Cobot Welding: From Science Project to Mainstream Automation

Multi-pass is a valuable feature in heavy welding / high deposition applications. The old school option is to teach every pass manually – start, finish and process. The more efficient approach is to teach a single root pass, followed by a series of offset passes to build up the required size of the weld.

While Reference Frames have been part of PolyScope from the outset, the application in welding required a full six dof implementation. The reference frame feature allows a complete program to be shifted to properly align with the physical parts. This required the teaching of a few points, versus touching up a complete program. Reference frames are particularly helpful in applications with multiple fixtures, or multiple parts within a fixture. It is also common on large parts in agricultural, mining, off-road and construction equipment, where precise fixturing is not practical.

Thru Arc Seam Tracking is a real-time tool that monitors the electrical characteristics of the arc to measure location relative to the weld path and makes program adjustments to properly follow the seam. It is particularly helpful on large parts with fit up and tolerance issues, component parts that were flame (oxy fuel) cut, and large weldments that suffer dimensional distortion from heat buildup during welding. The real time nature of Thru Arc Seam Tracking makes it a good fit in heavy duty welding applications.

Touch Sense, also called Wire Touch, uses a low voltage electrical current (note: not available on all power sources) passed through the weld wire or torch nozzle to locate parts. Prior to welding, the robot probes along the vector of a seam, adjusting the pre-programmed weld path. Touch Sense is good for large parts with fit-up variations, but not thin materials, and not for cycle time intensive parts as it is a two-step process.

The built in 6DOF force sensor in the e-series and UR20 can provide the same functionality, at a reduced cycle time.

A Pattern tool allows a programmer to copy and paste complex moves / welds in a program. It is very effective in programming multiple parts in a single fixture.

The Tack Tool is similar to a pattern tool but focused on short tack welds to hold individual parts together prior to welding.

Stitch welding is the intermittent welding along a joint. It is used when a continuous weld is not required for strength or would put too much heat into a part and thereby distort the original geometry. Stitch welds can be done straight line or curved, and the best stitch weld tools allow the programmer to define start and stop points and the number of welds or the centerline length of the weld.

Overriding all the above features is the unique Touch-to-Teach feature as implemented by various UR partners. Also commonly called Lead Through Teach, it involves the programmer’s ability to interact with the UR cobot manually, using Free Drive to position the torch precisely as a welder would. Conservative estimates show Touch-to-Teach improves complex weld path programming by a factor of 5x.