Water Jet Machining

WATER JET MACHINING

          Water Jet Machining  are two non-traditional or non-conventional machining processes. They belong to mechanical group of non-conventional processes like Ultrasonic Machining and Abrasive Jet Machining . Here, the mechanical energy of water and abrasive phases are used to achieve material removal or machining.

          Water jet machining  can be achieved using different approaches and methodologies as enumerated below:
 • Water Jet Machining  - Pure
 • Water Jet Machining - with stabilizer
 o Direct pumping
 o Indirect pumping
 o Bypass pumping

WORKING BACKGROUND

In Water Jet Machining all variants of the processes, The basic methodology remains the same. Water is pumped at a 

  --------->sufficiently high pressure, 

  --------->200-400 MPa  (2000- 4000 bar) [Using intensifier technology].

 An Intensifier works on the simple principle of pressure amplification using hydraulic cylinders of different cross- sections 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. Thus stabilisers (long chain polymers) that hinder the fragmentation of water jet are added to the water. 

 APPLICATIONS

The applications and materials, which are generally machined using WJ and AWJ, are given below: 
 

      • Paint removal 

      • Textile, Leather industry 

      • Mass Immunization 

      • Surgery

      • Cleaning

      • Peening 

      • Cutting 

      • Pocket Milling 

      • Drilling 

      • Turning

      • Cutting soft materials 

      • Cutting frozen meat 

      • Nuclear Plant Dismantling 

Materials 

          • Polymers

          • Glass Fibre Metal Laminates 

          • Steels 

          • Non-ferrous alloys 

          • Ti alloys, Ni- alloys 

          • Honeycombs 

          • Ceramic Matrix Composite

          • Metal Polymer Laminates

          • Metal Matrix Composite 

          • Concrete  

          • Reinforced plastics 

          • Stone – Granite 

          • Wood

           Other than cutting (machining) high pressure water jet also finds application in paint removal, cleaning, surgery, peening to remove residual stress etc.

          The cutting ability of water jet machining can be improved drastically by adding hard and sharp abrasive particles into the water jet. Thus, WJM is typically used to cut so called “softer” and “easy-to-machine” materials like thin sheets and foils, non-ferrous metallic alloys, wood, textiles, honeycomb, polymers, frozen meat, leather etc, but the domain of “harder and “difficult-to- machine” materials like thick plates of steels, aluminium and other commercial materials, metal matrix and ceramic matrix composites, reinforced plastics, layered composites etc are reserved for AWJM.  

ADVANTAGES

      • Machine thick plates 

      • Very low side forces during the machining  

      • Machine virtually any 2D shape on every material

      • highly fast set-up and programming

      • Almost no heat generated on the part 

      • Very MINUTE fixturing for most parts 

SOURCE : NPTEL MECHANICAL : ADVANCED MACHINING TECHNOLOGY