What Is Spot Welding?
Spot welding is a form of resistance welding that joins together two or more metals (usually sheets of metal) by applying pressure and heat. The heat is generated by an electrical current. This is directed at specific, localised ‘spots’ rather than having a continuously moving weld – hence the name spot welding.
The heat melts the metal at the points of contact, and when it cools a welded joint is created. Materials that can undergo spot welding include, but are not limited to:
- Stainless steel
- Galvanised steel
- Magnesium
- Aluminium
- Zinc alloys
- Nickel alloys
- Titanium
Spot welding is just one of a number of professional welding services we offer here at Salamander Fabrications. Carry on reading to find out what spot welding is and how it works, as well as the pros and cons of this method.
How does spot welding work?
Spot welding works in four different stages; first you prepare, next, you clamp the metal sheets together, then you weld them – until finally, you cool them and release the electrodes. Let’s explore the process you should follow in more detail below:
Preparation
- You should remove any dirt, grease, or oxidation from the metal surfaces being worked on pre-weld, otherwise this may interfere with the weld quality.
- Align and position the pieces to be welded between the electrodes of the spot welding machine.
Clamping
- Apply pressure to clamp the sheets together, but make sure it is the correct amount of pressure and electrode force. Too much pressure can result in cracking, and too little pressure may make the joint too weak.
Welding
- An electrical current is passed through the electrodes to the targeted area, generating heat. The metal at the interface between the sheets melts to form a weld. The amount of heat generated depends on the electrical resistance and thermal conductivity of the metal.
Cooling and Release
- When the current is turned off the molten metal cools and solidifies to form a strong joint. The rate at which the weld cools will affect the microstructure of the weld. You should control cooling to prevent cracking and improve the weld strength.
- The electrodes are released and the process is complete.
Other Factors to Consider When Spot Welding
Size of the tip diameter
The size of the welding tip diameter is extremely important as this controls the size of the spot weld itself. If it’s too big you run the risk of overheating the metals and causing voids or gas pockets in the weld. If it’s too small, the weld may be too weak.
Welding time cycle
The amount of time that the metals being worked on are subjected to electrode pressure and electrical current can affect your overall results. Short weld times can result in incomplete formation, whilst long weld times may cause excessive heat buildup. This leads to material degradation in most cases.
Material type
Metals with lower electrical conductivity (like steel) are easier to spot weld in comparison to those with higher conductivity, like aluminium and copper. These metals can make spot welding more challenging as they require higher currents to generate enough heat.
Thickness of the materials
The thickness of the materials being worked on directly affects the strength of the weld. Thicker materials require a higher current and longer weld times, and vice versa.
Electrode material and shape
Electrodes are usually made from copper alloys due to their electrical and thermal conductivity properties. The choice of alloy affects heat generation and the cooling rate at the weld spot. The tip can also come in several different shapes and sizes to suit the specific requirements of the weld.
Weld spacing
The distance between each individual spot weld needs to be carefully planned. If they are too far apart the integrity of the joint may be compromised. If they are too close together, the heat generated from one weld may weaken the adjacent weld.
Quality monitoring
Visual inspections are important after a weld is complete, but you might not always spot every issue. Non-Destructive Testing (NDT) methods like ultrasonic testing or X-ray inspections can be used to assess the integrity of spot welds, but they can be challenging. In automated production, methods such as Robotic MIG welding apply real-time monitoring of current, voltage, and pressure. This helps detect issues during the actual welding process, rather than afterward when it could be too late to save the quality of the weld.
Pros and Cons of Spot Welding
Pros
- Speed and efficiency: Spot welding is a quick and highly efficient process.
- Cost-effective: No filler materials or shielding gases are required, saving on costs.
- Ideal for thinner materials: Spot welding is particularly effective for joining thin sheets of metal.
- Automation: The process can be easily automated, making it suitable for high-volume production.
- Minimal distortion: Less thermal distortion compared to other types of welding methods due to localised application.
Cons
- Not ideal for thicker materials: Spot welding is typically used for sheet metals that are up to 3mm thick.
- Inspecting weld quality: Non-destructive testing of spot welds can be challenging, so quality is heavily reliant on visual inspection and careful control of the welding parameters.
- Not suitable for all joint configurations: Spot welding is best suited for lap joints where two pieces overlap.
- Localised heating: Spot welding can cause issues like cracking or improper fusion if not carefully controlled.
Applications of Spot Welding
Another important factor to consider when asking the question of ‘what is spot welding’, is its typical uses and applications. We have listed a few of them below:
Automotive industry: Spot welding is extensively used in car manufacturing and the transportation sector to assemble body panels and countless other parts.
Aerospace industry: Spot welding services are common for the aerospace industry as many aircraft components require this method for strength and to save on weight – especially the case when working with aluminium.
Retail and leisure sector: Sheet metal fabrication used alongside spot welding can help to build bespoke retail displays and visual merchandising platforms.
Household appliances: Refrigerators, microwaves, washing machines, dishwashers, and a whole lot more in your home will probably have undergone some form of spot welding to join the metal parts together.
Construction and security sector: Aluminium, steel, mild steel, and stainless steel are all commonly used within the construction industry – all of which can be subjected to spot welding for strength and durability.
Expert Welding Services from Salamander Fabrications
Our spot welding service encompasses just one part of the repertoire of services we provide here at Salamander Fabrications.
Not only do we maintain high-quality control with quality checks in our double ISO-accredited manufacturing facility, but we also have over 50 years of experience providing metal fabrications services, so we know how to turn your product requirements into reality.If you would like some more information or advice please feel free to contact us. Give us a call on 01484 843599 , or send an email to sales@salamanderfabs.com. Our friendly sales team will be more than happy to help.
