Automated Tandem MIG Welding--'Bolsters' Chassis Production

Aug. 1, 2000
GARDEN State Chassis in Woodbridge, New Jersey, a major producer of chassis, needed to increase its production dramatically to keep up with orders. The

GARDEN State Chassis in Woodbridge, New Jersey, a major producer of chassis, needed to increase its production dramatically to keep up with orders. The company realized that automating the welding of its rear bolster assembly would eliminate a major bottleneck. By switching from manual Gas Metal Arc Welding (GMAW) to the Tandem MIG process from The Lincoln Electric Company, the company increased production by 500 percent.

"We went from two men a day producing five or six rear bolster assemblies to one man operating the Tandem MIG to produce 25 pieces a day," said Pat Picazio, Director of Purchasing for Garden State Chassis.

The Tandem MIG process is a dual wire, high-speed welding process that coordinates two separately generated GMAW arcs in unison to create a finished weld. With two arcs, the process yields exceptionally high travel speeds. In the case of Garden State Chassis, this rate exceeds 40 inches per minute.

With business expanding each of the company's three years in operation, Garden State Chassis decided to automate the welding of its rear bolster assemblies. Each bolster requires an 8' fillet weld down each side. Rather than two arcs welding simultaneously on each side of the bolster at conventional travel speeds, the Tandem MIG system allows two arcs to make a single weld at travel speeds that are four to five times faster.

Tandem MIG offers high-speed quality without spatter. It is able to accomplish this due to the programmable Waveform Control Technology of Lincoln Electric's Tandem MIG 450 power sources. These power sources contain sophisticated software that can produce output waveforms engineered for weld puddle control and arc interaction of the specific application. Independent control of both the lead and trail wires of the tandem process is tolerant of common fit-up problems and resists burnthrough.

Perfect Weld "The weld is perfect," states Picazio. "It is clean, strong, and has a double bead. Our welds are much neater with the Tandem MIG than they were when we did them by hand. They are very smooth and have no spatter."

In addition, the independent torch configuration of the Tandem MIG permits selection of two different diameter wires - one on the lead torch and a separate diameter on the trail torch. Garden State Chassis uses Lincoln's SuperArc premium MIG wire on both torches. Both wires are .045" in diameter, which are supplied on 1,000-lb reels. The Tandem MIG system is run by a Programmable Logic Controller (PLC). The operator only has to hit the button for the system to complete the welds.

Getting Set Up At Garden State Chassis, the Tandem MIG makes one 8-ft-long weld on each side of the bolster assembly. To do this, a 3/8" A36 mild steel plate is welded to a 5/16" channel with two fillet welds. Two bolster assemblies are made at one time with the Tandem MIG. First, two rear bolster assemblies are tacked together, and end plates are welded in place. Then the two tacked assemblies are placed end to end in a flat fixture 16 ft long. Finally, the two bolster assemblies are welded with two 16-ft-long fillet welds.

The Tandem MIG system is mounted on a self-propelled carriage that travels on a fixed beam. When the system starts, it goes down the front side of both of the rear bolster assemblies laying end to end. Then the system's custom designed torch bracket swivels 180 degrees to weld the rear side of the bolster assemblies.

Because the system is supplied in pieces, Lincoln Electric worked onsite at Garden State Chassis for two weeks to install the Tandem MIG. Lincoln also trained the operators how to use the system, troubleshoot problems, and performed all initial programming.