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Design for assembly dramatically reduces complexity of plasma arc cutter

Boothroyd Dewhurst : 29 September, 2006  (Company News)
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.
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