| Titanium alloy has outstanding application and growing market demand in key industries such as aerospace.However,manufacturing process of titanium alloy has always been a challenge.Severe tool-chip interface friction,causing intense thermo-mechanical coupling,results in not only worse machinability but also poor surface quality in cutting titanium alloy.In the thesis,from the point of reducing friction,micro-textured tools fabricated are applied to turning titanium alloy under condition of lubricating,and then machinability of cutting tool and surface integrity of the finished workpieces are analyzed.The main work includes:Firstly,Three kinds of micro-textured cutting tools were prepared by laser processing technology:the micro-channel textured tools,named MCT;the micro-hole textured tools,named MHT;the micro-grid textured tools,named MGT.Through tests of contact angle of different kinds of liquids on tool surface,it is found that contact angle of cutting fluid and cutting oil on cutting tools surface are less than 90°,however the average contact angle of water on the surface of MGT is greater than 90°.In order to learn about abrasion&wear properties of cutting tools under different conditions,a series of related tests are carried out.According to the above experiments,compared to dry friction condition,friction coefficients of micro-textured tools with oil lubrication are reduced obviously,and when texture spacing is 200μm,friction coefficients of MCT,MHT and NT is about 0.2 ultimately,while that of MGT is about 0.4.The lubrication mechanism of micro-textured tool surface under lubrication condition is analyzed.By conducting the experiments of turning TC11 with micro-textured tools about machinability under lubrication and dry cutting conditions,cutting force is measured and wear morphology of rake face in machining is observed.The results show that micro-textured tools can effectively reduce the cutting force compared with the NT under two working conditions,and after lubrication,the cutting forces of MCT,MHT,MGT,and NT are reduced by 7%,6%,6%,and 2%respectively.Contrasting with other micro-textured tools,MCT has an advantage in magnitude and degree of reduction of cutting force.When texture spacing is 300μm or 200μm,cutting force of micro-textured tools is smaller.Adhesive wear is the most important wear mechanism in cutting titanium alloy.Under the condition of lubrication,tool wear was significantly reduced compared with dry cutting,while that of micro-textured tools were smaller than that of non-textured tools.Turning TC11 is carried out under the condition of minimal quantity lubrication(MQL)and non-lubrication respectively.The finished surface integrity(surface roughness,microhardness,surface residual stress)is studied.Under the condition of MQL,better surface quality is obtained.The surface roughness values of the workpiece processed by MCT,MHT and MGT were reduced by about 17.6%,29.2%and 33.7%respectively,while the surface roughness value of the workpiece processed by NT was increased by about 12.8%.Besides,compared to dry cutting conditions,smaller surface hardness is obtained,and the shallower hardened layer about 38μm is got.The surface hardness value of workpiece processed by MCT is the smallest.For MCT or MGT,with the decrease of texture spacing,the overall trend of work hardening of workpiece weakens at start and then strengthens.In any case,all datas obtained show compressive residual stress.The axial residual stress is smaller than the radial residual stress.The order of the residual compressive stress on the machined surface is from small to large:MCT<MHT<NT<MGT.Compared with dry cutting,after applying MQL,the increase ratio of residual compressive stress on the machined workpieces of MCT,MHT,MGT and NT reached 50.9%,61.9%,33.1%and 29.6%respectively. |
PDF Full Text Request