Faced with losing a contract, B. M. Welding Services substituted pulsed gmaw for ac gas-tungsten-arc welding and cut welding time from 30 minutes to five.
Welder Felipe Sanchez at B.M. Welding Services uses a Miller GMAW-P system to join 98.258.25-in. enclosures made from 1/8-in.-thick Type 5053 aluminum alloy.
"If you want to motivate me, just tell me it can't be done," says Duane Eason.
As owner of B.M. Welding Services, a 30-person fabrication and manufacturing company in Addison, Ill., Eason felt plenty of motivation when he landed a contract to build waterproof enclosures for outdoor lighting components. His cycle times on test parts were too slow to meet deadlines and too costly to produce using his current equipment.
The 9 8.258.25-in. enclosures, made from 1 /8-in.-thick Type 5053 aluminum alloy, require an internal weld to seal the top to withstand rain at 80 mph. The customer, a local utility company, also demanded good bead appearance and minimal distortion.
Normally, the firm would use an AC gas-tungsten-arc welding (GTAW) process. However, its experienced GTAW welders took 30 min to weld the sample enclosure with mostly fillet welds. Joining the cap to the enclosure requires a 34-in. weld. Internally, three 2-in.-long welds seal the base and two 2-in.-long welds hold a bracket. The outside seams receive a finish weld. These are ground flat and the enclosure prepped for painting.
Time and money
"The outside welding went fast enough, but it took forever to make the internal welds," notes Fred Petelle, plant manager for B.M. Welding Services. "The enclosure's small access port hampers the welder's ability to maneuver a GTAW torch or add filler wire. We needed to deliver 150 enclosures in a short time. Meeting the deadline would have absorbed three people, full time, for one week. That would have devastated our production schedule for other projects."
Eason adds that "we never would have acquired the business if we quoted the job based on the time with the GTAW process. Faced with these production challenges, it made sense to invest in new technology rather than lose the contract or fulfill it unprofitably."
Just prior to receiving the order for the enclosures, Eason's welding supply distributor, Terrace Supply Co., Villa Park, Ill., demonstrated a pulsed gas-metal-arc welding (GMAW-P) system from Miller Electric for another aluminum welding project. The advantages of GMAW-P, a modified spray-transfer process, compared to short-circuit or spray-transfer GMAW include lower overall heat input to prevent warping and burnthrough on thin metal, outstanding weld bead appearance without spatter or the black soot that often occurs with the GMAW process on aluminum, and increased travel speed compared to GTAW or short-circuit GMAW.
The GMAW-P system features Miller's XMT 304 inverter-based power source, the XR control push-pull feeder paired with a XR-Edge gooseneck-style gun, and an Optima MIG pulse control with 14 built-in pulsing programs. A control knob scrolls through the programs, displayed on a back-lighted LED panel.
To fine tune arc characteristics, the welder adjusts trim values and wirefeed speed, similar to conventional GMAW.
After the demonstration, Eason invested $7,000 in the system to solve the electrical enclo-sure challenge. Welder Felipe Sanchez, one of the company's best GMAW operators, was familiar with GMAW aluminum. He welded on scrap material that matched the enclosure. He decided on 0.035-in.-diameter AWS ER5356 over 0.047 ER4043 aluminum wire for better heat control and flow characteristics. He feeds 100% argon shielding gas through the contact tip and diffuser. In three or four days, Sanchez became confident in his results.
"After a careful start, Felipe just flew when he began welding for production," says Petelle. "He can weld an enclosure in 5 min. That's a 600% improvement in cycle time. Even better, his weld beads turn out just beautifully crowned. Filipe's GMAW-P beads look like GTAW. Our customer was impressed."
Eason states that "I've never seen GMAW welds that look that nice on aluminum. Most importantly, I'll pay for the system in three months."
Productivity demands often necessitate using a continuous wire welding process, as B.M. Welding Services discovered.
Pulsed GMAW, a modified spray-transfer process, provides the best of both short circuit and spray transfer. During the pulsing process, the control rapidly switches the inverter's output from high peak current to low background. For example, it can switch between a peak current of 300 amp and a background current of 50 amp in 1 msec. The peak current pinches off a spray-transfer droplet and propels it toward the weldment for fusion. The background current maintains the arc but is too low for metal transfer to occur.
Pulsing reduces overall heat input, yet provides the fusion associated with spray transfer. For example, pulsed welding 1 / 8- in. aluminum with the 0.035-in.-diameter wire produces an average of 127 amp. An 86-amp back-ground current eliminates worries about burnthrough, warping, and cold lap, while a 313-amp pulse of peak current provides good penetration and wet out.
Sanchez found that a 1.5-in. electrical stickout and a 3 / 4 to 1-in. contact tip height for manual welding works best in the flat position.
Pulsed GMAW provides good bead appearance because the tiny molten droplets do not create spatter. Welders have better directional control over the weld bead because the weld puddle cools in between pulses and freezes faster. This minimizes puddle sag or an excessive convex bead when welding out-of-position.
Petelle notes that "when Felipe first began working with GMAW-P, all the GTAW operators in the shop started to watch and wanted to try it. Operator interest in learning the process will become important as more projects shift to GMAW-P."
The firm's managers state that it takes less skill to obtain good results with GMAW-P than it does with GTAW, so finding and training new operators will be easier as the company grows.
"We're transforming the company from a welding shop serving second and third-tier suppliers into a manufacturing organization working with more OEMs," says Eason. "We do some forming, stamping, and cutting now, but I want to expand that so we can fabricate more complex components, not just parts. We'll solve customers' fabrication problems, and GMAW-P welding is going to be part of that equation."