Flux core arc welding was introduced in the 1950’s. Technically the introduction of this process was not new. It was just a new type of an electrode that can be used on a MIG welding machine. Flux cored arc welding is a process similar to MIG welding. Both processes using continues wire feeds, and similar equipment. The power supply for a FCAW, and a MIG welder, are the same machine. They are both considered semi automatic processes, and have a very high production rate.
The main difference between flux cored arc welding and MIG welding is the way the electrode is shielded from the air. Flux cored arc welding just like the name implies, has a hollow wire with flux in the center, similar to the candy called “pixy sticks”. Just as the name states, a “Flux Core”. The main difference between MIG welding and flux core arc welding is, FCAW gets its shielding from the flux core, and this allows the operator to weld outdoors where it is windy. It’s like a SMAW welding electrode turned inside out! MIG welding gets its shielding from a bottle of gas which has serious draw backs, when welding outdoors, or in drafty conditions.
Flux Cored Arc Welding Production
Flux cored arc welding is the most productive of the manual welding processes! When comparing MIG welding to flux core arc welding, there is a huge gap in production, in the amount of weld per hour. A MIG welder can typically produce 5 to 8 pounds of weld per hour, verses a FCA welder packing 25 plus pounds of weld per hour. On top of that flux core welding can weld 1/2" plates in a single pass with full penetration on both sides. Flux core arc welding for this reason is primarily used in the ship building industry. Ships are made of heavy plate, and have endless amounts of welding that needs to be done. Flux core welding produces high quality welds, fast, and even when in windy conditions.
Weld ability of Metals
Welding with flux core electrodes has some serious cons when it comes to the weld ability of metals. So far, FCAW has been perfected on most carbon steels, cast iron, nickel based alloys, and some stainless steels. Unfortunately most non ferrous exotic metals cannot be welded and that includes aluminum. On the upside for most hobbyists the flux core electrode may be an excellent choice for general garage work, because if used in a MIG welder there is no shielding gas required on some electrodes.
How Flux Cored Arc Welding Works
Flux cored arc welding just like MIG welding requires three main ingredients, electricity, filler metal, and a form of shielding from the air. Just like MIG weldering, flux core welding works by feeding an electrode continuously to the joint. First the welder squeezes the trigger, and then the wire feeder begins to feed the electrode to the joint, at the same time the electrode gets electrically charged. Once the electrode hits the metal joint, the electricity short circuits, and heats up the electrode till the electrode begins to melt. Once the electrode begins to melt, the metal also starts to melt, and then both of them start to create a puddle. This puddle at the same time melts the flux core, creating a shield from air, and at the same time produces a slag that protects the weld from contamination.
FCAW Self-Shielding vs. Dual Shield
Flux cored arc welding comes in two types of shielding. The first difference is in the electrode itself, it is a tubular wire with a shielding powder in the center. In technical terms this is called “Self-Shielding” or sometimes branded "Inner Shield". The second is the same type of electrode, but another ingredient is added. A bottle of gas is used in addition to the flux core shielding. The technical term for this is “Dual Shield”. In the case of dual shielding, you have a powder flux in the center of the electrode and an external shielding gas protecting the weld area.
FCAW Voltage Type - Welding Polarity – Power Supply
A flux cored welding power supply is also a MIG welding power supply, they are the same machine. That is a “Constant Voltage Power Supply”. Constant voltage power supplies keep the voltage near, or at the same level. Unlike a TIG, or Stick welder, that keeps the amperage consistent. In the flux cored welder the amperage is changed with the wire feed speed. The faster the wire feeds, the more contact the electrode has, producing more amperage, and heat.
The voltage type used is D/C direct current like the type current produced by a battery. The polarity used in industrial flux core arc welding is typically D/C electrode (+) positive. This means that the handle is the positive side of the circuit, or the electricity flows from the metal to the welding handle. This is typical when larger electrodes are used. When welding with smaller electrodes and sheet metals, the polarity is changed to D/C electrode (-) negative.
The main difference between FCAW, and a MIG welder’s are, flux cored arc welding power supplies are available with, much, more, power! Basically they are an extremely powerful MIG welder! Some flux core arc welders come with the capabilities of running over an extremely hot, 1000 plus amps! That is where they leave MIG welding in the dust for production.
Shielding Gasses for FCAW
In the case of dual shielding being used with a flux cored electrode the choices of shielding gasses are limited. The choices are as follows:
- CO2 – Carbon dioxide
- Ar – Argon
- CO2 / Ar – A mixture of the two
- Ar / Ox – A mixture of the two
CO2 by itself produces the deepest penetrating weld but has some draw backs. The mechanical properties of the weld are not the best due to fact the flux in the wire reacts with the shielding gas. Others draw backs are, it produces a lot of spatter, and the arc is stiff and not as stable as it can be.
Argon by itself will also weld with a flux cored electrode, but just like CO2, it reacts not favorable with the flux. Both Argon and Carbon dioxide can make a decent looking weld if used by themselves. What the weld looks like verses the actually quality of the weld are two different stories.
The most common gasses used for dual shield FCAW are a mixture of Carbon Dioxide and Argon or Argon and Oxygen. The most popular is C25 / 25% Carbon Dioxide and 75% Argon. This gas produces a stable arc, less spatter, and allows more of a spray transfer of metal. I recently used this mixture when taking my 3G flux cored arc welding certification. In some other cases a mixture of Argon and Oxygen may be used. Oxygen in small percentages stabilizes the weld arc and improves the mechanical properties of the weld.
Ultimately if using dual shield it’s always best to read the electrodes manufactures recommendations or ask you gas supplier for the proper gas.
FCAW Electrode Types
The electrodes used for flux cored welding are almost visually the same as a MIG welding electrode. The difference is that flux cored electrodes are tubular, or a hollow tube with flux in the center. MIG welding electrodes are solid metal.
Flux cored electrodes come in standard sizes. Some are the same size as most MIGwelding electrodes but others are comparable to the thickness of a stick welding electrode. Here are some of the more popular sizes for standard industrial applications:
- .035
- .045
- .052
- 1/16
As with most electrodes there is a standard classification code or designation code, on the spool they come on. To understand the classifications better it is important to know some basics about where the classification codes are different.
A somewhat common flux cored welding electrode is the “E71T – 1”. As with all electrodes the numbers and letters all mean something. There identifications are as follows.
- E – Stands for electrode.
- 7 – Stands for the minimum amount of tensile strength. In this case it is 70,000 lbs of tensile strength per square inch of weld. The way this number is figured is by adding four zeros to the number.
- 1– Stands for the position that this electrode can be welded in. There are only two designations and they are “0” for flat and horizontal welding, then there is “1” for all position welding.
- T – Stands for a tubular electrode. When “T” is used it is always assumed it is a flux cored electrode.
- 1 – The last is the shielding flux type designations.
As a note with all flux cored electrodes they need to be stored in a dry place. Otherwise the may pick up moisture and this will cause major weld defects.
Flux Cored Welding Transfer Types
When welding with a flux cored electrode there are two metal transfer types used! The transfer types are Spray Transfer and Globular. Spray transfer is the most commonly used. Just like the name states the metal from the electrode gets heated up to the point that it literally sprays the filler metal to the joint. Globular transfer heats up the electrode hot enough for globs of metal to drip off of the electrode to the weld joint. What separates the two transfer types are, voltage settings, wire speed, and the gasses used, if any.
Flux Cored Arc Welding Joint preparation
Joint preparation for flux core is not as critical as with MIG welding. FCAW can typically burn through mill scale and minor rust. In many cases when the metal is cut with a torch, it can be welded as-is, with no additional cleaning. For the ship building industry this is a huge savings in labor cost. In addition to easy joint preparation, beveled grove joints can be narrower for metals ½ inch or thinner, and they can be welded in a single pass with full penetration on both sides.
Ceramic Backing Tape
Commonly in the ship building industry many joints are welded from a single side using a ceramic backing tape. The ceramic backing tape is like a mold to pour metal in, but in this case the electrode will fill that mold. When ceramic backing tape is used it allows for full joint preparation and outstanding weld quality. This in return gives full control of the shape and penetration of the back side of the weld. Once the weld is finished, the ceramic tape is simply peeled off, and thrown away. The great think about using ceramic backing tape is that it is just like welding an open root butt joint, but requires much less skill! The pictures below are of the first time I used ceramic backing tape on a 3G weld joint. Its real easy as long as you keep the arc in the puddle!
