GM Unveils Spot-Welding System for Aluminum

Next year General Motors Co. plans to ramp up its use of a new spot-welding process for aluminum the company says will eliminate nearly two pounds of rivets normally used in aluminum hoods and doors.

GM is already using system, which it developed and patented, to make hoods for the Cadillac CTS-V sport sedan and liftgates for hybrid versions of the Chevrolet Tahoe and GMC Yukon SUVs.

Spot welding is performed by pinching sheet metal between electrodes that electrically melt and fuse the metal. The process is fast, inexpensive and effective with steel. But conventional spot-welding produces uneven results with aluminum, mainly because of the electrically insulating effect of oxides that form on the metal's surfaces.

Manufacturers typically sidestep the welding problem by using self-piercing rivets instead. GM notes that riveting boosts cost, adds weight and limits joint configuration options.

GM says its spot-welding system uses multi-ring domed electrodes that "disrupt" the oxide coating, thus allowing a stronger weld and eliminating the need for rivets. The company says it may license the technology to others in the aerospace, automotive, commercial truck and rail industries.