Prediction of weld data using process control based on surface temperature measurement for high-power energy flow processes

Abstract

The main aim of this article is to obtain the correlation between the thermal cycle and the mechanical properties in the weld seam and the heat-affected zone of mild and stainless steels. Key targeted process is welding using electron beam, laser and plasma. Since these processes are characterised by high heating and cooling rates, wide temperature range, small heat affected zones, they are difficult to control and automize. As a consequence, the quality of the product varies over a large range. Because either temperature measurement on one spot or quasi steady-state surface temperature distribution in a large area are generally unsuitable, temperature gradients need to be controlled directly on-line with a high accuracy. This requires the use of a two dimensional temperature control. An infrared camera system can be used in order to investigate the cooling process in the weld seam area as well as in the heat affected zone. On the one hand the aim of the experimentsis the estimation of the microstructure, especially of the hardness distribution using welding-time-temperature-conversiondiagrams and equations of regression. On the other hand the observation of the cooling cycle allows trends of mechanical properties like stretch limit, tensile strength, breaking elongation to be predicted. Simultaneously it is possible to recognize and to localize pores, voids and bonding defects, losses in penetration, problems with gap and height, appearing during the cooling ofthe weld.