assembly variation analysis

[runningman]

Has anyone any experience in estimating final assembly variation (i.e. expected gap size & tolerance) from component part variability? I've seen programs such as "Sigmund" that estimate variabilty using solid model data & known mfg process variabilty.

My assembly is a sheet metal sub structure composed of 15 to 20 hard or soft tooled parts that are welded togeather. Incorporated in the assembly are mounting points for thermoplastic trim panels, enclosures, hinges, etc. Inconsistent gaps and fit up issues are a major problem.

Does anyone have a comments or suggestions?

thanks

 

[miner00]

Your best bet is to work with your vendors. Since you are using sheet metal parts, there are some general rules that you have to keep in mind while designing. All sheet metal shops have a standard tolerance which they can hold, usually .005" to a cut feature and .010" to a bend. Hard tooled parts can come in somewhat better than that. The most reliable way to perform this analysis is to do it by hand. Add up all of the connection points between one side and the other to get your overall tolerance. It is a huge pain, but at least you can trust your own results.