Spot welding and Applications of resistance welding process

What is Spot Welding, and How Does it Work?

Spot welding is a resistance welding process that is used primarily for welding two or more metal sheets. To fuse the materials, pressure, and heat from an electric current are applied to the weld area. Pressure and heat are applied by copper alloy electrodes which induce current due to the electrical resistance of the metals such as low carbon steel.

The name spot welding originates from a tiny dot that forms at the place of the weld. The dot initially looks like a spot, but the weld created between the copper electrodes is sometimes called a nugget.

Over the years, spot welding found its place in various industries. However, the auto body manufacturing industry found the merits of resistance spot welding quite useful. Nonetheless, let’s take a look at how does it work.

How Does the Resistance Spot Welding Work?

Spot welding occurs in three basic steps: alignment, applying pressure, and actual welding.

What Affects the Results of Spot Weld?

By reading the last part of the text, you can conclude that the principles of resistance spot welding are pretty straightforward. However, several factors can affect the spot weld: the force applied by electrodes, time spent between using the force and welding, welding time, and resting time.

Prior to welding, it is essential to check that the welding conditions are not excessive and that the electrode material is correct for the job.

Force Applied By Electrodes

As you already know, to start spot welding, you will have to apply force to the sheet metal you are about to weld.

However, many wonder how to determine an adequate force. Keep in mind that the stronger the applied force, the lower the electrical resistance of the materials is.

So if your projects include higher force, you will have to provide a higher welding current.

For example, high pressure will result in a small spot whit reduced penetration power. Therefore, you should ensure that the force is suitable for the welded material.

Squeeze Time

Squeeze Time is the time interval between the initial application of the electrode force on the work and the first application of current. You will have to delay the start of the current to attain the proper electrode force. Failing to initialize the squeeze time might result in arching, premature electrode wear, or interfacial expulsion. 

While introducing squeeze time in the spot welding process is essential and may result in a high-quality weld, too much delay is not helpful. There is only a certain amount of time required, and if you exceed the limitations, the performances are not getting any better, and you are just wasting time. In addition, wasting time needed to weld can result in higher expenses.

Time Spent Welding

After the squeezing period is over, a current is finally applied. Welding time denotes the period from starting the current until the end of the process. Unfortunately, welding time can be hard to determine, and it is usually computed using line voltage cycles.

There are many different factors when determining the weld time. However, you should always try to make it as short as possible to prevent the distortion, burn through and wear of electrodes.

Spot welding thick sheets should result in a broader nugget, and if your spot welder is not capable enough, you should increase the weld time. Meanwhile, when welding thin metals, you should divide the weld time into a number of impulses to prevent the heat energy from growing.

Cooling Time

Like any other welding method, spot welding requires cooling, often referred to as holding time. Holding time occurs once you stop the current, but the pressure is still applied.

The electrodes conduct excess heat after the welding, letting the materials solidify without any defects. However, the holding time shouldn’t be too long, as the excess heat can damage the electrodes.

In addition, when dealing with low carbon steel, extended cooling time can result in brittle welds. Therefore, you should let the weld cool but not overdo it.

Weldable Materials

The versatility of the spot welding process allows it to weld nearly all electrically conductive materials, but you will have to change the methods and approaches.

Due to high electrical resistance and low thermal conductivity;

Spot Welding Application

Thanks to the ability to weld nearly all conductive materials, spot welding is widely used in many industries and has many applications. For example, it found its way into manufacturing gas sensors, solar panels, switches, high voltage cables, and circuit boards.

However, spot welding is one of the prevalent methods in the automotive industry. Why? Because it is cost-efficient and works excellent with metal sheets.

Thus, spot welding robots in high-volume manufacturing lines can achieve tremendous productivity with significantly lower costs compared to advanced methods.

Resistance spot welding is also used in industries like aerospace, rail, manufacturing, electronics, construction, battery, and others. For example, spot welding straps to nickel-metal hydride, lithium-ion batteries, or nickel-cadmium cells is highly recommended due to high electrical resistance. The method can also be used to heat or repair orthodontic materials in dental labs.