▶What is the difference between SMAW (stick), GMAW (MIG), and FCAW (flux-core) welding?
SMAW (Shielded Metal Arc Welding, or stick) uses a consumable electrode coated with flux that provides shielding gas and filler metal. It is slow but versatile, works in windy conditions, and requires no external gas supply. GMAW (Gas Metal Arc Welding, or MIG) uses a wire electrode fed continuously while inert gas (argon, argon-CO2 mix) shields the arc. It is fast and clean but requires a gas cylinder and is affected by wind. FCAW (Flux-Cored Arc Welding) is like MIG but uses a tubular wire filled with flux, providing shielding without external gas. It is fast, strong, and tolerates outdoor conditions well. Choose based on the application, material, speed required, and available equipment.
▶What are common weld defects and how do I avoid them?
Common defects: (1) Porosity (gas bubbles trapped in the weld), caused by dirty metal, high travel speed, or inadequate shielding. Avoid by cleaning the area, maintaining proper arc length, and monitoring shielding gas flow. (2) Spatter (tiny blobs of molten metal splattered around the weld), caused by high travel speed or wrong wire speed. Reduce by slowing travel and adjusting parameters. (3) Undercut (a groove melted into the base metal next to the weld), caused by too much heat or traveling too fast. Avoid by reducing amps or travel speed. (4) Lack of fusion (the weld fails to fuse to the base metal), caused by low heat, fast travel, or dirty surfaces. Ensure high enough amperage and clean base metal. Inspect welds visually and with ultrasonic or X-ray.
▶What is a weld test and how do I pass it?
A weld test (or certification test) is a practical exam where you weld a test coupon, which is then sectioned and inspected for defects. AWS D1.1 structural tests include flat, horizontal, vertical, and overhead positions with different material thicknesses and joint types. You must pass visual inspection (no undercut, spatter, or cracks) and mechanical testing (bend and tensile strength). To pass, focus on controlling heat input (right amperage and voltage), travel speed (steady, not rushed), and cleanliness (ground and wire brush between passes). Get formal training and practice extensively before taking the test; re-testing is expensive.
▶How do I read a welding symbol on a blueprint?
A welding symbol shows the type, size, and location of a weld. The symbol includes a reference line (horizontal), with the weld type drawn above or below (fillet, groove, plug, etc.), a tail (for notes), and dimensions (size and length). Above the line = weld on far side; below the line = weld on near side; through the line = weld on both sides. For example, a fillet weld symbol with a '¼' means a ¼-inch fillet weld. Letters in the tail (E, U, V, J, etc.) indicate the groove shape (bevel, U-groove, V-groove). Study AWS welding symbols before working; misreading can result in the wrong weld.
▶What is the heat-affected zone (HAZ) and how does it affect strength?
The heat-affected zone (HAZ) is the area next to the weld where metal is heated by the arc but not melted. Depending on the metal type and cooling rate, the HAZ can become brittle or weak. For carbon steel, slow cooling (from high heat input) can create large grain structures that are softer; fast cooling (low heat input or outdoors) can create martensite that is brittle. Stress-relief heat treatment after welding can restore toughness in critical applications (pressure vessels, bridges). Choosing the right heat input and, if needed, a post-weld heat treatment are essential for joint reliability.
▶What is shielding gas and why is it necessary?
Shielding gas surrounds the arc and molten puddle, protecting them from oxidation and nitrogen pickup from the air, which would embrittle the weld. Common gases: Pure argon (inert, for aluminum and stainless), argon-CO2 mix (for mild steel, 75/25 or 90/10), and argon-oxygen (for mild steel, 98/2). MIG systems use external gas fed from a cylinder; SMAW provides shielding via the flux coating on the electrode. Gas selection depends on material (steel, aluminum, stainless) and desired properties (penetration, spatter, travel speed). Low gas flow or wind can scatter the shield, causing porosity and weak welds. Monitor gas flow gauge (typically 20-40 CFH) and test shielding gas on every job.
▶What does amperage and voltage do in arc welding, and how do I set them?
Amperage (current) controls heat input and penetration; higher amperage melts more metal and goes deeper. Voltage affects the arc length and wire feed speed in MIG; higher voltage makes a longer arc and wetter puddle. For stick welding, amperage is set based on electrode diameter and material: a 3/32" electrode might run 80-120 amps. For MIG, voltage and wire speed work together; you adjust both to get a steady, smooth arc sound (like 'bacon sizzling'). Too low amperage results in a cold, weak weld; too high causes spatter and burn-through. Consult the electrode or wire manufacturer's chart for the right settings and adjust by listening and watching the puddle.
