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9 Non conventional Machining
Version 2 ME, IIT Kharagpur

37 Water Jet and Abrasive Water Jet Machining
Version 2 ME, IIT Kharagpur

Instructional Objectives
o o o o o o o o o o o o o List four different non conventional machining processes Differentiate between water and abrasive water jet machining List different WJM and AWJM systems List ten different modules of AWJM systems List four applications of AWJM List three advantages of AWJM List materials that can be processed by AWJM Mention functions of different elements of AWJM Identify mechanism of material removal Develop models for mechanism of material removal Identify parameters related to product quality Identify five limitations of AWJM Identify environmental issues in the area of AWJM

Water Jet Machining (WJM) and Abrasive Water Jet Machining (AWJM) are two non-traditional or non-conventional machining processes. They belong to mechanical group of non-conventional processes like Ultrasonic Machining (USM) and Abrasive Jet Machining (AJM). In these processes (WJM and AJWM), the mechanical energy of water and abrasive phases are used to achieve material removal or machining. The general grouping of some of the typical non-traditional processes are shown below: o Mechanical Processes ⎯ USM ⎯ AJM ⎯ WJM and AWJM o Thermal Processes ⎯ EBM ⎯ LBM ⎯ PAM ⎯ EDM and WEDM o Electrical Processes ⎯ ECM ⎯ EDG ⎯ EJD o Chemical Processes ⎯ Chemical milling ⎯ Photo chemical machining WJM and AWJM can be achieved using different approaches and methodologies as enumerated below: • WJM - Pure • WJM - with stabilizer • AWJM – entrained – three phase – abrasive, water and air • AWJM – suspended – two phase – abrasive and water

Version 2 ME, IIT Kharagpur

o Direct pumping o Indirect pumping o Bypass pumping However in all variants of the processes, the basic methodology remains the same. Water is pumped at a sufficiently high pressure, 200-400 MPa (20004000 bar) using intensifier technology. An intensifier works on the simple principle of pressure amplification using hydraulic cylinders of different crosssections as used in “Jute Bell Presses”. When water at such pressure is issued through a suitable orifice (generally of 0.2- 0.4 mm dia), the potential energy of water is converted into kinetic energy, yielding a high velocity jet (1000 m/s). Such high velocity water jet can machine thin sheets/foils of aluminium, leather, textile, frozen food etc. In pure WJM, commercially pure water (tap water) is used for machining purpose. However as the high velocity water jet is discharged from the orifice, the jet tends to entrain atmospheric air and flares out decreasing its cutting ability. Hence, quite often stabilisers (long chain polymers) that hinder the fragmentation of water jet are added to the water. In AWJM, abrasive particles like sand (SiO2), glass beads are added to the water jet to enhance its cutting ability by many folds. AWJ are mainly of two types – entrained and suspended type as mentioned earlier. In entrained type AWJM, the abrasive particles are allowed to entrain in water jet to form abrasive water jet with significant velocity of 800 m/s. Such high velocity abrasive jet can machine almost any material. Fig. 1 shows the photographic view of a commercial CNC water jet machining system along with close-up view of the cutting head.

Fig. 1 Commercial CNC water jet machining system and cutting heads (Photograph Courtesy – Omax Corporation, USA) Version 2 ME, IIT Kharagpur

The applications and materials, which are generally machined using WJ and AWJ, are given below: Application • Paint removal • Cleaning • Cutting soft materials • Cutting frozen meat • Textile, Leather industry • Mass Immunization • Surgery • Peening • Cutting • Pocket Milling • Drilling • Turning • Nuclear Plant Dismantling Materials • • • • • • • • • • • • •

Steels Non-ferrous alloys Ti alloys, Ni- alloys Polymers Honeycombs Metal Matrix...
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