Resistance Welding

What is resistance welding?

The resistance welding process is applied when it is desired to join two or more metals. It consists of the application of electric current through electrodes, which in turn exert pressure on the materials to be welded. These materials behave like electrical resistances, in addition to the resistances of the base materials of the electrodes.


The process is called resistance welding due to the fact that heat is generated as a result of the heating caused by the resistances involved. When the electric current passes through this set of resistances, heat is obtained, according to Joule’s Law:


Q=i² x R x t


The amount of heat generated, in Joules, is expressed by “Q”. The electric current, in Ampère, is expressed by “I”. The sum of the resistances involved in the process, in Ohm, is expressed by “R” and the current passing time, in seconds, is expressed by “T”.

Resistance welding process scheme drawing

Two opposing electrodes can be observed by pressing on two metallic materials (samples). The resistances involved in the process were highlighted, so that the resistances related to the electrode and sample materials themselves are presented as R1, R2, R3 and R4 and as the contact resistances as R5, R6 and R7.

The pressure applied to the parts directly influences the contact resistances, so that when it is high the tendency is to decrease the resistance and consequently the heat generated decreases. The opposite is also true, when there is a lower pressure there is an increase in resistance and consequently the heat generated increases.

It is important to note that according to the material and geometry of the parts to be welded, the material and geometry of the electrodes to be used are defined. The correct configuration of the tooling together with the right choice of equipment and parameterization is essential to obtain a satisfactory result with the process.

Benefits :

When compared to other welding technologies, such as TIG, MIG or electric arc welding, for example, it can be said that the resistance welding process has some considerable advantages, such as:

• The energy is focused on a single point which guarantees a better (visual) finish on the point;

• Possibility to automate (with greater ease);

• Welding with precision and repeatability;

High speed, as certain welds occur in a few milliseconds;

• The welding process itself is independent of the skill of the operator.

4 types of resistance welding are known:


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Spot Welding

In this modality the weld is concentrated in a single point, and because of that it receives this name. Machines that perform this welding process can be stationary (fixed in one position) or mobile, like the Trafo Gun model that resembles a large hanging pliers.

The biggest difference in application between these models is that in the stationary ones the part will adapt to the welding process, being able to be handled by the operator, robot or fixed in a device created especially for the application. In the Trafo Gun model, the welding machine will move around the part to perform the welding at the desired points. It can also be handled by an operator or robot, as appropriate.

Figure 1: Schematic Resistance Spot Welding

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Projection Welding

In the projection weld the process occurs in the same way as in the spot weld, however there is a particularity related to the application of one or more “projections” on the surface of the part to be welded. These projections can have different formats, according to the needs of the projects, but in the vast majority they have a spherical cap shape and are made in conjunction with the component stamping process.

This technique assists in the question of parameterization of the equipment and guarantees of product quality, since all the energy is concentrated in one or more projections. This fact makes it possible to achieve excellent quality results (material penetration, pullout, etc.) using less energy compared to the spot welding process.


Figure 2: Schematic Projection welding

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Seam Welding

The Seam Welding process, in some cases referred to as continuous spot welding, is used to join materials where it is necessary to create a large sequential welding line without interruption.

The materials welded by this process have a high degree of fixation due to the large welded area.

Figure 3: Seam Resistance Welding Schematic

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Upset Welding

Upset Welding or butt welding is used to join materials that need to fuse the entire section of the material, and it is common to find this welding process for joining tubes / wires.

This weld is divided into upset welding by resistance or sparking / sparking.


Figure 4: Upset Welding Schematic

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Meet our Welding Machines:

Isotron develops manual or automated welding machines, with pneumatic manipulations, rotary tables, Cartesian positioning by servomotors or stepper motors, integration with other equipment (laser engraving, vision systems, measurement, vibrating feeders, robots, etc.).

Example of Isotron Micro Spot Welding Machine

Isotron automatic welding machine with turntable for component assembly

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Welding head detail on Isotron automatic machine

Control systems by PLC, HMI, development of supervisory software, elaboration of electrical and pneumatic diagrams, elaboration of 3D mechanical projects, development of dedicated hardware and firmware, among others. These are some of the activities carried out by the Isotron technical team.

We can perform welding samples using low / medium / high frequency technologies to identify the best solution for your application.

Welding machine for energy meters (shunt)
Welding machine for automotive connectors
Spot and projection welding machine for automotive line

Contact us!

Machines customized for your need, with ISOTRON quality, see our portfolio below:


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Special welding machines

Standard welding machines

If you are looking for a welding application in metallic materials, talk to our team and we will look for the best solution, be it automated or manual.

Nossa Localização:

R. João Vicentini, 190 - Lotm Industrial, 83504-447
Almirante Tamandaré, PR - Brazil
Phone: +55 (41) 3138-8585
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