1
UNCONVENTIONAL MACHINING PROCESSES (UMP)
1.1 INTRODUCTION
Machines depend primarily on electric motor8, hydraulics, gravity and hard tool
materials to perform machining, where as non traditional machining gets its source
from electrochemical reactions, high temperature plasma, high velocity abrasive jets,
high frequency sound, coherent light etc. The hardness of the material being
machined is ofno signilicant importance.
1.2 NEED FOR UNCONVENTIONAL MACHINING PROCESSES
Rapid technological developments the field of new materials and alloys with ever
in
increasing strength, hardness, toughness, heat resistance and wear resistance. have
imposed many problems and difficulties during the machining of these materials by
conventional means.
Machining of intricate and complicated shapes, thin and fragile components and
accurate and economical forming of very hard, high strength materials which
are
being extensively used in aerospace and nuclear industries, have
forced the scien
tists, engineers and technologists to search for
new techniques of machining which
can readily provide an effective solution to these problems.
As a result of rese arch and development for the last forty yearsor so,
several new
methods of machining have emerged which can be grouped under the name
of:
Unconventional machining methods,or adanced maelhining re cesesoY
Non-traditional machining methods, or
Physical machining processesi or
New technologes, or
Modern machining methods.
1.3 CLASSIFICATION OF UNCONVENTIONAL MACHINING PROCESSES
Classification of Non-Traditional Machining Methods:The Non-traditional
Machining Methods are classified according to the major energy sources employed in
machining.
1. Thermal Energy Methods:In these methods, the thermal energy is employed to
Telt and vaporize tinv partices cwrkmaterial by concentrating the heat energv
Unconwentional MachiningProcesses (UMP)
(EDM), Laser beam Machining (LBM), Plasma Arc Machining (PAM), Electron Beam
Machining (EBM),and lon Beam Machining (IBM).
2. Electro -Chemical Energy Methods: These methods involve electrolytic (anodie)
dissolution of the workpiece material in contact with a chemical solution. These
methodsinclude: ElectroChemicalMachining (ECM),Electrochemical grinding (ECG),
Electro-Chemical Honing (ECH) and Electro-chemical Deburring (ECD).
3. Chemical Energy Methods: These methods involve controlled etching of the
workpiece material in contact with a chemical solution, for example, Chemical
Machining Method (CHM).
4. Mechanical Energy Methods: In these methods, the material is principally
removed by mechanicalerosion of the workpiece material. These methods include:
Ultra Sonic Machining (USM), Abrasive Jet Machining (AJM), and Water Jet
Machining (WJM).
1.4 FEATURES OF UNCONVENTIONAL MACHINING PROCESSES
Characteristicfeatures of Modern Machining Processes
The following are the characteristic features of nontraditional machining pro
cesses, when compared with traditional or conventional mnachining processes:
(1) Material is romoved from the workpiece without mechanicalcontact (with
the workpiece).
(2) In many processes material removal rate is independentof the hardness of
the workpiece.
(3) Cutting forces areindependentof the hardnessof the work material.
(4) The tool material need not be harder than the work material. (In many
cases, softer materials can be used as the tool material).
(6) Almost any work material, irrespective of its hardnessand strength, can be
machined.
(6) Generally tool wear is negligiblei hence tool wear is nota problem.
(7) No burr is left on the workpiece.
(8) No residual stresses are left on the surface machined.
(9) In most of the cases,entire contour or desired shape can be obtained in one
stageor in one setting. This is possible since material removal takes place
uniformlyover the entire area simultaneously.
(10) Inmajority of the cases "surface integrity" of the surfaces produced by modern
machining methods is superior.
(11) Intricalely shaped contours and fine machining of precision holes are
possible.
(12) Modern machining methods can be integrated easily with mieroprocessors
and numerical controls for better control of the proceas and for improving
the versatility and productivity of the machine.
meay ie oveal! quality aud
Sutace istegily
machined smtaee
handnem
Resdual sresses
MiC no- craels
mateuial propealies
Introduction 1.3
OF UNCONVENTIONAL MACHINING PROCESSES
1.5 PRINCIPLE
Busic Principle of Unconventional Machining Processes
new mothods is to apply some form of
The baaie principle of muchining by these
between the
without ulmoBt any physical contact
cnergy to the workpicce directly removal
tool nnd the workpicce nnd have
the deaired shape or contour by material
are:
from the workpicco. Different forms of energy applied to the workpiece
(1) Mochanical Enorgy
(2) Eloctrical (or Sloctrochemical energy)
(9) Thernal Enorgy (orThermoelectric energy), and
(4)Chemical Energy.
used for the
Type of energy uscd, mode or mechanism of metal removal, medium
transfer of enorgy for different material removal processes are shown
in Figure 1.
Suitable combination of various parameters of the proces8 result in a machining
method which is unconventional in nature. The actual mechanism or mode of metal
removal is different for different machining methods.
The actual mechanism or mode of metal removal (viz.the physical phenomenon
involved during machining) fordifferentprocesses.
Machining Processes Predominant Mechanism of
Motal Removal or Physical
Phenomenon involed during
Machíning
Conventional machining Shear failure of work material
methods (e.g., turning, milling,
etc.)
2. Abrasive jet machiningwater Erosion of work material
jet machining
3. Ultrasonic machining -Cavitation phenomenon
-Erosion of work material
-Brittle fracture of work material
4. Chemical machining or -Etching
chemilling Corrosion
-Vaporization
5. Electrochemical machining -Anodic dissolutionof work
piece material
-Ion displacement
6. Electrochemical grinding -Anodic dissolutionof work material
-Ion displacement
-Erosion of work material (due to
grinding action of abrasive whee)
7. Spark erosion machining -Vaporization of work material
8. Electron beam machining -Vaporization of work material
9. Laser beam machining -Vaporization of work material
10. lon beam machining -Vaporization of work material.
-Fusion of work material
11. Plasma Arc machining Fusion of work materia!
Fundamental Machining Material Removal
Work Piece Transfer Energy
Energy Removal Source Process
Medium
Shear Cutting Traditional Machining|
Physical
Contact Tool
High Velocity Pneumatic/ Abrasive Jet Machining
Mechanical
Abrasive Hydraulic Ultrasonic Machining
Particles |Pressure Water Jet Machining
Erosion Higb Velocity
|Liquid Electro-chemical Grinding
Ion High
Electro-chemical Displacement Electrolyte Current Electro-chemical Machining
Chem-electric|
Chenical Ablative Reactive Corrosive
Reaction Environment! Agent HHot Chlorine
Chemical Milling (Chemilling)
Electrons High Voltagek EDM-Capacitor Discharge|
Electron Beam Machining
Vaporization
Amplified
Radiation Ligbt Laser Beam Machining
Thermo-electric
|lonized
on Stream Material lon Beam Machiningl
Fusion
Hot Gases
Plasma Arc Machining |
Method
of Metal removal for Modern Machining
Fig. 1: Energy source and Mode
Iniroduction 1.5
1.6ADVANTAGES OF UNCONVENTIONAL MACHINING PROCESSES
Advantages of Non-traditional machining processes:
(The symbols of the nontraditional machining processes which have these spe
cific advantages are given in the brackets).
1. Material removed without mechanical contact with the workpiece.
(ECM,EDM, LBM,CHM)
2. Material removed rate is independent of workpiece hardnesa.
(ECM,LBM,EDM)
3. Cutting forces are independent of workpiece hardness.
(ECM,LBM,EDM,CHM)
4. Too material need not be harder than the workpiece material.
(ECM,LBM,EDM,CHM,USM)
5. Tool wear is not a problem.
(ECM,LBM,CHM)
6. Ability to machine any material.
(LBM)
7. Burrfree machining.
(ECM,EDM, CHM)
8. Stress-free machining.
(ECM, ECG, CHM)
9. Uniform material removal over the entire area simultaneously.
(ECM, CHM)
10. Superior surface integrity possible.
(ECM,CHM, ECG)
materials can be machined.
11. Intricately shaped, very hard and fragile
(USM)
12. Finely focussed micro-machining possible.
(EDM,LBM, EBM)
13. Micro-hole drilling at shallow entrance angles possible.
(EDM,ECM, LBM, EBM)
14. Easy compatibility with numerical control and mìni computer controls.
(ECM, EDM, LBM, EBM)
(.6 Unconventional Machining Processes (UMP)
1.7 DISADVANTAGES OF UNCONVENTIONAL MACHINING PROCESSES
Limitations of Non-Traditional Machining Processes:
(1) workpiece and tool must be electrically conductive (e.g., EDM, ECM)
(2) the depth of cut islimited (e.g., LBM)
(3) recast or heat affected zones (HAZ)or surfaces produced
may be troublesome.
the compatibility of the process
(e.g., EDM, LBM, EBM); For this purpose
material can be studied before
with the metallurgical state of the workpiece
process for production work.
using a particular non traditional machining
or cavities (e.g., EDM, LBM)
(4) there may be taper in the sidewalls of holes
and controlled, so that the advantages
Most of these limitations can be overcome
assurance.
can be obtained with good product quality
OF UNCONVENTIONAL MACHINING PROCESSES
1.8 APPLICATIONS
super alloys and
1. AJM (Abrasive Jet Machining) is suitable for machining for
and glass. AJM can also be used
refractory materials such as ceramics
machining plastics.
for refractory
2. USM (Ultrasonicmachining) has good machining performance be used for
and glass, USM can also
type materials such as ceramics
machining plastics.
machining steel and super
3. ECM (Electrochemical machining) is used for materials like
alloys,ECM cannot be used for machining non conducting
ceramics,plastics and glass.
for machining steel, super
4 EDM (Electrical discharge machining) is usedcannot be used for machining
materials. EDM
alloys, titanium and refractory
as ceramics,plastics and glass.
non conducting materials such
refractory
5 EBM (Electron beam machining) is most suitable for machining
and has a medium performance on glass and
plastics.
materials.
any substance and is suitable
LBM (Laser beam machining) can machine
and has a medium performance
6
for refractorymnaterials such as ceramics
on glass and plastics. steel
for machining aluminium,
7. PAM (Plasmaarc machining) is suitable machining ceramics and glass.
PAM is not suitable for
and super alloys.
