Research On Multifunctional Micro-WEDM System And Its Applications

With the rapid development and practical advancement of micro electro-mechanical system(MEMS)and micro system technology(MST),higher requirements are put forward for the high-performance fabrication of complex micro components.As a commonly used micro machining method,micro wire electrical discharge machining(micro-WEDM)technology has the advantages of high precision,low cost,no macro force and extensive processing material,and it has high processing flexibility by changing wire traveling scheme and relative motion mode between micro wire and workpiece,showing a certain potential for machining complex micro parts.But the current micro-WEDM setup has some drawbacks,such as sole function,poor processing stability and low efficiency,which limit its further application.For the above problems,this dissertation developed a multifunctional micro-WEDM system with the self-developed one as main body,and relevant processing rules and application technologies were studied.The multifunctional micro-WEDM system were constructed by adding indexing rotary spindle module,anti-copy and horizontal processing module,and developing constant tension control system.The precise and stable micro-WEDM could be achieved for complex microarray electrode,micro-rotary structure and large thickness workpiece,and so did the micro-EDM grinding with block/blade electrode as auxiliary processing,horizontal micro-EDM peripheral milling and so on.Multifunctional micro-WEDM system expanded the machining capability of the current one and provided an effective alternative for the fabrication of micro parts.To ensure the machining stability of multifunctional micro-WEDM system under different modes,the tension control is studied in this dissertation.The variation characteristic of micro wire tension under reciprocated wire traveling were analyzed.On this basis,a symmetrical micro-wire traveling mechanism was proposed to reduce the tension fluction caused by reciprocated wire traveling,and avoid the fatigue failure caused by the force on both sides of micro wire.The current tension control scheme was improved by developing a constant wire tension control system based on AC servo motor and STM32 microcontroller.An integrated mechanism with tension detection and control exective function was designed,which reduced the guide wheel number and processing costs.Besides,to avoid the tension jitter caused by frequent adjustment of AC servo motor,a constant tension control strategy for micro wire based on dead-zone PID algorithm was proposed.Vibration characteristics of micro wire in micro-WEDM are closely related to process stability and machining performance.In this dissertation,the effect of wire traveling system,working-fluid impact force and tension on the transverse displacement of micro wire was intuitively analyzed by building vibration observation platform for micro wire.Meanwhile,the theoretical analysis and experimenetal study on the micro wire vibration caused by discharge force under two machining modes of non-ratory and rotary workpiece were conducted.The mechanical model of micro wire vibration under the discharge force of continuous pulse was established.The transverse amplitude and discharge frequency of micro wire caused by discharge force under different parameters were obtained by orthogonal experiments.The single pulse discharge force was inversely calculated by numerical solution for the mechanical model based on finite difference method using MATLAB software.On this basis,the response surface between discharge frequency,force and the transverse amplitude of micro wire was established.The effects of discharge frequency and force on the transverse amplitude of micro wire were analyzed intuitively,and so did the amplitude difference caused by the two processing modes.Finally,the effects of discharge frequency and force on wire amplitude were qualitatively verified by cutting kerf tests,which was significant for explaining experimental phenomena and guiding processing parameters.The micro-WEDM technology for array and rotary microstructures were studied.The high aspect ratio microarray electrode was precisely machined by compensating the machining gap of different cutting thickness.The mathematical models of material removal rate and surface roughness of micro-rotary structure were established by central combination experiment and response surface methodology,and multi-objective parameters were optimized by improved genetic algorithm.Subsequently,the multiple cutting experiment of micro-WEDM for micro-rotary structure was conducted.In addition,a combined processing method consisted of micro-EDM grinding with block and blade electrode,and micro-WEDM was proposed to prepare the micro disc electrode with large scale feature.What's more,the prepared electrode was on-line used for micro-EDM peripheral milling of microarray kerf.The above verified the practicability and effectiveness of the multi-functional WEDM system.The micro-WEDM for large thickness workpiece i.e.micro gear mould was carried out.The cause for the machining defect of micro gear punch profile was analyzed.A secondary machining method of micro gear punch was proposed based on self-centering flexible fixture,ensuring the profile integrity of micro gear punch.Besides,the surface quality of micro gear die cavity was improved by multiple cutting.The above verified the validity of multifunctional micro-WEDM system to realize stable and precise machining for large thickness workpiece.Finally,the micro gear mould was used for the precision forging process,and the influence of forging stroke on forming quality of micro gears was explored,achieving the batch production of micro gears.A multi-wire micro-WEDM system was designed.The multi-wire cutting for the same workpiece was realized by forming parallel wire mesh in the processing area.Besides,the feasibility of improving the machining efficiency of micro-WEDM was explored.The multi-wire micro-WEDM of miniature relay was conducted,which verified the validity of multifunctional micro-WEDM system to guarantee machining accuracy and improve processing efficiency of multi-wire cutting.It further enriched the connotation of multifunctional micro-WEDM technology.