Stick welding (SMAW)
Shielded metal arc welding uses a consumable rod coated in flux. The arc melts the rod and the base metal while the burning flux releases a shielding gas and forms a slag that protects the cooling bead. The welder chips the slag off afterward. Common electrodes are E6010 and E6011 for deep penetration through rust and paint, E6013 for thin, clean work, and E7018, a low-hydrogen rod that produces tough, ductile welds on structural steel and equipment.
Strengths: it works in wind, rain-adjacent conditions and on dirty metal; the equipment is simple and rugged; an engine-driven machine on a truck needs no outside power; it welds thick steel and cast iron (with nickel rods) well. Limits: it is slow, every rod change interrupts the weld, it is hard on very thin material, and the slag and spatter mean more cleanup. Typical uses are pipe fence, gates in the field, farm equipment, trailer frames, heavy brackets and structural steel repairs where the metal cannot be brought to a shop.
MIG welding (GMAW)
Gas metal arc welding feeds a solid wire continuously through a gun while a bottled gas, usually 75% argon / 25% CO2 for steel, shields the puddle. There is no flux and no slag, so welds are clean and the process is fast and easy to control. The common steel wire is ER70S-6; aluminum uses 4043 or 5356 wire with pure argon, usually through a spool gun; stainless uses 308L or 309L wire.
Strengths: speed, appearance, low cleanup, excellent on sheet and light plate, and with pulsed settings very good on aluminum and stainless. Limits: the shielding gas blows away in even a light breeze, the metal must be clean, and short-circuit MIG can leave unfused areas on thick plate that look fine from the outside. Typical uses are shop fabrication of gates and railings, trailer decks, equipment guards, automotive sheet metal, and aluminum trailers, boats and railings.
Flux-cored welding (FCAW)
Flux-core uses the same wire feeder as MIG but the wire is a hollow tube filled with flux. Self-shielded flux-core (FCAW-S) needs no gas and is the go-to for windy job sites; gas-shielded flux-core (FCAW-G) adds CO2 or a mixed gas for a cleaner, deeper weld and is widely used on structural steel because it deposits metal quickly in vertical and overhead positions.
Strengths: continuous wire like MIG, outdoor tolerance like stick, high deposition on thick steel. Limits: smoky, more spatter, a slag to chip, and the self-shielded wires are not suited to thin sheet or to aluminum and are limited on stainless. Typical uses are fence and corral repair in open country, equipment buckets and frames, and on-site structural work where the welder cannot wait for the wind to die down.
TIG welding (GTAW)
Gas tungsten arc welding strikes the arc from a non-consumable tungsten electrode under pure argon and the welder adds filler rod by hand with the other hand, controlling heat with a foot pedal. It is the slowest process and the most skill-dependent, and it rewards that with the most precise, cleanest welds of the four.
Strengths: full control of heat and filler, no spatter, beautiful beads, and the ability to weld very thin material, stainless, aluminum, copper alloys and titanium. Limits: slow, expensive per inch, intolerant of wind and any contamination, and impractical on thick mild steel. Typical uses are stainless handrails, food-service and brewery equipment, aluminum castings, thin-wall tube, and any visible weld where appearance matters.
Choosing by material
- Mild and structural steel: all four processes work. Stick or flux-core outdoors and on heavy or dirty plate; MIG in the shop and on sheet; TIG for thin tube and show work.
- Stainless steel: TIG for thin and visible work; MIG with tri-mix gas or stainless flux-core for thicker fabrication; stick with E308L or E309L rods for field repairs. Keep carbon-steel brushes and grinding dust away to prevent rust staining.
- Aluminum: TIG with AC output or pulsed MIG with a spool gun and pure argon. Stick aluminum rods exist but are a last resort. Clean the oxide with a dedicated stainless brush right before welding.
- Cast iron: stick with nickel electrodes (ENi-CI or ENiFe-CI), preheat, short welds, peening and slow cooling. Many cast parts are better brazed or replaced than welded.
- Galvanized steel: grind the zinc back from the joint, weld with good ventilation, and recoat with cold galvanizing compound afterward.
Indoors versus outdoors
Indoors or inside a closed trailer, MIG and TIG are the first choice: clean, fast and controllable. Outdoors, wind decides. Stick and self-shielded flux-core tolerate a breeze that would ruin a MIG or TIG weld in seconds. A mobile welder can set up screens or park the truck as a windbreak, but a gate hanging on an open pasture fence in a south wind is a stick job. Humidity and cold matter too: low-hydrogen rods must be kept dry, and thick steel welded on a cold morning benefits from preheat so the heat-affected zone does not harden and crack.
Cutting, brazing and when welding is the wrong tool
Oxy-fuel cutting
An oxygen-acetylene or oxygen-propane torch preheats steel to its ignition point and then a jet of pure oxygen burns through it. It cuts thick carbon steel cleanly, needs no electricity, and also heats parts for bending and straightening. It does not cut stainless or aluminum, because those metals do not oxidize in a way the oxygen jet can sustain.
Plasma cutting
A plasma cutter forces compressed air through a constricted electric arc to blow molten metal out of the cut. It cuts any conductive metal, including stainless and aluminum, is fast on sheet and plate up to about an inch, and leaves a narrow kerf with little distortion. It needs power and clean, dry air, which a mobile truck can supply from an engine drive and a compressor.
Brazing and soldering
Brazing joins metal with a filler, usually a brass or silver alloy, that melts below the base metal’s melting point and flows into the joint by capillary action. The parts are never melted, so it suits cast iron, dissimilar metals, thin tubing and copper. Joints are strong in shear but not as strong as a fusion weld, and brazed parts should not be used where high heat or high load is expected.
When not to weld
Some parts should be bolted, replaced or engineered rather than welded. Heat-treated and high-strength components such as vehicle frame rails, suspension arms, steering parts, axle tubes on many trucks and wheel assemblies lose strength in the heat-affected zone, and the manufacturer’s repair procedure governs. Fuel tanks and pressure vessels require professional cleaning, purging and in many cases code-compliant work (ASME for pressure equipment). Structural steel in a building needs an engineer’s detail and a permit before the first bead. A good welder will say no to these jobs or redirect them, and that refusal is part of the service.
Not sure which process your job needs?
Describe the metal, the thickness and where the part lives, and a mobile welder can usually tell you the process, the filler and whether an engineer should be involved.
Joint types and weld types
The geometry of the joint matters as much as the process. The four joints you will meet most often:
- Butt joint: two pieces end to end in the same plane. Thin material can be welded with a square edge; above about 3/16 inch the edges are beveled so the weld can reach the root.
- Lap joint: one piece overlapping another, welded along the edge. Fast and tolerant of poor fit, common on sheet metal and trailer decking.
- T-joint: one piece standing perpendicular on another, as in a bracket on a plate or a post on a base. Welded on one or both sides.
- Corner joint: two pieces meeting at an edge to form an L, typical of boxes, frames and tube corners.
Two weld types fill those joints. A fillet weld is the triangular bead laid into the corner of a T, lap or corner joint; its strength is set by its leg size and length, and most repair welds are fillets. A groove weld fills a prepared groove in a butt joint, often with a root pass followed by fill and cap passes, and when done fully through the thickness it is called full-penetration. Engineers specify groove welds where the joint carries the full load of the member, which is why a cracked beam or loader arm cannot be fixed with a surface bead.
Preparation and finishing
Most weld failures trace back to preparation. Rust, paint, oil, galvanizing and mill scale all cause porosity and lack of fusion, so the joint and an inch on either side should be ground to bright metal. Edges on thick plate are beveled with a grinder, torch or plasma to 30 to 37.5 degrees per side. Parts are clamped or tack-welded square, because welds shrink as they cool and will pull a frame out of true if it is not fixtured or welded in a balanced sequence. Thick, cold or alloy steel is preheated with a torch to slow cooling and prevent hard, brittle zones.
After welding, slag is chipped and spatter is removed with a chisel or flap disc. Welds that will be painted are wire-brushed; welds that must be flush are ground smooth, which is acceptable on non-structural work but can reduce strength if a structural fillet is ground down. Outdoor steel gets primer within hours, because fresh weld metal and ground surfaces rust fast in Gulf Coast humidity. Stainless is passivated or at least cleaned with a dedicated brush and pickling paste so the chromium oxide layer re-forms, and aluminum is left bare or anodized. A finished repair should show a uniform bead with no undercut, no cracks at the ends, and no pinholes.
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