Welding isn’t just fire and sparks—it’s science, technique, and experience coming together to join metal in ways that last. Whether you’re fusing 8mm mild steel plates in a structural beam or laying a precision TIG weld on a stainless tank, understanding how welding works is key to doing it right.
This section breaks down what welding really is, how it works, and what goes into a sound weld. I’ll also share what we’ve learnt at Australian General Engineering (AGE) after years on the tools—from handheld MIG guns to automated TIG cells running stainless tube.
What Welding Actually Does
At its core, welding is the process of permanently joining two or more materials—typically metals—by applying heat, pressure, or both. In most welding methods, the base materials are melted and fused together, often with the help of a filler material, to form a single, continuous joint.
Key Characteristics of Welding:
- Heat or pressure (or both) applied to base material
- Materials reach fusion temperature
- Optional filler metal added to strengthen the joint
- Joint solidifies into a single structure upon cooling
This is what sets welding apart from other joining methods like bolting, riveting, or brazing—welding actually transforms two separate pieces into one.
Components of a Welding Process
To weld correctly, three main components must work together in harmony. We use this understanding every day at AGE when specifying weld procedures for fabrication jobs across Melbourne and regional Victoria.
1. Heat Source
Every weld starts with energy. It’s what melts the base metal and filler.
Common welding heat sources:
- Electric Arc (used in SMAW, MIG, TIG, FCAW)
- Gas Flame (oxy-acetylene welding)
- Laser Beam
- Electron Beam
- Frictional Heat (friction welding, ultrasonic)
In fabrication environments like ours, we primarily use electric arc processes due to their control, speed, and adaptability.
2. Shielding
Molten metal is reactive. When exposed to oxygen or nitrogen in the air, it can become brittle or porous. That’s where shielding comes in—protecting the weld pool from contamination.
Shielding Methods:
- Shielding gases: Argon, helium, carbon dioxide (used in MIG and TIG)
- Flux coatings: Found in stick electrodes (SMAW) or flux-cored wires (FCAW)
Tip from the field: In coastal or windy environments—like Portsea or Torquay—we often choose flux-cored wire or stick welding over MIG, because shielding gas blows away in high wind.
3. Filler Material
Not all welds need filler, but most structural joints do. Filler metal helps bridge the gap and reinforces the connection.
Types of filler:
- Wire (used in MIG/FCAW)
- Rod (used in TIG)
- Electrode (used in SMAW)
The filler should match the mechanical properties and corrosion resistance of the base metal. For example, 316 stainless filler for marine-grade steel structures.
Phases of a Typical Welding Operation
Let’s break down how a weld is actually laid out, whether it’s a basic butt joint on 3mm plate or a complex multi-pass weld in a pressure vessel.
Phase 1: Tack Welding
Before committing to a full weld, we use small tack welds to hold the parts in alignment. These tacks are strong enough to prevent movement during welding but easy to grind out if adjustments are needed.
Phase 2: Bead Welding
Once everything is aligned, we run the full welds—called “beads”—across the joint. Depending on the thickness and load requirements, this might be:
- Single-pass weld (common in light sheet metal)
- Multi-pass weld (used in heavy fabrication, e.g., 10mm plate or thicker)
Key Variables That Influence Weld Quality:
|
Parameter |
Effect on Weld |
|
Welding current & voltage |
Controls penetration and bead profile |
|
Travel speed |
Affects bead width and risk of defects (e.g., undercut, porosity) |
|
Arc length |
Short arc = better control; long arc = more spatter |
|
Electrode angle |
Influences heat focus and bead shape |
|
Filler feed rate |
Impacts joint strength and weld fusion |
In our shop, our welders are trained to read weld puddle behaviour and adjust on the fly—a skill that separates a good weld from a reject.
Types of Welding by Process
Welding isn’t one-size-fits-all. Different jobs need different processes. Below are the most widely used welding methods across Australian fabrication shops, job sites, and maintenance yards.
1. Shielded Metal Arc Welding (SMAW)
Also known as stick welding, SMAW is one of the most rugged and flexible processes.
- Best for: Outdoor work, pipelines, repairs, structural steel
- Why we use it: Works in wind, doesn’t need gas bottles, simple gear setup
We’ve used SMAW on-site in Gippsland to repair irrigation gates where a MIG machine just wasn’t practical.
2. Gas Metal Arc Welding (GMAW / MIG)
Uses a spool-fed wire electrode and shielding gas. It’s fast and ideal for clean, production-line welding.
- Best for: Fabrication shops, trailers, mild steel work, stainless enclosures
- Why we use it: Speed and control—great for repeatable work in mild environments
At AGE, most of our standard structural jobs are MIG welded using solid wire and Argoshield gas.
3. Gas Tungsten Arc Welding (GTAW / TIG)
Uses a tungsten electrode and is known for clean, precise welds. Filler rod is fed manually or not at all.
- Best for: Thin stainless, aluminium, precision jobs
- Why we use it: Cosmetic quality and precision on critical parts
I recall welding a polished stainless brewery tank for a microbrewery in Brunswick—TIG was the only way to get the hygiene level and finish they wanted.
4. Flux-Cored Arc Welding (FCAW)
Similar to MIG, but with a hollow wire filled with flux. Can be self-shielded or dual-shielded.
- Best for: Heavy fabrication, shipbuilding, outdoor structural welds
- Why we use it: High deposition rates and deep penetration
Great for welding thick sections where MIG might struggle to penetrate without multiple passes.
5. Laser, Friction, and Electron Beam Welding
These are specialist processes used in aerospace, medical devices, and high-tech manufacturing. They’re not common on a general workshop floor, but when tolerance matters, they shine.
- Example Use: Electron beam welding of titanium fuel cells for drones near Avalon
- Friction Stir Welding: Now being trialled on aluminium bus chassis for electric vehicle fleets
Common Joint Types in Welding
Different applications require different joint types. At AGE, we design and fabricate everything from basic fillet joints to full-penetration groove welds for load-bearing parts.
Common Joint Configurations:
- Butt Joint – Two pieces end-to-end; common in pipe and plate
- Lap Joint – Overlapping plates; often spot welded
- T-Joint – Vertical to horizontal; widely used in frames and brackets
- Corner Joint – Used in boxes, enclosures
- Edge Joint – Sheets joined at their edges; often TIG welded
Knowing the right joint type helps with both design efficiency and weld quality.
The Metallurgy Behind a Good Weld
This part doesn’t get enough attention. When you weld, you’re changing the microstructure of the metal. Cooling rate, heat input, and metal composition affect strength, ductility, and resistance to cracking.
Tips We Use at AGE to Manage Metallurgy:
- Use preheating on high-carbon steels to prevent cracking
- Avoid fast cooling rates to reduce residual stress
- Use correct filler wire to match mechanical properties
- Post-weld heat treatment where required (e.g. boiler codes)
Every WPS we develop takes metallurgical outcomes into account—especially for pressure-rated or structural parts.
Understanding what welding is, and how it works, goes far beyond striking an arc. It’s a blend of heat control, material science, process selection, and hands-on skill. From the shielding gas to the travel speed, every detail matters—because a weld doesn’t just look right, it has to be right.
In our work at Australian General Engineering, we’ve seen how foundational knowledge and trained hands produce strong, safe, and reliable welds—whether in a factory in Mordialloc or a field site in Moe. As materials and applications evolve, the principles of welding stay the same: know your material, control your process, and never stop learning.
