In my organization we use different symbols on manufacturing prints to signify different things. Any dimension that is circled is considered a "critical" dimension. The CpK must be established at FPI and must be maintained during production with documented readings.

We have elaborated on this concept to include circled dimensions that have "CpK" or "SPC" inside them. As you can guess, this means that the dimension must maintain CpK or SPC during production runs.

"Criticals" must be checked once per production run by our suppliers.

We have recently introduced "Tolerance Management" to the process. Tolerance Management dictates that critical tolerance chains, with a high influence on the fit and function of mating parts have a new designation (code plus box around dimension) on the print and must be checked at some frequency.

Here's my problem, some complicated injection molded parts can contain up to 60 TM and Critical dimensions! The supplier now complains that it is simply too many to manage given CMM time and resources.

So, I was wondering 2 things:

1) How do other organizations handle these types of "critical" dimensions and "TM" dimensions.

2) A supplier has suggested that the Automotive industry uses "Working" dimensions (with a triangle as designation). These dimensions represent the most important of the "criticals" and "TM" , but are not as many. The Working dimensions are checked at a more regular frequency than "Critical" or "TM".

3) What frequency do you use for your important dimensions?

Thanks for any insight you can provide to help me sort out this new mess we have created.

Regards,
Dominick

In my organization we use different symbols on manufacturing prints to signify different things. Any dimension that is circled is considered a "critical" dimension. The CpK must be established at FPI and must be maintained during production with documented readings.

We have elaborated on this concept to include circled dimensions that have "CpK" or "SPC" inside them. As you can guess, this means that the dimension must maintain CpK or SPC during production runs.

"Criticals" must be checked once per production run by our suppliers.

We have recently introduced "Tolerance Management" to the process. Tolerance Management dictates that critical tolerance chains, with a high influence on the fit and function of mating parts have a new designation (code plus box around dimension) on the print and must be checked at some frequency.

Here's my problem, some complicated injection molded parts can contain up to 60 TM and Critical dimensions! The supplier now complains that it is simply too many to manage given CMM time and resources.

So, I was wondering 2 things:

1) How do other organizations handle these types of "critical" dimensions and "TM" dimensions.

2) A supplier has suggested that the Automotive industry uses "Working" dimensions (with a triangle as designation). These dimensions represent the most important of the "criticals" and "TM" , but are not as many. The Working dimensions are checked at a more regular frequency than "Critical" or "TM".

3) What frequency do you use for your important dimensions?

Thanks for any insight you can provide to help me sort out this new mess we have created.

Regards,
Dominick

Hello Dominick! Welcome to The Cove Forums. :agree:

I read your post a few times, and I concluded that your company's system is very complex and adds unnecessary costs. Even OEM's such as Ford and others have a less complex system to identify critical characteristics than you have. More (confusing) stuff on a print typically accomplishes the opposite.

Expect your suppliers to "make it like the print." Use a simple symbol to highlight the special characteristics, and let the supplier do the rest.

Good luck.

Stijloor. (a Fellow Tar Heel)