| Titanium alloys have been widely used in the aerospace industry because of their excellent mechanical and physical properties. However, due to its low thermal conductivity, low modulus of elasticity and chemically reactive, the machinability of the metal is very poor, thus they are generally referred to as difficult-to-cut alloys. High cutting temperature generated during Ti machining usually leads to more rapid tool wear and causes surface damage to the workpiece, diminishing productivity due to the slower cutting speeds. Besides, large of titanium aircraft parts are thin walls and truss structures to make them lighter and ensure high strength, this involves chunking out large volumes of metal, resulting high production cost. Therefore, the contradiction between increasing machining demand and machining performance has been one of the bottlenecks, blocking the development of aerospace industry. Tool material is one key factor to realize high speed and high performance titanium machining. In recent years, the developed industry countries are all devoted to developing advanced cutting tool materials for efficiently machining. Tool material has a big influence on the tool life, metal removal rates, surface quality and cost. Coating technology has been used widely in cutting tools, coatings with excellent properties could significantly improve the surface properties of tools, like the high temperature hardness, heat insulation property, thermal stability, impact toughness and so on, and thus the cutting speed and tool life could be improved obviously. Simultaneously, as one of an effective green manufacturing technology, Minimum Quantity Lubrication (MQL) is widely applied to Ti machining, meanwhile, the combination of MQL and novel cutting tools is also growing.According to the state art of the machining process for Ti alloy, this paper aims to evaluate the cutting performance of several novel coated tools by high speed turning of TC4 alloy under dry and MQL condition, providing some reference for Ti machining. The main content of this paper is as follows:1. Turning experiments are done by Taguchi design. Cutting force and surface roughness were researched to evaluate cutting performance of the designated coated tool under MQL condition. Mathematical model were developed to further analyze the effects of cutting parameters on the cutting force and surface roughness.2. Iso-surface was obtained based on the above mathematical model. The coupling method of response surfaces is employed in this paper to select the optimum cutting parameters subjected to several constraints. The predicted results were in agreement with the experiment, which provided theoretical foundation for problem solving in industrial production.3. Metallographic of the chip Morphology under typical cutting parameters is analyzed to investigate the evolution and the variation of the chip deformation. It can be concluded that the saw-tooth chip generated during Ti machining is mainly caused by the adiabatic shear.4. Using the parameters selected from the optimizing results, tool wear variation of the coated tools was studied individually under dry and MQL by photograph the progress of the tool wear and the wear curves. Scanning electron microscope (SEM) analysis and energy dispersive spectrum (EDS) analysis also has been conducted in order to explain the wear process that occurs on the flank of the end turning inserts during dry and MQL machining. And provide foundation for tool selection in production line.
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