What is MIG welding and how does it work?

MIG welding, also called wire welding or gas metal arc welding (GMAW), is a way to join metal pieces together. It uses electricity to melt a metal wire that bonds the pieces together. This wire acts as both the heat source and the material to fill the joint.

Unlike TIG welding, which uses a tungsten electrode to directly heat and join metals, MIG welding feeds a consumable wire electrode into the weld pool. This makes it easier and faster to join metals.

In this blog, we’ll answer common questions about MIG welding and discuss its advantages and disadvantages in straightforward terms.

MIG welding uses a special power source that keeps the voltage steady. This makes an electric spark that melts the metal you’re working with. At the same time, a thin wire keeps feeding into the welding tool. This wire fills the gap between the pieces of metal you’re joining. Another gas is sent through the tool too. It keeps the area around the melted metal safe from getting dirty from the air.

MIG welding is great for big projects, like making metal gates. It’s faster than TIG welding, so projects get done quicker and cost less. Plus, it’s easier to learn. The welds it makes usually don’t need much cleaning or finishing. But if you need very exact, strong, and super clean welds, TIG welding is the better choice.

The MIG welding process

Welding makes strong connections to build sturdy structures. MIG welding is one method where cleanliness is crucial. Before starting, it’s important to clean the area well. MIG electrodes don’t work well if there’s rust, dirt, or oil around. Starting with a clean surface helps the welding process go smoothly and ensures strong joints.

1. Position and angle

When MIG welding, how you position the gun is crucial. There are two main angles to consider:
Travel Angle: This is how you tilt the gun away from perpendicular (straight up and down) as you weld along the joint. For most welding, keep the travel angle between 5 to 15 degrees. If you tilt the gun more than 20 to 25 degrees, you might get more spatter (small bits of molten metal flying around), less penetration (how deeply the weld goes into the metal), and the welding arc might not stay steady. Work Angle: This is how you point the gun relative to the angle of the welding joint. The exact angle can change depending on whether you’re welding on a flat surface, horizontal, vertical, or overhead. The goal is to find the best angle that helps melt the metal evenly without the filler metal sagging or rolling off the joint.

So, keeping the right travel and work angles helps you get a good weld that holds together well and looks smooth. Adjusting these angles correctly for each welding job is key to getting good results.

2. Speed

How fast you move the welding gun affects how the weld looks and how strong it is. Skilled MIG welders decide how fast to move by looking at how big the melted metal puddle is compared to the thickness of the metal they’re joining.

3. Modes of metal transfer

Short-circuit welding: uses lower current and voltage, resulting in less heat. It’s good for welding thin sections and in tricky positions. But, it can struggle with thick sections or multiple passes, sometimes leaving gaps in the weld.

Globular transfer: needs higher current and voltage than short-circuiting. It makes big, uneven drops of metal. This type works best for flat welding. However, it might not give consistent depth or smoothness in the weld.

Spray welding: cranks up current and voltage even more, like a powerful water hose. It’s great for thicker materials because it melts tiny droplets that dive deep into the weld. Spray welding gives strong, tidy welds with very little mess.

Pulsed mode: uses less heat, which is perfect for thinner materials. Metal goes in controlled droplets, making clean welds without splashes.

Materials used in MIG welding
let’s explore MIG gear and materials and what they do in the process:

Wire electrode

MIG welding uses an electrode that not only conducts electricity but also provides filler material to join metals together. There are two main types of wire electrodes: hard wire and flux-cored wire, each suited to different projects and metal types.

Hard wire is popular among MIG welders because it’s affordable, easy to control, and can be used effectively at various angles. It typically requires a shielding gas made up of 75% argon and 25% carbon dioxide to protect the weld from contamination and ensure quality.

On the other hand, flux-cored wire includes flux material within the wire itself, eliminating the need for an external shielding gas. This makes flux-cored welding advantageous for outdoor and windy conditions where gas shielding can be challenging. However, a drawback is that flux-cored wires produce slag during welding, which needs to be cleaned off after welding to achieve a smooth finish.

Inert gas

In MIG welding, shielding gas is crucial to protect the welding pool from contamination and maintain the integrity of the metal being joined. Typically, gases like argon and helium are chosen based on the specific material and welding requirements. These gases shield the weld area effectively without altering the properties of the metal. Sometimes, a mix of gases, including semi-inert ones like carbon dioxide, is used to balance cost and welding performance.

Carbon dioxide, being less expensive than argon and helium, allows for deeper penetration into the metal during welding. However, it tends to increase spattering, which can affect the weld’s appearance and cleanliness. In certain situations, small amounts of non-inert gases are added to enhance metal penetration further. Yet, the presence of oxygen from these gases can lead to rust and oxidation on the weld, potentially compromising its quality if not managed properly. Therefore, choosing the right shielding gas is critical to achieving strong, clean welds that meet specific application needs while controlling costs and ensuring welding efficiency.

Welding torch

A welding torch, also known as a welding gun, is a special tool used to melt and join metals together. MIG torches are quite versatile because they can be used with different types and thicknesses of metal. These torches are divided into two main types based on how they are cooled.

Gas-cooled welding torches are simpler and cheaper. They work well for smaller projects but can overheat if used for long periods. On the other hand, water-cooled welding torches can handle higher levels of heat and power. They provide better control over the welding process, especially the tip where the metal melts. However, they are more expensive, costing about 20-30% more than gas-cooled torches, and they require a special water-cooling system in the welding machine.

Power source

In modern MIG welding, the equipment automatically adjusts the welding current based on changes in arc length and wire feed speed. This feature ensures a stable weld puddle, which is crucial for achieving consistent bead quality and weld penetration. MIG welding predominantly uses DC positive polarity (DCEP), where electrons flow from the electrode’s contact tip to the base metal. This polarity setting offers excellent arc stability, reducing spatter and enabling effective welding of both thick and thin materials.

On the other hand, TIG welding can utilize both DC and AC power sources. When welding aluminum, AC (alternating current) is often employed. AC in TIG welding alternates between positive and negative currents rapidly. This alternating current provides a cleaning action, effectively removing the oxide layer from the metal’s surface before the weld. This is essential for achieving strong welds on aluminum, as the oxide layer can hinder fusion if not properly cleaned. AC in TIG welding allows for precise control over the welding process, ensuring high-quality welds with good appearance and mechanical properties.

In summary, while MIG welding typically operates on DC positive polarity for stability and versatility across material thicknesses, TIG welding uses AC specifically for welding aluminum due to its cleaning action that enhances weld quality and integrity.