Handbook of the EuroLaser Academy Volume 2

If in some processes oxygen is used, additional energy is provided at a rate P ch by chemical reactions. The flow of energy per unit time can then be written: (1. 2) From the above it can be made clear that it is the rate of energy fluxes, i. e. 2 intensities [J/ms] that determines into which channel the energy goes and how the interaction zone will be modified in its state (solid, liquid, gaseous) and geometrical shape (plane, dip, deep hole) -in other words which kind of treatment process will be established (hardening, welding, drilling etc. ). In the following, it will be shown that, in fact, it is the intensity of the beam, which together with the interaction time, primarily governs the interaction phenomena. 1. 1. 2 Laser beam properties determining interaction and energy coupling etJeets In order to yield an efficient process, it is necessary to obtain adequate intensity at the workpiece and to couple a fraction of the incident power as high as possible into the material. The beam properties being of importance in this respect are, (Hugel, 1992): 1. the wavelength A. , governing, in principle, the focusability and absorptivity; 2. the polarisation, having considerable influence on the absorptivity for large angles of incidence; 3. the power P which together with the achievable spot diameter d L f determines the intensity in the interaction zone; 4.

1 Interaction Phenomena.- 1.1 Introduction.- 1.2 Energy coupling.- 1.3 Interaction phenomena.- 1.4 Significance of coupling and interaction phenomena in laser treatment processes.- 1.5 References.- 2 Materials and Workpiece Classification.- 2.1 General aspects.- 2.2 Crystalline materials.- 2.3 Material classes and their properties.- 2.4 Laser treatment.- 2.5 Testing of materials.- 2.6 Seam geometry workpiece classification.- 2.7 Technological considerations.- 2.8 References.- 3 Cutting.- 3.1 Introduction.- 3.2 Process characteristics, advantages, disadvantages.- 3.3 Principles and theory in laser cutting.- 3.4 Productivity and obtainable cut qualities.- 3.5 Processing parameters.- 3.6 Safety in laser cutting.- 3.7 System types.- 3.8 Industrial applications.- 3.9 References.- 4 Welding.- 4.1 Introduction.- 4.2 Heat sources produced by laser beams.- 4.3 Behaviour of materials during laser welding.- 4.4 Engineering applications.- 4.5 Parameters to consider in the economic analysis of laser welding.- 4.6 References.- 5 Heat Treatment.- 5.1 Introduction.- 5.2. Process systematic of laser surface treatments.- 5.3 Conclusions and final remarks.- 5.4 Acknowledgements.- 5.5 References.- 6 Forming and Rapid Prototyping.- 6.1 The laser forming process.- 6.2 Process simulation.- 6.3 Applications and similar processes.- 6.4 List of variables.- 6.5 References.- 7 Marking and Scribing.- 7.1 Introduction.- 7.2 Marking methods.- 7.3 Systems.- 7.4 Economic aspects.- 7.5 References.- 8 Precision Ablation Processing.- 8.1 Introduction.- 8.2 Ablation mechanisms.- 8.3 Material interactions and applications.- 8.4 Laser ablation systems.- 8.5 Economical aspects.- 8.6 References.- 8.7 List of symbols.- 9 Drilling.- 9.1 Introduction.- 9.2 Mechanisms, models and techniques.- 9.3 Applications in the gas turbine industry.- 9.4 Other applications.- 9.5 References.- 10 Economics.- 10.1 Introduction.- 10.2 The laser process in perspective.- 10.3 Economic factors.- 10.4 Assessment methods.- 10.5 Case studies.- 10.6 Summary.- 10.7 Further reading.- 11 Assessment of Technology.- 11.1 Assessment of laser technology.- 11.2 Competing technologies.- 11.3 Assessment of laser machines.- 11.4 Test methods for laser systems.- 11.5 Quality evaluation of laser processed components.- 11.6 Basic economic considerations.- 11.7 References.- 12 Modelling.- 12.1 Basic equations and techniques.- 12.2 Analytical models.- 12.3 Numerical solutions.- 12.4 Semi quantitative models.- 12.5 References.