Tool design methodologies in hybrid strategies of lubrication and its influence on surface integrity of Ti-6Al-4V milling

Thèse présentée par Anshab KUMMAMKANDATH ABDUL LATHEEF à Polytech Tours au Département Mécanique à 14h00

Summary : The improved machinability of the Ti-6Al-4V alloy under cryogenic machining has already been well written in the literature. In this contest, the additional presence of MQL (minimum quantity lubrication) with cryogenic would be a key solution for higher productivity as well as improved surface integrity of the workpiece in Ti-6Al-4V machining. The main goal of this thesis is to investigate the machinability of the hybrid cryo-MQL (cooling-lubrication) in milling of Ti-6Al-4V for both CO2-MQL and LN2-MQL hybrid strategies.First, a comprehensive literature review has been conducted to introduce on overview of the different MWFs in sustainable point of view including all available hybrid cryo-MQL test methodologies, machinability results. Thereafter, the major technological gap in area of both cryogenic stands alone and hybrid cryo-MQL strategies have been identified to frame the main objectives of the current work.The second chapter sets out to investigate the optimal intermittent turning process and workpiece design to perform the LN2-MQL hybrid machining studies with transposable results to the reference milling; over observed unmatured application system in milling. The LN2 flow physics has been studied for different LN2 outlet nozzles; in terms of flow visualization, thermal map tracing and analysis of Leidenfrost effects for machining applications. Cooling curves of preheated carbide samples at LN2 jet are investigated both experimentally and numerically for understanding the Leidenfrost effect in machining. The LN2 rake face flow has also been optimised in terms of lower cutting temperature, cutting force and lower cold strength hardening of the workpiece while intermittent turning of Ti-6Al-4V. The third chapter offers the machinability of hybrid scCO2+MQL strategy and technical feasibility of the modified cutter in Ti-6Al-4V milling; with the comparison of scCO2, liquid CO2, MQL and emulsion strategies. Modified CoroMill600 cutter (TRL7) is used for all the MWF conditions and the cutter has modified by internal channels to rake and flank faces of MWFs. The channel outlet diameters to rake and flank faces are selected based on the reference studies and trial tests. The last chapter (fourth) discuss about the hybrid machining of LN2-MQL by intermittent turning process which transposable results to reference milling. Technical feasibility of the different rake and flank combination of the LN2 and MQL has been investigated in terms of machinability of the Ti-6Al-4V. The optimum flow of LN2 to rake, special MQL oil for titanium machining and optimum MQL flow are selected for the studies.All of this works brings a better understanding of the technical feasibility and machinability of hybrid cryo-MQL machining in Ti-6Al-4V alloy and provides the design solutions to cutting tool for hybrid cryo-MQL as well as cryogenic MWF condition; with optimum and technical precise application.

Keywords: Hybrid cryo-MQL, scCO2, CO2, LN2, MQL, milling tool, intermittent turning, flow characterization; Leidenfrost, machinability, Ti-6Al-4V, surface integrity..