Molly Ayala
Electric resistance welding (ERW) is a welding process that involves joining metal parts by applying heat and pressure. An electric current is passed through the metal, melting the metal at the joint and forming small pools of molten metal at the point of most electrical resistance. This process is widely used in various industries, such as the manufacture of steel pipes and automobile assembly. The weld power is generated by the material's resistance to the flow of electrical current, and the pressure is applied through electrodes or rollers. Different types of ERW include high-frequency (HF) and rotary contact wheel welding, with subcategories like HF contact and HF induction.
| Characteristics | Values |
|---|---|
| Definition | A welding process in which metal parts are joined by heating them with an electric current, melting the metal at the joint. |
| Other Names | Electric Resistance Welding (ERW), Resistance Welding (RW) |
| Process | Metal parts are carried into contact with one another, sandwiched between two electrode tips. |
| A strong electric current is passed through the metal combination to heat up and melt the metals at the joint. | |
| A force is applied before, during, and after the application of the current to confine the contact area at the weld interfaces and, in some cases, to forge the workpieces. | |
| The molten or plastic state grows to meet the welding tips. | |
| When the current is stopped, the metal solidifies under pressure and fuses together. | |
| Types | Spot Welding, Seam Welding, Flash Welding, Projection Welding, High-Frequency (HF) Induction Welding, HF Contact Welding, Rotary Contact Wheel Welding, AC Rotary Contact Wheel Welding, DC Rotary Contact Wheel Welding |
| Applications | Widely used in the manufacturing industry, especially in the production of steel pipes and assembly of automobile bodies. |
| Advantages | Efficient, low distortion, strong welds, cost-effective, high production rates, little pollution |
| Disadvantages | Limited applications due to limitations in material thickness, equipment costs, and maintenance issues. |
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What You'll Learn
Electric resistance welding (ERW)
The basic principle behind ERW is the use of an electric current, typically ranging from 100 to 100,000 amperes, to heat the metal at the point of most electrical resistance, which is where the connecting surfaces meet. This results in the formation of small pools of molten metal, which solidify under pressure when the current is stopped. The cooling process is accelerated by using water-cooled copper electrodes, as copper is an excellent conductor.
There are several variations of ERW, including spot welding, seam welding, flash welding, and projection welding. Spot welding, for example, is commonly used to join overlapping metal sheets, studs, and tubing. Seam welding creates impenetrable and water-tight welds, making it ideal for producing leak-proof joints in small tanks and boilers. Flash welding employs very high current intensity at small contact points, resulting in a flashing action before the workpieces are bonded. Projection welding, on the other hand, focuses the heat at specific points of contact, typically using lower currents and forces than spot welding.
The two main types of ERW are high-frequency (HF) and rotary contact wheel welding. In HF welding, the equipment providing the electrical current is independent of the equipment supplying the forge pressure. This method includes HF contact welding, which transfers weld current directly to the tube, and HF induction welding, where the weld current is transmitted through a work coil in front of the weld point. Rotary contact wheel welding, on the other hand, transfers the electrical current through a contact wheel, with sub-types such as AC, DC, and square wave.
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How it works
Electric resistance welding (ERW) is a process that uses electrical current and pressure to join two metal pieces. It is a popular technique due to its simplicity, speed, reliability, and low distortion.
The process typically begins with the metal parts being brought into contact with each other, sandwiched between two electrode tips. These electrodes apply pressure to ensure optimal contact and hold the parts in place during welding. The current is then passed through the workpieces, encountering resistance at the connection point, which creates a large amount of heat. This heat generation is due to the conversion of electric energy to thermal energy—the Joule heating effect. As the metal rapidly softens and melts, the semi-molten surfaces are pressed together, creating a fusion bond.
There are several variations of electric resistance welding, including spot welding, projection welding, seam welding, and flash welding. Spot welding is the simplest form, where the workpieces are held together by force. Projection welding is a modification of spot welding, where the weld is localised by using raised sections or projections on the workpieces. Seam welding produces a weld at the faying surfaces of two similar metals, and it can be either a continuous or non-continuous weld. Flash welding uses the heat generated by the resistance to the flow of current, along with the force of the workpieces being pushed together.
Electric resistance welding has found applications in various industries, especially automotive manufacturing. It offers advantages such as efficient energy use, limited workpiece deformation, high production rates, easy automation, and no need for filler materials. However, it also has limitations, such as material thickness constraints and equipment costs.
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Types of ERW
Electric resistance welding (ERW) is a process in which metal parts are joined by heating them with an electric current, melting the metal at the joint. The two main types of ERW are high-frequency (HF) and rotary contact wheel.
High-Frequency ERW
The two HF welding processes are HF contact and HF induction. In both processes, the equipment that provides the electrical current is independent from the equipment that supplies the forge pressure. In the case of HF induction welding, the weld current is transmitted to the material through a work coil in front of the weld point. The weld power is applied directly to the tube, which makes this process more electrically efficient than HF induction welding. Because it is more efficient, it is well-suited to heavy-wall and large-diameter tube production.
Rotary Contact Wheel ERW
The three main types of rotary contact wheel welders are AC, DC, and square wave. In all three power supplies, electrical current is transferred by brush assemblies that engage slip rings attached to a rotating shaft that supports the contact wheels. These contact wheels transfer the current to the strip edges. In an AC rotary contact wheel welding machine, the current is transferred through the brushes to the rotating shaft, which has a transformer mounted on it. The transformer reduces the voltage and increases the current, making it suitable for welding.
Other Types of ERW
Other ERW methods include flash welding, resistance projection welding, upset welding, seam welding, and spot welding. Flash welding is a type of resistance welding that does not use any filler metals. The pieces of metal to be welded are set apart at a predetermined distance and current is applied to create the arc required to melt the metal. Once the pieces reach the proper temperature, they are pressed together. Seam welding is commonly used during the manufacturing of round, square, and rectangular steel tubing. Spot welding is used to join two or more overlapping metal sheets, studs, projections, electrical wiring hangers, some heat exchanger fins, and some tubing.
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Applications
Electric resistance welding is a widely used technique in various industries, including automotive, aerospace, and construction. It is a reliable, efficient, and cost-effective method for joining metals and alloys, and it can produce high-quality welds quickly. Here are some common applications of electric resistance welding:
Automotive Industry
Resistance welding is commonly used in the automotive industry for various applications. Spot welding, for example, is used to join metal sheets, studs, projections, electrical wiring hangers, and tubing in vehicles. Projection welding is used in the production of nuts and bolts, while seam welding is used to create leak-proof joints required in small tanks, boilers, and other components. Flash welding is employed for welding pipes and tubes. The versatility and efficiency of resistance welding make it valuable in the automotive industry, where it can be used for both mass production and specialized applications.
Aerospace and Construction
In the aerospace industry, resistance welding is used for applications where strong and durable welds are required. This includes welding thin metal sheets, pipes, and other components used in aircraft construction. Similarly, in the construction industry, resistance welding is employed for welding pipes, tubes, boilers, small tanks, and containers. The ability to create high-quality welds efficiently makes resistance welding a preferred choice in these industries.
Industrial and Manufacturing
Resistance welding is widely used in industrial and manufacturing settings, especially when repetitive welds are needed. Its speed and efficiency make it ideal for high-volume production. Additionally, the lack of hazardous fumes and the ability to automate the process further enhance its applicability in these sectors.
Pipeline Fabrication and Machine Repair
Resistance welding is commonly used in pipeline fabrication and machine repair works. Its ability to create strong welds in thin materials makes it suitable for joining pipes and repairing machinery. The versatility of resistance welding allows it to be adapted to various materials and applications in these industries.
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Safety measures
Electric resistance welding (ERW) is a welding process that uses electric current to heat and join metal parts. This technique is widely used in manufacturing steel pipes and assembling automobile bodies.
- Personal Protective Equipment (PPE): It is crucial to wear appropriate PPE, including safety goggles, a face shield or safety glasses, long-sleeved shirts made from non-melting materials, dry insulated gloves, and welding gloves and overalls to minimise exposed skin.
- Ventilation and Fume Avoidance: Ensure adequate ventilation in the workspace to avoid inhaling harmful fumes. Read safety data sheets for metals, coatings, and cleaners to understand the potential hazards.
- Fire Safety: Keep flammables away from the welding area, and always have a fire extinguisher nearby. Know how to use the fire extinguisher effectively.
- Electrical Safety: Install and ground the unit according to electrical codes. When working with 3-phase welding circuits or single-phase circuits derived from different phases, segregate welding positions connected to different phases or transformers by partitions or distance to minimise the risk of electric shock.
- Machine Guarding: Keep all guards and panels in place. Use electronic eye or two-hand controls as additional protection during press welding machine operations to prevent injuries to the operator's fingers.
- Surface and Material Preparation: Ensure that the welding return path does not exhibit high electrical resistance by clamping onto clean metal surfaces instead of rusty ones. Eliminate contaminants between the faying surfaces to be welded.
- Cooling: Allow tongs, tips, and workpieces to cool before handling. The water-cooled copper electrodes used in resistance welding can help accelerate the cooling process.
- Maintenance and Inspection: Conduct regular checks and maintenance on welding equipment, ensuring that insulation, connectors, and clamps are undamaged and correctly rated for the required current.
These safety measures are essential to follow to protect operators from electrical hazards, burns, and exposure to harmful fumes during electric resistance welding operations.
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Frequently asked questions
Electric resistance welding (ERW) is a welding process in which metal parts are joined by applying heat and pressure, melting the metal at the joint.
An electric current is passed through the metal parts, causing heat buildup at the point of most electrical resistance (the connecting surfaces). Small pools of molten metal are formed, which solidify under pressure when the current is stopped.
The two main types of ERW are high-frequency (HF) and rotary contact wheel. There are six main resistance welding processes, including spot welding, seam welding, flash welding, and projection welding.
Resistance welding is efficient and causes little pollution, and does not require additional materials such as shielding gases or filler rods. It is widely used in industries such as automotive manufacturing and pipe production.
