Modeling And Process Research Of Micro Cutting Technology

Micro cutting technology refers to mechanical micromachining miniaturized components with 3D features ranging from 0.1μm to 1mm using cutting tool. Alough micro cutting is similar to conventional cutting it’s not a simple scaling of macro cutting. It’s fundamentally different from conventional cutting in many aspects, such as size effect and the minimum chip thickness. Thus experience of macro machining can not be directly used in micro cutting.In order to promote machining quality of micro cutting, this article focused on micro-milling and micro-drilling research which including material remove theory, chip formation, minimum chip thickness, cutting force, surface morphology, developing and optimization of machining process. The main research efforts are performed:(1) Development of micro three-axis CNC machineIn order to fulfill the needs of research work, a three-axis CNC machine was established and tested. The maximum spindle speed of this machine is 120000r/min and the run out less than 1μm. The X, Y, Z axis has a resolution of 10 nm and designed repeat precision of 100 nm. The maximum travel distance of X, Y, Z axis is 110 mm, 110 mm and 60 mm. Tests are done on traveling accurancy, dynamic characteristics and spindle run out. Results of testing indicate that this machine has a repeatability of 100nm~500nm in ordinary environment and its dynamic response time less than 50 ms, which meets the requirements of design.(2) Analysis of chip formation and minimum chip thicknessThe minimum chip thickness, which emerging because of size effects, is a key characteristic of micro cutting. Based on the analysis of chip formation and its influence factors during micro cutting, a calculating model of minimum chip thickness was developed through analysis of the cutting force when cutting around minimum chip thichness.To improve the model performance in describing cutting velocity and temperature influence the Bridgeman effect coefficient was introduced to the original model. Theory calculation(0.22 er ~0.38er) by using this method shows a good agreement with experimental results(0.19 er ~0.33er). Meanwhile, the specific cutting trajectory during micro-milling and micro-drilling were studied and the differences between micro cutting and conventional cutting were compared.(3) Modeling of instantaneous uncut chip thickness and cutting forceA mathematical model of calculating instantaneous uncut chip thickeness was established with consideration of cutting tool’s run out based on the cutting trajectory analysis during micro-milling. The calculation precision is as good as numerical method, such as New-Raphson method. Then a 3 dimensional cutting force prediction model was developed based on the analysis of cutting area which related to chip thickness, working edge of cutter and phenomenon of multi-fluents engaged in milling. A new method of calculating force coefficients was given in frequency domain. Also surface morphology of side wall after slot milling was discussed and surface quality was measured to verify the discussion.(4) Micro-drilling and ultrasonic vibration assisted drilling processIn order to solve the machining difficulties of micro holes in micro aeronautic components, ordinary micro-drilling process was analyzed and ultrasonic vibration assisted drilling was introduced. Ultrasonic vibration assisted drilling can greatly promote drilling quality and production rate. The ultrasonic assisted drilling was theoretical analized from drilling trajectory, chip thickness, cutting speed and cutting force to guide the chooseing of pramaters. Then an ultrasonic assisted drilling device was designed and drilling experiments on comparing ultrasonic assisted drilling process with other drilling process and producing thin wall between micro holes both on flat and round surface were executed. Experiment results shows ultrasonic assisted drilling reduced axial force by 16% and radial force by 30%~79% compared to ordinary drilling process. Meanwhile the drill sliding, hole entrance roundness and burr are also improved greatly. Hence ultrasonic assisted drilling is an effective process to machine aeronautic components.