158 Proceedings of 16th International Conference. Mechanika. 2011. Joining of Sheet Metals Using Different Welding Processes P. Kah*, R. Suoranta ** , J. Martikainen*** *Lappeenranta University of Technology, PO Box 20, 53851 Lappeenranta, Finland, E-mail: paul.kah@lut.fi ** Lappeenranta University of Technology, PO Box 20, 53851 Lappeenranta, Finland, E-mail: raimo.suoranta@lut.fi ** *Lappeenranta University of Technology, PO Box 20, 53851 Lappeenranta, Finland, E-mail: juk- ka.martikainen@lut.fi Abstract Light metals are widely used in industry and can be joined also by welding. This study investigates the most important industrial welding processes for joining sheet metals focusing on their possibilities and limitations. The two main difficulties encountered when welding sheet metals are distortion and burn-through. Each of the processes dis- cussed here features characteristics that help mitigate these problems. Beyond the welding process itself, methods commonly employed to improve the quality of thin sheet metal welding include precisely preparing joints for tight fit- up, carefully clamping the base materials, using many short and closely spaced tack welds, positioning a (suitable) (copper) backing, precise control of heat input, and welding with the highest possible uniform travel speed. The processes discussed include GMAW, GTAW, PAW, laser welding, electron beam welding, resistance spot welding and FSW. It was ascertained that the possibilities are limited by material thickness, cleanliness of the surface and welding parameters. When knowing the boundaries it is easier to choose a welding method, and it is also motivation for im- provements in welding technology. KEY WORDS: light metals, GMAW, GTAW, PAW, laser welding, electron beam welding, resistance spot welding, FSW. 1. Introduction There are numerous processes used to weld light metals. The discussion begins with an overview of the spe- cial problems associated with welding thin sheets and a short review of their typical remedies. The light metals welding processes most commonly used in industries and the suitable thin sheet joint types are shown. Welding light metal in- volves a different welding technique to ensure not to blow through the metal. Blowing through light metal allows the molten weld to transfer through the metal sheet. This increases stress on the weld and causes distortion at the point of blow-through. Using a welding technique that reduces heat at the thin metal weld joint eliminates blow-through and keeps the metal from building stress or distorting. By using an AC power source rather than a DC one, polarity is re- versed, which increases the melting rate at the wire and decreases the heat input at the workpiece. So, workpiece distor- tion is reduced. In addition, if the sheet being welded is a coated material, there is less burn-off of the coating. Other advantages are a significantly higher welding speed and better gap-bridging ability [1]. Light metals play an increasing role in many products. The purpose is to improve the quality of the products especially by the reduction of the weight of components [2]. Light metals were often joined by welding with established methods. But joining light metal with established methods has limitations and can cause difficulties. Light weight metals include aluminum, magnesium, titanium and beryllium alloys. Light alloys and light met- als are usually less toxic than heavy metals, even though beryllium is toxic. Light alloys and light metals have low density or are lightweight because, for a given unit volume, they have fewer units; this results in a lightweight material. The property of lightness contributes directly to material property en- hancement for many products since the greatest weight reduction is achieved by a decrease in density. High strength-to- weight ratios or specific strength and specific modulus are additional properties associated with light alloys and light metals. Specific strength is the yield strength (YS) or ultimate tensile strength (UTS) divided by the density of light alloys and light metals, which provides the strength per kilogram value. In addition, metallurgical engineers have uti- lized alloying and processing technologies to produce alloys with lighter weight and strength enhancements. Alumi- num-lithium alloys are examples of newer, high-performance light aluminum metal alloys. The special properties of light alloys and light metals include excellent corrosion resistance and stiffness. Tita- nium has superior corrosion resistance compared to most light alloys and light metals. The Mg-Li alloy is the lightest structural alloy available in the light alloys and light metals markets. Light alloys and light metals are useful in transportation applications where any decrease in vehicle weight can result in improvements in fuel efficiency. Light alloys and light metals are used in automotive, aircraft, aerospace ve- hicles and marine applications to provide weight savings and reduced fuel consumption. Light alloys and light metals are particularly important in the aerospace industry which has provided great stimulus to the development of light alloys during the last 50 years. The advantages of decreased density by utilizing light alloys and light metals become even more important in engineering design when parameters such as stiffness and resistance to buckling are involved; light metals and light alloys serve as better candidates in this scenario.