Flash welding is a method of welding in which the ends of the workpiece are pressed together during the welding process. Flash welding is a type of resistance welding.
In this welding process, a heavy current is passed through the joint.Resistance welding is a type of welding in which resistance is used to develop heat. In resistance welding, no filler material is used and no flux is used.
Now, Butt Welding is a type of resistance welding.
Butt Welding is classified into two types:
1) Flash Welding
2) Upset Welding
In this article, we will study flash welding.
The Flash welding process is mainly used to weld thicker materials like heavy anchor chains, rails, pipes and shaft axles.
Flash welding is mostly used for welding steel but can also be used for nickel, aluminum, and titanium alloys.
Parts Used in Flash Welding:
1. Transformer:
In flash welding, a transformer is used which is connected to AC supply.
2. AC Supply:
An AC supply is used to provide power to the flash welding or flash butt welding.
3. Clamps:
There are two types of clamp used in Flash Welding:
i) Stationary Clamp
The stationary clamp always remains in a fixed position and always clamps the workpiece.
ii) Movable Clamp
The movable clamp can move about its axis in a reciprocating motion.
Both the clamps are used to hold the workpieces in their position while the welding process is carried out.
Working:
At the starting both parts which are to be joined are placed at some distance and facing each other.
One part is attached to the fixed clamp and another part is fixed to the movable clamp.
Now, the air is present between the two parts and when continuous electricity flows then electric ions start jumping from the part clamped in a fixed clamp towards the part clamped in the movable clamp.
The parts to be joint completes the single turn secondary of a heavy duty transformer.
After that, the part in the movable clamp is slowly brought near to the part clamped in the fixed clamp. As it comes closer and closer, the gas present between the two parts starts getting ionized.
Hence heat is developed in the air present between the two parts to be joined. Now as the heat is developed, then both the ends of the two parts get heated.
Heat is generated at the interface and much of the molten metal is expelled as a flash and the moving clamp is advanced to keep a constant gap until a suitable temperature is reached at the interface.
Resistance is created due to the air present between the ends of the two parts and due to this resistance heat is developed between the two parts.
As resistance is used to develop heat in this welding that is why this welding is type of resistance welding.
When the suitable temperature is reached then using the movable clamp a very high force is applied from the part in the movable clamp towards the part held in the stationary clamp and both the parts are forged together. This applied force is in an axial force.
After the force is applied, the ends of both parts which are at the plastic stage come in contact with each other.
When the two ends collide, the molten metal flashes out in the outward direction, and this outward movement of the metal causes a flashing effect. Because of this flashing effect, this welding is known as flash welding.
During the flashing process, a weld is developed between the two ends. This welding process produces a neat, clean, and strong joint.
When the joint is formed completely, the AC Power supply is stopped.
After that two parts are held in the clamps for some time so that they can solidify. After solidification, we get a very strong joint using this welding process.
When welding heavy parts preheating is done b bringing the parts into contact a number of times and then separating them to create resistance heating but delaying the onset of flashing.
This welding process is generally used to weld the channel section of the beam.
This welding process can be used in mass production because this welding process takes very much less time to
Advantages Of Flash Butt Welding:
I) The power required is less in this welding process.
ii) The weld surface is not required to be prepared.
iii) This process is very cheap.
iv) Metals with different melting temperatures can be welded using this flash welding.
v) This process offers strength factor up to 100%.
Disadvantages of flash welding:
i) Chance of fire hazards is high.
ii) Welding Machine is very bulky.
iii) Metal is lost during flashing and upsetting.
iv) This process is very costly due to high power consumption.
v) The workpiece often loses its straightness during this welding process. The straightness of the workpiece is needed to be maintained.
Applications Of Flash Welding Process:
i) It is used for fitting metal sheets, bars, rod fittings etc.
ii) This welding process is used to manufacture automotive and aircrafts.
iii) It is also used in manufacturing household appliances, refrigerators and farm implements.
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