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Short term Vs Long Term
In my oppinion it exist two possibility to meassure the capability (Long Vs Short term).
Preliminary Study (100 parts)
1) 5 parts -> Pp1, Ppk1 (Normal Distribution)
2) 5 parts -> Pp2, Ppk2 (Normal Distribution)
3) 5 parts -> Pp3, Ppk3 (Normal Distribution)
....
20) 5 parts -> Pp4, Ppk4 (Normal Distribution)
you have 20 pp, ppk therefore you can map a potential preliminary curve haw well is improving your process. the curve tend to be exponential
pp
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- - -1-2-3-4-5-6-7-8-9-10-11-12-13-14-14-16----20 (Size)
At this stage the short term ppk, pp is ppk20,pp20 but if you want a long term indez which take into acount all the 100 points as the curve is noraml by the Limit theorema you can add normal distribution and you will have other normal distribution therefore you can calcaulate the pp,ppk with all the 100 part to calculate the pp,ppk aggregated index.
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You see that the curve tend to a well pp, ppk (Lets say 3) now you can start with Cp, Cpk
1) 5 parts -> cp1, cpk1 (Normal Distribution)
2) 5 parts -> cp2, cpk2 (Normal Distribution)
3) 5 parts -> cp3, cpk3 (Normal Distribution)
....
20) 5 parts -> cp4, cpk4 (Normal Distribution)
In my oppinion it exist two possibility to meassure the capability (Long Vs Short term).
Preliminary Study (100 parts)
1) 5 parts -> Pp1, Ppk1 (Normal Distribution)
2) 5 parts -> Pp2, Ppk2 (Normal Distribution)
3) 5 parts -> Pp3, Ppk3 (Normal Distribution)
....
20) 5 parts -> Pp4, Ppk4 (Normal Distribution)
you have 20 pp, ppk therefore you can map a potential preliminary curve haw well is improving your process. the curve tend to be exponential
pp
- -----------------------------------
- -
- -
- -
- -
- -
- - -1-2-3-4-5-6-7-8-9-10-11-12-13-14-14-16----20 (Size)
At this stage the short term ppk, pp is ppk20,pp20 but if you want a long term indez which take into acount all the 100 points as the curve is noraml by the Limit theorema you can add normal distribution and you will have other normal distribution therefore you can calcaulate the pp,ppk with all the 100 part to calculate the pp,ppk aggregated index.
----------------------
You see that the curve tend to a well pp, ppk (Lets say 3) now you can start with Cp, Cpk
1) 5 parts -> cp1, cpk1 (Normal Distribution)
2) 5 parts -> cp2, cpk2 (Normal Distribution)
3) 5 parts -> cp3, cpk3 (Normal Distribution)
....
20) 5 parts -> cp4, cpk4 (Normal Distribution)
.