Found this on the official FRC forums …
Question: We are using cast iron gears for our drive system, and while we were testing we had a lot of weight placed on our robot and one of the gears cracked and we welded it together and it is very solid. But the rules states no welding, now does this mean no strucutral welding or no welding at all.
Ok … so maybe I’m blind but where, in the rules, does it say anything about the illegality of welding anything? Help? 
[edit] I’ve searched and searched, and I cannot find anything on this. What’s the deal?[/edit]
im kinda curious too…ive never heard that before…and if there is a rule against it this is news to me…
if there is a rule against welding anything…then were in a whole lot of trouble. i can’t see them making a rule like that because a lot of teams weld things together…
You may weld while you are constructing your robot. You may not weld at the competition. If you need a part welded or re-welded at the competition, it will have to be sent out to the competition machine shop. Most competitions will have the ability to get a part welded.
this was the answer to the question so everybody don’t panic
Hehe, no welding at competitions. That makes sense. Thanks! ::wipes brow:: 
Whew, that would have sucked to learn that now!!!
Ok, we’re still all good!
OK, my heart skipped a few beats - but I’m alright now.
Whew.
No wielding at regionals I can understand: safety concerns.
No wielding during building - that’s ridiculous.
in other words, no difference then previous years 