The trend to shorter product cycles is also creating shorter design cycles, resulting in higher part costs, manufacturing problems, and even warranty issues down the road. Careful up-front work on product design can easily save 50% on total costs, and may even be America’s hidden weapon in winning manufacturing business back from China. Design News explored these ideas in an interview with Nick Dewhurst, a winner of the National Medal of Technology for his work on design for manufacturability and assembly at Boothroyd Dewhurst, Inc., Wakefield, RI. (www.dfma.com)
How much can you typically improve a product’s cost through careful up-front design?
Dewhurst: That’s the interesting dilemma we face all the time. If you have a project already in production and you do what we do --apply design for manufacturability and assembly (DFMA) techniques and take parts out and look at different materials and processes -- you get about a 50% reduction in product cost. That same thing is achievable if you do these things early.
How often do companies design the right way and save through careful early design analysis?
Dewhurst: Less than 20% of the time. And that’s probably on the high side. Most US companies today are struggling with time to market. Faster, shorter design cycles. And what they perceive at least as the way to solve that problem is hurry up and finish the design. That is the worst thing you can do. That ends up creating a design that has a bunch of problems in it you spend a lot of time later trying to fix. If design teams were given more time to investigate other options and explore opportunities for simplification of product structures early in the design phase, you wouldn’t have all of those problems later on.
In all of the years that you have been studying design for manufacturing and assembly are there any common mistakes that you have seen design engineers make?
Dewhurst: I think it’s the proliferation of lots of simple parts in products. A kind of oversimplified example is that if you want to attach a bracket to the inside of a cabinet, the easy way to design that is to put four holes in it and use four bolts four washers, four lock washers and four nuts. If you’re going to produce that for the next five years, you’re going to pay for that over the next five years by having people put in four bolts, four washers, f0ur lock washers and four nuts. Now If you had taken a few extra hours, maybe a day, in design you could have come up with some way to put features into sheet metal that secured this bracket to the other bracket without the need for those fasteners. And then for the next five years you are producing that product with the benefit of good design.
What about failing to design for the benefits of injection molding when people convert from metal?
Dewhurst: That happens all the time. The other thing that happens all the time is that if people are used to designing in sheet metal they are afraid to design plastic snap fits because they don’t know how to do it. There’s a perception that if we put plastic snap fit features on these parts to secure them together, they’re going to be cheap and they’re going to break and they’re not going to give us the same mechanical characteristics as metal threaded fasteners. I know that’s not true. If you know how to design plastic snap fits and choose the right materials, you can have very good mechanical properties. There’s a lack of understanding. The plastics industry has done a good on providing data on plastics materials, but other then a few short items on their Web sites there aren’t a lot of good resources on how to do good injection molded part design.
To what extent could better design for manufacturing and assembly keeps jobs in the United States?
Dewhurst: It would directly correlate. I told you that people see average savings of 50% on product costs by doing DFMA on their products. If you’re looking at producing a product in China, you need to save 60 or 70% to make it worth investigating. Interestingly enough, I’ve run into two companies in the last two months that have products in China that they are re-designing and bringing back to the United States for a percentage cost savings.
What kind of problems did they run into in China?
Dewhurst: Well one of them was a fuel module that was produced at six or seven suppliers in China. So they had to manage this supply chain on the other side of the world and then have the parts shipped back here. It turns out they redesigned it relying quite heavily on the use of plastics and are producing it in the United States at about a 15% cost savings. The second one was a shipping issue. The manufacturer in Chinas was having trouble keeping up with the demand. There also was a problem manufacturing a die casting that was an integral piece of one of these products. So the company needed 1,500 parts a day to keep their line moving. And the Chinese supplier couldn’t produce 1,500 parts a day that were meeting the specs. So they ended up putting the parts on a plane and flying them over every day. And it was costing them something like $35,000 to ship 1,500 of these die castings overnight from China. Every night.
How much thought went into the original decision to go to China?
Dewhurst: It was one of these off-the-cuff, well if we go to China we can make it there cheaper because their labor is 10 cents a day and we’re paying 50 bucks an hour. And that’s a real short-sighted view.