Due to the favorable combined properties of lightweight, high-strength and corrosion resistance, Ti-6Al-4V alloy is widely used in aviation and medical industries. Surface integrity of components, made from Ti-6Al-4V alloy, is important to such industrial applications. Machining is a major manufacturing operation commonly used for producing such components. In machining, the subsurface material is subjected to plastic deformation which is mainly caused by the combined effect of ploughing and material removal, and this will significantly affect the mechanical behavior and the functional performance of components and the machining performance including accuracy. Cooling and lubrication conditions affect the thermo-mechanical deformation during the cutting process. In this work, orthogonal cutting experiments with various uncut chip thicknesses (10 - 60 μm) were performed under a range of &nbsp;sustainable (dry, MQL, cryogenic and hybrid: MQL and cryogenic) cooling strategies to study the combined ploughing and cutting process for Ti-6Al-4V alloy.In this work, orthogonal cutting experiments of Ti-6Al-4V alloy were carried out on a HAAS TL-2 CNC lathe using carbide tool inserts with edge radius about 50 μm under a range of cooling/lubricating conditions. The principal and thrust force components were measured for a range of cutting conditions. With the increasing uncut chip thickness, from 20 μm to 60μm, the principal force components increased approximately linearly from 200 N to 480 N. However, the thrust force increased slightly from 400 N to 500 N. That is, for most conditions, the thrust force was higher than the principal forces due to the material flow ahead of cutting edge imposed by the finish machining conditions. For most conditions, the forces mesured during machining with MQL conditions were less than other cooling/lubrications, and the forces at cryogenic and hybrid conditions were slightly higher than other conditions. For the minimum uncut chip thickness (10 μm), the forces at the dry, MQL and hybrid conditions generated some fluctuation due to the unstable cutting process, which means that the materials accumulated ahead of cutting edge periodically due to the combined effects of sliding, ploughing and cutting. Note that, the principal and thrust forces at cryogenic conditions exhibited stable values during the whole cutting process, indicating a stable cutting process due to the cryogenic cooling effect. The surface roughness was measured by using a ZYGOTM (type: 7300) scanning white light interferometer. The measured surface roughness values were close to each other, however, maximum value appeared at the uncut chip thickness of 50 μm which was correlated with the periodically-fluctuating plastic deformation ahead of cutting edge.For most conditions, a refined grain layer with thickness of about 3-5 μm was produced at the top machined surface at uncut chip thickness of 10 μm, due to severe plastic deformation caused by edge radius. The thickness of the grain refinement layer with uncut chip thickness of 10 μm was thicker than those produced with larger uncut chip thickness. That is, more material was ploughed to machined surface at uncut chip thickness of 10μm than those at larger uncut chip thickness conditions. Additionally, the micro-hardness beneath the machined surface was measured by a SUN-TECTM Micro-Combi Tester with a Vickers indenter at 100 mN loading force and a 10 s dwell time. The measured micro-hardness of machined surface at the reduced uncut chip thickness (10 μm) at different cooling/lubrication conditions was about 380-395 HV, while, the surface hardness with uncut chip thickness of 50μm was approximately 350-360 HV. The increase of the surface hardness at the small uncut chip thickness was mainly caused by the grain refinement related to the sever plastic deformation due to the ploughing effect. Overall, the effect of uncut chip thickness and sustainable cooling strategies on surface integrity in orthogonal machining of Ti-6Al-4V alloy were discussed in this work.

The Influence of Sustainable Cooling Strategies and Uncut Chip Thickness on Surface Integrity in Finish Machining of Ti-6Al-4v Alloy

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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