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The world of welding can be a little intimidating to the beginner, but with a little bit of research, you will find that it is pretty straight forward. One of the first things you need to know involves a fundamental piece of the process: polarity.
MIG welding is electrode positive. MIG (metal inert gas) welding is also commonly referred to as DCEP (direct current electrode positive) and reverse polarity.
The various methods of welding are used for different types of metals and work. Certain polarities, and methods, are more appropriate for specific projects. Read on for more information about MIG welding, and the importance polarity plays on the craft.
When You Use a Positive Electrode?
MIG welding is done with a positive charge. If you were to attempt this method with a negative polarity, or DCEN, you would struggle with an unstable arc, several arc outages, and a messy weld.
MIG welding is typically used for longer welds and larger projects. Welding with a positive electrode is better when trying to achieve deeper penetration. Because of its simplicity, MIG welding is where almost all beginners start.
MIG welding is the process of creating a short circuit between a positive anode and a negative cathode. In this case, the wire from the welding gun is positive and the plate being welded is negative. This small arc of electricity combined with the inert gas, and wire as a filler, causes the metal to melt and fuse together.
The heat required to fuse metals comes from the flow of electrons from negative to positive. Localizing this heat into smaller areas can make for more precise and clean welds.
Common uses for MIG welding are structural materials, alloys, and medium-thick metals such as:
- Stainless and Carbon Steel
- Silicon Bronze
When Would You Use a Negative Electrode?
DCEN welding, also known as straight polarity, is commonly used in TIG (tungsten inert gas) welding. The primary difference between MIG and TIG is the use of a negative electrode.
In TIG welding the anode is the plate you are working on and the cathode is the welding gun. What this means is that the work is positively charged while the welding gun is negatively charged.
Tig welding is best applied to thin gauged metals, stainless steel, silver, gold, chrome alloys, and various others. Common uses for this method of welding include things such as:
- Lightweight bike frames
- Metal toys
- Jewelry repair
- Lawnmower decks
- Boat repair
As you can see, the uses for TIG can be applied to many different materials but the main benefit of TIG welding comes from its efficient use of localized heat in a small area.
Often, TIG welding is done in a form of tacking. What this refers to is the method of welding small areas on your plate instead of performing one long weld. This keeps your work from becoming too hot which can lead to warping and discoloration.
Typically, TIG welding is more precise than its positively charged counterpart MIG and leaves you with cleaner welds that should not need to be touched up with a grinder when performed properly.
What is the Difference Between DC and AC?
A direct current in welding is used much more commonly than an alternating current. The uses for direct current welding are broad and varied while alternating current welding is a little more specialized.
The key difference in direct and alternating current welding is the flow of polarity. In DC the flow is constant from the anode to the cathode. Remember, electrons always flow from negative to positive. This means that heat will be generated in kind.
AC welding is commonly used for things like:
- Aluminum welding
- Magnetized steel
Because of its alternating flow, more energy is transferred which means more heat is generated in a smaller area. This makes AC highly effective when working with materials that need a precise application of heat like aluminum.
What Role Does Gas Play in MIG Welding?
Shielding gas is an essential piece of the MIG system. The flow of gas keeps debris and contaminants from the atmosphere out of the molten metal. This ensures a strong bond free of foreign materials that could weaken the completed weld.
Our atmosphere is a cocktail mix of oxygen, nitrogen, carbon, argon, hydrogen, and various other gasses and particles which can negatively affect your weld. Although the gasses that comprise the shielding gas are present in our atmosphere, the concentration and ratio are totally out of whack. The mixed inert gas in MIG welding is constituted of:
- Carbon Dioxide
- Sometimes Helium
Too much nitrogen can be very problematic to the strength and durability of your weld. An excess of nitrogen can reduce the impact strength of steel which can cause cracks.
Another issue that you can run into when too much nitrogen enters your weld is porosity. This occurs when cavities of the gas are left in the metal which can severely weaken the strength of your work.
Porosity can also be created by oxygen mixing with other gasses such as carbon. When hydrogen mixes with iron or aluminum porosity can occur as well. This can lead to cold cracks under the weld.
Shielding gasses do more than protect the weld; they can even improve them. Helium has a significantly higher thermal conductivity than Argon. Despite the fact that more voltage is needed for arc stabilization when using helium more heat is generated at the weld resulting in deeper penetration.
Things to Avoid When MIG Welding.
Dirty and rusty surfaces can give you a hard time when MIG welding. While it is definitely within the capabilities of a MIG set up it is advised that you take a few minutes before welding to clean away any rust or debris from the plate. This will give you the best chance of creating a strong, clean weld, free of porosity, and other defects.
Rust and debris on the plate is not the only concern you should have when MIG welding. High levels of humidity can rust your MIG wire which will introduce unwanted elements into your weld. Placing your wire in a clean bag can greatly reduce the risk of contamination from rust and various debris.
Do not get in a hurry when welding materials that are over ¼” thick. The key to a good, strong weld on these thicker materials is deeper penetration. Welding slower will allow the metal to achieve higher temperatures and aid fusion. Slow is smooth and smooth is strong in these situations.
MIG welding is done with a positive electrode. This means that energy flows from the wire of the welding gun into the plate that is being welded.
Typically MIG DCEP is best applied to thin metals and structural materials that are less than an inch in thickness.
The most common use for a negative electrode is TIG DCEN. TIG tends to be a more precise method of welding when compared to MIG. TIG welding is even used in the repair of jewelry as it is effective on both gold and silver.
Direct currents and alternating currents are both used in different forms of welding. AC performs quite well when it comes to welding magnetized metal and aluminum which makes it the go-to polarity for these materials. DC is used on virtually everything.
The gasses employed in MIG welding can make or break a good weld. Shielding gasses are used to form a protective flow over the molten metal in a weld to keep unwanted gasses and debris from the atmosphere out. Porosity and cracks are just a few concerns when welding with no or incorrectly mixed gas.
To ensure that you are giving yourself the best chances of success make sure that you are welding on a clean surface that is free of rust and other debris. Take your time to allow heat to penetrate the metal for stronger welds.
There are so many variations of gas, polarity, and equipment in the world of welding. Make sure you take the time to see what’s right for you and your projects.
Disadvantages of Mig Welding | Autodesk Instructables (instructables.com)
How to Weld – MIG Welding | Autodesk Instructables (instructables.com)
What Is MIG Welding Gas? Shielding Gas Basics | WelditU (welditu.com)
How to Avoid Common MIG Welding Mistakes | BakersGas.com