Part Cutters

July 17, 2006

7 Min Read
Part Cutters

The engineers at Hypertherm Inc., a maker of plasma cutting systems,know a thing or two about cutting metals. They also know how to cut cost. A lot of cost. While redesigning one of the company's best-selling plasma cutting systems, they managed to reduce parts' count from more than 1,000 components to fewer than 500. System assembly time fell from 20 hours to less than five. And the output from the company's existing assembly operation quadrupled — without any additional floor space or an expensive second shift. Bottom line: the redesign saved the company about $5 million in assembly costs over the past 24 months alone, according to Engineering Manager Mike Shipulski.

And Hypertherm's engineering team didn't just design a cutter that's easier and cheaper to manufacture. They simultaneously made it better for the users. Both the old and new units have a tight (0.5-mm) cutting tolerance that makes them well-suited to precision cutting. But the redesigned model, a 130 amp unit called the HPR130, cuts as fast as some of the company's 200 amp units. The new unit also offers a reduced operating cost. Shipulski estimates that it costs two-thirds less to run than the unit it replaces thanks to a more efficient use of power and consumables.

So how did the design team do it? In a nutshell, they scrutinized every single component that goes into plasma cutters' power supply unit, torch and gas console. They then applied the design-for-assembly methods that helped them either eliminate or integrate hundreds of components. Here's a closer look at their strategy and at the design decisions that yielded the greatest reductions in parts count and assembly time.

Factory Work

Job one for Shipulski's engineering team was to spend some time on Hypertherm's assembly line — not just observing, but actually putting some of the company's products together. As Shipul-ski tells it, engineers won't hear complaints about their designs if they spend too much time sitting in their cubicles. So he banished four engineers to the factory floor for a week.

They spent their time hand-counting parts that went into the plasma cutter that was to be re-vamped (the HD3070) and creating a parts Pareto chart that detailed all the different types and quantities of parts in that unit. Roughly two-thirds of them turned out to be fasteners or connectors, Shipulski reports.

The engineers went on to to build a few of the HD3070 units and other models themselves. "They came back bloody, sweating and with a newfound disrespect for their designs," Shipulski says, only half-jokingly.

They also came back with a game plan for reducing the complexity of the plasma cutters. The time on the production floor helped the design team identify another product, the HT 2000, an entry-level model considered the easiest to assemble by the production staff.

Brian Currier, a mechanical applications designer and one of the four engineers who spent time on the factory floor, also walked away with open lines of communication with the production staffers. "At first, they laughed at us a lot," Currier says, "but later on they became more open with their suggestions." And those suggestions proved valuable given that hands-on assembly expertise really resides on the assembly line. "I came away amazed that they build as many systems as they do," Currier says.

Design Decisions

Armed with the Pareto chart and personal knowledge of plasma cutter assembly, Shipulski's design team began their design work for the revamped unit. For this part of the job, they relied heavily on a well-thumbed copy of the Design for Assembly (DFA) handbook from Boothroyd Dewhurst.

Some of what DFA turned up represented incremental changes, Shipulski recalls. "A part here, a part there," is how he describes it. But the process also helped identify some areas ripe for large-scale parts consolidation or elimination. The plasma cutter's pilot arc controller assembly, for example, went from 88 parts on the past model down to 16 parts on the new model. The new unit's heat exchanger assembly has just three parts compared to 20 in the past. And the coolant plumbing and filter assembly went from 11 parts in the old model down to just three in the new one.

The list goes on and on, but a common themes does emerge. Hypertherm's design team all but declared war on unnecessary fastening hardware of all kinds. A move from wires to PCB with surface mount and through hole components helped eliminate dozens of fasteners, according to Currier. "Each wire had four fasteners," he


The design team also rethought how it uses sheet metal. "In the past, we had simple shapes with lots of clearance holes and fasteners," Currier says. With the redesign, however, they brought in Hypertherm's sheet metal vendor for a brainstorming session dedicated to integrating fasteners and brackets. That effort paid off with dozens more parts and reductions in assembly time.

DFA also led the design team in counter-intuitive design directions. In previous models, for example, the gas selection and gas metering functionality had been combined into a single subassembly built around a 2 × 2 × 1-ft aluminum manifold. Made in two pieces, the manifold assembly required the placement of an intricate gasket in a channel. It then required 20 bolts, tightened in a specific torque sequence, to join the two halves. "We thought we were pretty slick to integrate everything," Currier recalls. But the manifold took 10 hours to assemble. The redesign, by contrast, splits the selection and metering functionality into two smaller consoles. The new design has a much simpler manifold, and all the connections are made with press-to-connect hoses which come from their supplier in color-coded kits. Going to two separate, yet simple, components rather than one complex one as in the past reduced assembly time by 87 percent.

More DFA To Come

Hypertherm's experience with DFA has been so positive that the company's engineering team has now adopted Boothroyd Dewhurst's Design for Manufacturing and Assembly (DFMA) software. While it embodies some of the same principles as the DFA handbook, the software delves further into assembly and manufacturing operations. Shipulski likes the fact that it generates reports representing a common language for engineers as they purge wasteful elements from their designs. "It's become part of all our design reviews for new products," he says. And the company's engineers are busy applying DFMA methods to some of the company's legacy products.

As for the HPR 130, the company's first DFA project, it has become one of the company's best-sellers with double the annual sales volumes of the plasma cutter it replaced. And even at these higher sales, its warranty costs have been just a tenth those of its predecessor. "It's not breaking. It's cutting parts," says Shipulski. And that doesn't surprise him in the least. "Remember that reduced parts' count is a stand-in for reliability and robustness," he says.

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