🔥 Stuff Every Welder Should Know: Training Guide

Arc welding processes at a glance

Arc welding uses an electric arc to heat metal so edges can be joined. The main processes in this guide are MIG, flux-cored, TIG and stick. Each process has its own equipment and settings.

Solid MIG wire joins mild steel with a wire fed through a gun. The polarity is DC electrode positive, also called reverse polarity.

Self-shielded flux-cored wire carries flux in its core and makes its own protective gas. It runs on DC electrode negative, also called straight polarity.

TIG welding is officially called gas tungsten arc welding, or GTAW. It uses a tungsten electrode that does not melt, and the welder adds filler rod by hand.

How shielding protects the weld

Solid MIG wire and most gas-shielded processes need an external gas bottle. The gas protects the molten weld pool from the air.

Self-shielded flux-cored wire makes its own gas from the flux inside the core, so no gas bottle is needed.

Gas-shielded flux-cored wire needs external gas and leaves a slag that is easy to remove. Solid wire leaves no slag to remove.

Wind can blow away shielding gas and cause visible porosity. Self-shielded wire is ideal outdoors in windy conditions.

Polarity and current basics

Polarity tells which side of the circuit is positive and which is negative. Solid MIG wire uses DC electrode positive, while self-shielded flux-cored wire uses DC electrode negative.

TIG welding uses DC electrode negative for steel and steel alloys, but AC for aluminum.

Shielding gases for MIG

The all-purpose gas for MIG welding mild steel is 75% argon and 25% carbon dioxide. It is called C-25 and runs smooth with little spatter.

100% carbon dioxide, called C-100, may produce a bit more spatter and a slightly erratic arc compared with C-25. A 90/10 argon and CO2 mix, called C-10, is a good option for some jobs.

Aluminum MIG welding commonly uses 100% argon. A helium-blend shielding gas can help reduce hydrogen porosity.

MIG welding stainless steel works well with 98% argon and 2% carbon dioxide. Keep CO2 under 5 percent to avoid excess carbon in the weld.

Too much heat for too long can cause carbide precipitation in stainless steel.

Wires and feeders

ER70S-6 solid MIG wire is the usual pick for dirty or rusty mild steel because it has more deoxidizers than ER70S-3. ER70S-3 is the all-purpose wire.

Aluminum wire is soft, like pushing a wet noodle. Use a spool gun or push-pull feeder to feed it a long distance without buckling.

Self-shielded E71T-11 wires are generally easy to use and forgiving of technique errors.

For E71T-11 self-shielded wire, use a 10 to 20 degree drag angle and a 1/2 to 3/4 inch stickout.

Stickout, travel and feed speed

Stickout is the length of unmelted wire sticking out of the contact tip. A typical MIG stickout is about 3/8 inch.

Too long a stickout reduces heat input and can compromise shielding gas coverage.

Wire feed speed mainly affects amperage and weld penetration. Faster wire feed means more amps and more penetration, but too much can cause burn-through.

Miller's rule for MIG mild steel is about 1 amp for every .001 inch of thickness. A 1/8 inch steel plate is .125 inch, so it needs about 125 amps.

For .030 inch wire, Miller uses about 2 inches per minute of wire feed for each amp. At 125 amps, that is about 250 inches per minute.

Gun angles

For a MIG fillet weld, aim at the middle of the corner at 45 degrees. A butt joint uses a 90 degree angle to the work.

Miller suggests a travel angle of 15 degrees as a good starting point for MIG.

With flux-cored welding, always use a drag or pull technique. If there is slag, you drag.

Flux-cored slag sits on top of the finished weld and must be chipped off.

Porosity and Undercut Troubleshooting

Porosity means tiny gas pockets trapped inside the weld. In MIG welding, the most common cause is poor shielding of the weld pool. If the shielding gas flow is blocked, too low, or blown away, outside air gets into the molten metal and makes holes.

Contaminants on the base metal can also create porosity. Oil, grease, mill scale, rust, and moisture vaporize in the arc and release gas that gets trapped in the weld. Clean the metal to a bright, dry surface before welding.

Undercut is a groove melted into the base metal beside the weld and left unfilled. Too much voltage or a travel speed that is too fast can cause undercut. The wire cannot deposit enough filler to replace the metal melted away.

TIG shielding gas and current

Argon works for all TIG applications, all metals and thicknesses. It protects and cools both the tungsten and the weld puddle.

For TIG welding steel, use DC electrode negative. For aluminum, switch the machine to AC.

On aluminum, AC balance controls the cleaning, or etching, of the oxide layer off the aluminum.

Miller suggests 2% ceriated tungsten as an all-purpose choice for both AC and DC.

TIG tungsten and technique

Grind a tungsten point about 2.5 times as long as its diameter using a 200 grit or finer wheel used only for tungsten.

Hold the TIG torch at about 70 to 80 degrees. The tungsten should stay no more than 1/16 to 1/8 inch off the workpiece.

The filler rod rests at about 15 degrees from the workpiece.

After the arc stops, allow about 1 second of post-flow gas for every 10 amps. At 100 amps, that is about 10 seconds.

Typical TIG shielding gas flow is 15 to 20 cubic feet per hour.

Reading stick electrode codes

In E7018, the 70 means 70,000 psi minimum tensile strength. The first two digits show strength in thousands of psi.

The third digit tells welding positions. A 1 means all positions. The fourth digit tells coating and current type, such as AC, DC or both.

A designator like -1 in 7018-1 means improved toughness. H4, H8 and H16 are diffusible hydrogen designators, and lower numbers mean less hydrogen risk.

Electrodes with AWS codes ending in 15, 16 or 18 are low hydrogen, which helps prevent cracking on thick material.

Choosing stick electrodes

E6010 digs through rust, oil and paint, has deep penetration, runs only on DC, and is popular for root passes on pipe.

E6011 does about the same job as E6010 but also runs on AC, so it works on simple AC machines.

E6013 gives a soft arc, minimal spatter and moderate penetration, but only on clean new sheet metal.

E7024 has a lot of iron powder to lay down metal fast. It is used for flat and horizontal fillet welds on plate at least 1/4 inch thick.

Store opened low hydrogen E7018 electrodes at 250 to 300 degrees F. Mild steel E6011 rods only need dry storage.

E7018 is one of the easiest stick electrodes to use.

Common weld joint designs

A T-joint happens when one piece sits flat and the edge of another piece is welded to its face at a right angle. Miller calls this the most common joint design.

A butt joint joins two workpieces in the same plane with their edges meeting. Edges can be square, beveled, gapped or backed.

A lap joint is formed when the surfaces of the two pieces overlap. Thicker material needs more overlap.

A corner joint joins pieces at 90 degrees to form an L shape. A closed corner has edges flush; an open corner leaves a gap showing each edge.

Corner joints are often used for square frames, such as a weld table.

Welding positions

In flat welding, the molten puddle sits level and stays put, so the welder is not fighting gravity.

When welding vertically, the weld puddle naturally tends to sag because gravity pulls it downward. Vertical up is more common than vertical down, especially on thicker material.

Overhead welding is necessary when the work is fixed or immovable. Overhead is the fourth basic welding position, 4G or 4F.

Each position has a number and letter, like 1G or 2F.

Reading weld symbols

The arrow points to the joint. The side of the joint to which the arrow points is the arrow side, and the opposite side is the other side.

The horizontal reference line is the anchor for all welding symbols.

An open circle where the arrow meets the reference line means weld all the way around the joint.

Leg size sits left of a fillet symbol and length sits to the right.

A flag at the arrow and reference line junction means the weld is made in the field, on site, rather than in the shop.

Plasma and oxy-fuel cutting

A plasma cutter uses a jet of ionized gas that conducts electricity to melt and blow through metal. It can cut aluminum, stainless steel and cast iron.

Oxy-fuel cutting is mainly for ferrous metals, like carbon steel. The oxygen jet reacts with the iron in the steel, and oxy-fuel can cut steel 6 to 12 inches thick, with some systems over 20 inches.

Typical plasma cutters run on compressed air plus electrical power. A hand-held system typically cuts up to about 1 inch of metal.

For steel thicker than 1 inch, oxy-fuel can cut faster than plasma. Plasma needs no preheating of the metal before cutting.

The four basic fuel gases used with oxygen for cutting are acetylene, propane, propylene and natural gas.

Metal identification and preheat

The magnet test helps sort ferrous from nonferrous metals, but it is not perfect because some stainless steels are non-magnetic.

In a chip test, aluminum comes off smooth, in long continuous strips with saw-tooth edges.

Aluminum's surface oxide melts at about 3,700 degrees F, while the aluminum underneath melts at about 1,221 degrees F. The oxide must be removed before welding.

Never clean aluminum with a liquid containing chlorine, because chlorine becomes toxic in the heat of the arc.

Preheating slows the cooling rate of the weld and drives out moisture. Shops commonly preheat steel plate or pipe 1 inch thick or more.

Fit-up and layout

A tight-fitting seam needs less filler metal, so less heat goes in, which helps limit warping on thin metal.

Shrinking can never be fully eliminated because it happens at the atomic level as metal heats and cools.

Layout dye removes glare and gives a uniform deep color that contrasts with scribe lines, so the lines are easy to see.

A scribe is a tool with a sharp point used to scratch lines during layout.

Drilling and bandsawing

On a drill press, hold metal in a vise or clamp to the drill table. A drill bit can grab the metal and spin it.

Remove chips with a brush, never by hand, and take the chuck key out right after use.

As the drill bit gets larger, reduce spindle speed. Use pilot holes for holes larger than 3/8 inch and enlarge in no more than 1/4 inch steps.

When bandsawing, at least three teeth should be in contact with the thickness of the material. When unsure between two pitches, the finer one generally performs better.

Fire safety and hot work

OSHA requires a fire watch for at least 30 minutes after welding or cutting stops, because sparks can smolder and start a fire later.

Fire watchers must have fire extinguishing equipment readily available and be trained in using it.

Move all combustibles at least 35 feet from the work site where practicable.

Near other workers, shield the arc with noncombustible or flameproof screens. Welding booths should have a low-reflectivity finish to soak up ultraviolet light.

Fumes and ventilation

Never use pure oxygen to ventilate a confined space. Use fresh air instead, because oxygen-enriched air makes clothing burn far faster.

In a confined space with a small opening, station an outside attendant who watches the welder at all times and knows the rescue plan. Keep gas cylinders and welding machines outside.

OSHA requires mechanical ventilation in rooms with less than 10,000 cubic feet per welder or a ceiling lower than 16 feet. The minimum rate is 2,000 cubic feet per minute per welder.

Welding galvanized steel indoors must use local exhaust hoods or booths, because zinc fumes can cause metal fume fever with chills, fever, aches and nausea.

Welding cadmium-coated metal indoors or in a confined space requires local exhaust or airline respirators. If ventilation is impossible in a confined space, use NIOSH-approved airline respirators.

Gas cylinders and hoses

Open an acetylene cylinder valve no more than one and one-half turns, and always open it slowly. OSHA prefers no more than three-quarters of a turn.

Stored oxygen cylinders must be at least 20 feet from fuel-gas cylinders or separated by a noncombustible barrier at least 5 feet high with a fire-resistance rating of at least one-half hour.

Keep valve protection caps in place and hand-tight on cylinders designed to take one when not in use.

Acetylene must not be used above 15 psig. Acetylene cylinders must be stored and used valve end up.

Never handle oxygen cylinders with oily hands or gloves, because oil and oxygen can ignite violently. Oxygen regulator gauges are marked USE NO OIL.

Close cylinder valves before moving cylinders. Keep cylinders away from radiators, heat and electric circuits. A leaking fuel-gas cylinder must go outdoors away from ignition sources.

Replace or repair oxy-fuel hose that shows leaks, burns or worn places. Hose connections must hold twice their normal working pressure and never less than 300 psi.

Electrical, PPE and shop safety

Ground the frame or case of every welding machine, except engine-driven machines. Check ground connections for mechanical strength. Attach the work lead firmly to the work.

Spread out coiled welding cable before use to avoid overheating. Clean magnetic work clamps of stuck spatter. Do not use welding cables with splices within 10 feet of the electrode holder.

Never use chains, wire ropes, cranes, hoists or elevators to carry welding current. Do not use pipelines as a permanent part of a work-lead circuit.

A wet welding machine must be dried thoroughly and tested before use. Replace cables with damaged insulation or exposed conductors. Report any equipment defect or safety hazard to a supervisor.

Arc welders need helmets or hand shields, except for submerged arc welding. Helpers and attendants also need proper eye protection. Filter lens shade numbers vary by process and electrode size.

Welder's flash, or arc eye, usually causes symptoms 6 to 12 hours after UV exposure. Never use numbing eye drops, because they can delay healing. Instead, see an eye doctor for arc eye.

Leather gloves, or equivalent, free of flammable or combustible materials must be used while welding, cutting or burning. Keep bench grinder work rests no more than 1/8 inch from the wheel. Before mounting a wheel, tap it and listen: a clear ring means sound, but a dull thud means a crack, and a cracked wheel can fly apart, so do not use it.

Electrode Holder Safety

When you are not using an electrode holder, place it so it cannot make electrical contact with a person. An energized holder can shock anyone who touches it. Put it in a safe rack or hang it away from people.