Effects of Laser Process Parameters on the Overlapped Multipass Laser Transformation Hardened Bead Geometry of Ti-6Al-4V Alloy Using a Continuous Wave (CW) Spherical Nd:YAG Laser Beam
D.S. Badkar and G. Buvanashekaran
An experimental investigation with a 2 kW Nd:YAG laser emitting a continuous wave (CW) spherical beam of 1.06 μm wavelength was used to study the effects of laser hardening process parameters on the overlapped multipass laser transformation hardening of Ti-6Al-4V. This study investigates the effects of two sets of laser processing parameters. Set 1. Low Laser Processing Parameters (LLPP): laser power of 600 W; scanning speed of 2000 mm/min; focused position of -10.00 mm. Set 2. High Laser Process Parameters (HLPP): laser power of 800 W; scanning speed of 3000 mm/min; focused position of -10.00 mm. On overlapped multi track laser transformation hardened bead geometry responses: hardened bead width, hardened depth, centre to centre pitch, overlapped region depth, angle of hardened bead profile, power density and overlapping ratio. The main reason for this is the role of scanning speed. The scanning speed has the most influent on hardened bead width, and hardened depth. As scanning speed decreases, hardened bead width and hardened depth increases thereby allowing more laser-material interaction time, which in turn increases centre to centre pitch, overlapped region depth, and angle of hardened bead profile naturally; therefore, low laser process parameter for CW spherical beam has ensured higher values of experimental measured responses of hardened- bead profile. The results demonstrated that in all the cases the overlapping ratio is found to be approximately equal to overlapping ratio 0 and hence overlapped laser surface transformation hardening of Ti-6Al-4V alloy, ensured a wide and uniform hardened zone of a multi-track.
Keywords: Nd:YAG laser, Ti-6Al-4V alloy, spherical beam, continuous wave (CW), laser transformation hardening, overlapped, multipass, bead geometry, processing parameters