Welds are actually pretty poor in IV. Parts must be touching, and flush. (their supposed to be working on gap, bevel welds etc) Choose fillet weld (not cosmetic) Pick the two faces to weld, chick the "arrow side" tab, and their you can set the size of the weld (X" x Y") and decide if you want a stitch weld (X" length every Y") AND set the contour shape.
It is pretty limited though and basically just looks pretty.
