Plasma welding derives its unique operating characteristics from the torch design. As in TIG welding, the arc is formed between the end of a small diameter tungsten electrode and the workpiece . However, in the plasma torch, the electrode is positioned behind a fine bore copper nozzle. Plasma is present in all arcs. If a constricting orifice is placed around the arc, the amount of ionization , or plasma , is increased. This results in a higher arc temperature and a more concentrated heat pattern than exists in TIG welding.
Three different operating modes can be produced by the choice of the nozzle bore diameter, current level and plasma gas flow rate:
Microplasma (0.1 to 15A) is equivalent to microTIG but the columnar arc allows the welder to operate with a much longer arc length. The arc is stable at low welding current levels producing a columnar beam which is suitable for welding very thin section material.
Medium current plasma (15 to 100A) similar to conventional TIG, is also used for precision welding operations and when a high level of weld quality is demanded.
Keyhole plasma (over 100A) is produced by increasing the current level and the plasma gas flow. It generates a very powerful arc plasma, similar to a laser beam. During welding, the plasma arc slices through the metal producing a keyhole, with the molten weld pool flowing around the keyhole to form the weld. Deep penetration and high welding speeds can be achieved with this operating mode.
Equipment Required List
- Power Supply
- Plasma Console
- Water re-circulator
- Plasma Welding Torch
- Torch Accessory Kit (Tips, ceramics, collets, electrodes set-up gages)
List of Plasma Welding Features
- Protected electrode, offers long times before electrode maintenance (usually one 8 Hr Shift) .
- Eliminates tungsten contamination.
- Low amperage welding capability (as low as 0.1 amp)
- Arc consistency and stable, gentle arc starting produce consistent welds, time after time
- Stable arc during arc starting and low amperage welding.
- Minimal high frequency noise interference, HF only initiates pilot arc start, not for each weld
- Heat content is higher , less current required compared to TIG.
- Higher weld speeds possible
- Weld times as short as 5 msecs (.005 secs)
- Concentrated energy density reduces heat affected zone, improves weld quality
- Less distortion due to less heat input to job.
- Diameter of arc chosen via nozzle orifice
- Penetration can be controlled by varying welding variables.
- Reasonable variations in torch standoff distance has little effect on bead width or heat concentration at the work, this makes out of position welding much easier.
In many applications, many of the unique advantages of plasma combine to benefit the overall welding process. Plasma arc welding is adaptable to both manual and mechanized operation , and can be used to produce either continuous or intermittent welds.
Small Part Welding: The plasma process can gently yet consistently start an arc to the tip of wires or other small components and make repeatable welds with very short weld time periods. This is advantageous when welding components such as needles, wires, light bulb filaments, thermocouples, probes and some surgical instruments.
Sealed Components: Medical and electronic components are often hermetically sealed via welding. The plasma process provides the ability to:
1.Reduce the heat input to the part
2.Weld near delicate insulating seals
3.Start the arc without high frequency electrical noise which could be damaging to the electrical , electronic internals
Applications include Pressure and Electrical Sensors, Bellows, Seals, Cans, Enclosures, Microswitches, Valves, Electronic Components, Motors, Batteries, Miniature Tube to Fitting/Flange, Food and Dairy Equipment, Tool Die & Mould Repair .
Plasma arc welding is used to join most of the metals commonly welded by GTAW. These metals include carbon and low alloy steels, stainless steels, copper alloys, nickel and cobalt based alloys, Titanium alloys.
Manual PAW generally is considered to be an all position process.Mechanized PAW is done in the flat and horizontal positions.
Comparison of GTAW and Plasma Welding Energy Input
The following is from a test made with the GTAW (Tig) and Plasma welding processes on a specific strip of test material in order to establish a comparison of the energy input of poth processes. The test results should be used as a general guideline comparison only.
Test Parameters: Manual welding, no clamping device, Cr/Ni steel, 2.59mm thickness. All values determined with measuring instruments.
GTAW: 125 Amps, 12 Volts, 10.24 I.P.M. (26 cm/min)
Plasma: 75 Amps, 18 Volts, 13.38 I.P.M. (34 cm/min)
||V x A x 60
Speed in cm/min
||12 x 125 x 60
|= 3.46 KJ
||18 x 75 x 60
|= 2.38 KJ
: Report prepared by welding application cell at Arcraft plasma equipments(I) pvt ltd.