Tenterfield Star

MIG welding fundamentals: Mastering mild steel techniques

This guide will give you with the knowledge and confidence to tackle your steel welding projects like a pro. Picture Shutterstock
This guide will give you with the knowledge and confidence to tackle your steel welding projects like a pro. Picture Shutterstock

Metal Inert Gas (MIG) welding, technically known as Gas Metal Arc Welding (GMAW), is a versatile arc welding technique, utilising a continuous, solid wire electrode that's fed through a welding gun into the weld pool to fuse two materials. Accompanied by a shielding gas that flows through the gun, it safeguards the molten weld pool from airborne contaminants.

Renowned for its adaptability, MIG welding empowers a diverse range of welders, from hobbyists and artists to farmers and DIY enthusiasts, to perform a breadth of fabrication and maintenance tasks on materials as thin as 24-gauge or as robust as half an inch thick. Its reputation for ease of learning makes it a go-to method for many, allowing for rapid skill acquisition with the right guidance and practice.

A range of miller welders are available in the market to cater to different needs, but mild steel is one of the most commonly welded materials. Its high strength and low cost make it a popular choice for various applications, from automotive and structural projects to household repairs.

In this guide, we will cover some essential techniques for mastering MIG welding on mild steel. From setting up your equipment correctly to proper technique and troubleshooting common issues, this guide will provide you with the knowledge and confidence to tackle your mild steel welding projects like a pro.

Prioritising safety in MIG welding

Before initiating any welding procedure, prioritising safety is paramount. Ensure you are fully equipped with the appropriate protective gear. High-quality safety apparel is your first line of defence against the inherent risks of welding. This includes durable leather footwear, cuff-less trousers that offer full leg coverage, and a flame-resistant jacket with long sleeves to shield against sparks and heat.

Adequate hand protection is achieved with a pair of robust leather gloves designed for welding tasks. A crucial element to your safety ensemble is the welding helmet, complemented by safety glasses to safeguard your eyes from ultraviolet and infrared rays.

Lastly, don't forget a bandana or skull cap to protect your scalp from stray sparks. Miller takes your safety seriously, providing an extensive selection of safety accessories that cater to the spectrum of welders, from casual hobbyists to dedicated professionals. Additional safety recommendations and precautions can be found in your owner's manual, which should be reviewed diligently to maintain a secure welding environment.

Setting up for MIG welding success

The preparation of your metal is a critical first step that cannot be overlooked. In MIG welding, the solid wire electrode doesn't have inherent cleaning capabilities, so it is crucial to ensure the metal surface is free of contaminants. A thorough cleaning with a metal brush or grinder down to shiny bare metal is essential for optimal results. Be especially vigilant about the connection point for your work clamp, as a good electrical ground is fundamental for consistent wire feeding and effective welding.

For projects involving thicker metals, a bevelled joint is key to achieving deep penetration and a strong, resilient weld, particularly for butt joints.

With the metal prepped, you're ready to set up the welding machine:

  • Inspect the cables: Start with a thorough inspection of your cables, ensuring connections are secure and free from damage to prevent any electrical hazards and maintain optimal performance.
  • Establish correct polarity: Set your machine to DC electrode positive (DCEP), or reverse polarity, to align with MIG welding requirements. Connections for this adjustment are commonly located within the interior of the machine.
  • Optimise gas flow rate: Activate the shielding gas, adjusting the flow typically between 20-25 cubic feet per hour to protect your weld. Check the gas hose for leaks by using a soapy water solution; if bubbles form, replace the faulty hose immediately.
  • Adjust tension: See to it that the tension on the drive rolls or wire spool hub is neither too tight nor too loose by referring to your machine's owner's manual for the proper setting.
  • Maintain consumables: Regularly clean away spatter from contact tubes, switch out worn contact tips and liners, and replace any rusty wire to ensure the quality and consistency of your welding output.

Selecting the right shielding gas for mild steel MIG welding

The selection of shielding gas is a crucial element in MIG welding, impacting the weld's overall quality, penetration, and appearance. For MIG welding mild steel, two prevalent options are primarily used:

  • Argon/Carbon Dioxide Mix (75/25): Frequently referred to as 75/25 or C25, this blend couples the advantages of both gases. The argon contributes to a stable arc and minimises spatter, resulting in cleaner beads and a more attractive finish. It is ideal for multi-purpose applications and especially beneficial when working with thinner metals to prevent burn-through.
  • Carbon Dioxide (100% CO2): A cost-effective choice, 100 per cent CO2 allows for deeper weld penetration, which is beneficial when dealing with thicker steel sections. However, it can lead to increased spatter and a more pronounced cleaning effort post-weld. The bead appearance is generally less smooth compared to the 75/25 mix.

Your choice will depend on the specific requirements of your project, balancing between aesthetics, weld penetration, and cost considerations.

Fine-tuning your MIG welding technique on mild steel

Mastering MIG welding not only involves setting up your welder properly but also honing your technique to produce strong and clean welds consistently. When welding mild steel, precise control over your wire stick-out and gun angles can significantly affect the outcome.

  • Optimise wire stick-out: Keep the wire stick-out to approximately 3/8 inch for optimal arc control and minimise spatter. This length of exposed wire is crucial for maintaining a steady, bacon-sizzle sound, indicating a healthy weld. If the sound is erratic, check for excessive stick-out, which is a common mistake among welders.
  • Choose the right technique - Push vs. Pull: For a flatter and wider bead with less penetration, employ the push technique, pushing the gun forward and allowing a clear view of the joint and weld puddle. Conversely, the pull technique will yield deeper penetration and a narrower bead, by dragging the gun at an angle and focusing the arc on the leading edge of the puddle.
  • Travel angle considerations: Maintain a travel angle between 5 to 15 degrees, whether welding flat, horizontal, vertical, or overhead. A travel angle that is too steep can cause more spatter and less penetration, which might compromise the weld integrity.
  • Adjust work angle with joint configuration: Your work angle must adapt to the specific joint you're welding. For example, a T-joint will require different positioning of the gun compared to a lap or butt joint. Always aim to direct the arc into the leading edge of the weld pool, ensuring proper fusion of the materials.

Honing these techniques can bring your MIG welding prowess to new heights, resulting in sturdy, visually appealing welds on mild steel.