Welding has been around in some form or fashion since the 4th century A.D., but modern welding techniques fueled the industrial revolution and are crucial to many modern industries.
Welding is a very broad term covering hundreds if not thousands of specific materials joining processes. Even if you are not a welder by trade or a materials joining engineer, understanding how various materials can be joined is crucial to excelling in your engineering profession. To start off our understanding of welding processes, let me throw out a bunch of acronyms and terms, then we can dive into specific processes a little later on.
The main welding processes are shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW/TIG) gas metal arc welding (GMAW/MIG), flux-cored arc welding (FCAW), submerged arc welding (SAW), electroslag welding (ESW), and lastly resistance welding. Did you get all that? Those are only the basic welding methods, and there are many different variations of each, along with techniques that weld using friction, lasers, or even electron beams. Each process is specifically designed for different metals, and there are even processes that can weld dissimilar metals. There’s no way we can cover an extensive review of all the welding processes in this blog post, but we can probably cover enough so you can keep up in a conversation about welding, if you ever find yourself in one of those…
All welding processes induce fusion through some energy source, in other words, the base metal is melted in some way. Processes like SMAW use an electrode that melts to both induce fusion on the base metal and act as a filler metal for the joint. GTAW, or what you might know by the name of TIG welding, uses a tungsten electrode and an inert gas (helium) to weld the base metal. What you will find in common between all of the processes mentioned above, is that there is some form of arc or electrode being used to spark the fusion reaction, thus the “A” in all of the acronyms. The only exception in the list above is resistance welding, which uses electric current to generate heat through the resistance of two overlapping metals; simply a slightly different use of electricity to weld.
Arc welding is the most common, but it is important to note that there is also gas welding and energy beam welding. These processes use gas or energy beams to heat up the material, rather than current and voltage. Gas and energy methods, while variant, are fairly simple to understand in basic mechanics. Each different arc technique uses a different electrode and a different setup of applying flux to the weld. Flux, is a purifying agent that helps welds bond materials and maintain uniform structure, therefore increasing strength.
For most of the welding techniques, you can somewhat infer how they work from their names. We are engineers after all, right? Flux-cored arc welding uses a wire with, you guessed it, a flux core. Contrary to what you may think, submerged arc welding isn’t an underwater process. It uses a consumable electrode to weld under a blanket of flux, therefore submerging the weld under the flux to keep it safe from the atmosphere. Now that we have some background on all of the various welding techniques, we can begin to understand how to weld various metals.
Instead of writing tons of text going into the welding of different metals, here’s a quick guide demonstrating the joining metal along with the processes you can use:
Steel: SMAW, MIG, FCAW, TIG (DC), Resistance
Stainless Steel: SMAW, MIG, FCAW, TIG (DC), Resistance
Aluminum: SMAW, MIG, TIG (AC)
Cast Iron: SMAW
Copper/Brass: TIG (DC)
Magnesium Alloy: TIG (AC)
Titanium: TIG (DC)
As you probably noticed iron based metals can be welded with various techniques, but other metals with less compatible cell structures take specific techniques to weld. The reason behind both steel’s wide range of techniques and other metals specific techniques has to do with cell structure, phase changes, melting points, and many other factors.
If you want to join two dissimilar metals, say, aluminum to steel, welders have to get creative in their techniques. The most common way to weld dissimilar metals, or metals not compatible with each other, is to use a filler metal that is compatible to both. In the case of aluminum and steel, zinc can be used as a transition metal, or special transition inserts can be fabricated. If you want to learn about the welding of dissimilar metals, these processes are on the cutting edge of materials joining techniques. Groundbreaking research is continually being made in the areas of friction-stir welding, laser welding, and even explosive welding (Google it, you won’t be sorry).
Welding is both an incredibly simple thing to grasp, yet also a process filled with endless complexities and sciences. Whether you use it on a daily basis or not at all, welding has aspects of almost every engineering discipline, and can surely captivate even the most dull of engineers.