Electrodes in Resistance Welding

ELECTRODES

Because they work under extremely unfavorable conditions, electrodes must have both electrical and mechanical qualities. They conduct high-intensity electrical current, should not overheat excessively, and must withstand high pressures during welding without excessive wear. Additionally, they should only lose hardness after a certain period of work.

The shape and composition of the electrodes are determined according to the materials to be welded. We have electrodes made of:

Copper – Chromium

Copper - Chromium - Zirconium

Copper - Cadmium

Copper - Beryllium

All are heat-treated to achieve the necessary characteristics, namely:

a) High electrical and thermal conductivity

b) High mechanical strength

c) Low tendency to form alloys with the material to be welded

d) Absolutely reliable cooling of the electrode tips

e) High softening point, the temperature at which, over a determined period, the material loses a large part of its hardness.

 

Correct cooling of the electrodes is of great importance for the execution of welds and their useful life. Water should be brought as close as possible to the electrode tip, approximately 12 mm from the tip. Periodically, an inspection of the electrodes is necessary because they wear out during operation, and their correct shape must be maintained to ensure consistent weld quality. The electrode tips must be correctly shaped and clean.

 

1 - Types of electrodes

Straight, curved electrodes, both with flat, rounded, inclined, eccentric tips, and other shapes. They are fixed using a Morse taper or thread.

 

2 - Functions of electrodes

- Conduct welding current

- Transmit mechanical force

- Keep workpieces aligned.

 

3 - Care for electrodes

It is important that the electrodes are in good working condition, as they determine the diameter of the weld spot. Therefore, good weld quality can only be achieved when electrodes receive special care from operators.

 

4 - Electrode life

Using a 5/8" electrode, 50 times more welds can be obtained during the last 1/16" than during the first. This is because the electrode face gets closer to the end of the hole in the electrode. Cooling conditions significantly improve. This is mentioned solely to avoid replacing them precisely when they are working under optimal conditions.

 

5 - Most common electrode problems

Contact area too large: we should re-sharpen or replace it.

Electrodes with embedded sheet particles: clean or replace.

Electrodes with a depression in the center indicating end of life: we should replace it.

Change in color of the electrode contact surface: indicates inadequate adjustment, we should check the cooling path.

 

6 - Errors in electrode replacement

Asymmetrical electrodes turned, truncated, and eccentric, result in misalignment of contact areas, leading to:

Material deformation at the spot;

Poor heating;

Poor formation of the weld nugget and poor appearance;

 

Excessive play: It is necessary to eliminate it or replace the clamp with another in good condition, to avoid accidental misalignment of the electrode contact areas.

Inclined electrodes cause contact failure and present problems such as:

Oval-shaped spot.

Material overheating.

Expulsion of material from the nugget in the form of a shower of sparks.

Burned spot and low mechanical strength.

 

7 - Positioning and cleaning of parts

The parts must be placed one on top of the other in the predetermined position, when assembled without the use of fixtures. When assembled with fixtures, we must verify if they are in working condition, observing the following:

- If there is debris on the part support base

- If the clamps are holding the parts correctly

- If the guide pins show wear

- If there are loose screws.

The parts must be perpendicular to the electrodes, otherwise, they will cause excessive wear on them, resulting in deformed spots and low mechanical strength.

 

Source: BRACARENSE, Alexandre Queiroz. Processo de Soldagem por Resistência [Resistance Welding Process]. Available at http://asmtreinamentos.com.br/downloads/soldador/arquivo95.pdf. Accessed on: July 02, 2021.

 

At Sukha, we manufacture all models of electrodes, from standard to special, tailored to the client's needs.

Our electrodes are made with high wear-resistant alloys and are recommended for high production in Spot welding, Projection welding, and Seam welding.

 

Contact us; our consultants will suggest the best solution to meet your production needs.