JNTU B.Tech IV UNCONVENTIONAL MACHINING PROCESSES Previous Question Paper (July/August - 2022 - R16)

Modern or unconventional machining processes are advanced material removal techniques that do not rely on direct mechanical contact or traditional cutting tools. Instead, they utilize thermal, chemical, electrochemical, or electrical energy to remove material at the atomic or molecular level. These processes are essential for machining materials that are too hard, brittle, or complex in geometry for conventional methods.

Unconventional processes have not replaced conventional machining due to several critical limitations:

1. Economic Viability: Conventional machining remains significantly cheaper for high-volume production and standard materials.
2. Material Removal Rate (MRR): Traditional methods like milling and turning offer much higher material removal rates for bulk material reduction.
3. Complexity and Cost: Non-traditional equipment requires specialized infrastructure, higher power consumption, and skilled operators, making them unsuitable for simple, routine tasks.
4. Surface Integrity: Some non-traditional processes induce thermal damage or recast layers, which may require secondary finishing operations that conventional methods avoid.

Ultrasonic Machining (USM) setup consists of an ultrasonic frequency generator, a transducer, a tool holder (concentrator), the tool, and an abrasive slurry delivery system. The transducer converts electrical energy into high-frequency mechanical vibrations (typically 20 kHz), which are amplified by the concentrator and transmitted to the tool. The tool vibrates at small amplitudes, driving abrasive particles in the slurry against the workpiece to erode material.

Feed mechanisms in USM are critical for maintaining a constant, optimal gap between the tool and the workpiece:

1. Constant Pressure Feed: A dead weight or spring-loaded mechanism applies a constant force to the tool head, ensuring it maintains contact with the abrasive slurry as material is removed.
2. Constant Feed Rate: A motor-driven system advances the tool at a predetermined speed. This is less common as it can lead to tool breakage or poor surface finish if the feed rate exceeds the material removal rate.
3. Servo-Controlled Feed: This is the most efficient mechanism, using a sensor to monitor the gap or the force. The servo system adjusts the tool position dynamically to maintain a constant machining gap, ensuring stable material removal and preventing tool-workpiece collision.