May 2009 - A term as sensational as murderball evokes images of armor-clad gladiators battling to the death. The truth isn't far off. Murderball is another term for wheelchair rugby, an intense recreation game turned Paralympic sport. Anyone familiar will agree: Its athletes--and wheelchairs--are as hard-core as those in any other contact sport.

Because of the aggressive nature of murderball, the athletes' wheelchairs must be designed to be light, swift and highly durable. One company that specializes in rugby chairs, Vesco Metal Craft, Chula Vista, Calif., has enhanced its productivity and overall chair quality by implementing an inverter-based welder with advanced waveform technology.

The Dynasty 350 AC/DC TIG inverter from Miller Electric Mfg. Co., Appleton, Wis., features independent amplitude control, extended balance control, AC frequency and waveform control, all designed so the operator can tailor the arc to specific welding applications.

Since using the Dynasty 350, VMC has reduced wall thickness on its chairs' 6061 seamless drawn aluminum tubes from 0.12 in. to 0.083 in., resulting in a weight reduction of 3 lbs. per chair.

"For someone of limited dexterity and muscle movement, that's a substantial change," said Neil Vesco, co-owner of VMC, in an in-house Miller article. "The player can definitely feel it."

VMC has seen its productivity increased 30 percent to 50 percent, meaning it can produce an additional chair and a half to two chairs per week on top of its usual production rate of three to four chairs. Key to this are the Dynasty 350's four waveforms: an advanced square wave for thicker material, a soft square wave for more puddle fluidity, a sine wave and a triangular wave for extra-thin aluminum. The triangular wave's focused arc, in particular, has allowed VMC to lighten its chairs without reducing structural integrity.

VMC can also set the EN and EP currents independently, along with adjusting the AC frequency anywhere from 20 hz to 400 hz.

In addition to this, a Dynasty 350's electrodes are designed to last. VMC uses a 1/8-in. electrode on everything from 1/4-in. plate to 0.065-in. tubing, virtually eliminating the need to switch tungsten to match weld requirements.

Powerful advantages
From the vantage point of John Luck, project manager for Miller, the flexibility and arc control of the Dynasty 350 make it an ideal match for an application like rugby wheelchairs because it involves many difficult welding angles and thin aluminum tubing.

"Whereas on a traditional machine, you may get some arc wander, meaning the arc jumps to one piece of tubing or another piece, with the Dynasty 350 and the AC frequency it operates at, it really stabilizes that arc in one particular area," says Luck. "It allows users to get down in those deep areas where they normally can't completely get their torch all the way in. When you put the torch in and step on the foot pedal, the arc goes right where you want it to."

Luck also points to the Dynasty's AC frequency control as well as its inverted power source as distinct advantages, the latter of which allows a welder to plug in anywhere, be it a one-phase power source or a three-phase source, 208 volts to 575 volts.

Together, these advantages allow a user to travel faster, weld more material and use less power, saving VMC time, energy and costs. So much so, in fact, the company now has time to research and develop other products for people with disabilities.

Murderball wheelchairs have to be as tough as the athletes who use them, meaning any advantage gained in the fabrication process will be felt on the court. And a key to this is welding flexibility.

"[The Dynasty 350] gives users the flexibility of being able to travel fast, point the arc where they want it to go and put a nice small bead in there," says Luck. "A traditional machine won't get you that kind of advantage." FFJ