The Quest for Imperfection 1

[drawoh]

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

http://www.designnews.com.

It is not very clear on what the Japanese actually do. It sounds like they design their assemblies to allow for sloppier tolerances.

In fact, it all sounds like good versus bad drafting practise. You can specify tolerances on your parts and do stackup analysis all you want, but it is a waste of time if you are too accurate for your manufacturers. Perhaps Japanese engineers talk to fabricators?

Comments?

JHG

 

[ewh]

The article seems to make sense. It boils down to system engineering. Perhaps they are seeing the forest instead of the trees?

 

[Heckler]

Here is the link to the article.

http://www.designnews.com/article/CA6262124.html

It's worth reading and doing more research to fully understand functional build concepts. Here is another concept that goes against common practices.


Anticipatory Failure Determination (AFD) is a failure analysis method. Like FMEA, it has the objective of identifying and mitigating failures. Rather than asking developers to look for a cause of a failure mode, it reverses the problem by asking developers to view the failure of interest as the intended consequence and try to devise ways to assure that the failure always happens reliably.

AFD offers an advantage over FMEA for more complex failure analysis in the following way. FMEA relies on failures and their root causes being identified by the application of personal experience or known (documented or applied) knowledge of others. However, the "denial phenomenon" comes into play with this analysis. When we ask "what can go wrong" with respect to a functioning system, we resist thinking about unpleasant possibilities that might occur unless we have actually experienced them and they become real. Even when problems have been experienced, people are reluctant to identify or document those problems. By reversing the problem, AFD overcomes the "denial phenomenon" and opens up creative insights into analysis of failures.

 

[TheTick]

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.

 

[MintJulep]

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.

 

[xgrigorix]

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.

 

[drawoh]

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

 

[ajack1]

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’t, 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’ll 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.

 

[Heckler]

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’ll 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.

 

[ajack1]

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 “desirable” 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 “fit and function” attitude as described in the above link.

If they are not getting such high ratings in reliability and customer satisfaction through “designing an impossible part and sticking really tight tolerances all over it” 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.