Mathematical and physical modeling of FE-SEM surface quality surrounded by the plasma channel within Al powder-mixed electrical discharge machining of Ti-6Al-4V

Abstract

Electrical discharge machining (EDM) is known as one of the well-defined advanced manufacturing techniques. The electro-thermal property of EDM enables us to capture the electrical and thermal changes within the plasma channel. Our research has studied the impact of the electro-thermal of the plasma channel on surface integrity. We have analyzed the changes in the plasma channel by considering its physical characteristics based on the EDM’s input parameters such as discharge current (I), pulse-on time (Ton), and concentration of added Al powder (Cp). In our experiment, adding Al powder decreased the dielectric resistance of kerosene. Furthermore, our mathematical and physical model demonstrated that adding powder had a positive effect up to 2.5 g/l. Moreover, the uneven distribution of powders into dielectric caused unstable discharge on the surface. We also studied the defects and changes of the plasma channel’s features by using field emission scanning electron microscopy (FE-SEM). The consequence of the plasma channel changes led to the crack’s disappearance entirely when the Al powder was used. It should be noted that with Ti-6Al-4V, it is hard to machine material, which is usually due to low thermal conductivity and its volume-specific heat. In our study, the fast-cooling rate created a diffusionless acicular martensitic microstructure, which led to a distorted hexagonal close-packed (HCP) crystal structure with the designation α′. This occurred while a high rate of quenching martensitic α′ was formed. The plasma channel creates a recast layer, which was affected by metallurgical changes within the EDM process. By using electron dispersive scanning (EDS) method and elemental mapping, we observed that the cross-section of the workpiece in the HAZ area led to the optimized oxidization, carbonization, and degree of fragility on the surface. Moreover, as the rate of the current intensity increased from 15 to 20-25A, the machining time improved by 16%, 12%, and 7%, respectively. Our experiment is consistent with our proposed mathematical model, and it can have practical applications, especially in medical, aerospace, and automobile industries. To the best of knowledge, our mathematical model that we have proposed for our experiment detects appearance and disappearance of metallurgical defects.