Key Technologies And Fundamental Research Of Micro-drilling And Micro-milling

The demand of micro-components and micro-machine are increasing duo to the development ofmicro-electronic and precision instruments industry. The size of micro-components is getting moreand more smaller which cause many new problems in manufacturing of micro-components. In orderto solve these problems, micro-cutting technology develops in recent years. The key point inmicro-cutting technology involves size effect, tool strength, tool radius strength and control ofmachining quality.The objective of this research is to study the mechanism of material removal process, sizeeffect, tool failure and optimize the tool geometry and manufacturing process in micro-drilling ofprinted circuit board and milling of alloy. The main contents and innovations are as followings:(1) Development of3-axis micro-cutting machine toolA3-axis micro-cutting machine tool was developed for the investigation of micro-cuttingtechnology. The maximum spindle speed is300000rev/min and the maximum moving speed is300mm/s. Some tests were carried out to analyze the performance of machine tool. The items oftests involve position accuracy, spindle error and natural frequency of frame. The results showedthat this machine met the requirements of micro-cutting experiments.(2) The mechanism and control of micro-burr formationThe mechanism of material removal process and micro-burr formation was investigatedthrough FEM simulation and micro-cutting experiments. The results of FEM simulation showedthat the burr size increased when tool edge radius increased. The friction coefficient has no obviouseffect on burr size. The increasing of exit angle can miniaturize the burr size. The experiments ofmicro-drilling of PCB were carried out to investigate the formation of micro-drilling burr. Theexperimental results showed that the entry burrs and exit burrs have different morphologies with thegeneration of entry burrs being mainly caused by burr bending, whereas the generation of an exitburr was more complicated. The effect of feed on burr size was bigger than sindle speed.(3) Size effect in micro-drilling of PCB and modeling of thrust force and torqueThe size effect of micro-drilling of PCB can be expressed by variation of torque. Thecalculated specific cutting energy decreased when feed increased. The experimental results showed that the specific cutting energy become constant when feed per tooth exceed5m. The empiricalmodel of thrust force and torque were established according to the drilling experiments. The resultsof the verification test showed that the established models had good agreement with experimentaldata. The experiments of drilling pilot hole with0.4mm and0.6mm micro-drill bits were carried out.The experimental results showed that the thrust force generated by chisel edge is50%of the wholethrust force. At the stage drilling GFRP, over70%of the trust force was generated by chisel edge.(4) Modeling of micro-tool geometry and design of tool edge radiusFirstly, a mathematical model of D-type micro-milling tool and the equation of calculating rakeangle were established. By these models, a D-type micro-tool can be designed by giving tool radiusand rake angle. After that, the geometric parameters of micro-tool were optimized by FEM method.Secondly, the equation of calculating stresses was established by analyzing drilling force. After that,a method of designing tool edge radius was given.(5) Investigation of tool wear condition monitoring based on Fuzzy neural networkDuo to the defect of slow convergence, BP neural network method was not fit for on-line toolmonitoring. Fuzzy neural network (FNN) method was used in this research to establish a predictionmodel for tool monitoring. This model was developed by training process, the results of verificationtests showed that the predicted output results had good agreement with ideal output results. It can beconcluded that FNN method is fit for on-line tool monitoring.(6) The strategies of controlling micro-machining qualityIn order to improve the machining quality, this paper gave different method for respectivemicro-machining processes. To mill the titanium alloy, minimum quantity lubrication (MQL)technology was advised. The experimental results showed that MQL can decrease burr formationand tool wear. To decrease burr formation in micro-milling, increasing exit angle is feasible. Toimprove the quality of drilling PCB, the optimization of tool geometry and machining parameterswere feasible. Composite desirability method was used to optimize the tool geometry and drillingparameters.