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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.

Nontraditional Machining Processes

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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.

Nontraditional Machining Processes

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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.

Chemical Machining

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Chemical Machining

Mixer

Workpiece

Maskant

Chemical etchant

Workpiece holder

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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).

Chemical Machining

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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 commonly, on large aerospace structures.

Etchant

(1) Raw part is cleaned/ degreased.

(2) Maskant is applied globally and cured.

(3) Maskant is removed from selected sections.

(4) Exposed sections of the workpiece are

etched.

(5) Maskant is removed completely and

workpiece is washed.

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Chemical Blanking

(1) Raw part is cleaned/ degreased.

(2) Maskant is applied globally and cured.

(3) Maskant is removed from selected sections.

(4) Exposed sections of the workpiece are etched.

(5) Maskant is removed completely and

workpiece is washed.

Some thin-walled part profiles

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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.)

Nontraditional Machining Processes

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Electrochemical Machining (ECM)

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.

Electrolyte

Insulation

Electrolyte supply

Tool holder and feed mechanism

Tool De-plated

material

Cavity created

by deplating

Tool

Workpiece

Forced

electrolyte

circulation

Cathode (-)

Anode (+)

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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.

Electrochemical Machining Processes

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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.

Electrochemical Machining Processes

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● 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.

Electrochemical Grinding (ECG)

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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)

Nontraditional Machining Processes

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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.

Mechanical NTM Processes

High frequency

oscillation

Tool

Workpiece

Slurry

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● 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.

Ultrasonic Machining (USM)

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● 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.

Ultrasonic Machining (USM)

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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

Mechanical NTM Processes

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● 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).

Hydrodynamic Jet Machining

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Hydrodynamic Jet Machining

Abrasives can

also be utilized

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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.

Mechanical NTM Processes

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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)

Thermal NTM Processes

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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.

Thermal NTM Processes

Material removed from workpiece

Cavity created by discharge

Tool (Electrode)

Workpiece

Flow of dielectric fluid

Discharge

Cathode (-)

Anode (+)

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● 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.

Electrodischarge Machining (EDM)

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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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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.

Electrodischarge Machining (EDM)

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● 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.

Electrodischarge Machining (EDM)

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Electrodischarge Machining (EDM)

Dielectric fluid

EDM, primarily, exists commercially in the form of

die-sinking machines (EDM) (Ram EDM / Sinker EDM)

and wire-cutting machines.

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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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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).

Thermal NTM Processes

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● 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.

Laser Beam Machining (LBM)

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Laser Beam Drilling

5-DOF Laser

drilling machine