Our team has used welded box and angle aluminum for our frames for every year we've competed, as far as I remember. Our primary sponsor (UTC) usually does the welding for us, as well as some CNC work on the robot, and powdercoating. The CNC is usually used just to create complex designs in the aluminum. For example, our mascots are the 4 Aces, so we usually have the 4 suits (Spade, Heart, Diamond, Club) cut into our aluminum.
Here you can see some of the CNC work, as well as the welding on our 2004 robot, which used mostly angle aluminum
http://www.aceshigh176.org/gallery2/...serialNumber=2