nontraditional manufacturing process
DESCRIPTION
This presentation includes classification of nontraditional manufacturing process, EDM and LBM.TRANSCRIPT
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.
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Unconventional machining processes
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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)
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Electrochemical Mechanics of material removal: Ion displacement
Energy source: Electric Current
Process: Electrochemical machining (ECM)
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Mechanical & Electrochemical
Mechanics of material removal: Ion displacement & Plastic Shear
Energy source: Electric Current and mechanical motion
Process: Electrochemical grinding (EGM)
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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
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Thermal
Energy source:-Powerful radiation Process:- Laser beam machining Energy source:-Ionized substance Process:- Ion beam machining & Plasma arc
machining
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Electrical Discharge Electrical Discharge MachiningMachining
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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
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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
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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.
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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
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Materials That can be EDMed
Titanium Hot rolled Steel Cold Rolled Steel Copper Brass High Temperature Alloys
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MECHANICS OF EDM
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EDM CIRCUITS Resistance-capacitance relaxation circuit
with a constant DC. Rotary impulse generator Controlled pulse circuit
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EDM CIRCUITS R-C relaxation
circuit
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EDM CIRCUITS Rotary impulse generator
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EDM CIRCUITS Controlled pulse
circuit
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CHARACTERISTICS OF MRR
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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
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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.
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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
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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.
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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.
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RAM EDM Subsystems Power Supply Dielectric System Electrode Servo System
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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.
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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
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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
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RAM EDM Subsystems Servo System It feeds the electrode into the work
piece maintaining a constant gap. Continuous check for a short circuit.
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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.
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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
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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)
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Laser Beam Machining
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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.
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Laser Fundamentals
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Acronym of Light Amplification Stimulated Emission of Radiation
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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.
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Stimulated Emission
1. Laser in OFF state
2. Flash Tube excite atoms in the Ruby Rod
3. Some Atoms emit Photons
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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
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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
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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.
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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.
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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.
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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
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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
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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.
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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.
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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.
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ApplicationsExamples of laser cutting using
pulsed CO2 LaserHeight following Laser nozzle
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ApplicationsRazor blades are spot welded using
laserModels created by rapid
prototyping
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