In this post, you’ll learn what is resistance welding and how it works. Different types of resistance welding explain with diagram and advantages, applications and more.
Resistance Welding and Types
Resistance welding is a liquid state welding process, in which a metal-to-metal joint is made in a liquid or molten state. The resistance welding is also known as the thermo-electric process in which heat is produced at the interface surfaces of welding plates due to electrical resistance and controlled low pressure is applied to these plates to form the weld joint.
It uses electrical resistance to generate heat therefore it is called as resistance welding. Resistance welding is a very efficient pollution-free welding process but its uses are limited due to its high material cost and limited material thickness.
Working Principle of Resistance Welding
It is a welding process in which heat is produced by the resistance offered by the workpieces for the flow of electric current through them. In this process, the parts to be welded are held together and a high current is passed. Due to the resistance to the flow of current heat is produced which is sufficient enough to fuse the metal.
At the same time pressure is applied to the weld region so that the fused workpieces join together. The heat produced is given by H = I2 Rt, where
- H = Heat developed in joules
- I = Current passing through the work in amps
- R = Electrical resistance of the work in ohms
- t = be the Time of current flow in seconds
Resistance welding is widely used and comprises of spot, projection, seam, butt and flash welding operations.
Types of Resistance Welding
Following are the 5 different types of resistance welding:
- Spot resistance welding
- Projection resistance welding
- Seam resistance welding
- Flash resistance welding
- Butt resistance welding
1. Spot Welding
In this process, the parts to be joined are held firmly between two heavy electrodes, which are connected in the secondary circuit of the step-down transformers. The maximum resistance exists at the contact surface of the two parts being joined and high heat is developed.
The heat developed fuses the workpiece at the electrode spot. At the same time pressure is applied to the workpiece through the electrodes and welding takes place. Current supply and amount of time must be sufficient for proper melting of interface surfaces.
The current stopped flowing but the pressure applied by the electrode remained for a fraction of a second, while the weld cooled rapidly. Subsequently, the electrode is removed and brought to contact another location. This will form a circular nugget. The size of the nugget depends on the size of the electrode. It is usually about 4–7 mm in diameter.
2. Projection Welding
The projection welding is similar to spot-welding but uses a flat electrode. In this current flow and resultant heating are localized of the projection, hence thick parts can be joined that cannot be joined by spot welding.
The workpiece is held between the electrode and a large number of current passes through it. A small amount of pressure is employed through the electrodes on the welding plates. The current passes through the dimple which melts it and causes the pressure dimple to level and form a weld.
3. Seam Welding
Similar to spot welding but in this a continuous weld is produced by passing the work between rotating wheel-shaped electrodes, which exert the welding pressure and also conduct the welding current. It may be continuous or intermittent.
First, the rollers are exposed to the workpiece. A high amount of ampere current is passed through these rollers. This interface surfaces will melt and form a weld joint. Now the rollers start rolling on the work plates. This will form a continuous weld joint.
The movement time of the weld and electrode is controlled to assure that the weld overlaps and the workpiece is not too hot. It is used to make airtight joints.
4. Flash Welding
It is a type of resistance welding process, which can be used for joining together the ends of sheets, wires, rods or tubes. Here electric arc is produced in the gap between the workpieces until the welding temperature is attained. Then pressure is applied to produce a continuous weld.
5. Butt Welding
The butt welding differs from flash welding, in that no arcing takes place between the surfaces being joined. The heat is produced solely by the electric resistance at the butting surface to the flow of current.
Advantages of Resistance Welding
Following are the advantages of resistance welding:
- No filler metal is required.
- Similar and dissimilar metals can be welded.
- It can weld both the thin (0.1 mm) and thick (20 mm) metals.
- High skilled labour is not needed because of the simple and fully automated process.
- It has a high production rate.
- It is an environmentally friendly process.
- This process has a high welding speed.
Disadvantages of Resistance Welding
Following are the disadvantages of resistance welding:
- The equipment cost of resistance welding is high.
- The thickness of the workpiece is limited due to the current demand.
- It is less suitable for high conductive materials.
- It has a high electric power required.
- The weld joints have low tensile and fatigue strength.
Application of Resistance Welding
Following are the applications of resistance welding:
- It is broadly used in the automotive industries.
- Projection welding is generally used in the production of nut and bolt.
- Seam welding is used to perform leak prove joint required in small tanks and boilers etc.
- Flash welding is adopted for welding pipes and tubes.
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