For welding intricate joints with unsurpassed strength for a broad range of metals, TIG welding has no peer. When it comes to cutting through metal with speed and agility, nothing produces clean, dross-free edges like a plasma cutter. Wouldn’t it be great if it was possible to TIG weld and plasma cut with the same machine?
It can be done, but how to TIG weld with a plasma cutter? The answer lies in what is commonly known as a multi-process machine that has three capabilities built-in: (1) TIG welder, (2) plasma cutter, and (3) stick welder. This machine is perfect for small shops and hobbyists. They allow the operator to plasma cut metal and seamlessly transition to TIG welding those very same pieces, eliminating the need and expense of having dedicated machines for each task.
Continue reading for the complete guide on how to TIG weld with a plasma cutter.
Key Differences Between TIG Welding and Plasma Cutting
At first glance, TIG welding and plasma cutting appear to be similar operations. Both involve electrical arcs, high temperatures, and handheld torches. However, there are significant differences in these two processes, both conceptually and functionally.
Simply put, TIG welding is a manual, two-handed process of fusing two or more pieces of metal together into a single piece that has the strength and structural properties of the parent metal. TIG welding utilizes a non-consuming tungsten electrode to create an electrical arc that melts metal to a molten state. The resulting weld pool is manipulated by the welder with a filler metal rod to create a weld joint.
When cooled, the weld joint assumes the same anti-corrosion properties as the parent metal. A shielding gas, typically argon, protects the weld joint from any impurities that may compromise the strength of the weld. TIG welds are known for their intricacy and strength.
We may all be familiar with the three states of matter: solids, liquids, and gases. Did you know that there is a fourth state of matter? It’s called plasma, and it is the result of gases that have become ionized and electrically conductive. Gases reach this state when they are subjected to high amounts of energy (usually in the form of heat).
Basically, what a plasma cutter does is force gas through a constricted opening and energize this pressurized gas with an electrical arc to produce plasma. Since plasma is electrically conductive, when the tip of the plasma torch is positioned near another conductive material (e.g. the metal that is being cut), the arc transfers to the work and the high speed gas (the “plasma jet”) cuts through the material.
For most entry level and conventional plasma cutters, the gas is simply shop air fed through an air compressor. Greater precision plasma cutters such that you would find in complex fabrication operations would require pressurized gases such as oxygen nitrogen, argon, or gas mixtures.
TIG Welding with a Multi-Process Machine
Multi-process machines with TIG welding capability function much the same way as TIG-only machines. Some multi-process machines have 20-200 amp output for AC and 5-200 amp output for DC, with pulse frequency from .5 to 250 pulses per second. With these ranges, the TIG welding function on a multi-process machine is quite capable of handling a broad spectrum of jobs.
It should be noted that there are also DC-only multi-process machines on the market, especially the entry level types that can be found at home improvement stores. The only metal which these machines will not be able to TIG weld is aluminum, as alternating current is needed to achieve the needed temperature while also cleaning away the oxides that form in the weld pool during the down wave.
Setting Up TIG Welding Connections to the Machine
Before you can start TIG welding with a multi-process machine, you need to ensure that the various components are properly connected. Some of these connections, such as the TIG torch and the foot pedal, are made at the front of the machine, while others, including the shielding gas connection, are connected at the back of the multi-process welder.
Connecting the Shielding Gas
Most TIG welding is performed using argon as the shielding gas. The argon gas is stored in metal cylinders of various sizes, ranging from 20 CF (cubic feet) up to 300 CF. Gas flow is opened via a shut-off valve at the top of the cylinder, and a regulator is typically attached to this valve to adjust the flow of gas from the cylinder to the equipment.
Once the regulator is attached to the gas cylinder, a gas hose will run from the regulator to a port on the back of the machine. At the machine-end of the hose will be a fitting (usually of the “quick-connect” variety) that attaches to a port on the back of the machine marked “gas inlet”. The minimum recommended gas flow rate is 5 CFM (cubic feet per minute) for TIG welding.
Before moving on to the next connection, ensure that the gas hose is properly connected on both ends. A leak of shielding gas in an enclosed workspace or with improper ventilation can create a hazardous work condition.
Connecting the Foot Pedal
TIG welding is a manual “hands-on” process that is largely performed by “feel,” and one of the key aspects that the welder must control throughout the welding job is controlling the amperage, which in turn controls the intensity (heat) of the electric arc.
Many TIG welders prefer to control the amperage via a foot pedal, which looks, feels, and functions much like the accelerator pedal in a car. Pressing down on the foot pedal will increase the amperage, and letting your foot off the pedal will decrease the amperage.
The foot pedal is connected to the multi-process machine via a serial cable that plugs into a control port on the front panel of the machine.
Connecting the TIG Torch
The typical set-up is three connections from the torch to the multi-process machine. There will be a serial connector and a control wire as well as a third line, which is for the shielding gas.
Certain TIG torches have a built-in modulator that functions the same way as a foot pedal as far as adjusting the amperage during welding. This type of torch has the same serial cable as the foot pedal and plugs into the same control port. Therefore, the welder will have to decide how the amperage will be adjusted via foot pedal or TIG torch, as there is only one control port on the front of the machine.
The TIG torch is to a TIG welder as a paintbrush is to an artist. The main components of a TIG torch are:
- Torch Body – The shielding gas, power, and control tubing go through the torch body from the welding machine. Most have a trigger to initiate and stop the electrical arc, and some also feature a rotary switch to control the amperage and, thereby, the intensity of the arc.
- Back Cap – This stabilizes the tungsten electrode by loosening and tightening the collet.
- Collet and Collet Holder – These two components act in unison to hold the tungsten electrode in place, and are used to extend the tip of the electrode to the desired distance beyond the edge of the ceramic cup or nozzle.
- Ceramic Cup/Nozzle – This bulb shaped component concentrates the flow of the shielding gas and acts as an insulator around the electrode. The electrode and shielding gas exit through an orifice at the end of the nozzle. These nozzles come in a wide variety of sizes to correspond to different size electrodes and for particular TIG welding applications.
- Electrode – Because it is made from Tungsten, which has the highest melting point of any metal (over 6,000° F) TIG welding electrodes are referred to as non-consuming, meaning they do not melt during welding and become part of the weld.
Electrodes are available in a wide range of lengths and diameters corresponding with the type of metal being welded, the thickness of the pieces, and the type of joints being welded. Electrode tips also vary depending on the application, with sharp point tips generally used for intricate and detailed welds and flat or round tips used for more penetrating welds and larger joints.
There are two types of torches, air-cooled and water-cooled. A water-cooled torch is recommended for larger welding jobs requiring higher temperatures or longer welding sessions and requires a separate water cooling unit.
Connecting the Work Cable (Ground Clamp)
TIG welding relies upon the electrical conductivity of metals for its effectiveness. With the exception of aluminum, the electrical flow for TIG welding metals is direct current (DC). Since an electrical circuit travels in a loop and DC flows in one direction, the electrical current will originate in the multi-process machine, flow through the TIG torch, into the work piece metal, and then back to the machine.
To complete the electrical circuit, a work cable is attached to the workpiece metal and plugged into the multi-process machine via a connector. The work cable is also referred to as a work lead or return lead and has a robust metal clamp on the workpiece end that grabs a firm hold of the metal being welded.
The TIG welding process is often referred to as DCEN, which stands for Direct Current Electrode Negative. As the term suggests, the TIG torch is the negative component in this polarity, and the workpiece metal is the positive. This is why the connector port on the multi-process machine for the TIG torch is marked negative (-), and the port for the work cable is marked positive (+).
Tips for TIG Welding with a Multi-Process Machine
A common mistake made by beginner TIG welders is allowing the electrode tip to contact the workpiece metal. This will cause some of the molten metal to attach to the electrode itself, which will turn create impurities during welding. Experienced TIG welders are able to keep the electrode tip a consistent distance away from the workpiece material while moving evenly down the welding line.
Expert TIG welders manipulate the shape and size of welds by adjusting the distance between the electrode tip and metal. Weld pools form a cone shape during welding with the point at the electrode tip and the base at the workpiece. A smaller distance between the electrode tip and the metal will result in finer, smaller welds, while a larger distance will pull the weld pool up and produce larger, wider welds.
The particular angle at which the TIG torch is held also contributes directly to the resulting weld quality. If the torch is held too upright, the weld pool will not develop properly, and if the workpiece material is thin then the electrical arc may punch through the metal completely. If the torch is held too flat, then the electrical arc is too dispersed, and penetration will be limited to the surface of the material.
The ideal starting point is a roughly 15° tilt away from the direction of the welding; in other words, holding the TIG torch upright (perpendicular to the workpiece metal), if the direction of the welding is to the left, then the cap end of the torch should be tilted slightly to the right.
This TIG torch angle focuses the proper amount of heat to the workpiece material while also providing the welder an ideal line of sight to position the filler rod in the weld pool. To maintain this angle, TIG welders will often brace their wrists or forearms on the work surface to keep their hand position stable and consistent.
Plasma Cutting with a Multi-Process Machine
The main advantage of owning a multi-process machine is plasma cutting your metal pieces and then TIG welding them together minutes later. The typical multi-process machine can plasma cut through metal 1/4” thick at the rate of 15 to 20 inches per minute. For thicker pieces 3/8” thick, the rate slows down but remains a respectable 3 to 4 inches per minute.
Plasma cutting equipment does differ from TIG welding equipment, so it is important to become familiar with connecting the various components.
Setting Up Plasma Cutting Connections on the Machine
Because multi-process machines support three to four different operations from a single machine, many of the ports and connections are shared across the different processes.
Between the TIG welding and plasma cutting processes, the shared connections or ports are:
- Gas inlet (rear of the machine)
- Torch connection (negative port)
- Torch control and gas lines
- The work cable (positive port)
Connecting the Compressed Air
For multi-process machines, conventional shop (or compressed) air is sufficient for plasma cutting purposes. Most manufacturers require an air compressor to supply a minimum of 70 to 75 PSI (pounds per square inch) and deliver at least 5 CFM (cubic feet per minute). To meet these requirements, an air compressor would need to be at least 25 gallons in size.
Just like the argon gas cylinder hookup for TIG welding, plasma cutting requires a regulator to adjust the flow and pressure of the compressed air feeding into the machine. This device is pre-installed on most multi-process machines and also includes a water trap and dirt filter to provide clean air to the plasma torch. (Many manufacturers also recommend the installation of an additional air dryer/oil filter between the machine and the air compressor to remove all impurities and produce the cleanest cuts.)
The air hose from the air compressor will connect to the inlet port of the air regulator. On the outlet side of the air regulator is another air hose that will connect to the “gas inlet” port that is also at the rear of the machine. This is the same port that is used to feed argon shielding gas to the machine during TIG welding operating mode.
(It is a shared port, and therefore, the argon gas line will need to be disconnected in order to plasma cut.)
Connecting the Plasma Torch
The connections for a plasma torch are identical to the connections for a TIG torch. One line is a serial connector that plugs into the negative (-) port on the front of the multi-process machine. The control line plugs into the control port, and the air hose is connected to the “gas outlet” port.
The main components of a plasma torch are:
- Torch Body – The compressed air, power, and control lines go into the torch body from the machine.
- Nozzle – The nozzle is located near the tip of the torch and has an orifice through which the pressurized air column and electrical arc pass. The nozzle constricts the flow of ionized gas to create the plasma jet.
- Swirl Ring – Positioned between the electrode and the nozzle, the swirl ring has small vent holes in its walls and creates a vortex of swirling plasma gas around the electrode.
- Electrode – Responsible for creating and maintaining the electrical arc that ionizes the swirling gas resulting in plasma.
- Shielding Cap – An additional means of improving plasma cut accuracy and quality by further constricting the plasma gas into a thin column.
- Retaining Caps – The inner and outer retaining caps hold all the plasma torch components together and keep them properly aligned.
Because of the extremely high temperatures involved in plasma cutting, virtually all of the components of the plasma torch will need to be replaced after repeated or prolonged use (they are therefore considered “consumables”). The most frequently replaced consumables are electrodes, swirl rings, and nozzles.
It is extremely important that all of the plasma cutting accessories are plugged into the correct ports. Correct torch polarity should always be confirmed prior to plasma cutting as attempting to use the plasma torch while it is connected to the positive (+) port will result in significant damage to the torch and its inner components.
Connecting the Work Cable (Ground Clamp)
Like TIG welding, plasma cutting involves a high-voltage electrical arc that is created and maintained through DC voltage. Any material that conducts electricity can be plasma cut. The plasma torch is connected to the negative port on the machine, and the work cable (return lead) is clamped on to the work piece and connected to the positive (+) port on the multi-process machine.
Tips for Plasma Cutting with a Multi-Process Machine
Here are some general tips that you might find useful when plasma cutting ith a multi-process machine.
- If you encounter difficulty initiating the arc and transferring it to the work material, confirm that your work cable is properly clamped on to the work. There needs to be direct and solid contact between the work and the clamp jaws. It may be necessary to re-locate the clamp to another part of the work or to grind the material to expose a raw surface and clamp there.
- Plasma torches have built-in safety features, and one of the most important is disabling arc starting if any of the inner components are missing or installed in the wrong sequence. Even seasoned plasma cutters have forgotten to place the swirl ring in their torches at some point.
- To achieve the cleanest and sharpest dross-free cut edges, it is important to achieve the proper torch angle and cutting speed. As a general rule, starting plasma cuts at the edge of the workpiece will result in better cuts and protect the torch components from rapid wear.
- For thinner material, start the torch upright and as the plasma jet penetrates through the metal, tilt the torch slightly so that the jet leads the cut (in other words, lean the plasma jet into the direction of the cut and the end of the torch away from the cut). For thicker material a more upright position of the torch will yield better results.
- When a cut is made properly, there should be a fan of sparks and flame that is between 10° to 30° trailing the cut underneath the material. Indications that the torch travel speed (down the line of the cut) is too slow are the lack of any angle in the sparks or flame (i.e., straight down underneath the metal). If the torch is traveling too fast, sparks will fly upward above the metal and sometimes toward the welder.
- Sparks from plasma cutting can travel up to 40 feet away. Proper gear is important to avoid injury, and this includes protective head and eye gear, non-flammable gloves, and non-flammable clothing.
As you can see, TIG welding with a plasma cutter is completely do able as long as you have access to a multi-process machine.