Flux-cored arc welding or FCAW is a subset of MIG welding. As the name implies, this technique utilizes a flux-cored electrode to provide filler material for the weld.
Apart from this difference, FCAW is the same as MIG welding. The same MIG welding machine is used for FCAW. It is only the electrode that is different.
Flux-cored arc welding is a feasible technique for bridge construction, heavy equipment repair, structural steel erection, and similar applications since the past several years. This is unsurprising when you consider the high deposition rate and simplicity of this welding process, which makes it very productive and economical.
Flux-Cored Arc Welding Power Supply
This welding process can be carried with a MIG welding machine – there is no need for any modification in many cases. For some situations, you may have to change the rollers for feeding the electrode. The contact tip must also be suitable to accommodate the thicker wire electrode. This is the same as making changes for different wire sizes.
There are some dedicated FCAW welding machines. However, these heavy-duty welders are to be found only in the industry. The primary difference between these FCAW welders and MIG welders is that the former has much higher current and voltage settings for welding thick metal plates.
Therefore, if you already possess a MIG welding machine, then you can start using it right away for flux-cored arc welding.
It is the electrodes that make FCAW slightly different from MIG welding. MIG welding uses solid wires as electrodes for filler material. FCAW uses electrode wires with a hollow center that is filled with flux. This flux protects the hot weld joint from corrosion and contamination by shielding it from the environment.
Since the flux can efficiently shield the weld joint from the atmosphere, flux-cored welding is well-suited for outdoor welding. FCAW process employs flux material just like stick welding. However, in FCAW electrodes, this flux is placed in the core rather than the exterior as in stick welding electrodes.
Due to flux, the FCAW technique possesses several advantages over the MIG welding process. Here are the four significant benefits.
- FCAW process has a higher deposit rate per hour
- FCAW method is suitable for welding rusted and dirty metals as much as ½ in. thick with just one pass
- This welding technique is excellent for outdoor welding. It also works well for hobbyists and DIY enthusiasts
- FCAW process is simple and can be learned quickly in a short time frame. It does not require a high level of manual dexterity like TIG welding.
FCAW has a superior deposit rate compared to other welding methods. With MIG welding, you can deposit a maximum of about 8 pounds of wire within an hour. With the FCAW method, you can deposit up to 25 pounds of metal per hour. This method, therefore, has very high productivity and is a particularly good option for welding thick metal sections and workpieces. The deposit rate of FCAW is unmatched. Hence, this welding process is a favorite among shipyards and other heavy industries.
FCAW Process with Rusted and Dirty Metals
You do not need to have a very clean joint to accomplish flux-cored arc welding. Unlike other conventional welding processes like TIG, MIG, and stick, FCAW can deal with all kinds of contaminants besides oils, water, and paint. It can even dissolve mill scale and rust. FCAW is so efficient at welding through rust and mill scale that it is capable of welding ½ in thick metal section with groove joint while achieving complete penetration on both sides in a single pass.
FCAW is also suitable for all kinds of positions, which makes it even more ideal for shipyards and heavy industries.
If you have any experience with MIG welding, you might be aware that MIG welding can be very problematic if it is carried out outdoors. You can resolve this problem by merely switching your solid wire electrode to a flux-cored electrode wire, that is, by employing FCAW. This switch is very convenient since you can replace the solid wire with flux-cored wire by making only minor modifications.
The reason why FCAW is resilient even in the outdoor environment is due to the flux. The flux serves to safeguard the hot weld against windy conditions in the same way as the stick welding process.
Those welding operators, who do welding either for hobby or repairs, can use FCAW without any shielding gas in most cases. Less equipment is needed, making the process simpler and more convenient.
Required Skill Level
Unlike other advanced welding methods, you do not need a high level of manual dexterity to make satisfactory welds with FCAW. It is quite similar to MIG welding. The only thing that you need to do is to configure the welding machine properly according to the welding application. Once that is accomplished, you need to aim the nozzle correctly to create the weld.
FCAW is much easier than TIG welding. In TIG welding, you need to use both hands –the non-consumable tungsten is held with one hand, and the filler wire is attached with the other. You must feed the filler wire manually at the right rate. You also need to control the foot pedal to vary the current. With FCAW, on the other hand, you need to hold the welding gun over the right spot. The wire is fed automatically. The machine needs to be set correctly for the best welding quality.
FCAW Electrode Types
There are two kinds of FCAW electrodes.
The self-shielding electrode does what its name implies. There is no need for shielding gas to protect the hot weld. This kind of FCAW electrode has flux material, which can provide adequate shielding from the atmosphere. Hence, it is an excellent choice for general repairs and one of the best options for outdoor welding. Since dual shielding electrodes do not rely on shielding gas, the process is much simpler, and costs can be also be reduced.
Dual-shielding electrode needs shielding gas for protection against corrosion and rust. For most cases, a blend of 25 percent carbon dioxide gas and 75 percent argon gas will suffice. The only way to get a good idea of the most appropriate shielding gas is to get in touch with the electrode manufacturer or welding supply store. It is better to be entirely sure rather than risk the rework that comes with removing poor quality and defective welds.
FCAW Electrode Sizes
FCAW wires come in different sizes. You will need the following wire sizes for most of your welding tasks.
There is a designation system to identify different electrodes. For instance, one such wire is the E71T-1. Here is what the name means.
E – This implies electrode
7 – This number gives the weld’s minimum tensile strength according to square inches. You have to add four zeros to this number to obtain the minimum tensile strength. In this case, it turns out to be 70,000 pounds per square inch. This implies that the minimum tensile strength of the filler metal is 70,000 pounds per square inch.
1 – Implies the welding positions that you can adopt with this wire. There are only two numbers that are used for this digit – zero and one. Zero means that you can only assume the horizontal and flat position with this electrode. One implies that you can use the electrode in any position.
T – Abbreviation for tubular. This is the shape that you would expect in a flux-cored wire. The wire is a tube of filler metal filled with flux. In MIG electrodes, the wire is solid. There will be an S designation in this case.
1 – States the kind of flux within the electrode.
Flux-Cored Arc Welding Machine Configuration
Setting up the machine is critical for effective FCAW welding performance and quality. Before setting up the device, you must ensure that the roller tension is adjusted correctly. There should be enough tension to feed the wire with no slip. If the rollers become too tight, then the wire may be crushed in which case you must feed the wire back again.
You can adjust heat settings by configuring the voltage and feed rate for the wire.
If you are using dual-shield electrodes, then there is the extra task of adjusting the shielding gas flow rate. The voltage is an indication of the rate at which heat will be directed into the weld. The wire feed speed regulates the rate at which the wire electrode will enter the weld pool. This is indicated in inches per minute.
As the process depends on a constant voltage power supply, the current varies according to the wire feed rate. Higher feed speed means greater current.
To facilitate you in making the right configuration, the manufacturer includes a chart within the welding machine, which shows you the guidelines for wire feed speed and voltage, according to different thicknesses of metal sections.
Although these recommendations are helpful, it is not necessary to follow them exactly. The settings should be enough so that the weld pool flows into the joint and penetrates the entire depth to weld the two opposing surfaces adequately. MIG welding, on the other hand, is more sensitive to these recommendations.
There are two different kinds of transfer mechanisms that you can utilize for FCAW.
- Spray transfer
- Globular transfer
When you switch your welding machine to spray transfer mode, then you will notice a distinct cracking sound. Welding is typically carried out with spray transfer.
As the name suggests, tiny droplets of molten metal are passed along the arc towards the weld pool in spray transfer. This is similar to how the spray comes out through the garden hose with the restricted opening. Spray transfer depends on the wire diameter and is done at high wire feed speed feed and voltages. Once the arc is developed, it lasts throughout the weld as opposed to short-circuit transfer. This transfer technique generates minimal spatter and is commonly used for thick sections either in a horizontal or flat position.
In globular transfer, the filler metal is transferred along the arc in the form of relatively big droplets. The size of these droplets is comparable to the electrode diameter. This transfer method is employed for carbon steel. Through globular transfer, welding is done in the horizontal or flat position owing to the large size of the droplets. The big droplet size makes this welding process more challenging in the overhead and vertical positions. Short circuit arc transfer is more natural in comparison. The large droplet size leads to high spattering.
A globular transfer is more suitable for thin sheets and metal sections. The wire feed speed and voltage are set so that the popping sound becomes audible during welding. You will be able to hear a few pops each second as small globules are formed, which fall into the weld pool. For globular transfer, you need to use a dual shielding electrode. The shielding gas must have a high proportion of argon gas to create a stable arc.
Flux-Cored Arc Welding Methods
The welding methods employed for this process are straightforward. You don’t need to have too much skill besides knowing how to set up the welding machine correctly.
You can carry out flux-cored arc welding using either the forehand or backhand method. These methods are also used in other welding processes.
In the forehand method, you are pushing the pool in the direction of the weld. With the forehand method, you get a wide but shallow weld with a low profile. This welding technique is suitable for thin sheets and metal sections.
On the other hand, backhand welding creates a penetrating, deep, and narrow weld with a high profile. It is, therefore, more suitable for thick metals.
You can use either the forehand or backhand method in conjunction with techniques such as circles, whipping, and weave patterns. For the majority of cases, you can weld at a steady travel speed. Shake the handle from side to side for spreading the weld. This is the most useful all-round technique, which works well for all positions whether you use the forehand or backhand method. You can do welding in the overhead, horizontal, or flat position with both forehand and backhand.
Here are further tips for improving FCAW quality
Tips to Improve FCAW Quality and Avoid Common Issues
Although flux-cored arc welding is more straightforward compared to other welding methods, you still have to take care to avoid common welding issues. You can prevent most of these problems by understanding the factors behind their development and practicing well. Find out about the solutions to these problems to make consistent and better quality welds.
Wire Feeding Problems
You can reduce downtime considerably by taking steps to ensure that wire feeding problems do not transpire. The two most common wire feeding issues are birdnesting and burnback. These problems tend to extinguish the arc during the welding process, which can lead to weld quality issues.
In burnback, the wire melts to form a deposit at the contact tip. This problem is quite often the result of a low wire feed rate. Holding the nozzle too close to the base metal will also cause this problem. To avoid this problem, make sure that the wire feed rate is appropriate and ensure that the distance between the workpiece and the contact tip does not exceed 1.25 in.
As the name suggests, birdnesting is the tangle of wire which can obstruct wire feeding. The best way to prevent this problem from occurring is to make use of U or V groove drive rolls in the wire feeder.
FCAW wire electrode is considerably softer in comparison to the solid wire electrode used in GMAW. As a result, if you use the wrong drive roll, it will compress the soft flux-cored wire easily.
Setting an appropriate drive roll tension will stop the wire from getting tangled or flattened. To adjust the tension correctly, you should start by releasing drive roll tension. From this point, you can begin raising the tension and go one-half turn beyond the point at which the wire stops slipping.
There are also other factors as well behind birdnesting such as liner blockages, wrong liner usage, and incorrectly trimmed liners. If during a regular inspection of the cables and welding gun, you notice that there is a blockage then replace the line immediately. Use the right tools to correctly trim the liner, as mentioned in the manufacturer recommendations. The liner should be free of sharp edges and burrs. Make sure that you are using the most appropriate liner for your wire diameter.
Porosity and Worm Tracking
Wormtracking and porosity are some of the most prevalent defects that can reduce the integrity of weld joints. Porosity develops when gas bubbles enter the weld pool and get trapped. The molten metal will solidify to form holes due to these bubbles. These holes can form at a point or along the entire length of the weld. To prevent such an occurrence, ensure that you remove all dirt, moisture, oil, coatings, paint, grease, and rust from the surface of the metal section before you begin welding.
You can also use flux-cored wires with deoxidizers that can remedy some of these contaminants. However, you should never think that these deoxidizers are a substitute for proper pre-weld cleaning and workpiece preparation.
Make sure that the electrode extension is appropriate. The general rule in this regard is that the wire should not extend beyond 1.25 in front of the contact tip.
Worm tracking refers to the marks created on the surface by flux gas entrapment. You can prevent worm tracking by avoiding overly high voltage. Set the voltage according to the wire feed speed and its corresponding current. You should refer to the electrode wire manufacturer directions for voltage settings. The required voltage will vary according to the wire diameter, as indicated in the manufacturer guidelines.
If you notice worm tracking while welding, then lower the voltage in increments of half a volt until the problem disappears.
The slag produced by molten flux can get trapped in the molten weld pool. This leads to a defect known as slag inclusion which can deteriorate the integrity of the weld. Slag inclusion has several factors. With the right welding technique, all of these factors can be avoided to prevent slag inclusion.
The first step you should take is to avoid improper weld bead placement. Take extra care while doing multiple passes on thicker metal sections. You must ensure that there is adequate space in the weld join to allow additional passes. Be careful in this regard, particularly with joints that need multiple passes.
You must also take care that the travel speed and travel angle are within the acceptable range. The drag angle should range from 15 to 45 degrees for overhead, horizontal, and flat positions. For the vertical up position, the drag angle should around 5 to 15 degrees. If you notice slag inclusions even for angles within these ranges then slowly increase the drag angle.
Keep the travel speed steady. If the travel speed is too low, then the weld pool will be ahead of the arc, which will lead to slag inclusions.
Next, you must be sure that the heat input is appropriate. Deficient welding heat can create slag inclusions. Always follow the electrode manufacturer guidelines for the diameter of the electrode wire. If you still find slag inclusions, then slowly raise the voltage until the problem of slag inclusion is eliminated.
Finally, you must chip off all solidified slag between weld passes. Use a chipping hammer followed by a wire brush or grinder to make sure that the surface is perfectly clean for the next weld pass.
Lack of Fusion and Undercutting
Lack of fusion and undercutting are weld defects that can reduce weld quality and weaken the weld. You should take the steps outlined below to remedy these problems and to lower costs as well as downtime that come with rework.
This groove may melt within the workpiece next to the weld surface without being filled with filler material. This is known as undercutting. There will be a weak region around the weld surface that can cause cracking. You can prevent undercutting by setting the appropriate values for welding voltage and current. Refer to welding parameters mentioned by the manufacturer and set the voltage and current accordingly.
Also, make sure that the gun angle is within the acceptable range. Keep a steady travel speed so that there is enough time for the filler metal to penetrate the molten regions of the base metal. If you are utilizing the weaving technique, then pause whenever you read the side of the weld bead.
Lack of fusion refers to the failure of the filler metal to fuse with the workpiece completely. You can prevent this problem by allowing the right level of heat and maintaining a suitable work angle. You can reach the correct work angle by widening the groove so that the bottom is accessible while welding. You can also retain the right work angle by keeping the stringer bead at the right location on the joint.
Make sure that the arc remains at the trailing edge of the weld pool and keep the gun angle between 15 to 45 degrees. During the weaving technique, momentarily pause whenever you reach the groove sidewalls. Adjust the wire feed rate and raise the voltage till there is complete fusion. If the wire is reaching ahead of the weld pool, you can make simple adjustments to prevent this from happening. You can set a higher welding current or increase the travel speed to solve the issue.
While welding, you must control the level of heat input to prevent problems such as extreme penetration. Extreme penetration is a weld defect in which the molten metal goes through the entire depth of the metal section to hang below the weld. It is often the result of excessive heat. You can prevent this problem by increasing travel speed, reducing the wire feed rate, and setting lower voltage.
Flux-cored arc welding or FCAW is a productive and straightforward welding method that is widely used in the industry. It will continue to remain relevant on account of its high deposition rate and ability to join thick metal sections efficiently.