6 types of resistance welding & how they work

What is resistance welding?

Resistance welding is a welding process that generates heat by passing an electrical current through the metal. 

Here’s how the whole thing works: 

• The metal pieces resist the flow of electricity, which causes them to heat up and melt at the point of contact. Once the current is removed, the metal pieces fuse together as they cool.
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• Two pieces of metal are pressed together and clamped by electrodes. An electrical current passes through the electrodes, heating the metal pieces and melting them at the point of contact. The current is then stopped, and the molten metal hardens, fusing the pieces together. 
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• The amount of heat generated depends on the amount of electrical current, its duration, and the resistance of the metal. The trick is to apply enough current for a long enough time to melt the metal without overheating the surrounding area.

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Pros and cons of using resistance welding

As with anything, resistance welding has some good, bad, and ugly.

Let’s explore its pros and cons: 

• Fewer welding mistakes and defects. Resistance welding is a fast, efficient process that produces strong, high-quality welds with few flaws, such as porosity or slag inclusion. The concentrated heat and pressure fuse materials together at a molecular level.
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• It can cost less. Resistance welding necessitates very little joint preparation and uses inexpensive equipment, so it is very cost-effective. Consumables are also cheap since they only require electricity and electrodes. High production rates. Resistance welding is also perfect for high-volume production because the equipment can quickly cycle.
  
  Automated resistance welding systems are capable of making several welds per second.
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• Not as many material choices. However, resistance welding only works on materials that conduct electricity well and can withstand the heat generated, such as low-carbon steels. It cannot be used on non-conductive materials like plastics.
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• You’ll need more maintenance. The high heat and pressures required can increase equipment wear and tear. Electrodes may need frequent replacement, adding to costs.
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• A real risk of overheating. There is a risk of overheating the materials if the current, time, or pressure settings are not properly controlled. This can weaken the weld or damage the materials. Close monitoring and experienced operators help minimize this risk.

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What are the types of resistance welding? 

There are various types of resistance welding making the rounds. 

Let’s break them down in more detail: 

• Resistance Spot Welding (RSW). Spot welding uses the heat generated by an electrical current to join metal sheets together. Electrodes clamp the metal sheets together, and an electric current is passed between them to create heat and form a weld nugget. Industries often use spot welding to join body panels in automotive manufacturing.
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• Resistance Seam Welding (RSEW). Seam welding is similar to spot welding but joins larger sections, like the seams of cans, drums or beams. Multiple spot welds are made along the joint line to create a continuous weld. Seam welding requires equipment to automatically feed and clamp the workpieces.
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• Resistance Projection Welding (RPW). Projection welding uses raised surfaces, called projections, that concentrate the current and generate heat. The projections melt and join the metal pieces together. Projection welding is often used to join crossed wires or attach brackets to metal surfaces.
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• Flash Welding (FW). Flash welding passes a high current through the joint area of two metal parts to quickly heat and join them. The rapid heating causes the metal to flash, or melt, at the joint. The flashing metal is then forced together under pressure to form a weld. Flash welding is useful for joining rods, bars, tubes, and rails.
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• Percussion Welding (PW). Percussion welding rapidly heats two metal surfaces through a series of high-current discharges. The heat causes the metals to melt instantly at the joint. The pieces are then forced together under high pressure. Percussion welding can join dissimilar metals and is often used for welding wire to terminals.
  
  By concentrating heat at the joint area, these welding methods avoid melting the entire workpiece. The concentrated heating also allows for fast cycle times, reducing energy.
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• Upset Welding (UW) is a solid-state welding process. In upset welding, the parts being joined are heated by the resistance generated by the flow of current through the parts at their interface, and then immediately forged together to create a bond. This process does not require any filler metal, and the heat is generated internally, resulting in minimal distortion and a strong, high-quality weld.

Real-world applications of the resistance welding process

Resistance welding is a common process used in many industries and for countless products we use daily. 

Here are some real-world examples of resistance welding in action: 

• The auto industry relies heavily on resistance welding for assembling vehicle bodies and parts. Spot welding, in particular, is used to join sheet metal panels together for car doors, hoods, trunk lids, and panels. Seam welding is also used on longer joints. These techniques are fast, efficient, and create strong bonds between panels.
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• Makers of appliances like refrigerators, washers, dryers, and ovens also leverage resistance welding in their assembly lines. The process is ideal for joining sheet metal and creating air-tight seals — both important for appliances. Spot welding and seam welding are commonly used.
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• Resistance welding, especially spot welding, is a standard in aircraft manufacturing. It is used to assemble the aluminum alloy sheet metal that makes up aircraft fuselages, wings, and other components. The high-strength welds it produces are essential for aircraft safety and durability.
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• Microspot welding joins very small electronic components, like wires, contacts, and microchips. The miniaturized process allows precise welds to be made without damaging heat-sensitive electronics. Resistance welding is also used for soldering some components onto printed circuit boards.
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• For large infrastructure projects like bridges, skyscrapers, and pipelines, resistance welding offers speed, strength, and efficiency. The process is suitable for welding thick steel plates and beams, as well as joining pipes for transporting liquids and gasses.

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Frequently asked questions

Is resistance welding the same as induction welding?

No. Resistance welding uses direct electrical current and pressure to join metals. Induction welding uses electromagnetic fields to heat metals before they're joined.

What is the difference between resistance welding and arc welding?

Resistance welding uses pressure and electrical current to join metals without filler material. Arc welding uses an electric arc to create intense heat, melting metals and often using filler material for a stronger join.

What are the problems with resistance welding?

• May not be suitable for all metals or thicknesses.
• Requires clean, oxide-free surfaces for optimal results.
• Can produce surface marks or indentations.
• Setup and maintenance of specialized equipment can be a factor.

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Summing up

Resistance welding is a super common manufacturing process that you've definitely encountered, even if you didn't realize it at the time. 

But now is the time to ask yourself: Is resistance welding the right process for your fab shop? 

To find out, you’ll have to assess your current industry, niche, application — and budget!

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Next steps 

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• Prioritizing safety: RO1 fosters a collaborative, human-centric workspace with its intuitive safety features.
• Smarter over time: Harnessing AI similar to GPT-4, RO1 continually learns and optimizes, ensuring continued efficiency gains.

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Our team partners with you for a smooth transition and helps you maximize the potential of your RO1 automation. Take advantage of our 30-day risk-free trial and witness the transformation!