Repairing delicate parts can be a challenging task, and it is no surprise that many welding methods come short. However, micro TIG welding, also known as the micro pulse arc welding process, thrives in delicate welding applications.
Micro TIG is capable of joining fragile materials down to 0.0002 square inches, using amperage down to 1 amp. So let’s look at how does micro tig welding process works and what makes it unique.
What is Micro TIG Welding?
Micro TIG is an arc welding process that takes fundamentals off the actual TIG welding, referred to as macro TIG. However, what makes it unique is that the plasma arc produces heat up to 9,000°F between a tungsten electrode and the workpiece. The resultant heat next creates the joint.
Like macro TIG, inert shielding gas, usually pure argon, removes the air out of the weld puddle. Lack of air in the pool lowers the resistance or voltage requirement to jump across the gap.
By supplying a lower current for shorter times and with more precise control than macro TIG welding, micro TIG is capable of joining materials thinner than 0.026 square inches, such as copper bus bar. You can use the Micro TIG welding process to weld materials such as thermocouple wires to 0.0002 square inches thick.
Micro TIG Equipment, Tools, and Consumables
To perform Micro TIG welding, you will need equipment that includes a power supply, torch, electrodes, and a cover nozzle. Sometimes, filler metal can be added, but you will also need a shielding gas.
Micro TIG Welding Machine
Micro tungsten inert gas welding produces high-quality welds, but machines must supply amperage that is sometimes less than 5 amps.
In addition, the pulse is mandatory to achieve high-quality welds. Usually, the pulse is limited to 4 seconds, but sometimes it can be divided into multiple mini pulses.
Micro TIG welder should provide a stable arc at low amperage. You should opt for a soft start that can help in generating arcs, then gradually increase the power to see the weld puddle form.
Most welding applications occur at 10-12 amps, while thicker parts go up to 30 amps. Occasionally, most delicate projects will require a current of fewer than 5 amps to create a proper joint
Accessories and Consumables
When it comes to TIG torches, you can opt for an air-cooled torch since it is cheaper, and the amperage is not so high.
Therefore, the torch is not the most essential part, but you will have to fit a small diameter non-consumable tungsten electrode.
Micro TIG welding can utilize even 0.020 tungsten electrodes. However, grinding that small tungsten can be challenging, and you should be extra careful when dealing with thoriated tungsten since thorium is radioactive.
Micro TIG tungsten material:
- Pure tungsten: primarily used in micro tig aluminum welding
- Thoriated tungsten: Widely used, common choice, contains radioactive ingredients; results may vary in AC applications
- Ceriated tungsten: Low cost and easy to use, can be suitable for both AC and DC
- Lanthanted tungsten: Low ware rate, less accidental arc starts, ideal for continual use such as automatic applications
- Ytred tungsten: Low wear rate, no spattering
The specific application will require accessories and consumables such as filler rods to produce better contact and joint. Depending on the size of the repair, you will usually need to provide 005- to .020-in. in the diameter filler material. Filler metal is either matched directly to the parent metal or chosen based on its hardness and final application.
Like conventional TIG, micro TIG usually requires pure argon shielding gas. An inert gas such as argon removes the air from the puddle, lowering the resistance and allowing proper part fit-up. Even though 100% argon is a go-to choice in many applications, 6061 and 7075 grades aluminum will require 100% helium.
Good practice to improve shielding gas coverage is using a gas lens. A gas lens replaces the standard collet body and creates a more extended, undisturbed laminar shielding gas flow. Since micro TIG welding is done in a controlled environment and at a low current, flow rates are also lower, usually between 5-10 cfh.
Micro TIG Weldable Materials
Since micro TIG welding is considered a non-contact process as it utilizes heat on the surface to join metal, the best results come from joining the same metal grades.
Nonetheless, this process can be used to join dissimilar metals.
Some of the most common weldable materials are copper, phosphor bronze, iron, nickel, stainless steel, molybdenum, tungsten, platinum, and titanium.
Zinc content can affect the quality of the weld and develop irregularities, so welding galvanized steel or brass is not recommended. DC welding aluminum can be challenging since aluminum oxide, which builds on the surface, has a much higher melting point than the aluminum base.
To make your aluminum welding job easier and a void corrosion and contamination, your welder should offer AC TIG technology with a low amp start down to 5 amps. Extended balance control, from 30 to 99 percent electrode negative will provide excellent cleanliness, while adjustable output frequency, from 20 to 400 Hz, helps with the force of the arc. A high-end function such as AC squarewave shaping is always a good option to have.
Plating is generally not an issue since the material typically has a lower melting point. However, issues may occur such as soot generation during the welding. Therefore, welding thinner plating exhibits the best results.
Laser welding vs. micro TIG welding
Laser welding has found its way into many industries and applications due to its excellent precision and low heat that allows it to work with thinner materials. The question that often emerges is which one is better, laser welding or micro TIG?
While laser welding surpassed micro TIG in many aspects, many experts give the advantage to pulse arc welding when it comes to penetration, ease of use, and accessibility.
Micro TIG welding in some cases displays much better penetration and durability. Since penetration is essential for filling holes and large damaged areas, many consider it a go-to method for delicate parts.
While laser welding shows better results in weld buildups of 0.005 to 0.010 inches on molds and inserts, many consider micro TIG more practical and easier to perform. Laser welding requires an external fixture to apply force to create proper part fit-up. This time-consuming procedure makes laser welding of large buildups an unreasonable application.
One more example is that everything that will be laser-welded must be critically clean. Any rough areas will cause problems, while the micro TIG can burn down problem areas. Finally, when there are different projects included, many shops combine the strengths of both processes to achieve the best results.
There is a full article that goes through this subject much more extensively and you can find it here.
Advantages and Drawbacks
- Minimal HeatAffected Zone
- Controlled small deposits of 0.005 inches, and as little as 0.002 inches
- Minimizes warp, stress, and fatigue on metal
- A high-Powered Microscope allows the welder to achieve small and intricate weld deposits
- Higher penetration compared to laser welding
- Can reach difficult areas
- Durable and discrete welds
- Lower cost than remaking the damaged part
- Faster and less expensive than LW
- Extremely high skill of the operator is required
- Requires welders with low amp start options, pulse, and balance controls
- Laser welding is capable of handling much larger buildups
- Certain metals can be difficult to weld
Micro Tungsten Inert Gas Welding Applications
Let’s take a look at some most common applications of pulsed micro TIG welding:
- Copper bus bars on the printed circuit board of an automotive engine control unit
- Copper bus ring and wire for the electric power steering unit; and a large-current relay for a hybrid electric vehicle
- Aerospace component repair and manufacturing.
- Plastic Injection Mold and component repair and engineering revisions.
- Machine component and critical part repair and manufacturing.
- Medical device repair and manufacturing.
- Relays and battery tabs in electronic devices;
- Motor cases in industrial devices; and lighting applications like high-intensity discharge lamps (HID lamps)