Solving the design engineer’s dilemma

Here is the tale of how product redesigns with DFMA (Design for Manufacturing and Assembly) helped two companies respond to shrinking development cycles, impress their customers and cut production costs.

Many are familiar with Moore's Law about the rate of change with which computers' processing speed increases. Design engineers can add to that a new one, dubbed "Android's Law", which describes what most of us have already observed, namely that product development lifecycles are rapidly shrinking. The poster-child for this effect is the Android smart phone, which has seen the duration of its release cycle decrease incrementally over recent years from about 10 months to just over six.

Although smart phones and consumer electronics tend to represent more extreme examples of this phenomenon, it's everywhere. Buyers want today's product to be better than the one they purchased last time-and they want it to cost less. In short, competitive pressure is increasing and designers, and naturally plastics processors, are getting squeezed.

Facing up to this design engineer's dilemma, two companies were recently helped through rapid and fruitful redesigns of key products by consultant Bill Devenish, a former R&D manager at Nokia, where he led the development of the first smart phone released in North America. Devenish tackled the projects with DFMA software from Boothroyd Dewhurst Inc., which he has used for much of his 23 years in technology product development.

Both manufacturers he worked with found that products designed for low volume manufacturing had become more popular and potentially more profitable than anticipated. However, their existing manufacturability and assembly characteristics resulted in costs that rose in lockstep with volume, eliminating economies of scale. Devenish aimed to help reduce those costs, improve functionality and deliver a product "refresh" on a tight timeline.  

Plastics in play for machine terminal re-design

At QSI Corporation, now Beijer Electronics, the challenge was to rework a small human-machine interface (HMI) terminal. Initially, when target volumes were low (the product was originally sold in quantities of a few hundred), the primary emphasis had been on time-to-market. As production went up, though, the company wanted to capture its full potential profit margin, so there was a need to develop a more cost-effective, long-term product configuration.

Devenish and a small team-primarily an electrical engineer and a mechanical engineer-looked at the challenge of improving profitability by radically simplifying the design. They used DFMA to compress development cycles and to identify ways to lower material and assembly costs while improving reliability and serviceability.

In terms of materials selection for the housing and structural components-traditionally made from formed sheet metal and machined aluminum-engineers had not previously flagged either the primary material or the fasteners as a cost or manufacturability issue. The terminal included a total of 31 fasteners of 13 different types-costly to kit and a great difficulty for assemblers, since some fasteners were nearly, but not quite, identical. Devenish knew that adopting molded plastic for the housing could potentially reduce fastener counts while simplifying manufacture, so with his encouragement, the team looked for every opportunity to adopt plastics.

However, since the HMI terminals had to function reliably in harsh environments, the catalogue of materials was narrowed significantly. Engineers had to select a plastic that could withstand conditions ranging from arctic oilrigs to desert construction equipment-including industrial applications that might get sprayed with hot, chlorinated water or other caustic materials. After reviewing a range of material data sheets, and using DFMA to look at how choices would impact costs, delivery time, assembly work and other factors, the team performed tests on a few sample materials and then selected a polycarbonate / acrylonitrile butadiene styrene (ABS) blend. "We wanted that combination so we could get the lower costs that we needed and still have the toughness and dimensional stability we were looking for," says Devenish.

Keeping molding close to home

As QSI looked to adopt plastics, the engineers teamed up with a local independent molding operation, Salt Lake City-based C & M Manufacturing. C&M had extensive expertise working with several popular polymer blends but had limited experience predicting costs related to using the PC/ABS compound specified by QSI. Because DFMA was able to accurately predict those costs, both parties were able to assess the challenges and quickly craft a plan for tooling, testing, and production.

Working locally with C&M proved fortuitous because the injection molder was able to accommodate minor last-minute design changes by QSI. The technical people at C&M also helped work through issues such as minor blemishes and knit lines. "It would have been much more difficult dealing with an offshore supplier if you figure in all the language and logistics issues," says Devenish.

DFMA guides the redesign

As the design process unfolded, the DFMA tools provided quantifiable information on costs throughout the development lifecycle. That information, in turn, made it easier to get agreement about choices. "In the past, designers simply gravitated toward the design concepts with which they were most familiar," says Devenish. DFMA provided concrete information on potential savings relative to each option being considered. "Sometimes people were sure they knew how to get cost out on their own but DFMA proved to be a better way to achieve that," he says.

As a result of the successful redesign, instead of multiple, complex and expensive metal parts-and a large number of fasteners-QSI ended up with an assembly composed of just a few molded PC/ABS components, with integrated features like slots, snaps and tabs-and a mere handful of fasteners (see photos). In addition, the new design replaced three printed circuit boards (PCBs) within the enclosure with just one, which in turn reduced the number of electronic components and reduced solder joint count. "The process greatly trimmed the fastener count and improved assembly efficiency, while also cutting total component costs," says Devenish. "Those improvements helped us meet our goal of curbing costs, and our local mold house helped us meet our aggressive delivery schedule."

Although the production department at QSI had initially been wary of the new design, "once they started building it, they loved it," says Devenish.  "They thought the engineers walked on water because the assembly process had been improved so much." The use of fewer types of fasteners, and fewer fasteners overall, reduced problems in the field that had often been traced to incorrect fastener installation.

A communications radio redesign: plastics versus metal

In this case, though, metal emerges the winner. Devenish was involved with another recent redesign effort for which he made great use on DFMA. This time the business challenge was at a large electronics company that specialized in ruggedized communications equipment. There, the target was a special-purpose communication radio.  Two new concepts were generated by the design team, the first-the "B" style radio-based on incremental modifications of the existing product and the second-the "J" style-representing a radical transformation.

At first, most of those involved in decision making supported the "B" style, because it seemed to present fewer "unknowns" and less risk. DFMA analysis provided a more credible basis for comparison and revealed the significant advantages of the second design, the "J" style, which included fewer PCBs and far less parts-saving more than $50 per unit-while also reducing assembly time and cost. Thanks to the DFMA metrics, the merits of the second design became clear to everyone.

DFMA also helped benchmark an effort to consider substituting plastic for metal in the radio housing (see chart) because it offered the potential of further lowering costs and reducing part count. However, it became clear in this instance that stringent RFI and EMI shielding requirements, and the need for thermal heat dissipation, gave the edge to metal enclosure components.


Alternative Design Cost Comparison


"B" Style                                                                   "J" Style



Product Life Volume                  50,000                  Product Life Volume                  50,000

Number of Parts                            147                  Number of Parts                         121

Theoretical Min. Parts                      14                  Theoretical Min. Parts                   13

DFA Index                                      3.7                  DFA Index                                  4.2

Assembly Time (Min.)                    18.7                 Assembly Time (Min.)                 15.0

Assembly Cost ($)                        26.67                Assembly Cost ($)                     21.48

Piece Part Cost ($)                      313.12               Piece Part Cost ($)                   262.19

TOTAL COST ($)                         339.79                TOTAL COST ($)                      283.87


Savings = 50,000 x $56.12 = $2,806,000


Lessons learned while solving the design engineer's dilemma

Devenish says his experience with these two programs showed that cross-functional teams are an important element in successful design and redesign efforts because they foster a necessary sense of collaboration. "DFMA complements that team approach," he adds.

Although DFMA is in some ways a tactical tool, it also has strategic implications. For instance, notes Devenish, leveraging DFMA provides opportunities to keep design and manufacturing "local."

"There are obviously some situations involving high-volume production where it makes sense to go offshore to lower cost countries," says Devenish. Indeed, he noted, many manufacturing facilities in North America are now geared to low- to medium-volume but few are set up for high-volume. "When it comes to small- to medium-volume North American operations, DFMA tools can help companies develop more cost-competitive and producible designs," he adds.

Devenish says customer expectations will continue to increase the pressures on product designers. These expectations are the result of generations of products that are smaller and cost less than their predecessors, yet offer more features and higher quality. The design engineer's dilemma is to continually deliver more for less. Utilizing the tools and methodologies of DFMA helps overcome this dilemma by providing quantifiable options for design optimization.

This helps design teams face redesign challenges with confidence so they can consistently achieve more successful outcomes.  "It all comes back to meeting customer expectations for lower cost, higher quality, and more features," Devenish says.


What is DFMA?

DFMA is a tool to help companies meet customer expectations through reduced cost and accelerated time-to-market; improved communication between internal functions, supply chain partners, and manufacturing, and improved manufacturing efficiency.

DFMA includes two main elements: The DFA Product Simplification module focuses on achieving parts consolidation and assembly simplification through a sequence of detailed questions that compel clear thinking about function and purpose. The DFM Concurrent Costing module calculates accurate part and tooling costs through a similar iterative process-including questions that focus on choices of material and manufacturing processes.

DFMA provides a series of cost estimates and comparisons from the start of the product development process and continues to support design and process refinement on an ongoing basis.

The cost data is based on looking at existing costs, performing separate Pareto analyses, and organizing choices by part category-fasteners and electro-mechanical parts, for example, says Bill Devenish. That effort produces a valuable and malleable portrait of the project and the trade-offs involved. "If we are doing a redesign it tells us where we need to place the emphasis and then quantifies the result of different approaches and choices," Devenish says.

In the QSI project, "We performed the DFMA analysis at multiple points. We used it up-front to come up with initial cost estimates, and we used it all through the development process to monitor how we were doing," says Devenish. "DFMA also validated quotes received from suppliers. We were able to compare actual assembly times from prototype builds to the DFMA analysis to check the assumptions of our assembly operations."

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