Introduction
Unconventional manufacturing processes is defined as a group of
processes that remove excess material by various techniques involving
mechanical, thermal, electrical or chemical energy or combinations of these
energies but do not use a sharp cutting tools as it needs to be used for
traditional manufacturing processes.
Extremely hard and brittle materials are difficult to machine by
traditional machining processes such as turning, drilling, shaping and milling.
Non-traditional machining processes, also called advanced manufacturing
processes, are employed where traditional machining processes are not
feasible, satisfactory or economical due to special reasons as outlined below.
- Very hard fragile materials
difficult to clamp for traditional machining.
- When the work piece is too
flexible or slender.
- When the shape of the part
is too complex.
Several types of non-traditional
machining processes have been developed to meet extra required machining
conditions. When these processes are employed properly, they offer many
advantages over non-traditional machining processes.
CM Process V/s UCM Process
Conventional Machining Processes mostly
remove material in the form of chips by applying forces on the work material
with a wedge shaped cutting tool that is harder than the work material under
machining condition.
The major characteristics of
conventional machining are:
- Generally macroscopic chip
formation by shear deformation.
- Material removal takes place
due to application of cutting forces – energy domain can be classified as
mechanical.
- Cutting tool is harder than
work piece at room temperature as well as under machining conditions.
Non-conventional manufacturing processes is defined as a group of
processes that remove excess material by various techniques involving
mechanical, thermal, electrical or chemical energy or combinations of these
energies but do not use a sharp cutting tools as it needs to be used for
traditional manufacturing processes.
NEED FOR UNCONVENTIONAL
MACHINING PROCESSES
Ø Extremely
hard and brittle materials or Difficult to machine material are difficult to
machine by traditional machining processes.
Ø When
the work piece is too flexible or slender to support the cutting or grinding
forces when the shape of the part is too complex.
CLASSIFICATION OF UCM PROCESSES:-
Abrasive Jet Machining
In abrasive jet machining, a focused stream of abrasive particles,
carried by high pressure air or gas is made to impinge on the work surface
through a nozzle and the work material is made to impinge on the work surface
through a nozzle and work material is removed by erosion by high velocity
abrasive particles.
Abrasive water jet cutting systems (abrasive jet) use a combination of
water and garnet to cut through materials considered "unmachineable"
by conventional cutting methods. Using small amounts of water while eliminating
the friction caused by tool-to-part contact, abrasive jet cutting avoids
thermal damage or heat affected zones (HAZ) which can adversely affect
metallurgic properties in materials being cut. The ability to pierce through
material also eliminates the need and cost of drilling starter holes. Because
abrasive jet cuts with a narrow kerf, parts can be tightly nested thus
maximizing material usage.
Ultrasonic Machining
Ultrasonic machining (USM) is a mechanical material removal process used
to erode holes and cavities in hard or brittle work pieces by using shaped
tools, high frequency mechanical motion, and an abrasive slurry. . A relatively
soft tool is shaped as desired and vibrated against the work piece while a
mixture of fine abrasive and water flows between them. The friction of the
abrasive particles gradually cuts the work piece.
It is also known as Ultrasonic impact grinding is an operation
that involves a vibrating tool fluctuating the ultrasonic frequencies in order
to remove the material from the work piece. The process involves an abrasive
slurry that runs between the tool and the work piece. Due to this, the tool and
the work piece never interact with each other. The process rarely exceeds two
pounds. All the operations done with the ultrasonic machining method are cost
effective and best in results. Ultrasonic machining is an abrasive process
which can create any material into hard and brittle form with the help of its
vibrating tool and the indirect passage of abrasive particles towards the work
piece. It is a low material removal rate machining process.
A water jet cutter is a tool capable of slicing into metal or other
materials using a jet of water at high velocity and pressure. It is often used
during fabrication or manufacture of parts for machinery and other devices. It
has found applications in a diverse number of industries from mining to
aerospace where it is used for operations such as cutting, shaping, carving,
and reaming.
The most important benefit of the water jet cutter is its ability to cut
material without interfering with the materials inherent structure as there is
no "heat affected zone" or HAZ. This allows metals to be cut without
harming their intrinsic properties.
Abrasive Water Jet Machining
AWJM is a well-established non-traditional machining process. Abrasive
water jet machining makes use of the principles of both abrasive jet machining
and water jet machining. AWJM is a non conventional machining process where
material is removed by impact erosion of high pressure high velocity of water
and untrained high velocity of grit abrasives on a work piece.
This technology is
most widely used compare to other non-conventional technology because of its
distinct advantages. It is used for cutting a wide variety of materials ranging
from soft to hard materials. This technique is especially suitable for very
soft, brittle and fibrous materials. This technology is less sensitive to
material properties as it does not cause chatter. This process is without much
heat generation so machined surface is free from heat affected zone and residual
stresses. AWJM has high machining versatility and high flexibility. The major
drawback of this process is, it generate loud noise and a messy working
environment.
Electrochemical Machining
Electrochemical machining (ECM) also uses electrical energy to remove
material. An electrolytic cell is created in an electrolyte medium, with the
tool as the cathode and the work piece as the anode. A high-amperage,
low-voltage current is used to dissolve the metal and to remove it from the
work piece, which must be electrically conductive. ECM is essentially a
depleting process that utilizes the principles of electrolysis. The ECM tool is
positioned very close to the work piece and a low voltage, high amperage DC
current is passed between the two via an electrolyte. Material is removed from
the work piece and the flowing electrolyte solution washes the ions away. These
ions form metal hydroxides which are removed from the electrolyte solution by
centrifugal separation. Both the electrolyte and the metal sludge are then
recycled.
Electrochemical Grinding
Electro-chemical grinding (ECG) is a variant process of the basic ECM.
It is a burr free and stress free material removal process, wherein material
removal of the electrically conductive material takes place through mechanical
(grinding) process and electro-chemical process. The abrasive laden grinding
wheel is negatively charged and the work piece is positively charged. They are
separated by an electrolyte fluid. The fine chips of the material that is
removed from the work piece (debris) stays in the electrolyte fluid, which is
further filtered out. Electrochemical grinding and electrochemical machining
are similar processes with a difference that a wheel substitutes the tool used
in ECM. The wheel shape is similar to the desired work shape.
The main feature of electrochemical grinding (ECG) process is the use of
a metallic grinding wheel which is embedded with insulating abrasive particles
such as diamond, set in the conducting material. Copper, brass, and nickel are
the most commonly used materials while aluminium oxide is a typical abrasive
used while grinding steels.
Electro Jet drilling
Electro jet drilling (EJD) process is picking up noticeable
quality in the machining of miniaturized scale and full-scale openings in hard
to-machine materials utilized as a part of aviation, gadgets, and PCs,
medicinal, and car ventures. As the pattern towards scaling down proceeds with,
this procedure is increasing expanding significance as it has demonstrated its
prevalence over other contemporary non-traditional miniaturized scale and large
scale gap penetrating procedures. This paper exhibits a two-dimensional limited
component demonstrate for the investigation of the EJD procedure utilizing
quadrilateral (rectangular) components. The created display predicts the
penetrating rate and spiral over cut. The test comes about show close
concurrence with the mimicked comes about.
Electrical Discharge Machining
Electrical Discharge Machining (EDM), also known as spark erosion,
employs electrical energy to remove metal from the work piece without touching
it. A pulsating high- frequency electric current is applied between the tool
point and the work piece, causing sparks to jump the gap and vaporize small
areas of the work piece. Because no cutting forces are involved, light,
delicate operations can be performed on thin work pieces. EDM can produce
shapes unobtainable by any conventional machining process.
Laser Jet Machining
Laser-Jet machining (LJM) is accomplished by precisely manipulating a jet of coherent light to vaporize unwanted material. LJM is particularly suited to making accurately placed holes. It can be used to perform precision micromachining on all microelectronic substrates such as ceramic, silicon, diamond, and graphite. Examples of microelectronic micromachining include cutting, scribing & drilling all substrates, trimming any hybrid resistors, patterning displays of glass or plastic and trace cutting on semiconductor wafers and chips.
Electron-beam machining
In electron-beam machining (EBM), electrons are accelerated to a
velocity nearly three-fourths that of light (~200,000 km/sec). The process is
performed in a vacuum chamber to reduce the scattering of electrons by gas
molecules in the atmosphere. The electron beam is aimed using magnets to
deflect the stream of electrons and is focused using an electromagnetic lens.
The stream of electrons is directed against a precisely limited area of the
work piece; on impact, the kinetic energy of the electrons is converted into
thermal energy that melts and vaporizes the material to be removed, forming
holes or cuts.
Typical applications are annealing, welding, and metal removal. A hole
in a sheet 1.25 mm thick up to 125 micro m diameter can be cut almost instantly
with a taper of 2 to 4 degrees. EBM equipment is commonly used by the
electronics industry to aid in the etching of circuits in microprocessors.
Chemical Milling
Chemical Milling aides in the manufacture of light gauge metal parts.
The photo etching process (also called chemical etching and chemical milling)
allows people to produce intricate metal components with close tolerances that
are impossible to duplicate by other production methods. It is also known as
chemical machining.
Chemical Milling is utilized in the manufacturing of encoders, masks,
filters, lead frames, flat springs, strain gauges, laminations, chip carriers,
step covers, fuel cell plates, heat sinks, shutter blades, electron grids,
fluidic circuit plates, reticles, drive bands, haptics, and shims.
Photochemical Machining
Photochemical
Machining (PCM) components are produced by the photo-etching technique using a
wide array of metal and alloys. This technique avoids burrs, no mechanical
stresses are built into the parts and the properties of the metal worked are
not affected. Hardened and tempered metals are machined as easily as regular
metals. The technique is ideal for machining thin metals and foils. Parts with
very precise and intricate designs can be produced without difficulty. The
photo chemical machining/milling processes can precisely etch lines and spaces
on all types of metals (alloys: kovar, nickel, brass, beryllium, copper,
stainless steel, aluminium, and others) with detailed accuracies. This is used
for creating specialty flex circuits, plus in engineering of other rigid
technologies. This results in a burr free part with very close tolerances. 
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