What is plasma arc welding (PAW)?
This is another type of arc welding process that uses a non-consumable electrode just like tungsten inert gas welding (TIG), making them a similar process. It creates an arc between the electrode and the workpiece.
Plasma arc welding (PAW) coalescence is produced by heat obtained from a constricted arc setup between a tungsten electrode and the constricting nozzle, which is a non-transferred arc. It can also be between a tungsten/alloy tungsten electrode and the workpiece, which is a transferred arc.
This process has the ability to use two inert gases, one forms the arc plasma and the other creates shields to the arc plasma. Same as TIG welding, filler metal may or may not be added.
PAW welding is said to be an advance of TIG welding. in TIG welding, the open arc is shielded by argon and helium, but in plasma, a special torch uses a nozzle to separately pushed the arc and shield gas to the torch.
The arc is constricted and pushed by a water-cooled small-diameter nozzle by squeezing the arc, increasing its temperature, pressure, and intense heat, helping to improve the arc stability.
Just as mentioned earlier, PAW arcs are formed by two gas flows: luminal and turbulent flow. The luminal flows at low pressure and low flow of plasma gas, which is employed to ensure that the molten metal is not blown out of the weld zone. Whilst, the turbulent flows at high pressure and high plasma gas flows. These gases are argon, helium, hydrogen, or could be their mixture.
Applications
Micro-plasma welding is traditionally used for welding thin sheets at a minimum of 0.1mm thickness and wire and mesh sections. It is used in the marine and aerospace industries. Plasma arc welding is used to weld pipes and tubes of stainless steel and titanium.
It is a good choice when repairing tools and dies. This welding process is also used for welding and coating on a turbine blade. Finally, plasma arc welding is widely used in electronic industries.
In essence, TIG welding is a traditional process used in the medical industry, but plasma welding (PAW) is a more efficient and efficient method for manufacturing steel tubes.
PAW offers high-speed welding with great metal penetration, making it ideal for delicate materials sensitive to environmental factors. Its low current mode allows for small metal component welding, making it ideal for the medical industry, where precise components are required for effective operation.
Related: How Does Tungsten Inert Gas (TIG) Welding Works?
Components of Plasma Arc Welding
The major parts of PAW machine include power supply, shieding gas, plasma torch, voltage current, current and gas decay control, fixture, voltage current, and high frequency generator. Here is a quick explanation of the machine parts.
The plasma welding process involves a high-power DC supply to generate an electric spark between the tungsten electrode and welding plates, similar to TIG welding. The plasma welding torch is crucial in this process, as it is water-cooled and can weld at low 2 amps. The power source consists of a transformer, rectifier, and control console.
The plasma welding torch is water-cooled, providing a water jacket outside the torch. A water re-circulator cools the torch by the continuous flow of water outside the torch. The tungsten electrode is used, which can withstand high temperatures.
Two inert gases, helium, argon, and hydrogen, are used in this process to maintain low pressure and prevent turbulence. Plasma gas, an ionized hot gas composed of nearly the same number of electrons and ions, is the main energy source for this welding.
Torch accessories are used to expand the performance of the welding torch. If filler material is used, it is directly fed into the weld zone. The plasma welding process requires a high-power DC supply, a tungsten electrode, shielding gases, and voltage current. The plasma gas is an ionized hot gas with sufficient energy to free electrons from molecules, atoms, and electrons to synchronize.
Diagram of Plasma Arc Welding Machine
How Does Plasma Arc Welding PAW Works?
Plasma arc welding involves striking an arc between a non-consumable tungsten electrode and the workpiece. The nozzle’s unique design allows the arc plasma to exit the torch separated from the shielding gas envelope.
The narrow opening of the nozzle increases plasma gas flow rate, allowing deeper penetration. The complexity of the plasma welding torch sets it apart from gas tungsten arc welding. Plasma welding torches operate at high temperatures, making it necessary to always be water-cooled.
Modern plasma welding guns are designed for automatic welding. Common defects associated with plasma welding include tungsten inclusions and undercutting. Tungsten inclusions occur when the welding current exceeds the electrode’s capabilities, while undercuts are common in keyhole mode PAW welding and can be avoided using activated fluxes.
Operating Modes of Plasma Arc Welding
Microplasma welding is a versatile welding technique that utilizes three operating modes: Microplasma (0.1-15A), Medium current (15-200A), and Keyhole mode (over 100A). Microplasma welding allows for low currents and stable arcs up to 20mm, making it ideal for joining thin sheets up to 0.1mm thick.
Medium current offers better penetration and protection, but requires maintenance and is bulkier than TIG welding. Keyhole mode, on the other hand, uses a powerful plasma beam to engage in high-current welding, allowing deep penetration and consistent weld pool creation from molten metal.
This mode is ideal for welding thicker materials at high welding speeds and is commonly used in mechanised welding, positional welding, and pipe welding. Filler material is typically added to ensure satisfactory welds.
Difference Between PAW and TIG
Plasma welding is a method that uses a welding torch to create a plasma jet with high heat concentration, offering deeper penetration. It differs from TIG welding, which uses a tungsten electrode to strike an arc between the torch and the workpiece.
Plasma welding offers greater precision and a smaller heat-affected zone, making it ideal for narrower welds. Its technology allows it to run with lower current demand and better arc stability, leading to better stand-off distance and tolerances.
However, TIG welding is simpler due to the complex parameters available for plasma gas welding, requiring extra training for operators. Despite this, TIG welding equipment is cheaper and requires less maintenance than plasma arc welding’s sensitive and complex torch.
Related: How Does Flux-Cored Arc Welding (FCAW) Works?
Advantages and Disadvantages of PAW
Plasma Arc Welding is a welding method that uses a torch design to control the arc, producing a high heat concentration and keyhole effect. This method allows for faster travel speeds and complete penetration of joints, with a smaller heat-affected zone compared to Gas Tungsten Arc Welding (GTAW).
However, it produces wider welds and heat-affected zones compared to LBW and EBW, requires costly equipment, requires training and specialization, produces ultraviolet and infrared radiation, and produces higher noise. The torch is bulky, making manual welding difficult and requiring training. Overall, Plasma Arc Welding offers advantages and disadvantages in welding processes.