The spot welding is one of the very old processes of welding. It used to be a choice of welding in industries where the overlapping of the sheets of metal requires like steel vehicle bodies. This process of welding primarily welds sheet up to 3 mm of thickness. The strength of the joint depends on the number and sizes of the weld spot. The diameter of spot weld ranges from 3mm -12.5 mm
The definition of spot welding in simple words is ” the process of welding for overlapping metal pieces at very small points by applying pressure and transmitting electric current “
The process of spot welding completed in the three following stages.
- The weld head of power source directs its electrode towards the surface of the metal to be welded and pressure/force is applied
- The electric current is passed through the electrodes to the material sheet or workpiece to be welded
- The time to remove the electric current in the electrodes but a force/pressure to continue at the workpiece until it becomes cools and solidifies.
The basic unit for the spot welding process consists of a power source, weld head with electrodes. The range in weld times is 0;01 to 0.63 seconds.
How does Spot Welding Works?
The resistance welding where two or more than two metals sheets are joined together without using any filler materials by applying constant pressure and electric current at the point of spot welding. The parts are locally heated in all types of resistance welding. The squeezing and heating of the material lead to the melting of the material and destroy the interface between the surfaces. The switching of the current lead on to Nugget formation on solidification to form the joint. The heat generation depends upon electric current passage through the copper electrode with electrical resistance and heat conductivity of the surface metal to be welded. To generate heat at the workpiece instead of electrodes, the copper electrode is commonly used as it has low resistance and high heat conductivity.
Material Appropriately Suitable for Spot Welding.
The steel due to its low carbon steel is easy to spot weld due to its low heat conductivity and high electric resistance. The high carbon steel may lead to the formation of a hard and brittle weld structure and prone to cracking and fracture. The galvanized steel may need little higher welding currents than to uncoated steel. The copper electrode rapidly disintegrates its surface leading to loss of welding quality. In need of welding zinc-coated steel, the electrodes must be exchanged frequently or the tip of the electrode surface should be dressed and cutter may be needed to remove contaminated material to reshape the electrode. The other material like Nickel alloy, Titanium, and Stainless steel are other materials suitable to spot weld.
The copper and its alloy can be suitable to join by spot welding but due to the similar characteristics with electrodes, the electrode material needs to change to molybdenum and tungsten to acquire the secure spot welding.
The Aluminum has the same heat conductivity and electrical resistance as of copper but a high level of current due to low resistance is required as compared to steel. The high temperature degrades the copper electrode fast thus making aluminum not a choice in spot welding.
Industries Where Spot Welding used.
This process of spot welding is being used in the construction of the steel car over the last more than 100 years. The spot welding can be used in rail, aerospace, automotive industries, metal furniture making, white goods, electronics, medical equipment making, construction, and infrastructure industries.
The robots and manipulation systems, when combined with spot welding, can lead to high volume manufacturing in industries.
What Material used for Electrodes?
The electrode material is commonly covered with ISO5182 is an alloying element to increase the hardness while maintaining its great conductivity. The copper/chromium/zirconium or combination is the most common material used for low carbon and high strength steel as there less heat at the surface due to low resistance at the contact point.
The harder sheet-like stainless steel may need class 3 electrodes such as copper/silicon/nickel for low welding current. The refractory electrode of copper/tungsten/, or tungsten, molybdenum may be used for projection welding.
How to Minimize Weld Splash?
We can offer near-perfect weld quality without a splash by taking care of the following points.
- The welding current should not be too high and weld time needs to be appropriate not longer.
- The size and shape of the tip of the electrode may lead to malalignment and splash.
- The lack in the flat surface of the sheet leading to poor fit so more force may be needed which can cause a splash.
- The inaccuracy and misaligned flanges may lead to too close welding.
- The dirty surface may lead on to high resistance thus more heat and splash.