Machining involves the removal of excess material from a workpiece to achieve desired dimensional and surface finish properties. There are several machining processes such as turning, drilling, milling, and grinding. Advanced processes like waterjet machining and abrasive jet water machining are used for hard or brittle materials. Ultrasonic machining, electrochemical machining, and electric discharge machining can machine conductive materials regardless of hardness. Laser machining uses an intense laser beam as a thermal energy source for material removal and provides advantages like no tool wear and ability to machine difficult materials.

1. Machining

6. Principle of Machining
Turning process - produce parts cylindrical in shape by a single point cutting tool

9. • Machining is a process of gradual removal of excess material from the
workpiece in the form of chips.
• Machining is a semi-finishing or finishing process essentially done to
impart required dimensional and form accuracy and surface finish to
enable the product to
• fulfill its basic functional requirements
• provide better or improved performance
• render long service life

10. • Drilling - circular hole in the work-piece by using a rotating cutter
called drill.

11. Milling - producing flat surface with the use of multi-point cutting tool

12. • Grinding is the most common form of abrasive machining.
• It is a material cutting process which engages an abrasive tool whose
cutting elements are grains of abrasive material known as grit.
• These grits are characterized by sharp cutting points, high hot hardness,
chemical stability and wear resistance.
• The grits are held together by a suitable bonding material to give shape of
an abrasive tool.

16. • Many situations in manufacturing where the workpiece material is
either too hard or too brittle, or its shape is difficult to produce
sufficient dimensional accuracy by any of the machining methods
discussed previously.
Need for Advanced manufacturing process

17. Need for Advanced manufacturing process

21. • In these processes (WJM and AJWM), the mechanical energy of
water and abrasive phases are used to achieve material removal
• In case of AWJM of brittle materials, material would be removed due
to crack initiation and propagation because of brittle failure of the
material.
• In AWJM of ductile materials, material is mainly removed by low
angle impact by abrasive particles leading to ploughing and micro
cutting`

23. Ultrasonic machining

27. • ECM technique removes material by atomic level dissolution of the same by
electrochemical action.
• Thus the material removal rate or machining is not dependent on the
mechanical or physical properties of the work material.
• It only depends on the atomic weight and valency of the work material and
the condition that it should be electrically conductive.
• Thus ECM can machine any electrically conductive work material irrespective
of their hardness, strength or even thermal properties.
• ECM leads to atomic level dissolution, the surface finish is excellent with
almost stress free machined surface and without any thermal damage.

28. EDM

31. • In EDM, a potential difference is applied between the tool and workpiece. Both the
tool and the work material are to be conductors of electricity.
• The tool and the work material are immersed in a dielectric medium. Generally
kerosene or deionised water is used as the dielectric medium.
• A gap is maintained between the tool and the workpiece. Depending upon the
applied potential difference and the gap between the tool and workpiece, an electric
field would be established.
• Generally the tool is connected to the negative terminal of the generator and the
workpiece is connected to positive terminal.
• As the electric field is established between the tool and the job, the free electrons on
the tool are subjected to electrostatic forces.

32. • movement of electrons and ions can be visually seen as a spark.
• Thus the electrical energy is dissipated as the thermal energy of the spark. The
high speed electrons then impinge on the job and ions on the tool.
• The kinetic energy of the electrons and ions on impact with the surface of the
job and tool respectively would be converted into thermal energy or heat flux.
• Such intense localised heat flux leads to extreme instantaneous confined rise in
temperature which would be in excess of 10,000 degree Celcius.

33. Laser machining

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LASER
Light Amplication by Simulation Emission of Radiation
Difference between ordinary light and laser
Ordinary light : Emit light in different wavelength and different directions
Laser : Monochromatic (single wavelength) moving in one direction

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 At absolute zero temperature an atom is considered to be at ground level,
when all the electrons occupy their respective lowest potential energy.
 The electrons at ground state can be excited to higher state of energy by
absorbing energy form external sources .
 On reaching the higher energy level, the electron reaches an unstable energy band.
 And it comes back to its ground state within a very small time by releasing a photon.
This is called spontaneous emission

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 Sometimes such change of energy state puts the electrons in a meta-stable
energy band. Instead of coming back to its ground state immediately (within tens
of ns) it stays at the elevated energy state for micro to milliseconds.
 In a material, if more number of electrons can be somehow pumped to the
higher meta-stable energy state as compared to number of atoms at ground
state, then it is called “population inversion”
 Such electrons at higher energy meta-stable state, can return to the ground state in the
form of an avalanche provided stimulated by a photon of suitable frequency or energy.
This is called stimulated emission

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Schematic of Nd:YAG laser beam cutting system

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Laser Beam Machining – Advantages
• 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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Laser Beam Machining – Limitations
• High initial capital cost
• High maintenance cost
• Not very efficient process
• Presence of Heat Affected Zone – specially in gas assist CO2 laser cutting
• Thermal process – not suitable for heat sensitive materials