Machining of Ceramic Materials Using Electrical Discharge Machining Process

[Completed and presented on July, 2020]

[Full article] [Brief description]

Supervisor: Dr. Muhammad Jahan, Department of Mechanical and Manufacturing Engineering, Miami University

Introduction:

• Electrical discharge Machining (EDM) is an established nontraditional method for precision machining of difficult-to-cut material
• This is especially applicable when there is a need for machining of structure like deep bores, grooves or undercuts in material with high wear resistance
• EDM is a well-established process for machining difficult-to-cut materials irrespective of the hardness and wear resistance of materials
• Advanced ceramics like engineering ceramics are extensively used in various industrial applications such as transport, energy, semiconductor, and biomedical due to their high heat resistant properties
• Ceramic materials cannot by conventionally machined by EDM process as ceramics are naturally electrically-conductive
• Implementing EDM process for machining of insulating ceramics will open up opportunities for using ceramics for many innovative and intricate industrial applications

Project Aim:

• The purpose of this project is to develop a comprehensive understanding of multi-scale EDM process of non-conductive advanced ceramics by conducting a systematic investigation of macro to micro EDM process
• If successful, the proposed method would allow extensive use of the EDM process for machining engineering ceramics at macro and micro scales with improved material removal rate, surface finish and dimensional accuracy

Research Approach:

• In the past years, assisting electrode method in EDM has been applied to machine insulating ceramics, which works by the mechanism of continuation of material removal even after the conductive layer is removed
• However this process is not very stable, when the conductive layer is exhausted
• We hypothesize that combining the assisting electrode technology with the powder mixed EDM would further enhance the machining speed and performance during EDM of non-conductive ceramics
• This research project aims to focus on EDM of Aluminum Nitride (AIN) and ATZ (Alumina Toughened Zirconia, ZrO2-Al2O3) composites, as both insulating ceramics are of particular interest to the industries due to their application in several engineering branches

Research Methodology:

• In this study, the assisting electrode and powder mixed dielectric will be incorporated simultaneously during EDM process to machine AIN and ATZ composites
• For assisting electrode methodology, EDM process is initiated by a conductive layer on the surface of insulating ceramics. Molecules of the hydrocarbon dielectric oil as well as the workpiece are cracked because of the high temperature generated by the electric discharges. This process assists carbon molecules to bind itself with ceramics materials. Since these carbon molecules are conductive in nature, discharge may continue to occur even though the conductive layer is removed
• As a result, both the conductive layer and ceramics materials beneath that layer will be removed
• Aluminum powder increases spark gap
• Addition of conductive powder with dielectric will increase the spark gap and will reduce the dielectric strength
• Even if enough carbon molecules are not available in the gap once the conductive layer is removed, conductive powder from dielectric may facilitate the EDM process

Research Objectives:

• Investigate the feasibility and effect of combined assisting electrode method and conductive powder mixed dielectric for EDM of insulating ceramics

• Experimental set up will be designed to accommodate the combined assistive electrode and conductive power mixed dielectric

• Feasibility of the set-up idea will be verified by varying the electrical parameters such as capacitance, voltage, current, pulse on time, pulse off time, as well as non-electrical parameters like flushing efficiency, tool rotation of the EDM process

• Experimental trials will be conducted to find the optimum parameters for the combined process

• Performance parameters that will be investigated are material removal rate, dimensional accuracy, tool wear, surface integrity, surface micro-hardness, and recast layer on the machined surface

• Study the effect of different conductive layers on the EDM process performance

• Experiments will be conducted using conductive layers of different coating materials on the electrode

• For conductive layer on the assistive electrode, the performance of silver, copper, and graphite coatings will be examined

• The performance of coating layers will be evaluated

• Investigate the effect of conductive powder mixed dielectric on the EDM process

• Conductive powder like carbon nanofibers, and Ti will be mixed with the dielectric for improving the conductivity during the combined assisting electrode and powder mixed EDM experiments.

• The effect of conductive powder will be investigated on both AIN and ATZ ceramics, and material removal rate, tool wear rate and surface integrity as a result of different powder addition will be investigated

• Parametric optimization of the process

A brief description of the research project can be found here.