Lecturer 1 machining

MECHANICAL & INDUSTRIAL ENGINEERING DDEEPPAARRTTMMEENNTT
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Chapter 1. Machining
08/30/14 Dr. Kaushik Pal

M.Tech 1st year
• MMII 557722 :: Advanced Manufacturing
Processes
• LL::TT::PP 33 :: 11 :: 22//22
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• Credit: 0044

DIAMOND TURNING
•

INTRODUCTION
• Diamond turning is a process of mechanical machining of
precision elements using lathes or derivative machine tools
(e.g., turn-mills, rotary transfers) equipped with natural or
synthetic diamond-tipped tool bits.
• The process of diamond turning is widely used to
manufacture high-quality aspheric optical elements from
crystals, metals, acrylic, and other materials.

PROCESS
• Diamond turning is a multi-stage process.
• Initial stages of machining are carried out using a series of
CNC lathes of increasing accuracy.
• A diamond-tipped lathe tool is used in the final stages of the
manufacturing process to achieve sub-nanometre level
surface finishes and sub-micrometre form accuracies.

• Quality of surface finish and form accuracy is monitored
throughout the manufacturing process using such
equipment as contact and laser profilometers, laser
interferometers, optical and electron microscopes.
• Temperature control is crucial, because the surface must be
accurate on distance scales shorter than the wavelength of
light. Temperature changes of a few degrees during
machining can alter the form of the surface enough to have
an effect.

TYPES OF TURNING
• TRADITIONAL TURNING is a turbocharged version of classic
lathe work. The part is chucked on a lathe having an incredibly
accurate spindle and slides. An ultra sharp diamond of
extremely accurate nose radius is used to turn and face the
part. The CNC interpolation of the X and Z axis of the machine
can produce arbitrary rotationally symmetric parts. In principle
it is just as easy to produce the parabola of a reflecting
telescope as it is to produce a basic cylindrical shape.

• OFF-AXIS TURNING is an approach where a workpiece is
mounted to the spindle in an asymmetric fashion. This
allows cutting of multiple parts simultaneously or producing
contours whose rotational center is not coincident with the
center of the part. Certain optical configurations take
advantage of this approach.

• FLY-CUTTING AND MILLING reverses the position of work
and tool. The tool is mounted to the spindle and the work is
mounted to the slide. This allows the generation of flat or
elliptical surfaces.

MATERIAL THAT CAN BE MACHINED
USING SPDT
• Plastics
– Acetal
– Acrylic
– Nylon
– Polycarbonate
– Polypropylene
– Polystyrene
– Zeonex

• Metals
– Aluminum and aluminium alloys
– Brass
– Copper
– Gold
– Electroless nickel plating on other materials
– Silver
– Tin
– Zinc

• Infrared crystals
– Cadmium sulfide
– Cadmium telluride
– Calcium fluoride
– Cesium iodide
– Gallium arsenide
– Germanium
– Lithium niobate
– Potassium bromide
– Potassium dihydrogen phosphate (KDP)

APPLICATIONS
• The process of diamond turning is widely used to
manufacture high-quality aspheric optical elements from
crystals, metals, acrylic, and other materials like:-
– assemblies in telescopes
– video projectors
– missile guidance systems
– Lasers
– scientific research instruments
– numerous other systems

DRAWBACK
• Ferrous materials are not readily machinable because the
carbon in the diamond tool chemically reacts with the
substrate, leading to tool damage and dulling after short
cut lengths.
• Several techniques have been investigated to prevent this
reaction, but few have been successful for long diamond
machining processes at mass production scales.

HYBRID MACHINING
•

INTRODUCTION
• Technological improvement of machining processes can be
achieved by combining different machining actions or phases
to be used on the material being removed for eg:-
• A mechanical conventional single cutting or MA action
process can be combined with the respective machining
phases of electrodischarge (ED) in electrodischarge
machining (EDM)

NEED OF HYBRID MACHINE
• To make use of the combined advantages and to avoid or
reduce some adverse effects the constituent processes
produce when they are individually applied.
• The performance characteristics of a hybrid process are
considerably different from those of the single-phase
processes in terms of:-
– Productivity
– Accuracy
– Surface quality

IINNDDIIAANN IINNSSTTIITTUUTTEE OOFF TTEECCHHNNOOLLOOGGYY RROOOORRKKEEEE DIFFERENT PROCESS COMBINATION AND
APPLICATION

HYBRID CHEMICAL AND ELECTROCHEMICAL
PROCESSES.
•

• In this family of hybrid machining processes, the major
material removal phase is either CD or ECD.
• machining action can be combined with the thermal
assistance by local heating in case of laser-assisted
electrochemical machining (ECML).

HYBRID THERMAL MACHINING PROCESS
•

• the main material removal mechanism is a thermal one.
• The combination of this phase with the ECD phase, MA
action, and ultrasonic (US) vibration generates a family of
double action processes.
• The triplex hybrid machining is also achievable by
combining the electrodischarge erosion (EDE) phase, the
ECD action, and the main grinding (G) as shown in above fig
1.9.

•

MICRO MACHINING
•

INTRODUCTION
• Refers to techniques for fabrication of 3D structures on the
micrometer scale
• Applications include MEMS devices e.g. airbag sensor,
medical devices, micro-dies and molds, etc.
• Most methods use silicon as substrate material

BASICS OF MICROMACHINING
• Two Different Approaches of Micromachining
• Bulk or Surface
• Fundamental Four Techniques of Micromachining
– Thin Film Deposition
– Photolithography
– Etching
– Sacrificial Release

PHOTOLITHOGRAPHY
•

• The wafers are chemically cleaned to remove particulate
matter, organic, ionic, and metallic impurities
• High-speed centrifugal whirling of silicon wafers known as
"Spin Coating" produces a thin uniform layer of photoresist
(a light sensitive polymer) on the wafers
• Photoresist is exposed to a set of lights through a mask
often made of quartz
• Wavelength of light ranges from 300-500 nm (UV) and X-rays
(wavelengths 4-50 Angstroms)

ETCHING
• Process Variations:
– Wet etching
– Dry etching

WET ETCHING
• The key ingredients are:
– Oxidizer (e.g. H2O2, HNO3)
– Acid or base to dissolve the oxidized surface (e.g. H2SO4,
NH4OH)
– Dilutent media to transport the products through (e.g.
H2O)

DRY ETCHING
•
THE ABOVE FIG SHOWS PLASMA
BASED ETCHING PROCESS PRODUCTS MANUFACTURED BY ETCHING

THIN FILM DEPOSITION
• Chemical Vapor Deposition

• sputtering

• evaporation

BULK OR SURFACE
• Process for producing 3D MEMS structures – older process
• Uses anisotropic etching of single crystal silicon

SURFACE
• Newer process for producing MEMS structures
• Uses etching techniques to pattern microscale structures
from polycrystalline (poly)silicon, or metal alloys

APPLICATIONS
• MEMS (Microelectromechanical systems)
• medical device
• Fabrication etc.

Lecturer 1 machining

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