Spot Welding Machines

Spot welding is a form of electric resistance welding that utilises resistance to weld two or more metal sheets together by means of pressure and heat applied to the weld part. It does not use any metal electrode, arc and electrode holder for its working, as it only works on the pressure and the electricity. Spot-Welding can be attained either with a fixed pedestal welding machine, operated automatically or by an operator, or through using a spot-welding gun attached to a robot. Using two rounded copper electrodes, heat is directed through them in focused or concentrated spots around the material as the gun opens and closes. This welding of small spots wherever the weld takes place is called spot-welding. 

A spot-welding machine comprises welding electrodes, transformers for the power supply, and other machinery that permit controlling the parameters in welding work (weld current, pressure, voltage, etc.). Portable Spot-Welding machines are also available in the form of welding guns. Spot-Welding Machine is either be manually operated or automated through the use of spot-welding robots.

The spot-welding process is used for joining sheet materials and utilises shaped copper alloy electrodes to put pressure and carry the electrical current through the workpieces. 

1. Firstly, the parts are locally heated. 
2. Then, the material between the electrodes yields and is pressed together.
3. This pressure can be applied manually, pneumatically, by springs or through hydraulics.
4. The second stage comprises the application of heavy current to the targeted area between the electrodes.
5. Molten metal forms as the current reacts with the metal’s internal resistance. 
6. The metals reach about 2000 °C, which is above their fusion point.
7. It then subsequently melts, destroying the interface between the parts. 
8. The current is then switched off and the "nugget" of molten materials solidifies creating the joint. 
9. To generate heat, copper electrodes convey an electric current through the workpieces. 
10. The heat produced depends on the electrical resistance and thermal conductivity of the metal, and the time that the current is supplied. 
11. The heat produced is expressed by the equation: E=I2*R*t 
12.  Where in above equation E is the heat energy, I is the current, R is the electrical resistance and t is the time that the current is applied.  
13. The final stage comprises the cooling and solidification of the nugget.
14. Copper material is used for electrodes as it has a low resistance and high thermal conductivity equated with most metals. 
15. This finally ensures that the heat is produced in the workpieces instead of the electrodes.

The degree of heat differs based on three factors:

• Thermal Conductivity
• Amount Of Time the Current Is Applied
• The Electrical Resistance of The Metal

List of materials generally deemed suitable for Spot-Welding:

• Low carbon steel (mild steel)
• Galvanized steel
• Stainless steels
• Aluminium
• Magnesium
• Zinc alloys
• Monel
• Nickel alloys
• Titanium
• Inconel
• Silicon bronze

Spot welding is mainly utilised for joining parts that are usually up to 3 mm in thickness. Thickness of the parts to be welded must be equal or the ratio of thickness must be less than 3:1. Spot-weld diameters can vary from 3 mm to 12.5 mm. The strength of the joint is subject to the number and size of the welds.

The capital expense will be offset substantially cost savings in labour and operational expenses such as consumables and machine upkeep.

The advantages of Spot-Welding Machines are:

• Quickest and most economical process of joining Weldable Base Metals.
• Low initial cost and less skilled workers can operate this welding.
• No open flame present contrary to some commonly known processes.
• Comparatively, an easy and straightforward welding process.
• No edge preparation is required.
• One of the fastest and cleanest welding methods.
• Multiple metal sheets can be joined at the same time.
• Economical as it doesn’t use inert gases or filler metals.
• No filler material is consumed, unlike some other methods (MIG welding).
• Processes can be effortlessly automated through the use of welding robots.

Applications of Spot-Welding Machine:

Electronics: Delicate electronic items are well-suited for spot-welding like connectors to solenoid assemblies, gas sensors, printed circuit boards, disc drive assemblies, even solar cells and panels, PCB, cables, connectors, switches, complex circuit boards and batteries, etc.

Kitchenware: Spatulas, handles, cookie cutters and tin cups are generally formed using spot-welding. 

Automotive Industry: Spot welding is utilised in the automotive industry in automating assembly lines by using spot welding robots. A metal sheet made from steel or aluminium alloy can easily be changed into a functional assembly part in seconds with extraordinary precision and repeatability.

Nail Manufacturing: Rolls of carbon steel are converted into nails by exposing it under the welding wheel with a supply of electric current which produces thousands of nails per minute.

Fabrication and Repair Shops: Used for repairing metal doors, windows and other damaged metallic items via spot-welding.

Small-scale Businesses and Shops: Small-scale businesses also utilize spot-welding processes for their industrial applications.

Medical Industry: Spot-Welding is utilized in orthodontics for fastening dental implants.