Machine Design

Linear motor controls stud welding

Edited by Lawrence Kren & Victoria Reitz

A new weld head uses a linear-motor drive to replace conventional electromagnetic devices in drawn arc stud welding machines.

A new weld head from Emhart Fastening Teknologies features a linear-motor drive that precisely times and controls lift heights, plunge velocity, and depth penetration of each attachment during welding. The new system replaces conventional electromagnetic devices and consistently welds to within 0.3 millimeters of spec by using a closed-loop optical encoder that monitors stud movement throughout each cycle.

"The linear motor is a major advancement in our line of nohole fastening systems for automotive assembly," says Steve Bleakley, automotive marketing director for Emhart Fastening Teknologies. "It delivers the consistency and accuracy customers need to reduce costs while maintaining quality standards."

Online programming of the linear motor allows variations in lift heights, including individual weld sequences. These instant adjustments maintain constant arc voltages and ensure proper melting of the base metal and stud head. The system reacts immediately to irregularities in the weld zone by modifying the speed and distance of the stud, letting the weld head operate without a reference probe in most applications.

Precise and consistent timing control eliminates overheating in the sheet metal, a crucial advantage in aluminum stud welding, where less heat is required to reach melting points. Control of stud plunge velocity and plunge depth, on the other hand, reduces expulsion and deformation in the weld zone. Conventional weld heads place studs onto the work piece with maximum velocity, causing splatter and deformation.

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