U N I T 3 UNCONVENTIONAL MACHINING PROCESSES This Unit deals with non-traditional machining processes. You will read about methods relying on ultrasounds, water, electricity, laser and chemical processes. A. MECHANICAL ENERGY-BASED PROCESSES Impractical or uneconomical traditional machining methods are being replaced by a new class of advanced machining processes. They rely on the direct application of energy for material removal and can be divided into four categories: mechanical, electrical, thermal and chemical/electrochemical machining processes. The most common mechanical energy based processes are Ultrasonic Machining (USM), Abrasive Jet Machining (AJM) and Water Jet Machining (WJM). Ultrasonic Machining is applicable to both conductive and non-conductive materials and is particularly suitable for making holes and cavities in hard and/or brittle materials such as graphite, glass and ceramics. USM involves shaped tools, high frequency mechanical motion and abrasive slurry: a tool is vibrated against the work-piece at ultrasonic frequency while a continuous stream of abrasive slurry flows between the work-piece and the tool surface. The friction caused by the abrasive grains in the slurry gradually creates a breakage on the work-piece. The most common fluid medium is water but benzene, glycerol and oils can also be employed. The abrasive grit is generally made up of low cost, easily-available materials such as aluminium oxide, silicon carbide or boron carbide. The selection depends on the hardness of the material being machined, the desired material s removal rate and the surface finish required. In Abrasive Jet Machining, the material is subjected to a high velocity and pressure jet of abrasive particles mixed with air or some other carrier gases. As the tool is not employed there is no heat generated, thus avoiding any harmful effects on the metallurgic properties of materials and causing negligible vibration. Its material removal rate is strictly related to the hardness of the work-piece material. In Water Jet Machining, water is forced through extremely small nozzles at very high pressure in order to operate on traditionally unmachinable materials such 124