Good design and bad design

[EngTechno]

What are the characteristics or a good design and a bad design?

[cronxeh]

http://www.npd-solutions.com/dfmguidelines.html

[Integral]

One bullet item missed in that link.

Design for maintainability. If a design has any moving parts it is going to break, unless the item is a consumable it will need to be repaired. Ease and cost of maintenance is something that is frequently overlooked by engineers working under a deadline.

Nothing like a high failure part that requires major disassembly to access. This type of engineering mistake causes increased down time and repair costs. If the design is part of a manufacturing process you will hear about it.

[FredGarvin]

Not to open up a debate but design for ease of manufacturing is not the only measuring stick for a good vs. bad design.

IMO, the top hitters are:

1.) Does the design work/do what it is supposed to?
2.) Is it manufacturable (better yet is it easy to manufacture?)?
3.) Is it efficient in the way it completes it's intended function?
4.) Is it cost efficient?
5.) Does it do any kind of harm to other items (i.e. the environment)?

There are tons of things that can denote a successful design. In the real world, it's usually the management and marketing types that will give you the criteria for success.

[Artman]

I agree with all of the points made so far. Also, it is important to make sure that the design will function under all expected conditions or at least to understand where it will fail and plan for that.

An example would be freeze protection on HVAC equipment. Or the point at which a system will overheat and how that should be handled. There are many ways to deal with these items, but many times, because they are not in the design range they are forgotten.

Part load operation is also frequently overlooked and is probably the point at which the system will usually function (very true of HVAC design). So modelling of partload conditions are important as well as designing for peak.

[BobG]

One bullet item missed in that link.

Design for maintainability. If a design has any moving parts it is going to break, unless the item is a consumable it will need to be repaired. Ease and cost of maintenance is something that is frequently overlooked by engineers working under a deadline.

Nothing like a high failure part that requires major disassembly to access. This type of engineering mistake causes increased down time and repair costs. If the design is part of a manufacturing process you will hear about it.

Someone should teach that to Ford. They seem to start with the engine component most likely to fail, then hang the rest of the engine from the part you're most likely to replace. And if it's not feasible to hang the entire engine from that part, weld a fuel line or other almost impossible to remove component to it.

[Integral]

Someone should teach that to Ford. They seem to start with the engine component most likely to fail, then hang the rest of the engine from the part you're most likely to replace. And if it's not feasible to hang the entire engine from that part, weld a fuel line or other almost impossible to remove component to it.
Having replaced the water pump in a Ford Probe (V6) last summer, I have first hand experience with that.

[philocrazy]

the charactiristics of good design in general are:
*usefulness
*visual appeal
*reliability

the charactiristics of bad design in general are:
*cost savings
*none of the above good design charactiristics

[Chronos]

Hmmm. The best possible design is the one that makes the most profit. Why beat around the bush here?