water jet machining / abrasive water jet machning

Abrasive Water Jet Machining/WJM

Abrasive Water Jet Machining/WJMMohit OstwalAssistant ProfessorJodhpur Institute of Engineering and Technology, Co-ed, Jodhpur2/12/2016Mohit Ostwal, Asst. Prof., JIET-coed, Jodhpur1

Content.IntroductionProcessMechanismProcess ParametersApplicationsAdvantagesDisadvantages

2/12/2016Mohit Ostwal, Asst. Prof., JIET-coed, Jodhpur2

IntroductionAbrasive Water Jet Machining (AWJM) is non-traditional or non-conventional machining process. `This 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.


If the process is used without abrasives, it is called as water jet machining (WJM).

The process is generally used for cutting operation and known as water jet cutting process (WJC).

WJM started in late 1960s for cutting.

In early 1980s abrasives were introduced into the water jet and there by the AWJM process was born.2/12/2016Mohit Ostwal, Asst. Prof., JIET-coed, Jodhpur4

Process.High pressure(1500-4000 bar), high velocity (supersonic about 2.5 Mach number)of water jet is bombarded onto the work surface.

High velocity water jet is directed at a target in such a way that the velocity is reduced to zero on striking the workpiece.


MechanismGiven amount of energy is concentrated onto a very small point to cause the material removal.

Energy is in order of 1010 watt/mm2.

Ductile erosion due to shearing action.


Setup- Machine


1. PumpWater is pumped at sufficiently high pressure , 200-400 Mpa (2000-4000 bar) using a intensifier technology.Intensifier pressure amplification using hydraulic cylinders of different cross sections .

Water is issued through a suitable orifice (0.2 to 0.4 mm dia.), the P.E is converted into K.E. resulting in high velocity jet (1000 m/s).

Pure WJM commercial tap water is used.AWJM Abrasive particles are entrained in water (silicon oxide/glass beads etc.) 800 m/s can machine almost any material.2/12/2016Mohit Ostwal, Asst. Prof., JIET-coed, Jodhpur8

PwPwPh(ALarge)(A small)Working of intensifier.2/12/2016Mohit Ostwal, Asst. Prof., JIET-coed, Jodhpur9


NozzleAbrasive particles are gradually accelerated due to the transfer of momentum from the water phase to abrasive phase and when jet leaves the focusing tube , water and jet are assumed to be at same velocity.Focusing tube WC(Tungston carbide)Small diameter 0.8 to 1.6mmLength 50 to 80mm


The mixing chamber has a typical dimension of inner diameter 6 mm and a length of 10 mm. As the high velocity water is issued from the orifice into the mixing chamber, low pressure (vacuum) is created within the mixing chamber.


Nozzle


CatcherSuch high-energy abrasive water jet needs to be contained before they can damage any part of the machine or operators. Catcher is used to absorb the residual energy of the AWJ and dissipate the same. Fig. shows three different types of catcher water basin type, submerged steel balls and TiB2 plate type. 2/12/2016Mohit Ostwal, Asst. Prof., JIET-coed, Jodhpur14

Catcher

(c) catcher plates (TiB2) (b) steel/WC/ceramic balls(a) water basin2/12/2016Mohit Ostwal, Asst. Prof., JIET-coed, Jodhpur15

Mechanism of metal removal

Brittle materials crack initiation and propagation- brittle failure.

Ductile erosion due to shearing action.


Process parameters:

Orifice Sapphires 0.1 to 0.3 mm Focusing Tube WC 0.8 to 2.4 mm Pressure 1500 to 4000 bar Abrasive garnet and olivine - #125 to #60 Abrasive flow - 0.1 to 1.0 Kg/min Stand off distance 1 to 2 mm Machine Impact Angle 60o to 900 Traverse Speed 100 mm/min to 5 m/min Depth of Cut 1 mm to 250 mm


Part accuracyJet dragAs the abrasive moves through the material, the lower portion of the jet legs behind the upper section as shown in figure.It depends upon flow rate, thickness etc.

Jet kerfThickness of the cut made by the jet,This is negligible for harder and thinner material.


ApplicationsPaint removal Cutting soft materials Cutting frozen meat Textile, Leather industry Mass Immunization Surgery Peening Cutting Pocket Milling Drilling


AdvantagesCheaper than other processes. Cut virtually any material. (pre hardened steel, mild steel, copper, brass, aluminum; brittle materials like glass, ceramic, quartz, stone)Make all sorts of shapes with only one tool. No heat generated. Leaves a satin smooth finish, thus reducing secondary operations. Clean cutting process without gasses or oils.Are very safe. Machine stacks of thin parts all at once.


Advantages (contd.)Unlike machining or grinding, water jet cutting does not produce any dust or particles that are harmful if inhaled. The kerf width in water jet cutting is very small, and very little material is wasted.


Disadvantageswaterjet cutting can be very costly Another disadvantage is that very thick parts can not be cut with waterjet cutting and still hold dimensional accuracy. If the part is too thick, the jet may dissipate some, and cause it to cut on a diagonal, or to have a wider cut at the bottom of the part than the top. It can also cause a rough wave pattern on the cut surface.


AWJM


AWJM


The End


THANK YOU!2/12/2016Mohit Ostwal, Asst. Prof., JIET-coed, Jodhpur26