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Techniques for Flux Core Welding
Technologies evolve by the day, but when it comes to welding — especially flux core welding — techniques remain an integral part of the trade.
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Push Technique
The push technique involves holding the welding gun at a slight angle and pushing the weld pool away from you. This method has its merits as it allows for greater visibility and control of the weld bead. Given the design of the gun and its cable, the push technique is also preferred for thinner materials. Because the weld bead is wider and shallower, push welding lowers the risk of burn-through. The most advantageous angle for the push technique is between 10 and 15 degrees.
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Drag Technique
The drag technique is quite unlike its predecessor. With the drag technique, a welder holds the gun, and the cable it’s connected to, at an angle. One drags the welding gun toward them, dragging the weld pool along with it (while watching the weld pool). In this instance, a deeper penetration is created. This technique is ideal for thicker materials.
What sets these two techniques apart?
Penetration: Drag welding offers a deeper penetration. On a 6mm steel plate, for example, one can achieve a penetration depth of up to 4mm. With push welding, penetration depth may only reach up to 2mm.
Weld Bead Appearance: The push technique results in a wider, flatter bead — optimal for thin sheets, such as when aesthetics are key. With drag welding, a more pronounced, narrow bead is produced.
Welding Speed and Efficiency: Because penetration is more shallow, the push technique can allow a welder to travel steep faster. On thin sheets, welding speeds can reach up to 30 inches per minute. On thicker sheets, drag welding allows for a speed of up to 20 inches per minute.
Material Suitability: Thinner sheets and soft materials like aluminum require heat control. They are best suited for the push technique. Also, to prevent burn-through, thin materials should be welded with the push technique. Thicker materials, such as structural steel, are best welded with the drag method.
In the end, the decision to push or to drag will depend on material thickness, the desired penetration, and the required appearance of the weld bead. Both techniques lend themselves to various advantages. That’s what makes them an indispensable part of a welder’s bag of tricks.
Advantages and Disadvantages
The push technique offers a number of advantages in flux core welding:
Improved Visibility: Since the weld pool is pushed in front of the arc, as opposed to being dragged behind it, the welding area is far more visible with the push technique. As a result, this technique is better suited for applications that require precision welding.
Wider Weld Bead: Pushing the weld pool also yields a wider and flatter weld bead, which is beneficial for thin materials in which aesthetics are of high concern, as is often the case in automotive applications.
Reduced Penetration: Since the push technique provides less penetration, it’s less likely to burn through thin materials. Using the push technique, a welder can handcuff a 2mm-thick sheet to 1mm penetration, greatly reducing distortion.
Increased Speed: The reduced penetration also means welders can travel faster using the push technique than they can the drag technique, making it more productive.
Advantages of Drag Technique
Conversely, the drag technique offers some advantages of its own:
Deeper Penetration: Deep penetration is a must when welding thicker materials and it’s something the drag technique delivers. With a 10mm steel plate, for example, welders can use the drag technique to penetrate 8mm.
Narrower Weld Bead: The drag technique also results in a narrower, more concentrated weld bead. This is ideal for thick materials that require lots of clean, strong joints, i.e. things that carry heavy loads.
Better Shielding Gas Coverage: Since the drag technique pulls the weld pool along, it makes it easier for a welder to maintain the gas coverage over the weld pool. This not only reduces the risk of porosity and a bad looking weld bead, it also creates a smoother weld profile, which often means less cleanup.
Selecting the Right Technique
Choosing one technique over the other won’t require as much analysis as some of the other selections welders have to make, but it’s important to know the right technique to use for the job. Here’s a quick guide:
Material Thickness: When welding thin materials, it’s go push or go home. Thicker materials will require the drag technique.
Desired Penetration: Whether using the push or the drag technique, the voltage, amperage and, particularly, the stickout will have a play a big part in determining weld bead penetration. To generate deep penetration, go with the drag technique; for a shallower weld bead, employ the drag technique.
Weld Appearance: Wanna make it look good? Use the push technique.
Welding Speed: Go with the push technique to travel faster.
Common Challenges and Solutions
Preventing Porosity
Porosity, in which gas pockets form within the weld, causing it to break or crack, is often a problem with flux core welding. It can be prevented by taking these steps:
Use clean materials. Keep the surface of the piece to which you are welding free from oil, rust, and moisture. Gas is less likely to form if you’re welding on a clean surface.
Maintain proper flow rates for your shielding gas. If you are using a shielding gas, make sure that the flow rate is set so that there is adequate protection. Typically, 20-25 cubic feet per hour of shielding gas is adequate.
Don’t weld too fast. Welding too quickly can trap gas in the weld. Keep your speed slow enough to allow gas to escape.
Avoiding Spatter
Spatter is the droplets of molten metal that scatter during welding. It results in a messy finish, but adjustments to your equipment’s settings can minimize it:
Wire feed speed. A well-reigned wire feed speed reduces spatter. Most welders find 250 inches per minute work for a 0.035-inch wire.
Voltage settings. The proper voltage settings help keep the arc stable, as well as reducing spatter. A voltage range of 18-22 volts is usually helpful for 0.035-inch wire.
Anti-spatter spray. Many welders have found that a spray is helpful in keeping spatter from sticking to the nozzle and workpiece.
Controlling Heat Input
Proper heat input helps in preventing warpage and distortion. Here’s how you can control the heat input in a flux core welding process:
Correct welding technique. Switching between the push and drag technique distributes heat evenly. These methods can be alternated.
Interpass cooling. Allowing your piece to cool between passes will help you control the overall heat input. Many flux cored welders take a 10-15 second cooling period.
Welding parameters. It’s important to use the appropriate combination of voltage and wire feed speed so that you manage the heat. Lower wire feed speed and a higher voltage decrease heat input in AT-6 .030” wire.