The objective of this research is to create a novel, hybrid, and high performance micromachining process for electrically non-conductive brittle hard materials such as glass, quartz and certain ceramics, and to reveal the fundamental material removal mechanisms and microscopic phenomena in micromachining of these materials. The approach includes experimental observations, physics-based modeling and simulation of the material removal processes due to thermal erosion, chemical dissolution or etching, mechanical cutting, and ultrasonic tool vibration. A material removal model based on synthesizing the contributions from each of these material removal mechanisms will be written for this proposed novel micromachining process. This model will then be utilized to design and optimize a robust process for micromachining sample brittle hard materials.
If successful, this project would widen the potential applications of micro components made of non-conductive brittle hard materials in emerging fields such as micro-fluidic systems and micro-electromechanical systems. This novel hybrid process will allow the cost effective machining of complex micro-features on many difficult-to-machine materials. The benefits of achieving these new micromachining capabilities include the creation of new and better devices for biomedical applications, microelectronics, and scientific research investigation. This research will extend the engineering application of advanced heat transfer and micro multiphase flow modeling techniques to further understand electrochemical discharge phenomenon.
The outcome for this project lies in both the development of the innovative drilling process and the fundamental modeling of ECDM. A hybrid machining process was developed using a combination of micro-cutting and electrochemical discharging. The process was optimized through the determination of appropriate process parameters, as well as incorporating auxiliary mechanisms including ultra-sonic vibrations. The specific findings and achievements are: 1. Development of drilling incorporated ECDM A drilling incorporated ECDM process was designed and implemented to enhance material removal rate in ECDM drilling process. Incorporating micro-drilling into ECDM significantly increased the rate of material removal, especially in deep hole drilling. As fundamentals of the machining process, material removal mechanisms were investigated to account for the increment in material removal rate by incorporating micro-drilling. Vibration of tool electrode, induced by a piezo-actuator, was introduced to further enhance material removal rate. Quantitative studies were conducted to determine the appropriate process parameters of the machining process. Vibration assisted micro-drilling incorporated ECDM was also introduced. Tool vibration established steady material removal scenario as machining depth increase, whereas conventional ECDM was limited by maximum machinable depth. Taguchi DOE results suggested the vibration should be neither too fierce nor too gentler. It can be also concluded that the improvement of micro-drilling incorporated ECDM with vibration in terms of machining depth over one minute is 60% or higher, depending on electrode voltage. 2. Modeling of sparks, discharging activity Conic tool electrodes were employed as tool electrode in the study of spark generation. Fabricated by ECM, conic tool electrodes could enhance consistency in spark generation comparing with conventional tools. Energy of each spark generated was measured and was fit in a stochastic model with a two-component mixture lognormal distribution. The energy distribution proved that tapered tool improved the consistency of spark generation and suppressed the generation of minor discharges. The average energy for sparks was 3.8 mJ with 34 V electrode voltage. A finite element based model was developed to predict the geometry of removed material and was validated through experimentation. 3. Modeling of micro-flow and gas film Modeling and experimental investigation of gas film in ECDM are conducted to characterize film thickness and transient behavior. A physics-based model is derived for gas film dynamics and electrolysis to correlate film characteristics with various process parameters. Meanwhile, mechanisms underneath the discharging phenomena are revealed through modeling and experimentation, including the process of bubble growth and the criterion of the transition from bubbles to gas film. Micro-fluid flow around the tool electrode is essential to maintaining stable gas film for discharging. The flow is simulated starting from the generation of single bubbles from nucleation sites over the tool electrodes, and preceded to the film stability issues. The results are compared to videos taken by high speed camera that revealed the transient behavior of gas film.
