Tool Wear and Surface Integrity Analysis of Machined Heat Treated Selective Laser Melted Ti-6Al-4V

Tool Wear and Surface Integrity Analysis of Machined Heat Treated Selective Laser Melted Ti-6Al-4V

Manikandakumar Shunmugavel (Deakin University, Waurnponds, Australia), Ashwin Polishetty (Deakin University, Waurnponds, Australia), Moshe Goldberg (Deakin University, Waurnponds, Australia), Rajkumar Prasad Singh (Kalyani Center for Technology and Innovation, Bharat Forge, Pune, India) and Guy Littlefair (Deakin University, Waurnponds, Australia)
DOI: 10.4018/IJMFMP.2016070103
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Abstract

In this study, the tool wear and surface integrity during machining of wrought and Selective Laser Melted (SLM) titanium alloy (after heat treatment) are studied. Face turning trails were carried out on both the materials at different cutting speeds of 60,120 and 180 m/min. Cutting tools and machined specimens collected are characterized using scanning electron microscope, surface profiler and optical microscope to study the tool wear, machined surface quality and machining induced microstructural alterations. It was found that high cutting speeds lead to rapid tool wear during machining of SLM Ti-6Al-4V materials. Rapid tool wear observed at high cutting speeds in machining SLM Ti-6Al-4V resulted in damaging the surface integrity by 1) Deposition of chip/work material on the machined surface giving rise to higher surface roughness and 2) Increasing the depth of plastic deformation on the machined sub surface.
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2. Experimental Procedure

Hollow cylindrical samples of wrought and additive manufactured Ti-6Al-4V were used as work materials in this research. A hollow cylindrical specimen of height 60 mm, outer diameter 50 mm and inner diameter 25 mm was fabricated using a SLM 125 metal additive manufacturing machine (as shown in Figure 1). Important process parameters such as meander build style, 0.2 mm laser focus diameter and 425 mm/s laser scan speed were used in fabricating this hollow cylinder. The sample was then heat treated in a vacuum furnace to 730oC and cooled slowly to 1) relieve the residual stresses and 2) soften and improve the materials ductility. Face turning machining operation was then performed on the material in a Nakumara tome CNC machine. TiAlN+TiN PVD coated rhombic carbide tools with positive rake angle and a tool nose radius of 0.8 mm was used for the machining tests. The designation of the cutting tool used is DNMG 150608-TF.The material was machined at different cutting speeds of 60,120 and 180 m/min using a constant feed rate of 0.1 mm/rev and depth of cut of 0.5 mm respectively. The tool specimens and the machined surface were collected and preserved after specific number of machining passes to study the tool wear and surface integrity. The tool wear and surface characteristics was measured and characterized using optical and scanning electron microscope. The surface roughness was measured using Alicona Infinite Focus 3D optical surface profilometer.

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