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Top Tips for Welding Mild Steel

Date: 18-10-2023

Top Tips for Welding Mild Steel - Alphaweld

Welding mild steel is relatively easy once you set your equipment correctly and apply some handy tips you'll learn in this guide. Mild steel is the least challenging material for welding, thanks to good ductility and flexibility. So, if you get some basics right, your welds will likely hold and achieve deep penetration.

Welding Safety and Personal Protective Equipment (PPE)

Welding is a dangerous occupation that requires wearing adequate PPE, whether you are welding professionally or working on a DIY project. Arc welding processes create immense UV and IR radiation that can harm your eyes and affect the quality of your vision. In addition, welding poses electrocution, flash burns, and respiratory hazards. So, it's vital to strictly follow fire and electricity safety procedures and wear the following PPE:

Auto-darkening welding helmet - Protects your eyes from arc flash and harmful UV/IR radiation. 

Welding gloves - Prevents skin burns and helps you manipulate a heated torch and welded metal.

Welding jacket and apron - Protects your body from sparks and molten spatter. Ensure a snug fit without crevices or openings where molten metal can latch on.

Welding respirator - Captures harmful welding fumes and reduces the amount of metal oxides you can inhale while welding.

Choosing Your Welding Process

Welding mild steel is easiest with the MIG welding process, but you can also use gasless MIG (flux-cored) and stick welding processes. In addition, you can use the TIG welding process when weld quality and aesthetic appearance are paramount. But, for most welding jobs, the MIG and gasless MIG are the best choices thanks to their ease of use and good finish quality.

The MIG welding process requires a shielding gas, while gasless MIG doesn't. These are wire welding processes, which means that the wire feeder automatically feeds the welding wire that acts as an electrode and a filler metal. Once the wire touches the welded metal, it short-circuits, melts, and deposits into the weld puddle. Gasless (self-shielded) MIG wires have a special flux compound in their core (hence the name "flux-cored"), which acts as a shielding agent against atmospheric contamination. In contrast, standard MIG wires require a shielding gas to prevent porosity and contamination.

Top Tips for MIG Welding Mild Steel

We’ll now focus on MIG welding mild steel, but we'll also share some tips for gasless MIG in case you prefer not to use a shielding gas. 

Choose a Suitable MIG Wire

We recommend using the ER70S-6 solid wire for MIG welding mild steel for most jobs. It contains additional deoxidizers and allows for welding dirtier metal, but pre-cleaning is always vital for quality welds. For gasless MIG, you can use the Lincoln Innershield E71T-8 for most jobs or choose any of our self-shielded flux-cored wires for specific applications. 

Use the Right Shielding Gas

The best shielding gas for MIG welding mild steel is the popular 75% argon and 25% CO2 mixture. It's often referred to as the "MIG gas," and almost every welding gas supplier will have it stocked. 

You can also use 100% CO2 to MIG weld mild steel, but the arc will likely get too erratic without the argon to keep it steady. However, welding thick mild steel benefits from pure CO2 because this gas improves penetration. You’ll need a special CO2 regulator if you wish to use 100% CO2. Standard regulators for argon/CO2 mix can freeze from pure CO2, so you'll need a heated regulator like the Lincoln CO2

Preparing the Mild Steel

Before welding, you should pre-clean the welding joint to remove any oil, paint, and rust. It's best to use a grinding wheel to lightly remove the top layer and make a shiny-clean metal surface.

When welding thick mild steel, you may also need to prepare the edges by grinding the joint into a single-bevel or double-bevel (V-groove) configuration. This will help you achieve adequate weld penetration, but you'll need to deposit more wire into the joint since it will become wider. Our guide on the most common types of weld joints can help you with joint preparation to find the best joint configuration.

Set Your Welder Correctly

MIG welders don't have amperage settings like stick or TIG welders. Instead, MIG machines have a wire feeding speed (WFS) and voltage as the two primary settings. However, WFS acts as an amperage setting. The higher the WFS, the higher the amperage output.

The voltage setting is responsible for arc length and weld bead width and profile. But, both WFS and voltage must be in synergy to produce a good result.

Regardless if your welder is small and portable, like the Lincoln Electric Power MIG 180C, or an industrial-grade machine, like the Weldmax 350 SWF, every welder has the manufacturer's recommended settings for the material type and thickness. This chart is a great starting point, but you can fine-tune your MIG machine settings to match your preferences depending on the welded position and travel speed. Check your owner's manual for recommended settings if the machine doesn't have the chart printed on its body or inside the spool wire compartment.

Stagger Your Welds When Welding Thin Metal Sheets

While you can run straight beads when welding medium-thickness and thick mild steel plates, you'll need to stagger the welds when welding thin sheets. Concentrating too much heat at one spot can lead to burn-through and warping on thin materials. So, spacing the welds apart gives the material time to cool off between the welds. 

Placing the welds strategically can also prevent warping. It's a good idea to move incrementally from the ends of the joint to its centre so that at no point does one end of the joint have too many welds. That way, you'll have a better chance to prevent unequal heat input and warping.

Push vs Pull

Pushing the MIG gun ahead of the weld puddle gives you a better view of the puddle but reduces penetration, which is desirable when welding thin metal. Pulling or dragging the MIG torch away from the deposited metal produces deeper penetration and more of a weld build-up. You can use either of the two, but it's best to stick to pulling the torch for thick metals and pushing for thinner materials.

Travel Angle

Keep your MIG torch at an angle of about 5-15 degrees relative to the gun in a perpendicular position. Higher than 20-degree travel angles can cause arc instability and increased spatter.

Need More Help with Welding Mild Steel?

If you need help choosing welding equipment for working with mild steel, the experts at Alphaweld are here for you. To speak now with an expert, call (08) 9456 8000 or send us an enquiry and we’ll gladly assist you.