MIG welding is one of the most straight forward a versatile process suitable for various metal thicknesses. However, it does require attention to equipment, preparation, and technique. Let’s explore how to MIG weld thin sheet metal, medium-thickness steel, and thick plates effectively.

How Does MIG Welding Deal With Different Thicknesses?

MIG welding is a pretty easy process to master and perform, and once you get the hang of it, you can weld different thickness metal without any issues. However, it will take time, practice, and an understanding of the fundamentals.

First, you should know that MIG welding deals well with thin and medium-thick metal but not so great with thick metal. Luckily, we saved you hours of grunt work and compiled a straightforward guide on how to deal with each one of these.

MIG Welding Sheet Metal

Gas metal arc welding (GMAW or MIG) can be successfully used to weld thin metal, but as long as you take extra care. The heat input is the main issue with sheet metal of 24 gauge up to 14 ga. Thin metal is not so forgiving, so even the slightest heat over the recommended can cause distortion, wrapping, or burn-through.

Therefore, welding thin metal requires adequate equipment, preparation, and technique. When chosen right, each of these will limit the heat and allow you to control the weld puddle perfectly.

Equipment

Use a MIG welder with low amperage capabilities. With MIG welders, that’s most commonly 20-30 amps, so you want to go as low as possible with thin metals. Ideally you would want to use a welder  with pulsed MIG feature for better heat control. This feature pulses the heat of the welding arc, allowing you to control heat while providing excellent arc stability and low spatter. Aesthetically, you can achieve TIG welding results with your MIG machine. 

Next is to choose a suitable filler wire diameter matching your base metal. Keep in mind that the filler wire diameter should not be thicker than your base metal. Welding 304 stainless steel requires either ER308, ER308L, or ER308LSI wires, while aluminium will need a general-purpose ER4043 aluminium wire.  

Shielding Gas

Shielding gas plays a crucial role in welding, protecting the weld puddle from contamination. Most welders agree that the C25 mixture (75% argon/25% CO2) is the best choice for mild steel, but you should be cautious with sheet metal. CO2 in the mixture stabilises an arc and produces a good weld bead but provides higher penetration. Therefore, to prevent burn-through, you should lower the content of CO2 in your mixture when welding thin metal. 

When working with an aluminium base metal, MIG welding sheet aluminium will require 100% argon shielding gas. Even though pure argon in MIG welding is not the best-performing shielding gas, there is no room for exceptions. With sheet stainless steel, the common choice is a tri-gas mix of 90% helium, 8% argon, and 2% CO2.

Preparation

Compared to Stick or Flux core welding, MIG is not so forgiving when dealing with dirty, greasy, or oily metal. Therefore, to successfully weld sheet metal, you must thoroughly clean welded pieces. You can use a wire brush, an old rag, and warm water or solvent to remove possible contaminants.

MIG, unlike Stick or Flux core welding, does not do well when dealing with dirty, greasy or oily metal. Therefore, to successfully weld sheet metal, you must thoroughly clean welded pieces. You can use a wire brush, an old rag, and warm water or solvent to remove possible contaminants.  

The next step is aligning and clamping pieces. When MIG welding sheet metal, you can opt to leave a small gap or overlap two ends of a sheet. Clean metal surfaces thoroughly and align pieces with a small gap or overlap. Consider using a backing bar to dissipate heat and prevent distortion.

This is the easiest welding method for beginners. The overlap seen in the image above makes it easier to access the weld joint, making it an ideal welding position for first time welders. However, as a first-time welder, you might find it hard to control the puddle and wire distribution with such delicate work.

If you can’t control the heat properly, you can add a backing bar during the weld preparation. The backing bar will act as a heatsink, allowing welds to cool faster and avoid wrapping or distortion. The backing bar should be made of copper or aluminium due to higher thermal conductivity than steel.

Parameters

Once you have chosen the right equipment and after preparing your weld pieces, you should select the proper welding parameters. Key parameters include; voltage, amperage, and wire speed. However, there is somewhat of a challenge when choosing the right parameters. Choosing the correct parameters depends on the thickness of the weld metal, wire size, type of metal, joint configuration, welding position, or shielding gas. Therefore, there is no universal approach to welding thin metal. 

The good news is that there is a solution. In order to get the best result, its important to follow manufacturer recommendations. Most of the time you can find this in the instruction manual or inside the wire compartment. Plus, you can use the synergic MIG feature that comes with some MIG welders. 

Synergic MIG will give you an estimated voltage, amperage, and wire feed speed based on the inputted thickness of metal, wire diameter, and shielding gas choice. However, remember that these serve as guidelines, as you might want to tweak them for the best results.

Technique:

The welding technique for MIG welding sheet metal is fairly straightforward. To achieve a solid weld bead, you want to keep your weld in a straight line. To avoid any unnecessary heat that can cause distortion, it is best to avoid any weaving during the welding process. 

Your MIG gun should be pointed at a 5-15 degree travel angle, with moderate speed. The everlasting discussion is whether to use the pull or push technique with MIG welding. Pushing is a better choice with sheet metal, as it allows a better view and control of the weld pool and lower penetration than pulling.

Another technique you can use is the skip welding technique. This technique can help if you are still struggling with wrapping and distortion. This technique involves making a series of intermittent or stitch welds to minimise distortion. That way, you evenly distribute the heat, which is crucial for thin materials.

MIG Welding Hobbyist Steel

The MIG welding process is best suited for medium or hobbyist steel as we call it. Hobbyist steel is regarded as a border between hobbyist and industrial welding applications with thickness up to 13mm ( ½ inches) as it is unlikely that you will work with any thicker metal in your own home.  

Welding medium-thickness mild steel is a lot less challenging and more accessible than sheet metal. However, this does not mean that you can immediately start welding your projects. You will also need welding equipment, wire, preparation, and technique to do so. But this time, they are a bit different.

Welding medium-thickness mild steel is a lot less challenging and more accessible than sheet metal. However, this does not mean that you can immediately start welding your projects. You will also need welding equipment, wire, preparation, and technique to do so. But this time, they are a bit different.

Equipment

A MIG welder with higher amperage capabilities (200-250 amps) and 220V input is the recommended choice when welding metal up to 6.35mm-13mm(1⁄4 to 1⁄2 inch) thickness.  Welders such as the MIG285 285-Amp MIG Welder have enough power to join thicker metal with ease. This perfectly fine, versatile, and easy-to-use welder, rated at 285 amps, will cover most of your hobbyist needs and deal with steel up to 5⁄8 inches thick. . 

Next is choosing the right wire size. As the thickness of the metal surpasses 12mm, you will need to switch to 0.76mm size wire. A 0.76mm ER70S-6 wire will cover most of your welding needs, but for steel over 5mm, you will need a 0.88 wire. Remember that most hobbyist MIG machines can feed the solid wire up to 0.88 in diameter.

The larger wires produce higher penetration, which makes them suitable for thicker steel, but they also cause more spatter. In addition, you should match the thickness of the base metal and wire diameter to avoid a lack of fusion and undercutting, as well as excessive penetration and reinforcement.

As for the metal transfer, you will primarily use the short circuit, but you can switch to spraying to get the job done faster. This time, you don’t have to worry too much about the heat-affected zone; nonetheless, you shouldn’t disregard its impact on the welding area.

Shielding Gas

When it comes to shielding gas for hobbyist steel, the common shielding gas used is a C25 mixture (75% argon/25% CO2). This mixture provides a stable arc, good penetration, and a good-looking weld bead with carbon steel.Plus, because hobbyist steel is thicker than thin metal, you wont have to worry about the CO2 content. Because the metal is thicker, you can use pure CO2 as an  economical solution.

 Welding with CO2 provides higher penetration, and shielding gas isn’t so expensive. However,  keep in mind that pure CO2 causes lots of spatter and bulky, rough-looking weld beads. Nonetheless, if you want to get the job done cheaper and you don’t care about aesthetics, 100% CO2 is the way.

Preparation

When it comes to welding medium-thickness steel there are two key factors; cleaning the weld joints and choosing the right joint designs. Preparation for hobbyist steel is a lot more manageable compared to thin metal. Keep in mind that you will also have to clean the weld joint but gives you more room for weld design. For example, you can use a butt weld, T-joint design, or fillet weld in a flat, horizontal, or overhead position. Of course, the joint design will depend on specific welding projects and metal thickness, but there are certainly more options to work around than with sheet metal.

Technique and Parameters. 

Because hobbyist steel has a lot less challenges compared to thinner material, you have more room to experiment with welding techniques and parameters. As a general rule, you will need 1 amp per 0.025mm of metal. However, do keep in mind that this is just a rough guideline and it is best to always follow the manufacturer’s recommendations.  

A thicker piece means more heat, so do not hesitate to crack your welder. Of course, as long as you don’t burn a hole in your welds. Like with sheet metal, you can use auto-set or synergic MIG controls to get things going, but you have a room full of opportunities to work your way up to the perfect results.

The same things apply to the welding technique. The travel angle of 5-15 degrees remains the same, but you should adjust the working angle to the joint configuration. In addition, you can push for better control of the weld puddle or pull when you need more penetration and a narrower bead with an immense buildup.

GMAW Welding Thick Plates

When it comes to welding thick plates, using MIG welding can be a challenge as there are more suitable welding processes for thicker plates. To deal with metals thicker than 1/2″, you will need a lot of effort and a powerful power source. Moreover, GMAW is not fundamentally designed for heavy-duty applications, so Stick or Flux core welding can perform better.

This does not mean that it is impossible to MIG weld thick metals. With the right approach and equipment you can weld just fine. To help you with some of the challenges, here are some tips on what to do if you encounter a thicker piece in your workshop.

Equipment

MIG welding is ideal for thin and medium sized plates due its power source. Welding thinner plates is more manageable because it can be done with a single-phase 110/220V machine. However, the challenges start when welding metals with a thickness that exceeds 76.2mm. You will need an industrial-grade MIG welder rated up to 500 amps. These are all massive welders, made to withstand even the harshest conditions and high heat, which is needed for a thicker piece.

Don’t get me wrong, you can weld thicker plates even with your 250 amp welder, but you will have to use special preparation and multiple passes. This takes time, proper preparation, and skill, but it can be a solution when there are no other options.

MIG wire diameter for thick plates increases to .039 or up to .045 in specific applications. Compared to the thinner wire, these industrial grade fillers come in significantly larger spools, commonly 20kgs , compared to hobbyist 0.9 or 4.5 lbs. To fill larger gaps, spray transfer is used for the highest penetration and deposition, allowing you to get the job easier.

Shielding gas choice depends on the application and base metal, but C25 is still the most suitable choice for steel.

Welding Preparation, Parameters, and Technique

The GMAW welding parameters and technique with thick plates still depend on material thickness, wire sizes, and results like with medium-thick materials. However, what differs is the weld preparation.

Welding extremely thick pieces will require you to grind and bevel the edges. That way, you ensure a better connection, and filling the gap will provide substantial results. In addition, certain preheating can be used. Heating the base metal to 150 and 300 degrees F will result in better penetration and more significant effects.

Final Thoughts

MIG welding offers versatility for different metal thicknesses, but proper equipment, preparation, and technique are crucial for successful welds. Whether welding thin sheet metal or thick plates, attention to detail and experimentation with settings will yield satisfactory results.