One of the purposes for welding is to join 2 or more components together in a mainly permanent fashion. This is also known as "Connecting".

As these images show, the weld piece (in this case two sheets of low carbon steel) are held between two Pincer-Like Electrodes and compressed under pressure while an electrical current is passed through the electrodes.


Video Courtesy of KTD

The Resistance to the flow of current through the weld piece at the pressure point creates heat. Enough current causes the weld piece to become plastic and eventually become molten. The pincer pressure forges the molten material to fuse together. Continued pressure initially after the fusing stage forges the weld into a "Weld Nugget". This process is also called Single Point Resistance Welding.


Video Courtesy of TWI

Spot Welding has many other names including the the acronym STRSW (Squeeze Type Resistance Spot welding)

Where is Spot Welding used?

There are many applications of Spot Welding. It is not unique to just connecting metals, and the metals in which Spot Welding is the preferred choice is very wide depending upon the metals' available, and the application.

The SpotTrack Project looks solely at the improvements in identifying welding failure and conversely weld quality i.e "Pass Rates" in repairs to automotive applications namely Car Collision Repairs.

To understand the role of Spot Welding, it has to be seen in context within Automotive Manufacturing.

Automotive Manufacturing

Firstly we should consider the complexities in modern vehicle body design. The design objectives are varied such as:-

Torsional Strength / Marketable Looks / Weight / Serviceability / Reparability / Economy of Manufacture / Longevity / Use of Common Parts / Survivability / Crashability / Recyclability / Occupant and Pedestrian Safety / Fuel consumption / CO2 emission and cost of ownership / Acceleration / Performance / Disposal at End of Life / Embracing New and Emerging technologies in materials, forming and connecting sciences.

As you can see, this is a very complex set of situations and in some circumstances has conflicting objectives. For example, weight reduction might improve performance. However, weight reduction could mean reducing the Torsional Rigidity and Overall Strength of the Body Structure.

To achieve lightweight construction they can either use lightweight material like Plastics, Carbon fibre, Magnesium, Aluminum or high strength steel or a combination of many materials.  Carbon fibre is absolutely too expensive for the cars of mass market.  Aluminum is very expensive as a mass production material, but can be applied on higher priced cars.  In some cases e.g. Audi TT, Aluminium is used for the whole body, supplemented by steel.  In some cases the front structure of middle class cars uses Aluminium to reduce the weight in the front where we have the engine weight.  In these cases to give a 50/50% weight distribution from front to rear.

Manufacturers may adopt a variety of strategies depending on the vehicle’s market profile, price range etc.

For example:-

  • Aluminium Trunk, Hood & Doors
  • Magnesium Front Panel
  • Plastic Fenders, Fuel Filler Flap.
  • Graphic courtesy of CAB
  • Laser Welding and Structural Bonding of panels
  • Steel Body Strategically using HSS of Different Grades.
 Body Shell exploded view
Graphic courtesy of CAB

It is this last category of Manufacturing Strategies to improve lightness ergo efficiency and fuel saving, whilst preserving and or improving strength which is at present the mainstay of most mass produced passenger cars.  So what is HSS?  

HSS = High Strength Steel, so let’s look at Steels >>