An experimental-numerical study of active cooling in wire arc additive manufacturing

Wire arc additive manufacturing (WAAM) is a metal additive manufacturing process based on gas metal arc welding and it is known to be economically convenient for large metal parts with low complexity. The main issue WAAM is the sensibility to heat accumulation, i.e., a progressive increase in the internal energy of the workpiece due to the high heat input of the deposition process, that is responsible of excessive remelting of the lower layers and the related change in bead geometry. A promising technique to mitigate such issue is to use an air jet impinging on the deposited material to increase the rate of convective heat transfer. This paper presents an analysis of air jet impingement performances by means of a hybrid numerical-experimental approach. Different samples are manufactured using AWS ER70S-6 as filler material, using as cooling approaches free convection and air jet impingement, with different interlayer idle times. The measurement of substrate temperatures has been used to validate the process simulation, used for obtaining the temperature field of the whole part. The results indicate that air jet impingement has a significant impact on the process, limiting the progressive increase in the interlayer temperature as compared to free convection cooling. From the results arise that the optimal idle time is 30 s, as a compromise between productivity and reduction of heat accumulation, independently from the cooling strategy.