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 machinin.
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 and difficult to machine ( by conventional
methods) metals such as hardened tool-steels, carbides, titanium, inconel
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. 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
7. 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.
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. The Wire EDM Process
Figure : Schematic illustration of the wire EDM
process. As many as 50 hours of machining can
be performed with one reel of wire, which is
then discarded.
Wire EDM is a variation of EDM and is commonly known as wire-cut EDM or wire cutting.
In this process, 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 and dies
from hard metals that are difficult to machine with other methods.
The wire, which is constantly fed from a spool, is held b/w upper & lower diamond guides.
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.
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.
13. Wire EDM
Figure : Cutting a thick plate with wire EDM.
(b) A computer-controlled wire EDM M/c.
14. 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 or pattern in almost all types of materials.
The laser beam is focused onto the work-piece and can be moved relatively to it.
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. The
spectrum of laser machinable materials includes hard and brittle materials as well as
soft materials. Some of the examples include metals, ceramics, leather etc.
LBM, find applications in following areas:
Heat treatment, Welding, Ablation or cutting
of plastics, glasses, ceramics, semiconductors
and metals , Material deposition, Laser-
enhanced jet plating and etching ,
Lithography, Surgery ,Photo-polymerization
µ-stereo-lithography
15. 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)
16. Advantages, Disadvantages &
Applications of LBMAdvantages
Ability to cut almost all materials including
fragile materials (which are easily cut by
laser)
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
17. 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 energy densities of
2 the order of 108W/cm2.
As a result of extremely high energy density of the
beam and the short duration of beam-workpiece
interaction, thermal effects on the workpiece material
are limited to a heat affected zone that seldom
exceeds 0.025 mm in depth.
High beam-power density also enables high aspect
ratio holes to be drilled, often as large as 15 to 1.
Figure: Schematic illustration of the electron-beam machining process.
Electron-beam
18. Advantages, disadvantages &
Applications of EBMAdvantages:
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 taperd 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
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.
19. Plasma Arc
CuttingPlasma - a superheated, electrically
ionized gas
PAC uses a plasma stream. operating
at temperatures in the range from
18,000o - 25,000o F to cut metal
The high-velocity plasma stream is
directed at the workpiece, melting it
and blowing the molten metal through
the kerf
20. Plasma Arc Machining
/Cutting (PAM/PAC)
PAM is a thermal cutting process which
uses plasma( ionized gas) to cut metals.
IN PAM/PAC arc formed between the
electrode and the workpiece is constricted
by a fine bore, copper nozzle which
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
The process differs from the oxy-fuel process in that the
plasma process operates by using the arc to melt the metal
whereas in the oxy-fuel process, the oxygen oxidises the
metal and the heat from the exothermic reaction melts the
metal.
Thus, 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 .
21. Advantages, disadvantages &
Applications of PACAdvantages :
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
Disadvantages :
1. Faster electrode and nozzle wear .
2. Increased cost of operation due to frequent replacement of electrode &
nozzle.
3. Cannot non-conductive materials such as wood or plastic.
4. Cut edges are beveled by 4-6 degree.
Applications:
• PAM/PAC is predominantly used in metal fabrication and sheet metal
industries for cutting and gauging of hard materials.
• PAM s is used for cutting conductive materials such as carbon steel, stainless
• steel, aluminum
23. • 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
25. • In ECM, material removal takes place due
to atomic dissolution of work material.
Electrochemical dissolution is governed by
Faraday’s laws.
• Electrical energy in combination with
chemical reactions to remove material -
Work material must be a conductor
• Reverse of electroplating
– Part is the anode (+) and the tool is the cathode (-)
– Metal is “pulled” away from work
26. Advantages:
1.MRR is not dependent on the mechanical or
physical properties of the work material.
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 machined.
5.Cutting tool can be made from soft
material.
6.Low heat generated during process.
Die sinking 3D Profiling
27. Electrochemical Machining
Electrochemical machining is the
controlled removal of metal by anodic
dissolution in an electrolytic medium in
which the workpiece is the anode and
the tool is the 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 the
electrodes, the ions existing in the
electrolyte migrate towards the
28. Manufacturing,
Engineering &
Parts Made by
Electrochemical Machining
Figure 27.7 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.
29. Manufacturing,
Engineering &
Knee Implants
Figure 27.8 (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.
31. Manufacturing,
Engineering &
Chemical Milling
Figure 27.2 (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.
32. Chemical milling:
• 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
33. 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
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
34. 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
Steps for photochemical blanking
35. Chemical-Machining
Figure 27.3 (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.
36. • This process is reversal of the electro plating
• Electrolyte acts as current carrier
• High rate of electrolyte movement in tool work piece gap washes
metal ions away from the work piece ( ANODE)
• This is washed just before they have a chance to plate on the tool
( cathode)
• Shaped tool made of brass , copper , bronze , or stainless steel
• Electrolyte is pumped at a high rate through the passages in the
tool
• Machines having current capacities as high as 40,000 A and as
low as 5A are available
Electrochemical machining
37. 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
38. Manufacturing,
Engineering &
Chemical-Machining
Figure 27.3 (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.
39. Manufacturing,
Engineering &
Parts Made by Chemical
Blanking
Figure 27.5 Various parts made by chemical blanking. Note the fine
detail. Source: Courtesy of Buckbee-Mears, St. Paul.
