TIG Welding



WHAT IS TIG WELDING?



TIG (Tungsten Inert Gas) Welding – known officially as Gas Tungsten Arc Welding (GTAW) - is an arc welding process that uses a non-consumable tungsten electrode to produce the weld.



The weld area is protected from atmospheric contamination by a shielding gas (usually an inert gas such as argon), and a filler metal is normally used, though some welds, known as autogenous welds, do not require it.



A constant-current welding power supply produces energy which is conducted across the arc through a column of highly ionized gas and metal vapours known as plasma.



TIG Welding is most commonly used to weld thin sections of stainless steel and non-ferrous metals such as aluminium, magnesium, and copper alloys. The process grants the operator greater control over the weld than competing procedures such as shielded metal arc welding and gas metal arc welding, allowing for stronger, higher quality welds.



However, TIG Welding is comparatively more complex and difficult to master, and furthermore, it is significantly slower than most other welding techniques.



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TYPES OF TIG WELDING



Direct Current (DC) – This method of welding is suitable on most types of materials with the EXCEPTION of Aluminium and Magnesium Alloys.



If you are not required to weld Aluminum and Magnesium, a DC-only capable TIG Welder will be sufficient for your needs.



Alternating Current (AC) – This method is ONLY used on Aluminium and Magnesium Alloys.



Should you need a machine capable of welding Aluminum then you will require a TIG Welder which has AC/DC capability.



Most modern AC Welding Machines are inverter types which also have DC Capacity.



TIG Welding



GAS DELIVERY



TIG welding requires insert gas shielding, so a method of connecting gas and introducing it into the weld is required.



More sophisticated machines will have an in-built gas valve, which the machine will turn on when the torch trigger is pressed.



These machines will usually have added features of post gas and pre-gas where the user can set a time – usually seconds – to add gas to purge the weld areas before welding is started, and continue gas flow to prevent oxygen contaminating the weld pool, and allow weld pool cooling at the end of the weld.



The less sophisticated machine has no in-built gas valve and will require a torch with in-built manually operated valve.



If TIG welding is the main task, then a machine with a gas valve will be necessary. If TIG welding is only required for occasional jobs, or a long-weld job, i.e. in cladding applications, then the manual gas valve might be quite adequate.



ARC STARTING



Arc starting is a major consideration when TIG Welding. There are three styles of starts:



Scratch start



This is an older style of starting technique usually associated with a transformer type machine. Not as common now with inverter machines.



Lift start



This type of start is possible with an inverter machine. The tungsten is gently touched on the job, the control circuit senses the touch and waits for the tungsten to be lifted off the job, and then quickly ignites the arc for welding.



HF start



The HF start allows the arc to be started without the tungsten touching the job. This feature can be important if the risk of tungsten contamination of the job is an issue, like pressure vessel welding.



REMOTE CONTROL



There are four different scenarios for remote control of TIG machines:



• No remote control – starting is by lift arc, gas is by manual valve, current adjustments is set using the machine control panel.



• Remote torch trigger control – starts the pre-gas sequence HF start, or lift arc. Then end of weld sequence.



• Remote torch trigger and current control – the torch remote trigger starts the pre-gas sequence HF start, or lift arc. Current adjustment can also be controlled from torch during welding, which can be useful to control the heat into the weld, particularly aluminium where extra heat is required at start of weld to preheat.



• Remote foot control of arc starts and current – foot control unit can be connected to the machine via the same connector as the remote torch. Pressing the foot control pedal starts the arc, then further depressing of the pedal increases the current. This allows hands-free current control and fine adjustments while welding.



DUTY CYCLE



The duty cycle of a machine is an indication of the machines ability to operate for extended time. The duty cycle is defined as the time the machine can operate at maximum output in 40C ambient temperature, over a 10-minute cycle. The duty cycle is expressed as a percentage. So, a 20% duty cycle, is maximum current for two minutes, then eight minutes with no current, then repeat.



The machine specification will give maximum duty cycle, and current, 100% duty cycle current, and often 60% duty cycle current. This data will help determine requirements.