FCAW welding fundamentals

The fundamentals of FCAW are about the same as those for other arc welding processes discussed in this text:

• Electrical characteristics (current, voltage, and polarity)
• Electrical stickout
• Work and travel angle
• Travel speed
• Electrode manipulation

Electrical characteristics will be recommended by the electrode manufacturer and controlled by the welding procedure specification. The required polarity for an electrode must be used. However, welding current and voltage will be recommended as a range and there is room for adjustment. Where you set the machine within this range is really a function of base metal thickness. Thicker base metals will require higher electrical settings which increase the heat of the welding arc. Remember, there is no direct way to control welding amperage; amperage is determined by wire feed speed and electrode diameter. With larger electrodes and higher speeds resulting in high welding amperage. At all times when making these adjustments you should remain within the range recommended by the manufacturer, or required by the welding procedure.

Electrical stickout is somewhat analogous to arc length (see SMAW or GTAW chapters). It is the distance the welding gun is held from the work. It is critical that the proper stickout is maintained as the electrode is moved down the joint. This takes practice, don’t get discouraged. Proper head position is helpful in maintaining proper stickout if the head is positioned to one side or the other of the welding gun allowing the welder to actually see the electrical stickout during welding. If the head is positioned directly behind, or nearly behind, the welding gun it is difficult or impossible to see the amount of stickout.

The angles of the electrode have a huge effect on where the heat of the arc is directed and the shape of the finished weld bead. Despite this, electrode angles are not controlled in welding procedures, they are left up to the discretion of the welder. Selecting the proper angle and maintaining it throughout welding is a practiced skill.

Remember, travel angle is the angle of the electrode relative to the length of the weld joint. Travel angle in FCAW is rather straightforward; a pulling or dragging angle of 10 to 30 degrees should be used. “If there’s slag you drag” is a common saying among welders engaged in welding processes that produce slag; it speaks to a problem with pushing these types of electrodes. If FCAW electrodes are pushed along the joint there is a strong chance a ball of slag will be pushed in front of the weld puddle resulting in a slag inclusion at the root of the weld bead. The one exception to this rule is when welding in the vertical position with an upward progression. In this position, a slight push angle of 10 to 15 degrees should be used.

Work angle, the angle of the electrode relative to a cross-section of the joint, is a more complicated matter. The exact work angle used is a matter of how the joint is designed and where the welder would like to direct the heat of the arc and deposited weld metal. In multiple pass welds the work angle of each weld pass may be different in order to properly fuse each pass and achieve the correct weld size. Take the example below of a three-pass fillet weld in a T joint:

• A 45o work angle is used in the first pass, directing the heat and weld metal straight into the joint root
• In the second pass a higher work angle of 60o is used to ensure proper fusion to the weld bead and base metal below
• In the third pass a lower work angle of about 30o is used, this helps to push the weld deposit upward and give the vertical leg of the weld its proper height

Travel speed is the speed the electrode progresses along the joint. Travel speed in FCAW, and GMAW, is significantly faster than SMAW or GTAW. This can present a challenge when learning the process. Travel speed is an essential variable, recommended by the manufacturer, and controlled by a WPS. Too slow a travel speed can result in an overly convex weld and overlap. Too fast a travel speed can leave undercut, lack of proper fusion, and an undersized weld. The proper travel speed for FCAW electrodes typically ranges from 8 to 12 inches per minute, but always consult the electrode manufacturer’s recommendations or the proper WPS, to ensure successful welding.

Electrode manipulation can be used to increase the size or width of an individual weld bead and can be helpful in controlling the heat of the welding puddle. FCAW has a high deposition rate and large-diameter electrodes are available, because of this a stringer bead is often sufficient, especially in the flat position. However, when welding with a smaller electrode, or in a position other than flat, a weaving technique can be favorable. Small oscillating motions, back and forth, along the path of the weld joint can also help increase bead size and thickness. Even when a stringer bead is sufficient, putting small repetitive motions into the electrode can set you into a rhythm which can help to maintain a consistent travel speed.

Attributions

1. Figure 9.15: Work Angle by Nicholas Malara, for WA Open ProfTech, © SBCTC, CC BY 4.0