Components

It was mentioned previously in this chapter that Flux Cored Arc Welding is a semi-automatic process, and this has an impact on the complexity of the equipment involved. With welding processes that are considered manual, the equipment is usually solid-state; that is, there are no moving parts. FCAW always involves a mechanical wire feeding unit that feeds the electrode into the weld pool with the touch of a button (or, more typically, a trigger). This results in a sharp increase in productivity and a reduction in the required operator skill; the trade-off is a higher initial investment in the equipment and a more in-depth troubleshooting process to solve welding issues.

What follows is a list of the major components necessary for the Flux Cored Arc Welding process:

• Welding power source
• Welding gun and cable
• Workpiece lead and clamp (ground cable/clamp)
• Wire feeder
• External shielding gas (not required for FCAW-S)
• Flux cored wire electrode

The rest of this section will be devoted to exploring these components in a greater depth, with the exception of electrodes and shielding gas which have devoted sections.

The Welding Power Source

Welding power sources for Flux Core may come in the form of transformer rectifiers, though inverter machines, capable of multiple welding processes, are becoming the mainstay of the modern welding industry. These welding machines may range in size from compact light-duty units, with the wire feeder and power source integrated into one unit, to large engine-driven “welder generators.” In industrial applications, an FCAW power source will typically be heavy duty, capable of operating at 100% duty cycle at currents of up to 400 amps or more.

Power sources for both GMAW and FCAW must be capable of producing constant voltage (cv) output, sometimes referred to as constant potential (CP). CV machines produce a volt-amp curve that is nearly flat; as opposed to constant current (CC), used in SMAW and GTAW, which produce a steeply sloped volt-amp curve. What this means for you, the welder, is that the welding arc will have small voltage changes and drastic amperage changes depending on your electrode extension. Also, unlike constant current, constant voltage processes do not give the welder direct control over welding amperage; instead, the welding voltage is controlled directly at the power source, while the amperage is dependent on the wire feed speed and electrode diameter. These three things, voltage, wire feed speed, and electrode diameter, must all be selected in conjunction with each other for a smooth welding operation. It should be noted that many modern welding machines are capable of producing either a CV or CC output.

When selecting the polarity at the power source, it is important to check the recommended welding parameters for whatever electrode you will be using. While some of the most commonly used FCAW electrodes for steel operate on direct current electrode positive (DCEP), many are designed to run on direct current electrode negative (DCEN). However, and this also applies to GMAW, another wire-fed process, alternating current (AC), should not be used with FCAW.

The Welding Gun and Cable

Welding guns, informally referred to as torches or whips, come in a number of configurations from many manufacturers. The primary function of the gun and cable is to conduct the electrode, shielding gas, and welding current from the wire feeding unit to the weld pool. The welding gun insulates the welder’s hand from the welding current and allows them to direct and manipulate the wire electrode.

It is especially worth discussing the different parts of the welding gun, as many items are consumable and must be replaced as they wear out.

• The handle is typically a heavy-duty plastic, non-conductive, and heat-resistant. It insulates the welder’s hands from electrical shock. A trigger will send a signal to the wire feeder to push the electrode and complete the welding circuit. Handles for FCAW-S often have a metal heat-shield to protect the welder’s hand further. If the handle has technical problems, it should be serviced by a qualified technician.
• The conductor tube, often simply called the “neck,” is a piece that screws into the handle. This tube conducts power, electrode, and shielding gas past the handle. Curved conductor tubes of various angles are usually used in semi-automatic applications. It is more common to see straight conductor tubes in mechanized operations. Flexible conductor tubes and length extensions are also available. The tube must be replaced when worn, but with proper care can have a very long service life.
• A gas diffuser, a consumable item, attaches to the conductor tube. Diffusers have a series of evenly spaced holes that distribute shielding gas evenly as it leaves the conductor tube. If porosity is encountered the holes in the diffuser may have become clogged or misshapen. The diffuser also typically conducts power to the next item on our list.
• The contact tip is where the wire electrode becomes electrified. Contact tips are simply copper cylinders with holes of a very specific size through the center. The hole is sized according to electrode diameter and must fit well to provide a good electrical connection. Over time, as the tip is heated and cooled repeatedly, the hole may become misshapen and prevent the wire from feeding. A worn tip may be to blame if wire is not feeding or feeding is irregular.
• The gas nozzle, or gas cup, directs the shielding gas towards the weld area. The nozzle acts like a shroud, covering the contact tip and gas diffuser. The nozzle must also be insulated from the welding circuit; the insulator, usually ceramic but always non-conductive, may be a separate piece that screws onto the conductor tube just below the gas diffuser, but many gas nozzles have integrated insulators. If the insulator fails, an electrical arc can jump between the base metal and gas nozzle, causing arc strikes. The nozzle should be cleaned regularly as it will fill up with weld spatter; a pair of ‘welpers’ or MIG pliers are useful for cleaning the nozzle. If the nozzle fills up with too much spatter, the flow of shielding gas will be impeded (causing porosity), or the gas nozzle may become electrified (causing arc strikes).

Like many components in the welding system, the welding gun will have an amperage rating. If the welding current exceeds the amperage rating of the gun, it will become overheated and rapidly deteriorate. Guns rated up to 400 amps are typically gas-cooled; the flow of shielding gas through the gun is sufficient to keep it cool. Welding guns with higher amperage ratings tend to be liquid-cooled, coolant is circulated through the gun as it is being operated. For liquid-cooled guns it is important to make sure coolant is present in the system and the coolant pump is running.

The cable of the welding gun contains a power cable to transmit the welding current, a gas line for shielding gas, and a liner through which the wire electrode is pushed. In the case of liquid-cooled torches, there will also be coolant out and coolant return lines. Of all the lines within the cable, there is one that you, the welder, may be expected to service: the cable liner the electrode moves through. As the wire is fed through the liner, it often introduces dust and debris to the liner; over time, this will cause wire feeding issues. This can be prevented by installing cleaning and lubricating pads over the wire at the wire feeder, though the cable liner will still need to be cleaned and possibly replaced over a long enough time.

There is another way in which the cable can lead to wire feeding issues. If, at any time during welding, you are experiencing erratic wire feeding, take a look at the cable. Does the cable have numerous sharp twists and turns in it? If so, this may be the source of the problem. Every tight turn in the gun cable makes it that much more difficult for the wire feeder to move the wire through the gun cable liner. Keep any curves in the cable large and gentle.

The Workpiece Lead and Clamp

The workpiece lead and clamp, often collectively referred to as the ground clamp, connect the work to the welding circuit. Both the lead (cable) and clamp have amperage ratings, just as with the welding gun; if this rating is exceeded, the components will rapidly heat up and deteriorate.

FCAW is a welding process that uses direct current electricity. These processes are susceptible to arc blow, an unstable welding arc caused by the strong magnetic force produced by the welding circuit. Arc blow can be a difficult issue to solve, but often moving the workpiece clamp to a different location will help minimize or eliminate it. Additionally, slowing the wire feed rate will result in a lower welding amperage, which may also be helpful.

The Wire Feeding Unit

Wire feeders, or really wire feeding systems, can come in a number of different configurations. In industry, it is most common to see wire feeders as separate machines that are connected to the welding power source. The electrode lead will run from the negative or positive terminal on the welder to a power block inside the wire feeder, this will provide electricity for both the motor in the wire feeder and the welding circuit itself. Shielding gas, if necessary, will also be piped in from the cylinder or gas system to a connection in the wire feeder. The coil of wire electrode will typically mount to a spindle on the wire feeder and pass through a set (or sets) of drive rolls that push (and in some cases pull) the electrode through the gun cable, along with the shielding gas and electricity of the welding circuit.

Though it is most common to see wire feeding systems as described above, that is not the only way they may be encountered. Smaller welding power sources, meant for hobbyists or light-duty work, may have the welding machine and wire feeder integrated into one unit. In the case of ‘push-pull’ systems part of the wire feeding system is integrated into the welding gun. In the case of spool guns, the entire wire feeding system is integrated into the welding gun itself.

The primary function of the wire feeding system is to feed the long coil of wire electrode to the welding area where it is melted off, transferred to the weld puddle and then solidifies into weld metal. The simplest and most common wire feeding system is a ‘push’ system. In this system a pair, or pairs, of motorized drive rolls pull the coiled wire electrode off the spool and push it through the gun cable, driven by an electric motor in the feeder, which is activated by the trigger on the welding gun.

Wire feeders are complex machines, if any serious repair is required a qualified technician should service the machine. There are parts of the system that must be changed out, replaced, or adjusted on a routine basis, it is a common expectation that the welders themselves will be able to recognize and service these items.

• Drive rolls are a pair of wheels with specifically sized grooves, the wire electrode fits inside the grooves and is squeezed. The drive rolls are turned by a variable-speed motor, pushing the electrode through the gun cable. As mentioned, drive rolls are specifically sized, and designed to work with a specific diameter of electrode. Additionally, there are several types of grooves that drive rolls may have:

• V groove drive rolls are commonly used for steel electrodes which have a solid composition
• U groove drive rolls are used with solid wire electrodes that are soft, like aluminum, and may be deformed if squeezed between V groove drive rolls. If the wire is deformed, or squished out of its round shape, it makes it difficult or impossible to feed it through the gun cable and contact tip.
• Knurled drive rolls have small teeth in the grooves. This allows the drive rolls to grip and push the electrode without applying too much pressure. These rolls are used for FCAW, as those electrodes are not solid, but consist of a tubular sheath filled with flux.

• The drive roll tension knob adjusts the pressure the drive rolls squeeze the electrode with. Too much tension deforms or damages the wire, leading to inconsistent feeding and introducing debris into the gun cable. Too little tension will cause the drive rolls to slip rather than push the wire.
• The wire guide ensures the wire accurately passes through the groove in the drive rolls. The wire feeder pictured above has a single guide that fits over the drive rolls. Other feeders may have two guides, one on the inlet and another on the outlet side of the drive rolls. Like drive rolls, wire guides are designed to work only with specific electrode diameters. A given electrode diameter must be used only with matching drive rolls and guides.
• The gun cable set screw secures the gun cable into a bushing in the wire feeder. This gun cable receiver bushing is where the electrode, power, and shielding gas enter the gun cable. This screw must be tightened securely to prevent the gun cable from working its way out of the wire feeder.

A push system is the simplest, most economical wire feeding system and is the one most often employed for FCAW. Spool guns and push-pull systems are most often used to feed particularly soft electrodes (like aluminum) or for very small diameter electrodes (0.023” and smaller), which have a high likelihood of bird-nesting. Bird nesting occurs when the wire electrode folds over the top of itself rather than smoothly traveling through the gun cable. This results in a tangle of wire balling up near the drive rolls and must be removed before welding can continue.

In industry, FCAW is mostly used for welding thicker sections of steel, using wire electrodes large and stiff enough to be fed with a push system. To ensure consistent wire feeding, a couple of things must be taken into consideration. First, the length of the gun cable should not be excessive. The longer the cable, the harder the wire feeder has to work; a 10 to 12-foot gun cable is common for most applications. Second, care should be taken to keep the gun cable free of sharp twists and turns. The straighter the gun cable, the easier it is for the wire feeder to successfully push the electrode through the length of the gun cable.

There are many adjustments and settings on modern wire feeders. Some of these, like wire feed speed, are essential variables to the welding process. Others, like trigger interlock, make the work easier and increase operator appeal.

• Wire feed speed, WFS, is controlled by a knob that adjusts the voltage sent to the motor, which turns the drive rolls. In the US, wire speed is measured in inches per minute, IPM. On the above wire feeder, the knob has a scale that reads in IPM; this is not only the case. To accurately determine wire speed, trim the wire flush with the gas nozzle, use a stopwatch to feed wire for exactly 15 seconds, then measure the inches of wire fed out of the gun in that time; multiply by four; this will calculate the inches of wire fed per minute. WFS, in conjunction with electrode diameter, will determine welding current or amperage.
• A gas purge and cold feed switch is common on most modern wire feeders. These are items of convenience. Cold feed, sometimes called jog, feeds wire without electrifying the welding circuit; it is helpful when fitting the machine with a new spool of electrode. The gas purge button pushes shielding gas through the system without feeding wire; it is used when adjusting gas flow rates or troubleshooting shielding gas problems.
• The trigger interlock switch changes how the gun trigger functions. Without trigger interlock, the gun trigger must be constantly held to continuously feed wire. With trigger interlock, the gun trigger functions with a toggle; pull the trigger once to begin feeding wire and again to stop. Trigger interlock can help reduce fatigue when making especially long welds.
• The gun cable receiver is a bushing where the gun cable attaches to the wire feeder and receives the electrode, power, and shielding gas.
• The gun trigger connection is where a communication cable connects from the gun cable to the feeder. This allows the gun trigger to communicate with switches inside the feeder, which control the drive rolls, power, and shielding gas flow. On some feeders, this cable can easily come unplugged and should be a point of interest if the wire feeder suddenly seems to stop working.

Setting up the welding system

The first step in setting up any arc welding system is getting power to the welding power source. This is as simple as plugging the machine in, but the circuit must have the proper voltage and amperage. Light and medium-duty machines may plug into 110 or 220-volt circuits, respectively; 20 or 30 amps on the circuit are common. Do not take these numbers at face value; the required electrical input for any welding machine will be specified by the manufacturer and listed on the machine itself or the owner’s manual. Heavy-duty machines commonly require a 480-volt 50-amp circuit. These types of circuits have what is called 3-phase power, this type of electrical power is not typical to a home or outside industrial environments.

Once power is supplied, the machine should be set up to run DCEP polarity . A properly sized power cable should be connected from the positive terminal of the machine to a terminal inside the wire feeding unit. The workpiece lead and clamp should be connected to the negative terminal of the welding machine. DCEP is overwhelmingly the norm for FCAW, but there are a few wire electrodes that should be used with DCEN; in any case, the electrode manufacturer’s recommendations should be followed. AC is not used in FCAW or GMAW.

Next, we’ll turn our attention to the wire feeder. FCAW-G, gas shielded flux core, will need a supply of external shielding gas to protect the molten weld puddle from atmospheric gasses properly. A cylinder of the proper shielding gas should be fitted with a regulator and flow meter. From the flow meter, a gas line is connected and run to a shielding gas inlet, usually located on the back of the wire feeder. The type of shielding gas used will depend on the material being welded. In this and all other cases, the high pressure cylinder of shielding gas should be anchored to the welding cart of a wall by a chain to prevent it from falling. If using FCAW-S, self-shielded flux core, shielding gas is not required.

The wire feeder must now be fitted with the proper drive rolls, wire inlet, and outlet guides. When installing these components, the diameter of the wire electrode must be considered, as these parts are made to accommodate specific wire sizes.

The spool of wire electrode can be put on. The spool must be oriented correctly so that the end of the wire rolls off the spool from the bottom. The end of the wire will be secured to the spool frame, it is critical that once the end of the wire is freed from the spool frame, do not let go of it. If you do, the spool of wire will uncoil and create a huge mess, it can be difficult or impossible to salvage the spool if this happens. Keeping hold of the wire, pass it through the inlet hole on the back of the feeder housing. Feed it through the wire guides and drive rolls, clamping the drive rolls onto the wire and securing them in place with the tension knob. Once the wire is clamped in the drive rolls there is no danger the spool will uncoil.

The wire can now be fed through the gun cable using the gun trigger or cold feed switch. When feeding new wire through the gun cable, the gas nozzle and contact tip should be removed from the gun as the wire can get hung up on the contact tip. The gun cable should also be kept as straight as possible to ease the feeding of the wire. Be sure to reinstall the contact tip and gas nozzle once the wire has been fed through the gun.

With this completed, the system is ready to weld. Connect the workpiece clamp to the work, and you can get to welding!

Attributions

1. Figure 9.3: Major Pieces Of Equipment Used In The FCAW Process by Nicholas Malara, for WA Open ProfTech, © SBCTC, CC BY 4.0
2. Figure 9.4: Two FCAW Welding Systems by Cameron Kjeldgaard, for WA Open ProfTech, © SBCTC, CC BY 4.0
3. Figure 9.5: Assembled Welding Gun by Cameron Kjeldgaard, for WA Open ProfTech, © SBCTC, CC BY 4.0
4. Figure 9.6: Disassembled Welding Gun and Consumables by Cameron Kjeldgaard, for WA Open ProfTech, © SBCTC, CC BY 4.0
5. Figure 9.7: FCAW Wire Feeder by Mgschuler is released under CC BY 3.0
6. Figure 9.8: Spool Gun by Cameron Kjeldgaard, for WA Open ProfTech, © SBCTC, CC BY 4.0
7. Figure 9.9: Push-Pull Welding Gun by Cameron Kjeldgaard, for WA Open ProfTech, © SBCTC, CC BY 4.0
8. Figure 9.10: Wire Feeder, Interior by Cameron Kjeldgaard, for WA Open ProfTech, © SBCTC, CC BY 4.0
9. Figure 9.11: Drive Rolls Used In Welding Wire Feeders by Nicholas Malara, for WA Open ProfTech, © SBCTC, CC BY 4.0
10. Figure 9.12: Wire Feeder, Front by Cameron Kjeldgaard, for WA Open ProfTech, © SBCTC, CC BY 4.0
11. Figure 9.13: Gun Cable End by Cameron Kjeldgaard, for WA Open ProfTech, © SBCTC, CC BY 4.0