wrote 10 Mar 2013
Pareto tools
Why do pareto : When we wan to know which defect that make your production yield lower than your company goal.We will use pareto chart we can get it either in excel or minitab the example I will show how to get pareto chart by Minitab.
1.Collect defect data which you must have individual defect and defect qty as example below.
AQL
AQL is stand for acceptance quality level is applied for quality sampling plan which I will explain how to define AQL from below table
At first you have to choose the sample code to properly with your productionas below table.
Ex. If your lot size are 501 - 1200 and you choose General sampling level 2
Your sample code is J.
Then you have to know what is your AQL level usually the people will select 0.4 or 0.65 for general sampling so from above your sample code are J so your sampling plan as below
If AQL = 0.65
Sample size = 80
If found defect = 1 can be accepted lot.
If found defect = 2 or more the lot will be rejected.
Cp = Process capability
Cpk = Process capability index(k is stand for katayori means shifted)
Pp = Process performance
Ppk = Process performance index
Calculating Cpk and Ppk
Cp = USL-LSL/6sigma
Pp = (USL – LSL)/6*Std.devCpl = (Mean – LSL)/3*Std.dev
Cpu = (USL – Mean)/3*Std.dev
Cpk= Min (Cpl, Cpu)
Ppu = USL-Xbar/3sigma
Ppl = Xbal-LSL/3sigma
Ppk = Min(Ppu,Ppl)
Cp Cpk intertpret
If cpk is cpl means the data mostly fall in LSL.
If cpk is cpu means the data mostly fall in USL.
If cpl more than cpu means mostly data fall in LSL.
If cpu more than cpl means mostly data fall in USL.
If cpl equal cpl means mostly data are in center.
Type of tolerance
1.Bilateral tolerance means tolerance 2 sides.
2.Unilateral maximum tolerance means tolerance one side only max.
3.Unilateral minimum tolerance means tolerance one side only min.
Capability studies for Bilateral tolerance
Capability studies for unilateral maximum
Capability studies for unilateral minimum
Cpk is cpl due to min is Cpl means the mostly data are on LSL.
