The Top 10 Resistance Welding Techniques You Need to Know for Optimal Bonding Strength [PDF]

What is Resistance Welding?

Resistance welding is one of the oldest of the electric welding process. It is widely used by industries nowadays. The weld is made by a combination of heat, pressure, and time. All resistance welding, spot welding, seam welding, projection welding, etc. work on the same principle as that of heat generation due to electric resistance.

Working Principle of Resistance Welding

When a current passes through an electric resistance, it produces heat. This is the same principle which is used in the electric coil. The amount of heat produced depends on the resistance of the material, surface conditions, a current supplied, time duration of current supplied, etc.

This heat generation takes place due to the conversion of electric energy into thermal energy.  The current is the same in the whole circuit. The highest Heat is developed where the resistance is at its maximum, exactly where it is needed for this process. Heat is proportional to the product of resistance by the square of the current and by time. Therefor The heat generation equation is  (H=I²Rt). 

Where,

H=Heat generated in joules.
I=Current in amperes (Amps). 
R=Resistance in ohms. 
T=flow time of the current in seconds.

Equipments / Parts of Resistance Welding

• Initiating Switch

To start the resistance welding process or supply the power for welding, first, we switch on using the ignition switch.

• Timer

The initiation switch is connected to the timer and from the timer, it is connected to two other devices namely contractor point and AC power supply where the switch gets on.

• Contractor Point

Contractor points work like the connection between AC power and Step down transformer. This works as an intermediate switch.

• Primary Winding

Here voltages are more which is further decreased in the step-down transformer.

• Step Down Transformer

The step-down transformer work is to reduce the voltage in the secondary winding as compared to the primary winding.

• Secondary winding

The secondary winding is connected to the step-down transformer for receiving the power from the electrode and also to reduce their electrical resistance between them.

• Electrode

An electrode is a conductor through which the current passes. Here it is also used to join the two workpieces.

• Air Valve

Air is coming through the port and this air is further utilized for making pressure.

• Pneumatic Cylinder

This is used for supplying the pressure by the use of the air valve.

Working of Resistance Welding

The main requirement of the process is low voltage and high current power supply. This is obtained by means of a step-down Transformer with a provision to have different tapping on the primary side, as required for different materials. The secondary windings are connected to the electrodes which are made of copper to reduce their electrical resistance. The time of the Electric Supply needs to be closely controlled so that the heat released is just enough to melt the joint and the subsequent fusion takes place due to the force (Forge welding) on the joint. The force required can be provided either mechanically, hydraulically or pneumatically.

To precisely control the time, sophisticated electronic timers are available. The critical variable in the resistance welding process is the contact resistance between the two workpiece plates and their resistance themselves. The contact resistance is affected by the surface finish on the plate since the rough surface has higher contact resistance. The contact resistance also will be affected by the cleanliness of the surface. Oxides or other contaminants if present, should be removed before attempting resistance welding.

Types of Resistance Welding

There are several types of resistance welding techniques available, each with its own unique advantages and applications. Following are some main types of resistance welding that we will discuss in detail.

• Resistance Projection Welding
• Resistance Spot Welding
• Resistance Seam Welding
• Resistance Butt Welding
• Single-Sided (One-Sided) Welding
• Resistance Weld Bonding
• Crosswire Welding
• Indirect Spot Welding
• Series Spot Welding
• Micro Resistance Welding

Resistance Projection Welding

Resistance projection welding is a type of resistance welding that is commonly used for joining small metal parts. This method involves the use of a specially designed electrode with a small projection that helps concentrate the heat and pressure at the point of welding. Resistance projection welding is ideal for creating strong and durable welds in parts that are too small or complex for other welding methods.

Advantages of Resistance projection welding

• It is suitable for welding complex shapes and configurations.
• The process produces strong, consistent, and high-quality welds.

Disadvantages of Resistance projection welding

• The equipment for projection welding is more expensive and complex than spot welding.
• The process is slower than spot welding, reducing the production rate.

Applications of Resistance projection welding

• Automotive industry – for welding nuts, bolts, and other components to metal sheets.
• Appliance industry – for welding components and parts.

Resistance Spot Welding

Resistance spot welding is another popular resistance welding technique that is used for joining metal parts that are up to 3mm thick. This method involves the use of two electrodes that are placed on opposite sides of the metal parts to be welded. A high current is passed through the electrodes, creating heat at the point of welding. The heat fuses the metal parts together, creating a strong and durable bond.

Advantages of Resistance spot welding

• It is fast, reliable, and can produce high-quality welds.
• It requires minimal preparation of the surfaces to be welded, reducing production time and cost.

Disadvantages of Resistance spot welding

• The process is limited to welding materials with relatively low thicknesses.
• The electrodes wear out over time and require frequent replacement, adding to the cost of production.

Applications of Resistance spot welding

• Automotive industry – for welding body panels, frames, and other components.
• Electronics industry – for welding components and wires.

Resistance Seam Welding

Resistance seam welding is a type of resistance welding that is commonly used for creating continuous welds in metal parts, such as tubes or pipes. This method involves passing the metal parts between two rotating electrodes that apply heat and pressure, creating a continuous seam weld. Resistance seam welding is ideal for creating strong and leak-proof welds in metal parts that need to withstand high pressure or harsh environments.

Advantages of Resistance seam welding

• The process is suitable for welding long and continuous seams.
• It can weld materials of varying thicknesses and shapes.

Disadvantages of Resistance seam welding

• The equipment for seam welding is more complex than for spot welding.
• The process is slower than spot welding, reducing the production rate.

Applications of Resistance seam welding

• Aerospace industry – for welding fuel tanks, engine components, and other structures.
• HVAC industry – for welding ducts and other components.

Resistance Butt Welding

Resistance butt welding is a type of resistance welding that is used for joining two metal parts that are of the same thickness. This method involves placing the two metal parts end-to-end and applying heat and pressure to the joint, creating a strong and permanent bond between the parts. Resistance butt welding is commonly used in the automotive and aerospace industries for creating strong and lightweight structures.

Advantages of Resistance butt welding

• The process is suitable for welding large sections of materials.
• It produces strong and consistent welds with minimal distortion.

Disadvantages of Resistance butt welding

• The process requires precise alignment and preparation of the materials to be welded.
• It is less suitable for welding materials with varying thicknesses.

Applications of Resistance butt welding

• Construction industry – for welding large metal beams and structures.
• Energy industry – for welding pipes, tubes, and other components.

Single-sided Welding

Single-sided (one-sided) welding is a type of resistance welding that is used for joining two metal parts together from one side only. This method involves the use of a specially designed electrode that applies heat and pressure to the joint from one side, creating a strong and durable weld. Single-sided welding is commonly used for creating welds in parts that are too complex or difficult to access from both sides.

Advantages of Single-sided Welding

• It is suitable for welding large and heavy structures.
• It is a time-saving process that reduces production costs.

Disadvantages of Single-sided Welding

• The process requires specialized equipment that can be expensive.
• It is less suitable for welding materials with thicknesses less than 3 mm.

Applications of Single-sided Welding

• Shipbuilding industry – for welding large ship components and structures.
• Construction industry – for welding large and complex steel structures.

Resistance Weld Bonding

This method is suitable for joining two dissimilar metals, such as aluminum and steel. In resistance weld bonding, a layer of intermediate metal is placed between the two parts to be bonded. The intermediate metal has a lower melting point than the base metals, allowing it to melt and fuse the two dissimilar metals without affecting their properties. This method produces a strong and durable bond that is resistant to corrosion and fatigue.

Advantages of Resistance Weld Bonding

• It can join dissimilar materials with different melting points.
• The process produces high-strength welds that are resistant to corrosion.

Disadvantages of Resistance Weld Bonding

• The process requires specialized equipment and skilled operators.
• It is more expensive than traditional welding techniques.

Applications of Resistance Weld Bonding

• Aerospace industry – for welding components made of different metals.
• Medical device industry – for welding components made of different materials.

Crosswire Welding

Crosswire welding is a variation of resistance welding used to join wires and thin sheets of metal. In this method, two or more wires are crossed at a right angle and then pressed together under high pressure while an electric current is passed through them. The heat generated by the current melts the wires at the point of contact, fusing them together. This method is commonly used in the production of wire mesh, grills, and screens.

Advantages of Crosswire Welding

• It can join multiple wires together with one welding operation.
• The process is fast and efficient, reducing production time and cost.

Disadvantages of Crosswire Welding

• The process is limited to welding materials with small diameters.
• The welding strength may be compromised if the wires are not aligned properly.

Applications of Crosswire Welding

• Electronics industry – for welding multiple wires and cables together
• Automotive industry – for welding wire harnesses used in vehicles.

Indirect Spot Welding

Indirect spot welding is a method used to join metal parts that are difficult to access, such as components inside an assembly or parts with limited access. In this method, a special electrode is used to apply pressure and heat to the weld area indirectly, through a thin layer of material. This process allows for precise control of the welding process, resulting in a strong and consistent bond.

Advantages of Indirect Spot Welding

• The process produces strong and high-quality welds without direct contact with the material.
• It is suitable for welding materials that are difficult to access.

Disadvantages of Indirect Spot Welding

• The process requires specialized equipment and skilled operators.
• It is more expensive than traditional welding techniques.

Applications of Indirect Spot Welding

• Aerospace industry – for welding components that require precise alignment and positioning.
• Automotive industry – for welding parts and components that are difficult to access.

Series Spot Welding

Series spot welding is a type of resistance welding that involves joining two or more metal parts in series, creating a chain of welds. This method is commonly used in the production of sheet metal parts, such as automotive bodies and appliance parts. Series spot welding is fast, efficient, and produces a strong and durable bond.

Advantages of Series spot welding

• The process is suitable for welding materials with high electrical resistance.
• It produces strong and consistent welds with minimal distortion.

Disadvantages of Series spot welding

• The process requires precise alignment and preparation of the materials to be welded.
• The equipment for series spot welding is more expensive than for spot welding.

Applications of Series spot welding

• Energy industry – for welding materials used in electrical systems.
• Electronics industry – for welding components that require a high level of accuracy and consistency.

Micro Resistance Welding

Micro resistance welding is a specialized form of resistance welding used to join small, delicate components such as wires, sensors, and microelectronic devices. This method uses a high-frequency current and a precision electrode to apply heat and pressure to the weld area, creating a strong and reliable bond without damaging the delicate components.

Advantages of Micro Resistance Welding

• It is suitable for welding small and delicate components.
• The process produces high-strength welds with minimal distortion.

Disadvantages of Micro Resistance Welding

• The process requires specialized equipment and skilled operators.
• It is limited to welding materials with thicknesses less than 1 mm.

Applications of Micro Resistance Welding

• Medical device industry – for welding small components used in implants and surgical instruments.
• Electronics industry – for welding small components used in micro-electronic devices.

Defects of Resistance Welding

• Cracks
• Electrode deposit on work
• Porosity or cavities
• Pinholes
• The electrode indentation
• Improper weld penetration

Application of Resistance Welding

• The main application of this welding is for manufacturing lap joint.
• It is used in automotive industries for manufacturing bolts and nuts.
• They are used for applications where high rate production is required.
• They are also used for boiler applications.

Advantages of Resistance Welding

• Capable of a high degree of process control
• Capable of a high degree of mechanization
• Good Mechanical properties
• high-speed welding
• Easily automated
• Suitable for high rate production
• Economical

Disadvantages of Resistance Welding

• High equipment and tooling costs.
• Limitation of joint design requirements
• Initial equipment costs
• Lower tensile and fatigue strength
• Irregularly shaped welds

Video on Resistance Welding

FAQ’s

Conclusion

Let’s summarize everything that we have discussed in this article. Resistance welding is a widely used welding technique in which heat is generated by passing an electric current through the workpiece, causing it to melt and fuse together. This method of welding is commonly used in industries such as automotive, aerospace, and construction due to its efficiency and cost-effectiveness. The process involves applying pressure to the workpiece while simultaneously passing an electric current through it. This creates a localized heat that causes the metal to melt and fuse together, creating a strong and durable bond.

In conclusion, resistance welding is an effective and widely used welding technique that offers a number of benefits for different industries. It is a cost-effective and efficient way to join metals, making it an attractive option for many businesses.