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					        ABRASIVE JET ANALYSIS
                   PROJECT REVIEW




Guide                         Presented By
B.Ch Nookaraju                M.N.V.Anil
Associate professor           S.SambhuPrakash
Mechanical department         K.Abhishek
                   CONTENTS
•   Introduction
•   Literature Review
•   Applications
•   Problem Definition
•   Navier Stoke Equations
•   CFD
•   Results
•   Conclusions
•   References
                        INTRODUCTION
•   Abrasive Jet Machining (AJM) is the process of material removal from a work piece
    by the application of a high speed stream of abrasive particles carried in a gas
    medium from a nozzle. The material removal process is mainly by erosion. The
    AJM will chiefly be used to cut shapes in hard and brittle materials like glass,
    ceramics etc .

•   In this project, a model of the work piece is analyzed using Computational fluid
    dynamics (CFD) or Finite Element Analysis (FEM). Numerical simulations have been
    conducted using the commercial code Fluent 6.3 by Ansys. Dynamic characteristics
    of the flow inside the AWJ head and downstream from the nozzle has been
    simulated under steady state, turbulent, two‐phase flow conditions.

•   Variables such as pump pressure, traverse rate, abrasive mass flow rate and others
    are analyzed and these are compared with standard experimental values for
    different materials.
                    LITERATURE REVIEW
•   Ref‐1 Computational fluid dynamics (CFD) simulation of the formation and discharge process
    of an air‐water flow in an abrasive water jet (AWJ) head is presented by Umberto Prisco &
    Maria Carmina D'Onofrio. Numerical simulations have been conducted using the commercial
    code Fluent® 6.3 by Ansys. Dynamic characteristics of the flow inside the AWJ head and
    downstream from the nozzle has been simulated under steady state, turbulent, two‐phase
    flow conditions. The final aim is to gain fundamental knowledge of the ultrahigh velocity flow
    dynamic features that could affect the quality of the jet, such as the velocity and pressure
    distributions in different parts of the AWJ head and at the outlet.

•   In recent years abrasive jet machining has been gaining increasing acceptability for deburring
    applications. The influence of abrasive jet deburring process parameters is not known clearly.
    AJM deburring has the advantage over manual deburring method that generates edge radius
    automatically. This increases the quality of the deburred components. The process of
    removal of burr and the generation of a convex edge were found to vary as a function of the
    parameters jet height and impingement angle, with a fixed SOD. The influence of other
    parameters, viz. nozzle pressure, mixing ratio and abrasive size are insignificant. The SOD was
    found to be the most influential factor on the size of the radius generated at the edges. The
    size of the edge radius generated was found to be limited to the burr root thickness.
•   (Ref‐2) Experiments have been performed on effect of jet pressure, abrasive flow rate and
    work feed rate on smoothness of the surface produced by abrasive water jet machining of
    carbide of grade P25. Carbide of grade P25 is very hard and cannot be machined by
    conventional techniques. The abrasive used in investigations was garnet of mesh size 80. It
    was tried to cut carbide with low and medium level of abrasive flow rate, but the jet failed to
    cut carbide since it is too hard and very high level of energy is required. Minimum rate of
    abrasive flow that made it possible to cut carbide efficiently was 135 g min‐1.



•    With increase in jet pressure the surface becomes smoother due to higher kinetic energy of
    the abrasives. But the surface near the jet entrance is smoother and the surface gradually
    becomes rougher downwards and is the roughest near the jet exit. Increase in abrasive flow
    rate also makes the surface smoother which is due to the availability of higher number of
    cutting edges per unit area per unit time. Feed rate didn’t show significant influence on the
    machined surface, but it was found that the surface roughness increases drastically near the
    jet entrance.
                              APPLICATION
•   The major field of application of AJM process is in the machining of essentially
    brittle materials and heat sensitive materials like glass, quartz, sapphire,
    semiconductor materials, mica and ceramics. It is also used in cutting slot, thin
    sections, countering, drilling, deburring, for producing integrate shapes in hard
    and brittle materials. It is often used for cleaning and polishing of plastics nylon
    and Teflon components. Delicate cleaning, such as removal of smudges from
    antique documents, is also possible with AJM.

     The study of the results of machining under various conditions approves that a
    commercial AJM machine was used, with nozzles of diameter ranging from 0.45 to
    0.65 mm, the nozzle materials being either tungsten carbide or sapphire, both of
    which have high tool lives.

•   Abrasive waterjet machines are becoming more widely used in mechanical
    machining. These machines offer great advantages in machining complex
    geometrical parts in almost any material. This ability to machine hard‐to‐machine
    materials, combined with advancements in both the hardware and software used
    in waterjet machining, has caused the technology to spread and become more
    widely used in industry.
              PROBLEM DEFINITION
• Here we are looking for the hydrodynamic characteristics of abrasive jets,
  hence ascertaining the influence of all operational variables on the
  process effectiveness including abrasive type, size and concentration,
  impact speed and angle of impingement.

• Physical model of nozzle is simulated using Catia and imported into
  Gambit.

• Dynamic characteristics of the flow inside the AWJ head and downstream
  from the nozzle has been simulated under steady state, turbulent,
  two‐phase flow conditions
Characteristics of different Variables:
•   Medium                          Air , CO2 ,N2

•   Abrasive                        SiC, Al2O3 (of size 20μ to 50μ )

•   Flow rate of abrasive           3 to 20 gram/min

•   Velocity                        150 to 300 m/min

•   Pressure                        2 to 8 kg/cm2

•   Nozzle size                     0.07 to 0.40 mm

•   Material of nozzle              WC, Sapphire

•   Nozzle life                     12 to 300 hr

•   Stand off distance              0.25 to 15 mm (8mm generally)

•   Work material                  Glass, ceramics, granites, germanium

•   part application               Drilling, cutting, deburring, cleaning
           NAVIER STOKE EQUATIONS
•   In physics the Navier–Stokes equations, named after Claude-Louis Navier and
    George Gabriel Stokes, describe the motion of fluid substances. These equations
    arise from applying Newton's second law to fluid motion, together with the
    assumption that the fluid stress is the sum of a diffusing viscous term
    (proportional to the gradient of velocity), plus a pressure term.

•   The equations are useful because they describe the physics of many things of
    academic and economic interest. They may be used to model the weather, ocean
    currents, water flow in a pipe and air flow around a wing. The Navier –Stokes
    equations in their full and simplified forms help with the design of aircraft and
    cars, the study of blood flow, the design of power stations, the analysis of
    pollution, and many other things. Coupled with Maxwell's equations they can be
    used to model and study magneto hydrodynamics.


•   The Navier –Stokes equations are also of great interest in a purely mathematical
    sense. Somewhat surprisingly, given their wide range of practical uses,
    mathematicians have not yet proven that in three dimensions solutions always
    exist (existence), or that if they do exist, then they do not contain any singularity
    (smoothness). These are called the Navier–Stokes existence and smoothness
    problems
                            What is CFD

• CFD is the science of predicting fluid flow, heat and mass transfer,
  chemical reactions and related phenomenon by solving numerically
  the set of governing mathematical equations
        • Conservation of mass, momentum, energy, species….
• The results of CFD analysis are relevant in:
        • conceptual studies of new designs
        • detailed product development
        • troubleshooting
        • redesign
• CFD analysis complements testing and experimentation
        • Reduces the total effort required in the experiment design and data
          acquisition
                Pre-processor: GAMBIT
•   A single integrated pre-processor for CFD analysis
•   Geometry creation
•   Mesh generation
•   Mesh quality examination
•   Boundary zone assignment
•
                 How Does CFD work ?
•   FLUENT solvers are based on the finite volume method
         • Domain is discretized into a finite set of controls
           volumes
         • General conservation (transport) equation for mass,
           momentum, energy, etc: Partial differential equations
           are discretized into a system of algebraic equations.
         • All algebraic equations are then solved numerically to
           render the solution field.




•    Equation               Ф
•   Continuity              1
•   x-mom.                  u
•   y-mom.                  v
•   Energy                  h
                        CFD Modeling Overview

                              Equations solved on mesh

                             • Transport Equations                • Physical Models
                             • mass                                     • Turbulence
  Pre-Processing
                                        • species mass fraction         • Combustion
• Solid        • Mesh                   • phase volume fraction         • Radiation
Modeler        Generator     • momentum
                                                                        • Multiphase
                             • energy
                                                                        • Phase Change
                             • Equation of State
                                                                        • Moving Zones
    • Solver                 • Supporting Physical Models               • Moving Mesh
    Settings




                                   • Material Properties
                                   • Boundary Conditions
  • Post- Processing
                                   • Initial Conditions
• Meshed diagram
 Set Up the Numerical Model
• Selected physical model:
    • Turbulence
• Material properties :
    • Mixture
    • Air abrasive
• Prescribed operating conditions gauge pressure = 0
• Prescribed boundary conditions :
                              Inlet velocity 20m-s
                              Outlet pressure 1atm
                              Adiabatic walls
                   Compute the Solution

•   The discretized conservation equations are solved iteratively :

         • A number of iterations are usually required to reach a converged solution
•   Convergence is reached when:
         • Changes in solution variables from one iteration to the next is negligible.
              • Residuals provide a mechanism to help monitor this trend.
         • Overall Property conservation is achieved.
•   The accuracy of a converged solution is dependent upon:
         • Appropriateness and accuracy of physical models.
         • Grid resolution and independence.
         • Problem setup.
                                   Results

•   We need to examine the results to review solution and extract useful data.
         • Visualization Tools can be used to answer such questions as:
              • What is the overall flow pattern?
              • Is there separation?
              • Where do shocks, shear layers, etc. form?
              • Are key flow features being resolved?
•   Numerically Reporting Tools can be used to calculate quantitative results:
         • Forces and Momentums
         • Average heat transfer coefficients
         • Surface and Volume integrated quantities
         • Flux Balances.
             Revisions to the Model
•   Are physical models appropriate?
         • Is flow turbulent?
         • Is flow unsteady?
         • Are there compressibility effects?
         • Are there 3D effects?
•   Are boundary conditions correct?
         • Is the computational domain large enough?
         • Are boundary conditions appropriate?
         • Are boundary values reasonable?
                             CONCLUSIONS
•   Hydrodynamic analysis of abrasive jet is done using CFD software
    package.Preprocessor,Numeric model have been set up, solving of problem is yet to be
    performed. By using these appropriate results are obtained and abrasive jet flow is analyzed
    in the nozzle. The variables that influence the rate of metal removal and accuracy of
    machining in this process viz

•   Carrier gas
•   Types of abrasive
•   Size of abrasive grain
•   Velocity of abrasive jet
•   Flow rate of abrasive
•   Work material
•   Geometry, composition and material of nozzle
•   Nozzle work distance (stand off distance)   are analyzed.
                                 REFERENCES
1. Three‐Dimensional CFD Simulation of Two‐Phase Flow Inside the Abrasive Water Jet Cutting
    Head
• Authors: Umberto Prisco; Maria Carmina D'Onofrio.
• Publication: International Journal of Computational Methods in Engineering Science and
    Mechanics 9 (5), pp. 300‐319 Publication Date: 01 September 2008
2.
• Modeling and simulation for material removal in abrasive jet precision finishing with wheel as
    restraint.
• Authors: Li, C.H., Ding, Y.C., Lu, B.H.
• Publication: Proceedings of the IEEE International Conference on Automation and Logistics,
    ICAL 2008, Article number 4636666, Pages 2869‐2873, 2008
BOOKS
• “Production technology”, HMT publication.
• “Modern machining process”, S Pandey and H N Shah, S.Chand and co.
WEBSITES
• www.scopus.com
• www.science direct .com