Principles of PAW
Plasma arc welding is basically an extension of gas metal tungsten welding (GMAW or TIG). Both welding processes generally use nonconsumable tungsten electrodes to carry power to the welding torch and into the orifice gas. The orifice gas represents much of what is different about the GMAW welding process and the PAW welding process. The design of a PAW torch allows for the orifice gas to build up in a chamber at the end of the torch. The arc heats up the orifice gas to nearly 30,000 degrees Fahrenheit. At this point, the orifice gas turns to plasma and is expelled through a narrow opening at the end of the welding torch. As in GMAW, a shielding gas surround the weld pool to create an inert environment to keep the weld pool clean and free from oxygen that will rust the metal.
Advantages and Limitations
The main advantage of plasma welding lies in the control and quality produced in the part being welded. The torch design allows for better control of the arc, as well as a higher tolerance for in torch standoff distance. Welds are typically cleaner and smoother when using the PAW process. Smaller heat-affected zones result in welds that are very strong and less noticeable, which is important for some parts.
A major limitation in implementing a plasma welding process is the relatively high startup costs. Plasma welding equipment tends to be expensive. Because it is a more specialized welding process, the training and expertise required is also more intense.
PAW and Industrial Robots
FANUC Robotics, Motoman Robotics, KUKA Robotics, and many other industrial robot manufacturers have developed robot arms specifically designed to automate welding applications. Any of these manufacturers’ arc welding robot arms can handle a plasma arc welding dressout package. FANUC’s ArcMate 120i and Motoman’s EA1400 robot arms are examples of these robots.