Which of these processes involve(s) melting in metallic workpieces?

The correct answer is Electron beam machining.

To understand why this is the correct process, let us analyze the working principles of both machining processes mentioned:

1. Electron Beam Machining (EBM):
In Electron Beam Machining, a high-velocity stream of focused electrons is directed towards the metallic workpiece. When these high-energy electrons collide with the workpiece surface, their kinetic energy is rapidly converted into thermal energy (heat). This localized heating raises the temperature of the workpiece material above its melting point, causing it to melt and vaporize. Thus, material removal in EBM is primarily achieved through localized melting and vaporization.

2. Electrochemical Machining (ECM):
In contrast, Electrochemical Machining is a non-thermal process. It operates on the principle of controlled anodic dissolution (Faraday's laws of electrolysis). During ECM, a high-density direct current passes through an electrolyte flowing between a cathode tool and an anode workpiece. Material is removed atom-by-atom by electrochemical dissolution, without any thermal energy or melting being involved.

Therefore, among the options provided, only Electron beam machining involves the melting of the metallic workpiece.