Introducing Aluminium Spot Welder

Posted on May 8, 2021

An aluminium spot welder is the specific resistance spot welding machine that is used for fusing the aluminium sheets or plates, which are generally challenging materials for spot welding.

What Is an Aluminium Spot Welder?

An aluminium spot welder is the specific resistance spot welding machine that is used for fusing the aluminium sheets or plates, which are generally challenging materials for spot welding. Also known as ERW machine, spot welder utilizes the efficient electro-thermo process, joining two or more metal sheets, which are made from various heavy gauge materials, plastic or general metals, together through high heat and the predetermined amount of force.

During the operations in an aluminium spot welder, as the stable currents are transferred to the weld joint, the interface of the aluminium sheets will be melted because of the high heat from the resistance, and the sheets will be permanently joined by the additional force.

With the development of robotic technology and other automated techniques, aluminium spot welders can provide efficient and reliable high-speed welding which uses a high density of electric current, making the welding equipment an invaluable investment for a wide range of assembly lines and production applications. Aluminium spot welder is an ideal solution for aluminium and other metal sheets fabrication, especially high volume productions, in electronics, metalworking, automotive, aerospace and even the medical industry.

What to Consider During Aluminium Spot Welding?

For resistance spot welding machines including aluminium spot welder, the weld current and the weld time are two important factors that significantly affect the quality of the final products and also the efficiency of raising the material temperature to the weld temperature (about 1400°C).

In general, the weld current used in the spot welders ranges from 3000 to 5000 A. As for the weld time, it is an extremely short period that permits the spot welding machine to join the metal sheets together, which is about 10 milliseconds. Proper weld time can prevent excessive heats from affecting unwanted areas on the sheet surfaces. Both the weld time and the current can be predetermined and controlled by the operators depending on the applications.

:: Read more: Aluminium Spot Welder: A How-To Guide

Aluminium Alloys Spot Welding

In general, harder metals are easier to be welded while pure aluminium is a more challenging welding material. Unlike steel materials like stainless steel sheets, aluminium and aluminium alloys are less suitable for spot welding since they have higher thermal and electrical conductivity. This means that the aluminium spot welder requires much greater weld currents since the welding machine relies on resistance heating. Moreover, the aluminium oxide that naturally generates on the surfaces of aluminium alloy sheets has a great level of electrical resistance. This critically affects the heat generation and the weldability of the materials.

In an aluminium spot welder, short weld times are required to generate the high heat fast, as a result, minimizing the heat lost by conduction. Compared to the steel materials that have the similar thickness, the aluminium spot welds typically have one third the value of the static and fatigue shear strengths.

Weld splash can lead to poor weld quality and should be prevented in aluminium spot welders. Especially during sensitive alloy welding, nugget porosity or cracking happens sometimes. Dual force operations are required when high-quality aluminium welds and ideal control of nugget flaws are needed.

Power Supply and Electrodes Conditions

In an aluminium spot welder, although AC power supply can be utilized, inverter DC power supply is more recommended to be used for welding aluminium alloy sheets, offering excellent control of the short time welding pulse and improving the weldability. The positive electrodes generally wear faster than the negative ones. With the DC power supply, there will be a significant polarity effect, and it ensures efficient welds when a higher weld current is needed.

General spot welding machines use electrodes made of copper alloys to convey the electric currents and heat to the weld spot, joining the metal sheets. This is because copper has excellent heat conductivity but low electrical resistance, the generated heat tends to work on the weld spot rather than electrodes themselves. The copper electrodes for sheet materials having a thickness of 1 to 3 mm have a dome face with a radius ranging from 5 to 10 cm, which increases depending on the sheet thickness. 

In aluminium spot welders, a great density of current and heat can be focused on a small weld spot through the high-conductive electrodes. However, due to the high currents and the great contact heats, and the nature that copper can easily form an alloy with aluminium, the copper electrodes wear fast in the aluminium spot welder. 

Some special surface treatments for the copper electrodes can reduce the wear and lengthen the tool life, or the electrodes should be critically checked after making hundreds of welds. Another strategy to maintain the electrode condition is to utilize the automated electrode dressing systems, regulating the electrode conditions in an aluminium spot welder and improving the weld quality. In some demanding applications like aerospace quality aluminium welds, the copper electrodes need to be dressed very frequently, keeping from any contamination to the faces. The treatment prevents visible alloy layers from the form on the electrodes and provides the aluminium spot welder ideal reproducibility and consistency of high weld quality, as well as longer equipment life.

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