Maritime Engineering and Technology – Guedes Soares et al. © 2012Taylor & Francis Group, London, ISBN 978-0-415-62146-5 Numerical investigations to study the effect of weld parameters on the temperature-time history in steel plates B.Q. Chen, M. Adak & C. Guedes Soares Centre for Marine Technology and Engineering (CENTEC), Instituto Superior Técnico, Technical University of Lisbon, Portugal ABSTRACT: Numerical investigations are carried out to study the effect of weld parameters on the temperature- time history in a butt-joint weld steel plate. A mathematical model of transient thermal process in welding is established to simulate the transient thermal analysis with moving heat source model (Gaussian function) by using finite element method. Results are compared to numerical and experimental results obtained from a previous study. Parametric studies based on numerical results are carried out for different weld parameters including welding speed, plate thickness, heat input, heat source type and finite element mesh. 1 INTRODUCTION 1.1 Introduction to welding Welding is a complex industrial process that often requires several trials before it can be done right. The welding processes are carried out by skilled work- ers, but in the past few years automated machines and robots are introduced in shipyards. To obtain the expected productivity through mechanization, high precision of parts to be assembled must be kept. Therefore in the shipbuilding industry dimensional predictability is important. In order to produce a high- quality product, the accuracy control should be kept through the whole assembly line. The concept of accu- racy control should be incorporated in the structural design, so that the designer can produce a better design accounting for the geometric inaccuracy. Generally, welding can be defined as any process in which two or more pieces of metal are joined together by the application of heat, pressure, or a combination of both. Most of the processes may be grouped into two main categories. pressure welding, in which the weld is achieved by pressure; and heat welding, in which the weld is achieved by heat. Heat welding is the most common welding used today. During the welding process, a liquid weld pool is created through the interaction of an intense heat source and the substrates being joined (see Figure 1). Melting on the front side of the weld pool eliminates the interface between the materials, while solidifi- cation on the back side of the weld pool fuses the substrates together to create a solid joined part. Sur- rounding the fusion zone is a heat-affected zone, where the substrate is heated to temperatures up to the melt- ing point of the metal being joined. Solidification in the fusion zone and solid-state phase transformations in the heat-affected zone are responsible for dramatic Figure 1. Illustration of a fusion weld. changes in the microstructure and properties of the welding joint. 1.2 Arc welding Arc welding, which is heat-type welding, is one of the most important manufacturing operations for the joining of structural elements for a wide range of applications, including guide way for ships, bridges, trains, building structures, automobiles, and nuclear reactors, to name a few. It requires a continuous supply of either direct or alternating electric current, which creates an electric arc to generate enough heat to melt the metal and form a weld. The arc welding process is a remarkably com- plex operation involving extremely high temperatures, which produce severe distortions and high levels of residual stresses. These extreme phenomena tend to reduce the strength of a structure, which becomes vulnerable to fracture, buckling, corrosion and other type of failures. The most widely used arc welding processes are shielded metal arc welding (SMAW), 285