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Resistance Spot Welding

Welding has proven to be a time tested method to permanently join two metal parts. This fabrication process has been in use for decades. It uses high heat to first melt the parts together and then once they cool, it causes fusion, enabling them to join together. Welding is far from the only method used for joining metals. 

Low-temperature methods like soldering and brazing exist, but they don’t melt the base metal, and thus can’t provide the sort of durability that welding does. 

To achieve a durable join, a filler material is used in addition to melting the base metal in order to create a pool of molten material. This then cools to form a joint that can often even be stronger than the base metal.

There are many different methods of welding metals together. Gas welding is the most common process and also happens to be one of the oldest. However, in recent years, it’s not being as widely used in industrial applications as it used to be. Many are now turning toward resistance spot welding.

What is resistance spot welding?

Resistance welding is a type of spot welding, a time-tested welding process, which joins two or more sheets of metal together without using any filler material. Pressure and heat are applied to the weld area through shaped alloy copper electrodes. 

They convey an electrical current through the weld pieces. When this is done, the material melts and fuses the sheets together and that’s when the electrical current is turned off but the pressure from the electrodes is maintained so that the moten nugget can solidify and form the joint.

Resistance welding has proven to be quite popular for industrial applications in recent years. It involves applying force to the surfaces in contact. 

The heat used for the welding is produced by the passage of electric current through the electrical resistance at and adjacent to the surfaces being joined together.

The process works by contacting copper alloy electrodes to the metal surfaces. Pressure and electric current are then applied to generate heat through the passage of current in resistive materials like low carbon steels. 

Spot welding vs. other kinds of welds

Spot welding is great for joining thinner metal pieces together while projection welding is used for projects which involve thicker metals, normally 0.035” and thicker. 

It is basically a modification of spot welding in that projection welding also uses heat generated from an electric current to join the metal pieces. The electrodes are just capable of carrying more current than spot welding electrodes.

Tack welding is a lot more different than spot welding. It’s basically a temporary form of welding which joins the two base metals together and keeps them joined for long enough for a proper weld to be done. 

Tack welds aren’t meant to hold for long periods of time. They are created by applying a series of small welding bursts across the base metals so that they keep pulled together and don’t move while the final welding work is being done.

Compared to spot welding, stud welding takes a slightly different approach to permanently join metals. It creates an electric arc between the fastener and the base metal. 

This heat melts the two together and then fuses them through return pressure. Stud welding doesn’t require high pressure equipment like spot welding does and it doesn’t require access to both sides of the material to be effective. This makes stud welding a more economical choice than spot welding in certain cases.

How strong are spot welds?

There are different methods of measuring the strength of a spot weld. Researchers define the strength of a spot weld as being directly proportional to the area of the weld nugget at the interface of the two metals being welded. 

Another method for the verification of spot weld quality is destructure testing. As the name implies, it requires the spot welds to be torn apart with externally applied force. 

This is done to break the parent metal away from the weld zone. Once the metal breaks, the weld zone is assessed for quality and its strength is quantified.

Cryogenics and resistance spot welding

Cryogenics can help improve the durability and extend the life of resistance welding electrodes. Research has shown that these welding electrodes last longer once they have been through cryogenic processing. 

The Linde Gas Division of Linde AG conducted research and also found that deep cryogenic treatment improves the life of the resistance welding electrodes. 

These electrodes tend to fail because of thermal cyclic fatigue. The contact surface starts to mushroom and that makes it bigger. This changes the welding parameters and throws precision off balance. 

This can be avoided by the deep cryogenic treatment of electrodes. The treatment has shown to enable these metal parts to last anywhere from two to nine times longer than they usually would.

How it works

The deep cryogenic treatment of welding electrodes is a new science. It does require flexibility and improvements on part of the company that’s opting for it but there’s much more value to be derived from it. 

Deep cryogenic processing works by submerging the metal parts, the welding electrodes in this case, in a bath of cryogenic material. These cryogenic materials or gases can be the likes of liquid nitrogen. 

It’s only through these materials that the temperature can be dropped down to the cryogenic range. 

Once the cryogenic temperature is achieved, the parts are kept submerged and at that constant temperature for up to 24 hours. 

This is required to make the change in the crystalline structure of the metal permanent. After that, the metal parts are brought back up to room temperature very gradually so as to seal in all of the improvements made to the metal’s structure at cryogenic temperatures. 

Resistance welding electrodes

Resistance welding electrodes are an important part of the process. The electrode material, shape and size needs to be considered to get the best welds. Other details matter a lot, such as the tip profile and cooling time. Copper alloys are used in the electrodes because that’s what makes them harder and improves conductivity.

The materials that are most commonly used in resistance welding electrodes are copper and chromium as well as copper, chromium and zirconium. These are utilized for both high-grade steels and for low carbon. 

For welding coating steels, the alloys with the better conductivity are used. These are copper and zirconium with dispersion strengthened copper. This is done due to their low contact resistance which helps not heat up the surface of the coated steel too much.

For welding hard sheet materials, a low welding current is used in conjunction with a higher electrode force. The electrodes that are made from copper, nickel, and silicon alloy tend to be harder.

Top 5 industries for resistance spot welding

  1. AutomotiveSpot welding is most commonly used in the automotive industry. That’s because it’s very effective for the steel metal that’s used in cars. It’s also preferred because spot welding can be automated with ease so robots and manipulation systems can be deployed to significantly increase the production rate in automotive factories.
  2. AerospaceSpot welding has also proven to be very useful for the aerospace industry. As you can probably imagine, the airframe of planes and helicopters experience immense stress and pressures at altitude.It’s imperative for the welding work to be strong enough in order to hold the panels together. Spot welding has been used for decades in the aerospace industry because of the durability that it provides.
  3. RailwaysA lot of metal work is done in the railway industry as well. There are a lot of load factors to consider there as well. So it becomes vital for the metals being joined together to withstand immense weight. Spot welding is utilized on railway tracks and stations for this reason.
  4. ElectronicsMicro-spot resistance welding is used in many different applications for the electronics industry. It’s particularly of note due to the delicate nature of electronics and the precision that’s required.This type of spot welding has proven to deliver great results in the electronics industry.
  5. ConstructionThe construction industry also makes use of spot welding to a large extent. It’s actually the primary joining method for metals in low carbon steel body construction.A conventional steel body-in-white has nearly 5000 resistance spot welds. It’s widespread use is because of its low cost and fast operation.

Get your resistance welding electrodes cryogenically treated

At Controlled Thermal Processing Cryogenics, we have found that our proprietary deep cryogenic treatment can extend the life and durability of any resistance welding electrode significantly. 

We have almost four decades of experience in cryogenics and are industry leaders in deep cryogenic treatment.

Contact us today for a free quote. If you are considering it, we do recommend that you change some of your welding parameters to extract the most benefit out of our deep cryogenic treatment.