Nontraditional Manufacturing Process

NONTRADITIONAL MANUFACTURING

PROCESSESBY

RAKESH CHANDER SAINIASST. PROF.

MAIT, DELHI, INDIA

RCSAINI.BLOGSPOT.COM

Rcsaini.blogspot.com

CLASSIFICATION OF

UNCONVENTIONAL MACHINING PROCESSES

Need of Unconventional Machining New materials & alloys with very low

mach inability. Producing complicated geometries. Machining a complicated turbine blade

made of super alloys.

rcsaini.blogspot.com

Unconventional machining processes


Energy Type

Mechanical ElectrochemicalMechanical

&Electrochemical

ThermalChemical

Mechanical Mechanics of material removal: Erosion Energy source: Mechanical / fluid motion Process: Abrasive jet machining(AJM) and Ultrasonic machining(USM)


Electrochemical Mechanics of material removal: Ion displacement

Energy source: Electric Current

Process: Electrochemical machining (ECM)


Mechanical & Electrochemical

Mechanics of material removal: Ion displacement & Plastic Shear

Energy source: Electric Current and mechanical motion

Process: Electrochemical grinding (EGM)


Chemical1. Mechanics of material removal: Corrosive action Energy source: Corrosive agent Process: Chemical Machining2. Mechanics of material removal :Fusion and vaporization Energy source: Electric spark & High speed electrons Process: Electric discharge machining and Electron

beam machining


Thermal

Energy source:-Powerful radiation Process:- Laser beam machining Energy source:-Ionized substance Process:- Ion beam machining & Plasma arc

machining

Rcsaini.blogspot.com

Electrical Discharge Electrical Discharge MachiningMachining


Electrical Discharge Machining (EDM) Thermal erosion process in which

an electrically generated spark burns or vaporizes electrically conductive material. The spark is generated due to a gap between the work piece and a tool. The smaller the gap the better the accuracy and the slower the MRR. The spark generates a temperature of 14000-21000 oF. Introduced in the 1940s


EDM Machining action forms a gap between the

part and the electrode (tool) which causes a spark that removes the material

Electrode is (-) and the part is (+) Electrodes can be made from

Brass Copper Graphite


EDM Cutting action takes place in a dielectric fluid

which helps to contain the spark and flush away chips

Metal removal rates (MRR) are low compared to other process like milling EDM, MRR= 1 cu. in to 15 cu. in per hr.


EDM Applications

Finish geometry for molds ( die sinking)Ram

Most common die material include:Hardened SteelHeat-treated SteelCarbides

Punch & dies for blanking, shearing, and progressive die toolingWire


Materials That can be EDMed

Titanium Hot rolled Steel Cold Rolled Steel Copper Brass High Temperature Alloys


MECHANICS OF EDM


EDM CIRCUITS Resistance-capacitance relaxation circuit

with a constant DC. Rotary impulse generator Controlled pulse circuit


EDM CIRCUITS R-C relaxation

circuit


EDM CIRCUITS Rotary impulse generator


EDM CIRCUITS Controlled pulse

circuit


CHARACTERISTICS OF MRR


Benefits No cutting force generated Intricate details Superior surface finish Accuracy/Repeatability Smaller/Deeper Holes Well suited for automation Allows heat treatment before EDMing

eliminating the risk of distortions.rcsaini.blogspot.com

Limitations Low MRR Electrodes require lead-time and are

consumable work piece must be electrically

conductive


EDM Surface Layers Resulting surface has three distinct layers

Top layer: Expelled molten material and electrode material

Recast (white) layer: Metallurgical altered. May be reduced using the right controls, or removed using polishing

Heat affected layer: Affected by the process heat, but not melted.


EDM Cycle Cycle consists of 2 parts: On-time: Spark is on Off-time: Spark is off All work takes place during the on-time Spark length is determined by: Work Material Electrode material Rough or finish cutting Desired surface finish Flushing conditions


EDM Cycle Long On-time

High MRRRough surfaceLarger recast layerDeeper heat-affected layer

Short On-timeAvoids problems above, butMetal may not be removed fast enough; disturbing the spark.


EDM- Types RAM EDM (Die sinker or vertical EDM)

Uses a tool with the negative of the desired shape as an electrode.

Wire EDM

Uses a wire as an electrode, mainly for cutting or contouring.


RAM EDM Subsystems Power Supply Dielectric System Electrode Servo System


RAM EDM Subsystems Power Supply Provides a series of DC current discharges

between the electrode and the work piece.

Controls the servo system to maintain the gap.

Power is automatically cutoff if a short circuit occurs.


RAM EDM Subsystems Dielectric System (dielectric = electrically nonconducting)

Introduces clean dielectric fluid into the cutting zone. Flushes away cutting debris Fluid is pumped through nozzles or holes in the

electrode and/or work piece. Low pressure holes are preferable.

Low Viscosity Absence of toxic vapours Chemically neutrality Absence of inflaming tendency Low Cost


RAM EDM Subsystems Electrode Shape is the negative of the cavity to be

generated. Has a -ve polarity. Made of high strength material with high

melting point, easy to machine (Brass, Copper, Graphite)

Orbiting could be used to contour complex shapes instead of straight sinking


RAM EDM Subsystems Servo System It feeds the electrode into the work

piece maintaining a constant gap. Continuous check for a short circuit.


Wire EDM A wire (reel) is used as an electrode and fresh wire is

introduced all the time through the wire subsystem.

Uses deionized water which removes heat and reduces the recast layer.

Wire diameter is usually 0.002-0.013”

speed is about 20-25 sq. in/hr.


Wire EDM Cut plates as thick as 300mm

Could produce holes with different top/bottom profiles. This is important for extrusion applications

Could be used for cutting stacked parts, but flushing is problematic

May be used for deep hole drilling L:D > 30:1


Modern Wire EDM Components Computer controls of cutter path Automatic self-threading features Multiheads for cutting more than one part at the

same time Wire breakage prevention controls Programmed machine cycles (similar to CNC)


Laser Beam Machining


Introduction Laser stands for light amplification by stimulated emission of radiation. The

underline working principle of laser was first put forward by Albert Einstein in 1917 though the first industrial laser for experimentation was developed around 1960s.

Laser beam can very easily be focused using optical lenses as their wavelength ranges from half micron to around 70 microns.

Focused laser beam as indicated earlier can have power density in excess of 1 MW/mm2. As laser interacts with the material, the energy of the photon is absorbed by the work material leading to rapid substantial rise in local temperature. This in turn results in melting and vaporization of the work material and finally material removal.


Laser Fundamentals


Acronym of Light Amplification Stimulated Emission of Radiation


Basics of Laser Atoms are present initially at the Ground State.

The atoms go to Excited State when a high energy is applied (called “pumping’”).

When atoms moves back to the ground state, photons (particle of light) are released.

Two mirrors reflect the photons back and forth and “excite” more electrons.

One mirror is partially reflective to allow some light to pass through which creates a narrow laser beam.


Stimulated Emission

1. Laser in OFF state

2. Flash Tube excite atoms in the Ruby Rod

3. Some Atoms emit Photons


Stimulated Emission Contd.4. 4. Photons run parallel to the rod direction & reflect back and forth

and thus stimulate emission on more atoms

5. Laser light passes through partially-reflective mirror


Laser Beam Characteristics Monochromaticity: The rays of laser beam are

monochromatic ie it has one wavelength. Coherence: All waves are in phase with wavelength varying

from 0.1- 70 µm. Collimated: The rays of laser beam are perfectly parallel . Polarized: Electric field oscillates in one plane. Extremely Bright: The rays of laser beam produce power

density as high as 107 W/mm2


Mechanics of Material Removal Machining by laser beam is achieved

through the following phases:- Interaction of laser beam with

work material: The absorbed light propogates into the medium and energy is transferred to lattice atoms in form of heat. The absorption is described by Lambert’s law.

Heat conduction and temperature rise

Melting , vapourisation.rcsaini.blogspot.com

Equipment Setup A coiled Xenon flash tube is

placed around the ruby rod .

Internal surface of the container is made highly reflecting.

Capacitor is charged and very high voltage is applied to triggering electrode for flash initiation.


Working Principle The emitted laser beam is focussed by a

lens system and the focussed beam meets the work surface removing small portion of the material by vapourisation.

A very small fraction of the molten metal is vapourised so quickly that substantial mechanical impulse is generated throwing out large portion of liquid metal.


Lasing Medium Many materials can be used as the heart of the laser. Depending on the lasing medium

lasers are classified as solid state and gas laser. Solid-state lasers are commonly of the following type • Ruby which is a chromium – alumina alloy having a wavelength of 0.7 μm • Nd-glass lasers having a wavelength of 1.64 μm • Nd-YAG laser having a wavelength of 1.06 μm

These solid-state lasers are generally used in material processing. The generally used gas lasers are

• Helium ,Neon , Argon , CO2 etc.

Lasers can be operated in continuous mode or pulsed mode. Typically CO2 gas laser is

operated in continuous mode and Nd – YAG laser is operated in pulsed mode.

Nd:YAG (neodymium-doped yttrium aluminium garnet; Nd:Y3Al5O12) is a crystal that is used as a lasing medium for solid-state lasers.


Expression for Surface temperature

θ(0,t)=2H/k(αt/∏)0.5 where K- thermal conductivityα- thermal diffusivityH- heat flux θ(0,t)- surface temperaturet-time


Time required to reach Melting Temperature

tm=∏/α(θmk/2H)2 where

α- thermal diffusivity k- thermal conductivity

θm – melting temperature of materialH- heat flux

tm- time required for surface to reach this temperature


Critical Parameters of Laser Beam Machining Mechanics of Material removal : Melting &

vaporization Medium : Normal Atmosphere Tool :High power laser beam Maximum material removal rate : 5mm3/min Specific power consumption:1000 W/mm3/min Critical Parameters: Beam power intensity , beam

diameter , melting temperature.


Advantages of Laser beam Machining Laser machining is a thermal process: it depends on

thermal and optical properties rather than the mechanical properties

Laser machining is a non-contact process: No cutting forces generated

Laser machining is a flexible process Laser machining produces a higher precision and

smaller kerb* widths results (as small as 0.005mm dia hole)

*Kerf is the gap created after melting away the material.rcsaini.blogspot.com

Advantages of Laser beam Machining For most industrial materials up to 10mm thick, laser cutting has a significantly higher

MRR. Laser Cutting has ability to cut from curved work-pieces. For cutting fibrous material (wood, paper, etc.) laser cutting eliminates residue and debris. In laser machining there is no physical tool. Thus no machining force or wear of the tool

takes place. Large aspect ratio in laser drilling can be achieved along with acceptable accuracy or

dimension, form or location Micro-holes can be drilled in difficult – to – machine materials Though laser processing is a thermal processing but heat affected zone specially in pulse

laser processing is not very significant due to shorter pulse duration.


Disadvantages of Laser beam Machining

It has very large power consumption. It cannot cut materials with high heat

conductivity and high reflectivity. Efficiency of LBM process is very low ie

about 0.3 to 0.5 %. Laser cutting effectiveness reduces as the

workpiece thickness increases.rcsaini.blogspot.com

Applications Manufacturing of metal sheets for truck bed

hitch plates. Splicing of aluminium sheets in the aircraft

industry Cutting of Multi Layered Insulation for spacecraft Laser beam is used for drilling micro holes(up to

250 µm diameter) and cutting very narrow slots.


ApplicationsExamples of laser cutting using

pulsed CO2 LaserHeight following Laser nozzle


ApplicationsRazor blades are spot welded using

laserModels created by rapid

prototyping


Nontraditional Manufacturing Process

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