Mr. Sanjay Kumar, I meant to say researches in any manufacturing processes like EDM or any machining processes, Rapid Prototyping or CNC machining Processes etc.....
There has to be one specific field for identifying research gaps. One field/type of mfg process may be chosen out of the list your good self mentioned.
Sir, I have referred many researches in EDM. So, Is there any research gap available in EDM ? then I"ll chose Rapid prototyping or CNC machining technology.