Investigation of the machinability of Ti6Al4V alloy by electrical discharge and electrochemical machining processes

Titanium and its alloys are extensively used in electronic, computer and aerospace industries because of these materials? excellent properties such as a high strength ? weight ratio, high temperature and exceptional corrosion resistance. Additionally, highly chemical reactivity, low elastic modules and thermal conductivity of titanium also impair machinability. It is advised to machine these materials by non ?traditional machining (NTM) processes. Electrical discharge machining (EDM) process is one of the NTM process. It is possible to machine all electrical conductive materials in micron tolerances to hard and complex shapes by this method. However, the macroscopic effect of heating produces much damages on the surface such as globules of debris, pockmarks, melted drops and varying size craters. These surface formations especially affect the failure process of machine elements under repetitive loading conditions. Thus, the EDMed surfaces are generally needed a second finish operation according to machining parameters. Although, several mechanical surface treatment methods have been employed to improve the EDMed surfaces, the electrochemical machining (ECM) process was found more suitable finish for EDM.In this study, Ti6Al4V alloy was machined by electrical discharge and electrochemical machining processes to determine machining characteristics. In EDM trials, current and pulse duration were taken as alternative when flushing pressure and pulse interval time were fixed. Three different tool electrode materials namely; graphite, electrolytic copper and aluminum were used to machine Ti alloy. At the end of the EDM experiments, the metallographic inspections of the samples were observed by scanning electron microscope (SEM), energy dispersive spectrograph (EDS), X ? ray diffraction (XRD) and surface hardness measurements. The surface roughness of the machined surfaces, microstructural changes, tool wear ratio, material removal rate, surface crack density and white layer thickness were the main performance characteristics under investigation. Then the same EDMed specimens (machined under same conditions for standardization purpose) were machined by electrochemical grinding (ECG) process. In ECG process, machining voltage, electrolyte flow rate and table feed rate parameters were changed while electrolyte concentration and type of electrolyte were constant. The surface roughness improvement ratio was determined based on the ECG parameters. The relative effect of each EDM and ECG parameters were determined in statistical manner and the processes were optimized. Both machining processes were modeled by using linear regression approach. The adequacies of models were checked by analysis of variance (ANOVA) and residual analysis techniques. As a consequence, the developed models were able to predict the both machining processes without making experiments.In the first chapter of this study, the subject was introduced. In the second chapter, the place in the literature of study was investigated and some novel studies were given concerning this subject. In the third chapter, titanium, its alloys and the main difficulties met in conventional machining processes were determined. In the fourth chapter, the EDM and ECM processes were introduced. In the fifth chapter, the method of experimental study and the preparation phases to experiments were presented. In the sixth chapter, the experimental results were given and discussed. In the seventh chapter, the statistical and economy analyses for both processes were given. In the eighth chapter, the processes were modeled by linear regression method. In the ninth and final chapter, general results and recommendations were given.