DFMA takes lean to the next level

Design for Manufacturing and Assembly dramatically improves plasma-cutting controller design.

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When the design engineering team at Hypertherm used DFMA to redesign the EDGE Pro CNC controller for plasma cutting, they achieved an overall reduction in part count of 27% while adding new features and performance capability. On the manufacturing side, the team saw even bigger gains, including a whopping 50% decrease in build and test time.

When Hypertherm of Lebanon, NH, was getting ready to design their next-generation, CNC (computed numerically controlled) plasma cutting system, the engineering team’s goal was to make improvements. But the controllers, which automate the company’s world-leading cutting tools and systems, already set the industry standard. So why redesign? And how?

In the world of high-temperature plasma cutting systems, working conditions are less than perfect. Factories and machine shops — for shipbuilding, automotive, construction, metal fabrication, and sign-making — expose tools to the harshest of conditions. Moisture, dust, dirt, gases, and extremes of temperature, as well as physical impacts and vibration, all need to be taken into account. The bottom line is that designs need to be nearly indestructible and easily serviceable. They also need to meet stringent performance standards.

Hypertherm’s controllers get high marks on all fronts. Returns and repairs are low. They can interface with a variety of systems where repeatability is essential. They are flexible enough to manage the typical two-cutting-head operation as well as stations with up to six heads. And they can guide both intricate cutting for artwork and high-speed ripping for heavy industrial manufacturing.

With a market-leading product and an interest in holding on to this enviable position, the company understands the need for continuous product evolution to stay competitive. So that’s why they redesign. How they do it — and do it so successfully — is with Design for Manufacturing and Assembly (DFMA), a unique design analysis methodology pioneered by Boothroyd Dewhurst of Wakefield, RI.

Benchmark, listen, and then design
John Sobr, design engineer in Hypertherm’s Automation Group, started the controller redesign project by benchmarking the existing EDGE II CNC’s design and assembly. “The software prompts you to evaluate the product part by part and document the assembly step by step,” said Sobr. “Following this, it yields a compelling Pareto chart that not only establishes a baseline from which you can measure success, but also quickly illuminates the parts and processes where there is the greatest opportunity for improvement.”

In general, the DFMA suite of software solutions helps engineers ask critical questions about their product designs early in the development process. The goal is to reduce part count and improve assembly, both of which contribute to lower costs and increased reliability. Such an evaluation can have major impacts downstream on the manufacturing, assembly, and organizational cost of those products. Companies of all sizes, including big players in the aerospace and automotive industries, have put DFMA to work with dramatic results.

At Hypertherm, where DFMA is enthusiastically embraced, a number of other best manufacturing practices, such as Continuous Improvement, Lean Manufacturing, and Voice of the Customer (VOC), are also used to push for superior product designs. With the controller redesign, VOC — a market research technique designed to identify customer wants and needs — complemented DFMA by surveying all of Hypertherm’s customers including end-users, integrator partners, and their own assembly-line workers. At stake were performance and reliability for the operators, serviceability and modularity for the integrators, and manufacturability for the assemblers.

From the VOC process, Sobr’s engineering team learned a number of key things. Regarding reliability, they identified the LCD display and the power supplies as the most vulnerable components. Related to serviceability, they decided that the interior of the controller needed to be even more accessible. And as for manufacturability, they watched their own assemblers twist, turn, lift, and rotate the controller as it moved down the assembly line. All of this input pointed to room for improvement and guided the creation of design goals for the new EDGE Pro CNC line.

“The VOC process tells us what the product has to do — its functions and features, for example,” said Mike Shipulski, engineering director at Hypertherm. “How you get there — that’s DFMA. And DFMA is the biggest lever in lean.” (see Sidebar)

Pulling the lean lever with DFMA
Having set the design goals in the concept stage — function first, robustness, modularity, reliability, and serviceability — the DFMA team next reviewed the virtual CAD model. Meticulously dissecting the model, they examined the product’s modularity scheme and looked at all the service issues, such as how to open the doors or reach into the unit without disturbing wires or cable connections. All the while, they collected data that suggested further refinements.

Then they went to work creating the first functional prototype. “Physical prototypes are important,” said Sobr. “You can model things like wire harnesses, but how you actually install them — how you put the tie-wraps in, how the wires dress — the model can’t tell you that.” But a physical prototype can and, with one in hand, the team met again and totally dismantled it down to the nut, bolt, and screw level. Throughout, DFMA was used to look for further parts consolidation and assembly efficiencies, all of which were then rolled into the final prototype, or Alpha units. From here there was exhaustive testing — HALT, Environmental, ESD, and drop testing — a Beta round of units, and shipment to customers for feedback.

When the design dust settled, DFMA had guided Sobr’s team to a number of significant design improvements for the EDGE Pro CNCs. Regarding reliability and robustness, the team designed better mounting for the main power supply, as well as consolidating the unit’s electronics onto a printed circuit board (see Figure 1). To achieve modularity, they created a standard front panel with multiple back panels — resulting in 10 unique product configurations — as well as other opportunities for customization (see Figure 2). To improve serviceability, they made the interior of the product accessible from three sides, rather than just through the back door, as had previously been the case (see Figure 3). And to enhance manufacturability, the lower part count and better-fitting components eliminated the previous twisting and turning experienced by the assembly-line workers and reduced the number of product lifts on the assembly line from seven to zero.

Figure 1. The 31 wiring components in the EDGE II CNC controller (left) were reduced to 11 in the EDGE Pro (right) following a DFMA-guided redesign. This parts consolidation greatly improved assembly and reliability of the unit: a central printed circuit board is mounted with four tool-less keyhole features and secured and grounded with only one screw; all wiring has pluggable rather than fork terminal connectors; fasteners have been significantly reduced; and PCB-mounted components are more durable. In addition, the power sub-assembly requires less overall space in the unit.

Figure 2. Modularity was a key DFMA redesign goal for the EDGE Pro CNC controller. The product can be ordered with a variety of back panels that create 10 unique interface configurations, so integrators can replace competitive units in a simple plug-and-play step.

Figure 3. Hypertherm’s original EDGE II CNC controller (left) was accessible for servicing through a hinged back panel, which typically had many cables connected to it. The DFMA-redesigned Edge Pro (right) was designed with three points of access — a hinged front panel, a hinged back panel, and side access — to make field repairs as easy as possible.

When engineers think about performance, they usually assume that part count will increase with the addition of features. “For a lot of engineers, the idea of more performance for less cost is contradictory. But it’s not,” said Sobr. “When DFMA is the lens through which you look at product design, you see it differently. Functionality can go up, while parts and costs go down.”

And that’s just what happened. When the final tallying was done, the design engineering team had achieved an overall reduction in part count of 27%, while adding features and performance capability (see Figure 4). “We were able to hold the price of the new product,” said Sobr. “At the same time, the value of the controller improved dramatically. That’s hard to do when the price of components continues to rise.”

Figure 4.Comparison chart of the Edge II and EDGE Pro shows the parts count reduction using the DFMA process. [Note: Parts were deliberately increased in one instance, by replacing a single-piece front control panel with a number of inexpensive individual switches and knobs (see above); this trade-off greatly improved user functionality and service as well as significantly reducing cost of repair.]

On the manufacturing side, the team saw even bigger gains, with a 50% decrease in build and test time. In addition — with the improvements in reliability, durability, and serviceability — the team projected warranty cost-savings of 50% per unit and, as a result, recommended that the new EDGE Pro CNC have a two-year warranty. In manufacturing environments, where conditions are tough and machine downtime can freeze your assembly line, improved durability can provide customers with a huge competitive edge.

With DFMA, product launch means the end of product engineering — really
“Some companies launch products too soon,” said Shipulski. “They say the project is over, but they still have their engineering team fixing problems for five or six more months.” With a DFMA-led design approach, things are different, according to Shipluski. “We wring it out first, and then we launch it. It’s actually faster that way.”

As for metrics, Sobr said that the best metrics he could hope for were the global acceptance of the product and the comments of the assemblers in his own factory: “Accessibility is terrific.” “Simpler.” “Faster and easier to build.” Sobr added that that there is no magic in DFMA, just simple robust engineering design. “DFMA is really common sense. But you need to embrace it early in the design process and include the entire team.”

Hypertherm does just that, and you can’t argue with the results. “We’ve had no failures or returns for the Edge Pro in the first six months since production began in August 2009,” said Sobr. “That’s something engineers dream of, or don’t think is even possible. But it is.”

Mike Shipulski, the engineering director at Hypertherm, is on a crusade for improving the American factory when he talks about DFMA and Lean Manufacturing. “Think about what it means to your factory when you introduce a product with half or a third less parts. That’s where your lean folks should start!”

Manufacturing companies have enthusiastically embraced Lean and Six Sigma, but Shipulski thinks that, from a product quality standpoint, if you are not also using DFMA, you are missing out on big benefits. “With DFMA, you can eliminate a significant amount of design and assembly time and labor,” says Shipulski. “You can also reduce the number of opportunities for people to make defects.” It’s formulaic, he says, because if you reduce the number of opportunities, your yield goes up.

But DFMA goes a step further, Shipulski says. “DFMA helps redesign parts so you can’t make mistakes. You can’t break the parts when you put them in. You can’t put them in backwards. You can reach everything. You can see everything.” In other words, DFMA not only reduces the opportunities for failure by lowering part count, it also increases the likelihood of success by improving part design with ease of assembly in mind.

While Shipulski clearly acknowledges that American businesses have seen success with the lean factory — with things like value-stream mapping — he firmly believes that the lean folks need to bring product design into the lean equation through the DFMA process. "Lean and DFMA complement each other nicely — DFMA eliminates parts, and lean reduces the waste of the ones that remain," Shipulski says. Beyond that, he sees DFMA as the key to reinventing product lines from a cost-per-unit performance standpoint. “It’s bigger than any other element that’s been used thus far,” Shipulski adds. “If you’re not doing DFMA, you’re really not doing all you can with lean. DFMA takes lean to the next level.”

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DFMA from Boothroyd Dewhurst
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Published February 2011

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