Nontraditional Machining Processes

Nontraditional Machining Processes
The NTM processes can be divided into four basic categories:
I. Chemical (Chemical reaction),
II. Electrochemical (Electrolytic dissolution),
III. Mechanical (Multipoint cutting or erosion),
IV. Thermal (High temperatures in very localized regions melt
and vaporize the material).
Characteristics of NTM processes are:
1. Low metal-removal rates,
2. Very high specific powers (W/cm3/min),
3. Better accuracy,
4. Less surface damaging,
5. Can be employed for materials that are too hard.
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Nontraditional Machining Processes
I. Chemical Machining
In chemical machining material is removed from selected
areas of a workpiece by immersing it in a chemical
reagent.
Material is removed by microscopic electrochemical cell
action as occurs in corrosion or chemical dissolution of
a metal, which is called etching.
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Chemical Machining
Etching is material removal from the unprotected sections
of the workpiece by means of microscopic
electrochemical cell action as in corrosion or chemical
dissolution of metal without the involvement of any
external circuit.
Chemical Machining is the targeted use of chemical
etchants (acids and alkaline solutions) in the removal of
material from metal parts’ surfaces.
In order to prevent the removal of material from unwanted
regions, a mask / resist on the surface of the
workpiece that is resistant to the etchant used.
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Chemical Machining
Workpiece holder
Mixer
Maskant
Workpiece
Chemical etchant
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Chemical Machining
The basic chemical machining processes are:
1. Chemical Milling,
used for pockets, contours and overall metal removal,
2. Chemical Blanking (etching through thin sheets),
3. Photochemical Machining
(photosensitive resists are used for masks),
4. Gel Milling (uses reagent in jel form),
5. Chemical or Electrochemical Polishing
(weak chemical reagents are used for polishing).
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Chemical Milling
Chemical Milling and Blanking
Used for pockets, contours and overall metal removal.
Shallow cavities are etched on the surface of a metal
workpiece -most
structures.
(1) Raw part is cleaned/
degreased.
(2) Maskant is applied
globally and cured.
commonly,
on
(3) Maskant is removed
from selected sections.
large
aerospace
(5) Maskant is removed
completely and
workpiece is washed.
(4) Exposed sections of
the workpiece are
etched.
Etchant
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Chemical Blanking
(1) Raw part is cleaned/
degreased.
(5) Maskant is removed
completely and
(3) Maskant is removed
workpiece is washed.
from selected sections.
(4) Exposed sections of the
(2) Maskant is applied
workpiece are etched.
globally and cured.
Some thin-walled
part profiles
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Nontraditional Machining Processes
II. Electrochemical Machining (ECM)
● Suitable for electrically conductive materials.
● Tool should also be electrically conductive.
● Process of removing metal from a workpiece by a
reverse-electroplating action.
(In electroplating, workpiece which is the negative
electrode (cathode), and plate metal which is the
positive electrode (anode) are dipped in a solution
which contains dissolved salts of the metal to be
deposited.)
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Electrochemical Machining (ECM)
Tool
Tool holder and
feed mechanism
Cathode (-)
Forced
electrolyte
circulation
De-plated
material
Cavity created
by deplating
Tool
Electrolyte
supply
Insulation
Electrolyte
Workpiece
Anode (+)
The electrolytes are highly
conductive solutions of inorganic
salts usually NaCl (Sodium
Chlorate), KCl, NaNO3 (Sodium
Nitrate), and are operated at
about 30° to 55°C.
Tools are usually made from
copper, brass, titanium or
sometimes stainless steel.
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Electrochemical Machining Processes
1. Electrochemical Polishing
Feed is halted, lower current density and slower electrolyte
flow rates reduce MRR so that a fine surface finish is
obtained.
2. Electrochemical Hole Drilling
a. Drilling of very small diameter holes
0.1 to 0.75 mm in diameter with 50:1 depth to diameter
ratios are accomplished in nickel and cobalt alloys.
b. Drilling of medium sized holes
sizes being 0.5 to 6 mm.
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Electrochemical Machining Processes
3. Electrochemical
Grinding (ECG)
Used for shaping and
sharpening carbide
cutting tools, which
cause high wear
rates on expensive
diamond wheels in
normal grinding.
Tool electrode is a
rotating, metal
bonded, diamond
grit grinding wheel.
Metal bond of the
wheel is the
cathode.
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Electrochemical Grinding (ECG)
● Diamond particles are used as an insulator to preserve
a gap between the cathode and the workpiece, to wipe
away residues, and to cut chips if the wheel should
contact the workpiece.
● MRR is competitive with conventional grinding.
● Less than 5 % of the material is removed by normal
chip removal.
● Lack of heat damage, burrs and residual stresses are
very beneficial.
● Used for fragile parts, surgical needles, tips of
assembled turbine blades etc.
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Nontraditional Machining Processes
III. Mechanical NTM Processes
Mechanical NTM Processes can be used for electrically
conductive or nonconductive materials.
1. Ultrasonic Machining (USM)
2. Hydrodynamic Jet Machining
3. Abrasive Jet Machining ( AJM )
4. Abrasive Waterjet Cutting (AWC)
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Mechanical NTM Processes
1. Ultrasonic Machining (USM)
● Employs an ultrasonically vibrating tool to impel the abrasive
(carbide, ceramic) particles in a slurry against a workpiece.
An inverse image of the tool in the workpiece is formed as
the abrasive particles abrade (machine) the material.
● A transducer is used to impart high frequency vibration
(100 kHz) to the tool holder.
High frequency
oscillation
Tool
Slurry
Workpiece
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Ultrasonic Machining (USM)
● The tool materials are usually brass, carbide, or mild or
tool steel.
● Abrasive particles (grit materials), most commonly are
Boron Carbide, Aluminum Oxide and Silicon Carbide.
● The process can cut virtually any material, conductive
or nonconductive, metallic, ceramic or composite.
● The tool wears continuously.
Wear ratios (material removed versus tool wear) of
1:1 to 100:1 are possible.
● There is an overcut during the machining by about
twice the size of the abrasive grit.
● Surface roughness is controlled by the size of the grit.
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Ultrasonic Machining (USM)
● USM is primarily targeted for the machining of brittle
materials (dielectric or conductive): Boron carbide,
ceramics, glass, titanium carbides, etc.
● The tool must be selected to be highly wear resistant,
such as low-carbon steels.
● The abrasives (25-60 m in diameter) in the slurry
(water-based, 20-60% solid volume) include boron
carbide, boron nitride, silicon carbide, aluminum oxide
and diamond.
● Surface finish in USM can be an order of magnitude
better than that achievable through milling.
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Mechanical NTM Processes
2. Water Jet Cutting (WJC) (Hydrodynamic Jet
Machining)
● Uses a fine, high-pressure, high velocity stream of
water (water jet).
● Velocity: Mach 2 (680 m/s); up to 900m/s (~Mach 3)
● Pressure: 70 to 415 MPa.
● Mainly used to cut soft, non-metallics like plastics,
paperboard, asbestos, leather, rubber, fiberglass,
textiles, composites, floor tile, carpet, leather, and
cardboard
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Hydrodynamic Jet Machining
● Cutting rates vary from 75 m/min up to 1750 m/min.
● Feed rates are between 5 mm/s to 500 mm/s
depending on material and its thickness.
● Advantages: no crushing or burning of work surface,
minimum material loss, no environmental pollution, and
ease of automation.
● CNC machines or industrial robots can be used to cut
along a desired complex shaped trajectory.
● Jet flows through small nozzle (made of sapphire, ruby
or diamond) opening of diameter (0.1 to 0.4 mm).
● A long-chain polymer is added to the water to make the
jet coherent (not come out of the nozzle as a mist).
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Hydrodynamic Jet Machining
Abrasives can
also be utilized
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Mechanical NTM Processes
3. Abrasive Jet Machining (AJM )
● AJM is mainly a finishing process that removes material
with the abrasive action of gas jet (air, nitrogen or
carbon-dioxide) loaded with abrasive powder particles
(silicon carbide, aluminum oxide or glass).
● Can also be used to cut slits, grooves or shapes or
holes.
● Works well in heat-sensitive, brittle, thin or hard
materials.
4. Abrasive Waterjet Cutting (AWC)
● Abrasives are added to a waterjet to improve the cutting
efficiency.
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Thermal NTM Processes
High temperatures in very localized regions melt and vaporize
the material.
1. Electrodischarge Machining (EDM)
2. Electron Beam Machining (EBM)
3. Laser Beam Machining (LBM)
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Thermal NTM Processes
1. Electrodischarge Machining (EDM)
● Suitable for electrically conductive materials.
Tool (electrode) should also be electrically conductive.
● EDM removes metal by the eroding action of small
electrical sparks.
Cathode (-)
Tool (Electrode)
Discharge
Material removed
from workpiece
Flow of dielectric fluid
Workpiece
Cavity created
by discharge
Anode (+)
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Electrodischarge Machining (EDM)
● In operation, both the electrode (tool) and the workpiece
are immersed in a dielectric fluid (non-conductive fluid).
● Thousands of sparks per second are generated and
each spark produces a tiny crater by vaporization,
thus eroding the shape of the tool into the workpiece.
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Electrodischarge Machining (EDM)
Crater formed by a single spark on a ground
surface. (Ground : Made by grinding.)
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Electrodischarge Machining (EDM)
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Electrodischarge Machining (EDM)
The dielectric fluid (hydrocarbon oils, kerosene and
deionized water) is an insulator between the tool and
the workpiece, a coolant and a flushing medium for the
removal of chips.
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Electrodischarge Machining (EDM)
● Materials of any hardness can be cut as long as the
material can conduct electricity.
● Absence of almost all mechanical forces makes it
possible to machine fragile parts.
● A primary disadvantage of EDM is tool wear.
● It is common to utilize several identical-geometry cutting
tools during the machining of one profile.
● Tool (electrode) materials can be, graphite, copper,
brass, tungsten, steel, aluminum, molybdenum, nickel,
etc.
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Electrodischarge Machining (EDM)
EDM, primarily, exists commercially in the form of
die-sinking machines (EDM) (Ram EDM / Sinker EDM)
and wire-cutting machines.
Dielectric fluid
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Wire-EDM (W-EDM)
Special form of EDM
is wire EDM, wherein
the electrode is a
continuously moving
conductive wire made
from copper, brass,
tungsten or
molybdenum.
The process is widely
used for the
manufacture of
punches, dies and
stripper plates.
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Wire-EDM (W-EDM)
Wire-EDM’ed parts.
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Thermal NTM Processes
3. Laser Beam Machining (LBM)
LBM is a thermal material removal process that utilizes a
high-energy, coherent light beam (laser) to melt and
vaporize materials (metallic and non-metallic).
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Laser Beam Machining (LBM)
● Can drill 0.125 mm diameter holes in 2.5 mm thick
material in seconds with a depth to diameter ratio of
10/1.
● High-energy solid state or gas lasers are used.
● Not a mass metal-removal process.
● Recast layer and heat-affected zone can be detrimental
to material properties.
● Can be used as well for welding, cutting, trimming,
blanking and heat-treating by varying power density,
beam intensity, focus and duration.
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Laser Beam Drilling
5-DOF Laser
drilling machine
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