INTRODUCTION
TO METAL CUTTING
Metal cutting is the process of producing a job
by removing a layer of unwanted material from a given workpiece.
Fig. shows the schematics of a
typical metal cutting process in which a wedge shaped, sharp edged tool is set
to a certain depth of cut and moves relative to the workpiece.
Under the action of force, pressure is exerted
on the workpiece metal causing its compression near the tip of the tool. The
metal undergoes shear type deformation and a piece or layer of metal gets
repeated in the form of a chip. If the tool is continued to move relative to
workpiece, there is continuous shearing of the metal ahead of the tool. The
shear occurs along a plane called the shear plane.
All machining processes
involve the formation of chips; this occurs by deforming the work material on
the surface of job with the help of a cutting tool. Depending upon the tool
geometry, cutting conditions and work material, chips are produced in different
shapes and sizes. The type of chip formed provides information about the
deformation suffered by the work material and the surface quality produced
during cutting.
Types
of Chips:
Continuous
chips: While machining ductile materials, large plastic
deformation of the work material occurs ahead of the cutting edge of the tool.
The metal of the workpiece is compressed and slides over the tool face in the
form of a long continuous chip.
Discontinuous
(segmented) chips: A discontinuous chip is a segmented chip
produced in the form of small pieces. The discontinuous chips are produced when
cutting brittle materials like cast iron, bronze and brass. The working on
ductile materials under poor cutting condition may also sometimes lead to the
formation of discontinuous chips.
Continuous
chips with built-up-edge: The term built-up-edge refers to the small
metal particles that stick to the cutting tool and the machined surfaces as
result of high temperature, high pressure and high frictional resistance during
machining. The building up and breaking down of the built-up-edge is periodic;
its size first increases, then decreases and again increases-the cycle gets
repeated rapidly.
