Cpk in relation to individual process parameters.

L

Low00Ranger

Registered
I should start by saying I have very little experience with Six Sigma. This forum has helped me greatly in recent weeks. Thank you all for that.

Onto the root of my issue... I have an engineering manager asking for Cpk data for injection molding processes. At first I thought he wanted samples run and measured to validate our current processes. I was wrong.

He's asking for continuous Cpk data as way to validate individual process parameters; cushion, fill time, recovery, etc... I already track those. So, applying the formulas is simple enough. The issue is the calculated Cpk is insanely high. As an example, my fill time spec is 3.00 +/-0.25, mean is 2.95, standard deviation is 0.002. Cpk calculates out to 66.667.

Is Cpk even applicable to in this situation? Is there a better SPC that I should be using. I've always just done basic trend monitoring, to show the repeatability of a process. Any time I've been involved with was pre-production; run a series of samples, measure critical dimensions, and calculate the reliability of the process. This just has me confused.
 
G

Golfman25

Trusted Information Resource
It's doable, but you'll have to come up with the proper parameters and make sure your equipment can measure to that requirement. Also make sure your conversion math and formula are correct as your using a time measurement vs. the standard MM/inches, etc. Some controls even have the spc built into them these days.
 
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