With the development of new materials more and more challenges are faced by scientists

Conventional Machining processes there is physical contact between tool and work piece.

In Unconventional no direct physical contact – so tool need not be harder than work.

Unconventional machining processes harness energy sources considered unconventional by yesterday's standards.

Material removal is accomplished using electrical, chemical, mechanical and light energies

During the last 55 years over 20 different non-traditional manufacturing processes have been invented and used successfully

INTRODUCTION

The requirements that lead to the development of Unconventional machining:

• Very high hardness and strength of the material. (above 400 HB.)

• The work piece is too flexible or slender to support the cutting or grinding forces.

• The shape of the part is complex, such as internal and external profiles, or small diameter holes or non-circular holes.

• Surface finish or tolerance better than those obtainable conventional process.

• Temperature rise or residual stress in the work piece are undesirable.

• Economy and High Production rates for advanced materials

Trend Of Increase Of Material Strength

Aerospace alloys are High strength to Weight ratio alloys

HSTR alloys – Nimonics, Titanium alloys, Hastalloys

Stainless steels, Maraging steels

ULTRASONIC MACHINING

ABRASIVE JET MACHINING

ELECTRICAL DISCHARGE MACHINING

ELECTROCHEMICAL MACHINING

LASER BEAM MACHINING

ELECTRON BEAM MACHINING

Process Applications

Abrasive Jet machining Materials: Hard and Brittle metals, alloys, non-metallic materials (Eg.,silicon,glass, ceramics, mica)Specially suitable for thin sectionsJob: Drilling, cutting, deburring, etching, cleaning

Ultrasonic machining Materials: Hard and Brittle materials, non-metals-glass, ceramicsJob: Round and Irregular holes, impressions

Electrical discharge machining Materials: All conducting metals and alloysJob: Blind complex cavities, micro holes for nozzles, through cutting of non-circular holes, narrow slots

Process Applications

Electrochemical machining Materials: All conducting metals and alloysJob: Blind complex cavities, curved surfaces, large through cavities

Laser beam machining Materials: All materialsJob: Drilling fine holes, cutting contours in sheets, cutting narrow slots

Electron beam machining Materials: All materialsJob: Drilling fine holes

ULTRASONIC MACHINING(USM)

Frequency: 20 KHz

Amplitude: 15-20μm

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Nozzle Abrasiveslurry

Transducer

Up-down vibration of toolhammers the abrasive particlesagainst workpiece, causing cutting

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Nozzle Abrasiveslurry

Transducer

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Nozzle Abrasiveslurry

Transducer

Up-down vibration of toolhammers the abrasive particlesagainst workpiece, causing cutting

Principle of Working:

An abrasive slurry is pumped between tool and work In USM the tip of the tool vibrates at low amplitude and high

frequency. This vibration transmits a high velocity to fine abrasive grains between tool and the surface of the work piece.

Material removal is by brittle fracture caused by impact abrasive grains due to vibration at high frquency

Tool material being tough and ductile wears out at much slower rate.

Equipment consists of Transducer, Tool holder and the Tool Linear oscillatory motion of tool obtained by magnetostrictive

transducer – converts electrical energy to mechanical Transducer consists of stack of nickel laminations that are

wound with a coil – high frequency current is passed – longitudinal strains in laminations – transmitted to tool thru tool holder

The abrasive grains are usually Al2O3,SiC, B4C, Diamond

ABRASIVE JET MACHINING

Principle of Working:

• In AJM a high velocity jet of dry air or some other gas mixed with abrasive particles is directed at the work piece.

• The material removal is due to brittle fracture caused by impinging abrasive grains at high speed

• The abrasive particles are contained in mixing chamber, compressed air is supplied to the chamber.

• The chamber is vibrated and amplitude of vibrations controls the flow of abrasive particles. From the chamber the stream of abrasives is directed to the workpiece through a nozzle.

• To resist abrasion and wear, nozzles are made up of Tungsten carbide and synthetic sapphire.

• Large size Abrasive grains used for rapid removal rate

Smaller size for good surface finish and precision.• Material removal rate depends on: Dia of nozzle, abrasives

composition, velocity of jet, distance of workpiece from nozzle tip

ELECTRIC DISCHARGE MACHINING

Principle of Working:Material removal takes place due to melting and evaporation caused by high temperature electric spark struck between cathode and anode

Material removal rate and resulting surface finish is controlled by proper variation in the energy and duration of spark discharge

For improving effectiveness the workpiece and the tool are submerged in a dielectric fluid (like mineral oil, kersone)

It has been observed that if both the electrodes are made of same material , the electrode connected to positive terminal generally erodes at a faster rate. For this reason the workpiece is normally made anode.

The main elements of the setup include, power supply source (DC), dielectric medium, tool, workpiece, servocontrol unit to maintain sparkgap

Tool material: brass, copper,graphite

Dielectric uses are two fold: (i) to flush away the chips at machining zone (ii) to increase the material removal rate

This process is based on principle of electrolysis This process is considered as reverse of electroplating with

some modifications A shaped tool or electrode is used which forms the cathode,

the work forms the anode. The shape of the tool is reproduced on the work.

A small gap is maintained between the tool and work and an electrode at a high pressure is pumped through it.

Low voltage DC is employed, which in the presence of electrolyte enables a controlled removal of metal from work by anodic dissolution

Workpiece is held stationary while tool is fed continuously The electrolyte so chosen that anode is dissolved but no

deposition takes place on the cathode Electrolyte used may be sodium nitrate, sodium chloride etc., Rate of metal removal is independent of work hardness

Typical parts made by electrochemical machining. (a) Turbine blade made of nickel alloy of 360 HB. Note the shape of the electrode on the right. (b) Thin slots on a 4340-steel roller-bearing cage. (c) Integral airfoils on a compressor disk.

(a) Two total knee replacement systems showing metal implants (top pieces) with an ultra-high molecular-weight polyethylene insert (bottom pieces). (b) Cross-section of the ECM process as applies to the metal implant. Source: Courtesy of Biomet, Inc.

Laser-Beam Machining

(LBM)

Principle of working:

Light Amplification by Stimulated Emission of Radiation

LASER beam is highly coherent, monochromatic and it can be focused to a very small diameter and can produce very high power density

The setup for producing laser consists of a coiled xenon flash tube placed around the ruby rod and the internal surface of the container walls is made highly reflecting so that maximum light falls on the ruby rod for the pumping operation

The emitted laser beam is focused by a lens system and focused beam meets the working surface removing a small portion of the material by melting & vaporization

Since the energy released by the flash tube is much more than the energy transmitted by the laser head, the system must be properly cooled

Electron-Beam Machining Process

Schematic illustration of the electron-beam machining process. Unlike LBM, this process requires a vacuum, so workpiece size is limited to the size of the vacuum chamber.

Principle of working:

Thermal Process

A stream of high speed electrons impinges on the work surface whereby the kinetic energy transferred to the work material producing intense heating – leading to melting and vaporization of work

The complete EBM setup is enclosed in a vacuum chamber else the beam of electrons will collide with air molecules and will scatter.

The electrons are emitted from the cathode (a hot tungsten filament) , the beam is shaped by the grid cup and the electrons are accelerated dueto a large potential difference between the cathode and anode

The beam is focused with the help of electromagnetic lenses. The deflecting coils are used to control the beam movement in any required manner The process of heating by an electron beam can depending on the intensity be used for annealing, welding or metal removal.

A suitable viewing device is incorporated to enable the operator to observe the progress of the machining operation