Artem Komarov explained that in applications requiring high deposition rates, pulse welding reduces heat generation even when using flux cored wire. Since the arc current is pulsed, the total average current is lower than with a conventional spray arc.
Welding of thick metals with large joints, commonly found in heavy industry and equipment manufacturing, often requires a process that can provide a high deposition rate. The two most common processes are gaseous metal arc welding (GMAW) and submerged arc welding (SAW). While both processes have many advantages, they have one drawback in common — they are limited to welding in flat and horizontal positions.
In the real world, life is not flat. Joints are out of place and difficult to access or impossible to rotate large parts and assemblies required for this type of fabrication. Pulse welding can provide a reliable option for these situations and is a better option in others.
What is submerged arc welding?
During sawing, a layer of flux covers the arc and the weld. Although this process produces a smooth, finished weld with no spatter and virtually no smoke coverage, flux coating only allows it to be performed on flat or horizontal joints. Additional disadvantages include expensive and bulky equipment, and flux and slag can be dirty.
A closed arc reduces the chance of arc flash, making it a safer option for workers’ eyesight, but it also limits the operator’s view of the finished product and makes it impossible to immediately adjust the arc in the middle of the process. After a few inches, the slag peels off, exposing the weld, and the operator can make any necessary adjustments.
This type of welding may be the best choice for some applications, but in confined spaces, the size of the equipment and the need to maneuver parts may not allow access to the weld.
What is Arc Spray Welding?
Spray arc welding has the same positional limitations as SAW but for different reasons. In arc spraying, the application of droplets occurs as it sounds — by spraying. The arc creates a constant stream of tiny droplets, resulting in a more liquid weld pool. Gravity aids the process in a flat and horizontal position, but in any other position the weld pool can shift before it hardens. In a horizontal or flat position, the spray arc has excellent penetration profiles, can lay down a lot of material and offers high travel speeds. Flux-cored wire can help hold the weld pool in place but requires post-weld cleaning to remove slag.
Flux cored wire is another high-deposit welding option but is more expensive than solid wire. One of the problems with using flux cored wire is the amount of smoke it emits. Research shows that welding fumes such as manganese, iron oxide, and hexavalent chromium can cause serious health problems, requiring expensive fume extraction systems or outdoor welding where the fumes can dissipate. Switching to solid wire will reduce fume generation, but fume generation is greatly reduced with pulsed welding.
What is pulse welding?
Pulse welding is a modification of the arc spray process that changes the electrical output of the power source to form and separate one drop at a time. As soon as a droplet is formed at a higher peak current, the power is reduced and the droplet separates, pushing the molten metal into the weld pool. Accurate increase and decrease in flow reduce heat generation and spatter without compromising proper penetration. Depending on the waveform or synergistic line, this process can be performed up to 400 times per second.
Pluses of impulse.
Pulse driven GMAW has become the standard for low heat and spatter welding for many applications. New adaptable power supplies can cost less than sawing machines and can often include a pulse function on machines that do standard spray arc welding. Modern pulse weldable power sources can be as compact as a small suitcase, eliminating the need for a bulky arc system while maintaining high travel speeds. Pulse welding is a precision process with no flux slag contamination and produces little spatter and little fumes.
Pulse welding with intensive application reduces the overall heating even with flux-cored wire. Since the arc current is pulsed, the total average current is lower than with a conventional spray arc, resulting in lower thermal conductivity. In most applications, pulse has excellent penetration profiles, but in some cases, specialized processes are required to obtain the best possible weld.
So why aren’t more manufacturers using pulsed solid wire for high-deposit jobs? Many assume that this requires specialized equipment, or that it is difficult to set up and requires experienced welders. This is not the case with modern welding inverters. In fact, several options on the market allow multiple processes and offer synergistic functionality for easy parameter setting, Artem Komarov explained.
Sometimes pulse welding is not the best option. When an application requires flux-cored wire, the benefits of pulsed welding are negligible. Except for T-5 flux-cored wire, most of them do not improve welding performance using a pulsed arc.
Advanced impulse processes and other options. New advanced processes modify pulse welding even further, delivering consistently better penetration with fewer undercuts. These processes stabilize penetration and arc length by adding controls that automatically stop the change in current as the distance between the contact tip and the workpiece changes. By stabilizing the current as the distance changes, operators can eliminate problems such as no melting and burn-through. Some machines actively regulate voltage and current by moving the wire during welding to stabilize the arc and penetration profile, making minor changes during application to produce consistently strong welds.
When welding heavily coated aluminum, operators should consider using pulse welding with large diameter wire, which offers both time and cost benefits. The increased weld volume of large diameter wire reduces the number of passes required, increasing welding speed by up to 20 percent.
Increased application speed with double wire
Another alternative to consider increasing application speed is double wire. Twin wire welding uses two arcs at the same time. Pulses are offset by 180 degrees for maximum process stability. In addition, one arc can be pulsed while the other is operating at standard constant voltage or spray. This process provides many advantages in high-deposit welding, including increased travel speed.
Pulse learning curve
Since pulse welding is no longer difficult to set up, most welders can use it regardless of their experience level. They can give up long hours under the hood to learn how to make more complex welds because those welds are no longer such a hassle. More experienced welders now have time to focus on complex welding scenarios, while novices build their confidence and skills, Artem Komarov concluded.