Advice on PPAP Attribute Data Capability - Go/No-Go

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tomvehoski

I'm rusty at capability, so I figure I will go to the experts here.

I've got a fineblanked stamped steel part with two holes in it. One receives a fitting that gets brazed in place. The other is a mounting hole for a bolt. The fitting hole is the only important feature. I've only got a .003" tolerance band on it, so I'm dead on a capability study using calipers since I don't even have enough resolution. Besides that, our biggest issue has been burrs that prevent the fitting from being inserted for brazing. For this reason, I am implementing a go/no-go gage as the true test of a good part.

Apparently I have killed off the brain cells that tell me if I can do a capability study on attribute data. If so, how?

In reality my customer will accept a capability study on any feature as long as it hits 1.67 cpk. I'm trying to break this place out of the "doing paperwork to prove we know how to do paperwork, even if it is pointless" mode, so I hate doing stuff like this.

Thoughts?
 
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David DeLong

Re: Advice on PPAP Capability - No/No-Go

Capability studies are performed on variable characteristics and not attribute. You cannot achieve a Ppk of 1.67 using an attribute gauge.

There are attribute studies which only reflect whether or not the method of measuring is effective.

You are out of luck here.
 

Howard Atkins

Forum Administrator
Leader
Admin
Normally if you can show capability at PPAP stage you should be able to use a gage for ongoing monitoring.

In your FMEA raise the burr issue and use the go/no go gage as a control.

In your control plan put the gage for process control with and a daily measurement as an inspection.

This should be acceptable to both sides.
 
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Oskar_S

Hi
We seems to be in the same businees. We produce brazed plate heat exchangers from steel coils. Have you tried to measure with a 3 point caliper (special type of caliper for hole dimensions, can be found in the Mitutoyo cathalogue)?
 
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