O Que É Soldagem Por Resistência?

What Is Resistance Welding?

  1. DEFINITION

In resistance welding, the parts to be welded are pressed against each other by means of consumable electrodes. A high current is passed through these electrodes, which, according to Joule's Law (Q = K R I2 t ), generates an amount of heat proportional to time, electrical resistance, and current intensity. This heat must be sufficient to allow the contact region between the parts to be welded to reach their melting point.

Almost all types of steel can be welded, such as light metals, steel, zinc, copper, and bronze. Metals of different natures can only be welded together if they are susceptible to forming an alloy or if an intermediate material is introduced between them that can bond to the base metals.

 

  1. WELDING PRINCIPLES

In order to weld a part with this process, it is necessary to verify 3 important factors: Heating, time, and pressure, and maintain a balance between them.

– Heating: This is the temperature to which the sheets to be welded must be subjected. This temperature must reach 1300ºC in the weld nugget to obtain adequate fusion, and it must not exceed 900ºC on the surface directly in contact with the electrode. Otherwise, the granular structure of the metal will be weakened. To reach this temperature, there must be high resistance at the contact surface between the sheets to be welded.

– Time: This is the time required for the current to flow and make the weld. Although the time during which the current flows affects the heat generated, we basically use time to develop the required weld nugget in order to obtain the necessary mechanical strength for the welded assembly. The longer the current flows, the larger the weld nugget will be, up to the limit of the diameter of the electrode used. The size of the weld nugget decreases rapidly as the weld time decreases.

– Pressure: This is the compression suffered by the sheets through the electrodes, and it is of vital importance in controlling the quality of the weld, because it affects the resistance at the contact face between the materials and, consequently, the heat generated.

 

  1. TYPES OF RESISTANCE WELDING SYSTEMS

Resistance welding represents another modality of pressure welding, in which the parts to be welded are joined together in a pasty state (or partially melted) under pressure, and without additional filler material.

Such systems are:

- Spot welding

  • In spot welding, the current passes directly through a single weld nugget being formed. There is no other path that allows deviation or creation of stray current. To make a good weld, it is necessary for the parts to make good metal-to-metal contact. All elements (parts and electrodes) must be designed in such a way that the welding current can reach the desired point by the shortest path.

 

- Projection welding

  • Projection welding is a variation of resistance welding, in which the current flow is concentrated at the contact points. These projections are used to concentrate the generation at the point of contact. This process is characterized by the use of low currents, low forces, and short weld times. It is often used in the most difficult resistance welding applications because a number of welds can be made at the same time, allowing for high production speeds.

 

- Seam welding

  • Seam welding is the process in which the heat generated by the resistance of the electrical current flow in the metal is combined with pressure to produce the welded seam. The seam consists of a series of spot welds.

Two rotating circular electrodes are used to provide current, force, and cooling to perform the weld.

 

- Butt welding

  • In butt welding, the two contact surfaces must have the same area, to make possible, across the entire section, the same current density and the same heating. In this type of welding, a distinction is made between two types of execution: butt resistance welding and flash butt welding.

 

  1. ADVANTAGES OF RESISTANCE WELDING

               - Equipment utilization.

- Higher electrical conductivity flow.

- Longer life, good resistance to work at high temperatures and pressure.

- Does not deform the material, obtaining higher yield.

- Greater material savings.

- Greater resistance to rupture.

- Cheaper maintenance.

Welded joints made by the resistance welding process offer greater resistance to mechanical vibrations. As an example, we can mention the assembly of a car body, where, if we used fastening elements, these would need to be retightened periodically. When resistance welding is performed correctly, there is no need for final finishing on the welded joint, as this process does not produce slag or spatter.

 

Source: BRACARENSE, Alexandre Queiroz. Resistance Welding Process. Available at http://asmtreinamentos.com.br/downloads/soldador/arquivo95.pdf. Accessed on: May 10, 2021.

 

At Sukha, we manufacture all models of resistance welding machines, from standard systems (butt, spot, projection, seam, and pliers) to robotic cells.

Contact us, our consultants will recommend the best solution to meet your production needs.

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