Adjusting joint design for metal thickness
Little thought is given to joint type or design while welding on light gauge metal. Occasionally on real thin metal, a lap weld will be made or some similar accommodation may be made, of course. But overall, until the material to be welded exceeds 11 gauge material, most of the time 100% penetration can be achieved with little effort.
As metal thickness increases, beveling and grooving the plate will be necessary. Very few experienced welders would think of trying to tackle a 3/8" weld without at least putting a simple V into the joint. Most of the time, a full 60 degree joint with a slight “land” will be made. Depending upon the thickness, a double bevel may be made as well so the joint can be welded from both sides. Joints under 3/8" will also receive some form of beveling, whether it is a "V", or a shallow "U" groove. On thinner metal, it may only be necessary to groove one side of the joint. On many thicker joints, a "V" grooved joint will be ground out on the back side, creating a shallow "V" or “U” to remove the first pass to eliminate possible weld defects that are trapped in the open root.
Actual determining factors in joint design, whether it is going to be welded with MIG, TIG, or Stick will depend upon the WPS or local codes, and relative position. The ultimate goal, of course, is to create the highest quality weld possible. A large thick, single pass at a high amp range will only serve to create weak welds, even if 100% penetration is able to be obtained, because of overheating the metal, and the metal cooling before all the slag can be floated out. In the groove, each pass should not be any thicker than the electrode itself, and the weld puddle no wider than 3 times the width of the electrode.