuring process performance on those indicators, finding best opportunities for improvement using process flowcharts, pareto, cause-effect, brainstorming, SPC, etc… to find causes and solutions, and making an implementation gannt (looks like DMA).
The next phase (do) was to folow the gannt. and the next phase (check) was to verify that a) the improvement was done, b) that it was due to the changes made and c) that no side harmful effects were pressent (looks like I).
The final stage (act) was to make the changes in all documents as needed (drawings, set-up sheets, control plans, working instructions, etc.), to review the training materials, and to provide training according to the new standards (looks like C).
Put all that together, and it looks like DMAIC, even when the name was PDCA. And I am sure it was not an original invention of that company.
This system was customized from materials about TQM which were pretty old, don’t know the exact date but surely before 1985.
Without a profound knowledge of Six Sigma, my impression is that Six Sigma is an evoultion of TQM, as TQM was an evolution of something else and so on… I think we are in a train which is the continous improvement of the quality improvement methods, which started running more than a century ago. Noone can calim himself as the owner of this train we are all building and running on with participations that can be more significative or less significative, but are there anyway.
I just try to put my 2 cents on this train.
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