chapter 2 literature review -...
TRANSCRIPT
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CHAPTER 2
LITERATURE REVIEW
2.1 INTRODUCTION
In the early stages of mankind, tools were made of stone. When
iron tools were invented, desirable metals and more sophisticated articles
could be produced. In the twentieth century products were made from the
most durable and consequently, the most unmachinable materials. In an effort
to meet the manufacturing challenges created by these materials, tools have
now evolved to include materials such as alloy steel, carbide, diamond, and
ceramics (Benedict 1986).
Since the 1940s, a revolution in manufacturing has been taking
place that once again allowed manufacturers to meet the demands imposed by
increasingly sophisticated designs and durability; but in many cases they were
nearly unmachineable materials. This manufacturing revolution is now, as it
has been in the past, centered on the use of new tools and new forms of
energy (Weller 1983). This has resulted in the introduction of new
manufacturing processes used for material removal known today as Non-
Traditional Machining Processes (NTMPs).
2.2 REVIEW OF LITERATURE ON NON-TRADITIONAL
MACHINING PROCESSES
The NTMPs may be classified on the basis of the type of energy,
namely, mechanical, electrical, chemical, thermal, or magnetic, applied to the
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work piece directly and have the desired shape transformation or material
removal from the work surface by using different scientific mechanism. Thus,
the NTMPs can be classified into various groups according to the basic requirements which are as follows (Springborn 1967, Bellows 1976):
1. Type of energy required, namely, mechanical, electrical, and
chemical etc.
2. Basic mechanism involved in the processes, such as erosion,
ionic dissolution, vaporization, etc.
3. Source of immediate energy required for material removal,
namely, hydrostatic pressure, high current density, high
voltage, ionized material, etc.
4. Medium for transfer of those energies such as high velocity particles, electrolyte, electron, hot gases, etc.
On the basis of above requirements, the various NTMPs may be
classified as shown in Table 2.1.
2.2.1 Comparative Analysis of Non-Traditional Machining Processes
A particular Non-Traditional Machining Process (NTMP) found
suitable under the given conditions may not be equally efficient under other
conditions. Therefore, a careful selection of the process for a given machining
problem is essential. The analysis of NTMPs can be made from the point of
view of the following (Singh 2007):
1. Physical parameters involved in the processes.
2. Capability of machining different shapes of work material.
3. Applicability of different processes to various types of
materials, e.g. metals, alloys, and non-metals.
4. Operational characteristics of NTMPs, and Economics
involved in the various processes.
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Physical Parameters
The physical parameters of NTMPs have a direct impact on the
metal removal as well as on the energy consumed in different processes and it
is shown in Table 2.2.
Capability to Shape
The capability of different processes can be analysed on the basis of
various machining operation point of view such as micro-drilling, drilling,
cavity sinking, pocketing (shallow and deep), contouring a surface, and
through cutting (shallow and deep). The shape application of various NTMPs
is shown in Table 2.3.
For micro-drilling operation, the only process which has good
capability to drill is LBM, whereas for drilling shapes having slenderness
ratio, L/D< 20, the process USM, ECM, and EDM will be most suitable.
EDM and ECM processes have good capacity to make pocketing operation
(shallow and deep). For surface contouring operation, ECM is most suitable
but other processes except EDM have no application for this operation.
Applicability to Materials
Material applications of the various NTMPs are summarized in
Tables 2.4 and 2.5 for metals and alloys and non-metals respectively. For the
machining of electrically non-conducting materials, both ECM and EDM are
unsuitable, whereas the mechanical methods can achieve the desired result.
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Table 2.1 Classification of NTMPs (Singh 2007)
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Table 2.2 Physical parameters of NTMPs (Singh 2007)
Parameters USM AJM ECM CHM EDM EBM LBM PAM
Potential (V) 220 220 10 - 45 1,50,000 4,500 100
Current (Amp)
12 (AC) 1.0 10,000 (D.C) - 50 (Pulsed D.C) 0.001 (Pulsed
D.C)
2 (Average) 200 (Peak)
500 (D.C)
Power (W) 2,400 220 1,00,000 - 2,700 150 - 50,000
Gap (mm) 0.25 0.75 0.20 - 0.025 100 150 7.5
Medium Abrasive in water
Abrasive in gas
Electrolyte Liquid chemical
Liquid dielectric Vacuum Air Argon or Hydrogen
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Table 2.3 Shape Application of NTMPs (Mishra 1997)
Holes Through cavities Surfacing Through cutting
Process Precision small holes Standard Precision Standard
Double contouring
Surface of revolution
Shallow Deep
Dia <.025 mm
Dia >.025 mm
L/D <20
L/D >20
USM - - good poor good good poor - poor -
AJM - - fair poor poor fair - - good -
ECM - - good good fair good good fair good good
CHM fair fair - - poor fair - - good -
EDM - - good fair good good fair - poor -
EBM good good fair poor poor poor - - - -
LBM good good fair poor poor poor - - good fair
PAM - - fair - poor poor - poor good good
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Table 2.4 Material Applications for Metals and Alloys (Cogun 1994)
Process Aluminium Steel Super alloy Titanium
Refractory Material
USM poor fair poor fair good
AJM fair fair good fair good
ECM fair good good fair fair
CHM good good fair fair poor
EDM fair good good good good
EBM fair fair fair fair good
LBM fair fair fair fair poor
PAM good good good fair poor
Table 2.5 Material Applications for Non-metals (Cogun 1994)
Process Ceramics Plastic Glass USM good fair good AJM good fair good ECM NA NA NA CHM poor poor fair EDM NA NA NA EBM good fair fair LBM good fair fair PAM NA NA NA
NA – Not Applicable
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Machining Characteristics
The machining characteristics of different NTMPs can be analysed
with respect to:
1. Metal removal rate (MRR),
2. Tolerance maintained,
3. Surface finish obtained,
4. Depth of surface damage, and
5. Power required for machining.
The metal removal rates by ECM and PAM are respectively one-
fourth and 1.25 times that of conventional rates whereas others are only a
small fraction of it. Power requirement of ECM and PAM is also very high
when compared with other NTMPs. The surface finish and tolerance obtained
by various NTMPs except that of PAM is satisfactory. The process
capabilities of various NTMPs are summarized in Table 2.6 (El Hofy 2005).
Table 2.6 Process Capabilities of NTMPs (El Hofy 2005)
Process MRR
(mm3/min) Tolerance
(µm)
Surface finish (µm)
Depth of surface damage
(µm)
Power (watts)
USM 300 7.5 0.2 – 0.5 25 2,400 AJM 0.8 50 0.5 – 1.2 2.5 250 ECM 15,000 50 0.1 – 2.5 5.0 1,00,000 CHM 15 50 0.5 – 2.5 50 - EDM 800 15 0.2 – 1.2 125 2,700 EBM 1.6 25 0.5 – 2.5 250 150(average)
2,000 (peak) LBM 0.1 25 0.5 – 1.2 125 2 (average) PAM 75,000 125 Rough 500 50,000
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Economics of the Non-Traditional Machining Processes
The economics of the various NTMPs are analyzed on the basis of
the following factors and is given in Table 2.7:
1. Capital cost,
2. Tooling cost,
3. Power consumption cost,
4. Material removal rate efficiency, and
5. Tool wear.
Table 2.7 Economics of the various NTMPs (Yurdakul et al 2003)
Process Capital
cost Tooling
cost
Power consumption
cost
Material removal rate
efficiency
Tool wear
USM low low low high medium
AJM very low low low high low
ECM very high medium medium low very low
CHM medium low high* medium very low
EDM medium high low high high
EBM high low low very high very low
LBM low low very low very high very low
PAM very low low very low very low very low * indicates cost of chemicals
The capital cost of ECM is very high, whereas capital costs for
AJM and PAM are comparatively low. EDM has got higher tooling cost than
other machining processes. Power consumption is very low for PAM and
LBM processes, whereas it is greater in the case of ECM. The material
removal rate efficiency is very high for EBM and LBM than for other
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processes. In conclusion, the suitability of application of any of the processes
is dependent on various factors and must be considered, all or some of them,
before selecting any NTMPs.
2.3 OVERVIEW OF NON-TRADITIONAL AND HYBRID NON-
TRADITIONAL MACHINING PROCESSES
Non-Traditional Machining Processes (NTMPs) are defined as a
group of processes that remove excess material by various techniques
involving mechanical, thermal, electrical or chemical energy, or combinations
of these energies but do not use sharp cutting tools as it needs to be used for
traditional machining processes (Bhattacharya 1973). Extremely hard and
brittle materials are difficult to machine by traditional machining processes
such as turning, drilling, shaping, and milling. NTMPs are employed where
traditional machining processes are not feasible, satisfactory, or economical
due to special reasons as outlined below (Kalpakjian et al 2006):
1. Machinability of workpiece material,
2. Workpiece shape complexity,
3. Automation of data communication,
4. Surface integrity and precision requirements, and
5. Miniaturization requirements.
The various techniques may be conveniently classified according to
the appearance of the applied energy, as shown in Figure 2.1 (Snoeys et al
1986).
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Figure 2.1 Models of various NTMPs (Snoeys et al 1986)
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2.3.1 Machinability
In modern manufacturing practice a more frequent use of harder,
tougher or stronger workpiece materials is noticed: Materials, in other words,
which are much more difficult to machine with traditional methods.
Reference is made to all kinds of high strength thermal resistant alloys, to
various kinds of carbides; fiber reinforced composite materials, stellites,
ceramic materials, various modern composite tool materials etc. The
introduction of new ways of machining is stimulated because of the high force
levels observed. In some particular cases, those levels may simply not be
sustained by the workpiece. Therefore, more attention is directed towards
machining processes in which mechanical properties of the workpiece
(mechanical strength, hardness, toughness etc.) are not imposing any limits. In
electro-physical processes the ‘cutability’ limits are indeed more associated
with material properties such as thermal conductivity, melting temperature,
electrical resistivity, and atomic valence (Snoeys et al 1986).
2.3.2 Shape Complexity
Geometrical restrictions, design requirements, problems related to
accessibility during machining or what could be conveniently defined as
'shape complexity', states another group of reasons for an increased interest in
using one of the more recent material removal processes. To give a rather
simple example: it is quite easy to drill a circular hole with conventional
techniques, however, to drill a square hole or just any other shape would be
impossible. For EDM or ECM on the contrary, the cross sectional shape of
the hole is of little concern. To cut some pattern of grooves with a depth of a
few microns would be a difficult task in conventional machining. A CHM
operation using some kind of masking procedure could yield a simple solution
(Snoeys et al 1986).
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2.3.3 Automated Data Transmission
In mechanical production, the automation of communication is
crucial. If the information flow is more automated, a considerable reduction
of the throughput time can be achieved, yielding decreased production cost,
reduced inventory etc. This aspect has been one of the reasons of the
considerable success of the introduction of Numerically Controlled (NC)
machines and later of Computer Aided Design (CAD), Computer Aided
Manufacturing (CAM), and Computer Integrated Manufacturing (CIM).
Those techniques may in some cases be integrated much easier with some
NTMPs. EDM and Wire Electric Discharge Machining (WEDM) are obvious
examples. Also NC Laser or electron beam cutting are applied partially
because of the improved automation in data transmission. There are many
other types of applications in which the use of NTMPs drastically reduced the
number of successive elementary machine jobs. A die plate made of carbides
for example, could be machined out of one piece using spark erosion; the
classical way would require atleast two pieces fitted together and produced
separately on a profile grinder (Snoeys et al 1986).
2.3.4 Precision Requirements
The trend of precision requirement as indicated by Taniguchi
(1983) refers to nano-machining in tomorrow's ultra high precision
machining. This kind of precision may be obtained by removing atoms or
molecules, rather than chips. Machining operations like sputtering IBM etc.
would be possible candidates. The distortion of the surface layer due to
mechanical or thermal action may be another reason to call upon some of the
same NTMPs.
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2.3.5 Miniaturisation
Trends toward reducing the workpiece dimensions already exist for
some time. Ultra small diameter holes (10 – 100 µm) would not be possible to
drill with conventional techniques. EDM, LBM, EBM or even Micro Electro
chemical Machining (Micro-ECM) techniques are now frequently applied for
such purposes. Micromachining has recently become an important issue,
further reducing possible attainable workpiece dimensions. Various
techniques developed for the production of micro electronic circuitry may be
used for manufacturing extremely small items. Especially in the area of
sensors, an integration of mechanical parts with the electronic circuitry may
become a new possibility bringing the design and production of various
sensors on the verge of drastic cost reductions.Several types of NTMPs have
been developed to meet a wide range of machining requirements. When these
processes are employed properly, they offer many advantages over traditional
machining processes. The most common NTMPs and selected Hybrid NTMPs
(HNTMPs) are described in this section (Snoeys et al 1986). The Surface
Roughness and Tolerance of various machining processes are shown in Figure
2.2(a) and (b) respectively.
2.3.6 Ultrasonic Machining
Ultrasonic Machining (USM) is a mechanical material removal
process or an abrasive process used to erode holes or cavities on hard or
brittle work piece by using shaped tools, high frequency mechanical motion,
and an abrasive slurry. USM offers a solution to the expanding need for
machining brittle materials such as single crystals, glasses and polycrystalline
ceramics, and increasing complex operations to provide intricate shapes and
work piece profiles. It is therefore used extensively in machining hard and
brittle materials that are difficult to machine by traditional manufacturing
processes (Kramer et al 1981). The hard particles in slurry are accelerated
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(a) (b)
Figure 2.2 (a) Surface Roughness and (b) Tolerance of various machining processes (Mishra 1997)
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towards the surface of the work piece by a tool oscillating at a frequency up to
100 kHz - through repeated abrasions, the tool machines a cavity of a cross-
section identical to its own (Groover 2002 , Kramer et al 1981). A schematic
representation of USM is shown in Figure 2.3.
Figure 2.3 Schematic representation of Ultrasonic Machining (Groover
2002)
2.3.7 Water Jet Machining
Water Jet Machining (WJM) uses the principle of pressurizing
water to extremely high pressures and allowing the water to escape through a
very small opening called ‘orifice’ or ‘jewel’. WJM uses the beam of water
exiting the orifice to cut soft materials. This method is not suitable for cutting
hard materials. The inlet water is typically pressurized between 1,300 and
4,000 bars. This high pressure is forced through a tiny hole in the jewel,
which is typically 0.18 to 0.4 mm in diameter. A picture of WJM is shown in
Figure 2.4. WJM can reduce the costs and speed up the processes by
eliminating or reducing expensive secondary machining process. Since no
heat is applied on the materials, cut edges appear clean with minimal burr.
Problems such as cracked edge defects, crystallisation, hardening, reduced
weld ability, and machinability are reduced in this process (Koenig et al 1985,
Ramesh Babu et al 2005, 2006).
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Figure 2.4 Basic scheme of WJM (Koenig et al 1985)
2.3.8 Abrasive Jet Machining
In Abrasive Jet Machining (AJM), the workpiece material is
removed by mechanical impact of a high velocity air jet with abrasive
particles. Figure 2.5 shows a schematic representation of the process. AJM is
a rather slow process (10 mg/min); however, it is quite cheap, forces on the
workpiece are limited and no thermal problems occur because of the cooling
effect of the expanding air. Most often, aluminium oxide or silicon carbide
powders are used as abrasive medium. Close control of the abrasive jet
process is possible. Nozzles are made of tungsten carbide or synthetic
sapphire, with circular openings from 0.15 to 2 mm diameter. The main
parameters influencing the material removal rate and surface quality are air
pressure, size of the abrasive particles (60 µm), spray angle, tool to work
distance (2 – 15 mm) and feed rate (0.2 mm/s). Another kind of AJM is
Abrasive Flow Machining (AFM). It is a finish machining process in which a
special abrasive-filled semi-solid plastic medium is flowed through and across
workpiece areas to produce a range of edge and surface conditioning effects
(Venkatesh 1984).
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Figure 2.5 Schematic representation of AJM (Venkatesh 1984)
2.3.9 Electrical Discharge Machining
Electrical Discharge Machining (EDM) is one of the most widely
used NTMPs. The main attraction of EDM over traditional machining
processes such as metal cutting using different tools and grinding is that this
technique utilizes thermoelectric process to erode undesired materials from
the workpiece by a series of discrete electrical sparks between the workpiece
and the electrode. A picture of EDM machine in operation is shown in
Figure 2.6. The traditional machining processes rely on harder tool or
abrasive material to remove the softer material, whereas NTMPs such as
EDM uses electrical spark or thermal energy to erode unwanted material in
order to create desired shape. So, the hardness of the material is no longer a
dominating factor for EDM process (Ghosh et al 1985).
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Figure 2.6 Electrical Discharge Machine in action (Mitsubishi 2008)
2.3.10 Wire Electrical Discharge Machining
Electrical Discharge Machining primarily, exists commercially in
the form of die-sinking machines and wire-cutting machines. In Wire
Electrical Discharge Machining (WEDM), a slowly moving wire travels along
a prescribed path and removes material from the work-piece. A WEDM
machine in action is shown in Figure 2.7. WEDM uses electro-thermal
mechanisms to cut electrically conductive materials. The material is removed
by a series of discrete discharges between the wire electrode and the
workpiece in the presence of dielectric fluid, which creates a path for each
discharge as the fluid becomes ionized in the gap. The area where discharge
takes place is heated to extremely high temperature, so that the surface is
melted and removed. The removed particles are flushed away by the flowing
dielectric fluids. The WEDM process can cut intricate components for the
electric and aerospace industries. WEDM is widely used to pattern tool steel
for die manufacturing.
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Figure 2.7 Schematic of a WEDM machine in action (Mitsubishi 2008)
2.3.11 Electrochemical Machining
Electrochemical machining (ECM) is a metal removal process
based on the principle of reverse electroplating. In this process, particles
travel from the anodic material (workpiece) towards the cathodic material
(machining tool). A current of electrolyte fluid carries away the deplated
material before it has a chance to reach the machining tool. The cavity
produced is the female mating image of the tool shape. A schematic
representation of ECM process is shown in Figure 2.8. Similar to EDM, the
workpiece hardness is not a factor, making ECM suitable for machining
difficult-to-machine materials. Difficult shapes can be made by this process
on materials regardless of their hardness. The ECM tool is positioned very
close to the workpiece and a low voltage, high amperage direct current (DC)
is passed between the workpiece and electrode.
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Figure 2.8 Schematic of ECM process (McGeough 1974)
2.3.12 Laser Beam Machining
Laser Beam Machining (LBM) is a thermal material removal
process that utilizes a high-energy, coherent light beam to melt and vaporize
particles on the surface of metallic and non-metallic workpieces (Orazia
1998). Lasers can be used to cut, drill, weld, and mark. LBM is particularly
suitable for making accurately placed holes. LBM can make very accurate
holes as small as 0.005 mm in refractory metals ceramics, and composite
material without warping the work-pieces. This process is used widely for
drilling and cutting of metallic and non-metallic materials. LBM is being used
extensively in the electronic and automotive industries (William et al 1994,
Bellows et al 1982). An LBM machine in action is shown in Figure 2.9. A
champion cut test specimen with cycle time 36 seconds which is used to
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check the overall performance of a Laser Beam Machine is shown in
Figure 2.10.
Figure 2.9 An LBM machine in action (Mitsubishi 2008)
Figure 2.10 The Champion cut test specimen made using LBM with
cycle time 36 seconds (Mitsubishi 2008)
2.3.13 Chemical Machining
Chemical Machining (CHM) is the controlled chemical dissolution
of the machined work piece material by contact with a strong acidic or
alkaline chemical reagent. Special coatings called maskants protect areas from
which the metal is not to be removed. The process is used to produce pockets
and contours and to remove materials from parts having a high strength-to-
weight ratio. Moreover, the machining method is widely used to produce
micro-components for various industrial applications such as micro-electro
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mechanical systems (MEMS) and semiconductor industries (Dini 1984, El
Hofy 2005).
In CHM, material is removed from selected areas of workpiece by
immersing it in chemical reagents or etchants; such as acids and alkaline
solutions. Material is removed by microscopic electro-chemical cell action, as
occurs in corrosion or chemical dissolution of a metal. This controlled
chemical dissolution will simultaneously etch all exposed surfaces even
though the penetration rates of the material removal may be only 0.0025–
0.1 mm/min. The basic process takes many forms: chemical milling of
pockets, contours, overall metal removal, chemical blanking for etching
through thin sheets; Photo Chemical Machining (PCM) for etching by using
photosensitive resists in microelectronics; Chemical or Electrochemical
Polishing (ECP) where weak chemical reagents are used for polishing or
deburring and Chemical Jet Machining (CJM) where a single chemically
active jet is used (Mcgeough 1988, Cakir et al 2007).
2.3.14 Electron Beam Machining
In Electron Beam Machining (EBM), electrons are accelerated to a
velocity nearly three-fourths of that of light (~ 2, 00,000 km/sec). The process
is performed in a vacuum chamber to reduce the scattering of electrons by gas
molecules in the atmosphere (Figure 2.11). The electron beam is aimed using
magnets to deflect the stream of electrons and is focussed using an
electromagnetic lens. The stream of electrons is directed against a precisely
limited area of the work piece; on impact, the kinetic energy of the electrons
is converted into thermal energy that melts and vaporizes the material to be
removed, forming holes or cuts (Siegfried 1982).
Typical applications of EBM are annealing, welding, and metal
removal. A hole in a sheet of 1.25 mm thick up to 125 µm diameter can be cut
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almost instantly with a taper of 2 to 4º. An EBM equipment shown in
Figure 2.11 is commonly used by the electronics industry to aid in the etching
of circuits in microprocessors. The main advantages of the process are high
degree of automation, high productivity, possibility to machine almost any
material and attainable high precision (Gettelman 1983).
Figure 2.11 An Electron Beam Processing Equipment (Taniguchi 1984)
2.3.15 Ion Beam Machining
In simple terms, Ion Beam Machining (IBM) can be viewed as an atomic sand blaster. The grains of sand are actually submicron ion particles
accelerated to bombard the surface of the work mounted on a rotating table
inside a vacuum chamber. The work is typically a wafer, substrate or element that requires material removal by atomic sandblasting or dry etching. A
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selectively applied protectant, photo-sensitive resist, is applied to the work element prior to introduction into the ion miller. The resist protects the
underlying material during the etching process which may be up to eight
hours or longer, depending on the amount to be removed and the etch rate of the materials. Everything that is exposed to the collimated ion beam etches
during the process cycle, even the resist. In most micromachining
applications, the desired material to be removed etches at a rate 3 to 10 times faster than the resist protectant thus preserving the material and features
underneath the resist. A high frequency plasma type sputter IBM equipment is shown in Figure 2.12 (Jolly et al 1983, Taniguchi 1984).
Figure 2.12 A high frequency Plasma type sputter IBM equipment
(Taniguchi 1984)
2.3.16 Plasma Arc Machining
Plasma Arc Machining (PAM) employs a high-velocity jet of high-
temperature gas to melt and displace material in its path. PAM is a method of
cutting metal with a plasma-arc, or tungsten inert-gas-arc torch. The torch
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produces a high-velocity jet of high-temperature ionized gas called plasma
that cuts by melting and removing material from the work piece (Esibyan
1973). Temperatures in the plasma zone range from 11,000 to 28,000°C.
PAM is used as an alternative to oxyfuel-gas cutting, employing an electric
arc at very high temperatures to melt and vaporize the metal. The plasma arc
beam (used for conductive material) and plasma jet beam (used for non-
conductive material) are shown in Figure 2.13(a) and (b) respectively
Figure 2.13 Plasma Beam Sources (a) Plasma Arc Beam and (b) Plasma
Jet Beam (Taniguchi 1984)
The materials cut by PAM are generally those that are difficult to
cut by any other means, such as stainless steels and aluminium alloys. It has
an accuracy of about 0.025 mm (Drozda 1983).
2.3.17 Hybrid Non-Traditional Machining Processes
With the demand for stringent technological and functional
requirements of the parts from the micro- to nanometre range, ultra-precision
finishing processes have evolved to meet the needs of the manufacturing
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scientists and engineers. The traditional finishing processes of this category
have various limitations, for example, complex shapes, miniature sizes, and
three-dimensional (3D) parts cannot be processed or finished economically
and rapidly by traditional machining finishing processes. This led to the
development of advanced finishing techniques, namely Abrasive Flow
Machining (AFM), Magnetic Abrasive Finishing (MAF), Magnetic Float
Polishing (MFP), Magneto Rheological Abrasive Finishing (MRAF) and Ion
Beam Machining (IBM). In all these processes, except IBM, abrasion of the
work piece takes place in a controlled fashion such that the depth of
penetration in the work piece is a small fraction of a micrometer so that the
final finish approaches the nano-range.
To enhance the performance of some thermal erosion process
(El Hofy 2005) a secondary erosion process can be added such as ECM+EDM
erosion to form Electrochemical Discharge Machining (ECDM). In other
situations mechanical erosion is combined to form Abrasive Electrical
Discharge Grinding (AEDG), or EDM is combined to grinding and ECM to
form Electrochemical Discharge Grinding (ECDG). Electrochemical erosion
can also be enhanced by combining with mechanical abrasion during Electro
chemical Grinding (ECG) or Ultrasonic erosion during ultrasonic assisted
ECM.
There are generally two categories of Hybrid Non-Traditional
Machining Processes (HNTMPs): Processes in which all constituent processes
are directly involved in the material removal, Processes in which only one of
the participating processes directly removes the material while the others only
assist in removal by changing the conditions of machining in a “positive”
direction from the point of view of improving capabilities of machining. In
both of these categories thermal, chemical, electro-chemical and mechanical
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interactions occur. A brief description of these interactions is given below
(Kozak et al 2000).
Thermal Interaction
Laser beam treatment (LBT), Laser beam welding (LBW) and
LBM, EBM, EDM, and PAM are thermal processes where material is
removed through a phase change, either by melting or vaporization.
Additionally, many secondary phenomena relating to surface quality which
occur during machining, such as micro-cracking, formation of heat-affected
zone and formation of striations, can also be related to the thermal effect of
the laser or electron beam or electrical discharges (Kozak et al 2000).
Chemical and electro-chemical interaction
Chemical milling (CM), Chemical etching (CHe), ECM, Pulse
Electrochemical Machining (PECM), Electropolishig (EP) are shaping and
finishing processes based on application of dissolution of material.CM is the
selective and controlled metal removal process by chemical action. It is
especially useful for removing metal from sheet components to reduce
weight, and it can be employed after parts have been formed and heat-treated.
Any metal that can be chemically dissolved in solution can be chemically
milled. Electrochemical shaping and finishing is based on controlled anodic
electrochemical dissolution process of the work piece (anode) with a cathode
tool in an electrolytic cell. Being a non-mechanical metal removal process,
ECM is capable of machining any electrically conductive material with high
stock removal rates regardless of their mechanical properties, such as
hardness, elasticity and brittleness (Kozak et al 2000).
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Mechanical interaction
Mechanical interaction with work piece material can change
conditions of the anodic dissolution process. Here, the main factor is
mechanical depassivation of the surface, by removing thin layers of oxides
and other compounds from anode, which makes surface dissolution and
smoothing process more intensive. The mechano-chemical effect, that is
present in micro-cutting process, consists of changes in chemical potential at
places where dislocations occur, and result in plastic deformations, that are
caused by mechanical action of the abrasive grains. As a result of the above
phenomena, both electrochemical heterogeneity of material and
electrochemical reaction rate increase. The material heterogeneity increases
residual stresses that are produced during micro-cutting, in particular when
machining metal-matrix composites, which influence the electrical potential
of individual phases of material structure. For example, in machining tungsten
carbides blank, the differences in electric potentials between metallic matrix
and carbides increase, and it results in an increase of dissolution rate. The
above brief description of main interactions shows the importance of
combining different machining methods based on different kind of
interactions for improving manufacturing characteristics of shaping and
finishing processes. Figure 2.14 shows the scheme for combination of
machining methods. The major cross/hybrid machining processes under
development are:
Abrasive Electrochemical Grinding (AECG)
Abrasive Electrochemical Honing (AECH)
Electrochemical Arc Machining (ECAM)
Electrochemical Discharge Machining (ECDM)
Abrasive Electrical Discharge Grinding (AEDG)
Abrasive Electrical Discharge Machining (Sinking) (AEDM)
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Magnetic Abrasive Finishing (MAF)
Ultrasonic Machining with Electrochemical assistance
(USMEC)
Ultrasonic Assistance Electrical Discharge Machining
(UAEDM)
Laser Assistance Turning (LAT)
Plasma Assistance Turning (PAT)
Laser assistance Electrochemical Machining (LECM)
Laser Assistance Etching (LAE), and
Mechano-Chemical Polishing (MCP), etc.
Electrical Hybrid Machining Processes
The most important electrical hybrid machining processes are:
1. Electrochemical Discharge Machining (ECDM)
2. Electrochemical Arc Machining (ECAM)
3. Electrical Discharge Machining with Ultrasonic Assistance
(EDMUS)
ECDM using pulse voltage and ECAM using constant or pulse voltage is the
combined methods of machining involving ECM and EDM.
ECM is characterized by high surface integrity, improved surface
finish, high machining rate, and the absence of tool-electrode wear. But as
compared with EDM, it has low accuracy of reproduction of the tool electrode
shape into the work piece. EDM can provide a high surface finish only with a
low productivity. An increase in the EDM rate results in a significantly higher
roughness and deeper damaged surface layer. However, a reduction in surface
roughness leads to increase in the tool electrode wear. ECDM, a combination
of ECM with EDM in one process in an electrolyte solution has shown to
35
contain the benefits of both processes, provided that the parameters of the
combined process are properly selected.
ED - electro discharge; LB - laser beam; EB - electron beam; PB - plasma
beam; CH - chemical; EC - electro chemical; A - abrasive; T - turning;
US -ultrasonic; F - flow.
Figure 2.14 Scheme for combinations of machining methods (Kozak
et al 2000)
In ultrasonically assisted EDM, it is recognised that the role of the
acoustic wave and cavitations phenomena is to improve the flushing and
material removal from the surface craters. These process conditions are
significant for micro drilling and production of slots and grooves. The
vibrating movement of the tool electrode or the work piece improves the
slurry circulation and the pumping action, by pushing the debris away and
sucking new fresh dielectric and which provides ideal condition for
discharges, their efficiency and gives higher metal removal rate. The second
beneficial effect that has been observed concerns structure modifications. The
alternate motion of the tool electrode/work piece with a high frequency due to
36
ultrasonic motion creates more turbulence and cavitations, and therefore
results in a better ejection of the molten metal from craters. This of course
increases the metal removal rate, but also lets less liquid material recast on the
surface. Thus, structure modifications are minimized, less micro-cracks are
observed, and fatigue life is increased (Kramer et al 1989).
Abrasive Hybrid Machining Processes
Abrasive Hybrid Machining (AHMPs) processes are the most
commonly used in industry. These can be classified in four main subgroups:
1. Abrasive Electrical Discharge Machining (AEDM),
2. Abrasive Electrochemical Machining (AECM), and
3. Abrasive Electro-Chemical-Discharge Machining (AECDM).
Essential conditions, under which any machining process is
performed, are type of the tool and movements of the tool in relation to the
work piece. The main type of tools are metallic electrodes containing abrasive
grains, i.e. grinding wheels or abrasive sticks with metallic bond, metallic
electrodes and free abrasive grit, and tools composed of abrasive segments
and segmented metallic electrodes. Depending on type of tool and working
movements, that are used in particular process, there are various methods as
shown in Figure 2.15 (Kozak et al 2001).
Abrasive Electrochemical Grinding (AECG), Abrasive Discharge
Grinding (AEDG), and Electrochemical Honing (ECH) use abrasive tool with
metallic bond. Abrasive Electrochemical Finishing (AECF), Abrasive
Electrical Discharge Finishing (AEDF), and Ultrasonic Electrochemical
Machining (USECM) use free abrasive grains (Kozak et al 2001).
37
(A – abrasive, D – dielectric, E – electrolyte)
Figure 2.15 Schematic diagrams of selected methods of Abrasive
Electrical Machining (Kozak et al 2001)
2.4 COMPUTER AIDED SELECTION OF NON-TRADITIONAL
MACHINING PROCESSES
To make efficient use of NTMPs, it is necessary to know the exact
nature of the machining problem. It is also understood that these methods
cannot replace the conventional machining processes and a particular
machining method found suitable under given conditions may not be equally
efficient under other conditions. Therefore, careful selection of the process for
a given problem is essential. Experienced design engineers make correct
decisions regarding processes almost instinctively, in particular when they are
dealing in areas of mature technology with which they are familiar. However,
as the rate of technological change continues to increase and become more
specialized, less experienced engineers become involved in design, and there
is a growing need for systems (in the form of interactive computer programs)
to aid the design engineer in making decisions regarding the selection of
appropriate NTMPs.
A number of selection procedures for the selection of conventional
machining process are already in existence (Dieter 1989). Most of them are
38
simple proprietary guidelines to aid customers in making a selection from a
company’s product line (General Electric Company 1970). A major
deficiency in most of the systems is that they assume that the material
processing method or part geometry is already fixed. Many selection
procedures are limited in their scope (Niebel 1966). Another problem with
many systems is that they are not organized in such a way so as to be
adaptable to computer processing (Kusy 1976). A more extensive review of
material and conventional process selection systems is done by Paremeshwar
(1980) and Dargie (1980).
Ebeid (1986) and Chetty et al (1988) present typical computerized
machinability database systems for electro chemical drilling and electro-
chemical machining (die sinking) processes, respectively. Alder et al (1986)
outline the background and some of the problems associated with the
selection of conventional and non-conventional machining processes. A range
of material types to achieve a given task by an expert system is also
examined. In their work, two small demonstration expert systems are
described for selection of conventional machining processes and the need for
a more comprehensive and detailed study on the selection of NTMPs is
emphasized.
Cogun (1993) developed a computer aided system for the selection
of NTMPs. In his work the important characteristics are expressed by means
of a 16-digits classification code in which different positions relate to
different characteristics of the part. For example, the first two digits are an
indication of part material, the second an indication of surface finish, and so
on. The selection of NTMPs is made by a computer program which can
interactively generate the limiting requirement code and used it to eliminate
processes progressively from consideration. The flow chart for the program
presented by Cogun (1993) is shown in Figure 2.16. The elimination scheme
39
uses data bases which relate the NTMPs to the 16 digit code. The data bases
contain information which relate the NTMPs to the coded ranges and
divisions of the limiting requirements of each. The data bases used in the
system deal with twelve processing methods and eight limiting requirements
as mentioned before. Only suitability matrices type of data bases are used.
The suitability matrices deal with suitability of processes in relation to the
characteristics expressed by the 16 digits of the part code used in the
elimination process. There is one matrix for each of eight characteristics
(limiting requirements). The column of these matrices correspond to the digit
Figure 2.16 Flow chart of the computer aided system for the selection of
NTMPs (Cogun 1993)
40
1 or 0 used to code the particular characteristic. The rows of the matrices
correspond to the NTMPs. The elements of the matrices are either 0
indicating unsuitability or 1 indicating suitability. A sample suitability data
base for surface finish (limiting requirement) proposed by Cogun (1993) is
given in Table 2.8.
Table 2.8 Sample suitability database for surface finish (Cogun 1993)
Process Codes
01 02 03 04 05 06 07 08 09 10 11 12 01 EDM 0 0 1 1 1 1 1 1 1 1 1 1 02 ECM 0 1 1 1 1 1 1 1 1 1 1 1 03 ECG 0 1 1 1 1 1 1 1 1 1 1 1 04 ECH 0 1 1 1 1 1 1 1 1 1 1 1 05 AJM 0 1 1 1 1 1 1 1 1 1 1 1 06 WJM 0 0 0 0 0 0 0 0 0 0 0 0 07 USM 0 1 1 1 1 1 1 1 1 1 1 1 08 CHM 0 0 0 0 1 1 1 1 1 1 1 1 09 LBM 0 0 0 1 1 1 1 1 1 1 1 1 10 PAM 0 0 0 0 0 0 0 0 0 1 1 1 11 EBM 0 0 0 0 0 0 0 0 0 1 1 1 12 WEDM 0 0 1 1 1 1 1 1 1 1 1 1
The digits in the right-hand columns are used to indicate whether the
process can be used or not. The data bases developed by Cogun (1993) are
prepared by using Data Base 4 package. From the main menu of the software
developed by Cogun (1993), two selections are possible, namely, utility menu
and process selection. The utility menu provides entering, adding, updating
and deleting of information related to processes, codes, coded data ranges of
limiting requirements and elements of matrices. When the process selection
alternative is selected from the main menu, the part limiting requirements are
41
asked by the computer. The user generates the part code digits interactively or
enters them directly into the program. In the interactive code generation
mode, the program asks the inexperienced user, the numerical values of
limiting requirements and uses the answers to code the part. Then, the
suitability matrix (0 and 1 digits) appears on the screen for the related data
range code selected. If, there is no information available about some of
limiting requirements, then, digit zero is entered. For this limiting requirement
a zero suitability matrix (all the elements are zero) appears on the screen and
then the cursor moves to the next position (i.e. next limiting requirement).
When limiting requirements are entered, elements of each
suitability matrix (0 and 1digits) are summed up. One exception is in case of
unsuitability of material property. If one of the elements, of the material
suitability matrix is zero, then the weighted value for this particular process
will be zero automatically. The summation procedure is called grading and
the final sum value for each process is called ‘weighted value of the process’.
The process with the highest value indicates the best selection for the entered
limiting requirements. If there is more than one process with the same
weighted value, this indicates that some other features of the process, like
economical characteristics should be taken into consideration for suggesting
the best candidate process among these.
Vinod et al (1997) presented a simplified procedure for computer-
aided selection of NTMPs. In their work, the work material and some of the
process capabilities such as surface finish, tolerance, corner radii, taper, hole
diameter, maximum height to diameter ratio, and minimum width of cut were
included. Their work is not intended to make final selection of NTMPs, but
rather to provide a short list of alternatives which will contain the best
combinations.
42
2.4.1 Knowledge Base System for Process Selection
Automation of knowledge through a ‘knowledge-base system’ will
greatly enhance the decision-making process. The benefits of building a
knowledge-based system for selection of NTMPs can be summarized as
follows (Turban 1986, Sirletworakul et al 1993, and Darwish et al 1997):
1. Helping the design engineer in selecting a suitable NTMP for
the problems at hand.
2. Dealing with a large amount of data related to NTMPs and
responding quickly.
3. Standardizing the conclusion for a given set of data related to
NTMPs.
4. Allowing the problem-solving capability of several people to
be combined.
5. Capturing the scarce expertise on NTMPs and making it
available for effective use, and
6. Updating knowledge base for the selection of most suitable
NTMPs.
Analytic Hierarchy Process - based Expert System
Shankar et al (2005) suggest a methodology of using the Analytic-
Hierarchy Process (AHP) to develop an user-friendly expert system that
makes decisions based on various options as chosen by the end user, and
evaluates the comparison matrices of an unbalanced hierarchy. Shankar et al
(2005) mainly focuses on the selection of an NTMP under constrained
material and machining conditions. Based on the priority values for different
criteria and sub-criteria for a specific NTMP selection problem, as calculated
43
by the AHP, the preference index values for different alternatives are
determined (Saaty 1990).
The expert system proposed by Shankar et al (2005), helps to
compute the acceptability zone and acceptability index values, showing only
those NTMPs that are applicable for a given material and machining
condition and finally, the process with the highest acceptability index value is
selected to be the optimal choice. Figure 2.17 shows the hierarchical structure
developed by Shankar et al (2005), in which the first level has the goal of
selecting the optimal NTMP. The second level consists of five criteria, under
which there are further sub-criteria and sub-sub-criteria. The last level of the
hierarchy comprises of seven alternatives for the available NTMPs.The
method discussed by Shankar et al (2005) is not made user friendly and needs
technical knowledge of NTMPs in assigning the priority values for different
criteria and sub-criteria for a specific NTMP selection problem.
Quality Function Deployment - based Expert System
Selection of an optimal NTMP for generating a desired feature on a
given material requires the consideration of several factors among which the
type of work piece material and shape to be machined are the most significant
ones. Shankar et al (2007) presents a Quality Function Deployment (QFD)
based methodology to case out the procedure for optimal selection of NTMPs.
Shankar et al (2007) discusses the design of a QFD-based expert system that
can automate the decision-making process with the help of graphical user
interfaces and visual aids. This expert system employs the use of a House of
Quality (HOQ) matrix for comparison of the relevant product and process
characteristics. The weights obtained for various process characteristics are
utilized to estimate an overall score for each of the NTMPs. Finally, if some
of the NTMPs satisfy certain critical criteria, they are again compared with
44
each other on the basis of their overall scores and the process having the
maximum score is selected as the optimal choice.
Figure 2.17 Hierarchical structure of the NTMPs (Shankar et al 2005)
45
Multi-Attribute Selection Procedure - based Expert System
Yurdakul et al (2003) present a multi-attribute selection procedure
to help manufacturing personnel in determining suitable NTMPs for a given
application requirement. Their selection procedure first enables the user to
narrow down the list of NTMPs to a short list containing feasible processes.
Then, the procedure ranks the feasible NTMPs according to their suitability
for the desired application. In ranking the feasible alternatives, the selection
procedure uses a combination of two multi-attribute decision-making tools,
namely the AHP and the Technique for Order Preference by Similarity to Idea
Solution (TOPSIS). List of NTMPs and their process capability attributes
listed by them are shown in Table 2.9.
Table 2.9 List of NTMPs and their process capability attributes
(Yurdakul et al 2003)
NTMPs Process capability attributes 1. Abrasive jet machining (AJM) 1. Tolerance 2. Water jet machining (WJM) 2. Surface finish 3. Abrasive water jet machining (AWJM) 3. Surface damage 4. Abrasive flow machining (AFM) 4. Corner radii 5. Ultrasonic machining (USM) 5. Taper 6. Electrochemical machining (ECM) 6. Hole diameter 7. Electrochemical grinding (ECG) 7. Depth/diameter ratio (for
cylindrical holes) 8. Electrochemical honing (ECH) 8. Depth/width ratio (for blind
cavities) 9. Electrochemical discharge grinding
(ECDG) 9. Width of cut
10. Electrostream drilling (ESD) 10. Material removal rate 11. Shaped-tube electrolytic machining
(STEM)
12. Chemical machining (CHM) 13. Electrical discharge machining (EDM) 14. Wire electrical discharge machining
(WEDM)
15. Electrical discharge grinding (EDG) 16. Electron beam machining (EBM) 17. Laser beam machining (LBM) 18. Plasma arc cutting (PAC) 19. Thermal energy method (TEM)
46
The structure of the approach proposed by Yurdakul et al (2003)
enables the user to remove unsuitable NTMPs and obtain a narrowed down
list of NTMPs, and then to rank them according to their suitability for the
desired application. The structure of the selection procedure proposed by
Yurdakul et al (2003) is given in Figure 2.18. It is necessary to know the
nature of application to select the suitable NTMPs. A NTMP can be used very
efficiently for a particular application, but changes in the application type and
requirement attributes can reduce the efficiency significantly. Therefore, the
selection approach must start with a clear identification (description) of the
application by the design engineer. The user has to identify the desired
application in terms of work piece material, shape application and technical
(functional), cost and material removal rate requirements to initiate the
selection procedure. The drawbacks of the multi-attribute selection procedure
discussed by Yurdakul et al (2003) is that it is not made user friendly and
simple selection cannot be made with ease.
Decision Tree - based Expert System
Edison et al (2008a) present a knowledge base system for selection
of most suitable NTMPs. Figure 2.19 shows the logical flowchart of the
software developed by them. Knowledge representation deals with how to
store and process information or knowledge. The information required for
efficient and accurate process selection is organized as a decision tree
consisting of a hierarchical collection of decision nodes as shown in
Figure 2.20. In this system, a simple depth-first search algorithm is used to
traverse through the tree and browse the knowledge base. The association of a
condition with a node has been made optional to allow headings and
comments in tables. The two main data types that can be entered into this
knowledge base are numbers and strings. Conditional consideration of
processes for the process selection procedure is also possible.
47
Figure 2.18 Structure of the multi-attribute selection procedure for
NTMPs (Yurdakul et al 2003)
The factors can reside in independent, inclusive and mutually
exclusive pools to provide flexibility in analyzing the tables for process
selection. Each factor can be assigned a suitable weight depending on its level
of importance in the process selection procedure. Dynamic memory allocation
facilitates the tree to grow and shrink as and when necessary. Strongly
encapsulated user-defined objects and liberal use of standard template library
containers ensure the robustness and efficient functioning of the application.
A set of utility functions have been specially designed by Edison et al (2008a)
to support operations relevant to the management of knowledge base (Alfred
1983, Miller et al 1991 and Krishnamoorthy 1996).
48
Figure 2.19 Logical workflow of the expert system (Edison et al 2008a)
49
Figure 2.20 Decision tree (Edison et al 2008a)
50
A Digraph-based Expert System
Nilanjan et al (2008) presents a digraph-based approach to ease out
the appropriate NTMPs selection problem. It includes the design and
development of an expert system that can automate the decision-making
process with the help of graphical user interface and visual aids. The approach
proposed by Nilanjan et al (2008) employs the use of pair-wise comparison
matrices to calculate the relative importance of different attributes affecting
the NTMPs selection decision. Based on the characteristics and capabilities of
the available NTMPs to machine the required shape feature on a given work
material, the permanent values of the matrices related to those processes are
computed. Finally, if some of the NTMPs satisfy a certain threshold value,
those are short listed as the acceptable processes for the given shape feature
and work material combination. The digraph-based expert system not only
segregates the accepted NTMPs from the list of the available processes but
also ranks them in decreasing order of preference. The NTMPs selection
criteria basically include workpiece material, power consumption, cost,
process capability attributes like MRR, tolerance, surface finish, surface
damage, corner radii, taper, hole diameter, depth/diameter ratio (slenderness
ratio) for cylindrical holes, depth to width ratio (aspect ratio) for cavities and
pockets, width of cut, heat affected zone, exterior and interior profiles (Rao
2006), etc. Almost all the attributes may affect the machining performance of
the NTMPs to some extent, but only six most significant attributes, such as
tolerance and surface finish (TSF), MRR, power requirement (PR), Cost ( C ),
shape feature (F) and work material type (M), are incorporated in the digraph-
based NTMPs selection procedure proposed by Nilanjan et al 2008. The
diagraph used by them for selection of NTMPs is shown in Figure 2.21.
51
Figure 2.21 NTMPs selection diagraph (Nilanjan et al 2008)
2.4.2 Web Based Process Selection
With the advancement of information technologies, data can be sent
through and information can be retrieved from Internet just in few eye clips.
The data can be transferred to and from virtually any place in the world
(Brown et al 1996). Intranet is a common infrastructure in an established
organization today. Generally, Intranet is using the Web as a part of their
internal information network. There are several reasons behind it:
1. Access to information: web severs are fairly easy to set up,
and companies are finding the web an easy way to distribute
information.
2. Platform independence: web because there are browsers on
every major platform, developers no longer need to worry
about cross-platform client development.
3. Multiple data types: developers can easily provide access to
multimedia as well as textual information.
Software for process selection stems from the more widespread use
of computer tools to assist with material selection. The advent of the web has
52
led many material suppliers to put database searches online, allowing users to
filter inventories based on user-entered material property ranges. Smith et al
(2003) discuss the main difficulties of creating the Manufacturing Advisory
Service (MAS) arose from the fact that different manufacturing processes are
constrained by different limitations. For example, a particular sand casting
company is limited by the maximum weight of component they can cast,
while small Computer Numerically Controlled (CNC) milling machines are
limited more by the bounding box volume around the part. To compare them,
a design engineer must decide on a plausible material, look up its density,
select a volume, and calculate its weight. Another difficulty arose from the
complexity of the input (all of the processes, materials, design requirements),
and the desire to establish only a simple ranked list of processes. The goal
was thus to give the user a better understanding of the coupling between their
design and the best manufacturing process.
Internet and Intranet Technologies
Intellectual and economic forces are now driving businesses and
individuals to exploit the power of the Internet and the newly coined intranet–
Internet technologies used in the corporate environment. It became the largest
TCP/IP (TCP stands for transmission control protocol; IP stands for Internet
protocol) network in the world. The Internet and the rapidly growing demand
for intranet have created an immediate demand for developers who
understand these technologies and can use them both at the Internet and at the
intranet level. The TCP portion of the TCP/IP provides data transmission
verification between client and server. The IP portion of TCP/IP moves data
packets from node to node. It decodes addresses and routes data to designated
destinations. The IP is what creates the network of networks, or Internet, by
linking systems at different levels. TCP/IP has been ported to most computer
systems, including personal computers, and has become the new standard in
53
inter-networking. It is the protocol set that provides the infrastructure for the
Internet today. TCP/IP includes services for remote log-on, file transfers, data
indexing, and retrieval, among others. Majority of the network including the
web is based on a client–server model. Client–server computing distributes
the basic components, user interface, program logic, and data, between the
client and server computers. In a client–server model, the client can request
data from the server, can post data back to the server for storage, can request a
process to run on the server and may provide functional logic. In a client–
server model, the server can send data to the client provides access to data
storage and may provide functional logic. The client in World Wide Web
(WWW) scenario is typically a Web browser. The Web browser is simply a
user interface to many kinds of data that are retrieved from the Web server.
The Internet Server Application Programming Interface (ISAPI) or Common
Gateway Interface (CGI) applications provide the functional logic to the
Hypertext Transfer Protocol (HTTP) server and the client displays the various
types of data from a specific Uniform Resource Locator (URL).The fat-client,
thin-server model moves the program logic from the server to the client. Each
client accessing the server makes program flow decisions based on the logic
or business rules that reside on the client computer. The thin server acts as a
gateway to data storage for clients. There are other models such as distributed
services in which program functionality is shared between clients and servers.
In the past, because Web browsers were simply a user interface, the Web
model was a fat server, thin client. However, with the innovation of
technologies which allow client-side programming, such as Microsoft
ActiveX/COM (Component Object Model) and Java the browser is now
rapidly being enabled to do client-side processing (Genusa 1997). A number
of interface options are available to deliver dynamic documents via the Web.
These include the CGI, the Windows CGI (WinCGI), Microsoft ActiveX
Server. ISAPI, Netscape’s Application Programming Interface (NSAPI), and
54
others such as Fast CGI, CGI and WinCGI are the most commonly used
interfaces to an HTTP server.
Literature on Web enabled Process Selection
Bock (1991) describes the Computer Aided Material and Process
Selector (CAMPS) as an upgraded version of one of the earliest conceptual
process selectors, the Material and Process Selector (Dargie et al 1982). In
CAMPS, a data file is submitted to a series of modules: a fuzzy logic based
material exclusion module, and a Knowledge Acquisition and Consultation
Module that ‘quizzes’ the design engineer about the part. The user is then
presented with two lists that fit all of the requirements: frequently and
infrequently used process/material pairs. The final module uses a spreadsheet
from Poggiali (1985) to obtain generalized cost estimates for material,
tooling, energy usage, and labour. Farris et al (1991) discuss a methodical
system for generating sequences of processes operating on a single material.
The system proposed by Farris et al (1991) first reduces material options
through requirement specification and fuzzy logic set matching.
Kunchithapatham (1996) created the Design Advisor around separate
qualitative material and process searches. The possible material and process
lists are reduced in a binary fashion: either they can or cannot meet the
requirements. Thus, the user has a list of materials and processes that are
unranked-each option is equally valid as far as the Design Advisor proposed
by Kunchithapatham (1996) is concerned. Giachetti (1998) discusses another
all-database solution for conceptual process selection. It uses parallel
material/process searches, followed by a combination step. All of the results
in the system are ranked lists. The Cambridge Engineering Selector (CES) is
the only commercially available process selection software. As discussed in
Esawi et al (1998) and Granta (2001), it contains information of more than
100 different manufacturing processes and process variations. The CES and
55
its process selection module are very expensive. This fact makes the software
somewhat inaccessible to most individual student design engineers. Instead of
going through the usual batch input, the user defines the part through a
requirement by requirement screening sequence. In CES, the user graphically
defines the upper and lower bound for each requirement-such as surface
roughness - and processes whose lines extend above and below the user
bounds can meet the current requirement. After the user has stepped through
all of the requirements, a final, unranked list of viable processes is generated
by taking the intersection of all of the result sets. The user may have many
possible processes at each screening step, only to discover that the
intersection set has no members. In contrast, Brown et al (1998) discussed the
Manufacturing Analysis Service that places the final solution set on screen at
all times, allowing the user to observe how a requirement changes modifies
the final solution set. The CES process search has only a single material
requirement: the user selects a material from a list of material groups. The
results of the material search can then be matched with the process search to
find valid combinations. The Manufacturing Analysis Service (Brown et al
1998) was intended to be a proof-of-concept online process selection tool,
using criteria and experience from various sources such as Kalpakjian (1997)
and Schey (1987).While it was the first to bring process selection online, it
had a hard coded database, overly simplified material selection, ambiguous
requirements, and inconsistent process classification.
Online Knowledge-based Fuzzy Expert System
Wong et al (2003) discussed a knowledge-based system that is
divided into three components which are data input web page, output web
page (including ActiveX control) and ISAPI Data Library Linking (ISAPI
DLL). The process flow and the integration of the above mentioned
components are shown in Figure 2.22.
56
Figure 2.22 System and data flow of the online knowledge-based expert
system (Wong et al 2003)
The input web page developed by Wong et al (2003) acts as an
interface or channel for the user to enter the inputs, they are tool type,
workpiece material hardness and depth of cut. The input interface is in the
form of Hypertext Markup Language (HTML) format for collecting and
sending the data to the web server. The sending method is GET instead of
POST. GET sends the data to the URL specified by ACTION and POST
enables an HTTP upload and data will not be ‘attached’ to ACTION. Figure
2.23 shows the input web page of the online knowledge base system proposed
by Wong et al (2003). The input web page will send a request to the web
57
server to activate the ISAPI DLL. The request comes together with the data
entered in the input web page form. The ISAPI DLL will then process the
provided data by using the appropriate fuzzy models to yield the outputs.
Min–max inference method and weighted-centroid method are used in the
system to calculate the outputs. After all the required processes, the ISAPI
DLL will automatically generate an output web page based on the calculated
output values. There are two types of ISAPI, which are ISAPI extension and
ISAPI filter. The system only uses ISAPI extension (Genusa 1997).
Figure 2.23 Input web page of the online knowledge-based expert system
(Wong et al 2003)
The DLL is neither loaded into the server memory nor occupying
any processing thread until a request being accepted. The ISAPI DLL itself
includes a fuzzy handling object to interpret the fuzzy models. The ISAPI
58
DLL supposes to be at its most optimum size in order to fully utilize the
server resources (Tom 2003). Normally, server resources are very critical and
can lead to a crash if not handle properly. Wong et al 2003 developed the
ISAPI DLL using Microsoft Visual C++ (MSVC++) with Microsoft
Foundation Class (MFC).The output web page consists of the yield
information and shows fuzzy relationships in graphs. They are the inputs
fuzzy membership function and the outputs membership function.
In order to have the dynamic fuzzy graphs in the output web page,
an ActiveX control has been developed by Wong et al (2003) using
MSVC++. Figure 2.24 shows the output web page and Figure 2.25 shows the
arrangement proposed by Wong et al (2003) for machining with the online
knowledge-based expert system.
Figure 2.24 Output web page of the online knowledge-based expert
system (Wong et al 2003)
59
Figure 2.25 Arrangement for machining with the online knowledge-
based expert system (Wong et al 2003)