As fabricators, we may be the only group of people on earth who look at an NFL goalpost and wonder about the fabrication techniques and welding methods that go into its construction. Naturally, the goal must be strong enough to withstand weather and the occasional group of fans determined to tear it down after a big win. But what’s it made of? How do they weld it? What welding and fabrication challenges do they face?
Sportsfield Specialties of Delhi, N.Y., manufactures athletic field equipment for a wide range of sports at all levels, from youth sports up to the pros. Its products include goalposts, soccer goals, sandpit jumps, hurdles, high jumps and batting cages. The company also specializes in modular products such as press boxes and dugouts. The majority of these products are fabricated out of aluminum and stainless steel for function, appearance and formability.
Aluminum, specifically, poses a unique set of challenges—especially when it comes to welding. It has a lower relative melting point than other metals yet requires heat to ensure proper puddle formation, cleanliness is critical, and it is more sensitive to heat input and distortion.
TIG welding has been used in most aluminum applications because MIG welding was traditionally thought to put too much heat into the part. Aluminum wire is also softer and more difficult to feed through a wire feeder and gun than other metals. Sportsfield Specialties found solutions to these challenges, and others, when it implemented a Pulsed MIG welding process. Those capabilities have been taken to the next level with the introduction of the new Millermatic® 350P Aluminum All-in-One MIG system from Miller Electric Mfg. Co. This dedicated aluminum system features new technology designed to provide smooth and consistent feeding of aluminum wire for greater quality and reduced downtime. It also features synergic “one knob” control in both MIG and Pulsed MIG settings, which automatically matches welding parameters to wire feed speed adjusted at the gun, eliminating trips back-and-forth to the machine.
Pulsed MIG versus TIG and Conventional MIG
According to Robert Barriger, production supervisor at Sportsfield Specialties, aluminum makes up the bulk of the company’s work. Goalposts, for instance, are constructed mostly of 11 ga. 6063. The crossbar and vertical posts are schedule 40 aluminum pipe.
“The gooseneck on the posts are 6061, so we can roll it. The wall thickness is roughly 5/16-inch,” he said. “The sheet is one-eighth inch or 11 gauge aluminum.”
Welding aluminum has historically been a TIG application for its ability to weld different thicknesses, and it’s easier for operators to control the heat input. The downside is that TIG welding is a substantially more complicated process. It’s also a slower process, which isn’t ideal in a manufacturing environment. Conventional MIG works well on thicker material, but the process can be too hot on thinner gauge aluminum and cause burn through and distortion.
Pulsed MIG welding provides the best of both processes by putting less heat into the weld to control distortion but still providing the good fusion and high deposition rate of regular MIG welding. The welding power source rapidly and automatically switches between a high peak current (ensuring good fusion) and a low background current (lowers heat input and reduces distortion). Because of the pulsing of the current, the operator can vary the heat input into the parts and weld thinner gauge material without burning through or warping the part.
“Personally I think Pulsed MIG is much faster,” said Barriger. “TIG welding gives you a neater bead, but it creates more heat than most people realize. TIG has its place, but Pulsed MIG is much quicker and you don’t get distortion from it (as you do with conventional MIG).”
Another major factor for aluminum fabricators is appearance. In addition to the reduced distortion, Pulsed MIG lays down a bead superior in aesthetics to conventional MIG welding. Barriger estimates that his welders might save as much as 15-20 minutes per part in cleanup thanks to reduced spatter.
“It gives you good appearance, and you don’t have the spatter all over it,” he continued. “That is one of the biggest benefits to the Pulsed MIG process. With aluminum a lot of it is not painted, so you need to clean or grind off the spatter, which will leave marks. With Pulsed MIG you can just wipe it down if needed and palletize it.”
The superior deposition rate of Pulsed MIG, combined with the ability to weld a bead that looks like TIG, is arguably its greatest benefit.
“I think if you had to line up and race the pulsed MIG and TIG, you would probably get four inches out of the TIG versus 12 inches out of Pulsed MIG,” Barriger said. “And that results in more parts per day. If I have a guy building a cover for a sand pit with a Pulsed MIG, it’s going to probably be three-to-one over a guy TIG welding one.”
Synergic Controls Simplify Adjustments, Save Time
Another challenge when welding aluminum is how to handle heat input when welding materials of dissimilar thicknesses and varying joint profiles. This occurs on a number of Sportsfield’s products, including base forms for long jump installations on track and field courses. With TIG welding, it’s relatively easy to control heat input into materials of varying thicknesses via puddle control and remote foot controls. To aide in MIG processes, Miller had introduced Synergic MIG and Pulsed MIG welding controls, which allow the welder to adjust wire feed speed via a knob on the MIG gun. As the welder manipulates the wire feed speed, the system automatically adjusts voltage and amperage to match the speed. This not only saves time, but also allows the welder to react to changing joint profiles and positions in real time, including bridging gaps.
“The ability to adjust the wire speed on the gun is great," says Robert Palmer, welder/fabricator, Sportsfield Specialties.” It makes it tremendously easier without having to stop, run over and turn the welder down. You can just look at the welder, see what you’re doing, turn it up and you’re done.”
“You don’t have to continually run a foot pedal for the amperage (compared to TIG),” says Barriger. “You set your amperage, and if you need a little more or a little less, you just turn the wire one way or the other and it corrects it. If they have a gap in the material, the operator can just turn wire speed down on the gun and not worry about the power source.”
Improving Aluminum Wire Feeding
Another notorious problem with MIG welding aluminum is wire feeding. Being softer and more pliable than other metals, aluminum filler wire has caused frequent birdsnesting in the past. This is a serious drain on productivity as it takes the operator time to purge the ruined wire, change out the contact tip (an added cost factor), re-feed the wire and start welding again. Aluminum spool guns—MIG guns with 1-pound spools of wire affixed to the gun—solved some of the feeding issues but hamper accessibility to certain joints because they add bulk to the gun. They also require frequent spool changes, as 1 pound of wire doesn’t last long in a production welding environment. It was also standard practice to change the contact tip each time a spool was changed out, which adds further cost and time.
“We used to weld with spool guns and it was very difficult to get in some of the tight areas,” said Barriger. “We tried flexible nozzles, but it created too much clean up and was very time consuming. The push-pull gun makes it easier to get into tight spots and there is a lot less spatter.”
“Between changing spools from a spool gun to one of these — and having a 16-pound spool vs. a one-pound spool — I could see it saving upwards of an hour a day,” adds Palmer.
Aluminum wire feeding with an All-in-One system has been substantially improved with the introduction of the Millermatic 350P Aluminum, as the machine features a new true torque feed motor that provides continuous push force to the wire while the gun motor controls the speed at the gun. The motors work together to provide accurate and positive wire feed speed without wire shaving or deformation. Matched with Miller’s XR™-Aluma-Pro™ push-pull MIG guns, the system improves feeding to a point where the company can rely on using 16-pound spools of wire housed in the power source versus one-pound spools on the gun.
“When you have smooth feed with the wire, you get a lot more consistent weld,” says Barriger. “The weld looks a lot nicer. The wire comes out consistently instead of backing off. It makes the appearance of the weld much nicer.”
The new system has helped substantially reduce birdsnesting when running off of a full spool of wire in an all-in-one system.
“It saves a lot on downtime, says Barriger. “You don’t have to pull out all the birdsnests, 25 feet of wire and clean it all up. It saves the tip, so you don’t have to replace the tip. It fits in very well.”
Better Starts and Finishes to Each Weld
Another challenge with welding aluminum is cracking, lumps and defects that occur at the beginning of the weld with a cold start. Similarly, cracks and defects are common in the crater at the end of the weld. The Millermatic 350P Aluminum solves these problems with its Hot Start™ and adjustable crater controls. The Hot Start eliminates incomplete fusion at the beginning of the weld, a common issue with aluminum welding. The adjustable crater control gradually decreases weld current at the end of the weld to eliminate crater defects.
“The Hot Start capability is great,” says Palmer. “You don’t have to worry about having the big lump at the beginning of your weld. You just stay there, let it weld, get a nice puddle and go.”
All together, Pulsed MIG on aluminum has proven to improve quality, reduce distortion, save time and cut costs for Sportsfield Specialties. Thanks to that performance, and the service provided by Miller and the company’s local distributor, Sportsfield will continue to advance its aluminum welding processes with each new sports fixture that comes through the doors.
“The machines hold up well,” concludes Barriger. “And these guys are here any time we need them. They never leave us hanging.”