knowledge institute of technology ......broaching, slotting, grinding etc. examples of non...

KNOWLEDGE INSTITUTE OF TECHNOLOGY DEPARTMENT OF MECHANICAL ENGINEERING

UNCONVENTIONAL MACHINING PROCESS

Presented by

S.Kamalakannan, AP/Mech.

UNIT I - INTRODUCTION

MECH-KIOT

Unconventional Machining Process – Need – Classification &

Brief overview.

Machining Processes

MECH-KIOT

Machining Processes

Abrasive Nontraditional Conventional

Turning Drilling Milling Other Grinding Lapping

Polishing Other

Mechanical Energy

Electrochemical Thermal Energy

Chemical Machining

To reduce machining costs

MECH-KIOT

• Avoid excess machining allowances during primary processing

• Achieve rough shape as “near net” as possible eg. Die casting a

piston instead of sand casting reduces machining

• Optimize initial shaping and final machining regarding the aspects

like machine tools, cutting tools and cutting parameters

Single – Point Tools

Surface of revolution

(Job rotating)

Plane Surfaces

Feed parallel to axis of rotation (Cylindrical surfaces)

Feed not parallel to axis of rotation

Tool reciprocates

shaping slotting

Job reciprocates

planing

External turning, screw cutting

Internal boring

internal screw

cutting

At any angle (Conical surfaces)

Simultaneous two axes motion contouring, copy

turning

External taper

turning, facing

Internal Taper boring

MECH-KIOT

Multi – Point Tools

Cylindrical Surface Plane

Surfaces

Two edge Cutting

drilling

Multi edge cutting

Sizeable Chips (Milling, Gear cutting) Spiral milling

Gear hobbing

Small Chips (Grinding) Cylindrical grinding

Centre less grinding

Sizeable Chips (Milling) Plane

milling Broaching Gear shaping

Small Chips (Grinding) Surface grinding Lapping

MECH-KIOT

PEMP

EMM2512

MECH-KIOT

MECH-KIOT

PEMP

EMM2512

MECH-KIOT

BASIC RULES OF METAL CUTTING

MECH-KIOT

• Strong cutting tools with good support

• Strong m/c to avoid bending / twisting

• Strong dovetail slide ways to give good support

• Non excessive depth of cut

• Secured work piece holding

• Cutting force application to avoid work piece deformation

WORK PIECE HOLDING CONSIDERATIONS

MECH-KIOT

• Chip removal

• Access for cutting tool

• Design the components to facilitate holding during

machining

• Avoid / reduce frequency of work removal and re-setting

• Use correct Fixtures and Jigs (if need be)

INTRODUCTION

MECH-KIOT

Mechanical Engineering

Design Manufacturing

Primary Manufacturing

Secondary Manufacturing

Thermal

INTRODUCTION

• What is Manufacturing?

MECH-KIOT

INTRODUCTION

Material removal processes can be further divided into mainly two groups 1. Conventional Machining Processes 2. Un Conventional Manufacturing Processes Examples of conventional machining processes are turning, boring, milling, shaping, broaching, slotting, grinding etc. Examples of non conventional ( or also called non traditional or unconventional) are 1. Abrasive Jet Machining (AJM), 2. Ultrasonic Machining (USM), 3. Water Jet and Abrasive Water Jet Machining (WJM and AWJM), 4. Electro-discharge Machining (EDM) , 5. Electro Chemical Machining (ECM).

MECH-KIOT

CONVENTIONAL MACHINING PROCESS

MECH-KIOT

Basic Process

MECH-KIOT

Turning

• To produce rotational, axis-symmetric parts.

• Feed motion

• Feed relative to work piece.

MECH-KIOT

Fig-2 Basic scheme of Turning

Turning Operations • Facing

• Parting

• Grooving

• Drilling

• Screw cutting

MECH-KIOT

Workpiece Materials • Aluminum • Brass • Plastics • Cast Iron • Mild Steel

Drilling

• Drilling Operations • Reaming

• Tapping

• Counterboring

• Countersinking

• Centering

• Spot facing

MECH-KIOT

Fig-3 Basic scheme of Drilling

Workpiece Materials

MECH-KIOT

• Aluminum alloys • Magnesium alloys • Copper alloys • Stainless steels • Cast iron • Plastics

Milling

MECH-KIOT

Fig-4 Basic scheme of Milling

Milling Operations

• Slab Milling

• Face Milling

• End Milling

MECH-KIOT

Fig-6 Face Milling Fig-5 Slab Milling

Workpiece Materials

• Aluminum

• Brass

• Magnesium

• Nickel

• Steel

• Thermostat plastics

• Titanium

• Zinc

MECH-KIOT

Boring

MECH-KIOT

Fig-7 Boring operation

Boring Operations

• Single-Edge Boring

• Multi-Edge Boring

• Step Boring

• Reaming

MECH-KIOT

Workpiece Materials

• Aluminum

• Brass

• Plastics

• Cast Iron

• Mild Steel

Broaching

Broaching Operations

• Surface Broaching

• Pull down Broaching

• Push Broaching

• Pot Broaching MECH-KIOT

Fig-8 Broaching Tool

Workpiece Materials

• Aluminum

• Brass

• Bronze

• Plastic

• Malleable Iron

MECH-KIOT

Ref: Tool and Manufacturing Engineers Handbook– Tom Drozda, Charles Wick, John T. Benedict, Raymond F. Veilleux

Shaping

MECH-KIOT

Fig-9 Basic scheme of Shaping

Planing

MECH-KIOT

Fig-11 Basic scheme of Planing

INTRODUCTION

Types of Manufacturing Processes:

• Manufacturing processes can be broadly divided into two groups

1. Primary manufacturing processes

2. Secondary manufacturing processes.

• The Primary manufacturing process provides basic shape and size to the material as per designer’s requirement. For example: Casting, forming, powder metallurgy processes provide the basic shape and size.

• The Secondary manufacturing processes provide the final shape and size with tighter control on dimension, surface characteristics etc. Most of Material removal processes are mainly the secondary manufacturing processes.

MECH-KIOT

COMPARISON

Conventional Non Conventional

Chip Formation

Generally macroscopic chip formation by shear deformation.

Material removal may occur with chip formation or even no chip formation may take place. For example in AJM, chips are of microscopic size and in case of Electrochemical machining material removal occurs due to electrochemical dissolution at atomic level

Tool There may be a physical tool present. for example a cutting tool in a Lathe Machine,

There may not be a physical tool present. For example in laser jet machining, machining is carried out by laser beam. However in Electrochemical Machining there is a physical tool that is very much required for machining.

MECH-KIOT


Characteristic of Tool

Cutting tool is harder than work piece at room temperature as well as under machining conditions

There may not be a physical tool present. For example in laser jet machining, machining is carried out by laser beam. However in Electrochemical Machining there is a physical tool that is very much required for machining.

Material Removal Process

Material removal takes place due to application of cutting forces – energy domain can be classified as mechanical

Mostly NTM processes do not necessarily use mechanical energy to provide material removal. They use different energy domains to provide machining. For example, in USM, AJM, WJM mechanical energy is used to machine material, whereas in ECM electrochemical dissolution constitutes material removal.

MECH-KIOT


Tool Contact

Conventional machining involves the direct contact of tool and

work –piece

Whereas unconventional machining does not require the direct contact of tool and work

piece.

Surface Finish Lower accuracy and surface finish. Higher accuracy and surface finish.

MECH-KIOT


Material Economy

Suitable for every type of material economically.

Not Suitable for every type of material economically

Tool Life

Tool life is less due to high surface contact and wear.

Tool life is more

Material Wastage Higher waste of material due to high wear.

Lower waste of material due to low or no wear.

Noise Level Noisy operation mostly cause sound pollutions

Quieter operation mostly no sound pollutions are produced.

Cost Lower capital cost Higher Capital Cost

MECH-KIOT


Equipment Setup Easy set-up of equipment. Complex set-up equipment.

Operator level Skilled or un-skilled operator may required

Skilled operator required.

Process Generally they are manual to operate.

Generally they are fully automated process.

Efficiency They cannot be used to produce prototype parts very efficiently and economically.

Can be used to produce prototype parts very efficiently And economically.

Spare Parts Easily Available Not so easily available

MECH-KIOT

Conventional Vs Unconventional

1) Conventional machining process involved tool wearing as there is a physical contact between the tool and the work piece. In non-

conventional process, this is not the case.

2) Non-conventional tools are more accurate and precise than the conventional tool.

3) No noise pollution is created as a result of non-conventional methods as these tools are much quieter.

4) Tool life is long for non-conventional processing.

5) Non-conventional tools are very expensive than the conventional tools.

6) Non-conventional tools have complex setup and hence requires a skilful operation by expert workers, whereas conventional tools do


7) Spare parts of conventional machines are easily available but not for non-conventional machines.

8) Extremely hard material can be cut easily with the help of non conventional machining but for conventional machining raw material

should be less hard than cutting tool.

9) In conventional machining: Material removal takes place due to application of cutting forces – energy domain can be classified as

mechanical. In Non Conventional Machining :Mostly NTM processes do not necessarily use mechanical energy to provide material

removal. They use different energy domains to provide machining. For example, in USM, AJM, WJM mechanical energy is used to machine material, whereas in ECM electrochemical dissolution


10) Non Conventional machines can handle very complex jobs as compare to Conventional machining.

11) In Conventional machining because of scrap and chip formation more wastage of material .In case of non conventional machining no

chip formation hence less scrap.

UNIT II - MECHANICAL ENERGY BASED PROCESSES

Abrasive Jet Machining – Water Jet Machining – Abrasive Water

Jet Machining - Ultrasonic Machining.(AJM, WJM, AWJM and

USM). Working Principles – Equipment Used – Process

Parameters – MRR

MECH-KIOT

PEMP

EMM2512

MECH-KIOT

PEMP

EMM2512

Introduction

MECH-KIOT

• Advanced Machining Processes or NTM can

be used when mechanical methods are not

satisfactory, economical or possible due to:

– High strength or hardness

– Too brittle or too flexible

– Complex shapes

– Special finish and dimensional tolerance

requirements

– Temperature rise and residual stresses

Introduction

MECH-KIOT

• These advanced methods began to be introduced in the 1940's.

• Removes material by chemical dissolution, etching, melting, evaporation, and hydrodynamic action.

• These requirements led to chemical, electrical, laser, and high-energy beams as energy sources for removing material from metallic or non-metallic workpieces.

NTM Classification

MECH-KIOT

• Mechanical processes

– Ultrasonic machining

– Ultrasonically assisted machining

– Rotary ultrasonically assisted machining

– Abrasive jet machining

– Water jet cutting

– Abrasive water jet cutting

• Electrical processes

– Electrochemical machining

– Electrochemical grinding

– Electrochemical deburring

– Electrochemical honing

– Shaped tube electrolytic machining

NTM Classification

MECH-KIOT

• Thermal processes

– Electron beam machining

– Laser beam machining

– Electric discharge machining

– Electric discharge wire cutting

– Plasma arc machining

– Plasma-assisted machining

– Thermal deburring

• Chemical processes

– Chemical material removal

– Chemical milling

– Chemical blanking

– Chemical engraving

P

M.S Ramaiah School of Advanced Studies - Bangalore 22

MECH-KIOT

Mechanical Processing Ultra Sonic Machining (USM)

MECH-KIOT

• Hard materials like stainless steel, glass, ceramics, carbide, quartz

and semi-conductors are machined by this process.

• It has been efficiently applied to machine glass, ceramics, precision

minerals stones, tungsten.

• Brittle materials

Principle of Ultrasonic Machining

MECH-KIOT

• Material removal due to combination of four mechanisms

– Hammering of abrasive particles in the work surface by the tool

– Impact of free abrasive particles on the work surface

– Cavitation erosion

– Chemical action associated with the fluid employed


MECH-KIOT

• In USM process, the tool, made of softer material than that of the workpiece, is oscillated by the Booster and Sonotrode at a frequency of about 20 kHz with an amplitude of about 25.4 m (0.001 in).

• The tool forces the abrasive grits, in the gap between the tool and the workpiece, to impact normally and successively on the work surface, thereby machining the work surface.


MECH-KIOT

This is the standard mechanism used in most of the universal Ultrasonic

machines

PEMP

EMM2512 Principle of Ultrasonic Machining

MECH-KIOT

• During one strike, the tool moves down from its most upper remote position with a starting speed at zero, then it speeds up to finally reach the maximum speed at the mean position.

• Then the tool slows down its speed and eventually reaches zero again at the lowest position.

• When the grit size is close to the mean position, the tool hits the grit with its full speed.

• The smaller the grit size, the lesser the momentum it receives from the tool.

• Therefore, there is an effective speed zone for the tool and, correspondingly there is an effective size range for the grits.

• In the machining process, the tool, at some point, impacts on the largest grits, which are forced into the tool and workpiece.

• As the tool continues to move downwards, the force acting on these grits

increases rapidly, therefore some of the grits may be fractured.

• As the tool moves further down, more grits with smaller sizes come in contact

with the tool, the force acting on each grit becomes less.

• Eventually, the tool comes to the end of its strike, the number of grits under

impact force from both the tool and the workpiece becomes maximum.

• Grits with size larger than the minimum gap will penetrate into the tool and

work surface to different extents according to their diameters and the hardness

of both surfaces.

MECH-KIOT

Various work samples machined by USM

MECH-KIOT

A plastic sample that has inner

grooves that are machined using

USM

A plastic sample that has complex

details on the surface A coin with the grooving done by

USM

Mechanism

MECH-KIOT

Abrasive Slurry

•The abrasive slurry contains fine abrasive grains. The grains are

usually boron carbide, aluminum oxide, or silicon carbide ranging in

grain size from 100 for roughing to 1000 for finishing.

•It is used to microchip or erode the work piece surface and it is also

used to carry debris away from the cutting area.

Mechanism

MECH-KIOT

Tool holder

•The shape of the tool holder is cylindrical or conical, or a modified cone which

helps in magnifying the tool tip vibrations.

•In order to reduce the fatigue failures, it should be free from nicks, scratches

and tool marks and polished smooth.

Mechanism

MECH-KIOT

Tool

•Tool material should be tough and ductile. Low carbon steels and stainless steels give good performance.

•Tools are usually 25 mm long ; its size is equal to the hole size minus twice the size of abrasives.

•Mass of tool should be minimum possible so that it does not absorb the ultrasonic energy.

Applications

MECH-KIOT

It is mainly used for

• Drilling

• Grinding,

• Profiling

• Coining

• Piercing of dies

Advantages of USM

MECH-KIOT

• Machining any materials regardless of their conductivity

• USM apply to machining semi-conductor such as silicon, germanium etc.

• USM is suitable to precise machining brittle material.

• USM does not produce electric, thermal, chemical abnormal surface.

• Can drill circular or non-circular holes in very hard materials

• Less stress because of its non-thermal characteristics

Disadvantages of USM

MECH-KIOT

• USM has low material removal rate.

• Tool wears fast in USM.

• Machining area and depth is restraint in USM.

USM Characteristics

MECH-KIOT

Principle Oscillating tool in water-Abrasive slurry

Abrasive B4C, Al2O3, SiC

100 to 800 grit size

Frequency 15-30KHz

Amplitude 0.03 to 0.10mm

Tool material Soft tool steel

Stock removal WC=1.5in (38mm)

Glass=100in(254cm)

Critical parameters Frequency, amplitude, tool holder shape, grit size, hole depth, slurry

Material application Metals and alloys (particularly hard metals) Non-metallic

Part applications Round and irregular holes

Limitations Low metal removal rate Tool wear

Hole depth

Water Jet Machining & Abrasive Water Jet Machining - Definition

• In these processes (WJM and AJWM), the mechanical energy of

water and abrasive phases are used to achieve material removal

or machining.

MECH-KIOT

Water Jet Machining & Abrasive Water Jet Machining

• WJM and AWJM can be achieved using different approaches and

methodologies as enumerated below: • WJM - Pure

• WJM - with stabilizer

• AWJM – entrained – three phase – abrasive, water and air

• AWJM – suspended – two phase – abrasive and water.

o Direct pumping o Indirect pumping o Bypass pumping

MECH-KIOT

Water Jet Machining & Abrasive Water Jet Machining - Process

• Water is pumped at a sufficiently high pressure, 200-400 MPa

(2000-4000 bar) using intensifier technology.

• Water at such pressure is issued through a suitable orifice

(generally of 0.2- 0.4 mm dia).

• Potential energy of water is converted into kinetic energy, yielding

a high velocity jet (1000 m/s).

MECH-KIOT

Water Jet Machining

• In pure WJM, commercially pure water (tap water) is used for

machining purpose. However as the high velocity water jet is

discharged from the orifice, the jet tends to entrain atmospheric

air and flares out decreasing its cutting ability.

• Hence, quite often stabilisers (long chain polymers) that hinder

the fragmentation of water jet are added to the water.

MECH-KIOT

Abrasive Water Jet Machining

• In AWJM, abrasive particles like sand (SiO2), glass beads are added

to the water jet to enhance its cutting ability by many folds.

• AWJ are mainly of two types – entrained and suspended type as

mentioned earlier.

• In entrained type AWJM, the abrasive particles are allowed to

entrain in water jet to form abrasive water jet with significant

velocity of 800 m/s. MECH-KIOT

Abrasive Water Jet Machining – Setup Entrained Type

• LP Booster

• Hydraulic Drive

• Additive Mixer

• Direction Control

• Intensifier

• LP Intensifier

• HP Intensifier

• Accumulator

MECH-KIOT

Abrasive Water Jet Machining(entrained) – Cutting Head

• Diameter of the orifice 0.2 - 0.4mm.

• The velocity of the water jet is

estimated, assuming no losses as vwj =

(2pw / ρw)1/2 using Bernoulli’s equation

where, pw is the water pressure and ρw

is the density of water.

• The orifices are typically made of

sapphire. MECH-KIOT

Abrasive Water Jet Machining(entrained) – Mixing

• Mixing means gradual entrainment of abrasive particles within

the water jet and finally the abrasive water jet comes out of the

focussing tube or the nozzle. MECH-KIOT

Abrasive Water Jet Machining(entrained) – Mixing

• Focussing tube is made up of Tungsten Carbide.

• Usual Dimensions of focussing tube

Inner diameter : 0.8-1.6

Length : 50-80mm.

• Tungsten Carbide is used due to its abrasive resistant property.

MECH-KIOT

Abrasive Water Jet Machining – Suspended Type

MECH-KIOT

In suspension AWJM the abrasive water jet is formed quite differently.

There are three different types of suspension AWJ formed by direct, indirect and Bypass pumping method.

In suspension AWJM, preformed mixture of water and abrasive particles is pumped to a sufficiently high pressure and

stored in pressure vessel.

Abrasive Water Jet Machining – Suspended Type Indirect Pumping

MECH-KIOT

Bypass Pumping

Abrasive Water Jet Machining – Catcher

MECH-KIOT

“Catcher” is used to absorb the residual energy of the AWJ and dissipate the same.

Other Types: Pocket Type & Line Type

Water Jet &Abrasive Water Jet Machining – Applications

MECH-KIOT

Paint removal

Cleaning

Cutting soft materials

Cutting frozen meat

Textile, Leather industry

Mass Immunization

Surgery

Peening

Cutting

Pocket Milling

Drilling

Turning

Nuclear Plant Dismantling

Water Jet &Abrasive Water Jet Machining – Materials

MECH-KIOT

Steels

Non-ferrous alloys

Ti alloys, Ni- alloys

Polymers

Honeycombs

Metal Matrix Composite

Ceramic Matrix Composite

Concrete

Stone – Granite

Wood

Reinforced plastics

Metal Polymer Laminates

Glass Fibre Metal Laminates

PEMP

EMM2512

Water Jet Machining

MECH-KIOT

• Also known as hydrodynamic

machining

• The water jet acts as a saw

and cuts a narrow groove in

the material

• Pressures range from 60ksi to

200ksi (1500- 4000 MN/m2 )

• Jet velocity > 900m/s

PEMP

EMM2512

Water Jet Machining

MECH-KIOT

(a) Schematic illustration of water-jet machining.

(b) A computer-controlled, water-jet cutting

machine cutting a granite plate. (c) Example of

various nonmetallic parts produced by the water-

jet cutting process.

c

PEMP

EMM2512

Water Jet Machining

MECH-KIOT

• Process capabilities

– Can be used on any material up to 1” thick

– Cuts can be started at any location without predrilled holes

– No heat produced

– No flex to the material being cut

• Suitable for flexible materials

– Little wetting of the workpiece

– Little to no burr produced

– Environmentally safe

PEMP

EMM2512

Pros and Cons

MECH-KIOT

• Pros:

– No work hardening of pieces

– Faster than EDM or Laser

– Initial cost is less

• Cons:

– Accuracy is poor (0.003 inch)

– Nozzle life is short (40 hours)

PEMP

EMM2512

Abrasive Jet Machining

MECH-KIOT

• Uses high velocity dry air, nitrogen, or

carbon dioxide containing abrasive

particles

• Supply pressure is on the order of

125psi

• The abrasive jet velocity can be as

high as 100 ft/sec

• Abrasive size is approximately 400-

2000 micro-inches

PEMP

EMM2512

Abrasive Jet Machining

MECH-KIOT

Schematic illustration of Abrasive Jet Machining

PEMP

EMM2512

Abrasive Water Jet Machining

MECH-KIOT

• Very similar to water jet machining

– Water contains abrasive material

• Silicon carbide

• Aluminum oxide

– Higher cutting speed than that of conventional water

jet machining

• Up to 25 ft/min (7.5 m/min) for reinforce plastics

– Minimum hole diameter thus far is approximately

0.12 inches (3 mm)

– Maximum hole depth is approximately 1 inch

(25mm)

PEMP

EMM2512

M.S Ramaiah School of Advanced Studies - Bangalore 49

Surface Roughness and Tolerance table

MECH-KIOT

UNIT III - ELECTRICAL ENERGY BASED PROCESSES

Electric Discharge Machining (EDM)- working Principle- equipment's -Process Parameters-

Surface Finish and MRR- electrode / Tool – Power and control Circuits-Tool Wear –

Dielectric – Flushing – Wire cut EDM – Applications.

MECH-KIOT

PEMP

EMM2512

Electrochemical Machining

MECH-KIOT

• An electrolyte acts as a current carrier which

washes metal ions away from the workpiece

(anode) before they have a chance to plate on the

tool (cathode).

• The shaped tool is either solid or tubular.

• Generally made of brass, copper, bronze or

stainless steel.

• The electrolyte is a highly conductive inorganic

fluid.

• The cavity produced is the female mating image

of the tool shape

PEMP

EMM2512

A

At gr

r

r

f CI

V CIt

MECH-KIOT

R gr

A I

EA

gr

V C(EAt)

gr

V f

CE

V: Volume of Metal Removed; C: Specific Removal Rate

R: Resistance; g: Gap between Electrode and Work

r: Resistivity of Electrode; E: Applied Voltage

I: Current; t: Time; fr: Feed Rate

PEMP

EMM2512

Electrochemical Machining

MECH-KIOT


– Generally used to machine complex cavities and shapes in high

strength materials.

• Design considerations

– Not suited for producing sharp square corners or flat bottoms.

– No irregular cavities.

PEMP

EMM2512

Typical parts made by electrochemical machining. (a) Turbine blade made of a nickel alloy, 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.

MECH-KIOT

PEMP

EMM2512

• Pulsed electrochemical machining (PECM)

– Refinement of ECM.

– The current is pulsed instead of a direct current.

– Lower electrolyte flow rate.

– Improves fatigue life.

– Tolerance obtained 20 to 100 micro-meters.

(a) (b)

57

(a) Two total knee replacement systems showing metal implants (top pieces) with an ultrahigh molecular weight polyethylene insert (bottom pieces) (b) Cross-section of the ECM process as applied to the metal implant.

MECH-KIOT

PEMP

EMM2512

• Electrochemical grinding (ECG)

– Combines ECM with conventional grinding.

– Similar to a conventional grinder, except that the wheel is a rotating cathode with abrasive particles.

• The abrasive particles serve as insulators and they remove electrolytic products from the working area.

– Less then 5% of the metal is removed by the abrasive action of the wheel.

Schematic illustration of the electrochemical – grinding process. (b) Thin slot produced on

a round nickel – alloy tube by this process.

MECH-KIOT

PEMP

EMM2512

• Electrochemical honing

– Combines the fine abrasive action of honing with electrochemical action.

– Costs more than conventional honing.

– 5 times faster than conventional honing.

– The tool lasts up to 10 times longer.

• Design considerations for ECG

– Avoid sharp inside radii.

MECH-KIOT

PEMP

EMM2512

Electric Discharge Machining (EDM)

MECH-KIOT

• Principle of operation

– Based on the erosion of metal by spark discharge

• Components of operation

– Shaped tool

• Electrode

– Workpiece

• Connected to a DC power supply

– Dielectric

• Nonconductive fluid

PEMP

EMM2512

(a) (b) (c)

(a)Schematic illustration of the electrical-discharge machining process. This is one of the most widely used machining processes, particularly for die-sinking operations.

(b)Examples of cavities produced by the electrical-discharge machining process, using shaped electrodes. Two round parts (rear) are the set of dies for extruding the aluminum the aluminum piece shown in front.

(c)A spiral cavity produced by ECM using a slowly rotating electrode, similar to a screw thread.

MECH-KIOT

Electric Discharge Machining

MECH-KIOT

• When the potential difference is sufficiently high, the dielectric breaks down and a transient spark discharges through the fluid, removing a very small amount of material from the workpiece

• Capacitor discharge

– 200-500 kHz

• This process can be used on any electrically conductive material


MECH-KIOT

T 1.23 MRR

KI

Example

A certain alloy whose melting point = 1100 C is to be machined in an EDM

operation. If discharged current = 25 amps, what is the expected metal removal rate?

Use Equation (MRR=KI/T 1.23), the anticipated metal removal m

rate is MRR = 664 (25)/(11001.23) = 3.01 mm3/s


MECH-KIOT

• Movement in the X&Y axis is controlled by CNC systems

• Overcut (in the Z axis) is the gap between the electrode and the workpiece

– Controlled by servomechanisms

– Critical to maintain a constant gap


MECH-KIOT

• Dielectric fluids

– Act as a dielectric

– Provide a cooling medium

– Provide a flushing medium

• Common fluids

– Mineral oils

– Distilled/Deionized water

– Kerosene

– Other clear low viscosity fluids are available which are easier to clean but more expensive


MECH-KIOT

• Electrodes

– Graphite

– Brass

– Copper-tungsten alloys

– Formed by casting, powder

metallurgy, or CNC machining

– On right, human hair with a

0.0012 inch hole drilled through


• Electrode wear

– Important factor in maintaining the gap between the electrode and the workpiece

– Wear ratio is defined as the amount of material removed to the volume of electrode wear

• 3:1 to 100:1 is typical

– No-wear EDM is defined as the EDM process with reversed polarity using copper electrodes

MECH-KIOT


MECH-KIOT


– Used in the forming of dies

for forging, extrusion, die

casting, and injection

molding

– Typically intricate shapes


MECH-KIOT

• Material removal rates affect finish quality

– High removal rates produce very rough surface finish with poor surface integrity

– Finishing cuts are often made at low removal rates so surface finish can be improved


– Design so that electrodes can be simple/economical to produce

– Deep slots and narrow openings should be avoided

– Conventional techniques should be used to remove the bulk of material

PEMP

Schematic illustration of producing an inner cavity by EDM, using a specially designed electrode with a hinged tip, which is slowly opened and rotated to produce the large cavity.

MECH-KIOT

Wire EDM

MECH-KIOT

• Similar to contour cutting with a bandsaw

• Typically used to cut thicker material

– Up to 12” thick

– Also used to make punches, tools and dies from hard materials

Schematic illustration of the

wire EDM process.

As much as 50 hours of

machining can be performed

with one reel of wire, which is

then discarded.

Wire EDM

MECH-KIOT

• Wire

– Usually made of brass, copper, or tungsten

– Range in diameter from 0.012 – 0.008 inches

– Typically used at 60% of tensile strength

– Used once since it is relatively inexpensive

– Travels at a constant velocity ranging from 6-360 in/min

– Cutting speed is measured in cross sectional area per unit time (varies with

material)

• 18,000 mm^2/hour

• 28 in^2/hour

Wire EDM

MECH-KIOT

• Multiaxis EDM

– Computer controls for controlling the cutting path of the wire and its angle with respect to the workpiece plane

– Multiheads for cutting multiple parts

– Features to prevent and correct wire breakage

– Programming to optimize the operation

Electric Discharge Grinding

MECH-KIOT

• Similar to the standard grinder

• Grinding wheel is made of graphite or brass and contains no abrasives

• Material is removed by spark discharge between the workpiece and rotating wheel

• Typically used to sharpen carbide tools and dies

• Can also be used on fragile parts such as surgical needles, thin-wall tubes, and honeycomb structures

• Process can be combined with electrochemical discharge grinding

• Material removal rate is similar to that of EDM

– MRR = KI where K is the workpiece material factor in mm^3/A- min

Laser Beam Machining

MECH-KIOT

• The source of the energy is the laser

– Light Amplification by Stimulated Emission of Radiation

• The focus of optical energy on the surface of the workpiece melts and evaporates portions of the workpiece in a controlled manner

– Works on both metallic and non-metallic materials

• Important considerations include the reflectivity and thermal conductivity of the material

• The lower these quantities the more efficient the process

(a) Schematic illustration of the laser-beam machining process. (b) and

(c) Examples of holes produced in nonmetallic parts by LBM.

MECH-KIOT


MECH-KIOT

• Lasers may be used in conjunction with a gas such as oxygen, nitrogen, or

argon to aid in energy absorption

– Commonly referred to as laser beam torches

– The gas helps blow away molten and vaporized material

• Process capabilities also include welding, localized heat treating, and

marking

• Very flexible process

– Fiber optic beam delivery

– Simple fixtures

– Low setup times


MECH-KIOT


– Sharp corners should be avoided

– Deep cuts will produce tapered walls

– Reflectivity is an important consideration

• Dull and unpolished surfaces are preferable

– Any adverse effects on the properties of the machined

materials caused by the high local temperatures and heat

affected zones should be investigated

Electron Beam Machining

MECH-KIOT

• Energy source is high velocity electrons which strike the workpiece

• Voltages range from 50- 200kV

• Electron speeds range from 50-80% the speed of light

• Requires vacuum

Electron Beam Machining

MECH-KIOT

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

Plasma Arc cutting

MECH-KIOT

– Ionized gas is used to rapidly cut ferrous and nonferrous sheets and plates

– Temperatures range from 9400-17,000 F (> 100000 C)

– The process is fast, the kerf width is small, and the surface finish is good

– Parts as thick as 6” can be cut

– Much faster than the EDM and LBM process

– Design considerations

• Parts must fit in vacuum chamber

• Parts that only require EBM machining on a small portion should be manufactured as a number of smaller components

Laser cutting

MECH-KIOT

Light Amplification by Stimulated Emission of Radiation

• High energy density (small focus area)

• Uses: Cutting, welding, precision holes

• Common lasers: CO2, Nd:YAG

• Continuous power or Pulsed (more precise)

Nd:YAG laser cut: larger dia and

heat-affected zone

Femtosecond laser cut: smaller diameter, lower thermal damage Microscope image of laser cut hole

Cost of Machining/Surface Finish Required

MECH-KIOT

Increase in the cost of

machining and finishing a

part as a function of the

surface finish required.

Ultrasonic Machining - Definition

• Ultrasonic Machining is a non-traditional process, in which

abrasives contained in a slurry are driven against the work by a

tool of desired shape oscillating at low amplitude (25-100

microns) and high frequency (15-30 kHz)

MECH-KIOT

Ultrasonic Machining - Process

• It is employed to machine hard and brittle materials (both electrically

conductive and non conductive material) having hardness usually

greater than 40 HRC.

MECH-KIOT


• In Ultrasonic machining material removal is due to crack

initiation, propagation and brittle fracture of material.

MECH-KIOT


MECH-KIOT


High power sine wave generator

• This unit converts low frequency (60 Hz) electrical power to high frequency

(20kHz) electrical power.

Transducer

• The high frequency electrical signal is transmitted to traducer which converts

it into high frequency low amplitude vibration.

• Essentially transducer converts electrical energy to mechanical vibration.

There are two types of transducer used

1. Piezo electric transducer

2. Magneto-stricitve transducer. MECH-KIOT

Piezo electric transducer

• These transducer generate a small electric current when they are

compressed. Also when the electric current is passed though

crystal it expands. When the current is removed , crystal attains

its original size and shape.

• Such transducers are available up to 900 Watts.

• Piezo electric crystals have high conversion efficiency of 95%.

MECH-KIOT

Magneto-stricitve transducer.

• These also changes its length when subjected to strong magnetic

field. These transducer are made of nickel , nickel alloy sheets.

• Their conversion efficiency is about 20-30%.


• The maximum change in length can be achieved is about 25

microns.

MECH-KIOT


Tool holder. OR Horn.

• The tool holder holds and connects the tool to the transducer.

• It virtually transmits the energy and in some cases, amplifies the

amplitude of vibration.

• Material of tool should have good acoustic properties, high

resistance to fatigue cracking.

• Commonly used tool holders are Monel, titanium, stainless steel.

• Tool holders are more expensive, demand higher operating cost. MECH-KIOT


Tool

• Tools are made of relatively ductile materials like Brass, Stainless

steel or Mild steel.

• Tool wear rate (TWR) can be minimized.

• The value of ratio of TWR and MRR depends on kind of abrasive,

work material and tool materials.

MECH-KIOT

Ultrasonic Machining - Process parameters

• Amplitude of vibration ( 15 to 50 microns)

• Frequency of vibration ( 19 to 25 kHz).

• Feed force (F) related to tool dimensions

• Feed pressure

• Abrasive size

• Abrasive material Al203, SiC, B4C, Boron silicarbide, Diamond.

• Flow strength of the work material

• Flow strength of the tool material

• Contact area of the tool

• Volume concentration of abrasive in water slurry MECH-KIOT

Ultrasonic Machining - Process parameters

• Tool

Material of tool

Shape

Amplitude of vibration

Frequency of vibration

Strength developed in tool

• Work material

Material

Impact strength

Surface fatigue strength

• Slurry

Abrasive – hardness, size, shape and quantity of abrasive flow MECH-KIOT

Abrasive Jet Machining - 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 removed by

erosion by high velocity abrasive particles.

MECH-KIOT

Abrasive Jet Machining - Process

MECH-KIOT

Abrasive Jet Machining - Process

MECH-KIOT

The high velocity stream of abrasives is generated by converting pressure energy of carrier gas or air to its Kinetic

energy and hence high velocity jet.

Nozzles directs abrasive jet in a controlled manner onto work material.

The high velocity abrasive particles remove the material by micro-cutting action as well as brittle fracture of the

work material.

ULTRASONIC MACHINING

• Introduction.

• Equipment.

• Tool Materials and Tool Size and Abrasive Slurry.

• Cutting tool system design

• Effect of parameter: Effect of amplitude and frequency and vibration.

• Effect of abrasive grain diameter.

• Effect of applied static load.

• Effect of slurry, tool and work material.

• USM process characteristics: Material removal rate, tool wear, Accuracy, surface finish, applications,

MECH-KIOT

INTRODUCTION

• What is the Difference between Frequency, Wavelength and Amplitude?

• Frequency tells us how many waves pass through a point at a second.

• Wavelength tells us the length of those waves.

• Amplitude tells us how big the wave is.

• In USM, abrasives contained in a slurry are driven against the work by a tool oscillating at low amplitude (25-100 microns) and high frequency (15-30 kHz).

MECH-KIOT

PRINCIPLE

• The machining zone (between the tool and the work piece) is flooded with hard abrasive particles generally in the form of water based slurry.

• As the tool vibrates over the work piece, abrasive particles acts as indenter and indent both work and tool material .

• Abrasive particles , as they indent , the work material would remove the material from both tool and work piece.

• In Ultrasonic machining material removal is due to crack initiation, propagation and brittle fracture of material.

MECH-KIOT

EQUIPMENT

MECH-KIOT

EQUIPMENT

• Ultrasonic Machining consists of :

1. High Power sine wave generator.

2. Magneto-strictive Transducer.

3. Tool Holder.

4. Tool.

MECH-KIOT

MECH-KIOT

High Power Sine Wave Generator

• This unit converts low frequency (50 Hz) electrical power to high frequency (20kHz) electrical power.

MECH-KIOT

TRANSDUCER

• The high frequency electrical signal is transmitted to traducer which converts it into high frequency low amplitude vibration.

• Essentially transducer converts electrical energy to mechanical vibration. There are two types of transducer used

1. Piezo electric transducer

2. Magneto-stricitve transducer.

MECH-KIOT

MAGNETOSTRICTIVE TRANSDUCER

• These transducer are made of nickel , nickel alloy sheets.

• Their conversion efficiency is about 20-30%.


• The maximum change in length can be achieved is about 25 microns.

MECH-KIOT

TOOL HOLDER OR HORN

• The tool holder holds and connects the tool to the transducer. It virtually transmits the energy and in some cases, amplifies the amplitude of vibration.

• Material of tool should have good acoustic properties, high resistance to fatigue cracking.

• Due measures should be taken to avoid ultrasonic welding between transducer and tool holder.

• Commonly used tool holders are Monel, titanium, stainless steel.

• Tool holders are more expensive, demand higher operating cost.

MECH-KIOT

TOOL

• Tools are made of relatively ductile materials like Brass, Stainless steel or Mild steel so that Tool wear rate (TWR) can be minimized.

• The value of ratio of TWR and MRR depends on kind of abrasive, work material and tool materials.

MECH-KIOT

Mechanism of Material Removal

MECH-KIOT

Material Removal Models in USM

The following are the Material Removal Models used in USM

1. Throwing of abrasive grains.

2. Hammering of abrasive grains.

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

4. Chemical erosion due to micro –agitations.

MECH-KIOT

MECH-KIOT

Effect of Slurry, Tool and Work Material

• MRR increases with slurry concentration.

• Slurry saturation occurs at 30 to 40% abrasive/water mixture.

• Material Removal rate drops with increasing viscosity.

• The pressure with which the slurry is fed into the cutting zone affects MRR .

• In some cases MRR can be increased even ten times by supplying the slurry at increased pressure.

• The shape of the tool affects the MRR. Narrower rectangular tool gives more MRR compared to square cross section.

MECH-KIOT

• Conical tool gives twice MRR compared to cylindrical tool.

• The brittle behavior of material is important in determining the MRR.

• Brittle material can be cut at higher rates than ductile materials.

MECH-KIOT

APPLICATIONS

• Machining of cavities in electrically non-conductive ceramics

• Used to machine fragile components in which otherwise the scrap rate is high

• Used for multistep processing for fabricating silicon nitride (Si3N4) turbine blades

• Large number of holes of small diameter could be machined. 930 holes with 0.32mm has been reported ( Benedict, 1973) using hypodermic needles

• Used for machining hard, brittle metallic alloys, semiconductors, glass, ceramics, carbides etc.

MECH-KIOT

• Used for machining round, square, irregular shaped holes and surface impressions.

• Used in machining of dies for wire drawing, punching and blanking operations

• USM can perform machining operations like drilling, grinding and milling operations on all materials which can be treated suitably with abrasives.

• USM has been used for piercing of dies and for parting off and blanking operations.

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

MECH-KIOT

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

• USM can be used to cut industrial diamonds

• USM is used for grinding Quartz, Glass, ceramics

• Cutting holes with curved or spiral centre lines and cutting threads in glass and mineral or metallo-ceramics.

MECH-KIOT

ADVANTAGES

• It can be used machine hard, brittle, fragile and non conductive material

• No heat is generated in work, therefore no significant changes in physical structure of work material

• Non-metal (because of the poor electrical conductivity) that cannot be machined by EDM and ECM can very well be machined by USM.

• It is burr less and distortion less processes.

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

MECH-KIOT

DISADVANTAGES

• Low Metal removal rate.

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

• 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.

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

MECH-KIOT

UNIT IV - CHEMICAL AND ELECTRO-CHEMICAL ENERGY BASED PROCESSES

Chemical Machining and Electro-Chemical machining (CHM

and ECM)-Etchants – Maskant - Techniques of Applying

Maskants - Process Parameters – Surface Finish and MRR-

Applications. Principles of ECM- Equipments- Surface

Roughness and MRR Electrical Circuit- Process Parameters-

ECG and ECH - Applications.. MECH-KIOT

Chemical Process

MECH-KIOT

Chemical machining

–Uses chemical dissolution to dissolve material from the

workpiece.

–Can be used on stones, most metals and some ceramics.

–Oldest of the advanced machining processes.

(a)Missile skin-panel section contoured by chemical milling to improve the stiffness-to weight ratio of the

part.

(b)Weight reduction of space launch vehicles by chemical milling aluminum-alloy plates.

These panels are chemically milled after the plates have first been formed into shape by processes such as roll

forming or stretch forming. The design of the chemically machined rib patterns can be modified readily at

minimal cost.

MECH-KIOT

Chemical milling

MECH-KIOT

• Chemical milling - shallow cavities are produced on plates,

sheets, forgings, and extrusions, generally for the overall

reduction of weight.

– Can be used with depths of metal removal as large as 12 mm.

– Masking is used to protect areas that are not meant to be

attacked by the chemical.

(a)Schematic illustration of the chemical machining process. Note that no forces or machine

tools are involved in this process.

(b)Stages in producing a profiled cavity by machining; not the undercut.

Chemical milling

MECH-KIOT

Chemical Blanking

MECH-KIOT

• Similar to the blanking of sheet metals with the exception

that the material is removed by chemical dissolution rather

than by shearing.

– Printed circuit boards.

– Decorative panels.

– Thin sheet-metal stampings.

– Complex or small shapes.

• Photochemical blanking/machining

– Modification of chemical milling.

– Can be used on metals as thin as .0025 mm.

• Applications

– Fine screens.

– Printed circuit boards.

– Electric-motor laminations.

– Flat springs.

– Masks for color televisions

(i) Clean (ii) Apply resist (iii) UV exposure (iv) Development (v) Etching (v) Stripping

MECH-KIOT

Chemical Machining Design Considerations

MECH-KIOT

• No sharp corners, deep or narrow cavities, severe tapers,

folded seam, or porous workpiece materials.

• Undercuts may develop.

• The bulk of the workpiece should be shaped by other

processes prior to chemical machining.

THANK YOU

MECH-KIOT

knowledge institute of technology ......broaching, slotting, grinding etc. examples of non...

Documents