Today, we are embarking on a 7-part series exploring pulsed micro tungsten inert gas (TIG) welding, also known as micro pulse arc welding. In our first installment, I’ll cover general features of a pulsed micro TIG system, and review the welding applications for which it is best suited. Later blog posts will cover setup tips, improving TIG results, touchstart, pulsation, monitoring, and safety.
What is pulsed micro TIG?
Micro TIG is an arc welding process that creates a high‐temperature (5,000°C) plasma arc between a tungsten electrode and the work piece. An inert gas (typically argon) helps plasma arc generation by displacing air from the weld area, thus lowering the resistance or voltage requirement to jump across the gap.
Micro TIG (as distinguished from macro TIG), is geared toward weld areas that are <18mm^2, for example a copper buss bar, and reaching spots as small as 0.14mm^2, for example, 2 thermocouple wires. This is achieved by supplying a lower current for shorter times and with more precise control than macro TIG welding. See illustration below.
Micro TIG welders typically supply a current from 5 to 300 Amps with pulse durations of up to 4 seconds. Sometimes the pulse is divided into multiple mini-pulses by rapidly turning the current off and on. This feature, called “pulsation,” reduces the porosity of the completed weld nugget.
The graphic below illustrates the components of a complete pulsed micro TIG system, which includes a power supply, torch, electrodes, and a cover gas nozzle. One type of micro TIG is DC pulsed TIG welding, which features a power supply with a non‐consumable electrode.
What are the best materials for micro TIG welding?
Micro TIG welds by heating metal material through the arc formation; the materials melt and fuse together. The best results come from joining two pieces of the same metal of similar size. However, it is also possible to weld dissimilar metals.
Good materials for micro TIG welding include copper, phosphor bronze, iron, nickel, stainless steel, molybdenum, tungsten, platinum, and titanium.
Brass and galvanized steel are not considered appropriate for micro TIG welding because their zinc content causes welding issues. Aluminum is usually difficult to weld with DC pulsed TIG power supplies. This is because aluminum oxide, which builds on the surface, has a much higher melting point than the aluminum base. There are several tips and tricks around this, but it should still be taken into consideration when selecting a power supply. See the accompanying chart to review material weldability for pulsed micro TIG.
Plating is generally not an issue since the plating material typically has a lower melting point. However, if not removed completely, it may compromise the weld with contaminants. Plating may also cause some soot generation during the weld. Therefore, the thinner the plating, the better the results.
Applications of pulsed micro TIG welding include, for example, copper bus bars on the printed circuit board of an automotive engine control unit (see accompanying photo); copper bus ring and wire for the electric power steering unit; and a large-current relay for a hybrid electric vehicle.
The technology is also used for relays and battery tabs in electronic devices; motor cases in industrial devices; and lighting applications like high-intensity discharge lamps (HID lamps).
Since no burrs and wrinkles are allowed on tips and edges of devices inserted into the body, pulsed TIG welding is prized for medical devices like catheters, guide wires and endoscopes, because it makes wire tips smoother and rounder than laser welding.