Machining: Various manufacturing processes are used to bring the metal into desired shape. In some of the processes, metal is brought to desired shape under the action of pressure and heat or both. The examples of such type of processes are forging, drawing, rolling, extrusion etc. While in others we need to remove unwanted material from parent metal in the form of chips through machining. Some of machining processes are Milling, drilling, Broaching, Turning, shaping, planning, boring etc.
The basic objectives of efficient and economical machining practice are
- The machine tool should remain idle for lesser time
- Less power should be consumed during machining
- Quick metal removal rate
- Better surface finish
- Tool cost should be low
- Cost of replacement and sharpening of tool should be low
Basic elements of Machining: The basic elements of machining are workpiece, tool and chip. For any cutting action, it is necessary to have relative motion between tool and workpiece. Unwanted material is removed from workpiece by the cutting action of the tool. The type of chips formed is greatly affected by the workpiece material, geometry of cutting tool and method of cutting. The chip formed can be continuous, discontinuous or segmental and continuous chips with built up edge. Ductile material, High cutting speeds and large rake angle produce continuous chips. Mild steel and copper are considered most desirable metals for producing continuous chips. Brittle material (cast iron and bronze), low cutting speeds and small rake angles are the main reasons for producing discontinuous chips. Continuous chips with built up edge are mainly produced due to high local temperature, high pressure while cutting ductile material.