Application of robots in the process of spot welding – Spot Welding

It is almost unthinkable to see the automotive industry without spot welding, more precisely spot welding. Spot welding is one of the techniques for joining sheets, especially steel. This technique is also called resistance welding. The welding device consists of two electrodes that form welding pliers, one electrode is fixed, while the other is movable, most often it is a servo motor and there are pneumatic guns, an electrode “controlled” by a pneumatic cylinder, as well as hydraulic where we need large pressure forces.

In order to be able to weld two sheets by the method of spot welding, it is necessary to place the sheets next to each other, and then tighten them with a gun, the time of joining, that is. welding takes a little less than one second, and it depends on the thickness of the sheets, the force and the diameter of the electrodes. When it comes to the clamping force, it depends on the thickness of the sheets that are joined and ranges from 1kN to 6kN.

A high current of up to 15 kA is passed through the electrodes and through the sheets. Since the electrical resistance is greatest at the junction of the two sheets, the greatest heat will be developed at the point of current flow. This heat is enough to melt the metal at the joint and thus create a strong bond. As a rule, sheet metal is joined by a long series of point welds.

One of the most well-known applications of spot welding is in the automotive industry. The sheet metal parts of the body, shaped under the press, are connected to each other by spot welding, we can freely say that almost the entire body is connected to the parts that are connected by spot welding. The main application of industrial robots, back in the seventies of the last century, in the automotive industry was the application in welding applications. And, today, spot welding is one of the most important applications of industrial robots, where it is used in more than 30% of the total applications of robots in the automotive industry.

In spot welding, we distinguish two basic parts of the tool, whose characteristics essentially affect the whole process: the gun (gun) and its type, and the size and shape of the electrode. In such an application, where the gan should be as strong as possible due to the large application forces, e.g. in the welding of thick materials, the type C gun is widely used. In addition to the high resulting stiffness, this parameter leads to high tool flexibility, because the movement of the electrodes is collinear. Unlike the C-type, the so-called X-type (scissors) provides less rigidity, although the working space available is much larger than with the C-type, so this type is very common, where thin and flat materials are processed (e.g. floor or roof panels). However, it offers less flexibility in terms of tools, because the paths of the moving electrodes are not collinear, so a dome-shaped electrode tip should be used.

The electrodes used in spot welding can vary significantly depending on the application. Each type of tool has a different purpose. Radius electrodes are used for high heat applications, high-pressure shortened tip electrodes, eccentric angles for angle welding, displaced eccentric tips for reaching corners and small spaces, and finally shifting shortened ones for reaching into the workpiece itself.

Certainly the most famous welding controller for spot welding is the company Bosch Rexroth, while for the manufacturers of gans we have several companies and some of the most famous are Comau, Aro, CenterLine, Heron, Nimak.

The principle of operation of the cleaning station and electrode replacement

Cleaning station, ie. tips dress is an integral part of spot welding application. After a certain number of welded points, the robot goes to the cleaning station, after that the robot closes the electrodes and measures the thickness of the electrode and thus knows what thickness is in question. After the extreme limit of electrode wear, the robot goes to the service position where the caps are changed, ie. electrodes. Electrode replacement can be manual, which is the most common example, and there are also automatic stations that are used so as not to interrupt the operation of the line, but the robot does the electrode replacement itself. This is an expensive solution but you get on the continuous operation of the line, which results in the production of a larger number of parts.

Getting the quality of welded points and testing

As we mentioned that we have one electrode that is fixed and one moves, the principle of digestion is as follows: the fixed electrode is brought to the part itself, to be perpendicular to the part. If not, we get irregular lime, cracking and splashing (syringe) during welding, which can give poor test results. It should be mentioned that the cooling of the electrodes is done with water flowing through the electrodes, welding without water can lead to the electrodes distorting and sticking to a fixed part of the gana, which must then be completely removed, which requires additional cost and downtime. Obtaining quality is mainly obtained by moving the position of the electrode, ie. small rotations. Testing of parts is done by the method of tearing, the rule is clear, the part, material, sheet metal can burst or the point must not give way, it is also done to check the quality with ultrasound. You can see an example in the pictures below.

And finally, here is some useful information, if you are buying a used car and you suspect that it may not have been hit and previously damaged, look at the doors, wings, under the hood, on the sills, pillars, if spot welding is missing, make sure the car was hit.

More information on industrial robot programming, robot programming training, maintenance, process learning such as spot and arc welding, painting, glue and sealant application, material handling, palletizing, SafeOperation with robots from KUKA, ABB, DÜRR, MITSUBISHI and others to find HERE.

You can also contact us via the following e-mail address: [email protected] where you can get all the information for the design, simulation, programming, maintenance and installation of automated welding lines and other robot applications.

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