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Thursday, August 8, 2013




2.Advanced Machining Processes

Mechanical energy process
Ultrasonic Machining
Water & Abrasive Jet
Electrochemical Machining( Deburring, Grinding)
Thermal Energy Process
Electric Discharge
Electron Beam
Laser Beam
Arc Cutting
Oxyfuel cutting
 Chemical Machining
Mechanics and Chemistry of Chemical Machining
CHM Processes
 Application Considerations

The need to machine newly developed metals and non-metals.
These materials often have special properties (e.g., high strength, high hardness, high toughness) that make them difficult or impossible to machine by conventional methods.
The need for unusual and/or complex part geometries that cannot easily be accomplished and in some cases are impossible to achieve by conventional machining.
The need to avoid surface damage that often accompanies the stresses created by conventional machining.
Many of these requirements are associated with the aerospace and electronics industries.

5.Classification of non traditional Machining
The classification is based on principal form of energy used

Several of the nontraditional processes that use mechanical energy other than a sharp cutting tool:
ultrasonic machining,
water jet processes,and
other abrasive processes.

7.Ultrasonic Machining (USM)
Used for Hard and Brittle Materials like Ceramics and glass
Abrasive particles impacts on workpiece to achieve metal removal
The tool drives the abrasives contained in a slurry
The tool oscillates perpendicular to work surface at high frequency(20,000 HZ) and low amplitude(0.075mm) and fed slowly in the work surface
Tool Material is normally soft steel & Stainless Steel
Abrasive slurry includes boron nitride, boron carbide, Aluminum Oxide etc mixed with water(20% ~60%) and the grit size is propotional to amplitude
Tool and work both undergo abrasion with a ratio of 100:1 to 1:1.

8.Abrasives contained in a slurry are driven at high velocity against the work by a tool vibrating at low amplitude and high frequency.
The amplitudes are around 0.075 mm , and the frequencies are approximately 20,000 Hz.
The tool oscillates perpendicular to the work surface, and is fed slowly into the work,
the shape of the tool is formed in the part.
It is the action of the abrasives, impinging against the work surface, that performs the cutting.
Common tool materials are soft steel and stainless steel.

9.Abrasive materials in USM include
boron nitride,
boron carbide,
aluminum oxide,
silicon carbide, and
Grit size ranges between 100 and 2000.
The vibration amplitude should be set approximately equal to the grit size,
the gap size maintained at about twice grit size.
To a significant degree, grit size determines the surface finish on the new work surface.
the material removal rate increases with increasing frequency and amplitude of vibration.

10.The slurry consists of a mixture of water and abrasive particles.
Concentration of abrasives in water ranges from 20% to 60%.
The slurry must be continuously circulated to bring fresh grains into action.
It also washes away chips and worn grits.
The cutting action operates on the tool as well as the work.
As the abrasive erode the work surface, they also erode the tool.
It is therefore important to know the relative volumes of work material and tool material removed.
This ratio varies for different work materials,
100:1 for cutting glass
1:1 for cutting tool steel.

11.Used for
hard, brittle work materials, such as ceramics, glass, and carbides.
stainless steel and titanium.
Shapes obtained by USM
Shapes obtained include
non-round holes,
holes along a curved axis, and
coining operations,
in which an image pattern on the tool is imparted to a flat work surface.

12.Water Jet Cutting (WJC)
Hydrodynamic or Water Jet cutting (WJC)
High Pressure (400 MPA)
High Velocity stream(900 m/s) from  a nozzle opening of 0.1 to 0.4 mm diameter
The nozzle unit consists of
a holder made of stainless steel, and
a jewel nozzle made of sapphire, ruby, or diamond
Filtration systems is used to separate the swarf produced during cutting.
Preferred cutting fluids are polymer solutions,
because of their tendency to produce a coherent stream.

13.Water Jet Cutting (WJC)

14.Standoff distance: the separation between the nozzle opening and the work surface.
generally desirable to be small to minimize dispersion of the fluid stream ( typically 3.2 mm). 
size of nozzle orifice affects the precision of cut;
smaller openings are used for finer cuts on thinner materials.
thicker jet streams and higher pressures are required to cut thicker stock.
Typical feed rates range from 5 to 500 mm/s, depending on work material and its thickness
Used for plastics, leather, textiles, composites, tile, carpet, cardboard etc

15.Applications / advantages include:
no crushing or burning of the work surface typical in other mechanical or thermal processes,
Minimum material loss because of the narrow cut slit,
no environmental pollution, and
ease of automating the process.
A limitation of the process -- not suitable for cutting brittle materials (e.g., glass)
because of their tendency to crack during cutting.

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