It amazes me how many robotic welding applications are still done without sensors and software to adapt to part variations. Without adaptive control, you need precise part shape and placement, plus a precise tool center point (TCP) or you produce bad welds.
Once you start making bad welds you must determine if you have a part problem, a fixture problem, or a torch problem. After you resolve the problem you must “touch up” the program and the cycle starts anew.
In the 21st century, robots can be equipped with a wide range of sensor options from tactile probes all the way to 3D point cloud vision.
One of the oldest adaptive techniques is touch work. But it is far from obsolete. You trim the welding wire to a known length, energize it and use the wire as the sensor. On the plus side the sensor is the TCP so there is never any calibration issue. No additional sensor, such as a camera or laser is needed, so you don’t constrain the robot with added equipment hanging off the torch. On the minus side, touch work takes time to execute.
Today’s example is a multipass pipe to plate weld. The weld volume is large and takes time. This means that adding touch work to the program only adds a small percentage to the cycle time.
Jim Walker wrote the program to correct for ovality in the part, fixturing issues and run out. He also detected the part diameter and selected the correct program to match.
Thanks to our friends Gary Kowalski with FANUC America Corporation for the bot, James Nielander with Lincoln Electric for the welding power supply, and howard fisher with American Weldquip for the torch and cleaning station. We couldn’t do it without you!
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