Forget about transportationthese chairs are built for combat
December 11, 2007
Vesco Metal Craft, a manufacturer of rugby wheelchairs, makes specialized wheelchairs from 6061 seamless aluminum tubing. This violent, collision-oriented sport causes cracks in the welds' heat-affected zone, so the company sought better manufacturing methods. It added heat-treating to its process and switched to an inverter-based welding unit that gives the company's welders advanced waveform control.
Although it's called "wheelchair rugby" or "quad rugby"—it's played by quadriplegic athletes in wheelchairs—neither term really captures the sport's speed or intensity as does its original name: murderball.
Nor do the athletes fit the stereotypical image of quadriplegics, and their chairs bear only a passing resemblance to standard wheelchairs. This, as the name "murderball" implies, is a tough sport. The rugby chairs are specialized pieces of sporting equipment, designed to withstand full-speed, violent collisions; some are designed with special pickers in the front to hook an opponent's wheelchair, which is in turn designed with wings to prevent this.
It is a highly competitive sport, and each athlete wants the lightest, toughest, and fastest chair available. Only a few manufacturers have risen to meet the increasing demand for rugby chairs. Of these, Vesco Metal Craft (VMC) is arguably the leader—10 of the 12 players on the U.S. national team compete in VMC's rugby chairs.
Although the wheelchairs it makes eventually will be beaten, dented, and twisted, VMC prides itself on the initial appearance of the chairs and the amount of abuse they can take. A key component in the appearance and sturdiness is the weld quality.
VMC is a small company with an enviable reputation for delivering high-quality products. It is owned and operated by Neil Vesco, his father, Tom Vesco, and Paul Richardson. Neil does the welding, as well as fabricating the wings and pickers, and uses his expertise as a mechanical engineer to design and evaluate new products for the company. Until recently Tom did all the chair fit-up. Now with a new fabricator onboard, Tom splits his time between fit-up and final assembly. Paul Richardson, a quad rugby competitor himself, handles customer service.
Although an everyday wheelchair could be used for wheelchair rugby, it is doubtful that it could withstand the punishment dished out in a wheelchair rugby game. Made from 6061 seamless drawn aluminum tubing, which is heat-treated to T6 condition after welding, VMC chairs are lightweight and custom-made to each athlete's requirements. They're designed to take a beating.
"There are chairs out there that are five years old and that are beat up almost beyond recognition, but you can tell by looking at the welds that they're our chairs," said Neil. "The first thing 90 percent of our customers notice when they first see one of our chairs is how phenomenal the welds are. That's one thing that makes our chairs stand out." See Figure 1.
It wouldn't be rugby without a little violence. Although the players are forbidden from contacting each other, they use their chairs to contact opponents' chairs. The chairs have features intended to block, stop, and flip other chairs.
VMC makes offensive, defensive, and midpoint chairs. Defensive features include pickers to grab an offensive player's chair; offensive features include wings that block the pickers; midpoint chairs have some defensive and offensive features. See Figure 2. Each chair is custom-made to suit the player's physique and preferences. Variables include seat (or dump) angle, rear seat height, front seat height, seat width, seat depth, inside wheel clearance, wheel camber, frame length, footrest position, and picker style.
To be legal for competition, chairs must meet specifications set by the International Wheelchair Rugby Federation. Initially VMC frequently changed the design of its chairs to keep up with changes in the sport and to find better ways to decrease weight.
"For the first two years, I don't think we ever put out more than five chairs where we didn't make another change," Neil said. "The sport evolved quickly. The faster the guys got, the better they got, and the more they were abusing the chairs and occasionally cracking them. Chair components needed to be improvised constantly—gussets here and there. It got to the point where we were adding many gussets and tubes, trying to make them strong enough, but they were still cracking and were getting too heavy."
It seemed VMC would have to trade speed for weight for the chairs to withstand the rigors of the sport. Initially VMC used 0.095-inch-wall-thickness tubes, and the cracks, when they occurred, were in the heat-affected zone (HAZ). The company subsequently switched to 0.120-in.-wall-thickness tube. This helped minimize cracking but added weight to the chairs. Also, the limitations of VMC's conventional gas tungsten arc welding (GTAW) unit would not allow Neil to weld in all the spots he felt he needed to. Those spots could be a source of failure.
VMC used two main strategies—adding heat-treating and upgrading its welding unit-to reduce the weight of the competition wheelchairs it manufactures. These two steps allowed the company to reduce the tubing's wall thickness and rely less on gussets, resulting in stronger, lighter chairs. In addition, the new welding machine cut the welding time approximately 40 percent.
To resolve these problems, VMC explored two solutions. First, Tom tried heat-treating the aluminum. Then, Don Peterson from Miller Electric recommended a Dynasty® 350 AC/DC GTAW inverter and arranged for VMC to test a unit. Both steps had immediate benefits.
"Since we began heat-treating, we haven't had one break in the HAZ, and we were able to change the wall thickness from 0.120 to 0.083, which reduced the weight from 38 to 35 pounds," Neil said. "For someone with limited dexterity and muscle movement, that's a substantial change. The player can definitely feel it."
VMC now sends a batch of four chairs at a time to a local company to be heat-treated. The subcontractor gussets the frames and mounts them to fixtures to maintain the dimensions; heats them to 985 degrees F for 45 minutes; then drops them into a glycol solution for quenching. This puts the frames in a T0 state and makes them easy to tweak. After striking and aligning the frames, the heat-treater puts them into another oven at 350 degrees F for eight hours to bring them to a T6 condition.
Peterson's suggestion, the Miller Dynasty 350 field-test unit, worked so well that VMC bought a second one. The welding unit has independent amplitude and amperage controls, extended balance control, AC frequency control, and AC waveforms control (advance square wave, soft square wave, sine wave, and triangular wave). These features allow the welder to tailor the arc to his specific job requirements and preferences. See Figure 3.
By switching to the new unit, the company increased productivity by 30 percent to 50 percent. Since VMC manufactures three to four chairs per week, each requiring a substantial amount of welding, this increase meant producing an additional 1.5 to two chairs per week, while also improving the quality and appearance of the weld.
"The unit welds phenomenally," said Neil. "The diversity of the different waveforms—from welding thick aluminum with an advanced square wave to welding thin aluminum with the triangular wave—is what makes it ideal as far as we're concerned. Then add in the ability to set EN and EP current independently, along with the ability to vary the frequency from 20 to 400 hertz, and we get better-looking, deeper-penetrating welds than ever before."
The ability to maintain a sharp electrode and concentrated arc allows co-owner Neil Vesco to weld in corners he previously could not unless he extended the electrode outside the shielding gas, which exposed the weld to contamination.
Because of aluminum's unique properties, such as its excellent thermal conductivity coupled with a low melting point, the welding unit's ability to control heat precisely led to significant savings.
"With our previous unit, the colder the material, the more heat you had to put into it initially," Neil said. "Developing the weld puddle was time-consuming.
"When we first got the Dynasty 350, it was still set with the factory settings, and it welded better than any machine I've ever used. Then I found out how much I could actually change the characteristics of the arc, which really surprised me. It actually got better than where it started. By turning the frequency up and the balance down, we're able to get a deeper-penetrating weld and put much less heat into the frames," Neil said.
Neil also used it on an aluminum bicycle that needed repair.
"I had never welded anything that thin [0.030 in.], but this welding unit's triangular wave provided such a focused arc that's so easy to control, even on material that thin. I don't have to worry about the heat absorption of the material. I can just strike an arc and immediately get a weld pool going and continue without a lot of heat being absorbed in the material."
Additional time is saved because switching tungsten, either because of balling or for different weld requirements, has become unnecessary.
"With this machine, I weld everything with a 1/8-inch electrode," said Neil. "I can use it on everything from 0.065 tubing all the way up to the -inch plate on the front of the chair. To make the welds aesthetically pleasing and structurally sound with our previous unit, I had to match the tungsten to the weld, which required a lot of tungsten changing. Our [previous machine] demanded you use as small as a 1/16-inch electrode."
Additionally, the electrodes last much longer on the new welding unit. Previously Neil would have to dress them frequently because at 230 amps, the tungsten would start melting, leading to balling and a large dispersion arc.
"On our old machine, the cleaning action [a characteristic of EP welding] was so poor that you had to turn the balance down to get proper cleaning. Then you could no longer maintain the correct electrode geometry," said Neil. "Now I don't have to dress the electrode due to balling. You can actually maintain a sharp point on the electrode with the Dynasty 350.
"Now I can keep the tungsten back in the cup and still get the arc way back in the corners where I wasn't able to get them before. Previously those spots went unwelded and could be a source of cracking," Neil said. See Figure 4.
The weld quality is a continuing source of pride for VMC. "All of our customers call to congratulate us on how good the frame looks," Neil said. "I would say the first thing they say when they see the chairs is how phenomenal the welds are. We set a new standard on the market, and our chairs are substantially better-crafted than the next guy's out there. The welds are phenomenal on our chairs, and that's one thing that stands out."
With the increased productivity, improved weld quality, and lower power costs, the VMC team sees the welding unit as having a huge impact on its business.
"Because all of our jobs depend on everyone else getting their jobs done, if I can get in here and weld more chairs for the week, then everyone else has something to do the following week," said Neil. "If I don't get my job done in time, Tom can't do his and Paul can't do his."
This time savings has allowed VMC to catch up with its backorders for the first time, freeing up time to devote to R&D to other products for people with disabilities. They are now also able to expand their operation with the addition of another trained welder. Finding someone highly skilled in aluminum GTAW can be difficult, but the new welding unit even made that easier.
Assuming the rate of a skilled aluminum TIG welder is $30 an hour, a company cutting its welding time by one-third to one-half would save $1,600 to $2,400 in welding time alone per month, enough to pay for one of these welding machines in two to five months.
Neil estimated that the new welding unit has paid for itself in the first six weeks of operation, through increased productivity and decreased energy bills. With its low power draw (26 amps at 230 V, three-phase, for welding 250 amps, 30 V at 100 percent duty cycle), the new welding unit is much more efficient than the company's previous single-phase unit.
The new machine delivers 5 amps to 350 amps (300 amps at 32 V, 60 percent duty cycle), enough power to weld -in.- thick aluminum. It runs on any input power from 208 to 575 V, single- or three-phase.
"With the previous unit, I used to watch how fast the meter would turn when he'd start welding and it looked like a fan spinning," Tom said. "Now power consumption is so low, it's ridiculous. I know Neil likes the way the machine works, but I like the power factor. It's a major, major difference in what we're saving on power."
But even more than the power, Tom likes the increased productivity and what it means to VMC's future.
"Now we have time to do other things," said Tom. "If we're constantly trying to keep up with orders for rugby chairs, we really can't grow and expand. Now we can devote some time to R&D for other products. The Dynasty 350 has freed up time to do that."