Cathode Structure Optimization and Process Experiment in Electrochemical Machining of Multi-stage Internal Cone Hole

In order to solve the problems of uneven gap distribution and flow pattern in complex parts with multi-stage internal cone holes in electrochemical machining, a method of computer simulation assisted cathode design was proposed. The electric field and flow field models of machining gaps were established respectively, and the simulation of different cathode profiles was carried out. When the cathode cone angle is 2°, the electric field distribution between the cathode and the workpiece is reasonable, and the electrolyte distribution in the machining gap is uniform. With the conditions of processing voltage 10 V, electrolyte inlet pressure 1.5 MPa, electrolyte temperature 28 ℃ and cathode feed speed 5mm/min, the ECM processing of multi-stage internal cone hole was carried out by using the optimized cathode. The results show that the surface of the workpiece has no flow pattern, the dimensional forming accuracy is better than 0.1mm, and the surface roughness reaches Ra0.697µm. Research shows that the optimization of cathode structure with computer simulation can shorten the cathode development cycle and reduce the cost of cathode design effectively in ECM, which provides an efficient and feasible method for the optimization of complex cathode structure.

Thermal Analysis and Testing of Different Designs of LaB6 Hollow Cathodes to Be Used in Electric Propulsion Applications

LaB6 emitters are commonly used in hollow cathodes that are utilized in electric space propulsion systems. In order to obtain necessary surface current emission densities of 1–10 A/cm2 for cathode operations, LaB6 emitters require temperatures above 1500 °C. Hence, the design for LaB6 cathodes presents thermal and mechanical challenges. In this paper, several design iterations for LaB6 hollow cathodes are presented and thermal analyses are conducted for each design. Temperature and heat flux distributions that are obtained from thermal analyses are investigated. The designs are evaluated according to the required heat input to the emitter, and the radiative and conductive heat loss mechanisms. In addition to the thermal analyses, experimental tests are conducted for different cathode designs and, based on these tests, various modes of failure are determined. Revising the cathode design and the material selection iteratively to eliminate the encountered failure mechanisms, a novel cathode design is achieved. Experimental tests of this novel cathode are conducted and current-voltage characteristics are presented for different mass flow rates and for discharge currents between 0.5 and 12 A. Tests and analysis results show that the selection of materials and design are crucial for a sturdy and long lifetime cathode.

Cathode Design for Proton Exchange Membrane Fuel Cells in Automotive Applications

An advanced cathode design can improve the power performance and durability of proton exchange membrane fuel cells (PEMFCs), thus reducing the stack cost of fuel cell vehicles (FCVs). Recent studies on highly active Pt alloy catalysts, short-side-chain polyfluorinated sulfonic acid (PFSA) ionomer and 3D-ordered electrodes have imparted PEMFCs with boosted power density. To achieve the compacted stack target of 6 kW/L or above for the wide commercialization of FCVs, developing available cathodes for high-power-density operation is critical for the PEMFC. However, current developments still remain extremely challenging with respect to highly active and stable catalysts in practical operation, controlled distribution of ionomer on the catalyst surface for reducing catalyst poisoning and oxygen penetration losses and 3D (three-dimensional)-ordered catalyst layers with low Knudsen diffusion losses of oxygen molecular. This review paper focuses on impacts of the cathode development on automotive fuel cell systems and concludes design directions to provide the greatest benefit.