Jawaharlal Nehru Technological University Hyderabad B.Tech III UNCONVENTIONAL MACHINING PROCESSES Previous Question Paper (August - 2022 - R18)

Conventional machining processes, such as turning, milling, and drilling, rely on mechanical energy and direct tool-workpiece contact. Their primary limitations include: 1) The tool material must be harder than the workpiece material, making the machining of superalloys and ceramics difficult; 2) High cutting forces can cause deformation in thin-walled or fragile components; 3) The process often induces significant residual stresses and heat-affected zones; 4) Complex geometries, such as deep holes or non-circular cavities, are difficult or impossible to produce; and 5) Tool wear is rapid when machining hardened materials, leading to poor surface finish and dimensional inaccuracy.

The need for unconventional machining processes in modern manufacturing is justified by the requirement for high-strength, heat-resistant, and chemically inert materials in aerospace, nuclear, and medical industries. These industries demand complex, intricate shapes with high precision and superior surface integrity that conventional methods cannot achieve economically or technically. Unconventional processes allow for the machining of materials regardless of their hardness or toughness, minimize mechanical and thermal damage, and enable the fabrication of micro-scale features essential for modern technological advancement.

Ultrasonic Machining (USM) is a non-traditional machining process that uses high-frequency, low-amplitude vibrations of a tool against a workpiece in the presence of an abrasive slurry to remove material through micro-chipping or erosion.

The material removal mechanism in USM involves several key actions:

1. Abrasive Impact: The tool vibrates at ultrasonic frequencies (typically 20 kHz) with a small amplitude. These vibrations are transmitted to the abrasive grains suspended in the slurry, which are then hammered against the workpiece surface.
2. Brittle Fracture: As the abrasive particles strike the workpiece, they cause localized brittle fracture and micro-chipping. This is highly effective for hard and brittle materials like glass, ceramics, and carbides.
3. Erosion: The continuous bombardment by the abrasive particles erodes the material, gradually replicating the tool shape into the workpiece.
4. Slurry Circulation: The slurry serves two critical roles: it carries the abrasive particles to the machining zone and flushes away the fractured material debris, preventing tool clogging and ensuring a consistent cutting rate.