---
type: process
name: "Arc Welding"
category: "Joining"
subcategory: "Thermal"
materials: ["Metal"]
tolerances: "±1/16 in (±1.6 mm) on welded assembly dimensions; ±1/32 in (±0.8 mm) with hard fixturing; tighter only by machining after welding"
volumes: "1 to 1,000,000+ per year — manual for one-offs and short runs, robotic cells for repeat production"
lead_time: "Same day to 1 week for manual one-off weldments; 4–8 weeks to bring a robotic cell online including fixture build and WPS/PQR qualification"
url: https://manufacturingprocesses.org/processes/joining/arc-welding
---

# Arc Welding

Arc welding melts and fuses metal with an electric arc between an electrode and the work, shielded from the atmosphere by gas or flux.

- **Category**: [Joining](https://manufacturingprocesses.org/processes/joining.md)
- **Family**: Thermal
- **Materials**: Metal
- **Typical tolerances**: ±1/16 in (±1.6 mm) on welded assembly dimensions; ±1/32 in (±0.8 mm) with hard fixturing; tighter only by machining after welding
- **Typical volumes**: 1 to 1,000,000+ per year — manual for one-offs and short runs, robotic cells for repeat production
- **Lead time**: Same day to 1 week for manual one-off weldments; 4–8 weeks to bring a robotic cell online including fixture build and WPS/PQR qualification

## Overview

Arc welding fuses metal by drawing an electric arc between an electrode and the workpiece, melting both faces and — in every variant except autogenous TIG — adding filler metal that solidifies into a continuous joint. The arc column runs above 10,000 °F (5,500 °C), so the process melts anything from 0.030 in (0.8 mm) sheet to plate of effectively unlimited thickness in multiple passes.

The family covers five industrial variants: manual metal arc (MMA/SMAW), metal inert gas (MIG/MAG, GMAW), tungsten inert gas (TIG/GTAW), plasma arc (PAW) and submerged arc (SAW). Between them they cover carbon and low-alloy steel, stainless, aluminum, nickel alloys, copper alloys and titanium.

The number that characterizes arc welding: a full-penetration groove weld made with matching or overmatching filler develops 100% of base-metal tensile strength — in a qualified tensile test the coupon fails in the parent plate, not the weld. Volumes run from a single fabricated frame to robotic lines producing hundreds of thousands of assemblies a year.

## How it works

1. **Joint preparation.** Plate over about 1/4 in (6 mm) is beveled — 30–37.5° per side for a single-V groove (60–75° included), 1/16 in (1.6 mm) root face, 1/16–1/8 in (1.6–3.2 mm) root opening. Scale, rust, paint, oil and moisture come off at least 1/2 in (13 mm) back from the joint.
2. **Shielding.** MIG uses argon, argon/CO2 blends (75/25 for steel) or straight CO2 at 20–50 CFH (10–24 L/min); TIG uses argon or argon/helium; SMAW and flux-cored wires make their own gas and slag from the flux; SAW buries the arc under granular flux.
3. **Heat input.** Heat input = (arc volts x amps x 60) / travel speed, landing between roughly 12 and 64 kJ/in (0.5–2.5 kJ/mm) on structural work. That one number governs bead size, penetration, HAZ width and distortion.
4. **Deposition.** Thick joints are filled in multiple passes with interpass temperature controlled — commonly under 350 °F (175 °C) on austenitic stainless to limit sensitization.
5. **Cooling.** Parent metal that got hot but never melted becomes the heat-affected zone, typically 1/16–1/4 in (1.5–6 mm) wide. Cooling rate sets HAZ hardness, so thick sections and high-carbon-equivalent steels are preheated to 150–300 °F (65–150 °C) to avoid hydrogen cracking.
6. **Post-weld.** Slag chipping, back-gouging for double-sided joints, and on heavy pressure-boundary steel a stress relief at 1,100–1,250 °F (595–675 °C).

### How do the five variants differ?

**MMA / SMAW (stick).** A flux-coated consumable electrode at 40–300 A. No gas bottle, so it works outdoors; deposition is only 1–5 lb/hr (0.5–2.3 kg/hr) and slag is chipped between passes.

**MIG / MAG (GMAW).** Continuously fed solid wire, 0.023–0.045 in (0.6–1.2 mm), with external gas, at 5–12 lb/hr (2.3–5.5 kg/hr). Spray transfer in argon-rich gas for thick plate flat; short-circuit transfer for thin sheet and out-of-position work.

**TIG / GTAW.** A non-consumable tungsten electrode from 5 to 300 A with heat and filler controlled independently. Well under 2 lb/hr, but the cleanest — the only practical arc route for titanium and the normal choice below 0.060 in (1.5 mm).

**Plasma (PAW).** A TIG arc constricted through a nozzle orifice, giving higher energy density and a stable arc down to 0.1 A for foil. In keyhole mode it makes a single-pass full-penetration weld to about 1/4 in (6 mm).

**Submerged arc (SAW).** Wire fed under granular flux at 300–1,500 A, reaching 10–45 lb/hr (5–20 kg/hr). The flux must sit on the joint, so it is limited to flat and horizontal seams — heavy plate, pipe mills, pressure vessels.

## Design guidelines

### How big should the fillet be?

AWS D1.1 sets minimum fillet size by the thicker part joined: 1/8 in (3 mm) up to 1/4 in (6 mm) base metal; 3/16 in (5 mm) over 1/4 through 1/2 in (6–12 mm); 1/4 in (6 mm) over 1/2 through 3/4 in (12–20 mm); 5/16 in (8 mm) above 3/4 in (20 mm) — an undersized fillet on thick plate cools too fast and cracks.

Fillets are then checked on the throat, not the leg: effective throat = 0.707 x leg, and nominal shear strength is 0.60 x the electrode classification strength on that throat — 42 ksi (290 MPa) for E70 filler. Throat scales with the leg but deposited volume scales with the leg squared, so a 3/8 in fillet buys 50% more strength than a 1/4 in for 125% more weld metal.

### Groove welds, access and distortion

Keep 60° included angle on single-V groove welds; below about 45° the electrode cannot reach the sidewall and lack-of-fusion follows. Design so welds fall in the flat (1F/1G) or horizontal (2F) position — vertical and overhead work roughly halves deposition rate.

Weld metal shrinks about 3–5% by volume as it solidifies, pulling the joint transversely and rotating it angularly. Balance welds about the neutral axis, alternate sides on double-sided joints, and specify the smallest weld that carries the load. Expect ±1/16 in (1.6 mm) over a 3 ft (1 m) weldment without hard fixturing; if a surface must be true, leave 0.030–0.060 in (0.8–1.5 mm) of stock and machine after welding.

### Which material pairs actually weld?

| Pair | Arc weldable? | Notes |
| --- | --- | --- |
| Carbon steel to carbon steel | Yes | E70XX / ER70S-6 matching filler; the default case |
| Carbon steel to 300-series stainless | Yes | ER309L filler; expect differential expansion |
| 304 to 304 / 316 to 316 | Yes | ER308L and ER316L; hold interpass under 350 °F (175 °C) |
| Aluminum 6xxx to 6xxx | Yes | ER4043 resists cracking, ER5356 is stronger and anodizes to a closer color match |
| Aluminum 2024 / 7075 | No, practically | Hot-cracks and loses temper; rivet, bond or friction weld instead |
| Aluminum to steel | No | Brittle Fe-Al intermetallics; use friction welding or a bimetallic transition insert |
| Titanium to titanium | TIG or plasma only | Full inert coverage plus trailing and backing gas; oxygen pickup embrittles |
| Galvanized steel | Yes, with care | Zinc boils below the pool and causes porosity; grind back 1/2 in (13 mm), extract fume |

Melting points are on the [metal melting points chart](/charts/metal-melting-points); strength and expansion figures for sizing welds and predicting distortion are on the [material properties chart](/charts/material-properties).

### How are arc welds inspected?

Visual inspection to AWS D1.1 is the baseline. Dye penetrant (PT) finds surface cracks on any metal; magnetic particle (MT) finds surface and near-surface flaws in ferromagnetic material only; ultrasonic (UT) is the normal volumetric method for groove welds above 5/16 in (8 mm); radiography (RT) is better for porosity and slag. Procedure and welder qualification (WPS/PQR) is what actually controls quality — inspection only samples it.

| Feature | Recommended | Limit | Why |
| --- | --- | --- | --- |
| Fillet leg on 1/2 in (12 mm) plate | Size for the calculated load | 3/16 in (5 mm) minimum | Undersized fillets on thick plate quench and crack |
| Included groove angle | 60° | 45° | Electrode access to the sidewall |
| Root opening, open-root V | 1/8 in (3 mm) | ±1/32 in (0.8 mm) of nominal | Too wide burns through, too tight leaves lack of penetration |
| Weld reinforcement (cap height) | Flush to 1/16 in (1.6 mm) | 1/8 in (3 mm) | Toe angle drives the fatigue stress concentration |
| Torch access around joint | 1 in (25 mm) | 5/8 in (16 mm) | Gas cup and electrode extension |
| Distortion over 3 ft (1 m) | ±1/16 in (1.6 mm) | ±1/32 in (0.8 mm) fixtured | Transverse and angular shrinkage |

## Variants

- Manual Metal Arc Welding (MMA)
- Metal Inert Gas Welding (MIG)
- Tungsten Inert Gas Welding (TIG)
- Plasma Welding
- Submerged Arc Welding (SAW)

## Cost drivers

Arc welding is a labor process with a consumable bill attached, not a tooling process. On manual stick work, arc-on time is typically only 10–30% of the welder's shift; semi-automatic MIG reaches 30–50%, and a robotic cell 50–80%. That operator factor — not wire price — is what separates a cheap weldment from an expensive one.

Weld volume is the second driver, and it scales badly. A fillet's cross-sectional area goes with the square of the leg, so specifying 3/8 in where 1/4 in carries the load costs 2.25x the deposited metal and 2.25x the arc time, plus proportionally more distortion to straighten afterward. Consumables are usually a small fraction of joint cost next to labor. Inspection can dominate on critical work: blanket 100% radiography on non-critical welds is one of the most common overspecs in fabrication.

1. **Size fillets to the calculated load.** Use the 0.707 throat rule rather than a habitual leg size; the area penalty is quadratic.
2. **Use intermittent fillets** where the joint is not fatigue-loaded or leak-tight — a 2 in on / 6 in off pattern deposits a quarter of the metal.
3. **Design for the flat and horizontal positions.** Out-of-position welding roughly halves deposition rate and needs a more skilled welder.
4. **Delete joints upstream.** A single laser-cut and formed part often replaces three welded pieces and two joints.
5. **Specify NDT per joint, not per drawing.** Reserve UT and RT for full-penetration structural or pressure joints and use visual plus PT elsewhere.

## FAQ

### How strong is an arc weld compared to the base metal?

A full-penetration groove weld made with matching or overmatching filler develops 100% of base-metal tensile strength — in a qualified tensile test the coupon breaks in the parent plate. Fillet welds are different: they are sized on shear across the effective throat, which is 0.707 x the leg, at 0.60 x the filler classification strength (42 ksi / 290 MPa for E70 filler).

### What is the minimum fillet weld size for 1/2 inch plate?

3/16 in (5 mm) per AWS D1.1 for base metal over 1/4 in through 1/2 in (6–12 mm). Minimum sizes exist because a small fillet deposited onto a thick, cold section cools too quickly, hardens the heat-affected zone and cracks. Above 3/4 in (20 mm) the minimum rises to 5/16 in (8 mm).

### Can you arc weld aluminum to steel?

No. Iron and aluminum form brittle Fe-Al intermetallic layers at the fusion line that crack under almost any load. The production routes are friction welding (rotary or friction stir), an explosion-bonded bimetallic transition insert, adhesive bonding, or self-piercing rivets.

### MIG or TIG — which should I specify?

MIG where deposition rate matters: 5–12 lb/hr (2.3–5.5 kg/hr) versus under 2 lb/hr for TIG. TIG below about 0.060 in (1.5 mm), for titanium and other reactive metals, and where the bead is a visible design feature, because heat and filler are controlled independently.

### How much distortion should I expect from welding?

Weld metal shrinks 3–5% by volume as it solidifies, producing transverse shrinkage across the joint and angular rotation of the plates. Without hard fixturing, ±1/16 in (1.6 mm) over a 3 ft (1 m) weldment is normal. Balanced sequence, back-stepping and the smallest adequate weld are the practical controls.

### When does carbon steel need preheat before welding?

AWS D1.1 sets preheat from thickness and steel group, and typical structural carbon steel above 3/4 in (20 mm) calls for 150–300 °F (65–150 °C). Preheat slows cooling through the martensite range, lowering HAZ hardness and giving diffusible hydrogen time to escape before the joint is cold.

## Alternative processes

- [Soldering and Brazing](https://manufacturingprocesses.org/processes/joining/soldering-and-brazing.md): Soldering and brazing join metals with a molten filler that wets the joint by capillary action while the parent metal stays solid.
- [Riveting](https://manufacturingprocesses.org/processes/joining/riveting.md): Riveting sets a rivet through aligned holes and upsets its tail so the joint clamps permanently, with no heat and no access to both sides for blind types.
- [Adhesive Bonding](https://manufacturingprocesses.org/processes/joining/adhesive-bonding.md): Adhesive bonding joins parts with a cured polymer layer that spreads load over the whole bond area instead of concentrating it at fastener points.
- [Mechanical Fastening](https://manufacturingprocesses.org/processes/joining/mechanical-fastening.md): Mechanical fastening joins parts with screws, inserts, clinch hardware or snap fits so the joint can be assembled and taken apart again.

## Related processes

- [Resistance Welding](https://manufacturingprocesses.org/processes/joining/resistance-welding.md): Resistance welding passes a heavy current through the joint so its own electrical resistance melts a nugget between the sheets.
- [Power Beam Welding](https://manufacturingprocesses.org/processes/joining/power-beam-welding.md): Power beam welding fuses metal with a laser or electron beam focused to a very small spot, producing deep, narrow welds with little distortion.
- [Friction Welding](https://manufacturingprocesses.org/processes/joining/friction-welding.md): Friction welding rubs two parts together under load until the interface plasticises and forges together, with no melting and no filler metal.
- [Sheet Metal Fabrication](https://manufacturingprocesses.org/processes/forming/sheet-metal-fabrication.md): Sheet metal fabrication cuts, bends and joins flat stock into a finished assembly, typically laser cutting followed by press braking, hardware and welding.
- [Heat Treatment](https://manufacturingprocesses.org/processes/forming/heat-treatment.md): Heat treatment cycles metal through controlled heating and cooling to change its hardness, strength, ductility or internal stress state.

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*Source: [Manufacturing Processes](https://manufacturingprocesses.org/processes/joining/arc-welding)*

*Last updated: August 11, 2026*