Download non traditional machining process

UNIT - III
NON TRADITIONAL
(OR)
UNCONVENTIONAL
MACHINING PROCESS
Prepared by
M.Saravana kumar
AP/Mech
SNSCT
UnConventional Machining process
• The UCM do not employ a conventional or traditional
tool for metal removal, instead, they directly utilize
some form of energy for metal machining.
• In this process, there is no direct physical contact
between the tool and the workpiece. Therefore the
tool material need not be harder than the workpiece
material as in conventional machining.
Need for unconventional machining
1. A harder and difficult to machine materials such as carbides,
stainless steel, hastalloy, nitralloy and other high strength
temperature resistant alloys find wide application in
aerospace and nuclear engg industries.
2. For such materials the conventional edged tool machining is
highly uneconomical and the degree of accuracy and surface
finish attainable are poor.
3. The unconventional machining process have been developed
to over come the all these difficulties.
Types
1. Electrical Discharge Machining (EDM)
2. Wire cut Electro Discharge Machining
(WCEDM)
3. Electro Chemical Machining (ECM)
4. Laser Beam Machining (LBM)
5. Electron Beam Machining (EBM)
Electrical Energy based process
In electrical energy based processes, electrical
energy is directly used to cut the material to get
the final shape and size.
Ex: EDM, WCEDM
Electro - Chemical Energy based process
In electro chemical energy methods, the metal is
removed by ion displacement of the workpiece
material in contact with a chemical solution.
Ex : ECM
Thermal Energy based Process
In these methods, heat energy is concentrated
on a small area of the workpiece to melt and
vaporise the tiny bits of work material. The
required shape is obtained by the continued
repetition of this process
Ex : EBM, LBM
1. Electro-Discharge Machining (EDM)
Electrode EDM
- Sparks between electrode-workpiece
- Dielectric flushes the metal powder
- Inexpensive, precise, complex shapes
- Workpiece must be a conductor
[source: iprod.auc.dk]
[source: www.magnix.co.kr]
Working Principle
• In EDM also known as spark erosion machining, metal is
removed by producing powerful electric spark discharge
between the tool (cathode) and the work material
(anode).
• When the D.C supply is given to circuit, spark (temp
10,000 deg) is produced across the gap between the tool
and the w/p.
• At this high pressure and temperature, w/p metal is
melted, eroded and some of it is vaporised. In this way
the metal is removed from the workpiece.
Contd..,
• This spark occurs in an interval of 10 to 30
microseconds and with a current density of 15- 500 A
per mm2.
• The metal removal rate depends on the spark gap
maintained
• Dielectric fluids : kerosene, mineral oil, paraffin,
hydrocarbon fluids, deionized water.
• Electrode materials are graphite, copper, copper –
tungsten.
Advantages
• It can be used for machining various materials such
as tungsten carbides, electrically conductive
materials.
• It gives good surface finish.
• Machining of very thin section is possible.
• It is well suited for complicated components.
• High accuracy is obtained
• Fine holes can be easily drilled
• It is a quicker process.
Disadvantages
• Non metallics such as plastics, ceremics, or glass can not be
machined in EDM.
• It is suitable only for machining small workpieces.
• Electrode wear and over cut are serious problem.
• Metal removal is slow
• Perfectly square corners cannot be made by EDM.
• Power requirement is very high
• In many cases , the surface machined has been found to have
micro cracks.
Applications
• Production of complicated and irregular
shaped profiles.
• Thread cutting in jobs
• Drilling of micro holes
• Helical profile drilling
• Curved hole drilling
• Resharpening of cutting tools and broaches.
Machined parts by EDM
2. WIRE CUT ELECTRO DISCHARGE MACHINING
WORKING PRINCIPLE
• A thin wire (0.02 to 0.03mm) made of brass or molybdenum
having circular cross section is used as electrode (tool).
• The wire is stretched and moved between two rollers. The
parts of wire is eroded by the spark.
• The workpiece to be machined is mounted on the table which
is operated by control unit.
• When the D.C supply is given to the circuit, spark is produced
across the gap between the wire and workpiece.
Contd
• This sparks occurs in an interval of 10 to 30 micro
seconds and with a current density of 15- 500 A per
mm2 approximately.
• So , thousands of spark discharge occur per second
across the very small gap between the wire and
workpiece, which results in increasing temperature
of about 10,000 deg.
Advantages
• Easy to use of wire electrode.
• No electrode wear
• Good surface finish can obtained.
• Complicated shapes can be produced
• Micro holes can be produced.
Disadvantages:
• Capital cost is high
• Cutting rate is slow
• It is not suitable for large workpieces
Applications
• Production of gears, tools, dies, rotors, turbine
blades and cams
3. Electro Chemical Machining
• ECM is one of the recent and most useful
machining process. In this process, electrolysis
method is used to remove the metal from the
workpiece.
• It is best suited for the metals and alloys
which are difficult to be machined by
mechanical machining processes.
Principle
• The process is based on the principle of faraday’s law of
electrolysis which may be stated as follows
1. The first law states that the amount of any material
dissolved or deposited, is proportional to the quantity of
electricity passed.
2. The second law proposes that the amount of change
produced in the material is proportional to its
electrochemical equivalent of the material.
Basically in the electroplating, the metal is deposited on the
work piece, while in ECM, the objective is to remove the metal
from the workpiece.
Contd..,
• So, the reverse of electro plating is applied in ECM process.
• Therefore, the work piece is connected to positive terminal
(anode) and the tool is connected to negative terminal
(cathode).
• When the current is passed, the workpiece loses metal and
the dissolved metal is carried out by circulating and
electrolyte between the work and tool.
• Most widely used electrolyte in this process is sodium nitrate
solution. Sodium chloride solution in water is a good
alternative but it is more corrosive than the former.(Sodium
hydroxide, sodium sulphate, sodium flouride, pottasium
nitrate & chloride)
Working Principle
• The tool and workpiece are held close to each other with a very small gap
(0.05 to 0.5 mm) between them by using servo motor.
• The electrolyte from the reservoir is pumped at high pressure and flows
through the gap between the w/p and tool at velocity of 30 to 60 m/s.
• A mild D.C voltage about 5 to 30 volts is applied between the tool and
w/p.
• Due to the applied voltage, the current flows through the electrolyte with
positively charged ions and negatively charged ions. The positive ions
move towards the tool (cathode) while negative ions move towards
workpiece (anode)
Advantages
•
•
•
•
•
•
•
MRR is High
Wear and tear of tool is negligible.
Machining is done at low voltage.
Complex shapes can be machined.
High surface finish can be obtained (0.2 to 0.8 microns)
Very thin sections can be easily machined
Toughness and brittleness of a material has no effect on the
machining process.
Disadvantages
• Non conducting materials cannot be machined.
• Consumption of power is nearly 100 times more than
in turning or milling the steel.
• Machining process is comparatively slow.
• Initial investment is quite high.
• More space is required.
Application
• Machining complicated profiles, such as jet engine
blades, turbine blades, turbine wheels.
• Drilling small deep holes, such as in nozzles.
• Machining of cavities and holes of irregular shapes.
• Machining of blind holes and pockets such as in
forging dies.
• Machining of hard materials and heat resistant
materials.
Laser Beam Machining
LASER - Light Amplification by stimulated Emission of Radiation
Fig : (a) Schematic illustration of the laser-beam machining process. (b) and (c) Examples
of holes produced in nonmetallic parts by LBM.
Contd.,,
• It produces a powerful, monochromatic, collimated beam of light in which
the waves are coherent.
• Types of laser are solid state, gas laser, liquid laser. The most commonly
used solid laser is ruby laser.
• The xeon or argon gas present in the flash tube is fired by discharging a
large capacitor through it. The electric power of 250 to 1000 watts may
need this operation.
• This optical energy i.e light energy from the flash tube is passed into the
ruby rod.
• The emitted photons in the axis of ruby rod are allowed to pass
back and forth millions of times in the ruby with the help of mirror
at the two ends. The emitted photons other than the axis, will
escape out the rod.
• The powerful beam of red light goes out of the partially reflective
mirror at one end of the ruby rod.
• The high intensity converged laser beam, when falls on the
workpiece, melts and vaporize the work material.
Advantages
• Machining of Non metal is possible.
• Micro holes can be machined.
• No tool wear
Electron -Beam Machining
Fig : 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.
Working Principle
• In EBM process, high velocity focused beam of electrons are used to
remove the metal from the w/p. These electrons are travelling at half the
velocity of light 1.6 * 10^8 m/s.
• This process is best suited for micro cutting of metals.
• When the high velocity beam of electrons strike the workpiece, its kinetic
energy is converted into heat. This concentrates heat raises the
temperature of workpiece material and vaporizes a small amount of it,
resulting in removal of material from the workpiece.
Contd..,
• When the high voltage DC source is given to electron gun, Tungsten
filament wire gets heated and the temperature raises upto 2500 c
• When the electron beam impacts on the workpiece surface, the kinetic
energy of high velocity electrons is immediately converted into heat
energy. This high intensity heat metals and vaporizes the work material at
the spot of beam impact.