What Is Spot Welding And How To Use It?

What Is Spot Welding

In the field of welding and brazing, there are many different techniques. Each has its pros and cons. Among them, one of the oldest known welding processes is spot welding. Also known as resistance welding, the way it works is simple.

It has a simple set-up. If you are a novice in welding, you may not be that familiar with this process. But you need to know the ins and outs of every type of welding to call yourself an expert. In this article, you can find all the details you need about spot welding. Go through to the end to understand the set-up and using the method of this welding.

What is Spot Welding?

As mentioned, spot welding is a type of resistance welding. People use it in order to weld two or more metals with each other. To do that, the power source of the welding is electricity. You will use electrodes made of copper alloys to connect to the workpiece metals. Afterward, the workpiece will gain heat via electric current and pressure added to it.

How Does It Work?

Understanding the working process of spot welding is not hard. One thing that differentiates this process from other welding methods is that it doesn’t use any filler material. Instead, the metal sheets are placed together, and two copper electrodes press them from both sides.

At the same time, electric current flows towards and into the workpiece, generating heat. As a result, the workpiece melts down and starts to bond because of the applied pressure. After the bonding begins, the electricity gets disconnected. They get bonded perfectly due to the electrodes still pressing on them. The diagram shows the basic working process of spot welding-

basic working process of spot welding

Difference Between Spot Welding and Arc Welding

The differences between spot and arc welding processes are an important matter you should know. While both use electricity as the power source, their working process and set-up are different.

  • Arc welding takes the help of electric arcs to melt the materials. Spot welding does this using electric resistance.
  • Arc welding uses a filler material that spot welding does not.
  • During arc welding, the welding zone stays protected via gases or flux. Spot welding does not use or need anything like that.
  • You can weld materials of any thickness you want with arc welding. Spot welding can only weld thin materials.
  • Arc welding is normally used for fixing, combining, or connecting materials of different sizes. Meanwhile, Spot welding is ideal for industrial processes to combine two to three thin sheets swiftly and repeatedly.
  • Arc welding requires the user to do most of the work. In spot welding, most of it is done by the welding machine.

If you still do not understand their difference, think of arc welding as electricity and spot welding as electrical appliances. While arc welding heats the material using electrical arcs, spot welding gradually transfers the electricity to the workpiece like an electrical plate.

Spot Welding Electrodes

For spot welding, the electrodes are usually made of copper alloys. It is because of how copper can transfer heat and electricity at higher amounts than many other materials. But for different applications, manufacturers add alloys of other materials to the copper allow. There are three classes to that..

Class 2 electrodes

Class 2 electrodes are good for materials with high strength. It is the most common electrode type. People mostly weld coated steel using class 2 electrodes. Materials used for class 2 electrodes are-

  • Alloy, made of chromium, copper, and zirconium mixture.
  • Alloy, made of copper and chromium mixture.

Class 3 electrodes

These electrodes have high contact resistance. They conduct low amounts of current while providing much pressure. Stainless steels are the most common workpiece for class 3 electrodes. Their materials are mostly-

  • Alloys of nickel, silicon, and copper mixture.

Refractory electrodes

Materials used for refractory electrodes can conduct low current and has high heat resistance. They are also pretty tough. Apparently, you can only use them for welding copper workpieces. They are mostly made of-

  • Molybdenum alloy.
  • Tungsten alloy.
  • Alloys of tungsten and copper mixture.

Spot Welding Machine

A spot welding machine is different than an arc or MIG welding machine. The main part of the machine is usually vertical, and the electrodes stay at a higher position where it is easier to pass or remove metals from between them. For light-duty DIY spot welding, there are small and portable welding machines too. But for industrial usages, they appear bigger.

Since the heat and pressure requirements are different for many applications, the machine should allow you to adjust them separately. Ones with regulators to control the heat are easy to operate.

There should also be a handle, knob, or foot treadle to open up the electrodes so that you can pass or remove metals from between them. To cool down the electrodes quickly, most have water cooling systems through two hoses connected to each electrode. The diagram below shows the parts of a spot-welding machine-

parts of a spot-welding machine

How to Use Spot Weld?

You should have a decent amount of knowledge on spot welding by now. Let’s show you the method of using it. Read the points below for a step-by-step guide-

  • Make sure that the electrodes are cooled down from any previous usages.
  • Wear safety goggles and gloves.
  • Clean the workpiece metals and the electrodes using clean cloths. Avoid wet clothes or water.
  • Position the metals like how you want to weld them. Hold them with vice grip pliers. Make sure that they don’t move an inch from the desired position.
  • Adjust the required heat and pressure. Then plug in the machine but don’t switch it on yet.
  • Open the electrodes using the handle, knob, or foot treadle. Pass the area of the metal you want to weld between the electrodes.
  • Switch the machine on.
  • The machine will start to heat the electrode and the workpieces. It will take 2-3 seconds for the metals to be welded.
  • Decrease the heat to zero but keep the pressure on so that the metals bond together properly.
  • After 5 seconds, remove the bonded metals. It should be cool after 5 minutes.
  • Remove them from the grip of the vice grip pliers.

Final Note

If you compare among different welding processes, you will see how spot-welding is a quicker welding process. Most other welding processes are not able to weld middle to middle metal sheets. But it is possible with spot welding. After using it for few times, you will be used to it.

Last Updated on 2 years by Richard Boyer

  • June 8, 2022
Richard Boyer

Richard Boyer has been a professional welder for over 27 years of his life, and now he is a trainer and blogger providing critical information to anyone interested in welding. He is helping out both hobbyists, novice and professional welders to learn newer and better techniques. Read more about me

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