JNTU B.Tech III UNCONVENTIONAL MACHINING PROCESSES Previous Question Paper (August/September - 2021 - R18)

Conventional machining processes are classified based on the primary source of energy used for material removal:

• Mechanical Energy: These processes rely on the mechanical action of a cutting tool or abrasive particles to remove material in the form of chips. Examples include turning, milling, drilling, and grinding. The material removal is governed by the shear strength of the workpiece.
• Thermal Energy: These processes utilize heat generated by chemical reactions or electrical arcs to melt or vaporize the material. Examples include oxy-fuel gas cutting and plasma arc cutting.
• Chemical Energy: These processes involve the controlled dissolution of material through chemical reactions with an etchant. Examples include chemical milling and chemical blanking.
• Electrical Energy: These processes use electrical energy to remove material through electrochemical dissolution or spark erosion. Examples include electrochemical machining and electrical discharge machining.

The material removal rate (MRR) in unconventional machining processes is significantly influenced by specific operating parameters:

• Current/Power Density: In processes like EDM or ECM, increasing the discharge current or current density directly increases the energy available for material removal, thereby raising the MRR.
• Pulse Parameters: In EDM, the pulse-on time and pulse-off time are critical. A longer pulse-on time increases the energy per spark, enhancing MRR, but excessive duration may lead to poor surface finish.
• Tool Feed Rate: Maintaining an optimal feed rate is essential to keep the inter-electrode gap constant. If the feed rate is too high, it may cause short-circuiting; if too low, it reduces the efficiency of material removal.
• Electrolyte/Dielectric Flow Rate: Effective flushing of debris is necessary to maintain a stable machining process. Higher flow rates prevent the accumulation of particles in the gap, which prevents arcing and sustains a higher MRR.
• Abrasive Concentration/Size: In processes like AJM or USM, increasing the concentration and size of abrasive particles increases the number of impacts and the energy per impact, leading to a higher MRR up to a saturation point.