Tolerance Stackup Analysis
Tolerance Stackup Analysis
(OP)
Are there any spreadsheet templates or cheap programs available for performing tolerance stackup analysis.
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Tolerance Stackup Analysis
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RE: Tolerance Stackup Analysis
Is tolerance stack-up really that difficult?
JHG
RE: Tolerance Stackup Analysis
RE: Tolerance Stackup Analysis
Jay
RE: Tolerance Stackup Analysis
I am concerned because tolerance stack-up is not absolutely simple, and I do not see how far you can automate it. You have to type in each tolerance, and you have to account for the direction each tolerance works in. This requires an operator skilled enough to recognize all this, as well as recognizing tolerances that are not reasonable. A tolerance of +/-0.1mm may work on your spreadsheet, but it will not work in your welding shop. Thermal expansion and contraction can be a problem too.
Automation works when it saves work and eliminates error. I do not see much work being saved here, and the errors are eliminated buy someone paying attention to what they are doing.
JHG
RE: Tolerance Stackup Analysis
What I am looking for is to check a number of tolerances inside of an assembly to ensure that mathematically it is possible. If it is not mathematically possible then there is no way for it to be manufactured. It also requires working with the vendors (machine shops, sheet metal shops, etc.) to understand their process cabilities and get as much input from them while in the design stage.
Thanks
RE: Tolerance Stackup Analysis
"I would like to have something that will show Worst Case, RSS, Six Sigma, CP, Cpk, DPPM, and graph the results."
I'm not sure you're going to get this from stackup analysis. Most of these quantities are process quality data that are developed after a process is implemented. These are tracking data and are used to determine how much processes change & improve by process changes.
From my own experience, one can develop an arithmetic stackup which is simply additive plus/minus values of all tolerances in a direction. Usually it isn't reasonable because the total stackup is huge. Besides, statistically one would probably not experience such wide variation in stackup, which sort of fits common sense. Juran's quality manual states that if you have capable in-control processes with Cpk's of 1.33 or better, then the arithmetic tolerance stack can be reduced through some sort (can't exactly remember the details) of a squareroot-of-sum-of-squares analysis.
TygerDawg
RE: Tolerance Stackup Analysis
ex.
Part1 Overall = 1.000 ±.010
Part2 Overall = 1.000 ±.005
Assembly Overall = 2 ±.010
Normal distribution used
Assembly Worst Case = .015
Assembly One Standard Deviation = .003727
Assembly Statistical Tolerance = ±.011180
Cp = .894
Cpk = .894
DPPM = 7290.358
If 7290 defective parts per million is acceptable then the part tolerances are OK, but if not then the part tolerance need to be tightened, or the assembly tolerance needs to be opened up. In order to achieve a Cp of 1.414 both part tolerance would have to be ±.005.
Thanks
RE: Tolerance Stackup Analysis
RE: Tolerance Stackup Analysis
RE: Tolerance Stackup Analysis
RE: Tolerance Stackup Analysis
Why not check it out and let us know if it works?
http://adcats.et.byu.edu/WWW/ADCATS/software/
Monkeydog
RE: Tolerance Stackup Analysis
RE: Tolerance Stackup Analysis
RE: Tolerance Stackup Analysis
TTFN
RE: Tolerance Stackup Analysis
RE: Tolerance Stackup Analysis
Why would you not verify a stranger's sheet?
TTFN
RE: Tolerance Stackup Analysis
RE: Tolerance Stackup Analysis
Are you really willing to bet your project on unchecked code?
Cheers
Greg Locock
RE: Tolerance Stackup Analysis