I have not used a UR Cobot in a welding application yet. But this is commonplace with Cobots and Industrial Robots.
From a UR Cobot standpoint, please look at the UR+ Website to see if there is an existing off-the-shelf solution for you (search "Welding")! There are UR+ partners that have developed easy-to-use software and hardware bundles to get your application up and running fast. I recommend UR+ solutions because they severely decrease the amount of engineering time to develop an application for your company's needs.
UR+ Website: UR+
Please feel free to ask me any more questions you can think of.