Fundamental Research On High Speed Milling Of Titanium Alloys With Super-hard Cutting Tools

Titanium alloys are widely used in aerospace, shipbuilding chemical, and nuclear because of theirhigh specific strength, good corrosion resistance and high thermal stability. However, titanium alloy iswell known as a difficult to machine material, because of its low thermal conductivity, small elasticmodule, and high chemical activity. Nowadays, both in home and abroad, titanium alloys aremachined with carbide cutting tools, and the cutting speed is about60m/min. So it is crucial toenhance the machining efficiency level. Compared with uncoated carbide cutting tools, thepolycrystalline diamond (PCD) cutting tools can have higher cutting speed and longer tool life. Thefundamental research on high speed milling of titanium alloys with super-hard tools has been carriedout. The major research works are included as follows:1. Parameter design of super-hard tools in high speed milling titanium alloy. According to thefeatures of titanium alloy and high speed milling experiments, a PCD tool was designed reasonablyfor high speed milling titanium alloy. Chipping of super-hard tool was effectively controlled inhigh-speed intermittent cutting. The contact stress field on cutting edge in high-speed cutting titaniumalloy with PCD tool was simulated. The effect of tool geometric parameters on the tool breakage wasanalyzed. It verified that the design tool parameters were reasonable.2. Study on chip formation mechanism in high speed milling of titanium alloy with Super-hard tool.The process of chip formation, chip shape and chip deformation were studied from both theoreticaland experimental aspects. Finite element analysis was used to simulate the process of chip formationin high-speed cutting titanium alloy with PCD tool. The effects of tool materials, cutting parametersand tool wear on macro and micro morphology of the chip were analyzed. By means of microanalysisof metallographic sample, effects of cutting parameters and tool wear on chip deformation werestudied. Variation of the saw tooth level, concentrated shear rate, shear angle and slip angle with thecutting parameters were studied comparatively with different tool materials.3. Tool life in high speed milling of titanium alloy with super-hard tool. The three-dimensionalvideo microscope, SEM and EDS were utilized to investigate the effect of cutting speed on tool wearof the titanium alloy. Tool life and tool wear morphology of PCD and carbide cutting tools werestudied comparatively in high-speed finishing milling titanium alloys. It would be helpful forrevealing the tool wear mechanism.4. Tool wear mechanism in high speed milling of titanium alloy with super-hard tool. Firstly, thefriction and wear behavior of super-hard tool sliding against TA15alloy were investigated at high sliding speeds. The test platform was established to simulate high speed cutting process. The frictiontests between cutting tool and TA15were carried out. A single point and double point thermocouplecalibration method were used to calibrate the natural thermocouple used in the experiments. The basictribological properties and friction parameters of carbide-TA15friction pair and PCD-TA15frictionpair were measured and analyzed. The friction wear mechanism was revealed deeply. The SEM andEDS were utilized to reveal the super-hard tool wear mechanism.5. Surface integrity in high speed cutting of titanium alloy with super-hard tool. By means ofthree-dimensional video microscope, micro hardness tester and surface roughness and otherequipments, effects of the milling parameters and tool wear on surface integrity are investigated. Atheoretical model and prediction model of surface roughness were established. Effects of the millingparameters and tool wear on work hardening and microstructure were studied. Finite element analysisand experimental methods were used to study the effect of cutting speed on residual stress, and theformation mechanism of residual stress was analyzed.