Unconventional or Nontraditional Machining

These are known as non-traditional/unconventional method because compared to conventional method there is no contact between tool and workpiece, specific power consumption is very large, MRR is low and used in situations where traditional/conventional machining processes are unsatisfactory or uneconomical:

• Workpiece is too hard, ot tough.
• Workpiece is too flexible to resist cutting forces or too difficult to clamp
• Part shape is very complex with internal or external profiles or small holes
• Requirements for surface finish and tolerances are very high

Classification Based on Energy Source

1. Electro-Chemical Processes

• Electro-Chemical Machining (ECM) 
• Electro-Chemical grinding (ECG) 
• Electro-Chemical Honing (ECH) 
• Electro-Chemical Deburring (ECD)

2. Chemical Processes

• Chemical Machining Method (CHM)
• Photochemical Machining (PCM)

3. Electro-Thermal Processes

• Electrical discharge machining (EDM)
• Laser beam Machining (LBM) 
• Plasma Arc Machining (PAM) 
• Electron Beam Machining(EBM) 
• Ion Beam Machining (IBM)

4. Mechanical Processes

• Ultra Sonic Machining (USM) 
• Abrasive Jet Machining (AJM) 
• Water Jet Machining (WJM)

Electro-Chemical Machining (ECM)

The work-piece is made the anode, which is placed in close proximity to an electrode (cathode), and a high-amperage direct current is passed between them through an electrolyte, such as salt water, flowing in the anode-cathode gap.

The tool is fed with constant velocity towards the workpiece and the electrolyte pumped at high pressure through the small gap between the tool and work.

The mechanism of material removal is anodic dissolution.

The electrolyte is so chosen that the anode (workpiece) is dissolved but no deposition takes place on the tool.

Properties of electrolyte:

• High electrical and thermal conductivity 
• Low viscosity
• High specific heat
• Non corrosive and notoxic
• Chemically stable

Material Removal Rate is given by Faraday's law:

\[\boxed{MRR = \frac{AI}{\rho Z F} = \frac{EI}{\rho F}} cm^3/s\]

where, A : gram atomic weight of workpiece (anode)

E = A/Z : equivalence weight

Z : Valency

I : Current (amp.)

$\rho$ : density of workpiece ($g/cm^3$)

F: Faraday's constant = 96500 columbs

Electro-Chemical grinding (ECG)

• The tool as electrode is rotating, metal bonded, diamond grit grinding wheel and workpiece as anode.
• As the current flows the surface metal is changed to oxide film and this oxide film is removed.
• The abrasive particles are non-conductive material such as aluminum oxide, diamond and borazon (BCN).  

Applications:

• Shaping and sharpening carbide cutting tool
• Fragile parts (honeycomb structures), surgical needles, and tips of assembled turbine blades have been ECG-processed successfully.

Chemical Machining Method (CHM)

• Chemical machining is basically an etching process, it is the oldest nontraditional machining process.
• Material is removed from by chemical dissolution using chemical reagents, or etchants, such as acids and alkaline solutions.
• The workpiece is immersed in a bath containing an etchant. Special coating called maskant protects area from which area is not to be removed.
• Cutting speed (0.0025-0.1 mm/min) is very slow.

Photochemical Machining (PCM)

• This process is also known as photochemical milling or photo etching, is a photo chemical blanking.
• Coat both sides of the plate with photoresist which is a polymer that adheres to the metal when exposed to UV light. 
• Spray metal with etchant or dip it in hot acidic solution to etch all material other than part covered with photoresist.
• This process is burr free and high precision.

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