CHAPTER CONTENTS

65

5 FUNDAMENTALS OF METAL CUTTING

5.1 Overview of Machining5.2 Mechanics of Machining5.3 Cutting Forces5.4 Cutting Temperature5.5 Tool Wear and Tool Life5.6 Cutting fluids5.7 Surface Finish5.8 Cutting Tool Materials5.9 Machinability5.10 Selection of Cutting Conditions

5.1 OVERVIEW OF MACHINING

Definitions

v Machining: term applied to all material-removal processes v 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

work surface

chip

cutting tool

feed motion

prim

ar

ym

otion

machinedsurface

Close-up view of a turning operation in which a thin layer of metal (chip) is

removed from the work surface of a rotating workpiece by a coated cemented carbide cutting tool. The newly generated surface

is referred to as a machined surface. Cutting process requires both primary and feed

motions.

direction of primary motion

direction offeed motion

workpiece

chip

toolcut

work surface

machined surface

Schematics of metal cutting process showing the basic terminology.

Overview of Machining66 Valery Marinov, Manufacturing Technology

v 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

v Non-traditional processes: machining with electrical, optical or chemical sources of energy

Set-up of the grinding operation showing the workpiece, abrasive bonded wheel and the spray of burned chips

Cutting operation performed by a five-axis CO

2 laser

The place of machining operations

Metallurgical processes

Casting Metal forming Powder metallurgy

Material-removal processes

Assembly

Sing

le-p

art

prod

uctio

nFi

nal

prod

ucts

Star

ting

mat

eria

ls

Ê

Diagram showing the place of machining operations within the entire production cycle.

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.