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Nontraditional cutting processes

Date post: 17-Jul-2015
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The nontraditional processes that use mechanical

energy other than a sharp cutting tool.

Types:

(1) ultrasonic machining.

(2) water jet processes.

(3) abrasive jet process.

Ultrasonic machining is a non-traditional

mechanical means of uniform stock removal,

applicable to both conductive and nonconductive

materials. Particularly suited for very hard and

brittle materials such as graphite, glass, carbide, and

ceramics.

It uses medium to high frequency vibrations (in the

area of 20KHz) through a designed or formed tool

having the shape of the cavity to be machined,

combined with a fine abrasive slurry to produce

accurate holes or cavities of regular or irregular

shapes. Vibration of the tool top is obtained through

a transducer.

The two processes described in this section remove

material by means of:

1) high-velocity streams of water.

2)a combination of water and abrasives

A water jet cutter is an industrial tool capable of

cutting a wide variety of materials using a very

high-pressure jet of water.

Pure water jets use the beam of water exiting the

orifice to cut soft material like candy bars, and thin

soft wood.

They use the technology of high-pressure water

being forced through a small hole (typically called

the "orifice" or "jewel") to concentrate an extreme

amount of energy in a small area. The restriction of

the tiny orifice create high-velocity beam, much like

putting your finger over the end of a garden hose.

In Abrasive Jet Machining abrasive particles are

made to impinge on the work material at a high

velocity. The jet of abrasive particles is carried by

carrier gas or air.

The high velocity stream of abrasive is generated

by converting the pressure energy of the carrier gas

or water to its kinetic energy and hence high

velocity jet.

The high velocity abrasive particles remove the

material.

Abrasive jet machining also known as micro-

abrasive blasting, is a mechanical energy based

unconventional machining process used to remove

unwanted material from a given workpiece.

The process makes use of an abrasive jet with high

velocity, to remove material and provide smooth

surface finish to hard metallic workpieces. It is

similar to water jet machining.

Material is removed by fine abrasive particles,

usually about 0.001 inch (0.025 mm) in diameter,

driven by a high velocity fluid stream;

common gases are air or inert gases. Pressures for

the gas range from 25 to 130 psi (170–900 kpa) and

speeds can be as high as 300 m/s.

• AFM can

Polish and deburr parts internally.

Through holes.

Intersecting holes.

Calibrate fuel injection nozzles to a specific flow

rate.

Produce surface finish as good as 0.05 μm deburr

holes as small as 0.2 mm radius edges from 0.025

mm to 1.5 mm.

1)One-way AFM.

One-way flow AFM processing pushes abrasive

media through the work piece in only one direction,

allowing the media to exit freely from the part.

2)Two-way AFM.

The typical two-way flow AFM process uses two

vertically opposed cylinders to extrude an abrasive

media back and forth through or around passages

formed by the workpiece and tooling.

ECM is used to machine workpieces by

electrolytically dissolving the metal. The process is

used in aerospace engineering and the automotive,

medical equipment, micro system and power supply

industries. Almost all kinds of metal can be electro-

chemically machined, even high-alloyed nickel- or

titanium-based ones, as well as hardened materials.

Material is depleted from anode workpiece and

transported to a cathode tool in an electrolyte bath.

Electrolyte flows rapidly between the two poles to

carry off depleted material, so it does not plate onto

tool.

Electrode materials: cupper, brass, or stainless steel.

Tool has inverse shape of part.

Tool size and shape must allow for the gap.

Electrochemical deburring (ECD) is an adaptation

of ECM designed to remove burrs or to round sharp

corners on metal work parts by anodic dissolution.

It is a highly productive, precision technology for

deburring especially at the intersections of internal

passages, or other difficult to access features of a

workpiece.

The electrode tool is designed to focus the metal

removal action on the burr. Portions of the tool not

being used for machining are insulated. The

electrolyte flows through the hole to carry away the

burr particles.

Electrochemical Grinding, is a variation of ECM

(Electrochemical Machining) that combines

electrolytic activity with the physical removal of

material by means of charged grinding wheels.

Electrochemical Grinding (ECG) can produce burr

free and stress free parts without heat or other

metallurgical damage .

Material removal processes based on thermal energy

are characterized by very high local temperatures—

hot enough to remove material by fusion or

vaporization. Because of the high temperatures,

these processes cause physical and metallurgical

damage to the new work surface.

Electrical discharge machining:

EDM is the thermal erosion process in which metal

is removed by a series of recurring electrical

discharges between a cutting tool acting as an

electrode and a conductive workpiece, in the

presence of a dielectric fluid.

1) A preshaped or formed electrode (tool),usually

made from graphite or copper, is shaped to the form

of the cavity it is to reproduce.

The formed electrode is fed vertically down and the

reverse shape of the electrode is eroded (burned)

into the solid workpiece.

2.Electric Discharge Wire Cutting

Wire EDM machining (Electrical DischargeMachining) is an electro thermal productionprocess in which a thin single-strand metalwire in conjunction with de-ionized waterallows the wire to cut through metal by the useof heat from electrical sparks.

Electron beam machining is a thermalnontraditional process, uses electrical energy togenerate thermal energy for removing material.A pulsating stream of high-speed electronsproduced by a generator is focused byelectrostatic and electromagnetic fields toconcentrate energy on a very small area ofwork.

Uses a high-velocity stream of electrons capable to

remove any material.

EB gun accelerates a continuous stream of electrons

to about 75% of light speed.

Kinetic energy of electrons is converted to thermal

energy of extremely high density which vaporizes

material in a very localized area.

Beam focused through electromagnetic lens.

Laser beam machining is an unconventional

machining process in which a laser is directed

towards the work piece for machining. Since the

rays of a laser beam are monochromatic and parallel

it can be focused to a very small diameter and can

produce energy as high as 100 MW of energy for a

square millimeter of area.

Light amplification by stimulated emission of

radiation.

A laser converts electrical energy into a highly

coherent light beam with the following properties:

– Monochromatic (theoretically, single wave length)

– Highly collimated (light rays are almost perfectly

parallel)

These properties allow laser light to be focused,

using optical lenses, onto a very small spot with

resulting high power densities.

The intense heat from an electric arc can be used to

melt virtually any metal for the purpose of welding

or cutting. Most arc-cutting processes use the heat

generated by an arc between an electrode and a

metallic work part to melt a kerfs that separates the

part. The most common arc-cutting processes are

(1) plasma arc cutting.

(2) air carbon arc cutting.

Plasma cutting is a process that is used to cut steel

and other metals of different thicknesses (or

sometimes other materials) using a plasma torch.

In this process, a gas (oxygen, air, inert and others

dependant on material) is blown at high speed out of

a nozzle; at the same time an electrical arc is formed

through that gas from the nozzle to the surface being

cut, turning some of that gas to plasma. The plasma

is hot enough to melt the metal being cut .

Air carbon arc cutting, previously known as air

arc cutting, is an arc cutting process where metal is

cut and melted by the heat of a carbon arc.

In this process, an intense arc is used to form a

molten pool on a metal workpiece, and compressed

air is used for blowing the molten metal thoroughly

from the metal surface. It is important that the metal

is only cut along the airflow direction. Moreover,

appropriate arc length has to be maintained to

completely remove the molten metal.

Oxy-fuel welding (commonly called oxyacetylene

welding, oxy welding, or gas welding) and oxy-

fuel cutting are processes that use fuel gases and

oxygen to weld and cut metals, respectively.

Use heat of combustion of fuel gases combined withexothermic reaction of metal with oxygen

Popularly known as flame cutting

Cutting torch delivers a mixture of fuel gas andoxygen and directs a stream of oxygen to cuttingregion.

Fuel:

– Acetylene (C2H2)

– Propylene (C3H6)

– Propane (C3H8)

Chemical machining is a nontraditional process inwhich material is removed by means of a strongchemical etchant. Applications as an industrialprocess began shortly after world war II in theaircraft industry.

Types

(1) chemical milling,

(2) chemical blanking,

(3) chemical engraving,

(4) photochemical machining

Chemical milling is the process of removing large

amounts of metal by means of chemical etching. All

metal types and shapes are candidates for chemical

milling, especially contoured parts which are not

easily machined.

Clean - to insure uniform etching.

Apply maskant - a maskant (chemically resistant toetchant) to portions of work surface not to beetched.

Materials: neoprene, polyvinylchloride,polyethylene, and other polymers.

Selectively remove maskant.

Etch - part is immersed in etchant which chemicallyattacks those portions not masked.

Remove maskant and clean.

Uses chemical erosion to cut very thin sheet metal

parts - down to 0.025 mm (0.001 in) thick and/or for

intricate cutting patterns

Conventional punch and die does not work because

stamping forces damage the thin sheet metal, or

tooling or both.

Maskant methods are either photo resist or screen

resist

PCM is a process of selectively removing material

by using a chemical action. The process begins with

cleaning the material of all debris, grease, and other

any contaminants; proper metal preparation is

essential to the quality of the final product.

Once it is fully cleaned, it is then coated with aphotosensitive film and etchant resistant, used forcutting the metal, reducing the surfacecontamination and oxidation. Dry film or a liquidresist is applied to both sides of the work piece toallow etching of both sides simultaneously. Thephotosensitive coating is then exposed to a UVlight, which transfers the photo tool image onto thecoated material. Then the material is developed.During this process any material not protected bythe resist is eroded.


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