Welding Techniques and Joint Preparation
Joint types and positions
Know the five joint types (butt, lap, tee, corner, edge) and the positions: flat (1G/1F), horizontal (2G/2F), vertical (3G/3F), overhead (4G/4F), and pipe positions (5G, 6G). Understand how position changes heat input, travel speed and technique.
Technique fundamentals
Control arc length, travel angle (push vs drag), work angle, and travel speed. For GMAW, a push angle gives flatter, wider beads and better visibility; drag gives deeper penetration. For vertical-up, use a weave or stringer with controlled pause at the edges to avoid undercut. Root passes need keyhole control and consistent gap; hot pass and fill passes build uniformly; cap pass controls profile.
Joint preparation
Bevel angles, root gap and root face must match the procedure. Tack welds should be of sound quality and consumed into the final weld. Backing, ceramic or copper, and purge gas for stainless root protection. Preheating and interpass temperature checks.
Traps
- Confusing push and drag effects on penetration.
- Underestimating undercut from too-fast weave at edges.
- Treating tacks as non-structural; poor tacks cause root defects.
- Forgetting that vertical-up gives better penetration and profile than vertical-down on thick sections.
Worked example
On a 10 mm tee fillet in the 3F position, set a slight drag angle, keep arc length short, pause briefly at the root and toe, and move steadily. If undercut appears at the toe, reduce travel speed or current, or increase the pause, then re-check leg length against the drawing.