ME5520 Unconventional
Machining Processes
UNIT I INTRODUCTION
• Rapid technological developments in the field
of new materials and alloys with ever
increasing strength, hardness, toughness heat
and wear resistance have imposed many
problems and difficulties during the machining
of these materials by conventional machining
methods.
Machining of
– intricate and complicated shapes
- thin and fragile components
– accurate and economical forming of very hard
high strength materials
which are being extensively used in aerospace
and nuclear industries have forced the scientists,
engineers and technologists to search for new
techniques of machining which can readily
provide an effective solution to these problems.
• As a result of research and development for
the last forty years or so, several new methods
of machining have emerged which can be
grouped
under
the
name
of
“UNCONVENTIONAL MACHINING METHODS”.
NEED FOR UNCONVENTIONAL MACHINING
PROCESSES
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Limitations of conventional machining methods
Rapid improvements in the properties of materials
Tool material hardness > W/p hardness
Complex shapes
Machining of inaccessible areas
Better surface integrity
High surface finish
• High production rate
• Low cost of production
• Precision and Ultra precision machining
PRINCIPLE OF UNCONVENTIONAL MACHINING PROCESSES
The basic principle of machining by these
new methods is to apply some form of energy to
the work piece directly without almost any
physical contact between the tool and the work
piece and have the desired shape or contour by
material removal from the work piece.
CLASSIFICATION
Different forms of energy applied to the work piece are:
• Mechanical energy
• Electrical energy
• Chemical and electro chemical energy
• Thermal energy
Mechanical energy methods
The material is principally removed by
mechanical erosion of the work piece material.
These methods include:
Ultrasonic machining (USM)
Abrasive Jet Machining (AJM) and
Water Jet Machining.
Chemical energy methods
These methods involve controlled etching
of the work piece material in contact with a
chemical solution, for example, Chemical
Machining Method (CHM).
Electro-Chemical energy methods
These methods involve electrolytic
(anodic) dissolution of the work piece material
in contact with a chemical solution. These
methods include:
Electrochemical Machining (ECM)
Electro Chemical Grinding (ECG)
Electro Chemical Honing.
Thermal energy (Thermoelectric) methods
The thermal energy is employed to melt and
vaporize tiny particles of work material by concentrating
the heat energy on a small area of the work piece. The
required shape is obtained by the continued repetition of
this process. These methods include:
Laser beam machining (LBM)
Plasma arc machining (PAM)
Electron beam machining (EBM) and
Ion beam machining (IBM).
Characteristic features
– Material is removed from the work piece without
physical contact.
– In many processes material removal rate is
independent of the hardness of the work piece.
– Cutting forces are independent of the hardness of
the work material.
– The tool material need not be harder than the
work material. Almost any work material,
irrespective of its hardness and strength, can be
used.
– Generally tool wear is negligible. Hence tool wear is
not a problem. No burr is left on the work piece.
– In most of the cases, entire contour or desired shape
can be obtained in one stage or in one setting.
– Intricately shaped contours and fine machining of
precision holes are possible.
– Modern machining methods can be integrated easily
with microprocessors and numerical controls for
better control of the process and for improving the
versatility and productivity of the machine.
Advantages of unconventional machining
processes
• Material removed from the work piece without
physical contact (ECM, EDM, LBM, CHM).
• Material removal rate is independent of the
hardness of the work piece (ECM, LBM, EDM)
• Cutting forces are independent of work piece
hardness.
• Tool material need not be harder than the work
piece material (ECM, LBM, EDM, CHM, USM).
• Tool wear is not a problem (ECM, LBM, CHM).
• Ability to machine any material (LBM).
LIMITATIONS
• Work piece and tool must be electrically
conductive (EDM, ECM).
• The depth of cut is limited (LBM).
• There may be taper in the sidewalls of holes
or cavities (EDM,LBM).
• Most of these limitations can be overcome
and controlled.
APPLICATIONS
• AJM is suitable for machining super alloys and
refractory materials such as ceramics and glass.
• USM has good machining performance for
refractory type materials such as ceramics and
glass.
• ECM is used for machining steel and super alloys,
ECM cannot be used for machining nonconducting materials like ceramics, plastics and
glass.