CO2 Laser Cutting

Inhaltsverzeichnis

1. The Basic Principles.- 1.1 The Cutting Process.- 1.1.1 Cutting Parameters.- 1.2 How Materials Respond to Laser Light.- 1.3 How CO2 Lasers Work.- 1.3.1 The Storage and Release of Energy from a CO2 Molecule.- 1.3.2 Lasing.- 1.3.3 The Role of Nitrogen.- 1.3.4 The Role of Helium.- 1.3.5 Gas Mixture Cooling.- 1.3.6 Gas Recirculation.- 1.3.7 A Summary of the Basic Energy Exchanges in a CO2 Laser.- 1.4 Laser Modes.- 1.4.1 Mode Types.- 1.4.2 A Quick Guide to TEM Nomenclature.- 1.4.3 The Effect of Laser Design on Mode and the Implications for Materials Processing.- 2. Laser Cutting Steels.- 2.1 Mild steels.- 2.1.1 Introduction.- 2.1.2 The Cutting Mechanism for Mild Steels.- 2.1.3 Cutting Speeds and Cut Quality.- 2.1.4 Cut Initiation and Termination.- 2.1.5 Techniques to Avoid Unwanted Material Burning.- 2.1.6 The Effect of Sheet Surface Finish on the Cutting Process.- 2.1.7 The Importance of Axial Symmetry of the Energy Input to the Cutting Zone.- 2.1.8 Pulsed Laser Cutting of Mild Steels.- 2.2 Alloy Steels.- 2.2.1 Introduction.- 2.2.2 Stainless Steels.- 2.2.3 Low Alloy Steels.- 2.2.4 Silicon Iron.- 2.2.5 Free Cutting Steels.- 2.2.6 Carbon Steels.- 3. Cutting Non-ferrous Metals.- 3.1 Introduction.- 3.2 Titanium Alloys.- 3.2.1 Laser-Oxidation Cutting.- 3.2.2 Laser-Inert Gas Cutting.- 3.3 Aluminium Alloys.- 3.3.1 Introduction.- 3.3.2 The Effect of Surface Condition on Cutting (Anodising etc.).- 3.3.3 Pulsed Laser Cutting.- 3.3.4 Piercing a High Reflectivity Metal.- 3.4 Nickel Alloys.- 3.5 Copper Alloys.- 3.6 General Comments.- 4. Cutting Non-metals.- 4.1 Introduction.- 4.1.1 Melt Shearing.- 4.1.2 Vaporisation.- 4.1.3 Chemical Degradation.- 4.2 Polymers.- 4.2.1 Cutting by Melt Shearing.- 4.2.2 Cutting by Vaporisation.- 4.2.3 Cutting by Chemical Degradation.- 4.2.4 Cutting Speeds for Polymers.- 4.2.5 Cut Speed Forecasting for Polymers Using a Standard Processing Curve.- 4.3 Wood Based Products.- 4.4 Ceramics and Glasses.- 4.4.1 Ceramics.- 4.4.2 Glasses.- 4.5 Composites and Miscellaneous Materials.- 4.5.1 Composite Materials.- 4.5.2 Miscellaneous Materials.- 5. Setting Up for Cutting.- 5.1 Introduction.- 5.2 Beam Alignment.- 5.2.1 Introduction.- 5.2.2 Taking a Beam Print.- 5.2.3 Alignment by the Beam Print Method.- 5.2.4 Alignment by use of a HeNe Laser.- 5.3 Finding the Focus Position.- 5.3.1 Introduction.- 5.3.2 The Blue Flash Test.- 5.3.3 The Drilling Test.- 5.4 Nozzles and Nozzle Alignment.- 5.4.1 General Comments.- 5.4.2 Practical Considerations.- 5.4.3 Nozzle Alignment.- 5.4.4 The Gas Dynamics of Nozzles.- 5.5 Jigging.- 5.5.1 Methods of Supporting the Workpiece.- 5.5.2 Laser Cut Supports.- 5.5.3 Chutes.- 5.5.4 Overlay Jigging for Flimsy Materials.- 5.5.5 Clamps and Vices.- 5.6 Tuning the Laser.- 5.6.1 Fine Tuning.- 5.6.2 Mode Prints.- 5.6.3 Use of a Laser Beam Analyser.- 5.6.4 Laser Alignment.- 6. Troubleshooting.- 6.1 Introduction and Checklist.- 6.2 Notes on Checklist.- 6.2.1 Nozzle Contamination.- 6.2.2 Laser Power Level and Type.- 6.2.3 Cutting Speed.- 6.2.4 Cutting Gas Type, Pressure and/or Flow Rate.- 6.2.5 Nozzle-Material Standoff.- 6.2.6 Nozzle Type, Condition and Alignment.- 6.2.7 Material Specification.- 6.2.8 Lens Type, Condition and Alignment.- 6.2.9 Laser Mode Quality.- 6.2.10 External Mirror Condition and Alignment.- 7. Safety Guidelines.- 7.1 Introduction.- 7.2 Beam Exposure.- 7.2.1 Skin Damage.- 7.2.2 Eye Safety.- 7.3 Fumes.- 7.3.1 Metals.- 7.3.2 Non-metals.- 7.4 Electrocution.- 7.5 Fires.- 8. Alternative Cutting Methods.- 8.1 Nd:YAG Laser Cutting.- 8.1.1 The Principle of Operation of Nd:YAG Lasers.- 8.2 Plasma Arc Cutting.- 8.3 Abrasive Water Jet Cutting.- 8.3.1 Abrasive-Free Fluid Jets.- 8.4 Oxygen-Flame Cutting.- 8.5 A Summary of the Strengths and Weaknesses of Each Process Compared with CO2 Laser Cutting.- 9. The Physics and Design of CO2 Lasers.- 9.1 Introduction.- 9.2 The Physics of CO2 Lasers.- 9.2.1 The CO2 Energy Spectrum.- 9.2.2 Interactions in a Pure CO2 Laser.- 9.2.3 The Role of Nitrogen.- 9.2.4 The Role of Helium.- 9.2.5 The Energy Cycle of Mixed Gas CO2 Lasers.- 9.2.6 Population Inversion.- 9.2.7 Laser Modes and TEM Nomenclature.- 9.3 Aspects of the Design of CO2 Lasers.- 9.3.1 Introduction.- 9.3.2 Methods of Exciting the Lasing Gas Mixture.- 9.3.3 Methods of Cooling the Lasing Gas Mixture.- 9.3.4 Designs of Optical Cavity.- 10. Some Aspects of the Physics and Chemistry of Laser Cutting.- 10.1 Introduction.- 10.2 The Energy Balance in the Cut Zone and Its Relationship to the Efficiency of the Process.- 10.2.1 The Effect of Decreasing the Material Thickness on Cutting Speeds.- 10.2.2 The Limits on Material Thickness.- 10.2.3 The Implications of the Energy Balance Argument to Changes in Laser Power.- 10.3 The Role of Oxidation when Cutting Steels.- 10.3.1 Mild Steel.- 10.3.2 Stainless Steel.- 10.4 Conductive Losses Experienced when Cutting Steels.- 10.5 Notes on Reflected, Transmitted, Radiated and Convective Losses from the Cut Zone.- 10.5.1 Reflected and Transmitted Losses.- 10.5.2 Radiation and Convective Losses.- 10.6 Notes on the Focusing Characteristics of CO2 Lasers.- 10.6.1 Theoretical Focused Spot Size and Depth of Focus.- 10.6.2 The Discrepancy Between Theory and Practice.- 10.6.3 Concluding Comments.- 11. Bibliography and Further Reading.- 11.1 Conference Proceedings and Journals.- 11.1.1 Conference Proceedings.- 11.1.2 Journals.- 11.2 Books.- 11.3 Specific Papers.- 11.3.1 General Reviews of Laser Processing and Cutting.- 11.3.2 Cutting Metals.- 11.3.3 Cutting Non-metals.- 11.3.4 Theoretical Analyses of the Cutting Process.- 11.3.5 CO2 Lasers.- 11.3.6 Nozzle Design and Gas Dynamics.- 11.3.7 Laser Beam Analysis.- 11.3.8 Alternative Cutting Methods.- 11.4 Miscellaneous References.

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