2. Title of slide
Lesson Objectives
In this chapter we shall discuss the following:
1. Electro Chemical Machining.
2. Electro discharge machining
3. Electron beam machining.
4. Laser beam machining.
5. process parameters; Applications;
Advantages and limitations
Learning Activities
1. Look up
Keywords
2. View Slides;
3. Read Notes,
4. Listen to
lecture
Keywords:
3. Parts Made by Advanced
Machining Processes
Figure :Examples of parts produced by advanced machining processes. (a) Samples of parts
produced from water jet cutting. (b) Turbine blade, produced by plunge EDM, in a fixture to
produce the holes by EDM.
(a)
(b)
4. Electrical Discharge Machining
• EDM is a thermal process which makes use of spark discharges to erode
material from the workpiece. Since spark discharges occur in EDM, it is
also called as "spark machining".
• The material removal takes place in EDM through a rapid series of
electrical discharges, passing between the electrode and the workpiece
being machined.
• The fine chips of material removed from the workpiece gets flushed away
by the continuous flowing di-electric fluid.
• Repetitive discharge creates a set of successively deeper craters in the work
piece until the final shape is produced.
• The cavity formed in EDM is a replica of the tool shape used as the
erosions occur in the confined area.
• EDM process is best suited for making intricate cavities and contours in
electrically conducting hard & difficult to m/c ( by conventional methods)
metals such as hardened tool-steels, carbides, titanium, inconel & kovar.
5. Electrical-Discharge Machining Process
Figure (b) Examples of cavities produced by EDM process, using shaped electrodes. Two round parts (rear) are the set
of dies for extruding the aluminum piece shown in front (c) A spiral cavity produced by EDM using a slowly rotating
electrode similar to a screw thread. (d) Holes in a fuel-injection nozzle made by EDM; the material is heat-treated steel.
Figure : Schematic illustration of the electrical-discharge machining process.
6. Mechanism of Material Removal
in EDM Process
The material removal process by a single spark is as follows:
• An intense electric field develops in the gap between electrode and workpiece.
• There are some contaminants inside the dielectric fluid which build a high
conductivity bridge between the electrode and workpiece.
• When the voltage increases, the bridge and dielectric fluid between the
electrode and workpiece heat up.
• The dielectric is ionized to form a spark channel.
• The temperature and pressure rapidly increase and a spark is generated.
• A small amount of material is evaporated on the electrode and workpiece at the
spark contact point.
• Bubbles rapidly expand & explode during sparking until voltage is turned off.
• Next the heating channel collapses and the dielectric fluid enters into the gap
• in-order to flush away the molten metal particles.
7. Operation of EDM
• In EDM process, the workpiece and tool are submerged into a non-conducting,
dielectric fluid which is separated by a small gap (for sparking).
• Dielectric fluid (hydrocarbon oil or de-ionized water) insulates the workpiece from
the tool and creates the resistance to the flow of electricity between the electrodes.
• It also helps in cooling down the tool and workpiece, clears the inter-electrode gap
(IEG), and concentrates the spark energy to a small CS area under the electrode.
• As the two electrodes come closer to one another, the electric field intensity increases
beyond the strength of the dielectric enabling it to break and thereby allow the
current to flow between the two electrodes.
• As a result of this effect, intense heat gets generated near the zone, which melts and
evaporates the material in the sparking zone. As the flow of current is momentarily
stopped, some fresh dielectric liquid particles come in position between the inter-
electrode gap which restores the insulating properties of the dielectric.
• The solid particles (debris) are carried away by the flowing dielectric. Flushing refers
to the addition of new liquid dielectric to the inter-electrode volume.
• The sparks occur at spots where the tool and the workpiece surfaces are the closest
and since the spots change after each spark (because of the material removal after
each spark), the spark travels all over the surfaces. This results in uniform removal of
material, hence exact shape get reproduced on the workpiece
8. Advantages of EDM
• Any materials that are electrically conductive can be
machined by EDM, regardless of their hardness, strength,
toughness and microstructure
• Tool (electrode) and workpiece are free from cutting forces.
• Edge machining & sharp corners are possible in EDM process
• The tool making is easier (copper, brass and graphite).
• The process produces good surface finish (SF) (free from
burr), accuracy and repeatability.
• Hard die materials with complicated shapes can be easily
finished with good SF and accuracy.
• Due to the presence of dielectric fluid, there is very little
heating of the bulk material.
Advantages of EDM
9. Limitations of EDM
• Low MRR, process is economical only for very hard and
difficult to machine materials.
• Poor surface quality due to re-cast layers and micro-cracks,
needs further polishing .
• The EDM process is not suitable for non-conductors.
• Rapid electrode wear makes the process more costly.
Disadvantages of EDM
10. Applications of EDM
• EDM is used for making die for wire drawing, extrusion,
heading, forging etc. from hardened steel and stamping tool
with intricate cavities.
• In machining of exotic materials that are used in aerospace
and automatic industries.
• For making fragile parts which cannot take the stress of
machining.
• Deep cavities, slots and ribs can be easily made by EDM for
collets, jet engine blade slots,
• Micro-EDM process can successfully produce micro-pins,
micro-nozzles and micro-cavities.
Applications of EDM
11. Stepped Cavities Produced by
EDM Process
Figure : Stepped cavities produced with a square electrode by the EDM process. The
workpiece moves in the two principle horizontal directions (x – y), and its motion is
synchronized with the downward movement of the electrode to produce these cavities.
Also shown is a round electrode capable of producing round or elliptical cavities.
12. Wire EDM Process
Fig : Schematic illustration of wire EDM process.
• Wire EDM is a variation of EDM and is commonly known as wire-cut EDM
or wire cutting.
• In WEDM, a thin metallic wire is fed on-to the workpiece, which is
submerged in a tank of dielectric fluid such as deionized water.
• WEDM can cut plates as thick as 300mm and is used for making punches,
tools & dies from hard metals that are difficult to machine by other
method
• The wire, which is constantly fed from a spool, is held b/w upper & lower
diamond guides.
• As many as 50 hours of machining can be performed with one reel of wire,
which is then discarded.
• The guides are usually CNC-controlled and
move in the x–y plane.
• Greater flexibility due to independent
movement of upper guide helps in
programming the wire-cut EDM, for
cutting very intricate and delicate shapes.
13. Applications of Wire EDM
The process is used in the following areas:
• Aerospace, Medical, Electronics and Semiconductor
applications
• Tool & Die making industries.
• For cutting the hard Extrusion Dies
• In making Fixtures, Gauges & Cams
• Cutting of Gears, Strippers, Punches & Dies
• Manufacturing hard Electrodes.
• Manufacturing micro-tooling for Micro-EDM, Micro-USM
and such other micromachining applications.
14. Wire EDM
Figure : Cutting a thick plate with wire EDM.
(b) A computer-controlled wire EDM M/c.
15. Laser-Beam Machining (LBM)
• LASER (Light Amplification by the Stimulated Emission of Radiation)
machining is localized, non-contact thermal machining and is almost
reaction-force free.
• LBM uses a laser beam (narrow beam of intense monochromatic light) to
machine or cut required shapes or profile in almost all materials.
• The laser beam is focused onto the work-piece and can be moved.
• Photon energy is absorbed by target material in the form of thermal
energy or photochemical energy.
• The high amount of heat thus generated either melts, burns, or vaporizes
away the material at the focused region.
• Any material that can properly absorb the
laser irradiation can be laser machined e.g.
hard and brittle materials as well as soft
materials such as metals, ceramics, leather
etc.
16. Applications of LBM
• LASER, find applications in following areas:
• Heat treatment, Welding, Machining, Material deposition,
Lithography, Surgery ,Photo-polymerization µ-stereo-
lithography, Laser-enhanced jet plating and etching ,
• LBM is used for Ablation or cutting of plastics, glasses,
ceramics, semiconductors and metals.
17. General Applications of
Lasers in Manufacturing
Gas is blown into the cut to clear away molten
metals, or other materials in the cutting zone.
In some cases, the gas jet can be chosen to react
chemically with the workpiece to produce heat and
accelerate the cutting speed (LACE)
18. Advantages of LBM
Advantages
• Ability to cut almost all materials including fragile
materials.
• No limit to cutting paths as the laser point can move in
any paths.
• No direct contact b/w tool and workpiece; thus no need
of the work holding system.
• Flexibility exists in precision cutting of simple or complex
parts.
• There is no tooling cost or associated wear costs.
• Laser produces high quality cuts without extra finishing
requirements.
19. Disadvantages of LBM
• Disadvantages
• Laser processes involve high capital investments and high
operating costs.
• Laser holes are tapered to some extent (approximately 1%
of the drill depth)
• It cannot drill blind holes to precise depths.
• Heat of lasers may change mechanical properties of
metallic materials & alloys in HAZ
• Long processing time in larger holes due to trepanning
action.
• Reflected laser lights can lead to safety hazards.
• Assist or cover gases are required for safety purposes.
20. Applications of LBM
• Applications
• Electronic and automotive industries.
• LBM is used for making very accurate sized holes as small
as 5 microns in metals, ceramics and composites without
wrapage.
• It is widely used for fine & accurate drilling & cutting of
metallic & non-metallic materials.
• LBM can cut wood, plastics, leather, glass, ceramics and
fiber optics.
21. Electron Beam Machining (EBM)
• In EBM, material is removed by means of a focused beam of high velocity
electrons that strike the workpiece.
• Electrons are emitted from an electron gun and are accelerated to speeds
(200,000 km/s ) of about 75% of the speed of light, by voltages as high
as 50 kV between the anode and cathode.
• A magnetic lens focuses the electron beam onto the workpiece, and high
energy densities of the order of 108W/cm2 are produced.
• K.E. of the electrons is converted into heat that is sufficient to cause
rapid melting and vaporization of the workpiece material .
Figure: Schematic illustration of the electron-beam machining process.
Electron-beam
• To eliminate scattering of the beam
of electrons, the work is done in a
high-vacuum chamber.
• Electron-beam machining can process
a wide range of materials.
22. Advantages of EBM
Advantages:
1. Extremely high energy density of the beam and the short
duration of beam-workpiece interaction,
2. Limited thermal effects on the workpiece material,
3. Extremely limited and small HAZ ( 0.025 mm in depth).
Disadvantages:
1. Unlike LBM, this process requires a vacuum, so workpiece
size is limited to the size of the vacuum chamber.
2. Holes are tapered if thickness is more than 0.13 mm.
3. Cumbersome and expensive process.
4. Low MRR.
5. Recast and metal spatter from the spot of beam strike need
removal by abrasive cleaning
23. Applications of EBM
Applications:
1. EBM is mainly used for micromachining operations such as drilling,
perforating, slotting, engraving etc. on thin materials.
2. EBM is suited particularly for materials with high melting points and
low thermal conductivity.
3. To drill extremely small hole of diameter 0.03 mm in turbine blades
for transpiration cooling, holes in mixer plates, combustion chamber
rings.
24. Principle of ECM
• ECM is opposite of electrochemical or galvanic coating or
deposition process.
• ECM technique removes material by atomic level dissolution of
the same by electrochemical action.
• Thus ECM can be thought of a controlled anodic dissolution
at atomic level of the work piece that is electrically
conductive by a shaped tool due to flow of high current at
relatively low potential difference through an electrolyte
which is quite often water based neutral salt solution.
Fig. : schematically shows the basic principle of ECM.
Initial state of ECM Steady state of ECM
26. Electrochemical Machining
• ECM is controlled removal of metal by anodic dissolution in an
electrolytic medium in which workpiece is anode and tool is cathode.
• Two electrodes are placed closely with a gap of about 0.5mm and
immersed in an electrolyte which is a solution of sodium chloride.
• When an electrical potential of about 20V is applied between
electrodes, ions existing in electrolyte migrate towards electrodes.
• Positively charged ions are attracted towards the cathode and the
negatively charged ions are attracted towards the anode.
• This initiates the flow of current in the electrolyte.
• The rate at which the ions arrive at their respective electrode
determines density of current and varies in direct proportion to
applied voltage, number of ions present & gap between electrodes.
• The electrolysis process that takes place at the cathode liberates
hydroxyl ions (negatively charged) and free hydrogen.
• The hydroxyl ions combine with the metal ions of anode to form
insoluble metal hydroxides & material is thus removed from the anode.
• This process continues and tool reproduces its shape in the workpiece
27. • In ECM, material removal occurs due to atomic dissolution of work
(conductive) material.
• Electrochemical dissolution is governed by Faraday’s laws.
• Electrical energy in combination with chemical reactions to remove
material.
• Simply ECM is reverse of electroplating
– Part is the anode (+) and the tool is the cathode (-)
– Metal is “pulled” away from work (positive pole) and transported to
a cathode tool (negative pole) in an electrolyte bath.
• Electrolyte flows rapidly between the two poles to carry off
deplated material, so it does not plate onto tool.
• Electrode materials: Cu, brass, or stainless steel
• Tool has inverse shape of part : Tool size & shape must allow for gap.
• No surface damage, no burr, low tool wear, high MRR for hard-to
machine materials
29. Advantage of ECM
Advantages:
1. MRR is not dependent on mechanical or physical properties of WP.
2. No surface damage, no burr, low tool wear,
3. High MRR for hard-to machine materials
4. Hard to soft materials made of conductive material can be m/ced.
5. Cutting tool can be made from soft material.
6. Low heat generated during process.
7. No cutting forces.
8. Excellent surface finish.
Disadvantages:
1. Since ECM depends on atomic weight & valency of work material
therefore work material should be electrically conductive.
2. Low machining accuracy due to its wider machining gap.
30. Applications of ECM
.
Application:
1. ECM can machine any electrically conductive work
material irrespective of their hardness, strength or
even thermal properties.
2. Moreover as ECM leads to atomic level dissolution, the
surface finish is excellent with almost stress free
machined surface and without any thermal damage so
fragile and thin section can be machined.
3. ECM is used for : Die sinking, Profiling and contouring,
Trepanning , Grinding , Drilling , Micro-machining etc.
Die sinking 3D Profiling
31. ECM Process Capabilities
• Used to machine complex cavities in high strength material
• Applications in aerospace industry,jet engines parts and nozzles
• ECM process gives a burr free surface
• No thermal damage
• Lack of tool forces prevents distortion of the part
• No tool wear
• Capable of producing complex shapes and hard materials
32. Parts Made by
Electrochemical Machining
Fig: Typical parts made by electrochemical machining. (a) Turbine blade made of nickel alloy of 360
HB. Note the shape of the electrode on the right. (b) Thin slots on a 4340-steel roller-bearing cage.
(c) Integral airfoils on a compressor disk.
33. Case Study: Knee Implants
Fig: (a) Two total knee replacement systems showing metal implants (top pieces) with
an ultra-high molecular-weight polyethylene insert (bottom pieces). (b) Cross-section
of the ECM process as applies to the metal implant. Source: Courtesy of Biomet, Inc.
34. Electrochemical-Grinding Process
Fig: (a) Schematic illustration of the electrochemical-grinding process.
(b) Thin slot produced on a round nickel-alloy tube by this process.
• In ECG, Electrode is in the form of rotating grinding wheel.
36. Plasma Arc Machining /Cutting
(PAM/PAC)
• PAM is a thermal cutting process which uses plasma (a superheated,
electrically ionized gas) to cut metals.
• In PAM arc formed between the tungsten electrode and the workpiece
is constricted by a fine bore, copper nozzle.
• Nozzle increases the temperature (≈ 20 000°C) and velocity (≈ speed of
sound) of the plasma emanating from the nozzle.
• On initiation, the pilot arc is formed within the body of the torch
between the electrode and the nozzle.
• For cutting, the arc must be transferred to the
workpiece and the plasma gas flow is increased so
that the deeply penetrating plasma jet cuts
through the material & molten material is
removed by efflux plasma.
• Electrode (tungsten) has a negative polarity and
workpiece a positive polarity so that majority of
arc energy (≈ two thirds) is used for cutting.
• It can be applied for cutting conductive metals which
form refractory oxides e.g. SS, Al, CI, Ni, Cu & Ti
38. Plasma Arc Cutting
Vs Oxy Fuel Cutting
• PAC differs from oxy-fuel process. Plasma process operates
by using the arc to melt the metal whereas in the oxy-fuel
process, oxygen oxidises the metal and heat from the
exothermic reaction melts the metal.
• Thus, unlike the oxy-fuel process, plasma process can be
applied for cutting conductive metals like stainless steel,
aluminium, cast iron and nickel based materials, copper alloys,
titanium alloys .
•
39. Advantages of PAC
Advantages :
1. PAC is a low cost alternative to oxy-fuel and laser profiling.
2. Superior quality, more versatile and enhanced accuracy.
3. Cut faster than oxy-fuel and LBM.
4. Economical due to faster production rate.
5. Wide range of materials (ferrous & nonferrous) & thickness
( up to 80 cm )
6. Easy to use
40. Disadvantages of PAC
Disadvantages :
1.Faster electrode and nozzle wear .
2. Increased cost of operation due to frequent
replacement of electrode & nozzle.
3. Cannot cut non-conductive materials such as wood or
plastic.
4. Cut edges are beveled by 4-6 degree.
41. Applications of PAC
Applications:
• PAM/PAC is predominantly used in metal fabrication
and sheet metal industries for cutting and gauging of
hard materials.
• Unlike the oxy-fuel process, the plasma process can be
applied for cutting conductive metals which form
refractory oxides such as stainless steel, aluminium,
cast iron and nickel based materials, copper alloys,
titanium alloys .
42. Chemical Milling
Fig: (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 the chemical milling of aluminum-alloy plates. These panels are
chemically milled after the plates first have been formed into shape by a process
such as roll forming or stretch forming. The design of the chemically machined
rib patterns can be modified readily at minimal cost.
43. • Shallow cavities produced on plates, sheets, forgings, and
extrusions
Procedure for chemical milling Steps :
1 – Residual stresses should relieved in order to prevent warping
2 – Surfaces to be thoroughly degreased and cleaned
3 - Masking material(tapes,paints,elastomers & plastics ) is applied
4 – masking is peeled off by scribe and peel technique
5 – The exposed surfaces are etched with etchants
6 – After machining the parts to be thoroughly washed to prevent further
reactions with residue etchant
7 – rest of the masking material is removed and the part is cleaned and
inspected
8 – additional finishing operations are performed on chemically milled parts
9 – this sequence is repeated to produce stepped cavities and various
contours
Chemical Milling
44. Process capabilities:
• Chemical milling used in the aerospace industry
• Tank capacities for reagents are as large as 3.7m
x15m
• Process also used for micro electronic devices
• Surface damage may result due to preferential etching
and intergranular attack
45. Chemical blanking:
• Chemical blanking is similar to chemical milling
• Material is removed by chemical dissolution rather
than by shearing
• Burr free etching of printed-circuit boards, decorative
panels, thin sheet metal stampings as well as
production of small and complex shapes
Chemical Blanking
46. Parts Made by
Chemical Blanking
Fig: Various parts made by chemical blanking. Note the fine detail. Source: Courtesy of Buckbee-
Mears, St. Paul.
47. • Photochemical blanking Modification of chemical milling
• Material removed from flat thin sheet by photographic
techniques
• Design is prepared at a magnification of 100x
• Photographic negative is reduced to the size of finished part
• Sheet blank is coated with photosensitive material (Emulsion)
• Negative placed over coated blank and exposed to ultra violet
light which hardens the exposed area
• Blank is developed which dissolves the exposed areas
• Blank is then immersed into a bath of reagent or sprayed
with the reagent which etches away the exposed areas
• The masking material is removed and the part is washed
thoroughly to remove all chemical residues
Photochemical Blanking
48. Chemical-Machining
Fig (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 chemical machining; note the undercut.
