HI sir

I have collect reading 98 numbers for process with diameter 32.3+/-0.2 mm.All data is coming with this tolerence limit .still cp and cpk is coming 0.6 and 0.34 respectively.Can anybody suggest me what interpret this result.

How i can get 6 sigma.should i have to increase tolerence limit.

what is sub group.

regards

Anil gupta

Your process's upper limit is 32.5 and lower limit is 32.1.  But on calculating on the basis of the input you have given the Upper specification limit (USL) and lower specification limit (LSL) as per client are 32.36 and 32.12 respectively.  As you can see that the window offered by client is only .24 (32.36-32.12) , where as your window is (.4) . More over you need to center your process. Now the process is a bit skewed.

If you want get 6 sigma then your limits shold be 32.36 and 32.24 with the mean value being 32.3.

Only when you give the entire data,i would be able to arrive at the correct inference.But then,from the details that you have given,i could figure out that the std dev is around 0.11.You need to reduce your variation as much as possible.Also center the process to the mean.

What process is this? Is it a drilling or turning process? Please give more clarity.

From process Cp and Cpk value it is clear that process has variation as well as not centered. Cp at least should be equal to 1.67 and Cpk 1.33 for good process. 

 

Cp is about variation while. 

Cpk is about variation and process mean.

Look for achieving Cpk >1.33 for the process.

 

For more details provide data set.