【转帖】he quest for imperfection

yang686526

the quest for imperfection
   the cover story in what i assume to be the october 10 issue of design news has an article on something called "functional build".  the concept is that instead of thoroughly inspecting each fabricated part, japanese manufacturers focus on system quality.  this is explains at least part of why they design better quality cars.  someone presumably is racking up consultant fees on this, and i guess i wasted my youth.  
   the article probably is up somewhere on
the article seems to make sense.  it boils down to system engineering.  perhaps they are seeing the forest instead of the trees?
here is the link to the article.
i've seen plenty of design demi-competence originating from japan.  they may make there parts better, but it's a stretch to say their designs are better.
interesting article, but i think it vastly over-simplifies some things, glosses over other very important issues, and outright misrepresentes others.
"functional build" seems like just a new name for good engineering and design, giving proper consideration to ease of manufacturing, assembly and product life cycle.
far too many engineers and designers just don't understand the purpose of tolerances.  tolerances serve to define the maximum deviation from the nominal part dimensions that will still allow proper function.  tighter tolerances do not mean a higher quality part, just a more expensive one.  if you design an assembly that cannot accomodate any variation from the nominal then you need perfectly nominal parts to build it.  the concept of "functional build" says, rather than specify tigher tolerances on individual parts, go back to the assembly and design that so that it can accomodate a wider range of variation.  this lets all the parts be "loser", less costly, and results in an assembly that is less likely to fail due to things like contamination, thermal expansion, and wear.
the article makes frequent use of the phrase "out of spec".  i really doubt this is true of the japanese auto makers.  i'm sure all the parts are within tolerance.  probably far more not at exact nominal dimensions, but still "in spec."
the article gives only a single sentence to stable manufacturing processes.  this is what the japanese do really well.  establish appropriate tolerances, then set up a manufacturing process so that all the parts are good.  build in quality rather than try to inspect in quality.
good article.  makes sense to me.  you can build lots of really great components, but if those components don't work in concert as a whole, then the components are pretty worthless in the end.
mintjulep,
   just following up on your comment...
   when you generate a manufacturing drawing and you apply tolerances and you realize they are not manufacturable, your stack-up analysis is wrong.  you have to fix the design.  a lot of bad design slips through because of sloppy drafting.  
                   jhg
a really good article, but is not just a step back in time? years ago fit and function was the key, some things obviously matter but many don鈥檛, knowing which was which was the key.
as cad and cnc machining have come to the fore it seems there are less really good engineers about, lets design something that is impossible to make and stick really tight tolerances all over it, that鈥檒l do the trick, as long as it has been drawn to the correct standards that will be just fine and dandy. obviously visual parts are different but 98% of most parts just displace fresh air.
however even if the engineer in charge of the project is smart enough to realise it, just try getting it changed!!!
much of engineering these days, at least automotive in the uk/ europe is the tail wagging the dog.
quote (ajack1):
as cad and cnc machining have come to the fore it seems there are less really good engineers about, lets design something that is impossible to make and stick really tight tolerances all over it, that鈥檒l do the trick, as long as it has been drawn to the correct standards that will be just fine and dandy. obviously visual parts are different but 98% of most parts just displace fresh air.
don't you think that's a little over simplification of today's high tech machines.  in todays product/functional driven world beit commerical or military designs are getting more complex just take a look at a 1970 datsun 240z and the new nissan 300z....worlds apart.  the "impossible to make and stick really tight tolerances all over it" comes with advancements in technology and need.
yes heckler i was oversimplifying things. that is an interesting example you use, again i can only speak from a european perspective but the 240z was the first 鈥渄esirable鈥?car that datsun built, before that they really were basic but very cheap.
it would be hard to argue that the 300z is not a vastly superior car, but then again it is japanese and they do favour the 鈥渇it and function鈥?attitude as described in the above link.
if they are not getting such high ratings in reliability and customer satisfaction through 鈥渄esigning an impossible part and sticking really tight tolerances all over it鈥?are they perhaps doing so through better engineering?
the fact that datsun/ nissan now builds cars that are more reliable than mercedes, bmw, and jaguar for example is nearly funny.