Micro Welding Explained: An In-depth Guide

Micro Welding
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Welding is done in tiny and delicate regions of a weld and is highly precision-based. It is basically done by depositing blobs of weld to the welding joints of metals.

Here, while doing micro-welding other than the joint that is fused the other areas do not get heated up easily.

The same TIG welding equipment is used but the size of it is much smaller than a pen. This ‘Micro TIG welding’ is the latest welding technology available today. Here, a 5mm thick edge or joint can be welded down to 0.007mm weld.

“Various Types Under ‘Micro Welding’
  • Pulsed Micro TIG Welding
  • Fine Spot Micro Welding
  • Thermocompression Micro Welding
  • Laser Micro Welding

Pulsed Micro TIG Welding:

When the plasma arc between the tungsten electrode and work piece is burning hot at around 5000°C is known as ‘Micro TIG Welding’. An inert gas is applied at the welding joint because it helps in removing and displacing air from that region that promotes plasma arc generation. Inert gases like Argon is generally used.

Pulsed Micro TIG Welding
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  • In this TIG welding if pulses of a duration of 4 seconds is given with a current of 5 to 300 Amps is known as ‘Pulse Micro TIG Welding’.
  • It is a zero-contact process where an arc is struck between electrode and the target metal.
  • This process begins from the outside and moves inside.
  • The energy density generated by that electrical arc is very high and concentrated that lead to the production of intensely high temperatures in the welding point.
  • Linear power supplies which are close-looped are actually used for power supplies as they help restrict and maintain the electrical arc under controlled electrical conditions.
  • In this way the heating pattern and the welding process may be entirely brought under control.
  • Coin to pin termination, thermocouple manufacture and battery ta welding are some of the basic applications of pulsed micro TIG welding.
  • The main advantage behind this type of micro welding is that very less amount of heat is used to make the weld.
  • This ensures that even if the joint or metal is heat sensitive, they would have very less chances of thermal damage to their physical properties.
  • Fill wire is used as an additional material to add additional strength to the weld.

Fine Spot Micro TIG Welding:

Fine Spot Micro TIG Welding
Source: https://sunstonewelders.com
Spot welding is a highly economical and easy welding process.

It is also known as ‘Resistance Welding’. Here, we use two electrodes, a positive and a negative one and are used to make contact with the metal to be welded.

After the pressure is applied, a pinch (or) pulse of electrical current is applied at that particular joint to melt the two edges of metals to fuse them together.

As a welding spot is created, it is known as ‘Spot Weld’.

  • In order to obtain consistent weld results, contact resistance, proper fixture composition, and other geometric measures must be taken care of.
  • This type of welding reduces distortion and the chance of damage done to the welding metal due to heat as the energy supplied here is extremely low.
  • As spot welding uses less amount of energy density, the overall welding costs are low and hence large-scale production is feasible.

Thermocompression Micro Welding:

Thermocompression Micro Welding
Source: https://sunstonewelders.com
Thermocompression micro welding is the process of welding having the highest degree of precision using a specially-designed electrode.

Here, the electrode used is uniquely used to create a tiny isolated path to weld the joint with a very controlled amount of heat supplied to it.

Hence, an excess amount of heat or energy does not conduct through the metal melting it away.

  • It is majorly used to weld magnet wires.
  • Thermocompression welding is mainly used for these magnet wires as they have electrical resistance as they have that resistance coating on it and prevents any kind of damage to electrically-sensitive components.

Laser Micro Welding:

Laser Micro Welding
Source: https://sunstonewelders.com

Laser micro-welding is a welding technique highly used in automatic machines.

In laser micro-welding collimated, that is parallel rays of light due to electromagnetic radiation is used to fuse metals together.

Laser welding, similar to pulse welding is used for welding edges frequently and regions that are difficult to reach.
 

  • There will not be any need of adding an additional metal by adding material using the fill wire.
  • Even though the amount of heat and radiation is very high in laser micro-welding, as it is focused and collimated, it does not affect the entire metal or regions other than the fused joints.
  • So overall distortion is avoided. Laser micro-welding is economical and multifaceted in the automated welding industry.

    Equipment:

    Micro Welding Equipments
    Source:
    https://theunboxfactory.com
    A minimum of 300 amps power supply is the primary requirement. We need a torch with an electrode and a torch stand for it. Something that need to be checked on regularly for the quality and quantity is the shielding gas that is present in the black cylinder on the left of the image.

    Typical Applications:
    • Relays and battery units in electrical appliances.
    • Copper bus bars in a PCB of an automotive engine.
    • Large current relay for an electrical car.
    • HID lamps.
    • Catheters, guide wires, and endoscopes.

Micro-welding of Copper and Stainless-Steel:

Micro-welding of Copper and Stainless-Steel
Source: https://tigweldingproject.wordpress.com
The trend nowadays in welding is to weld dissimilar metals that is used in MEMS devices using thin metals.

These thin metals are susceptible to heavy heat damage.

Welding extremely thin stainless-steel foil (AISI 304) with copper foils of ten-micron thickness is done using a nano-second pulsed fiber laser.

There are two modes used in welding the aluminum and copper foils and is by using “weld brazing” and “full fusion” modes.

  • Optical and electronic microscopy is used to identify the microstructure of the welded metal.
  • X-Ray radiography is used to see how well the weld is done without any distortions and the mechanical properties of the weld is also analyzed.
  • The “weld brazing” technique produces mechanical stronger weld than the “full fusion” one.
  • There are no cracks, poor integrity, lack of fusion, distortions and pores in the weld.

Nano-Welding:

Nano-Welding
Source: https://safe-welding.com
The latest inventions in welding is the technology of “nano-welding”. Metal nanowires are joined/welded together using white light.

Touchscreens of devices and photovoltaic cells can be fused and fabricated using these nanowires.

A researcher named Erik Garnett and his colleagues of Stanford University used a technique known as the “polyol” method to manufacture these nanowires made out of silver of radius around 15-40nm in radius and 3-10nm in length.

These nanowires get a polyvinylpyrrolidone (PVP) sheath around them.

  • These coating help produce crisscross patterned nanowires.
  • When white light is brought on their surfaces, their gaps melt due to the heat produced there to fuse together.
  • This technique is considered to be very quick and versatile in nature.
  • It prevents overheating and conducting excessive heat to the entire metal or unwanted sections other than the metal joints.
  • The same team is currently working on copper, silver and other metallic and non-metallic compounds.
  • A nano solder can be used to bring or join things that have come apart and are too tiny in size.
  • This nano welding technology is widely used in nano sensors and nano electronics that come from some nano objects welded together.

Laser Micro-Welding for Ribbon Bonding:

Laser Micro-Welding for Ribbon Bonding
Source: https://sciencedirectassets.com
Ribbon bonding is done by using ‘Laser micro welding’ and is one of the newest and brightest inventions used in the electronics industry where they make nanochips and nano sensors.

The bond/weld between the copper ribbon and the conductive surface is done by using ultrasonic radiation alone in the earlier days.

Nowadays a fiber laser, galvanometric scanner, and a beam focusing on the weld is used to do ribbon bonding accurately.
 

  • Spatial power modulation is used for laser ribbon-bonding method.
  • The thickness of the copper coating must be more than 200μm.
  • The strength of the weld is increased at the joints by increasing the surface area using spatial power modulation, linear feed of current and a circular modulation.

Micro Friction Stir Welding:

The “Micro Friction Stir Welding” process is used to weld together any kind of dissimilar metals. It is widely used in thin walls, micro- electronic and electrical devices and microchips and micro – mechanical assemblies.

This process mainly works on the thermo-mechanical principle. It was invented and optimized by Wayne Thomas and his colleagues. Here, it does not work like a normal welding process involving any kind of molten metals, red-hot fire, distortion, and spattering.

The major advantages are:
  • Welding together even plasticisable materials.
  • As no filler metals are used in the joints, they are completely contamination-free.
  • Aluminum can be easily welded without using any kind of shielding gas.
  • No flaws or crack are produced in the final weld.

This micro friction stir welding can be carried out in aluminum, zinc, and copper alloys with dimensions less than 1000μm. The structure is fine-grained and free of coarse grains that make fusion welds prone to holes and cracks. Refined tools with accurate geometries and proper material flow are necessary for an optimal weld.

Micro Friction Stir Welding
Source: https://www.researchgate.net
The major drawback of downscaling Micro Friction Stir Welding might be:
  • The decrease in the radius of the one leads to the increase in the plastic zone’s surface area/volume ratio which in-turn produces a higher rate of heat dissipation.
  • Similarly, when the plastic size and weld thickness decreases, the back anvil will experience a larger heat loss than before.
  • Probe length must be kept under the limit specified which again reduces the heating of the weld.
  • Complex geometries are impossible to be made at the nano-scale dimensions.
  • As the size decreases, the weld requires more heat per unit volume.
 
Factors affecting ‘Micro Friction Stir Welding’ are:
  • Lower surface friction.
  • Lower thermal-conductivity with high softening.
  • Higher thermal-conductivity with low softening.
  • Welding dissimilar metals together.

Micro Orbital Welding:

Micro Orbital Welding
Source: https://wikipedia.org
Micro orbital welding is an extension of “Orbital Welding”, where the welding is done by rotating the arc by 360. °mostly around a static workpiece or in a continuous process.

Here, most of the welding process is done and controlled by a computer and its automation.

And as it is done periodically by a machine, it is done for large welding operations that require the welding to be repeated continuously.

This process was invented by Rodrick Rohrberg of North American Aviation to give the world an idea about how much fuel and fluids kept leaking in the X-15 Rocket Research plane.

The equipment used here for this weld was:
  • A heavy power supply with computer-controlled automation.
  • Welding head.
  • Wire-feed.
  • Water-coolant system.
  • Shielding gas.
  • Filler material.
  • Orbital welding is used widely for thick walls, tubes of small radius and unusual metals, and parts at extremely uncomfortable conditions.
  • The expense for a single weld is around 5-10 times the initial cost used to build this entire Orbital Welding setup without a compromise in the performance and productivity.
  • The technique used in this welding is basically a modification of Tungsten Inert Gas (TIG/GTAW) welding using electrodes and wire feed.
  • The TIG welding method is inculcated into orbital welding because the heat input is monitored and controlled using orbital welding heads.
  • The metals welded here are of high tensile-strength, corrosion-resistant, and distortion-free alloys and low-alloyed metals.

Micro Fissures Welding:

The word “fissure” means a “crack”. Generally, most of the low-alloyed steels that have additional chromium and molybdenum or vanadium get cracks on their weld surfaces during the post-weld heat-treatment process.

The temperatures in the chamber during those processes are about 350°C to 500°C. Such regions are commonly called as ‘Heat Affected Zones’ (HAZ) and are located at the coarse-grained surfaces of the weld.

Micro-cracks are found as colonies having an extensive branching to its root along the HAZ and weld regions.

Micro Fissures Welding
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  • Micro-cracks are found as colonies having an extensive branching to its root along the HAZ and weld regions.
  • Carbide precipitation in the stronger interior regions of the weld during heat treatment causes creep deformation at its boundaries.
  • The presence of toxic substances also promotes embrittlement and subsequent cracking.
  • Moreover, as we generally weld the joints; we must know that joints by nature contain stresses of varied nature.
  • This furthermore adds up to the stress that causes deformation and micro-cracks.
  • When large weld beads are used in the arc welding process, heavier and coarse grains are formed within the weld metal.
  • By utilizing highly-resistant steel with its maximum impurity level and technique to weld can help prevent cracking.
 
 
Welding technique:
  • Welding using a backing bar.
  • Using partial penetration weld method.
  • Internal weld imperfections.
  • Sharp weld toes and edges.
Below is an example of choosing the steel of choice:
5 Crlower risk
2.25Cr 1 Mo
0.5Mo B
0.5Cr 0.5Mo 0.25Vhigher risk
Advantages:
  • Refinement in the coarse-grained HAZ of weld under buttered layer.
  • No more stress concentrations at one spot.
  • Austenite grain growth can also be reduced.