Co2 Laser Cutting

ISBN-13: 9781852330477 / Angielski / Miękka / 1998 / 248 str.

John Powell;Powell

Opis

The laser has given manufacturing industry a new tool. When the laser beam is focused it can generate one of the world's most intense energy sources, more intense than flames and arcs, though similar to an electron beam. In fact the intensity is such that it can vaporise most known materials. The laser material processing industry has been growing swiftly as the quality, speed and new manufacturing possibilities become better understood. In the fore of these new technologies is the process of laser cutting. Laser cutting leads because it is a direct process substitu tion and the laser can usually do the job with greater flexibility, speed and quality than its competitors. However, to achieve these high speeds with high quality con siderable know how and experience is required. This information is usually carefully guarded by the businesses concerned and has to be gained by hard experience and technical understanding. Yet in this book John Powell explains in lucid and almost non technical language many of these process wrinkles concerning alignment, cornering, pulsing, water jets, material properties, cutting speeds as well as tricks with surface coating and much much more. It is a book which managers and technicians in laser job shops and laser processing facilities would be foolish not to read."

Spis treści

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.- 11.5 Further reading update for the second edition of this book.