Development and Experimental Study of MWEDM Prototype

A Micro Wire Electrical Discharge Machining (MWEDM) prototype is developed for fabricating micro complex parts. It mainly includes granite basement, micro energy pulse generator, precise servo mechanics, detection and servo control system, constant tension winding systems. Experiments are done on the prototype. Experimental results show that: the peak current and pulse duration have obvious influence on surface roughness and machining time, and they also have an optimum value for the highest cutting speed. The servo reference voltage also influences the surface roughness and machining time. Utilizing micro wire electrode with diameter in 30m, the MWEDM can machine micro slot with minimum size of 38m, which proves that the discharge gap width can be controlled not more than 4um, and so small discharge gap is beneficial for part’s machining accuracy. All kinds of complex micro part (such as micro gear, micro bearing bracket, micro shaped holes, etc.) can also be machined by this prototype.

Investigation on Wire Electrochemical Micro Machining

Wire electrochemical micro machining (WEMM) using the online-fabricated micro wire electrode is proposed as a new method of micro machining. Based on electrochemical principle, the mechanism of nanosecond pulses WEMM was investigated. The hardware of the control system was founded using devices of virtual instruments, and the software of the system was designed based on Labwindows/CVI. The micrometer scale wire electrode was online fabricated, the diameter of wire electrode was real-time monitored by precisely measuring the variation in resistance of the electrode, and it is possible that accomplish the fabrication of wire electrode and the following processes continuously in the same machining system. The relations between the machining accuracy and parameters, such as velocity of feed forward and pulses parameters was experimentally studied, and a series of high-aspect-ration micro structure and multi-microgrooves were fabricated. The research of the paper sets up a firm foundation for application of the proposed wire electrochemical micro-machining.

A Hybrid Microfluidic Mini System Towards a “Lab-on-a-Chip” for Biochemical Immunoassay

Hand-held, fully automated microfluidic systems have been developed and characterized to perform a magnetic bead-based biochemical immunoassay. The magnetic beads were coated with a polymer on which a dendritic antibody had been prepared to form the basis of a “sandwich” immunoassay for sensing biomolecules. With the press of a button, a complete immunoassay is performed to detect biohazards, and the result of the assay is displayed on a LCD. One system was made by using biocompatible silicone tubing for interconnections between the devices while another system was fabricated on a micromachined “glass-on-silicon” motherboard (Dharmatilleke et al.,. 2000). The first system consists of four collapsible reservoirs for reagent storage, made of very thin biocompatible Teflon™; an array of zero dead volume pinch valves; two magnetic curtain magnetic particle separators; a micro wire electrode or IDA for detection; a flow sensor, a valveless rotary pump to pull the reagents through the microfluidic system and associated electronics. On the second system, the mini pinch valves have been replaced by “collapsible” membrane type zero dead volume valves and pumping is by peristaltic operation of the valves. This work preceeds the next step, which is an all-MEMS system “on-a-chip”.