Principles of Abrasive Water Jet Machining

Abrasive water jet machining was introduced to manufacturing ten years ago and has been increasingly used for treating hard-to-machine and multi-layered materials and as an alternative tool for milling, turning, drilling and polishing. This is the first comprehensive review of the technique, dealing with a broad range of issues including mixing and acceleration processes, material removal mechanisms, process optimization and fluid mechanics. Explanations are given as the book follows the development of an abrasive water jet machining process, from tool generation through to machining results, supervision and control. This methodical journey through the field is marked by drawings, graphs and tables, many of which are being published here for the first time. Though the book is written at an academic level, it focuses very much on practical applications, which reflects the authors' extensive involvement with both laboratory research and industrial practices.

1 Introduction.- 1.2 Classification of High-Speed Fluid Jets.- 1.3 State-of-the-Art Application of the Water-Jet Technique.- 2 Classification and Characterization of Abrasive Materials.- 2.1 Classification and Properties of Abrasive Materials.- 2.1.1 General Classification of Abrasive Materials.- 2.1.2 Global Abrasive-Evaluation Parameter.- 2.2 Abrasive-Material Structure and Hardness.- 2.2.1 Structural Aspects of Abrasive Materials.- 2.2.2 Hardness of Abrasive Materials.- 2.3 Abrasive-Particle Shape Parameters.- 2.3.1 Relative Proportions of Abrasive Particles.- 2.3.2 Geometrical Form of Particles.- 2.4 Abrasive-Particle Size Distribution and Abrasive-Particle Diameter.- 2.4.1 Particle-Size Distribution.- 2.4.1.1 General Definitions.- 2.4.1.2 Sieve Analysis.- 2.4.1.3 Particle-Size Distribution Models.- 2.4.2 ‘Average’ Particle Diameter.- 2.5 Number and Kinetic Energy of Abrasive Particles.- 2.5.1 Abrasive-Particle Number and Frequency.- 2.5.2 Kinetic Energy of Abrasive Particles.- 3 Generation of Abrasive Water Jets.- 3.1 Properties and Structure of High-Speed Water Jets.- 3.1.1 Velocity of High-Speed Water Jets.- 3.1.1.1 Integral Pressure Balance.- 3.1.1.2 Momentum-Transfer Efficiency.- 3.1.2 Kinetic Energy of High-Speed Water Jets.- 3.1.3 Structure and Properties of High-Speed Water Jets.- 3.1.3.1 Structure in Axial Direction.- 3.1.3.2 Structure in Radial Direction.- 3.2 Abrasive Particle — Water Jet Mixing Principles in Injection Systems.- 3.2.1 General Design Principles.- 3.2.2 Internal Design Parameters.- 3.2.2.1 Distance Between Orifice Exit and Focus Entrance.- 3.2.2.2 Distance Between Abrasive Inlet and Focus Entrance.- 3.2.2.3 Alignment Between Orifice and Focus.- 3.2.2.4 Mixing-Chamber Length.- 3.2.3 Alternative Injection-System Designs.- 3.2.3.1 Annular Jet Systems.- 3.2.3.2 Vortex-Flow System.- 3.2.3.3 Multiple Water-Jet System.- 3.3 Abrasive Suction in Injection Systems.- 3.3.1 Pressure Difference for Pneumatic Transport.- 3.3.2 Air-Flow Rate.- 3.3.3 Abrasive-Particle Entry Velocity.- 3.3.4 Internal Focus Pressure-Profile.- 3.4 Abrasive-Particle Acceleration in Injection Systems.- 3.4.1 Simplified Momentum-Transfer Model.- 3.4.1.1 Integral Impulse Balance.- 3.4.1.2 Momentum-Transfer Efficiency.- 3.4.2 Improved Acceleration Model.- 3.4.2.1 Velocity Components.- 3.4.2.2 Force Balance in Axial Direction.- 3.4.2.3 Friction Coefficient and Reynolds-Number.- 3.4.2.4 Force Balance in Radial Direction.- 3.4.2.5 Approximate Solution.- 3.4.2.6 Rigorous Solution.- 3.4.2.7 Numerical Solutions in Axial Direction.- 3.4.2.8 Numerical Solutions in Radial Solution.- 3.4.2.9 Results of Steel-Ball Projection Experiments.- 3.4.3 Regression Model.- 3.5 Abrasive-Particle Fragmentation in Injection Systems.- 3.5.1 Solid-Particle Impact Comminution.- 3.5.1.1 Impact Velocity and Impact Angle.- 3.5.1.2 Fracture Zones During Impact.- 3.5.1.3 Size Effects.- 3.5.1.4 Other Material Properties.- 3.5.2 Abrasive-Particle Size Reduction During Mixing and Acceleration.- 3.5.2.1 General Observations.- 3.5.2.2 The ‘Disintegration-Number’.- 3.5.2.3 Influence of Abrasive-Particle Structure and Properties.- 3.5.2.4 Energy Absorption During Abrasive-Particle Fragmentation.- 3.5.3 Abrasive-Particle Shape Modification During Mixing and Acceleration.- 3.6 Focus Wear in Injection Systems.- 3.6.1 General Features of Focus Wear.- 3.6.2 Focus-Exit Diameter.- 3.6.2.1 Early Observations.- 3.6.2.2 Focus-Wear Rate.- 3.6.2.3 Process-Parameter Influence.- 3.6.2.4 Hardness Influence.- 3.6.3 Other Focus-Wear Features.- 3.6.3.1 General Aspects.- 3.6.3.2 Focus-Mass Loss and Focus-Wear Pattern.- 3.6.3.3 ‘Selective’ Focus Wear.- 3.6.3.4 Eccentricity of Focus-Exit Wear.- 3.6.4 Modeling the Focus-Wear Process.- 3.6.4.1 Phenomenological Focus-Wear Model.- 3.6.4.2 ‘Two-Material’ Focus Concept.- 3.6.4.3 Lifetime-Estimation Model.- 3.7 Generation of Suspension-Abrasive Water Jets.- 3.7.1 General System Features.- 3.7.1.1 System Components.- 3.7.1.2 Bypass-Systems.- 3.7.1.3 Direct-Pumping Systems.- 3.7.2 Abrasive-Particle Acceleration.- 3.7.2.1 Acceleration-Nozzle Design.- 3.7.2.2 Simple Momentum-Transfer Model.- 3.7.2.3 Numerical Simulations.- 3.7.2.4 Finite-Element Modeling.- 3.7.2.5 Acceleration-Nozzle Wear.- 4 Structure and Hydrodynamics of Abrasive Water Jets.- 4.1 General Structure of Injection-Abrasive Water Jets.- 4.1.1 General Structural Features.- 4.1.2 Optical Examinations.- 4.2 Phase Distributions in Injection-Abrasive Water Jets.- 4.2.1 Average Abrasive-Density Distribution.- 4.2.2 Radial-Zone Model.- 4.2.3 Phase Estimation by X-Ray Densitometer.- 4.2.3.1 Water-Phase Distribution.- 4.2.3.2 Abrasive-Phase Distribution.- 4.2.3.3 Air Content.- 4.3 Abrasive-Particle Velocity Distribution in Injection-Abrasive Water Jets.- 4.3.1 Radial Velocity-Profile.- 4.3.2 Turbulence Profile.- 4.3.3 Statistical Abrasive-Particle Velocity Distribution.- 4.4 Structure of Suspension-Abrasive Water Jets.- 5 Material-Removal Mechanisms in Abrasive Water-Jet Machining.- 5.1 Erosion by Single Solid-Particle Impact.- 5.1.1 General Aspects of Solid-Particle Impact.- 5.1.2 Erosion of Ductile-Behaving Materials.- 5.1.2.1 Generalized Erosion Equation.- 5.1.2.2 ‘Micro-Cutting’ Model.- 5.1.2.3 ‘Extended ‘Cutting-Deformation’ Model.- 5.1.2.4 ‘Ploughing-Deformation’ Model.- 5.1.2.5 Low-Cycle Fatigue and Thermal Effects.- 5.1.2.6 Comparison of Models for Ductile-Behaving Materials.- 5.7.5 Erosion of Brittle-Behaving Materials.- 5.1.3.1 Generalized Erosion Equation.- 5.1.3.2 Elastic Model.- 5.1.3.3 Elastic-Plastic Model.- 5.1.3.4 Grain-Ejection Model.- 5.1.3.5 Comparison of Models for Brittle-Behaving Materials.- 5.2 Micro-Mechanisms of Abrasive-Particle Material-Removal in Abrasive Water-Jet Machining.- 5.2.1 Observations on Ductile-Behaving Materials.- 5.2.1.1 SEM-Observations.- 5.2.1.2 Stress Measurements.- 5.2.2 Observations on Composite Materials.- 5.2.2.1 SEM-Observations on Metal-Matrix Composites.- 5.2.2.2 SEM-Observations on Fiber Reinforced Composites.- 5.2.3 Observations on Brittle-Behaving Materials.- 5.2.3.1 SEM-Observations on Polycrystalline Ceramics.- 5.2.3.2 SEM-Observations on Refractory Ceramics.- 5.2.3.3 Acoustic-Emission Measurements on Brittle-Behaving Materials.- 5.2.3.4 Photoelasticity Investigations on Brittle-Behaving Materials.- 5.2.3.5 Microboiling in Ceramics and Metal-Matrix Composites.- 5.2.3.6 Observations on Glass.- 5.3 Material Removal by the High-Speed Water Flow.- 5.3.1 General Observations.- 5.3.2 Observations in Pre-Cracked Materials.- 5.3.2.1 Effect of ‘Water Wedging’.- 5.3.2.2 ‘Transition-Velocity’ Concept.- 5.3.2.3 Pocket Formation in Soft Materials.- 5.4 Macro-Mechanisms of Abrasive Water-Jet Material Removal.- 5.4.1 Some Observations of the Surface Topography.- 5.4.1.1 General Statement.- 5.4.1.2 Surface-Profile Inspections.- 5.4.1.3 Wavelength Decomposition.- 5.4.2 Two-Dimensional Model of the Integral Material Removal.- 5.4.2.1 Traverse-Direction Stages.- 5.4.2.2 Penetration-Direction Stages.- 5.4.2.3 Further Development of the Model.- 5.4.2.4 Step Formation on the Cutting Front.- 5.4.3 Three-Dimensional Model of the Integral Material Removal.- 5.4.3.1 Three-Dimensional Step Formation.- 5.4.3.2 Influence of Machine Vibrations.- 5.4.4 Alternative Models of the Integral Material Removal.- 5.4.1.1 General Comments.- 5.4.1.2 Two-Stage Impact Zone Model.- 5.4.1.3 ‘Three-Zone’ Cutting Front Model.- 5.4.1.4 Energetic Cutting Model.- 5.4.1.5 Numerical Simulation of the Cutting Front.- 5.5 Energy Balance of Abrasive Water-Jet Material Removal.- 5.5.1 General Energy Situation.- 5.5.1.1 Dissipated Energy.- 5.5.1.2 Energy-Dissipation Function.- 5.5.2 Geometrical Energy-Dissipation Model.- 5.5.2.1 Special Solutions of the Energy-Dissipation Function.- 5.5.2.2 Basics for a General Solution.- 5.5.2.3 Striation Geometry.- 5.5.2.4 General Solution of the Energy-Dissipation Function.- 5.5.2.5 Solution for the Relative Depth of Cut.- 5.5.2.6 Local Energy-Dissipation Intensity.- 5.6 Erosion-Debris