Practical MIG Welding: Shielding Gas

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Shielding Gas

06.43

00:00	As we've already learned, in the MIG welding process, shielding gas is used to prevent exposure of the molten weld pool to the oxygen, nitrogen and hydrogen present in the atmosphere around us.
00:10	If we didn't shield these elements from the weld pool, it'd cause a variety of problems including porosity, spatter and damage to our consumables, not to mention compromising the strength of our weld.
00:21	Unlike TIG welding where we only use argon as the shielding gas, MIG welding uses a mixture of different shielding gases to suit the specific application.
00:30	Strictly speaking, MIG stands for Metal Inert Gas and when we introduce active gases into the MIG welding process, it's sometimes referred to as MAG welding which stands for Metal Active Gas.
00:42	First let's take a look at the types of shielding gases used for this process.
00:47	Argon, helium, carbon dioxide and oxygen are the four most common.
00:52	Each has its own advantages and will play a different role in altering the way the weld performs.
00:57	One important thing to note here is that if you're MIG welding a non ferrous metal, like aluminium, then your only option is going to be 100% argon.
01:06	Carbon dioxide or CO2 is the most common active gas used in MIG welding.
01:12	It's also the only one that can be used in its pure form without the addition of an inert gas like argon.
01:18	CO2 is also the least expensive of the common shielding gases, making it an attractive choice for large industries where material costs are the main priority.
01:28	Pure CO2 provides very deep weld penetration which is useful for welding thick material.
01:33	With that said, it also produces a less stable arc and more spatter than when it's mixed with other gases.
01:39	For many companies, especially those that place an emphasis on weld quality, appearance and reducing post weld clean up, a mixture of between 75 and 95% argon and 5 to 25% CO2 will provide a more desirable combination of arc stability, puddle control and reduced spatter than pure CO2.
02:00	Oxygen is also a reactive gas and is used in small ratios to improve weld pool fluidity, penetration and arc stability in low carbon and stainless steels.
02:11	Helium is generally used with non ferrous metals and stainless steels because it produces a wide deep penetration profile that's popular when working with thick materials.
02:20	This is usually used in ratios between 25 to 75% helium and 75 to 25% argon.
02:28	By adjusting these ratios, we can change the penetration, feed profile and travel speed to our needs.
02:35	Helium also creates a hotter arc which allows for faster travel speeds and higher productivity rates.
02:41	Now, that we have a brief understanding of the role that each of the individual gases play, let's look at the common MIG welding shielding gas bottles and the contents to get a better idea of what's available to us and what we should be using.
02:54	Bottles hold pressures of up to 20,000 kPa or 3000 psi and are available in a series of different sizes to suit specific applications.
03:03	The most common bottles are known as D size which hold around 2m3 while E size holds 4m3, F size holds close to 10m3 and G size holds 15m3.
03:16	We use a couple of products known in New Zealand as Argo Shield Lite and Argo Shield Universal.
03:23	As motorsport applications tend to focus on lighter material thicknesses, we don't need to have large amounts of CO2 that assist in penetration, but we do require weld stability and minimal spatter.
03:35	Argo Shield Lite consists of 3.1% oxygen, 5% CO2 and the remainder is argon.
03:41	Argo Shield Universal on the other hand consists of 2.75% oxygen, 16% CO2 and the remainder is argon.
03:49	As you can see the Argo Shield Universal has a larger amount of CO2 making it better suited to heavier fabrication.
03:56	The Lite on the other hand has a larger concentration of argon and oxygen which will assist in the stability of the arc.
04:03	Distributing this gas out of the high pressure bottle and into our MIG welding machines is the job of a regulator.
04:08	This will consist of 2 gauges, one which indicates the level of gas remaining in the bottle shown by the amount of pressure and the other indicates the flow rate of the gas entering the MIG welder when the internal solenoid is activated.
04:21	This is shown on the gauge as litres per minute or cubic feet per hour.
04:25	The majority of these regulators on the market will have a marked guide on the flow gauge indicating that MIG welding generally needs between 7-20 litres per minute.
04:34	The float style of regulator is more common in TIG welding, but can also be used for MIG welding.
04:40	This style of gauge uses a floating ball bearing and allows us to see the exact amount of gas exiting the regulator.
04:46	When fitting the regulator onto the bottle and the hose into the machine, it's important that all mating surfaces are clean and tight because we don't want any gas leaks out of our connections.
04:57	These gas fittings are designed to be a tapered seal so we don't need to use any thread tape or sealants.
05:02	If we did, then we'd almost certainly raise the chances of contamination in the weld.
05:07	How long each of these bottles will last is going to depend of course on our gas flow rate as well as how much welding we're actually doing.
05:14	You may need to consider your options with either outright purchase of these bottles or renting them.
05:19	The general consensus from most people we've spoken to in the industry is that a lot of money can be saved by purchasing the bottles outright and only paying for them to be filled when they need it.
05:29	Different locations can have different deals so it's a good idea to shop around and work out what's going to be best for you.
05:35	As you can see there's a lot of information on the different gases available for MIG welding, but don't get too hung up on trying all of the different mixes as this can be an expensive and time consuming job and this is usually only performed in industrial production processes.
05:51	Also note that if your MIG welding machine has a synergic mode, then it will have a list of the gases that it's programmed for so make sure that you check these out before shopping for your gas bottle.
06:01	Before we move on, let's quickly summarise what we've covered here.
06:05	Shielding gas in MIG welding prevents the molten weld pool being exposed to the atmosphere, avoiding issues like porosity and spatter.
06:13	Common gases include argon, helium, CO2 and oxygen, each influencing weld performance in different ways.
06:21	CO2 is affordable and offers deep penetration, but produces more spatter.
06:25	Argon CO2 mixes enhance arc stability and reduce spatter.
06:30	Oxygen will improve fluidity in low carbon and stainless steel while helium aids deep penetration and higher productivity in non -ferrous metals.