The basic idea
Arc welding uses electricity to make a very hot arc, which is a sustained electrical discharge across a small gap. The arc is hot enough to melt steel and other metals. When the edges of two parts are melted together, often with extra metal from the electrode, they fuse into one piece as they cool.
The word “arc welding” is a broad family. The version most people picture, and the one this article centers on, is shielded metal arc welding, usually called stick welding. Wire-fed and tungsten-based processes also use an arc, and they are compared separately in the article on MIG welding.
The main parts of a stick welding setup
- Power source. A welder supplies a controlled electrical current, typically adjustable. Some are designed for household power and others need heavier circuits, so the electrical supply matters.
- Electrode holder. A hand-held clamp that grips the electrode, called a rod or stick.
- Work clamp. The ground clamp attaches to the workpiece or the welding table and completes the electrical circuit.
- Cables. They carry current between the machine, the holder and the clamp.
- Electrode. A metal rod covered in a flux coating.
What happens when you strike an arc
When the tip of the electrode touches the work and is pulled back slightly, an arc forms across the gap. Several things occur at once:
- The arc melts the base metal, creating a small molten pool.
- The core of the electrode melts and is deposited in the pool as filler metal.
- The flux coating burns and releases gas, which shields the molten metal from oxygen and nitrogen in the air.
- Part of the coating melts and floats to the surface as slag, a hard crust that protects the weld while it cools.
Once the weld cools, the slag is chipped off and brushed away, leaving the weld bead. Without shielding, the molten metal tends to react with air and become porous and weak, which is why shielding is central to the whole process.
Variables the welder controls
Beginners quickly learn that several variables affect the weld:
- Current setting. Too low and the electrode sticks or the weld is shallow. Too high and the metal can burn through or the weld looks messy. Electrode makers usually print a recommended range for each size and type.
- Arc length. A short, steady arc is typical. A long arc is unstable and wastes the shielding.
- Travel speed. Moving too fast leaves a thin, narrow bead, and moving too slowly piles up metal.
- Angle of the electrode. Holding it at a consistent angle to the joint helps control the pool.
- Electrode type. Different coatings suit different metals, positions and power sources.
These take practice. Many people spend hours running beads on scrap steel before welding anything that matters.
Why prepare the metal
Welding works best on clean metal. Mill scale, rust, paint, oil and galvanized coatings interfere with the weld and may produce harmful fumes. Clean the joint area to bright metal, make sure parts fit tightly, and clamp them so they do not move as the weld shrinks. Cutting and edge preparation usually come first, as described in the guide to cutting metal.
The hazards
Arc welding is one of the more hazardous workshop activities, and the risks are specific:
- Intense light. The arc emits bright visible light plus ultraviolet and infrared radiation. Looking at it without proper eye protection can cause painful eye damage, sometimes called arc eye, and the skin can be burned in a way that resembles sunburn.
- Heat, sparks and spatter. Molten droplets can burn skin and start fires.
- Fumes and gases. The fumes contain metal particles and gases from the flux and coatings. Some coatings, such as galvanizing, produce fumes that can make you ill, so avoid welding them without proper controls.
- Electric shock. Damp conditions, damaged cables and poor connections raise the risk. Keep the work area dry.
- Fire. Combustible materials must be cleared from the area.
Protective gear
The basic kit for stick welding generally includes:
- A welding helmet with an appropriate filter lens, discussed in the article on the welding helmet.
- Safety glasses worn under the helmet.
- Flame-resistant long sleeves and trousers, with no rolled cuffs that can catch sparks.
- Insulated welding gloves, typically leather and gauntlet style.
- Leather or sturdy boots that cover the ankles.
- Hearing protection if grinding or chipping is involved.
- Ventilation or fume extraction, with a respirator where appropriate.
Bystanders also need protection from the light. Screens or curtains help keep others from looking at the arc.
Learning safely
Welding is best learned with a class or an experienced welder. Read the machine manual, check that the electrical supply and cables are suitable, and keep a fire extinguisher nearby. Structural and pressure-bearing welds should be done only by qualified people, since a bad weld can fail without warning.
This article is general information and not professional trade advice.