Mech Vi Non Traditional Machining [10me665] Notes

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Non Traditional Machining 10ME665

DEPARTMENT OF MECHANICAL ENGG, SJBIT Page 5

1943 DM was developed by B R Lazarenko and N I Lazarenko in USSR. They first developed

the idea of spark erosion machining. In the early nineteen-sixties, the idea of Ultrasonic

machining began to to develop widely in USSR and basis of this development was laid on

extensive investigation that took place in the mechanism of ultrasonic machining and in the

design of Magneto-strictive transducers, converters and wave guides.

1950The basis of laser machining was established by the process which Which were developed

by Basov, Prokhorov and Fabrikanth in USSR in 1950.

1950Electro chemical Grinding has practically been developed in about 1950.

1960The concept of whirling jet machining was innovated.

1.3 Classification of NTM processes

Classification of NTM processes is carried out depending on the nature of energy used for

material removal.

1. Mechanical Processes

a) Abrasive Jet Machining (AJM)

b) Ultrasonic Machining (USM)

c) Water Jet Machining (WJM)

d) Abrasive Water Jet Machining (AWJM)

2. Electrochemical Processes

a) Electrochemical Machining (ECM)

b)

Electro Chemical Grinding (ECG)c) Electro Jet Drilling (EJD)

3. Electro-Thermal Processes

a) Electro-discharge machining (EDM)

b) Laser Jet Machining (LJM)


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9. USM has been used for piercing of dies and for parting off and blankingoperations.

10.USM enables a dentist to drill a hole of any shape on teeth without any pain

11. Ferrites and steel parts , precision mineral stones can be machined using USM

12. USM can be used to cut industrial diamonds

13.USM is used for grinding Quartz, Glass, and ceramics

14.Cutting holes with curved or spiral centre lines and cutting threads in glass and mineral or

metallo-ceramics

2.6 Advantages

1. It can be used machine hard, brittle, fragile and non-conductive material

2. No heat is generated in work, therefore no significant changes in physical structure of

work material

3.

Non-metal (because of the poor electrical conductivity) that cannot be machined by EDM

and ECM can very well be machined by USM.

4. It is burr less and distortion less processes.

5. It can be adopted in conjunction with other new technologies like EDM,ECG,ECM.

2.7 Disadvantages

1. Low Metal removal rate

2. It is difficult to drill deep holes, as slurry movement is restricted.

3. Tool wear rate is high due to abrasive particles. Tools made from brass, tungsten carbide,

MS or tool steel will wear from the action of abrasive grit with a ratio that ranges from

1:1 to 200:1

4. USM can be used only when the hardness of work is more than 45 HRC.

2.8 Material removal models in USM

Theoretical analysis and experimental results have revealed that USM is a form of abrasion and

material removal in the form of small grains by four mechanisms

i. Throwing of abrasive grains

ii.

Hammering of abrasive grains

iii. Cavitations in the fluid medium arising out of ultrasonic vibration of tool.

iv. Chemical erosion due to microagitation

Material removal due to throwing and hammering is significant and MR due to cavitations and

chemical erosion can be ignored.


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UNIT-3

3.1 Definition

In abrasive jet machining, a focused stream of abrasive particles, carried by high pressure air or

gas is made to impinge on the work surface through a nozzle and the work material is made to

impinge on the work surface through a nozzle and work material is removed by erosion by high

velocity abrasive particles.

3.2 Abrasive Jet Machining Equipment

In Abrasive Jet Machining (AJM), abrasive particles are made to impinge on the work material at

a high velocity. The high velocity abrasive particles remove the material by micro-cutting action

as well as brittle fracture of the work material.


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b) shapeirregular/regular

c) Size10 to 50 microns

d) Mass flow2-20 gm/min Carrier Gas

a) CompositionAir, CO2, N2

b) Density1.3 kg/m3

c) Velocity - 500 to 700 m/s

d) Pressure - 2 to 10 bar

e) Flow rate - 5 to 30 microns

Abrasive Jet

a) Velocity - 100 to 300 m/s

b) Mixing ratioVolume flow rate of abrasives/Volume flow rate of gas

c) Standoff distanceSOD- 0.5 to 15mm.

d) Impingement angle60 to 90 deg

Nozzle

a) MaterialWC/Sapphire

b) Diameter0.2 to 0.8 mm

c) Life300 hours for sapphire, 20 to 30 hours for WC3.5 Applications

1. This is used for abrading and frosting glass more economically as compared to etching or

grinding

2. Cleaning of metallic smears on ceramics, oxides on metals, resistive coating etc.

3. AJM is useful in manufacture of electronic devices , drilling of glass wafers, de burring

of plastics, making of nylon and Teflon parts permanent marking on rubber stencils,

cutting titanium foils

4. Deflating small castings, engraving registration numbers on toughened glass used for car

windows

5. Used for cutting thin fragile components like germanium, silicon etc.

6. Register treaming can be done very easily and micro module fabrication for electrical

contact, semiconductor processing can also be done effectively.


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7. Used for drilling, cutting, deburring etching and polishing of hard and brittle materials.

8. Most suitable for machining brittle and heat sensitive materials like glass, quartz,

sapphire, mica, ceramics germanium , silicon and gallium.

9.

It is also good method for deburring small hole like in hypodermic needles and for smallmilled slots in hard metallic components.

3.6 Advantages of AJM

1.

High surface finish can be obtained depending upon the grain sizes

2. Depth of damage is low ( around2.5 microns)

3. It provides cool cutting action, so it can machine delicate and heat sensitive material

4. Process is free from chatter and vibration as there is no contact between the tool and work

piece5. Capital cost is low and it is easy to operate and maintain AJM.

6. Thin sections of hard brittle materials like germanium, mica, silicon, glass and ceramics

can be machined.

7. It has the capability of cutting holes of intricate shape in hard materials.

3.7 Disadvantages of AJM

1. Limited capacity due to low MRR. MRR for glass is 40 gm/minute

2.

Abrasives may get embedded in the work surface, especially while machining soft

material like elastomers or soft plastics.

3. The accuracy of cutting is hampered by tapering of hole due to unavoidable flaring of

abrasive jet.

4. Stray cutting is difficult to avoid

5. A dust collection system is a basic requirement to prevent atmospheric pollution and

health hazards.

6.

Nozzle life is limited (300 hours)

7. Abrasive powders cannot be reused as the sharp edges are worn and smaller particles can

clog the nozzle.

8. Short standoff distances when used for cutting, damages the nozzle.


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UNIT5

5.1 Introduction

Chemical machining is one of the non-conventional machining processes where material is

removed by bringing it in contact of a strong chemical enchant. There are different chemical

machining methods base on this like chemical milling, chemical blanking, photochemical

machining, etc.

5.2 Working Principle of ECM

Electrochemical machining removes material of electrically conductor workpiece. The

workpiece is made anode of the setup and material is removed by anodic dissolution. Tool is

made cathode and kept in close proximity to the workpiece and current is passed through the

circuit. Both electrodes are immersed into the electrolyte solution. The working principle and

process details are shown in the Figure. This works on the basis of Faradays law of electrolysis.

The cavity machined is the mirror image of the tool. MRR in this process can easily be

calculated according to Faradays law.

Process details of ECM are shown in Figure and described as below:

Workpiece

Workpiece is made anode, electrolyte is pumped between workpiece and the tool. Material of workpiece

is removed by anodic dissolution. Only electrically conducting materials can be processed by ECM.

Tool

A specially designed and shaped tool is used for ECM, which forms cathode in the ECM setup. The tool

is usually made of copper, brass, stainless steel, and it is a mirror image of the desired machined cavity.

Proper allowances are given in the tool size to get the dimensional accuracy of the machined surface.


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In EDM ram or sinker machining, a relatively soft graphite or metallic electrode can be used to

cut hardened steel, or even carbide. The EDM process produces a cavity slightly larger than the

electrode because of the overcut.

6.5 Wire-Cut EDM

The wire-cut EDM is a discharge machine that uses CNC movement to produce the desired

contour or shape. It does not require a special shaped electrode, instead it uses a continuous-

traveling vertical wire under tension as the electrode. The electrode in wire-cut EDM is about as

thick as a small diameter needle whose path is controlled by the machine computer to produce

the shape required.

6.6 Dielectric Fluids

Conventional EDM During the EDM process the workpiece and the electrode are submerged in

the dielectric oil, which is an electrical insulator that helps to control the arc discharge. The

dielectric oil, that provides a means of flushing, is pumped through the arc gap. This removes

suspended particles of workpiece material and electrode from the work cavity.

6.7 Flushing

One of the most important factors in a successful EDM operation is the removal of the metal

particles (chips) from the working gap. Flushing these particles out of the gap between the

workpiece to prevent them from forming bridges that cause short circuits.

6.8 Flushing Ram Type EDM

Flushing is the most important function in any electrical discharge machining operation.

Flushing is the process of introducing clean filtered dielectric fluid into the spark gap. Flushing

applied incorrectly can result in erratic cutting and poor machining conditions.

There are a number of flushing methods used to remove the metal particles efficiently while

assisting in the machining process. Too much fluid pressure will remove the chips before they

can assist in the cutting action, resulting in slower metal removal. Too little pressure will not

remove the chips quickly enough and may result in short-circuiting the erosion process


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Process Details of PAM

Details of PAM are described below.

Plasma Gun

Gases are used to create plasma like, nitrogen, argon, hydrogen or mixture of these gases. The

plasma gun consists of a tungsten electrode fitted in the chamber. The electrode is given negative

polarity and nozzle of the gun is given positive polarity. Supply of gases is maintained into the

gun. A strong arc is established between the two terminals anode and cathode. There is a

collision between molecules of gas and electrons of the established arc. As a result of this

collision gas molecules get ionized and heat is evolved. This hot and ionized gas called plasma is

directed to the workpiece with high velocity. The established arc is controlled by the supply rate

of gases.

Power Supply and Terminals

Power supply (DC) is used to develop two terminals in the plasma gun. A tungsten electrode is

inserted to the gun and made cathode and nozzle of the gun is made anode. Heavy potential

difference is applied across the electrodes to develop plasma state of gases.

Cooling Mechanism

As we know that hot gases continuously comes out of nozzle so there are chances of its

overheating. A water jacket is used to surround the nozzle to avoid its overheating.

Tooling

There is no direct visible tool used in PAM. Focused spray of ho0t, plasma state gases works as a

cutting tool.

Workpiece

Workpiece of different materials can be processed by PAM process. These materials are

aluminium, magnesium, stainless steels and carbon and alloy steels. All those material which can

be processed by LBM can also be processed by PAM process.

7.3 Material removal rate

During PBM absorbing the heat energy from the plasma jet directed to theworkpiece activates

metal removal. The plasma torch blows the molten andevaporated metal away as a fine spray or

vapor. The resulting cuttingrates and hence the machinability depend on the workpiece

beingmachined as well as the type of the cutting and shielding gases that determinethe maximum


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7.4 Accuracy and surface quality

The edges of the workpieces cut by PBM are often beveled. McGeough (1988) reported that the

right side of the plasma arc relative to the cutting direction produces a square edge to within 3.

The left-handedge is beveled to about 15 due to the clockwise swirling of the machininggas.

Owing to the high rate of heat transfer the depth of fused metalextends to about 0.18 mm below

the cut surface. The high machiningspeed does not allow the heat to penetrate more than a few

microns from the edges of the cut which produces little or no distortion in the cut workpiece.

The cut edge of the material tends to be harder than the base material. Afurther heat-affected

zone (HAZ) of thickness 0.25 to 1.12 mm has been reported. Additionally due to the rapid

cooling, cracks may arise beyond the heat-affected zone to 1.6 mm. A clean, smooth surface is

produced by PBM. Large tolerances of 1.6 mm can be achieved. Finish cuts are, therefore,

required when narrow tolerances are required.

7.5 Applications of PAM

The chief application of this process is profile cutting as controlling movement of spray focus

point is easy in case of PAM process. This is also recommended for smaller machining of

difficult to machining materials.

7.6 Advantages of PAM Process

Advantages of PAM are given below:

i. It gives faster production rate.

ii. Very hard and brittle metals can be machined.

iii. Small cavities can be machined with good dimensional accuracy.

7.7 Disadvantages of PAM Process

i. Its initial cost is very high.

ii. The process requires over safety precautions which further enhance the initial cost of the

setup.

iii. Some of the workpiece materials are very much prone to metallurgical changes on

excessive heating so this fact imposes limitations to this process.

iv. It is uneconomical for bigger cavities to be machined.


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but method of generation of heat is different. The application of heat is very finely focused in

case of LBM as compared to EDM.

Laser Tube and Lamp Assembly

This is the main part of LBM setup. It consists of a laser tube, a pair of reflectors, one at each

end of the tube, a flash tube or lamp, an amplification source, a power supply unit and a cooling

system. This whole setup is fitted inside a enclosure, which carries good quality reflecting

surfaces inside. In this setup the flash lamp goes to laser tube, that excites the atoms of the inside

media, which absorb the radiation of incoming light energy. This enables the light to travel to

and fro between two reflecting mirrors. The partial reflecting mirror does not reflect the total

light back and apart of it goes out in the form of a coherent stream of monochromatic light. This

highly amplified stream of light is focused on the workpiece with the help of converging lense.

The converging lense is also the part of this assembly.

Workpiece

The range of workpiece material that can be machined by LBM includes high hardness

and strength materials like ceramics, glass to softer materials like plastics, rubber wood, etc. A

good workpiece material high light energy absorption power, poor reflectivity, poor thermal

conductivity, low specific heat, low melting point and low latent heat.

Cooling Mechanism

A cooling mechanism circulates coolant in the laser tube assembly to avoid itsoverheatingin long continuous operation.

Tool Feed Mechanism

There is no tool used in the LBM process. Focusing laser beam at a pre-decided point in

the workpiece serve the purpose of tool. As the requirement of being focused shifts during the

operation, its focus point can also be shifted gradually and accordingly by moving the

converging lense in a controlled manner. This movement of the converging lense is the tool feed

mechanism in LBM process.

8.3 Applications of LBM

LBM is used to perform different machining operations like drilling, slitting, slotting, scribing operations.

It is used for drilling holes of small diameter of the order of 0.025 mm. It is used for very thin stocks.

Other applications are listed below:


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Electron Beam Machining

8.6 Introduction

The earliest work of material removal utilizing an electron beam wasattributed to Steigerwald

who designed a prototype machine in 1947.Electron beam machining (EBM) has been used in

industry since the1960s, initially in nuclear and aerospace welding applications. Drillingsmall

holes, cutting, engraving, and heat treatment are a set of modernapplications used in

semiconductor manufacturing as well as micromachiningareas.

8.7 Principles, equipment and operation ofElectron Beam Machining

The main components of EBM installation, shown in Fig. 5.43 arehoused in a vacuum chamber,

evacuated to about 104 torr. The tungsten filament cathode is heated to about 2500 to 3000C in

order to emit electrons. A measure of this effect is the emission current, the magnitude of which

varies between 20 and 100 mA. Corresponding current densities lie between 5 and 15 A/cm2.

Emission current depends on the cathode material, temperature, and the high voltage that is

usually about 150 kV. Such a high voltage accelerates a stream of electrons in the direction of

the workpiece. After acceleration, electrons, focused by the field, travel through a hole in the

anode. The electron beam isthen refocused by a magnetic or electronic lens system so that the

beam is directed under control toward the workpiece. The electrons the velocity (228 103

km/s) imparted by the acceleration voltage until they strike the workpiece, over a well-defined

area, typically 0.25 mm in diameter.


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Mech Vi Non Traditional Machining [10me665] Notes

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