An investigation of different welding manufacturing procedures to minimize distortion

Abstract

In the ship construction industry, the use of welding is of great importance. In fact, 40% of the manufacturing process of a ship consists of joining metal sheets together with the use of welding. The trend in modern ship construction is to introduce as much thin metal sheets as possible. This approach gives a more efficient and lighter design of the vessel. Unfortunately, with the use of thinner metal sheets, distortion is increased. This distortion effect will have a detrimental impact on the manufacturing process and the design of the vessel. The main aim of the dissertation was to carry out an investigation on different welding manufacturing procedures to reduce distortion during welding of S355 metal sheets. The metal sheets are considered thin metal sheets at 6 mm thickness. The focus of the study was on transient thermal tensioning and the use of heat sinks in conjunction with clamping. Laboratory studies and Finite Element Analysis of the different welding procedures were carried out and validated. The experimental validations were carried out using an automatic MIG welding rig at the University of Malta. Thermocouples were used to determine the thermal gradients during the welding process. This was further used to validate the Finite Element Analysis models. The models of finite element analysis result concurred very closely to the ones of the experimental validation. Moreover, these different welding manufacturing procedures resulted in a reduction of the final distortion both in the angular distortion and in the longitudinal distortion. From these results, the ship industry can implement these procedures confidently to reduce their manufacturing process times by reducing post welding treatments of the welded metal sheets.