UNIT 3: FUNDAMENTALS OF CUTTING PROCESSES

Introduction.

Definitions

Machining: term applied to all material-removal processes

Metal cutting: the process in which a thin layer of excess metal (chip) is removed by a wedge-shaped single-point or multipoint cutting tool with defined geometry from a workpiece, through a process of extensive plastic deformation.

Abrasive processes: material removal by the action of hard, abrasive particles that are usually in the form of a bonded wheel. Each single particle acts like a single-point cutting tool. Since the particular geometry of a particle is not known, abrasive processes are referred to as machining with geometrically undefined tools

Machining operations are capable of producing more precise dimensions and smooth surface finishes than all other manufacturing processes. They are performed after other processes, which create the general shape of the parts. Machining then provides the final geometry, dimensions and finish.

PART 1: CUTTING TOOL MATERIALS

A. READING

CUTTING TOOL MATERIALS

Requirements

The cutting tool materials must possess a number of important properties to avoid excessive wear, fracture failure and high temperatures in cutting, The following characteristics are essential for cutting materials to withstand the heavy conditions of the cutting process and to produce high quality and economical parts:

1) hardness at elevated temperatures (so-called hot hardness) so that hardness and strength of the tool edge are maintained in high cutting temperatures:

2) toughness: ability of the material to absorb energy without failing. Cutting if often accompanied by impact forces especially if cutting is interrupted, and cutting tool may fail very soon if it is not strong enough.

3) wear resistance: although there is a strong correlation between hot hardness and wear resistance, later depends on more than just hot hardness.

Other important characteristics include surface finish on the tool:

4) chemical inertness of the tool material with respect to the work material.

5) thermal conductivity of the tool material, which affects the maximum value of the cutting temperature at tool-chip interface.