Welding and fabrication basics

Why it matters

Maintenance mechanics fabricate brackets and guards, repair cracked frames, build up worn shafts and cut out seized parts. Even mechanics who are not certified welders need to know the processes, read a weld symbol on a drawing, and set up hot work so it does not start a fire. This lesson is awareness only: welding and cutting must be learned hands-on in a supervised shop or class, and hot work in a plant requires a permit.

Arc welding processes

All of these melt the base metal and a filler with an electric arc, and shield the molten pool from air.

• SMAW (shielded metal arc, "stick"): a flux-coated rod. The flux burns to make shielding gas and slag. Portable, tolerant of dirty steel and wind, good for structural repairs outdoors. Slower, with slag to chip off.
• GMAW (gas metal arc, "MIG"): a wire fed continuously through a gun, shielded by gas (often argon and CO₂ mix for steel). Fast and easy to learn, common in fabrication shops. Needs clean metal and still air.
• FCAW (flux-cored arc): like MIG with a flux-filled wire, with or without extra gas. Good penetration and usable outdoors.
• GTAW (gas tungsten arc, "TIG"): a non-consumable tungsten electrode with a separate filler rod, shielded by argon. Slow but very precise and clean; used for stainless steel, aluminum, thin material and critical welds.

A quick rule: stick for outdoor and dirty work, MIG for speed in the shop, TIG for precision and non-ferrous metals.

Cutting and other processes

• Oxy-fuel cutting: an oxygen and fuel-gas (acetylene, propane) flame preheats steel, then a jet of oxygen burns through it. Also used for heating and brazing.
• Plasma cutting: an electric arc and compressed gas cut any conductive metal, including stainless and aluminum, quickly and cleanly.
• Brazing and soldering: join parts with a filler metal that melts below the base metal, without melting the base metal.
• Grinding prepares joints and finishes welds. Abrasive wheels have maximum speeds and must be guarded.

Joints and weld symbols

Common joints are butt, tee, lap, corner and edge. On drawings, the American Welding Society (AWS A2.4) symbol tells you what to make:

• A horizontal reference line with an arrow pointing to the joint.
• The weld symbol below the line means the weld goes on the arrow side; above means the other side.
• A triangle is a fillet weld; the number to its left is the leg size (for example, 1/4 in).
• A flag at the bend means weld in the field (on site); a circle means weld all around.

Weld quality

Good welds have consistent width and ripple, proper fusion into both pieces and no cracks. Defects include porosity (gas holes, often from dirty metal or lost shielding gas), undercut (a groove melted into the base metal), lack of fusion, cracks and slag inclusions. Structural and pressure welds are made to a written procedure by a certified welder and inspected.

Hazards and controls

• Arc radiation: ultraviolet and infrared light burn eyes ("arc eye") and skin within seconds. Use a welding helmet with the correct shade, flame-resistant clothing covering all skin and welding screens to protect people nearby.
• Fumes and gases: welding fume contains metal oxides; stainless steel releases hexavalent chromium, galvanized steel releases zinc oxide, and some coatings release toxic gases. Use local exhaust ventilation and, where required, respirators. Never weld on degreased parts still wet with chlorinated solvent.
• Electric shock: keep cables, gloves and clothing dry and in good repair; never stand in water.
• Fire and explosion: sparks travel up to 35 ft (about 11 m) and fall through cracks. Never weld or cut containers that held flammables unless cleaned and certified safe.
• Compressed gas cylinders: secure upright, caps on when not in use, oxygen stored away from fuel gases, regulators and hoses with flashback arrestors.
• Burns and hot metal: mark hot parts "HOT".

Hot work permits

In a plant, welding, cutting and grinding outside a designated shop needs a hot work permit (NFPA 51B). The permit confirms that combustibles within 35 ft are removed or covered, a fire watch with an extinguisher is in place during the work and for a set time afterwards (often at least 30 to 60 minutes), sprinklers and detectors are handled correctly, and the area is checked before the permit closes.

Beyond the platform

Learn welding in a supervised school, community college or apprenticeship shop. Certification is commonly through AWS (https://www.aws.org/) or employer procedure tests. OSHA's welding, cutting and brazing rules: https://www.osha.gov/welding-cutting-brazing. NFPA 51B for hot work: https://www.nfpa.org/codes-and-standards/nfpa-51b-standard-development/51b (Checked on 2026-10-23.)

Common mistakes

• Watching an arc without a helmet, even for a moment.
• Welding near combustibles without a permit or fire watch.
• Welding galvanized or coated parts without removing the coating and ventilating.
• Leaving oxygen and acetylene cylinders unsecured or with regulators loose.

Recap

• Stick for outdoor and dirty work, MIG for speed, flux core for penetration outdoors, TIG for precision and non-ferrous metals.
• Weld symbol below the reference line = arrow side; triangle = fillet weld.
• Control arc light, fumes, shock, fire and cylinders.
• Hot work outside the shop needs a permit and a fire watch; real welding needs supervised training.

Try it

Open the Do tab and take the quiz on welding processes and safety rules.