| Pulse Electrochemical Machining (PECM) is a potentially cost-effective technology meeting the increasing needs of precision manufacturing of superalloys, like titanium alloys, into complex shapes such as turbine airfoils. This dissertation reports (1) an assessment of the worldwide state-of-the-art PECM research and industrial practice, (2) PECM process model development, (3) PECM of a superalloy (Ti-6Al-4V), and (4) key issues in future PECM research. The assessment focuses on identifying dimensional control problems with continuous ECM and how PECM can offer a solution. Previous research on PECM system design, process mechanisms, and dimensional control is analyzed, leading to a clearer understanding of key issues in PECM development such as process characterization and modeling. New interelectrode gap dynamic models describing the gap evolution with time are developed for different PECM processes with an emphasis on the frontal gaps and a typical two-dimensional case. A "PECM cosine{dollar}theta{dollar} principle" and several tool design formulae are also derived. PECM processes are characterized using concepts such as quasi-equilibrium gap and dissolution localization. Process simulation is performed to evaluate the effects of process inputs on dimensional accuracy control. Analysis is made on three types (single-phase, homogeneous, and inhomogeneous) of models concerning the physical processes (such as the electrolyte flow, Joule heating, and bubble generation) in the interelectrode gap. A physical model is introduced for the PECM with short pulses, which addresses the effect of electrolyte conductivity change on anodic dissolution. PECM of the titanium alloy is studied from a new perspective on the pulsating currents influence on surface quality and dimension control. An experimental methodology is developed to acquire instantaneous currents and to accurately measure the coefficient of machinability. The influence of pulse parameters on the surface passivation is explained based on the correlation among the instantaneous current, gap resistance, and surface microscopical features. A planned research is also introduced including a new concept of gap on-line recognition. In summary, this dissertation presents PECM problem identification, dynamic and physical modeling, and application to machining a titanium alloy. |
