Can someone help me with a method to study Process Capability for a specification with Maximum Material Condition (MMC)??
Thanks.

Can someone help me with a method to study Process Capability for a specification with Maximum Material Condition (MMC)??
Thanks.

Ganeshsundaresan,

This may help (http://elsmar.com/Forums/showthread.php?t=4610) to get started.

Look here as well (http://www.google.com/custom?domains=Elsmar.com&q=Capability+for+MMC&sa=Search&sitesearch=Elsmar.com&client=pub-1385417534940691&forid=1&channel=6124086287&ie=ISO-8859-1&oe=ISO-8859-1&cof=GALT%3A%23008000%3BGL%3A1%3BDIV%3A%23336699%3BVLC%3A663399%3BAH%3Acenter%3BBGC%3AFFFFFF%3BLBGC%3A000099%3BALC%3A000000%3BLC%3A000000%3BT%3A0000FF%3BGFNT%3A0000FF%3BGIMP%3A0000FF%3BLH%3A50%3BLW%3A350%3BL%3Ahttp%3A%2F%2Felsmar.com%2Fpng%2Fheader-G-search.png%3BS%3Ahttp%3A%2F%2FElsmar.com%2FForums%2F%3BFORID%3A1%3B&hl=en). Some more searching is required..;)

Stijloor.

Can someone help me with a method to study Process Capability for a specification with Maximum Material Condition (MMC)??
Thanks.


Hum, you’re making my tiny brain go back in time. :bonk: I presume you are wondering about how MMC can be applied as Bonus Tolerance, such as, example: If the actual hole is larger than the smallest allowable hole, a bonus tolerance can be added to the stated tolerance value (or opposite for a shaft). That being said, theoretically every part could have a different USL, which is not conducive to a Capability Study. The Basic Formulas for Cpk, Ppk require Constant Value Limits.

I recall this situation a number of times in Automotive Stamping and we simply set the LSL and USL to the Minimum Tolerance Values, without factoring in Bonus tolerances. This forced us to Control the process and not have any extra help from MMC. During Production, we would only use MMC Bonus Tolerance if we encountered a situation that caused us to Pass or Fail a part, or lot of Product. Hope this Helps-----D.

noboxwine is correct. The best way to do this is to simply ignore the bonus tolerance. Focus on determining the true variation of the features involved and controlling it. An adjunct that I have used is categorical data for the proportion of failures with the bonus tolerance applied and the proportion of times that the bonus tolerance had to be applied. this is a quantification of the waste that results from processes that are not capable of meeting tolerances.

remember the intent of studying process capability is not to achieve mediocrity, but to achieve excellence.

Bev,

Given that, the intent of studying process capability is not to achieve mediocrity, but to achieve excellence should the target for the size of feature that is controlled with a variable location or orientation tolerance (@MMC or LMC) be the same as one that is controlled with a constant value location or orientation tolerance?

If one evaluates a variable location or orientation tolerance that is specified zero @ MMC is attribute gauging the only option available to analyze it?

ganeshsundaresan,

If you read through the threads that Stijloor references you will find a PowerPoint presentation "ppkmmc.pdf" and a couple of spreadsheets that show how to analyze variable limit geometric tolerances and how process parameters can be examined and optimized to achieve the excellence that Bev suggests.

Paul