Influence of a pulsed laser regime on surface finish induced by thedirect metal deposition process on a Ti64 alloy

Abstract

tThe direct metal deposition (DMD) laser technique is a free-form metal deposition process, which allowsgenerating a prototype or small series of near net-shape structures. Despite numerous advantages, oneof the most critical issues of the technique is that produced pieces have a deleterious surface finish whichrequires post machining steps. Following recent investigations where the use of laser pulses instead of acontinuous regime was successful to obtain smoother DMD structures, this paper relates investigationson the influence of a pulsed laser regime on the surface finish induced by DMD on a widely used titaniumalloy (Ti64). Findings confirm that using high mean powers improves surface finish but also indicate aspecific effect of the laser operating mode: using a quasi-continuous pulsed mode instead of fully-cw laserheating is an efficient way for surface finish improvement. For similar average powers, the use of a pulsedmode with large duty cycles is clearly shown to provide smoothening effects. The formation of larger andstable melt pools having less pronounced lateral curvatures, and the reduction of thermal gradients andMarangoni flow in the external side of the fusion zone were assumed to be the main reasons for surfacefinish improvement. Additional results indicate that combining the benefits from a pulsed regime and auniform laser irradiation does not provide further reduction of surface roughness.