GMAW vs. FCAW for beginners: Choose the best process for your small operation

Practical Welding Today March/April 2000
August 16, 2001
By: Lincoln Electric Weld Technology Center Staff

There are several pros and cons to using the gas metal arc welding process versus the flux cored arc welding process in compact applications.

When you prepare to buy your first wire-feed welding machine, you don't want to waste your money on a toy that goes out with the trash in a few weeks. You probably want to use 115-V input for portability, but might want to step up to a 230-V-input machine to weld thicker material.

After you've made this decision, one more question will remain: Which welding process will I use — gas metal arc (GMAW) or flux cored arc welding (FCAW)?

If you are like many beginning welding operators, you may be confused about which process to choose. The choice depends on three variables:

  1. What you are welding
  2. Where you are welding
  3. The surface finish requirements of what you are welding

Defining GMAW

GMAW uses a continuous solid wire electrode for filler metal and an externally supplied gas, typically from a high-pressure cylinder, for shielding.

The wire usually is mild steel, which typically is copper-colored because it's electroplated with a thin layer of copper to protect it from rusting, improve electrical conductivity, increase contact tip life, and improve arc performance.

The shielding gas, usually carbon dioxide or a mixture of carbon dioxide and argon, protects the molten metal from reacting with the atmosphere. Shielding gas flows through the gun and cable assembly and out the gun nozzle with the welding wire to shield and protect the molten weld pool.

If exposed, molten metal reacts with oxygen, nitrogen, and hydrogen in the atmosphere. The inert gas usually continues to flow for some time after welding to protect the metal as it cools. A slight breeze can blow the shielding away and cause porosity in the weld, so you should avoid welding outdoors unless you erect special windscreens.

If done properly, GMAW can yield excellent results. The finished weld has no slag and almost no spatter. If the material you're welding is dirty, rusty, or painted, you must clean it by grinding until you see shiny, bare metal. A novice can use GMAW successfully with common commercial metals — low-carbon steel, low-alloy steel, stainless steel, and aluminum.

Defining FCAW

FCAW uses a wire that contains materials in its core that, when burned by the heat of the arc, produces shielding gases and fluxing agents to help produce a sound weld without the need for external shielding gas. The shielding can endure a strong breeze. The arc is forceful but creates spatter. When finished, the weld is covered with slag that usually must be removed.

The settings on the wire feeder and power source are more critical for this process. An improper technique can magnify poor results. You can use this type of welding primarily on mild steel in outdoor applications.

General Usage Rules

GMAW. Experts recommend you use a compact 115-V or 230-V-input GMAW wire feeder and welding machine indoors on new, clean steel from 24- to 12-ga. Twelve gauge material is a little less than 1/8 in. thick, while 24-ga. is less than 1/16 in. thick. The smallest wire (0.025 in.) can make it easier to weld thinner material.

If you need to weld 1/8- to 1/4-in.-thick material with GMAW, you will need a higher-capacity, compact machine, which requires 230-V input. The higher amperage range of this machine can handle your welding needs in a single pass, so you may not have to waste time with second or third passes. The 230-V machine also can run 0.035-in.-dia. wire.

To weld material thicker than 1/4 in., you need a higher-capacity industrial machine. If you perform most of your welding indoors on clean material 1/8 in. thick or less, a GMAW machine that operates on 115 V probably is more economical than a 230-V-input machine.

FCAW. Experts recommend that FCAW be used only on materials no thinner than 20-ga., a bit thicker than the 24-ga. for GMAW. In general, this process is best for welding thicker materials with a single pass, especially when welding outdoors. With the proper electrode and the right machine, you can weld steel up to 1/2 in. thick.

Choosing Wire

One concern with FCAW is how to choose the best wire. Proper electrode diameter is related to metal plate thickness and the welding machine you use. A smaller wire makes it easier to weld thinner metal.

Small machines cannot do everything. Electrodes for production welding, hard facing to resist wear, and most specialty electrodes will exceed the capacity of these machines. You must be careful to match the output voltage of your machine with the voltage of the electrode and the appropriate wire diameter and wire-feed speeds to make sure you have a compatible system.

Tips for Both Processes

For both processes, welders need to follow certain tips. For instance, you should clean or grind the surface of the metal thoroughly before tightly attaching the work clamp to get a solid work connection.

Some other tips to consider include the following:

  1. Put the welding machine on a separate circuit breaker that is fused properly, as stated in its operator's manual. You can't melt steel at about 5,000 degrees F without adequate input power.
  2. Strive for good fit-up. Avoid gaps whenever possible to minimize burn-through. This is critical, especially on thin sheet metal.
  3. Keep the gun cable as straight as possible for smooth wire feeding. Don't bend it sharply.
  4. Make sure the contact tip is not elongated or melted and is tightened in place.
  5. Cut the wire at an angle to form a point for better starts.
  6. Use and maintain correct electrode stickout and proper welding procedures.
  7. Make sure the drive rolls feed smoothly with proper tension.
  8. Try to hold the gun steadily and smoothly.
  9. Observe and follow all welding safety precautions as specified in your operator's manual. Pay special attention to the potential for electric shock, arc rays that can burn skin and eyes, fire and explosion, and proper ventilation. For more details, consult ANSI Z 49.1.

Lincoln Electric Weld Technology Center Staff

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