describe the processes involved in manufacturing of three main components of a typical gear box.?

Question

the components are MAIN CAS ,ONE SHAFT AND ONE GEAR.

Answer 1

Casting to make the case -- molten metal is poured or injected into molds and allowed to cool, forming the basic shape of the case parts.

Milling of the case -- the faces of the case which must mate to each other or to a bearing race are milled to precision tolerances.

Lathing of the shaft -- the gear shaft is turned on a lathe to provide precision surfaces for the bearings.

Cutting of the gear teeth -- the gear teeth are cut using a specialized machine that performs an action similar to both milling and lathing.

Drilling and tapping to make the threaded holes where the bolts hold it all together

Lathing to make the bearing races and grinding to make the bearing balls (the bearings are not mentioned in your list of components, so I left this for last).

Answer 2

There isn't enough space here to do that in any real sense.

That is to say, so that you could go into a shop and actually do it.