Trans-gun Tool Changing
Reprinted by permission from Robotics World Magazine
Robotic spot welding has become the metal joining method of choice in many manufacturing operations, primarily the production of automotive body parts. To keep robots flexible and make the best use of limited floor space, robotic tool changers for trans-gun resistance spot welding have become common. However, underbody or re-spot welding operations require a higher electrical current (20,000 Amps or higher is common) generated by a hip-mounted transformer that must supply this current to the welding gun; this arrangement is called a Secondary Kick-less Cable operation.
The size of these large secondary welding guns are upwards of 400 pounds with large throats and may approach the robot’s payload limit and restrict its ability to perform. This presents manufacturing engineers with the challenge of how to incorporate a seventh-axis robot that can tool-change up to six or seven different weld guns.
ATI Industrial Automation has developed a patented tool changer with a secondary-power module that transfers secondary current up to and exceeding 20,000 amps current across a tool changer for spot-welding applications. This module has a method for reliably attaching kickless or shunt cables. As an example of how this technology has improved flexibility, a large automotive company recently implemented a seven-axis re-spot line. This application was only made possible because the ATI tool changer was capable of changing out a variety of secondary-powered weld guns.
A major Midwest assembly plant recently completed a retrofit project and used ATI’s tool changer, despite not having integrated the kickless system in a robotic application before.
‘‘ATI admitted up front that they had done similar projects in manual applications but never actually integrated a kickless cable system on a robot,’‘ the plant’s project manager said. ‘‘They promised if we were willing to work with them that they would dedicate their entire engineering staff to developing a robotic version of the kickless cable system.
‘‘The ATI units are very appealing; for example, the tool changer has a six-way locking mechanism with a single motion. The single center piston method reduces failure modes and reduces downtime between tool changes. We actually save money as the result of a more efficient system.