The Performance Analysis Of Serial-parallel Machine Tool For Blade Grinding And Polishing

Blades are widely used in propulsion systems, such as steam turbines, aircraft engines.As the key components, their quality will affect the performance of systems directly. To meetthe fluid dynamics requirements, blades are always designed as complex space free surfaces,which are swept and twisted by several blade sections. Blades always work in harshconditions with high pressure, high temperature and complex stress, so the design of bladesshould not only meet the fluid dynamics, but also consider stiffness, strength, fatigue strength,life expectancy and etc. The design of blade is to balance each design parameter, which is acomplicated and repeated process. As the widely use of computer aided software, such asCAD and CAE, the design of blade surface is gradually mature and perfect. Good bladesurface can make the systems perform best and keep the system function smoothly with lownoise and long life. The manufacturing of blade should satisfy shape precision and surfacequality. Any tidy flaws can lead vibration, noise, short life expectancy. And more seriously,the system would be destroyed. The process of blade manufacturing is casting or forging–rough milling–finish milling–finish polishing. In traditional manufacturing process, finishpolishing is to get high surface quality and done by hand. Workers can feel the texture orflaws and adjust the polishing position and gesture, through which can get stable polishingforce and even polishing quantity. However, manual polishing will produce dust and noisewhich are harmful to workers’ health. The quality of blade surface depends on workers’technical level and experience, so the polishing efficiency is low and the expense is high.Moreover, automated process is limited because of scattering working process.To realize automated process of blade manufacturing and liberate workers from badworking environment, our lab developed parallel-serial machine for blade grinding andpolishing. This machine adopted the frame of serial-parallel, which take advantage of bothserial machine and parallel machine. Serial-parallel machine can extract workers’ polishingtechnology, that is simulating workers’ wrist to adjust the gesture between workpieces andmachining tool, which can realize polishing even with constant force. This machine can move along axis X, Y, Z, A and B. The movement along X, Y and Z can adjust the position betweenworkpieces and machining tool, and the movement along A and B can adjust the gesturebetween workpieces and machining tool.Under the support of National Natural Science Foundation, This paper has complete thedesign of the serial-parallel machine tool for blade grinding and polishing, the manufacture ofcomponents and assembling of machine tool. And now, we are commissioned machine tool,connecting the control system and the error measurement of key components is on theschedule.According to the characteristics of blade, analyze the freedoms requirements of blademanufacturing to ensure the movement of machine. Overall considering the advantages ofserial machine and parallel machine to determine the configuration of machine. Further,introduce the structure and principles of key components, such as3-RPS parallel mechanism,machining tool, in-situ measurement system and control system.Use the FEA software to conduct statics analysis, modal analysis and harmonic responseanalysis. From the statics analysis result, the stress and deformation of machine can be got.The modal analysis can get the first ten natural frequencies of machine, which will be helpfulto select reasonable machining speed to avoid resonance. harmonic response analysis acquiresthe response under harmonic force.Construct the comprehensive analysis model of serial-parallel machine for bladegrinding and polishing based on multi-body system theory. This model consider thecombination of positioning error, straightness error, angle error of each axis andperpendicularity error, parallelism error between axes. The correctness and effectiveness ofthis model are tested by MATLAB and this model will support the error compensation withtheory base.Use Renishaw double frequency laser interferometer to measure positioning error,straightness error, pitch error and yaw error of X axis and Y axis. With the large amount ofmeasured data, the distribution trend of each error can be got. Take the measured error intothe error model, move X and Y axis to complete circular interpolation motion on XOY plane,and analyze the distribution of comprehensive error in spatial space. The conclusion can begot that positioning errors and straightness errors are the main errors that effect thecomprehensive error, and the effect of positioning errors is most significant.