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Practical TIG Welding: Mild Steel

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Mild Steel


00:00 - In this section of the course, we're going to focus on the materials commonly used in motorsport fabrication.
00:05 Each material has its pros, its cons and its own nuances that need to be understood before your tungsten gets anywhere near them.
00:13 Let's start with the most widely used of them all, mild steel.
00:17 Its strength, availability and price make it a great all rounder for not only motorsport use but general fabrication too.
00:25 The term mild steel covers a wide range of low carbon steels that are inherently ductile and great for learning and perfecting our TIG welding skills.
00:34 Mild steel doesn't carry as much risk or cost for beginners learning to TIG weld and is perfect for optimising our parameters like amperage, arc length, travel speeds and filler rod feed input.
00:47 Because the material is more ductile, it can cope with a larger amount of heat input without having a great effect on its strength.
00:54 When choosing what material we'll be using for our TIG welding project, first we should weigh up our options and our intended outcomes.
01:03 For example, for the majority of us working on our own vehicles at home, the weight savings of using a higher carbon steel like chromoly won't be justified in the added expense and complexity of the fabrication process.
01:16 Let's take a roll cage for example which could require around 20 metres of tube.
01:21 By choosing chromoly over mild steel we can save around 12 kg in comparison to the same cage constructed from a mild steel tube such as CDS 1020.
01:31 This weight saving is due to our ability to choose a thinner wall thickness in chromoly tube due to its superior strength over mild steel.
01:40 This also costs us around a third more than our mild steel cage and will result in a more involved fabrication process which we'll look at closely in the next module.
01:51 This may be all well and good if you're an experienced TIG welder trying to save every gram for a professional motorsport series but for the majority of us, 12 kg would be difficult to justify.
02:02 That money is likely to be much better spent in other areas.
02:05 That also means that mild steel is going to be the best option for many of us.
02:10 Some mild steels will be hot rolled which leaves a darkened mil scale on the surface.
02:15 If this is the case then it's essential that we remove this with a linisher to expose the shiny surface beneath to achieve the best quality weld possible.
02:24 Cold rolled mild steel won't have the scale but still benefits from a quick polish with sandpaper or scotch brite before finishing the preparation of the material with a wipe with acetone to remove any oils or contaminants on the surface.
02:38 When TIG welding mild steel, there are a few good options for filler rod but the most common choice is the ER70S-2 in either 1.6 or 2.4 mm diameter.
02:51 This is a standard mild steel filler rod and like the material, it's easy to get your hands on.
02:56 It's also important to recognise that mild steel will make up the majority of sheet metal in factory vehicles and when we're modifying them we're often tasked with TIG welding to this sometimes extremely thin sheet metal.
03:09 ER70S-2 or S-6 is a great filler that'll match these metals and structurally join them together.
03:17 Although mild steel is great to weld, it does have some downsides.
03:20 First off, it's often painted, oiled or has the mil scale that we just discussed which requires preparation before we can begin welding.
03:29 It also lacks elements that fend off oxidation that forms as rust which means that unfinished projects or exposed areas will need to be oiled or painted prior to storage.
03:40 A good weld on mild steel should look shiny and silver with some potential blue and purple discolouration.
03:47 A brown or grey weld indicates poor torch positioning, poor shielding gas coverage or excessive heat input.
03:54 Any pin holes or craters that are present in our weld will require immediate attention and this points to inadequate shielding gas coverage or potentially contamination of the weld.
04:05 In our resources section you'll find a PDF that lists baselines for all settings when working with mild steel.
04:11 It's a good idea to print this out and have it next to your machine for easy reference.

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