Welding and joining processes are essential for the development of virtually every manufactured product. This article discusses the fundamentals of fusion welding processes, with an emphasis on the underlying scientific principles. It reviews the role of energy-source intensity and the width of the heat-affected zone in fusion welding processes. The article contains figures from which the properties of any heat source can be estimated readily.

During fusion welding, the thermal cycles produced by the moving heat source cause physical state changes, metallurgical phase transformation, and transient thermal stress and metal movement. This article presents an analysis of heat...