Principles of Abrasive Water Jet Machining

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 Generation and Acceleration.- 5.6.1 Properties of Generated Erosion Debris.- 5.6.1.1 Structure, Size and Shape of Erosion Debris.- 5.6.1.2 Contact-Number Estimation.- 5.6.1.3 Erosion-Debris Size Distribution Function.- 5.6.2 Efficiency of Erosion-Debris Generation.- 5.6.2.1 Surface-Based Efficiency Estimation-Model.- 5.6.2.2 Fracture-Based Efficiency Estimation-Model.- 5.6.2.3 Parameter Influence on the Efficiency.- 5.6.3 Erosion-Debris Acceleration.- 5.7 Damping Effects in Abrasive Water-Jet Material Removal.- 5.7.1 Damping During Single Particle-Impact.- 5.7.1.1 Observations in Solid-Particle Erosion.- 5.7.1.2 Damping of Free-Falling Objects.- 5.7.1.3 Critical Particle Velocities for Damping.- 5.7.2 Damping During Abrasive Water-J et Penetration.- 5.7.2.1 Concept of Force Measurements for Damping Estimation.- 5.7.2.2 Results of Force Measurements.- 5.7.2.3 Efficiency Losses due to Damping.- 5.8 Heat Generation During Abrasive Water-Jet Material Removal.- 5.8.1 Sources of Heat Generation.- 5.8.2 Results from Thermocouple Measurements.- 5.8.2.1 General Results.- 5.8.2.2 Process-Parameter Influence.- 5.8.2.3 Local Temperature Distribution.- 5.8.3 Results from Infrared-Thermography Measurements.- 5.8.3.1 General Remarks.- 5.8.3.2 Process-Parameter Influence on Linescans.- 5.8.3.3 Material Isotherms.- 5.8.4 Comparison Between Thermocouple and Infrared-Thermography.- 5.8.5 Modeling of the Heat-Generation Process.- 5.8.5.1 Basic Equations.- 5.8.5.2 Results of the Modeling.- 5.9 Target-Material Property Influence on Material Removal.- 5.9.1 Hardness and Modulus of Fracture.- 5.9.1.1 General Observations.- 5.9.1.2 ‘Two-Stage’ Resistance Approach.- 5.9.2 Concepts of Material Machinability.- 5.9.2.1 The ‘Machinability-Number’.- 5.9.2.2 Other Machinability Concepts.- 5.9.3 Properties of Pre-Cracked Materials.- 5.9.3.1 Stress-Strain Behavior.- 5.9.3.2 Relations to Conventional Testing Procedures.- 5.9.4 Other Material Properties.- 5.9.4.1 Material Porosity.- 5.9.4.2 Thermal-Shock Factor.- 6 Modeling of Abrasive Water Jet Cutting Processes.- 6.1 Introduction.- 6.2 Volume-Displacement Models.- 6.2.1 Volume-Displacement Model for Ductile Materials.- 6.2.3 Volume-Displacement Model for Brittle Materials.- 6.2.2 Generalized Volume-Displacement Model.- 6.3 Energy-Conservation Models.- 6.3.1 Two-Parameter Energy-Conservation Model.- 6.3.2 Regression Energy-Conservation Model.- 6.3.3 Semi-Empirical Energy-Conservation Model.- 6.3.4 Elasto-Plastic Energy-Conservation Model.- 6.3.5 Energy-Conservation Models for Pre-Cracked Materials.- 6.4 Regression Models.- 6.4.1 Multi-Factorial Regression Models.- 6.4.2 Further Regression Models.- 6.4.3 Regression Model for Cutting with Suspension-Abrasive Water Jets.- 6.5 Kinetic Model of the Abrasive Water-Jet Cutting Process.- 6.6 Fuzzy Rule-Based Model of the Abrasive Water-Jet Cutting Process.- 6.7 Numerical Models.- 6.7.1 Numerical Simulations.- 6.7.2 Numerical Process Model.- 7 Process Parameter Optimization.- 7.1 Definition of Process and Target Parameters.- 7.1.1 Process Parameters.- 7.1.2 Target Parameters.- 7.2 Influence of Hydraulic Process Parameters.- 7.2.1 Influence of Pump Pressure.- 7.2.1.1 General Trendss.- 7.2.1.2 Incubation Stage and Threshold Pressure.- 7.2.1.3 Linear Stage and Decreasing Stage.- 7.2.1.4 Optimization Aspects.- 7.2.2 Influence of Water-Orifice Diameter.- 7.2.2.1 General Trends.- 7.2.2.2 Threshold Orifice Diameter.- 7.2.2.3 Optimization Aspects.- 7.3 Influence of Cutting Parameters.- 7.3.1 Influence of Traverse Rate.- 7.3.1.1 General Trends.- 7.3.1.2 Threshold Traverse Rate.- 7.3.1.3 Exposure Time.- 7.3.1.4 Particle-Impact Frequency and Damping Effects.- 7.3.1.5 Influence on the Cutting Rate.- 7.3.2 Influence of Number of Passes.- 7.3.2.1 General Trends.- 7.3.2.2 Multipass Cutting.- 7.3.3 Influence of Standoff Distance.- 7.3.3.1 General Trends.- 7.3.3.2 Special Observations.- 7.3.4 Influence of Impact Angle.- 7.3.4.1 Influence on Ductile-Behaving Materials.- 7.3.4.2 Influence on Brittle-Behaving Materials.- 7.4 Influence of Mixing Parameters.- 7.4.1 Influence of Focus Diameter.- 7.4.1.1 General Trends.- 7.4.1.2 Optimum Focus Diameter.- 4.4.2 Influence of Focus Length.- 7.4.2.1 General Trend.- 7.4.2.2 Optimum Focus Length.- 7.5 Influence of Abrasive Parameters.- 7.5.1 Influence of Abrasive-Mass Flow Rate.- 7.5.1.1 General Trends.- 7.5.1.2 Optimization Aspects.- 7.5.1.3 Influence on Cutting Rate.- 7.5.2 Influence of Abrasive-Particle Diameter.- 7.5.2.1 General Trends.- 7.5.2.2 Optimization Aspects.- 7.5.3 Influence of Abrasive-Particle Size Distribution.- 7.5.4 Influence of Abrasive-Particle Shape.- 7.5.4.1 General Trends.- 7.5.4.2 Influence on Ductile-Behaving Materials.- 7.5.4.3 Influence on Brittle-Behaving Materials.- 7.5.5 Influence of Abrasive-Material Hardness.- 7.5.5.1 General Trends.- 7.5.5.2 Observations in Abrasive Water-Jet Cutting.- 7.5.6 Recycling Capacity of Abrasives.- 7.5.6.1 Early Observations.- 7.5.6.2 Parameter Influence on Disintegration.- 7.5.6.3 Particle-Shape Modification.- 7.5.6.4 Suspension Abrasive Water Jets.- 7.5.6.5 Modelling of Recycling Processes.- 8 Geometry, Topography and Integrity of Abrasive Water-Jet Machined Parts.- 8.1 Cut Geometry and Structure.- 8.1.1 Definition of Cut Geometry Parameters.- 8.1.2 Width on Top of the Cut.- 8.1.2.1 Ductile-Behaving Materials.- 8.1.2.2 Brittle-Behaving Composite Materials.- 8.1.2.3 Ceramics, Glass and Metal-Matrix Compounds.- 8.1.2.4 Models for Top-Width Estimation.- 8.1.3 Width on the Bottom of the Cut.- 8.1.3.1 Ductile-Behaving Materials.- 8.1.3.2 Brittle-Behaving Composite Materials.- 8.1.3.3 Ceramics and Glass.- 8.1.4 Taper of the Cut and Flank Angle.- 8.1.4.1 Ductile-Behaving Materials.- 8.1.4.2 Brittle-Behaving Composite Materials.- 8.1.4.3 Ceramics, Glass and Metal-Matrix Compounds.- 8.1.4.4 Models for Taper Estimation.- 8.1.5 General Cut Profile.- 8.1.5.1 Experimental Results.- 8.1.5.2 General Cut-Geometry Model.- 8.1.6 Initial-Damage Geometry.- 8.1.6.1 General Relations.- 8.1.6.2 Ductile-Behaving Materials.- 8.1.6.3 Brittle-Behaving Composite Materials.- 8.1.6.4 Model for Initial Damage Zone Geometry.- 8.2 Topography of Abrasive Water-Jet Generated Surfaces.- 8.2.1 General Characterzation.- 8.2.1.1 Introductional Aspects.- 8.2.1.2 Static Characterization.- 8.2.1.3 Dynamic Characterization.- 8.2.1.4 Wavelength Decomposition.- 8.2.2 Surface Roughness.- 8.2.2.1 General Relations.- 8.2.2.2 Influence of Hydraulic Parameters.- 8.2.2.3 Influence of Cutting Parameters.- 8.2.2.4 Influence of Mixing Parameters.- 8.2.2.5 Influence of Abrasive Parameters.- 8.2.2.6 Influence of Target-Material Structure.- 8.2.2.7 Models for Roughness Estimation.- 8.2.3 Surface Waviness.- 8.2.3.1 General Relations.- 8.2.3.2 Influence of Process Parameters.- 8.2.3.3 Models for Waviness Estimation.- 8.3 Integrity of Abrasive Water-Jet Generated Surfaces.- 8.3.1 Fatigue Life.- 8.3.2 Surface Hardening.- 8.3.2.1 Hardness Measurements.- 8.3.2.2 Stress Measurements.- 8.3.3 Micro-Structural Aspects.- 8.3.3.1 General Aspects of Alteration.- 8.3.3.2 Surface Cracking in Brittle-Behaving Materials.- 8.3.3.3 Phase Modifications in Ceramics.- 8.3.4 Abrasive-Particle Fragment Embedding.- 8.3.5 Delamination in Composite Materials.- 8.3.6 Burr Formation.- 9 Alternative Machining Operations with Abrasive Water Jet.- 9.1 Capability of Abrasive Water Jets for Alternative Machining.- 9.2 Milling with Abrasive Water Jets.- 9.2.1 Concepts of Abrasive Water-Jet Milling.- 9.2.2 Parameter Optimization in Abrasive Water-Jet Milling.- 9.2.3 Quality of Abrasive Water-Jet Milling.- 9.2.4 Modeling of Abrasive Water-Jet Milling.- 9.2.4.1 General Milling Model.- 9.2.4.2 Milling Model for Fiber-Reinforced Plastics.- 9.2.4.3 Model for Discrete Milling.- 9.2.4.4 Numerical Milling Model.- 9.3 Turning with Abrasive Water Jets.- 9.3.1 Macromechanism of Abrasive Water-Jet Turning.- 9.3.2 Parameter Optimization in Abrasive Water-J et Turning.- 9.3.3 Quality of Abrasive Water-Jet Turning.- 9.3.4 Modeling of Abrasive Water-Jet Turning.- 9.3.4.1 Analytical Turning Model.- 9.3.4.2 Regression Turning Model.- 9.4 Piercing with Abrasive Water Jets.- 9.4.1 Macromechanism of Abrasive Water-Jet Piercing.- 9.4.2 Parameter Optimization in Abrasive Water-J et Piercing.- 9.4.3 Geometry and Quality of Abrasive Water-Jet Pierced Holes.- 9.4.3.1 Hole Geometry.- 9.4.3.2 Hole Quality.- 9.4.4 Modeling of Abrasive Water-Jet Piercing.- 9.4.4.1 Phenomenological Piercing Model.- 9.4.4.2 Analytical Piercing Model.- 9.4.4.3 Regression Piercing Model.- 9.4.4.4 Simulation Model for Piercing.- 9.5 Hole Trepanning and Deep-Hole Drilling with Abrasive Water Jets.- 9.5.1 Hole Trepanning with Abrasive Water Jets.- 9.5.2 Deep-Hole Drilling with Abrasive Water Jets.- 9.6 Polishing with Abrasive Water Jet.- 9.6.1 Abrasive Water-Jet Polishing Concepts.- 9.6.2 Quality Aspects of Abrasive Water-Jet Polishing.- 9.7 Screw-Thread Machining with Abrasive Water Jets.- 10 Control and Supervision of Abrasive Water-Jet Machining Processes.- 10.1 General Aspects of Process Control.- 10.2 Control of the Abrasive-Particle Suction Process.- 10.2.1 General Demands.- 10.2.2 Acoustic Sensing.- 10.2.3 Workpiece Reaction-Force Measurement.- 10.2.4 Vacuum Sensor.- 10.2.5 Actual Abrasive-Mass Flow Rate.- 10.3 Control of Water-Orifice Condition and Wear.- 10.3.1 Optical Jet Inspection.- 10.3.2 Vacuum-Pressure Measurement.- 10.4 Control of Focus Condition and Wear.- 10.4.1 General Comments.- 10.4.2 Direct Tracking.- 10.4.3 Jet-Structure Monitoring.- 10.4.4 Air-Flow Measurements.- 10.4.5 Infrared Thermography.- 10.4.6 Acoustic Sensing.- 10.4.7 Workpiece Reaction-Force Measurement.- 10.4.8 Off-Line Focus-Diameter Measurement.- 10.5 Measurement and Control of Abrasive Water-Jet Velocity.- 10.5.1 Inductive Methods.- 10.5.2 Measurement by Impact Crater Counting.- 10.5.3 Laser-Based Methods.- 10.5.3.1 Laser-2-Focus-Velocimeter.- 10.5.3.2 Laser-Transit-Velocimeter.- 10.5.3.3 Laser-Doppler-Velocimeter.- 10.5.3.4 Laser-Light-Section Procedure Technique.- 10.5.4 Other Optical Methods.- 10.5.4.1 Schlieren-Photography.- 10.5.4.2 High-Speed-Photography.- 10.5.5 Jet Impact-Force Measurements.- 10.6 Measurement and Control of Abrasive Water-Jet Structure.- 10.6.1 Scanning-X-Ray Densitometry.- 10.6.2 Flow-Separation Technique.- 10.7 Control of Material-Removal Processes.- 10.7.1 Acoustic-Emission Technique.- 10.7.1.1 Material-Removal Visualization.- 10.7.1.2 Cutting-Process Visualization and Cutting-Through Control.- 10.7.1.3 Cutting-Efficiency Control.- 10.7.2 Control by Infrared Thermography.- 10.8 Control of Depth of Penetration.- 10.8.1 Acoustic Sensing.- 10.8.2 Acoustic-Emission Technique.- 10.8.3 Workpiece Reaction-Force.- 10.8.4 Supervision and Copntrol of Piercing Processes.- 10.8.4.1 Monitoring by Pressure Sensors.- 10.8.4.2 Monitoring by Acoustic-Emission Technique.- 10.9 Control of the Generated Surface Topography.- 10.9.1 Roughness Control by Static Workpiece Reaction-Force.- 10.9.2 Roughness Control by Dynamic Workpiece Reaction-Force.- 10.9.3 Surface Quality Monitoring by Acoustic-Emission Technique.- 10.10 Expert Systems for Abrasive Water-Jet Machining.- References.