I’m sure many of you have tried your hand at welding in your shed or garage, or have a family member which plays around building things from time to time. For most hobby welders, you simply have to plug in the machine, choose the settings from a door chart, press the trigger and you’re away! (Ok maybe there’s a bit more than that). But what about the physics of how the arc is created and how different gases affect the weld?
To start with you need to think about the makeup of an atom. An atom is comprised of a nucleus formed of protons and neutrons which are orbited by negatively charged electrons. It is this flow of negative electrons which produces electricity.
For these electrons to flow, causing electricity and thus forming an arc, they need to be able to jump from atom to atom.
In MIG welding, you will have a wire which has a positive charge, and a base metal that will have a negative charge. But there will be a space between these two elements so the electrons won’t be able to jump from one atom to another because electrons do not pass through the air very well.
To bridge this gap, you need to use shielding gas to transfer the electrons. Different shielding gases have different ionisation properties and will affect the weld and electricity in a range of ways producing different results.
The most common gases used are Helium, Carbon Dioxide, Argon, and Oxygen.
e.g. 1 Helium
So in our first example let’s imagine we’re welding with Helium.
Helium is an atom which has a nucleus that is orbited by two electrons. The ionisation of an atom refers to the ability of an atom to release electrons and transfer them to the next element. This is was creates the current flow/amperage.
As this Helium atom is heated up, electrons will be released and the charge will flow through the gas.
e.g. 2 Argon
The difference with Argon is that an Argon atom is orbited by a whopping 18 electrons.
This means that not as much heat will be required to release the electrons for the current to flow.
So Argon requires a lower arc voltage and amperage in order to become conductive.
When choosing your welder you will have to choose one of two polarity settings. These are:
- Straight Polarity (DC electrode negative)
- Reverse Polarity (DC electrode positive) – used for MIG/GMAW Welding.
The importance of polarity related to the direction that the electrons are flowing. For DC electrode positive (MIG) the electrons are flowing from the base metal to the electrode. You will need to switch this over when doing flux cored welding.
Hopefully this has given you a better understanding of what exactly is happening at a particle level when you’re welding. If you haven’t tried welding, give it a go! It’s great fun and you’ll be surprised at how easy it is even if you have no experience in it at all.