Study On Machining Surface Integrity Of Typical Titanium Alloys

Titanium alloys have excellent material and mechanical properties.Their high corrosion resistance,high specific strength and low density are especially suitable for aerospace manufacturing.They are an important metal resource.At the same time,titanium alloys have become typical hard-to-machine materials due to their low elastic modulus,high cutting force and high cutting heat.At present,in the traditional production process,the shape accuracy of parts is the main detection index,and little attention is paid to the material structure and mechanical properties of the material surface and below the surface layer.As an effective concept to evaluate machined surface quality,surface integrity plays an important role in processing technology and fatigue life.With the increase of the amount of titanium alloy used in the manufacturing process,the study of surface integrity can be used to evaluate the manufacturing effect of typical titanium alloy processing technology more comprehensively.In this paper,a systematic evaluation method of surface integrity is established and two typical titanium alloys TA11 and TC4 are used as test objects.The main work and related research results are as follows:Establish surface integrity evaluation method,unified detection process and scheme.According to the processing characteristics,the surface morphology,material mechanical properties and material structure changes of the machined surface were evaluated comprehensively.Five parameters,including surface micromorphology,surface roughness,surface microstructure,surface micro-hardness and surface residual stress,were selected as the evaluation indicators for the surface integrity of typical titanium alloys.The wet shot peening test of TA11 titanium alloy was carried out to study the effect of shot peening parameters on the surface integrity.The results show that the surface quality decreases with the increase of shot peening strength and time,the density of craters increases,and micro-cracks and grain spalling occur at local locations,which leads to the increase of surface roughness.Shot peening intensifies grain crushing and refines grain.Increasing shot peening strength and time will increase grain refinement,increase surface microhardness and work-hardening depth,as well as residual compressive stress on workpiece surface.In addition,too long shot peening time will lead to the decrease of surface hardness,the softening of surface structure and the weakening of shot peening strengthening.The milling experiment of TC4 titanium alloy was designed to study the influence of milling parameters on the surface integrity of TC4 titanium alloy.In this paper,milling methods,milling speed,feed per tooth,milling depth and milling width are studied,and the mechanism of milling process parameters on surface integrity is analyzed from the point of view of material thermo-mechanical coupling effect and cutting state.Based on the study of surface integrity in single processing mode,two typical processing routes in aviation manufacturing process are studied: TA11 titanium alloy vibration polishing-shot peening-secondary vibration polishing,TC4 titanium alloy milling-grinding-shot peening.The influence of processing mode on surface integrity was studied and the machined surface quality was evaluated through the change rule of surface integrity in continuous process.