why does temperature in cutting depends on cutting speed, feed & depth of cut.Explain with process variables.?

Answer 1

The higher the cutting speed the faster the surface feet that the tool travels (whether the tool is rotating or the part) the more heat will be generated by friction. The higher the feed, as well as depth of cut, result in more material being removed, which result in higher friction.
Sometimes people confuse surface speed with RPM. Surface feed is the important factor, and the first calculation in any speeds and feeds question.
Many other factor come into play as well. Tools, coolant material are just a few more.

Answer 2

The higher the tool speed, the more grinding of the tool into the part there is, so more heat will be created.

The higher the feed rate, the larger the chip that is removed. The larger chips carry more heat away with them, so there is generally slightly less heat transferred to the part (and more heat transferred to the chips) with a higher feed right.

If you're doing a horizontal cut on a mill, greater z-depth of the tool will increase the surface area, increasing friction, increasing heat. Cutting further into the part sideways will have a similar effect.

Answer 3

Primary variable is heat dissipation. If you put more energy into a given unit of area (i.e, speed, force, frictional area) then the material can carry away, temperature will increase up to a point where the gradient between the cutting surface and bulk material will allow for sufficient energy transfer.

The variable you list above, all contribute to the amount of energy in the cutting area.