The 154-foot-long, 25-foot-wide patrol boat is built out of a combination of steel and aluminum. The hull and deck are steel, while the superstructure and the pilot house are constructed entirely of aluminum (mostly grade 5456) ranging in thickness from 3/16 to 1/4 inch. Aluminum is increasingly specified in marine applications because it’s lighter without sacrificing strength and functionality. This makes ships faster, saves on fuel, and provides them with excellent anti-corrosive properties. It does, however, present difficulties: distortion, cleanliness, aesthetics, burn through and difficult wire feeding, to name a few.
To best meet these challenges, Bollinger overhauled its entire aluminum welding facility to include a new bulk gas delivery system, wall-mounted booms for wire feeders, and new AlumaFeed™ synergic aluminum welding systems from Miller Electric Mfg. Co. The system is designed to simplify and improve MIG and Pulsed MIG aluminum welding applications and has proven a good fit at Bollinger. Improvements include:
Aluminum Provides Speed, Strength — and Challenges
Each of the FRC patrol boats is built to the standards put forth by the American Bureau of Shipping (ABS) High Speed Naval Craft Guide, while all aluminum welding of the superstructure is covered under AWS D1.2 structural welding codes. Dennis Fanguy, vice president – quality management systems, Bollinger, points to the high speed of the FRC as one of the main reasons aluminum is required. A lighter ship also helps save fuel.
“We have a speed requirement of 28 knots on this patrol boat,” he says. “That’s pretty fast for this size of a vessel. In order to do that, we have to save weight in a number of ways. Using thin steel and aluminum is one of those ways.”
The aluminum welding performed in the Lockport yard (Bollinger has 12 facilities throughout Louisiana and Texas) ranges from a semi-automated Pulsed MIG process on long sections of aluminum deck to manual MIG and Pulsed MIG throughout the superstructure and pilot house. In the past, Bollinger relied upon conventional MIG power sources outfitted with spool guns that contained 1-pound spools of aluminum wire. Going into the FRC contract, the company knew it wanted to address a number of common challenges with aluminum welding:
- Reduce distortion: Aluminum is more sensitive to heat input than other metals.
- Increase speed: Determine how to increase productivity while maintaining quality standards.
- Improve quality: Achieve reduced distortion and increased speed while also ensuring proper starts, stops, penetration and aesthetics.
- Improve wire feeding: Maintain consistency and reduce bird nesting.
- Simplify operator interface and operation while making training easier.
In trying to find a solution that addressed these issues, Bollinger also knew that any equipment would have to earn the trust of the welders in the yard and prove profitable for the company.
“We’ll get the welder involved first to see if it will work for us,” says Fanguy, “then we’ll determine what the payback is going to be. We’re looking at quality, productivity, and whether that system will provide us a payback within two years. The first thing we do, however, is ensure that we have buy-in from the welders. If they’re not comfortable using it, it will never work.”
Pulsed MIG Battles Distortion
Arguably the most critical challenge in all aluminum welding applications is distortion. Some in the industry have viewed MIG processes on aluminum with skepticism due to a perception that the heat involved with spray transfer is too much for thin materials to handle and leads to distortion and burn through. Conversely, there’s a perception that a “cold process” such as short arc, which puts less heat into the piece, does not always provide the penetration that some applications demand. The answer to these problems is Pulsed MIG welding.
“Distortion was a big factor for us,” says Johnny Boudreaux, inspector – quality assurance, Bollinger. “Our previous MIG process caused distortion and it created rework. We moved to Pulsed MIG because of the distortion control and the speed. We also had to come together and create welding sequences that would properly disperse the heat into the material.”
Bollinger now relies on the Pulsed MIG capabilities of the AlumaFeed System to provide the proper mix of speed, quality and appearance. The key benefit of Pulsed MIG welding in this application is the balance between providing sufficient energy to ensure good fusion yet controlling heat input to prevent warping or burn through. The welder rapidly and automatically switches between a high peak current (ensuring good fusion) and a low background current (lowers heat input and reduces distortion). The AlumaFeed System features built-in Pulsed MIG programs that automatically set the optimal parameters for the most commonly used aluminum alloys, such as 4000 and 5000 Series, but it’s two newer technologies — synergic Pulsed MIG welding and Profile Pulse™ — that provide the greatest benefits in aluminum shipbuilding applications (information follows).
Weld sequencing is also critical. This involves moving from one area to another and not putting too much heat into one section so as not to lock in structural stresses. When welding flat aluminum deck panels, for instance, Bollinger starts in the center and works out, first working from forward to aft, then from port to starboard. This helps reduce distortion and ensures that stresses aren’t being locked into the material. Large magnets are also positioned along the length of the weld/seam to prevent distortion and movement. Similar sequencing is performed — in both the semi-automatic and manual applications — throughout the entire structure.
Enhancing Productivity without Sacrificing Quality
Increasing welding speed and productivity is another priority for Bollinger. When looking at the overall scope of the operation, Fanguy and his team looked at areas where new efficiencies could be achieved. One task that stood out was when the welder would leave his work area and walk all the way back to the power source to adjust his parameters. Depending on how often the welder changes parameters, this could add minutes, if not hours, to daily welding activities. This inefficiency is addressed by the AlumaFeed’s synergic welding controls. This features a knob on the MIG gun that controls the wire feed speed. As the welder manipulates the wire feed speed, the system automatically adjusts voltage and amperage as the welder is working to match that wire feed speed. This not only saves time, but also allows the welder to react in real time to changing joint profiles and positions.
“If a guy was getting into a different position to weld and had to change the parameters,” says Boudreaux, “with the old system they had to put the gun down and walk all the way back to the machine, which may be 50 feet away, change the settings and then walk back to the weld area. With the synergic capabilities, it’s a blessing because they do not have to leave to change the machine. All the settings are really there. You set your wire feed speed as soon as you hit that trigger, and your volts and amps and everything are pre-set. It’s saving a lot of time and these welders love it.”
“If I’m welding on the top of a boat, I don’t have to go all the way down the stairs (to change my parameters) and then come back up,” says Mark Guidry, welder, Bollinger. “If I’m welding something thin, I can just make the adjustment with the knob. I can turn it up if I go to something thicker. I don’t have to move. I don’t have to get off my job. You just stay right there. It saves a lot of time.”
“I would say that, on an average day, guys are saving an hour or two a day (by controlling weld parameters on the gun),” says Conrad Perrillioux, craft leader, Bollinger.
Quality Improvements at Beginning, End of Well
While less distortion and reduced rework certainly fit in the “quality” category, the AlumaFeed system also addresses two specific quality issues common with aluminum welding that lead to weld defects and rework: cold starts and crater fill. Bollinger’s new systems feature Hot Start technology, which eliminates incomplete fusion at the beginning of the weld, and a Crater function that gradually decreases weld current at the end of the weld to eliminate crater defects.
“With the Hot Start, it’s hot as soon as you start welding,” says Guidry. “Once it hits, you just go. You don’t have to sit there and let it get hot and then start. Aluminum is tricky to weld and, if you start out cold, that leaves more work for you to do — you have to grind out where you start. With Hot Start, you just go. It also ends better than any of the other machines. With other machines, you have to stop and make a crater and you have to dab it until the crater is gone. With this, once you finish, it’s perfect. The machine itself has a Crater button. You turn it on and, right at the end of the weld, it just fills it right up for you.”
Getting the Look of TIG with the Production Speeds of MIG
One of the knocks on MIG welding aluminum has always been that it’s difficult to achieve the same aesthetics as TIG. In a welding intensive application such as shipbuilding, however, TIG welding at production speeds isn’t feasible (MIG is often more than twice as fast — although there are some applications, such as detail finish work on extremely thin and delicate materials, that will always be TIG welded). Miller’s exclusive Profile Pulse™ technology, however, bridges that gap and provides the “stacked dimes” look of TIG without back-stepping or other manipulations of the welding gun. It even allows the operator to change the pulsing frequency to increase or decrease the spacing between the ripple pattern to achieve the desired weld appearance. This ensures a beautiful, easy-to-lay weld across long stretches and becomes particularly helpful when welding in corners and hard to reach places.
“You can change your pulse frequency to fit the different areas that we weld,” says Guidry. “I lower the pulse when welding the corners and butt joints and it makes a beautiful weld. It almost looks like you TIG’d it. You just have to drag it and it almost makes the weld for you.”
“They don’t have to sit there and weave a bead,” says Boudreaux. “The machine does it for you and you just guide it. It’s very simple, and that’s what we were looking for.”
Feeding Improvements Reduce Hassle, Increase Productivity
Because aluminum wire is softer and has a greater tendency to bend and snag, feeding it has always been a challenge. Bollinger relied on spool guns — MIG welding guns with a 1 lb. spool of aluminum wire attached to it — to eliminate these problems. This created other inefficiencies, however, as that 1-pound spool required frequent replacement, and it proved cumbersome for getting in to tight corners.
The AlumaFeed system, however, eliminates these problems with true push-pull wire feed performance that ensures consistent feeding and arc quality. Matched with Miller’s XR-Aluma-Pro™ or XR™ Pistol Grip push-pull welding gun, this system allows for a 12-inch spool of aluminum wire to be housed in the wire feeder (either boom mounted or back at the power source in Bollinger’s shop) and fed smoothly through the liner, to the gun and into the weld.
“You’ve got a 12-inch spool in there,” says Guidry. “That will last you a long time compared to the little 1-pound spools in the spool gun. When those ran out, you’ve got to take one out, walk back to the tool room, get another one, come back and put it in. With this feeder, you don’t have to keep going back and forth. And it gets into some pretty tight spots — better than the other guns used to. We also have different nozzles that you could put on there besides the ones we use. Some smaller, some crooked, some with flex nozzles. They get in tight places, and it’s not heavy like those spool guns. It’s a lot lighter.”
“The bulk of the gun itself is smaller than what we had in the past,” says Perrilloux. “It’s lighter, and the reach of the nozzle is better for getting in to tight places. I’d also say that the system eliminated about 98 percent of our bird-nesting issues because I just don’t see it anymore. We’ve also been able to go to a larger wire (3/64-inch) compared to the other spools we were using (.030- and .035-inch). That really allows you to turn up your heat and increase your travel speed.”
Simplified Operation Ensures Employee Buy-In, Performance
Between the simplified operator interface, the one-knob control of the synergic welding function, the aesthetics of the Pro-Pulse process, and the quality and operational benefits achieved by the AlumaFeed system, Bollinger has implemented a solution that addresses the main pain points of aluminum welding while also simplifying the welding process for the guys out in the yard.
“We have the technology we were looking for,” says Boudreaux, “and it’s user friendly for our welders out there. If it’s something that’s going to scare them, it’s never going to work out there. It’s also a lot easier to train and to get a person qualified on it now compared to what we had in the past.”
“They are very good machines, I can tell you that” concludes Guidry. “It saves a lot of time on everything. The performance is better, the quality is better. You can’t ask for anything better. It helps out a lot and saves a lot of time. It makes your work look better and it welds beautiful.”