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ME2026

UNCONVENTIONAL MACHINING

PROCESSES

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IntroductionUnconventional machining Process Need classification Brief overview

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Parts manufactured by casting, forming, and various shaping processes often require

further operations before they are ready for use or assembly.

In many engineering applications, parts have to be interchangeable in order to

function properly and reliably during their expected service lives.

Thus control of the dimensional accuracy and surface finish of the parts is required

during manufacture.

Machining involves the removal of some material from the workpiece (machining

allowance) in order to produce a specific geometry at a definite degree of accuracy

and surface quality.

UNIT 1

IntroductionUnconventional machining ProcessNeedclassificationBrief overview

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UNIT 1

IntroductionUnconventional machining ProcessNeedclassificationBrief overview

From the earliest of times methods of cutting materials have been adopted

using hand tools made from bone, stick, or stone.

Later, hand tools made of elementary metals such as bronze and iron were

employed over a period of almost one million years.

Indeed up to the seventeenth century, tools continued to be either hand operated

or mechanically driven by very elementary methods.

By such methods, wagons, ships, and furniture, as well as the basic utensils for

everyday use, were manufactured.

The introduction of water, steam, and, later, electricity as useful sources of energy

led to the production of power-driven machine tools which rapidly replaced

manually driven tools in many applications.

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Based on these advances and together with the metallurgical development of alloy steels

as cutting tool materials, a new machine tool industry began to arise in the eighteenth

and nineteenth centuries.

A major original contribution to this new industry came from John Wilkinson in

1774. He constructed a precision machine for boring engine cylinders, thereby

overcoming a problem associated with the first machine tools, which were powered

by steam

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Twenty-three years later, Henry Maudslay made a further advancement in machining

when he devised a screw-cutting engine lathe.

James Nasmyth invented the second basic machine tool for shaping and planing

Whitney in about 1818 introduced the first milling machine to cut grooves, dovetails, and

T-slots as well as flat surfaces.

The first universal milling machine, constructed in 1862 by J. R. Brown, was employed

to cut helical flutes of twist drills.

In the late nineteenth century, the grinding machine was introduced.

An advanced form of this technology is the lapping process used to produce a high-

quality surface finish and a very tight tolerance, as small as 0.00005 millimeters (mm)

compared to the 0.0025 mm achieved during grinding.

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Band saws and circular discsaws are used for cutting shapes in metal plates, for making

external and internal contours, and for making angular cuts.

A notable development includes the turret lathe made in the middle of the

nineteenth century for the automatic production of screws.

Another significant advance came in 1896, when F. W. Fellows built a machine that

could produce any kind of gear. An example of the significance of early achievements

in grinding technology came from C. N. Nortonswork in reducing the time needed to

grind a car crankshaft from 5 hours (h) to 15 minutes (min).

Multiple-station vertical lathes, gang drills, production millers, and special-purpose

machines (for example, for broaching, honing, and boring) are other noteworthy

examples of advances in machine tool technology (McGeough, 1988).

In the later part of the nineteenth century and in the twentieth century, machinetools became increasin l owered b electricit rather than steam.

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The basic machine tools underwent further refinement; for instance, multiple-point

cutters for milling machines were introduced.

Even with these advances, conventional machine tool practice still relies on the principle

whereby the tool must be made of a material that is harder than the workpiece that is to

be cut.

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During machining by these conventional methods the operator is given a drawing of

the finished part. He or she determines the machining strategy, sets up the machine,

and selects tooling, speeds, and feeds.

The operator manipulates the machine control to cut the part that passes inspection.

Under such circumstances, the product accuracy and surface quality are not

satisfactory.

Further developments for these conventional machines came by the introduction of

copying techniques, cams, and automatic mechanisms that reduced labor and,

consequently, raised the product accuracy.

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The introduction of numerical control (NC) technology in 1953 opened wide doors to

computer numerical control (CNC) and direct numerical control (DNC) machining

centers that enhanced the product accuracy and uniformity.

Developments in machining processes and their machine tools have continued

throughout the last 50 years due to the rapid enhancements in the electronics and

computer industries.

Ingenious designs of conventional machine tools have enabled complex shapes to be

produced at an accuracy of 1 micrometers (m).

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As shown in Fig. the most recent developments in conventional machining include

precision jig borers, jig grinding, and superfinishing machines.

These made the accuracy level of 1 m possible. Such a high level of accuracy can

be measured using pneumatic or electronic instruments as well as optical

comparators. Future trends may also include precision grinding and lapping

machines as well as precision diamond lathes.

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In modern machining practice, harder, stronger, and tougher materials that are more

difficult to cut are frequently used.

More attention is, therefore, directed toward machining processes where the

mechanical properties of the workpiece material are not imposing any limits on the

material removal process.

In this regard, the nonconventional machining techniques came into practice as a

possible alternative concerning machinability, shape complexity, surface integrity,

and miniaturization requirements.

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Innovative machining techniques or modifications to the existing method by

combining different machining processes were needed.

Hybrid machining made use of the combined or mutually enhanced advantages and

avoided the adverse effects of the constituent processes produced when they are

individually applied.

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A particular manufacturing process found suitable under the given conditions may not

be equally efficient under other conditions. Therefore, a careful selection of the

process for a given manufacturing problem is essential. The analysis has been made

from the point of view of :

(i) Physical parameters involved in the processes;

(ii) Capability of machining different shapes of work material;

(iii) Applicability of different processes to various types of material, e.g. metals, alloys

and non-metals;

(iv) Operational characteristics of manufacturing and

(v) Economics involved in the various processes.

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Physical parameters

The physical parameters of non-conventional machining processes have a direct impact on

the metal removal as well as on the energy consumed in different processes.

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It is found that some of the processes

(e.g. EBM, ECM) above the mean power

consumption line consume a greater

amount of power than the processes

(e.g. EDM, PAM, ECG) below the mean

power consumption line. Thus, the

capital cost involved in the processes

(EBM, ECM etc.) lying above the mean

line is high whereas for the processes

below that line (e.g., EDM, PAM, MCG)

is comparatively low.

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Capability to shape

The capability of different processes can be analyzed on the basis of various machining

operation point of view such as micro-drilling, drilling, cavity sinking, pocketing (shallow

and deep), contouring a surface, through cutting (shallow and deep) etc.

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For micro-drilling operation, the only process which has good capability to micro drill

is laser beam machining while for drilling shapes having slenderness ratio,

< 20,

the process USM, ECM and EDM will be most suitable.

EDM and ECM processes have good capability to make pocketing operation (shallow

or deep).

For surface contouring operation, ECM process is most suitable but other processes

except EDM have no application for contouring operation.

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Applicability to materials

For the machining of electrically non-conducting materials, both ECM and EDM are

unsuitable, whereas the mechanical methods can achieve the desired results.

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USM is suitable for machining of refractory type of material while AJM are for super

alloys and refractory materials.

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Machining characteristics

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The machining characteristics of different non-conventional processes can be analyzed

with respect to

(i) Metal removal rate

(ii) Tolerance maintained

(iii) Surface finish obtained

(iv) Depth of surface damage

(v) Power required for machining

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The process capabilities

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Power requirement of ECM and PAM is also very high when compared with other

non-conventional machining processes. This involves higher capital cost for those

processes.

ECM has very low tool wear rate but it has certain fairly serious problems

regarding the contamination of the electrolyte used and the corrosion of machine

parts.

The surface finish and tolerance obtained by various processes except PAM is

satisfactory.

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Economics of the processes

The economics of the various processes are analysed on the basis of following factors

(i) Capital cost

(ii) Tooling cost

(iii) Consumed power cost

(iv) Metal removal rate efficiency

(v) Tool wear.

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The capital cost of ECM is very high when compared with traditional mechanical

contour grinding and other non-conventional machining processes 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 case of ECM.

The metal removal efficiency is very high for EBM and LBM than for other processes.

In conclusion, the suitability of application of any of the processes is dependent upon

various factors and must be considered all or some of them before applying

nonconventional processes.

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Question bankPart A

1. Need of the unconventional M/cing

Sustain productivity with increasing strength of the work material.

Maintain productivity with desired shape, accuracy, and surface integrity

requirements.

Improve the capability of automation system and decreasing their sophistication

(decreasing the investment cost) requirements.

2. Define unconventional M/cing process

There is a need for m/c tools and processes which can accurately and easily

m/c the most difficult to m/c materials to intricate and accurate shapes.

The m/c tools should be easily adaptable for automation as well. In order to meet this

challenge, a number of newer material removal processes have been developed to the

level of commercial utilization. These newer methods are also called as unconventional

M/cing process.

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3. Classification of advanced m/cing processes.*Mechanical

*Thermoelectric

*Electrochemical & chemical

4. Types of mechanical advanced m/cing processes.

*Abrasive jet m/cing

*Ultrasonic m/cing

*Water jet m/cing

*Abrasive water jet m/cing

* Abrasive flow m/cing

*Magnetic abrasive finishing

5. Types of Thermoelectric advanced m/cing processes.*Plasma arc m/cing

*Laser beam m/cing

*Electron beam m/cing

*Electric discharge m/cing

*Ion beam m/cing

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6. Types of Electrochemical advanced m/cing processes.*Electrochemical m/cing

*Chemical m/cing

*Bio chemical m/cing

1.State the needs of nontraditional machining processes.

2. List down various mechanical energy based unconventional machining

processes.

3.Write down the energy transfer media, energy source and mechanism of metal removal for

the following process

a. Water jet machining

b. Electrochemical grinding

4.Enlist the requirement that demands the use of advanced machining process

5.Why unconventional mechanical machining process is not so effective on soft metals like

aluminum

6.Distinguish traditional and non traditional machining process

7.What are the characteristic of unconventional machining process

8.List the unconventional machining process which uses mechanical energy

Assignment

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Question bankPart B

1.What is the need for the development of Unconventional Machining Process? Explain with

examples.

2.Classify unconventional machining processes based on basic mechanism , involved in the

process, sources of energy required for material removal , medium for transfer of energies and

type of energy required to shape materials.

3.How the developments in the area of materials are partly responsible for evolution of

advanced m/cing techniques.

4. Enlist the requirements that demand the use of AMPs

5 What are the industrial needs for unconventional m/cing processes?

6. How the unconventional m/cing processes are classified?

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7.List the various process parameters recommended for various unconventional machining

process in the form of table

8.How will you analyze the applicability of different process to different types of materials,

Namely metals ,alloys and non metals? Present it in the form of table.

9.Explain the factors that should be consider during the selection of an appropriate

unconventional machining process for a given job

10.Compare and contrast the various unconventional machining process on the basis of the type

of energy employed, material removal rate transfer media and economical aspects.

11.Discuss how the process variables influence MRR ,HAZ and Pattern generation

12.Explain the reasons for development of unconventional machining process. Discuss about

the criteria recommended in selection of these processes

13.Compare the mechanical and electrical energy processes in terms of physical parameters ,

me2026 ucmp unit 1

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