JoiningDissimilarMetalsThe long-standing challenge faced by welding and design engineers of joining dissimilar metals has finally been met. The challenge lies in the differing physical properties and metallurgical incompatibility amongst dissimilar metals that has been found to prove difficult for a welding task. However, it is now possible to use a nanosecond welding process where most combinations of widely used metals can be joined, and achieve acceptable joint strength.

Lasers from the SPI RedEnergy pulsed range have been designed to offer greater power and control during the welding process, and can work with all of the key metals including aluminium, brass, copper, and various types of steel. A continuous wave range of lasers offering strengths of 200W to 1kW, can weld everything from thin steel to thick carbon steel and stainless steel. Regardless of the thickness, or how different the chemical and mechanical properties of two dissimilar metals are, successful welding can be achieved using fibre lasers.

The complication with dissimilar metal welding occurs when two very distinct and very different metals are welded together. It is not always as easy as simply melting the two parts together to form a bond. The problem arises in the transition zone between the two metals, where the intermetallic compounds are formed. Copper and steel are two other metals which are often welded together, but both possess very different properties and are not mutually soluble. A successful weld occurs where the new joint is as strong as the metal with the weaker tensile strength. In this way, the joint will be able to withstand any stresses that it faces.

Like traditional laser welding, dissimilar metal welding requires an understanding of the metals being used as key factors need to be considered by the metallurgist before beginning, regarding solubility of each metal, researching the intermetallic compounds that will form the transition zone, and the weldability of these compounds to ensure no negative outcomes. Additionally, consideration must be given to the coefficient of thermal expansion of the two metals, their melting rates, the possibility of corrosion and finally it is essential to consider the conditions where the weld will be in operation.

The considerations of joining dissimilar metals prior to laser welding is of great importance as joining of dissimilar metals is commonly used in high-volume industries such as the automotive and aircraft industries. Here joins need to handle incredible pressures to provide a high level of safety and security, for example, where two separate parts of an airplane fuselage are welded together, high levels of strength are required to withstand the pressures from high altitudes. The need for dissimilar metal welding is also found in power plants, chemical plants and food processing applications, joining ferritic low alloy steel with austenitic stainless steel, a metal that is commonly used in these industry. In the electronics industry the manufacturing of batteries, fine wires, fuel cells, and even medical devices use welds of dissimilar metals. Industrial applications for fittings, forgings, and tubes, commonly found in heat exchangers, liquid metal reactors, and boilers require welding of dissimilar metals.

The demands of differing industries bring with it the need to create effective manufacturing technologies such as the inclusion of nanosecond infrared fiber lasers in production as they offer high reproducibility, accuracy and productivity along with the all-important low cost in terms of capital and maintenance.

Until now the use of nanosecond (ns) pulsed lasers has been limited but recent pioneering development by SPI Lasers saw the introduction of the master oscillator power amplifier (MOPA) in ns fibre lasers. Viewed as extremely versatile tools due to their ability to control and tailor the pulse characteristics to the requirements of applications, this is achieved through the ability to change the pulse duration and frequency. Regardless of the thickness, or how different the chemical and mechanical properties of two dissimilar metals, successful welding can be achieved using ns fiber lasers.

The nanosecond welding process offers multiple options in join design that includes weld geometry flexibility, for example, joining copper on 718 super alloy, aluminium on brass, aluminium on copper, stainless steel on aluminium, stainless steel on copper, titanium on aluminium, and titanium on copper. SPI RedEnergy pulsed lasers provide an economic and effective solution to the welding of dissimilar metals. SPI products are available in Australia and New Zealand from Raymax Applications.