How Does a Welding Machine Work? A Complete Guide

A first-time welder clamps the ground clamp to the bench instead of the workpiece, strikes an arc, and gets a wild, spitting mess that refuses to stick to the plate. The machine was fine. The arc was fine. The circuit was not. In the ten seconds it took somebody to explain that a welder is simply a controlled heat source, the whole trade revealed itself: a welding machine does not “weld” anything, it manufactures a small, deliberate sun and points it at metal.

The Short Answer: What a Welding Machine Actually Does

The short answer: a welding machine is a controlled heat source. It converts mains electricity into a stable arc between an electrode and the workpiece, then lets you decide how much heat that arc delivers. It does not “weld” anything by itself. It creates the conditions under which two pieces of metal melt into one.

The trade’s own definition is sharper. As TWI explains in its guidance on power source characteristics, a welding power source is best defined by one thing: it delivers controllable current at whatever voltage the welding process demands. Notice what is not in that definition. The machine is not selling you power or penetration. It holds the setting you chose while everything else about the arc shifts underneath you.

The four parts of any welding machine

Strip away the housing, the knobs and the brand name, and every arc welding setup is the same four things in a closed loop:

Part	What it is	What it does
Power source	The bench box or the truck-bed unit	Converts mains electricity into controlled current and voltage
Electrode and circuit	Holder, work lead, ground clamp, rod or wire	Carries current to the work and back again
Arc	Ionized gas bridging two electrodes	Turns electrical energy into heat, roughly 10,000 F and above
Workpiece	The metal being joined	Absorbs heat, melts, and cools into the finished joint

An arc is, by definition, an electric current flowing between two electrodes through an ionized column of gas, with a negatively charged cathode and a positively charged anode generating the heat. Current leaves the power source, travels down the electrode, jumps the gap as the arc, spreads through the workpiece, and returns through the work lead. Break that loop and nothing happens, which is why a poor ground connection or a damaged cable gets blamed on the machine more often than it deserves.

The three variables you actually control

• Current (amps) is how much current flows through the circuit, and roughly how much heat lands in the metal. It is the primary dial on stick and TIG machines.
• Voltage is the electrical pressure pushing that current along. On MIG and flux core it is usually a fixed setting, because wire feed speed sets the current.
• Arc length is the distance between the electrode tip and the molten pool, the variable you change by hand dozens of times per weld.

Here is the trap for beginners: arc length changes the resistance in the circuit, so it changes voltage and current as well. A welder is not making three independent adjustments. They are making one adjustment, constantly, while the machine quietly compensates for the other two. So the machine’s real job is not to make heat. It is to keep the arc stable and focused while the welder changes arc length, which is the difference between a tool that feels good in your hands and one that feels like a fight.

Two formulas make the rest of this article click. Heat at the arc is a function of electrical power, and power equals voltage times current; add time and you have total heat input. EWI’s breakdown of welding current and voltage goes deeper into how each behaves. Every symptom you will eventually troubleshoot, from spatter to burn-through, comes down to where you sit on those numbers.

What people mean when they say “welding machine”

In the trade, “welding machine” usually means the whole working kit, not just the power box:

1. The power source, delivering DC or AC output
2. The electrode lead and work lead with the ground clamp
3. The electrode holder or torch
4. The consumables: stick rod, MIG wire, flux core wire, tungsten, shielding gas, contact tips

Getting the box without the rest is a common and expensive surprise. If you are setting up for the first time, walk through Airgas’s welding equipment guide to see what a complete kit involves, then use the all position welding rod guide to pick stick consumables.

Three processes cover nearly all arc welding you will meet: SMAW (stick), GMAW (MIG) and GTAW (TIG). They differ in electrode arrangement and shielding, not in principle. Stick melts a consumable electrode that is also its own shield, a large part of why SMAW still wins in plenty of shops. MIG melts a continuous wire in a stream of shielding gas. TIG uses a non-consumable tungsten and depends entirely on the gas for protection. Power supplies deliver either direct current (DC) or alternating current (AC), and that choice shows up in the arc, the bead and the molten pool.

The mental model to carry through the rest of this guide

Everything a welding machine does reduces to a five-step chain: Electricity → resistance → heat → melting → fusion. Push electricity through a column of gas and the gas resists. That resistance makes heat. Enough heat melts the metal. When molten filler touches molten base metal, you have fusion, and once it cools you have a weld.

The rest of this guide opens the arc up, compares constant current with constant voltage, takes the power source apart, follows the circuit through cables and consumables, and turns it into settings you can use tomorrow morning.

Inside the Arc: The Physics of Melting Metal

A welding arc looks simple: a glow, a hiss, a puddle that hardens into a bead. The gap inside is closer to a miniature lightning strike, and that physics is what turns a vague complaint into a specific diagnosis.

Ignition: Why a Cold Electrode Will Not Strike

An arc cannot begin on its own: air between cold metal surfaces is an insulator with no path for current. Processes solve this two ways. The classic method is contact and withdrawal: touch the electrode to the workpiece, current flows through the contact point, the metal heats, and pulling away leaves ionized gas the current can hold. So welders scratch or strike an arc rather than hovering over the plate and pressing the trigger. The alternative is a hot start: the machine delivers a very high initial voltage for a fraction of a second to punch a conductive path through the gap. Modern inverters add a low-amplitude pilot or high-frequency start that establishes the arc cleanly on rusty or dirty steel. Once the arc strikes, open-circuit voltage may be a few tens of volts on some machines and around 120 on others, and the moment the gap turns conductive it collapses to the much lower arc voltage that sustains the arc.

What the Gap Actually Contains

Once ignited, the gap is no longer air. It is a plasma: current and electron bombardment strip electrons from gas atoms, leaving ions and free electrons, and that ionized cloud conducts current across a gap ordinary air cannot bridge. The column runs at several thousand degrees Celsius, far above the melting point of the steel being joined, with a hot core and cooler edges. That gradient gives the arc a bright core and a fuzzy halo, and it shows in your technique: a short “barking” arc is dense and focused, a long, spitting arc is thin and spread out. The arc is not a beam of heat aimed at the plate. It is a column of superheated gas conducting electricity, and heat is generated inside it, in the collision zones where electrons and ions recombine at the electrode and workpiece surfaces.

The Heat Split: Two-Thirds Goes Into the Metal

In DC welding, roughly two-thirds of the arc heat is generated at the workpiece (the anode) and one-third at the electrode (the cathode). That asymmetry, called anode heat distribution, is why filler metal melts faster and pools deeper in some setups. Under AC, electrode and workpiece trade places each half cycle, so the split comes out closer to even, which makes AC harder to keep a tight, stable arc on aluminum: heat is less focused and the arc feels less “grabby.” Aluminum processes lean on DC, and prep matters just as much, which is why how to prep aluminum right is part of the physics, not a separate chore. The split also explains polarity: DCEN (electrode negative) puts more heat into the work and less into the electrode, so the electrode lasts longer and the workpiece melts deeper, while DCEP (electrode positive) melts the electrode faster, narrows the bead and deposits more filler. If a GTAW weld wanders or the tungsten loads up, check polarity first.

Arc Length Is a Real Distance, Not a Vague Feeling

Arc length is the physical gap between electrode tip and melt surface. It should be felt, but it is also measurable, and it changes the circuit. A longer arc means higher voltage, more heat spread wide and less penetration. A shorter arc means lower voltage, a tighter and hotter bead with deeper penetration, and a greater risk of shorting or stubbing. The reason is resistance: a longer plasma column is a longer path for current, so more voltage is needed to push the same current through, and some extra energy heats the electrode and boils the air instead of the joint. Keeping a tight arc is not mystical. It is a specific distance controlling how much of the arc’s energy lands in the work versus the air.

The Pool, the Bead, and the Heat Affected Zone

Below the arc sits the molten pool, a puddle of liquid metal that travels with the arc. At the leading edge, cold base metal joins the pool; at the trailing edge the pool solidifies almost instantly into the bead. Behind it lies the heat affected zone, base metal that was not melted but was heated enough to change its microstructure. Depending on carbon content and heat input, that band can turn hard, brittle, or prone to cracking. Filler metal must melt before it can fuse with the base metal, because fusion is the joining of molten surfaces. Swishing an unmelted rod tip in the pool contaminates the weld with filler that never became part of the bead. That is why stick rods are held at an angle and fed into the front of the pool, and why TIG filler always goes to the puddle, never plunged cold into the root gap.

Why Low Voltage Still Bites

A machine rated at 30 or 40 volts still bites. OSHA’s welding equipment standard treats the full range of arc welding voltages as capable of causing shock, and in damp conditions, around wet ground clamps, or with damaged cable insulation, even modest figures can open a serious path to ground. A machine pushing 120 volts open-circuit is not delivering 120 volts to the metal. Once the arc establishes, arc voltage collapses, so the heat source becomes something a welder controls by hand rather than something that can electrocute them. The gap between open-circuit and arc voltage is the safety margin, and it is one reason inverter machines start arcs cleanly: they manage that transition in milliseconds.

Picture the arc as a hot, conductive gas that makes heat where it touches metal, with two-thirds of that heat landing in the workpiece and one-third in the electrode, and everything else gets easier. Every symptom from spatter to stubbing to lack of fusion comes down to where the heat went and how long the arc was. For the electrical side in more depth, the TWI guide to power source characteristics covers how current and voltage behave across processes, and the EWI breakdown of GMAW current and voltage connects this arc behavior to a wire feed system you will actually use.

Constant Current vs Constant Voltage: The Concept That Explains Every Machine

The single biggest difference between one welding machine and another is not size, brand, or price. It is how the machine reacts when conditions change. Every arc welding power source falls into one of two families: constant current (CC) or constant voltage (CV). Once you understand the difference, the rest of the controls on that machine stop being guesswork.

Constant Current: Stability Through Self-Adjustment

Constant current, often called constant amperage, is the mode of choice for manual processes such as Shielded Metal Arc Welding (SMAW) and Gas Tungsten Arc Welding (GTAW). On a CC machine the welder dials in the amperage for the job and the power source handles everything else.

That self-handling matters because arc length never stays perfectly still. The smallest hand movement shortens or lengthens the arc. A CC source responds by raising or lowering its voltage to hold the set current, which makes it ideal for hand work. As power source characteristics explains, the most common curve for these processes is a drooping one.

A drooping curve means output current falls as voltage rises. If the arc gets too long, voltage climbs and current gently drops, preventing an erratic, uncontrollable arc. If the arc gets too short, voltage falls and current rises, helping stop the electrode from sticking. This built-in self-adjustment is exactly what a human welder depends on, since no wire feeder is making corrections for them.

Constant Voltage: Let the Machine Feed the Arc

Constant voltage is built for processes that feed filler metal continuously, most notably Gas Metal Arc Welding (GMAW), better known as MIG. Here the welder dials in voltage rather than amperage, and the machine supplies whatever current is needed to hold a stable arc.

A CV source holds voltage relatively flat across a wide range of currents, so internal circuitry pushes current up or down to keep that voltage consistent. But the real dial on a CV setup is wire feed speed. As EWI’s breakdown of GMAW current and voltage shows, wire feed speed and welding current are directly related: more wire means more current. On a standard CV machine the two cannot be adjusted independently.

That is why CV is almost always paired with a wire feeder. The speed filler metal is pushed through the gun determines how much heat the machine must deliver. Feed too fast for the set voltage and the arc turns harsh and stubby. Feed too slow and it stretches long and sputtery. Balancing those two is the whole game in GMAW-CV.

Flat vs Drooping, and Smarter Control Modes

The easiest way to picture both modes is with a curve. A CC drooping curve slopes down, so the machine fights to keep amps stable. A CV flat curve stays level, so the machine fights to keep volts stable. The first is built for a hand-held electrode consumed at its own rate, the second for a mechanically fed wire that dictates its own demand for current.

Modern machines blur the line. Synergic mode appears on many CV GMAW sources. Instead of manually juggling voltage and wire feed speed, the machine holds a pre-programmed relationship between them for a given wire type and diameter. The welder selects material and thickness, the machine picks a balanced starting point, and small adjustments are made as the joint dictates.

Pulse welding is another common addition. It alternates a high peak current to establish and transfer droplets with a low background current that lets the puddle cool. Pulse can be applied to both advanced CC and CV systems and is especially useful for holding heat in check on thinner material. It does not change the fundamental classification of the machine, only how precisely that machine delivers current.

CC vs CV at a Glance

Feature	Constant Current (CC)	Constant Voltage (CV)
What you dial in	Amperage (amps)	Voltage (volts), with wire feed speed as the real dial
Voltage-Current Curve	Drooping (slopes down)	Flat (stays relatively level)
Reaction to arc length change	Self-adjusts voltage to hold set amps	Self-adjusts current to hold set volts
Common Processes	SMAW (Stick), GTAW (TIG)	GMAW-CV (MIG), FCAW-CV (Flux-Cored)
Best suited for	Manual welding with consumable or non-consumable electrodes	Semi-automatic welding with continuous filler wire
Smarter options	Hot start, arc force, anti-stick	Synergic, pulse, inductance control

The takeaway is simple. CC protects a manual arc from the welder’s hand movement. CV protects a fed arc from the relentless demand of continuous wire. Neither is universally better; they are designed for different ways of depositing metal. Know which one you are holding and every other setting on that machine starts to have a reason behind it.

Inside the Power Source: Transformers vs Inverter Technology

Step inside any welding machine and you find the same job: turn messy mains electricity into a steady, predictable current for an arc. Two very different machines have done that for nearly a century.

From the 1930s through the 1980s, nearly every arc welding machine sold was transformer-based. Inverters arrived in the 1980s and were widely adopted by the early 2000s. Today the inverter is the default in almost every shop, and the iron-core transformer is mostly a budget backup unit.

The Transformer Approach: Heavy Iron, Simple Physics

A transformer machine is wonderfully simple. Mains power arrives at roughly 240 volts and passes through a primary winding on a large laminated iron core, where a secondary winding with far fewer turns steps the voltage down to around 20 to 40 volts for welding. A reactor or tap switch dials the output current.

The heavy iron does two jobs: it steps voltage down and produces the drooping output characteristic that makes stick welding self-regulating, and it is why the machine is heavy, bulky and hot. A typical 250 ampere transformer welder weighs around 60 to 90 kilograms, takes two people and a truck to move, and runs at 50 or 60 hertz, wasting a meaningful share of input energy as heat.

It also endures abuse: it can sit in a dusty yard, get drenched and knocked around and still work, because almost nothing in it is sensitive to humidity or dust. That is why old shops kept them for decades and why tradespeople still keep one as a backup. The Fabricator covers the old versus new debate in useful detail.

The Inverter Approach: Switching Fast, Thinking Faster

An inverter does not step voltage down with a big iron core. Instead it converts, switches and steps in stages.

1. Rectify. The incoming AC from the wall is converted to DC, often called a DC link bus.
2. Chop it up fast. That DC is switched on and off at very high frequency, typically a few kilohertz up to 100 kHz or more, using solid-state devices such as IGBTs or MOSFETs. Switching a DC supply thousands of times a second is how the machine makes a controllable AC or chopped DC signal.
3. Step down. Because the switching frequency is so high, a much smaller high-frequency transformer steps the voltage down. One that had to be huge for 50 Hz can be a fraction of the size at 20 kHz.
4. Rectify again. The output is rectified back to smooth DC, and the duty cycle of the switching stage, how long the machine is on versus off, is what actually regulates amperage.

That high-frequency switching is the inverter’s advantage: the machine can change its output thousands of times per second, so it responds to the arc in real time, seeing the arc length change, the voltage change and the stick happen, then adjusting current before the welder reacts. TWI’s notes on power source characteristics explain how the drooping output characteristic is generated, and EWI’s breakdown of welding current and voltage covers the same behavior from a practical angle.

That fast response is what makes modern features possible: hot start boosts current briefly when the electrode touches the work so the arc strikes before the puddle cools, arc force adds a controlled push that helps the arc behave, and anti-stick detects a dead short, drops current in milliseconds and lets the electrode release instead of welding itself to the plate. Constant current and constant voltage control, spool-gun compatibility and synergic or programmed settings all follow from one capability: changing output faster than the arc can misbehave.

Factor	Transformer	Inverter
Weight at 250 A	60 to 90 kg	A few kg
Output response	Slow, tied to mains frequency	Thousands of changes per second
Arc features	Often none	Hot start, arc force, anti-stick, pulse, synergic
VRD	Generally absent	Common on quality units
Ruggedness	Ignores dust and moisture	Sensitive electronics, needs protection
Upkeep	Low, simple parts	Higher after warranty expires

Duty Cycle: Why Size and Output Stopped Being Linked

Duty cycle is the percentage of a ten minute cycle a machine can weld without exceeding its thermal limits. A machine rated at 60 percent duty cycle can weld for 10 minutes, then needs 4 minutes to cool, and the nameplate number is often written as 60% @ 250A.

That is why inverters are so much smaller for the same output. Their parts heat up quickly but cool fast, so they reach much higher duty cycles for their size. A transformer is limited by how much iron and thermal mass it holds, an inverter by heat sinks, fans and semiconductor capability, and a welder you can carry up a staircase in one hand can now deliver 250 amps that would have needed a cart-mounted transformer a generation earlier.

The Honest Trade-Offs

Inverters win on capability, but they are not the right choice in every situation, and pretending otherwise is bad advice.

• Electronics need protection. Dirty, dusty, high-moisture environments can cause inverter board failures, while transformers shrug off the same conditions. If your work is mostly outdoors on a farm, a demolition site or a dusty fabrication shed, keep the inverter in a sealed enclosure or keep a transformer as a backup.
• Gouging stresses inverters. Carbon arc gouging and heavy electrode grinding punish the output stage, and gouging with an inverter is generally not recommended because it stresses certain inverter components. Air carbon arc gouging has its own dedicated equipment and safety rules, covered in our guide to air arc welding and carbon arc gouging.
• Repairs cost more. A failed transformer is usually a straightforward part swap, while a failed IGBT module or control board is a specialist repair. Per The Fabricator, inverters generally use less electricity than transformers, but maintenance costs run higher once the warranty period ends.

For aluminum work, filler selection and machine features matter even more than usual, so read aluminum MIG welding and aluminum flux core welding references before you dial in a machine for the job.

Which One Should You Buy?

For a beginner buying a first machine, the honest answer is an inverter, every time. It is lighter, safer and easier to control, and features like anti-stick and hot start take years off your learning curve. The exception is a genuinely harsh work environment, where a secondhand transformer kept as a shop backup alongside a modern inverter is a sensible pairing rather than a contradiction.

What matters most is that you know what is happening inside the box. The machine is not magic. It is either a heavy iron core stepping voltage down, or a fast switcher pretending to be one, and both deliver the same thing: a controlled, repeatable current for an arc that melts metal.

Note: This overview of power source types is one part of a larger guide. See also the background on arc welding processes and OSHA’s welding safety fact sheet for the full safety picture.

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const text = `Before any metal fuses, electricity has to finish what it started. The basic welding circuit connects an AC or DC power source through a work cable to the workpiece and through a hot cable to an electrode holder that makes contact with the welding electrode. From there, current jumps across the arc and returns through the work lead back to the machine to complete the loop. If any part of that loop is broken or has too much resistance, the arc simply won't stay stable.

Every inch of this circuit matters. The work lead and its ground clamp are responsible for returning current to the power source. A classic mistake is clamping that ground to the welding bench instead of the actual workpiece. If you do this, you're forcing the current to travel through painted metal, greasy brackets, or even loose bolts to reach your plate. All of that added resistance eats up amperage, makes striking an arc harder, and can lead to erratic, weak welds.

The other side of the loop is the electrode holder, which must grip the electrode firmly. Loose grips create arcing at the jaws, overheat the holder, and waste current. All cables should have intact cable insulation as well. Cracked or frayed insulation is more than a wear item, as it creates unnecessary shock risk. Finally, cable length and voltage drop go hand in hand. The longer the cable run, the more resistance it builds. For extremely long runs, that voltage drop can be enough to prevent the machine from holding its set parameters, especially on smaller output machines.

Once the loop is solid, polarity decides where the majority of that heat goes. For DC machines, there are two choices: DCEN (direct current electrode negative) and DCEP (direct current electrode positive).

With DCEN, roughly two-thirds of the heat goes into the workpiece, leaving about one-third at the electrode. With DCEP, that balance flips, concentrating more heat at the electrode. Many stick electrodes are designed for DCEP to melt their thick flux coating properly, whilst TIG on steel is often ran with DCEN to put the bulk of its heat into the base metal. AC alternates between the two, which is why it's so useful for cleaning and welding aluminum with GTAW. Choosing the wrong polarity for a given electrode will almost always result in poor arc control, excessive sticking, or little to no penetration.

Not every process feeds filler the same way. For SMAW (stick), you're using consumable electrodes that both carry current and become filler metal. Stick rods follow an AWS classification, such as E6013 and E7018. The 'E' stands for electrode. The first two digits represent the minimum tensile strength in ksi (so 60,000 psi for E60xx, 70,000 psi for E70xx). The third digit indicates the coating type and position capability, with some rods rated for all position welding. The fourth and final digit refers to the specific chemistry and polarity recommendations. E6013 is a very forgiving, general purpose rod, whilst E7018 is a low hydrogen rod that demands clean, dry storage to avoid moisture picking up in its flux. For specific applications that require more strength or toughness, welders will look into alloy steel welding electrodes as well.

For GMAW (MIG), the filler is a continuous solid wire. A common example is ER70S-6. The 'ER' denotes an electrode or rod, '70' matches a 70,000 psi tensile strength, and the 'S-6' designates its deoxidizer package for welding over mildly rusty or mill scale contaminated steel with an external shielding gas. FCAW (flux-cored arc welding) uses flux-cored wire instead. Some flux-cored wires are self-shielded (generating their own shielding), whilst gas-shielded flux-cored wires rely on an external gas, allowing for higher deposition in many heavy fabrication jobs.

Lastly, GTAW (TIG) flips this entirely. It utilizes a non-consumable tungsten electrode to establish and maintain the arc, whilst filler metal is added separately by hand when needed. This separation of arc and filler is what grants TIG its unmatched precision.

With the consumable chosen, two distances will dictate your amperage more than most realize. Contact tip to work distance (CTWD) is the distance from the end of your MIG contact tip to the surface of the workpiece. Electrode extension (also known as stickout) is the length of wire protruding past that contact tip, before it hits the arc.

These are directly tied to resistance. As electrode extension decreases, the resistance to welding current in the wire drops. With voltage held constant on a CV machine, that drop in resistance allows more current to flow. This increase can be enough to shift the metal transfer mode from globular all the way to spray transfer. Conversely, excessive stickout adds resistance, drops your effective amperage, and can make the arc unstable.

For GMAW in particular, voltage primarily controls arc length, the distance between the molten weld pool and the wire melting point. As voltage increases, that arc lengthens, the bead flattens out, and the width-to-depth ratio increases. Current is then largely controlled by your wire feed speed. Keeping your CTWD and stickout consistent is just as important as turning either dial.

The circuit doesn't care about intent, only continuity. A solid ground, correct polarity, and consistent stickout will solve more mystery arc problems than blindly cranking up amperage ever will. For any work involving electrical hazards, it's worth referencing the guidance laid out in OSHA 1910.252 for safe welding practices.`;

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Choosing a Machine: MIG vs TIG vs Stick, Compared Honestly

Most people buy a welding machine backwards, then blame the machine months later. There are four arc welding processes, and each answers a different kind of work.

Stick (SMAW): the one that goes anywhere

Stick is the most portable process in the trade: no gas cylinder to haul, no wire feeder to maintain, no polarity beyond a simple switch. Machine, holder, rod, ground clamp, somewhere to stand. That is the whole list.

So it is the go-to for field repair, pipeline, shipyard, outdoor structural work, and dirty, rusty, or painted metal, where even welding over the paint works. The trade-offs are real: more spatter, slag to chip off, a thicker and less consistent bead than good MIG, and rods changed every few minutes. Why SMAW still wins covers when that lumpy structural bead is what you actually want.

MIG (GMAW): the speed and volume option

Gas metal arc welding is the fastest process for thin-to-medium steel and the easiest to learn. Wire feeds continuously, the trigger controls the feed, and you pick up the gun’s feel in an afternoon. Deposition efficiency in shop use runs roughly 60 to 70 percent, so most of the wire you feed ends up in the joint instead of spattering off as droplets.

The trade-offs: shielding gas, so a cylinder, regulator, hose, and storage. Clean metal is required, and on rusty steel the arc spits and porosity shows up. It is less forgiving of fit-up gaps than stick, which bridges larger ones. Aluminum MIG demands the right wire and clean metal, as the aluminum MIG guide explains.

TIG (GTAW): quality and control at the cost of effort

Gas tungsten arc welding gives the highest quality and the most control of the four. A non-consumable tungsten electrode makes the arc, filler rod is added by hand, and you control heat input, bead profile, and puddle shape. It is standard for thin gauge, stainless, and aerospace work, and the process of choice for aluminum on AC, because alternating polarity breaks up the oxide layer that would otherwise kill the arc.

Here is the honest part: GTAW demands more skill than any other process and takes longer per inch of weld, managing heat, travel speed, filler, and arc length at once. One caveat for 2026: modern inverters with pulse GMAW control heat input cycle by cycle, and on many applications pulse MIG performs comparably to highly skilled GTAW. Skilled TIG still sets the quality benchmark on thin material and stainless, and aerospace TIG welding shows how far the process has pushed.

Flux Core (FCAW): the fabrication workhorse

Flux-cored wire carries flux inside the core, so it needs no external shielding gas. It lays a larger, hotter, more forgiving bead with slag, and handles rust, mill scale, and out-of-position work far better than solid wire MIG.

Heavy fab shops use it on structural steel, shipbuilding, and pipeline work, often as the first pass on thick material before a cap pass in MIG or TIG. The downside is more spatter, slag, cleanup, and a hotter, less attractive bead. Self-shielded flux core produces far more fume, so ventilation matters. Aluminum flux core has different chemistry, which aluminum flux core welding covers in detail.

Variable	Stick (SMAW)	MIG (GMAW)	TIG (GTAW)	Flux Core (FCAW)
Shielding	None, coated rod	Gas required	Gas required	None if self-shielded
Thickness	3 mm and up	Thin to medium	Sheet to medium	Medium to heavy
Best on	Dirty or rusty steel	Clean carbon steel	Thin, stainless, aluminum	Heavy fab, out of position
All-position	Excellent	Best flat and horizontal	Needs technique	Excellent
Learning curve	Moderate	Lowest	Highest	Moderate
Speed	Slow	Fastest	Slowest	Fast on heavy
Spatter and slag	Moderate, heavy	Low, little	Minimal, none	High, heavy
Fume	Moderate to high	Moderate	Lowest	High
Equipment cost	Low	Medium	Medium to high	Medium
Typical use	Field repair, pipeline	Production, hobby	Aerospace, thin, stainless	Shipbuilding, structural

One box or three?

Modern multi-process inverters run stick, MIG, and TIG from one case, switching with a mode selector and typically two parameter sets. For a beginner buying one machine, that is the sensible purchase: stick outdoors, TIG for stainless and aluminum, MIG for production. Check that the TIG function is real DC TIG with a foot pedal, not MIG with the gas set to argon. Entry-level units sometimes restrict TIG output or skip AC, so if aluminum is in your plans confirm AC TIG, and read our explanation of aluminum flux welding on why non-AC approaches need extra steps.

Does the machine limit you or your skill?

A decent 200 amp multi-process inverter handles almost anything a beginner or working fabricator throws at it. What stops good welds is technique: travel speed, work angle, joint preparation, filler metal choice, and cleaning the metal first. Machine quality matters where it lets you repeat a result: stable output, a reliable ground clamp, a clean torch, and settings that hold when arc length changes. Beyond that, spending more on a machine is a weaker investment than the same money on a decent all-position welding rod guide, proper PPE, and a good regulator.

Consumables drive your exposure, so choose them carefully

In electric arc welding, most fume comes from the consumable, not the base metal: rod coating, wire, and flux are melted and vaporized in the arc. Choosing filler metal is therefore a safety decision, not just a metallurgy decision. Coated and stainless consumables are common sources of hexavalent chromium, along with stainless base metal and some fluxes. OSHA sets a permissible exposure limit of 5 micrograms per cubic meter for Cr(VI) with an action level of 2.5 micrograms per cubic meter, and those limits inform ventilation requirements in OSHA’s welding and cutting standard. Read the safety data sheet for the consumable in your hand.

Let the material and the joint decide the process, then focus on the three levers that actually make the bead: current, voltage, and heat input. The machine is the easy part.

Safety: What the Machine Is Doing to Your Body

A welder is a controlled heat source, but heat is only half the story. Your machine also pushes three things into your body at once: current that wants a path through you, radiant energy that wants to reach your eyes, and fumes you cannot see but can inhale. Almost every serious welding injury is preventable with rules written down decades ago. Those rules are simple, and easy to ignore on a Friday afternoon when you are behind schedule.

The Three Hazards a Welding Machine Creates

• Electric shock. Open-circuit voltage can run well above 60 volts AC, enough to push current through a sweaty hand and cause ventricular fibrillation or a severe burn.
• Radiant arc energy. The arc emits intense ultraviolet, visible, and infrared radiation. Ultraviolet causes arc eye; infrared and visible light cook your skin and clothing.
• Welding fume. Hot vapor rising off the molten pool carries metal oxides, gases, and particulates that lodge deep in the lungs. This is the hazard that kills welders slowly.

Shock: Why Low Voltage Is Not a Green Light

Modern welders carry a voltage reduction device, or VRD, which drops output voltage to a safe level when the arc is not established. It reduces risk, but it does not eliminate it.

Once an arc is live, you are part of the circuit whether you intend to be or not. A damp glove, a scratched work boot, a concrete floor, a metal ladder, or a vehicle frame completes a path to ground. VRD helps during setup and restrike. It does nothing once you are welding.

OSHA’s welding safety guide emphasizes a rule that covers most shock incidents: never touch the electrode, the holder, or the work lead when the machine is energized, and never work wet or damp. Inspect cable insulation before every shift. Cracked insulation is the most common preventable cause of shock.

Arc Eye and Burns: Getting the Shade Number Right

Arc eye, or photokeratitis, is a corneal burn from ultraviolet radiation, and symptoms often start hours later, which is why people keep working through it. Once it starts, no shield helps.

Helmets or hand shields must be used during all arc welding operations, and the correct shade matters as much as using one. OSHA’s welding, cutting, and brazing guidance sets out the standard filter shade recommendations:

Operation	Minimum filter shade
Shielded metal arc welding (SMAW), electrodes 1/16 to 1/8 in.	Shade 10
Gas-shielded arc welding, ferrous metal	Shade 12
Shielded metal arc welding (SMAW), electrodes 5/16 to 3/8 in.	Shade 14

Non-ferrous gas-shielded work such as aluminum and copper typically takes a lighter shade, commonly 7 to 8, because the arc radiates less UV at lower current. Never grind your shield down to improve visibility; a replacement shade window is cheap.

Welding Fume: What Is Actually in the Air

Hexavalent chromium (Cr(VI)) is generated when welding stainless steel, chrome-plated parts, and many coated or plated steels. OSHA sets the permissible exposure limit at 5 micrograms per cubic meter of air as an 8-hour time-weighted average, with an action level of 2.5 micrograms per cubic meter, and Cr(VI) is a confirmed human carcinogen. Under the same rule, 29 CFR 1910.1026, employers must use engineering and work practice controls to reach or beat that PEL, with respirators supplementing those controls rather than replacing them. Monitoring is required at least every six months at or above the action level and every three months when exposure exceeds the PEL, with results shared within 15 work days.

Manganese is the fume component most associated with welding, and it is why welders can get a metal fume fever headache or, over years, neurological damage. NIOSH recommends an exposure limit of 1 mg/m3 as an 8-hour TWA and 3 mg/m3 as a short-term limit, and notes that prolonged exposure above 1 mg/m3 may lead to a Parkinsonian syndrome known as manganism. OSHA’s general manganese PEL is a 5 mg/m3 ceiling, while the ACGIH TLV for respirable manganese is far stricter at 0.02 mg/m3. NIOSH also warns that confined space welding can significantly increase manganese exposure, since ventilation is poor and the welder works in a limited volume.

Stopping Fume at the Source

The hierarchy of controls ranks hazard removal: elimination, substitution, engineering controls, administrative controls, then PPE. For welding fume, engineering controls come first.

• Local exhaust ventilation. A fume extraction arm or hood placed near the arc captures fumes before they reach the breathing zone. It should be your first purchase, not your last.
• Source capture. Positioning matters as much as equipment. A hood 18 inches from the arc removes far more fume than the same hood across the shop.
• General ventilation and housekeeping. Grinding and cutting dust, plus accumulated fume, needs to be vacuumed rather than dry swept.
• Respirators. These cover the gap that remains, or short-duration tasks where extraction cannot be positioned. They need fit testing and a written program.

Fire Watch, Confined Spaces, and Cylinders

29 CFR 1910.252 requires a fire watch whenever appreciable combustible material is within 35 feet (10.7 m) of the point of operation, and the watch must be maintained for at least 30 minutes after welding or cutting finishes. Slag and hot metal can travel, land on a floor or tarp, and smolder for a long time before showing flame.

When work stops, the electrode must come out of the holder and the holder placed where it cannot contact grounded metal. A hot electrode left in a clamp can arc and start a fire hours later, a common and preventable cause of shop burns.

For confined space work, gas cylinders and welding machines stay outside the space, and heavy portable equipment on wheels must be blocked. A welder inside a tank will not hear a machine rolling toward an open manway.

Cylinder rules are specific. 29 CFR 1910.253 prohibits generating, piping, or using acetylene above 15 psig, and it is illegal to strike an electrode against a cylinder to start an arc, which scars the shell and can set the contents off. Store cylinders upright, capped, secured, and away from heat and traffic. Matching filler is also a safety decision, which our guides on alloy steel welding electrodes and aluminum MIG welding cover in detail.

Finally, the last line of defense is the one you wear: leather gloves with gauntlets, flame-resistant clothing, safety boots, and a properly shaded helmet. The best machine on the market will still cook your forearm if your sleeve is a cotton T-shirt.

Troubleshooting: What Your Machine Is Trying to Tell You

A machine that spits, pops, and refuses to hold an arc is usually not broken. It is talking. Every odd noise, failed bead, and speck of black on the plate points back to a setting, a consumable, or a preparation problem. Learn to read the symptoms and troubleshooting stops being guesswork.

Heat Input Is the Organizing Principle

Almost every weld defect falls out of one relationship: how much heat went into the metal, and where did it go? Heat input is roughly arc power multiplied by the time the arc spends on a given length of joint, and arc power is your amperage multiplied by your voltage. More amperage means deeper penetration and a fingerlike profile in the cross-section. More voltage means a longer arc and a wider, flatter bead. More travel speed spreads the same heat over a longer distance, so the bead gets narrower and colder.

That is the whole game. Spatter, cold laps, undercut, burn-through, and cracked toes are all faces of too much or too little of the same thing in the wrong place.

The Symptom Table

Symptom	Most likely cause	First thing to change
Heavy spatter	Arc too long, voltage too high for the wire and gas, wrong polarity, dirty base metal, wind	Shorten the arc, lower voltage, clean the joint
Electrode sticks to the work	Too much amperage, arc too long, or DCEP on a low-hydrogen electrode	Drop amps, shorten the arc, check polarity
Arc will not strike	Dead ground on the clamp, wrong polarity, no shielding gas on MIG	Clamp to the workpiece, verify polarity, open the cylinder
Harsh crackling, stubbing in MIG	Wire feed speed too high for the voltage, recessed or worn contact tip	Slow the wire down, replace the contact tip
Porosity	Moisture, low gas flow, contaminated gas, dirty or oily metal	Dry the gas lines, set proper flow, clean the joint
Lack of fusion	Not enough heat, cold lap, travel speed too fast	Raise amps or voltage, slow down, grind out the cold lap
Undercut	Travel speed too fast, wrong work angle, excessive filler addition	Slow down, fix your angle, reduce filler
Burn-through on thin material	Too much heat, no backing support	Lower amps and travel speed, add a backing bar
Cutout or overheat warning	Duty cycle exceeded, dusty or hot machine, inadequate circuit	Stop and cool it down, check the nameplate duty cycle

Spatter: The Machine Is Telling You the Arc Is Too Long

Spatter is the sound and the mess that comes from an arc longer and hotter than the job wants. Welding voltage primarily controls arc length, so holding current steady while raising voltage lengthens the arc, makes the sound harsher and cracklier, and increases spatter. Spatter also climbs sharply when voltage is pushed well above the proportional range for your wire and gas combination.

Wrong polarity in a GMAW setup reverses the transfer characteristics and throws droplets. Mill scale, rust, paint, and oil vaporize into spatter. So does a breeze, because wind breaks the shielding envelope and lets the atmosphere attack the arc.

Sticking and Stubbing

When a stick electrode glues itself to the plate and you have to twist it off, the amperage is usually too high for the electrode diameter or the arc was stretched too far. Over-amperage boils the electrode tip before it can shed a droplet cleanly, and the pool grows until it grabs the rod.

Polarity matters too. A low-hydrogen electrode such as E7018 wants DCEN, which puts roughly two-thirds of the heat into the workpiece and keeps the electrode cooler. Running it backwards on DCEP overheats the coating and the rod, and sticking gets far more likely.

In MIG, stubbing is the audio equivalent. The wire touches the pool, the machine goes into a sudden high-current event, and the gun pops. Almost always the wire feed speed is outrunning the voltage, or the contact tip is recessed and worn. Change one variable at a time: pull the wire speed back a little, or swap the contact tip before touching anything else.

Porosity: Holes in the Bead

Porosity is trapped gas, and the gas comes from somewhere. Common sources are moisture in the base metal or on the electrode, shielding gas flowing too low, a contaminated cylinder or regulator, dirty metal, and, in flux-cored wire, damp flux that has been opened too long.

Check gas flow against the manufacturer’s chart, not by eye. Purge the hose before you start, since the line fills with air. Secure the cylinder upright, and keep the nozzle cup in good shape so gas actually reaches the arc.

Cold Laps, Lack of Fusion, Undercut, and Burn-Through

Lack of fusion means the puddle did not melt into the parent metal. Causes: not enough heat, a travel speed that outruns the pool, a dirty or oxidized surface, and a cold lap where filler metal flowed over the base without wetting it. If you hear a dull, quiet “tink” instead of the sizzle of a real crackle, you are moving too fast or too cold.

Undercut is a groove dug into the toe of the weld where the arc swept too fast or the work angle pulled the puddle forward. Pull the torch angle back toward a 10 to 15 degree drag, slow down, and use less filler.

Burn-through on thin material is too much heat in too small a place. Drop amperage, slow the travel, and put a backing bar behind the joint. The welding fundamentals library on this site covers how amperage maps to penetration on different thicknesses.

Settings Starting Points and Cutout

Shop rule of thumb: roughly 1 amp per 0.001 inch of material thickness for SMAW, and about 1 volt per 0.001 inch, though joint design and electrode type move those numbers. For GMAW, metal transfer typically shifts from globular to spray above approximately 190 amps of welding current for certain metal and shielding gas combinations. Below that you see more spatter; above it, more penetration and a wider spray pattern.

If the machine shuts itself off mid-weld with a hot light or error code, it hit its duty cycle. Check the nameplate, let it cool, and clean the dust out of the vents. OSHA’s welding standard and the OSHA welding safety fact sheet both cover equipment condition and ventilation requirements worth checking while you are in there.

The habit that makes this easier: change one variable, weld a short test bead on scrap of the same thickness and alloy, and look at the cross-section. Give the machine one question at a time and it will answer.

Setting Up and Running Your Machine: A Practical Checklist

Before you ever strike an arc, the difference between a clean bead and a frustrating mess is almost always your setup. Taking the time to run through a checklist ensures your machine is safe, your circuit is complete, and your settings are appropriate for the job at hand. Follow this order every time you power up, and it’ll quickly become second nature.

1. Know Your Machine and Its Limits

Never guess your machine’s capabilities. Start by reading its nameplate data. Most modern welding power sources list both input and output ratings, including output amperage ranges and duty cycle at a given output current. The duty cycle figure means the machine can be used at its rated output for that percentage of a 10-minute cycle. For example, a 60% duty cycle equals 6 minutes on and 4 minutes off at full rated output. Ignoring this will cause your machine to overheat and trigger its thermal cutout.

2. Check Power, Grounding, and Pairing

With limits in mind, verify your power supply. Typical household single-phase 240V circuits in the United States support a limited range of machines, so always check the nameplate input amperage and the circuit before first use. If you’re running off of a generator, pay extra attention to pairing. Undersized generators are one of the most common causes of unstable arcs for inverter machines, so ensure your generator has enough headroom to handle your machine’s input draw.

Most importantly, focus on your return path. Grounding correctly is non-negotiable. Attach your work lead to clean, bare metal as close to the joint as possible. A loose, painted, or rusty ground is the number one reason a machine will refuse to strike an arc, no matter how perfect your other settings are.

3. Choose Your Process, Polarity, and Settings

Now that your circuit is safe, dial in your process. Your consumable will dictate both your process and polarity, so always double check its requirements before changing anything. For constant current (CC) processes such as SMAW or GTAW, your main adjustment will be amperage. For constant voltage (CV) processes such as GMAW or FCAW, the logic flips. In GMAW, the welder sets wire feed speed on the wire feeder and voltage on the power supply; the machine’s internal circuitry then supplies the current needed to hold a stable arc. Small changes to either one of these will drastically change your heat input.

For any process that requires shielding gas, set your shielding gas flow before striking an arc, and regulators should be checked for leaks and correct pressure before the torch is lit. This simple step prevents a huge amount of porosity before it ever happens.

4. Prep Your Area, Ventilation, and PPE

With your machine tuned, shift focus to your environment. Clear all combustibles within the area, ensure adequate ventilation, and have your personal protective equipment on before you strike anything. For fire safety requirements, be sure to follow the guidance found in OSHA 1910.252, as well as general welding hazard guidance from OSHA’s welding safety fact sheet. At the bare minimum, have a welding helmet with the correct shade, fire resistant gear, gloves, and leather, closed toe boots.

5. Practice, Power Awareness, and Record Your Settings

Now you’re ready for the most underrated step: practice. Before jumping onto your finished part, run test beads on scrap of the same thickness and alloy as your project. This allows you to fine tune your travel speed, arc length, and heat input without wasting material.

As you do this, be mindful of power consumption. A good rule of thumb is to think of what your machine draws from the wall based off of its nameplate input amperage. This is especially important when working off of a smaller circuit, as it’s very easy to trip a breaker even if the machine’s output seems low.

Finally, record your successes. A weld procedure specification (WPS) is the standard way to record the material, electrode or wire, amperage, voltage, travel speed, and shielding gas that produced a qualified weld. For the home shop, a simple note in your phone will do the same thing. The fastest way to get better isn’t changing your machine, it’s repeating a good weld. Once you have those numbers saved, all that’s left to do is strike your arc with confidence.

Conclusion: The Mental Model That Makes Welding Click

Around your tenth hour at the bench, something shifts. A weld that sputtered two hours ago suddenly holds, and you already know the numbers before you strike an arc. The machine did not change. You did. You built a model in your head, and now it behaves predictably inside it.

That model takes few pieces. A welding machine is a controlled heat source whose job, per the fundamentals of power source design, is to deliver controllable welding current at whatever voltage the process demands. Own that and most of how a welding machine works falls into place.

The Four Parts, and Why the Order Matters

Every arc welding setup, from a $200 stick machine to a $3,000 multi-process inverter, is the same four-part system:

1. A controlled power source turning mains electricity into stable, adjustable current.
2. A closed circuit carrying current from the machine, through the electrode, across the arc, through the workpiece, and back. Break the loop and the welder stops.
3. An ionized arc, a plasma column of superheated gas that conducts current and does the heating.
4. A molten pool that forms, mixes, and cools into a joint.

The order matters because each part depends on the one before it: no stable pool without a stable arc, no stable arc without a closed circuit. That is why the loose ground clamp in our opening story produced spitting chaos. Not bad luck, but a broken circuit telling you what was wrong.

Fast response is why inverters dominate modern welding equipment. An arc is dynamic: it lengthens when you move, shortens when you change angle, pushes back when the pool deepens, so a machine that corrects in milliseconds keeps it steady. Older transformers, with heavy iron cores and a sluggish drooping characteristic, managed it too, less gracefully. The TWI overview of power source characteristics covers the details.

Every Symptom Maps to a Lever

Troubleshooting stops being guesswork once the four-part model is in place. Once the arc is stable, your inputs reduce to four: amperage, voltage, travel speed, and work angle. Heat input is what those four produce together.

Symptom	Usual cause	Lever
Excessive spatter	Long arc, wrong polarity, dirty metal, wind	Arc length, voltage
Electrode sticking	Amps too high, arc too long, wrong polarity	Amps down, shorter arc
Arc will not strike	Poor ground, wrong polarity, no gas	Clamp, polarity, gas
MIG crackling or stubbing	Wire feed outrunning voltage, worn tip	Wire feed, voltage
Porosity	Moisture, low gas flow, dirty metal	Gas flow, cleanliness
Lack of fusion	Too little heat, cold lap, travel too fast	Amps up, travel down, angle
Undercut	Travel too fast, wrong angle, too much amps	Travel speed, angle
Burn-through on thin metal	Too much heat, no backing bar	Amps down, travel up, backing

Every row ends in the same place: current, voltage, arc length, heat input. That is the model working. Diagnosis becomes arithmetic instead of superstition, and consumable choices become decisions rather than guesses.

The Machine Is the Easy Part

Good welds do not come from knowing the machine. The machine is the easy part. It does what the dial says and asks for nothing.

The discipline lives in the four things around it. Setup: ground clamp on the workpiece, joint prepared, area clear. Consumables: electrode or wire matched to the base metal, right shielding gas, tungsten sized for the amperage. Joint preparation: clean edges, tight fit-up, backing where needed. Safety: shields, ventilation, cylinders, fire watch, the OSHA welding, cutting, and brazing standard in your head, plus the fume limits that apply to your material.

Your Clear Next Step

Take scrap matching your project’s thickness and alloy and run beads, changing one variable at a time: amperage up a step, then down, arc long then short, same filler, same position, same travel speed. Break the beads and see what each change did. Twenty minutes of that beats twenty hours of reading. Then write down what worked: “3/8 inch mild steel, E7018, 90 amps DCEN, 2 inch pad, flat” beats any manual, because it fits your machine, your hands, your conditions.

That is the whole story: four pieces, a few levers. Learn them and you can fix a bad bead on purpose instead of turning knobs and hoping. The arc is not magic, and the machine is not a mystery box. It is a circuit, a plasma column, and a pool of metal. Go make something that holds.

Frequently Asked Questions

What is a welding machine in simple terms?

A welding machine is a power supply that turns household or shop electricity into a controlled electric arc between an electrode and the metal. The arc reaches temperatures hot enough to melt the workpiece and filler metal, and the molten metal cools into a solid joint. Everything else, the cables, holder, clamp, and shielding gas, supports that one job.

Is a welding machine dangerous to use?

Yes, and it is manageable with standard precautions. The main risks are electric shock from the secondary side, radiant arc energy that causes arc eye and skin burns, and inhalation of welding fume. OSHA requires helmets or hand shields during arc welding, ventilation to keep fume below maximum allowable concentrations, and fire watches when combustibles are within 35 feet of the work.

Do I need a welding machine to learn welding?

You need access to one, but not necessarily your own. Many community colleges, trade schools, and makerspaces rent or share machines, and buying a good used stick machine is a reasonable way to start. For MIG and TIG you also need consumables and shielding gas, so borrowing a full setup for a few sessions is often cheaper than buying everything at once.

Why does my arc spatter so much?

Spatter is almost always a symptom of a mismatched setting rather than a broken machine. The most common causes are an arc that is too long, voltage set too high for the wire and gas combination, wrong polarity, dirty or coated base metal, and wind disturbing the shielding gas. Fix the ground clamp, clean the metal, confirm polarity for your process, and shorten the arc before changing anything else.

What is the difference between a constant current and constant voltage welder?

A constant current machine, used for stick and TIG, holds the amperage you set and automatically raises voltage as the arc length changes. A constant voltage machine, used for MIG and flux core, holds the voltage you set and supplies whatever current is needed, which is why you set wire feed speed instead of amps on those machines. That single distinction explains most of the behavioral differences you see between processes.

Why should I buy an inverter machine instead of a transformer?

Inverters are lighter, smaller, more efficient, and far more adjustable, including features like hot start, arc force, and anti-stick. Transformers are heavier but very rugged and are still favored for rough, dusty, or high-moisture environments and for heavy gouging work, which stresses inverter electronics. For most hobbyists and fabricators, an inverter is the better buy.

How much electricity does a welding machine use?

It depends on the model and the output you demand, so the nameplate is the only reliable answer. A 250 amp machine running at full output on a 240 volt circuit pulls on the order of 40 to 50 amps, which is close to a heavy household circuit limit. Check the machine’s input amperage rating before plugging it in, and never use an extension cord that is too long or too thin.

Can I weld aluminum with a basic stick welder?

Not properly. Aluminum needs AC or DCEN TIG, or a MIG setup with a spool gun and the correct aluminum wire and shielding gas, because aluminum’s oxide layer melts at a very different temperature than the metal itself. A standard steel stick machine will not give you a sound aluminum weld.

What does duty cycle mean on a welding machine?

Duty cycle tells you how long the machine can run at its rated output before it needs to cool, expressed over a 10-minute cycle. A machine rated at 60% duty cycle at 250 amps means 6 minutes of welding followed by 4 minutes of rest. Exceeding it causes overheating, shutdown, and shortened machine life.

How hot does a welding arc actually get?

Hotter than most anything else in a typical workshop. The arc core reaches several thousand degrees Celsius, while the molten weld pool sits above the melting point of the steel, around 1,500 degrees Celsius. That is why arc welding requires heat-resistant clothing, gloves, and face protection, and why finished parts stay hot enough to cause burns long after the arc is off.