Hello all,
I haven't posted much on here, but I do read a ton of the content on the site. I love it, and it has come in handy often in my career. So a brief kudos to those who take the time to answer so many questions and add tons of value to the site. Thank you.
On to my question, I am currently a Quality supervisor at a manufacturing facility and have been in debate with the Engineering Manager about how many samples should be used to form a good Cpk.
Our customer requires a 100 percent inspection on multiple features and wants to see a good Cpk on those dimensions before lifting that requirement. What we are attempting to do is to use data that has been collected throughout 2013 and show a Cpk. My Concern is that the Engineering Manager would like to use a 30piece sample from data collected over 7 manufacturing runs (each run using multiple lots of material). Using his idea, we would collect about 4+ parts per manufacturing run and use this to establish a Cpk. While the Cpk may look ok, I don't feel comfortable that this Cpk would show the true story behind our process. Also, our production has ramped up significantly half way through the year (Manufacturing runs that are approximately 18x greater in quantity). I don't want to come off as accusing, but at times it seems like as long as a Cpk number can be created not much thought is put into its accuracy. (also, the conversation about why the Engineering Manger is so heavily involved in this process or where the Quality Manager is in all this will have to be for another day )
I'm curious if anyone has any input as to what would be the best route to calculate an accurate Cpk? Also, is this where something like confidence intervals would help me make the case that the sample size should be much greater?
Thank you!
I haven't posted much on here, but I do read a ton of the content on the site. I love it, and it has come in handy often in my career. So a brief kudos to those who take the time to answer so many questions and add tons of value to the site. Thank you.
On to my question, I am currently a Quality supervisor at a manufacturing facility and have been in debate with the Engineering Manager about how many samples should be used to form a good Cpk.
Our customer requires a 100 percent inspection on multiple features and wants to see a good Cpk on those dimensions before lifting that requirement. What we are attempting to do is to use data that has been collected throughout 2013 and show a Cpk. My Concern is that the Engineering Manager would like to use a 30piece sample from data collected over 7 manufacturing runs (each run using multiple lots of material). Using his idea, we would collect about 4+ parts per manufacturing run and use this to establish a Cpk. While the Cpk may look ok, I don't feel comfortable that this Cpk would show the true story behind our process. Also, our production has ramped up significantly half way through the year (Manufacturing runs that are approximately 18x greater in quantity). I don't want to come off as accusing, but at times it seems like as long as a Cpk number can be created not much thought is put into its accuracy. (also, the conversation about why the Engineering Manger is so heavily involved in this process or where the Quality Manager is in all this will have to be for another day )
I'm curious if anyone has any input as to what would be the best route to calculate an accurate Cpk? Also, is this where something like confidence intervals would help me make the case that the sample size should be much greater?
Thank you!