MIG Welding Cast Iron: A Step-By-Step Guide

If you’re a welding enthusiast who likes challenges, taking up MIG welding cast iron can be a pretty sweet deal. But with different alternative welding options available, the technique has lost its popularity over the last few years.

In theory, the process of MIG welding cast iron is pretty straightforward. First, you’ll need to carefully prepare the metal for welding. Then, preheat the metal to prevent it from breaking down. Finally, execute the welding process. Keep an eye out to slowly cool the workpiece down, as it’s at that stage when the weld is the most vulnerable to cracking.

The intricacy of MIG welding can be a bit intimidating. But fret not, because this step-by-step guide will hold your hand through the entire process.

Difficulties Of Welding Casting Iron

Before you move on to the welding process, it’s essential to understand what you’re up against. You see, the fall in the popularity of MIG welding cast iron occurred due to the difficulty of the task. So, here are some of the drawbacks of the process to get you up to speed.

No Exact Estimates of Strength

First of all, cast iron constitutes different proportions of different materials. So, it’s difficult to pinpoint its exact strength.

As a result, you’ve to work without an estimate of how much the cast iron will be able to withstand before breaking down.

High Carbon Content

Secondly, cast iron contains high carbon content, which can transfer to the welded item. This transfer can cause post-weld cracks due to the increased hardness of the item. This is one of the major issues of welding cast iron.

Change In Temperature

Finally, you have to heat the metal in MIG welding and cool it down to room temperature and let it solidify. Cast iron contains high carbon and, therefore, has an increased brittleness. Any sudden temperature change can make it shrink or expand, causing it to break down.

Because of all these reasons, MIG welding cast iron has a success ratio of 50%. So, if you don’t want to end up with a failed welding project after putting in all the work, you need to go through the welding process with utmost care.

How MIG Welding Works?

To maximize your chances of success, it’s a good idea to familiarize yourself with the MIG welding

There are different terminologies that welders use in their work. Knowing these terms will help you go through the process with ease. First, let’s take a look at them.

  • Parent Metal – It’s the metal that you’re going to join by welding.
  • Weld Metal – The weld metal constitutes all the metal that forms the weld.
  • Filler Metal – You use the filler metal to join the metals together. It’s the bridge between the parent metal and the weld metal.
  • Heat Affected Zone – Commonly referred to as HAZ, it’s the area between the base parent metal and the weld. The HAZ goes through the changes in metallurgy as you expose it to heat.
  • Fusion Line – The fusion line is the intersecting line between the HAZ and the weld metal. You may also know it as the weld junction.
  • Weld Zone – The weld zone is basically where the HAZ and the weld metal resides.

MIG welding has various names. One commonly used name amongst welders is wire welding. They call it that because MIG welding, or rather wire welding, involves a wire electrode in its welding process. The wire electrode has a thin wire that continuously feeds the welding machine. This wire feed can either be solid or cored.

When you pull the trigger of the welding machine, the wire feed will create an arc between the end of the electrode and the metal surface that you’re working on. As the arc forms, it melts both the metal and the wire to form a weld pool.

So, the wire basically serves as both the filler metal and the heat source for the joint. And for that reason, many welders call the MIG welding process wire welding.

The MIG welding process is semi-automatic. The power source automatically controls the wire-feeding rate and the arc length, but you’ll have to determine the position of the wire and the speed at which the arc travels to make it work.

Steps to MIG Weld Cast Iron

Unfortunately, the success rate of MIG welding cast iron is very low. But by going through the following steps, you can increase the chances of success significantly.

Step 01: Run A Trial Assembly

Trying out a trial assembly will help you see how the parts would fit together. That way, you can visualize how you should go about in your welding process.

It’ll also help you assess if you need any more parts or if you’re good to go.

Step 02: Identify the Alloy

As mentioned before, cast irons contain high carbon as they’re a family of iron-carbon alloys. This increased carbon content is what gives cast iron its hardness. But, an effect of this hardness comes at a cost. Cast iron tends to be tensile because of its carbon content.

As the cast iron goes through subsequent heating and cooling during the welding process, the metal goes through massive tensile stress. But, cast iron can’t stretch when heated or cooled—instead, the alloy cracks, resulting in failure.

However, some cast iron alloys have a higher possibility of yielding better results.

White Cast Iron: As the carbon in the solution solidifies but can’t form graphite, that’s when white cast iron is formed. Rather than precipitating the carbon as graphite, the white cast iron retains it as iron carbide. Because of that, it’s tough and brittle, making it unsuitable for welding or machining.

Nodular, Ductile, or Malleable Iron: Malleable iron carries a lot of similarities with white cast iron, except one. Due to the difference in their manufacturing process, the malleable or ductile, or nodular iron is less prone to break down or has a lower degree of brittleness.

In addition, these three types of cast iron have spheroidal carbon microstructures, which allow them to bend relatively easily upon impact.

Grey Cast Iron: Grey cast iron is the most common form of cast iron. It gets its name from the grey color its graphitic microstructure forms.

Unlike the white cast iron, the grey cast iron forms and precipitates graphite when it solidifies. As it spews out graphite flakes, the grey cast iron is manufactured into a pearlite or ferrite crystalline microstructure.

Because of its crystalline microstructure, the grey cast iron is more flexible than white cast iron and, therefore, more weldable. But it still poses some challenges as the precipitated graphite can get into the weld and add impurity to the workpiece, making it prone to brittle fracture.

You can check what you’re working on with the spectrochemical analysis. This analysis should provide you with the original specifications of the cast iron to help you determine its type.

You can also try spark testing to determine the type of iron. However, you’ll need an expert metallurgist to examine the results.

Also check our other article::

How to Weld Steel to Cast Iron: The Complete Guide

Step 03: Clean Out the Contaminants

Once you’ve determined the nature of the workpiece, it’s time to move on to the cleaning phase. In this phase, you must eliminate any impurities or contaminants that may affect the weld.

Clean the Workpiece

First, you’ll need to clean out the surface area to get rid of any impurities, whether grease, paint, oil, or other foreign materials. There are different techniques you can use to clean the surface.

A popular way to clean out the impurities is to use an angle grinder with a flap disc. It’s a very successful way of getting rid of any impurities in both MIG and TIG welding.

You can also use sandpaper to clear out the contaminants. But note that it can be pretty time-consuming, and sandpapers can’t remove all of the contaminants, reducing the chance of success.

Check Its Readiness

Once you’ve thoroughly cleaned out the surface of the workpiece, you need to check the workpiece if it’s ready for the welding process.

First, try passing a weld pass on the metal. If the metal is porous, get back to the cleaning process because it still has some contaminants left on its surface.

Repeat this process a few times and proceed once the workpiece is ready.

Step 04: Use Tack

While it’s an optional step, using tack will help your chances of success. The word ‘tack’ here doesn’t mean that you need to use superglue. It just means ensuring a way to keep the workpiece still in its place so that it doesn’t disrupt the welding process.

For example, you can use a fabrication table to hold it in place with different tools. Of course, if you don’t feel comfortable doing so, you can skip this step if you wish.

Step 05: Gauge the Thickness

You need to gauge the thickness of your workpiece to know what you’re working with. It’ll later go to the preparation of your welder when setting the amperage, voltage, and other factors.

You can use a thickness gauge to measure the metal’s thickness.

Step 06: Prep Your Welder

Plug in your welder and turn it on. Since you’ve previously gauged your workpiece, you should have all the information you need to input into the machine.

If your welding machine has an automated setting, it should fill up the gaps if there’s any in your information. Otherwise, you’ll need to adjust the settings according to your needs manually.

Turn It On

First, turn on the shielding gas. Do it slowly and carefully to open it up all the way. Once you’ve turned on the shielding gas, turn on the solenoid valve on your welding machine.

After turning on the solenoid valve, you should be able to determine the pressure (CFA) of the device.

If you don’t turn on the solenoid valve, the machine’s safety mode should turn off the device within 30 seconds so that all the gas doesn’t leak out.

Wire and Gas

Next, you’ll have to toggle down to the type of wire you’re using. Here’s where the thickness that you measured earlier will come in. For example, if the thickness of your workpiece is 0.8 mm, toggle down the setting to match that setting.

After setting up the wire thickness, toggle down to the type of shielding gas you’re using. Your machine should have some predetermined setting. Again, make sure to match what you’re using.

Amperage and Voltage

Since you know the thickness of the workpiece, you can use that to determine the machine’s amperage and voltage. Alternatively, if you know the rate of wire-feeding, you can also use that information to work the machine.

Toggle to the thickness option and use the tuning dial to set the welder to the particular amperage you need.

If your machine has a synergic mode, it will do its own calculation and set the voltage as needed. If not, you can also calculate the voltage and input the required information.

With that, your machine is all ready to go.

Step 07: Preheat the Metal

This step is a precautionary measure. Many welders don’t preheat their workpiece and follow another method known as cold welding.

However, cast irons are brittle and may break down once under stress. Ensuring heat control is one of the most significant ways to avoid such unfortunate circumstances.

By preheating the metal, you’ll be heating the entire workpiece, not any localized part. When cold welding, the welder heats up and cools down one localized region of the metal, causing it to induce stress.

This localized heating causes a restricted expansion of the structure. And as the difference between the HAZ and the casting body widens, the more significant the possibility of the cast breaking down.

In the case of cast iron, the risk is more prominent. As cast iron is more brittle than other components because of its high carbon content, it’s more vulnerable to stress-induced cracks, which may result in failure.

So, you’ll need to preheat the entire cast at a low heat input to increase your chances. And when it’s time to cool it down, let it cool down slowly to avoid sudden restrictions.

One way to slowly cool down the weld is to use insulating materials. Alternatively, you can slow down the cooling process by heating the welded cast from time to time.

Step 08: Start the Weld

Now that you’ve set up the best way you can, you can start the welding process. Maybe it’s a psychological thing, but the more comfortable you are with your prep, the better the weld will come out.

You can start with tiny tack welds to see how you’re doing. Make these tack welds about half an inch to one inch, whatever you think works best for you.

As you make the tacks, use a peening hammer to peen them so they stay clean. But make sure to use the peening hammer when the weld is relatively ductile, which is right afterward you put on the tacks. Otherwise, it’ll have harmful effects on the weld rather than helping it.

As you know, MIG welding doesn’t yield the cleanest or the prettiest result unless you’re oxy-fuel brazing or TIG brazing. So, don’t be discouraged once you see that the results aren’t looking good.

If you’ve successfully come out of the weld, you’re already better at it than fifty percent of welders. Congratulations!

Some Helpful Tips On MIG Welding Cast Iron

  • When choosing your gas, it’s best to go for an 80/20. It means 20% carbon dioxide and 80% argon. However, if you’re afraid of metal rusting, later on, you should avoid this method as cast iron is naturally vulnerable to rust and corrosion.
  • When wire welding, go for the specialty nickel wire as your choice for wire. However, using specialty nickel wire can be a bit heavy on your wallet. So, if you’re looking for a more budget-friendly option, you can consider stainless steel an alternative.
  • As said earlier, MIG welding doesn’t yield the best-looking results. So, you can bond the piece with brazing wire. Be careful, though! If you use brazing wire, it can result in a weaker weld that is more likely to break down sooner rather than later.
  • If you’re going for a repair, try chipping off the cast iron rather than grinding it. It’ll reduce the risk of smearing graphite all over the surface of the workpiece.
  • Suppose your workpiece has come into contact with oil. Heat its edge until it has a dull red color. Then allow it to cool down. Once it has cooled down, brush the carbon with a wire brush from the surface.

Final Words

MIG welding cast iron can be quite challenging. But that just means it’s that much gratifying once you come out of the challenge victorious. So, for whatever reason you want to weld cast iron, it doesn’t hurt to have a step-by-step guide.

Just follow this post, and you should be good to go. And remember to be safe while welding!

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