A stick welder, also called a shielded metal arc welder, joins metals by using an electric arc to melt a metal electrode and the workpiece. The arc is extremely hot, often several thousand degrees Celsius, so it can create a molten weld pool in steel within seconds. Stick welding matters because it is rugged, portable, and widely used for construction, repair, pipelines, farm equipment, and structural steel.
Understanding the machine helps students connect electricity, heat transfer, materials science, and safe workshop practice.
Understanding Tools & Workshop Machines: Stick Welder
A stick welding setup is an electrical circuit with a controlled break in it. One lead connects to the electrode holder. The other lead connects to the work through a work clamp.
The clamp is often called a ground clamp, but it does not connect the job to the Earth. It provides the return path for current. To start, the welder briefly touches the electrode to the metal, then lifts it slightly.
This creates an ionised path of hot gas that can carry current. The power source is designed to keep the current fairly steady as the arc length changes.
Older machines often use a heavy transformer. Modern inverter welders use electronic switching, which can make the machine smaller and give smoother control.
The visible bead is only part of the weld. Heat spreads into metal beside the joint, creating a heat affected zone. This metal does not melt completely, yet its internal structure can change.
In some steels, rapid cooling can make this zone hard and brittle. A weld can look neat on top while lacking fusion at the edges or containing cracks below the surface. Joint preparation matters for this reason.
Rust, paint, oil, moisture, and a large gap can contaminate the molten pool or make it hard to control. Thick steel often needs a bevel at the edge so the molten metal can reach deep into the joint. Several passes may then fill the groove.
Electrode choice changes the result. The number printed on an electrode identifies its strength, positions of use, and coating type. Some electrodes are easy to run on thin, clean steel.
Others are made for structural work where strong, tough welds are needed. The flux coating contains materials that clean the molten metal and form a protective layer while it cools. After welding, this solid slag must be chipped away before another pass.
If slag becomes trapped between passes, it creates a weak inclusion. Some low hydrogen electrodes need careful dry storage. Their coating can absorb water from air, which adds hydrogen to the weld and raises the risk of delayed cracking in certain steels.
Skill comes from observing the puddle rather than only watching the bright arc. The welder must keep a consistent gap, travel at a suitable speed, and hold the electrode at an angle that guides the molten metal. Moving too fast can leave a narrow bead with poor fusion.
Moving too slowly can make a wide, overheated deposit with undercut along the edges. Practice on scrap steel helps students compare beads, break test pieces, and inspect cross sections when possible. Safety is part of the technique.
The arc gives off intense ultraviolet light that can injure eyes and burn skin. Welding fumes need ventilation.
Sparks can travel far enough to start fires, so flammable materials must be removed. Gloves, a suitable helmet, dry clothing, and sound cable insulation reduce the main risks.
Key Facts
- Electrical power input is P = VI, where P is power in watts, V is voltage, and I is current.
- Heat energy delivered over time is E = Pt = VIt, ignoring losses.
- A short, steady arc length helps keep voltage and heat input stable.
- The coated electrode supplies filler metal and produces shielding gas plus slag to protect the hot weld.
- Direct current electrode positive, DCEP, usually gives deeper penetration than direct current electrode negative, DCEN.
- Duty cycle is the fraction of a 10 minute period a welder can operate without overheating, such as 60% meaning 6 minutes welding and 4 minutes cooling.
Vocabulary
- Arc
- An arc is a bright electrical discharge through ionized gas between the electrode and the workpiece.
- Electrode
- An electrode is a coated metal rod that carries current and melts to add filler metal to the joint.
- Weld pool
- The weld pool is the small region of molten metal formed where the arc heats the joint.
- Slag
- Slag is the solid protective layer formed from melted electrode coating on top of the cooling weld.
- Duty cycle
- Duty cycle is the percentage of a 10 minute interval that a welder can run at a rated current before it must cool.
Common Mistakes to Avoid
- Using too long an arc, which raises voltage, increases spatter, and makes the weld bead unstable.
- Choosing the wrong current setting, which can cause poor penetration if too low or burn-through and excess spatter if too high.
- Forgetting to clamp the work lead to clean metal, which increases electrical resistance and can make the arc hard to start.
- Removing slag before the weld has solidified, which can damage the bead and expose hot metal before it is ready.
Practice Questions
- 1 A stick welder operates at 24 V and 120 A while welding. What electrical power is being delivered to the arc, in watts?
- 2 A welder has a 40% duty cycle at 180 A. During a 10 minute interval, how many minutes can it weld and how many minutes should it cool?
- 3 A student notices that increasing the arc length makes the arc louder and the bead more uneven. Explain why a longer arc can reduce weld quality.