DFM and DFA – The Key Words Are “Design For”

By

Ken Haven

July 25, 2017

In a previous blog we talked about the definitions of DFM and DFA (note that there are other “DFx” acronyms as well – Quality, Reliability, and Service are 3 others that are used). The implementation of a DFM/DFA approach to design can have a significant impact on the overall development cost, as well as timeline for getting a design into production. And while DFM/DFA analysis can be done after the design is “completed”, it is far from the optimum approach from either a cost or time perspective.

For post-design DFM/DFA, you’ve already invested time and $$$ creating the current version – any changes you make at this stage may impact other areas of the design which have already been completed. So in addition to changes you make for the parts of the design that are creating potential DFM/DFA issues must be analyzed in the context of the impact of those changes on the larger system. Those changes will also need to be verified or tested to determine if there is any impact on performance, quality, reliability, etc. This needs to be assessed for each change you make, costing both time and $$$.

In addition, the DFM/DFA analysis is typically done by someone who has not necessarily been involved with the design from the beginning, so this person(s) need to go back to the design engineers with their concerns. If you’ve built prototypes and already tested them, the changes may need to be fabricated, incorporated into the prototype, and retested. This back and forth at this stage in the design is costly from a time and $$$ perspective.

The later in the design cycle all of this is done, the more costly the changes are as you potentially have to rework and retest much of the work that was already done. Indeed, if the design has already gone thru several iterations, and is in the process of being transferred to manufacturing, any changes could potentially be even more costly and time consuming. Studies have shown that the cost of changes increase by a factor of anywhere from 4X to as much as 10X each time the design moves from one stage to another. And this is not only true for the mechanical side, but also for the EE and software development side.

Here is an excerpt from an article “Manufacturing by Design” from the Harvard Business Review” that provides some additional insight:

“Converting a concept into a complex, high-technology product is an involved procedure consisting of many steps of refinement. The initial idea never quite     works as intended or performs as well as desired. So designers make many modifications, including increasingly subtle choices of materials, fasteners, coatings, adhesives, and electronic adjustments. Expensive analyses and experiments may be necessary to verify design choices.”

“In many cases, designers find that the options become more and more difficult; negotiations over technical issues, budgets, and schedules become intense. As the design evolves, the choices become interdependent, taking on the character of an interwoven, historical chain in which later decisions are conditioned by those made previously.”

“Imagine, then, that a production or manufacturing engineer enters such detailed negotiations late in the game and asks for changes. If the product designers accede to the requests, a large part of the design may simply unravel. Many difficult and pivotal choices will have been made for nothing. Where close calls went one way, they may now go another; new materials analyses and production experiments may be necessary.”

“…consider the manufacturer whose household appliance depended on close tolerances for proper operation. Edicts from the styling department prevented designs from achieving required tolerances; the designers wanted a particular shape and appearance and would not budge when they were apprised of the problems they caused to manufacturing. Nor was the machine designed in modules that could be tested before final assembly. The entire product was built from single parts on one long line. So each finished product had to be adjusted into operation—or taken apart after assembly to find out why it didn’t work. No one who understood the problem had enough authority to solve it, and no one with enough authority understood the problem until it was too late. This company is no longer in business.”

Note that any design may require modifications when transitioning to production – the key is to minimize these such that their impact on the performance, cost, quality, and reliability of the design is reduced.

Next time we’ll talk about strategies/processes that Acorn utilizes to design for manufacturability, assembly, and value.

About the author

Ken Haven has been CEO of Acorn Product Development since the company’s founding in 1993. Ken has more than 25 years of product development experience including technical leadership roles with NeXT Computer, Attain, Inc., and Hewlett-Packard. He holds MS and BS degrees in mechanical engineering from Cornell University.