yeah, but none of us can afford these http://compare.ebay.com/like/230746968231?var=lv<yp=AllFixedPriceItemTypes&var=sbar&_lwgsi=y&cbt=y. I'm talking about something hobbyists can use...
Why would a hobbyist want a welding robot??
Whatever we do, we do it for love or for money...
Mass production (make money) is as far from hobby tinkering (something you love doing) as can be. If welding is a hobby of yours, you don't want a robot to take the fun away and if your hobby is only the automation part, you have no use for a welding robot, beyond the fun of making it work.
I'm not saying that you shouldn't dive in if you feel for it, just that, if you want to throw a load of money at something, you could just as well choose something with a more usable afterlife than dust collecting
Like if you know someone into (hobby?) farming, perhaps make a sowing robot with settable depth and distance etc.
Or perhaps a pancake robot that makes pancakes in "endless" sheets and roll them up like wallpaper, serves in precise user selected portions, with a selection of toppings - *I'm all done, so only about 4 inches for me*
Imagine the time saved