MODELING OF THE WELD PRIMARY MACROSTRUCTURE FORMATION AT LASER WELDING

Abstract

In modern shipbuilding, those enterprises and shipyards that introduce innovative and highly efficient technologies gain an advantage in the competitive struggle. The experience of the largest European shipyards, such as Meyer Werft and Blohm und Voss in Germany, Kvaerner Massa Yard in Finland, Fincantieri in Italy, shows the great potential of laser equipment in creating breakthrough technologies in shipbuilding. The leading role among the developed technologies is played by the technologies of laser and laser-arc welding. Compared to arc welding, laser and laser-arc welding increase the welding speed by 2-3 times, and a decrease in butt gaps leads to a decrease in the need for welding consumables. The approaches to creating a model for predicting the metal structure and mechanical properties of a welded joint in laser welding are discussed in the paper. This will make it possible to establish welding modes at the preproduction stage and obtain the properties of welded joints specified by the designer. This model is based on mathematical calculations of the thermal regime of welding and the process of crystallization of welds. A mathematical model of laser welding is used, taking into account the presence of a vapor-gas channel, which allows laser radiation to penetrate the entire thickness of the weld, which ensures the formation of a deep, narrow weld. The results of the calculation make it possible to determine the shape of the penetration pool and the position of the main temperature lines in the heat-affected zone. For beam welding methods, it is proposed to approximate the surface of the melt pool (crystallization front) by a cubic spline. Its main advantage is that the entire shape of the surface is modeled most accurately and completely, which allows you to build the surfaces of all areas of the bath without excluding any parts. On the basis of such a spline, the predominant direction of crystallite growth, their growth rate in the direction of welding are determined, and the integral characteristics of the emerging primary macrostructure of the weld metal are found. Based on the criteria characterizing the process of crystallization, a prediction of the macrostructure of the weld metal is given.