By Jim Harris
Contributor
TIG welding, also know as Gas Tungsten Arc Welding (GTAW), has long enjoyed a reputation as a highly skilled, precise welding process. It is frequently used for highly cosmetic applications or those involving thinner metals that require strict heat control.
This process is becoming more popular as technology improves and more welding applications, such as exotic metals, require TIG welding. Selecting the right TIG welding machine for your application is easy if you follow the right criteria. The challenge becomes how to select the right TIG welding machine for the best performance on the application. Deciding on a machine based on price alone can end up costing more money if it does not meet your welding needs, both now, and in the future. Let’s take a look at some of the factors to consider in making a TIG welding equipment decision.
Why TIG Is So Popular
TIG welding is an extremely precise process that provides very clean welds with no spatter and minimal smoke. This makes it attractive for highly cosmetic applications such as automotive, sculpture, experimental aircraft, and some home-hobbyist jobs.
It is commonly used in applications with thin-gauge sections of stainless steel, chrome-moly tubing or lighter metals like aluminum, and copper alloys. These thinner materials require precise heat control in order to prevent warping or burn through of the base metal. TIG machines effectively operate at the lower amperages needed to provide this control.
Choosing the Right TIG Welder
There are a wide range of factors to take into consideration when selecting the right TIG welder:
Amperage Range
Always consider amperage range when selecting a TIG machine. You want one that provides the widest amperage range at the best possible cost. A TIG machine with too narrow an amperage range can severely limit the variety of materials on which you can weld. A machine with a range of 5 to 230 amps provides the flexibility you need to weld on thin materials like 24 gauge stainless and up to 1/4" thick aluminum.
Aluminum requires higher amperages than steel or stainless. Having a machine that cannot reach at least 200 amps will limit the maximum thickness of aluminum you can weld from 1/8" to 3/16". The wider the range, the more applications you can perform without having to purchase multiple machines.
Low Amperage Welding Performance
In addition to operating with a wide amperage range, you should select a TIG machine that has good arc stability at below 10 amps. This provides easier starting, better arc control, and excellent crater fill capability at the end of the weld. TIG welding is often done on thin materials, so you want to be able to start the arc without a lot of high frequency or hot start.
Some machines claim to have starting technologies to help establish the arc, but those technologies produce only a hot start. In a hot start, the machine actually spikes up to a higher amperage to start the arc for a few milliseconds. This higher starting amperage can produce an arc which could be too intense and burn through the material you are welding on. Also, hot start does not help with arc stability while welding, and does not help the operator maintain good arc control while crater filling, which we will discuss next.
Not only is arc stability important for starting the arc, you also need good arc stability while welding. Let’s say you are making an edge weld on thin material to build-up or repair a boat propeller. The last thing you want is to burn the material away at the start or have the arc wandering off the edge of the material.
Stability at low amps is also critical when finishing the weld. In TIG welding, it is common to ramp the output amperage down at the end of the weld to fill in the weld crater (the concave divot in the end of the weld bead).
When welding on aluminum, creating a large concave weld crater at the finish can lead to cracking as the material cools. Being able to control the arc while gradually lowering the amperage makes the weld crater less concave, and allows the weld puddle to slowly cool, reducing stresses that can cause cracking. TIG welders with special background circuit technology deliver extremely stable, low amperage starting, as well as welding and crater filling for both AC and DC welding.
AC and DC Welding
If you plan on welding more than just steel or stainless, the right TIG machine should offer both AC (alternating current) and DC (direct current) options. For example, you should use AC on self-oxidizing soft metals like aluminum and magnesium. However, you will need DC for welding on hard metals, such as steel, stainless steel, and deoxidized copper.
With alternating current (AC), the current cycle alternates between a positive half and a negative half. Aluminum requires the positive half of the AC cycle to clean away oxides, while the negative half of the AC cycle facilitates penetration into the base metal. In other words, the positive current cleans, and the negative current welds.
When selecting an AC TIG welder, a must-have control is AC balance. AC balance control allows you to set the amount of time during the alternating current cycle that the welder is in the negative half of the cycle versus the positive half of the cycle. In simple terms, this allows you to set the level of cleaning vs. penetration. Machines on the market with a fixed AC balance setting do not allow you to adjust this level for more oxidized aluminums or for the appropriate level for the amperage you are welding at. Look for at least a manual AC balance control when shopping for a TIG machine.
TIG machines such as what Lincoln Electric offers not only comes with a manual balance control, but also with Auto-Balance technology. When in auto balance mode, the machine sets the percentage of cleaning versus penetration automatically based on the welding amperage of the machine. This gives you the simplicity of not having to manually set the machine without compromising on a fixed level that may not be right for your welding application. This especially helps improve both the quality and appearance of the welds.
The Right Controls
Heat control is another critical factor for successful TIG welding. On thinner materials, controlling the heat input reduces warpage of the metal. One way to control heat input into the weld without sacrificing weld penetration is to pulse weld. With pulsed TIG welding, the machine alternates between a higher peak current and a lower background current. This maintains the arc while allowing the welded joint to cool.
Some machines include a built-in TIG pulser to provide good heat input control. This feature is a popular training tool that can be adjusted to help you time the application of filler metal into the weld puddle. In other words, during the peak amperage, dip the filler metal into the weld puddle, and during background amperage, withdraw the filler metal. This helps the beginner achieve a consistent looking “stacked dime” weld bead appearance often associated with good TIG welds.
Easy to Use
TIG welding is a high-skill process, but that doesn’t mean the machine has to be complicated to use. The best TIG machines are user friendly and offer easy to understand controls. A durable, metal foot pedal amperage control is a key accessory to further simplify the process by allowing users to increase or decrease the welding amperage as needed. Foot amperage controls are a must-have, especially for aluminum welds. Cold aluminum requires more amperage to weld, but aluminum will quickly heat up during the course of the weld.
A good foot amperage control allows you to reduce the amperage as the aluminum heats up. This allows you to maintain a constant travel speed and consistent weld bead shape. Foot amperage control also allows you to ramp the amperage down at the end of the weld to achieve good crater fill for controlled weld quality. Hand amperage controls exist in the market, but to fully understand the importance of a foot amperage control, imagine trying to drive a car without a foot pedal accelerator.
Quality Design
Many TIG machines also include a number of extra features contributing to overall durability and lifespan. A cooling fan is one such feature. Many TIG machines have fans that run continuously, or a fan that runs after the machine heats up and trips a thermostat. A constantly running fan can shorten the life of the machine by drawing in a lot of dust and dirt.
A thermostatically controlled fan allows the internal components of the machine to thermally cycle between hot and cold, which stresses internal components. Ideally, a fan should only provide cooling when it is most needed.
Lincoln, for example, uses a technology that turns on the fan when an arc is struck, and runs for several minutes after the end of the weld. This reduces dirt intake into the machine since the fan does not run continuously, while avoiding stressful thermal cycling by regulating a constant temperature inside the machine.
Manufacturers like Lincoln, follow strict design and manufacturing practices to prolong the life of its machines, such as environmentally coated PC boards and double-dip varnish and non-wooden transformer windings. Wooden spacers swell in high moisture conditions and shrink as they dry out, which eventually may cause loose transformer windings.
Other Considerations
There are a few final things to look for when selecting your first TIG welder. Make sure you select a TIG welder that has a quick change removable TIG torch. When TIG welding, sometimes you might want to change the torch to a smaller lightweight torch, a longer torch, or a pencil torch to get at those hard-to-reach welds.
If the torch is permanently wired into the machine, you’re stuck with only one torch, which can be disappointing as your skill level grows. Also, if you ever damage that torch, you will need to have a service shop electrically connect a new torch to your machine.
Before purchasing a TIG welder, consider whether you may want to utilize other welding processes in the future. If so, make sure your TIG welder has a stick mode to expand your welding capabilities. Stick welding is normally associated with heavier construction type welds where appearance and spatter are not a primary concern. For example, you might opt to TIG weld a go-kart frame made of lightweight chrome-moly tubing. However, if you want to build a heavy-duty trailer to haul it, you would choose to stick weld the heavier materials.
Conclusion
Selecting the right TIG welder involves more than just shopping for the lowest price. You are choosing the TIG process to make high quality, good looking welds, often on very heat sensitive materials – arc performance should be the most important factor considered. Beyond that, you need to make sure you select a quality machine with enough versatility, amperage range and the right controls.
By asking the right questions, carefully shopping and taking these factors into consideration, you should have no problem choosing the right TIG welder that won’t be outgrown by your welding needs or skill level.
Jim Harris is Product Manager of Lincoln Electric’s TIG product lines.
For information on products offered by Lincoln Electric, visit www.lincolnelectric.com.
