Author
Bradley, Curtis
Other Contributors
Samuel, Johnson; Walczyk Daniel F.; Chung, Aram; Chakrapani, Vidhya;
Date Issued
2018-08
Subject
Mechanical engineering
Degree
PhD;
Terms of Use
This electronic version is a licensed copy owned by Rensselaer Polytechnic Institute, Troy, NY. Copyright of original work retained by author.;
Abstract
The electrochemical machining study presented in this thesis uses the novel testbed to reveal that phase-controlled waveform interactions between the three assistances affect both the material removal rate (MRR) and surface roughness (Ra) performance metrics. Experiments used a 7075 aluminum anode in an NaNO3 electrolyte with a 316 stainless steel cathode. The triad-assisted ECM case involving phase-specific combinations of all three high-frequency (15.625 kHz) assistance waveforms is found to be capable of achieving a 52% increase in MRR while also simultaneously yielding a 78% improvement in the surface roughness value over the baseline pulsed-ECM case. This result is encouraging because assisted ECM processes reported in literature typically improve only one of these performance metrics at the expense of the other.; Electrochemical machining (ECM) is a non-traditional machining process that uses an anodic dissolution electrochemical cell to preferentially dissolve a positively charged metal workpiece using a negatively charged tool, thereby creating a precise shape with a good surface finish. ECM is currently used to manufacture superalloy turbine blisks and medical implants as well as other complex profiles requiring superb surface finishes.; Finally, the thesis presents an ECM cell design methodology that spans two hierarchical time scales to effectively model magnetically assisted PECM. Total MRR is simulated in a large time scale model, on the order of the machining time duration (seconds). The diffusion layer thickness, simulated by a model on the order of the pulse duration, is then mapped to Ra by using an empirical function derived from the experimental data sets. The numerical models use characterizing minimum-order polynomials to estimate average conductivity, efficiency and peak current as functions of magnetic flux density and PECM voltage frequency. The models are then cross-validated by using 67% of the PECM test data for training the polynomial estimates. The average of the MRR and Ra model predictions are within 8% of the experimental value. The thesis concludes by presenting a microchannel use-case to demonstrate that capability of the proposed ECM cell design methodology to effectively navigate the complex ECM parameter space.; The research in this thesis presents a machining cell that combines pulsed electric waveforms, ultrasonic motion, and magnetic fields to form a novel, triad-assisted ECM cell. The pulsed electric field has a wide variety of asymmetric, bipolar configurations possible using two independent controlled power supplies. The workpiece is ultrasonically actuated from below the cell. Either a constant or sinusoidal magnetic field can be generated using an electromagnet or pair of permanent magnets, respectively.;
Description
August 2018; School of Engineering
Department
Dept. of Mechanical, Aerospace, and Nuclear Engineering;
Publisher
Rensselaer Polytechnic Institute, Troy, NY
Relationships
Rensselaer Theses and Dissertations Online Collection;
Access
Restricted to current Rensselaer faculty, staff and students. Access inquiries may be directed to the Rensselaer Libraries.;