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Über dieses Buch

Lasers now play a major part in the processing of the disparate materials used in engineering and manufacturing. The range of procedures in which they are involved is ever increasing. With this growing prominence comes a need for clear and instructive textbooks to teach the next generation of laser users. The informal style of Laser Material Processing (3rd Edition) will guide you smoothly from the basics of laser physics to the detailed treatment of all the major materials processing techniques for which lasers are now essential.

- Helps you to understand how the laser works and to decide which laser is best for your purposes
- New chapters on bending and cleaning reflect the changes in the field since the last edition completing the range of practical knowledge about the processes possible with lasers already familiar to users of this well-known text.
- Provides a firm grounding in the safety aspects of laser use.
- Professor Steen's lively presentation is supported by a number of original cartoons by Patrick Wright and Noel Ford which will bring a smile to your face and ease the learning process.

Laser Material Processing (3rd Edition) will be of use as university or industrial course material for senior undergraduate, graduate and non-degree technical training in optoelectronics, laser processing and advanced manufacturing. Practising engineers and technicians in these areas will also find the book an authoritative source of information on the rapidly expanding use of industrial lasers in material processing.

"Written in a style that includes both technical detail and humor, Bill Steen's book on laser material processing is the standard by which others are judged. It is the text in my graduate-level course on the subject." C.E. Albright, The Ohio State University

"I have used two previous editions for my class. The third edition has included some of the more recent applications. It is easy to read and explanations are lucid. I expect it will receive wide acceptance in class rooms world wide." J. Mazumder, University of Michigan

"It is the great merit of this book to offer a compact survey on laser material processing. A useful and fascinating book, pleasant to read with many useful figures and examples of industrial applications. It is a textbook for advanced students in this field, but also a reference book for engineers." H. Weber, Technische Universität Berlin

Inhaltsverzeichnis

Frontmatter

Prologue

Abstract
It has been true throughout history that every time mankind has mastered a new form of energy there has been a significant, if not massive, step forward in our quality of life. Due to the discovery of the laser in 1960, optical energy in large quantities and in a controlled form is now available as a new form of energy for the civilised world. It is therefore reasonable to have great expectations.
William M. Steen

1. Background and General Applications

Abstract
The basic laser consists of two mirrors which are placed parallel to each other to form an optical oscillator, that is, a chamber in which light travelling down the optic axis between the mirrors would oscillate back and forth between the mirrors forever, if not prevented by some mechanism such as absorption. Between the mirrors is an active medium which is capable of amplifying the light oscillations by the mechanism of stimulated emission (the process after which the laser is named — Light Amplification by the Stimulated Emission of Radiation). We will return to this process in a moment. There is also some system for pumping the active medium so that it has the energy to become active. This is usually a DC or RF power supply, for gas lasers such as CO2, excimer and He/Ne lasers, or a focused pulse of light for the Nd-YAG laser. It may, however, be a chemical reaction, as with the iodine laser. The optical arrangement is shown in Figures 1.la,b,c. One of the two mirrors is partially transparent to allow some of the oscillating power to emerge as the operating beam. The other mirror is totally reflecting, to the best that can be achieved (99.999% or some such figure). This mirror is also usually curved to reduce the diffraction losses of the oscillating power and to make it possible to align both the mirrors without undue difficulty — this would be the case if both mirrors were flat. The design of the laser cavity hinges on the length of the cavity and the shape of these mirrors, including any others in a folded system.
William M. Steen

2. Basic Laser Optics

Abstract
In this chapter the basic nature of light and its interaction with matter is described and the fundamentals of how such energy can be manipulated in direction and shape are presented.
William M. Steen

3. Laser Cutting

Abstract
The idea of cutting with light has appealed to many from the first time they burnt paper on a sunny day with the help of a magnifying glass. Cutting centimetre thick steel (Figure 3.1) with a laser beam is even more fascinating!
William M. Steen

4. Laser Welding

Abstract
The focused laser beam is one of the highest power density sources available to industry today. It is similar in power density to an electron beam. Together these two processes represent part of the new technology of high-energy-density processing. Table 4.1 compares the power density of various welding processes.
William M. Steen

5. Heat Flow Theory

Abstract
When considering the prospect of mathematical modelling a process there are at least two schools of thought. One says “why bother?” and hopes it will go away; the other says “why not?” and plunges in with glee regardless of direction. Both these attitudes miss the point that mathematical modelling is only a tool to help our understanding or control of a process. The status of modelling has changed dramatically with easy access to computers. Scientific reasoning no longer stops with the derivation of a differential equation since these are now all soluble by numerical methods. Software packages can be made which are the models, and once they are made they are available to anyone who wishes to turn them on!
William M. Steen

6. Laser Surface Treatment

Abstract
The laser has some unique properties for surface heating. The electromagnetic radiation of a laser beam is absorbed within the first few atomic layers for opaque materials, such as metals, and there are no associated hot gas jets, eddy currents or even radiation spillage outside the optically defined beam area. In fact the applied energy can be placed precisely on the surface only where it is needed. Thus it is a true surface heater and a unique tool for surface engineering. The range of possible processes with the laser is illustrated in Figure 6.1. Common advantages of laser surfacing compared to alternative processes are:
  • chemical cleanliness;
  • controlled thermal penetration and therefore distortion;
  • controlled thermal profile and therefore shape and location of heat affected region;
  • less after machining, if any, is required;
  • remote non-contact processing is usually possible;
  • relatively easy to automate.
William M. Steen

7. Rapid Prototyping and Low-volume Manufacture

Abstract
In recent years two things have happened. The first is the astounding growth of computer memories which now allow the design of “three-dimensional” models which can be rotated, visualised, surfaces accurately placed in a three-dimensional (3D) coordinate system, surface tangents and normals calculated and the model sliced. The second is the invention of the laser and methods for accurately guiding the finely focused beam. The result of combining the two is the growth of a new industrial sector in rapid construction of models, prototypes or manufactured parts for small batch runs of up to a few 100 pieces. The construction can be done within a small number of working hours, fully automatically using a powerful computer, a very flexible fabrication system and some after-treatment techniques.
William M. Steen

8. Laser Bending or Forming

Abstract
When a material is heated the atoms it contains vibrate; the hotter it is the stronger the vibrations and hence the atoms push each other apart and the material expands. If it is restrained from expanding the atoms rearrange themselves in what is described as elastic or plastic deformation. With elastic deformation the atoms can slide back into their original positions on cooling because they have not moved into a different energy well. With plastic deformation the atoms remain in their new positions on cooling because they have found new stable positions.
William M. Steen

9. Laser Cleaning

Abstract
Laser cleaning is growing in importance, particularly in applications such as the removal of small debris particles from semiconductors and in art conservation. With the introduction of the Montreal protocol, which proposes long-term reduction on environmental and public health grounds in the use of organic solvents such as CFCs that are often used in industrial cleaning, it is to be expected that more generally available industrial embodiments of laser cleaning will emerge in the next few years.
K. G. Watkins

10. Laser Automation and In-process Sensing

Abstract
The recent developments in industry, particularly through the activities of the Ford Motor Company, where the word “automation” was first used in the 1940s, have sketched a progression through “mechanisation” — the use of machines which enhanced speed, force or reach, but where the control was human, to “automatic” machinery — in which the machine will go through its programmed movements without human intervention and the machine is self-regulating, until today we have “automation” — in which there is usually a sequence of machines all controlling themselves under some overall control. In the future there is the prospect of “adaptive control” or “intelligent” machines — in which the machine can be set a task and it teaches itself to do the task better and better according to some preset criteria. The drive towards automation is powered by the possibility of cost reductions, increased productivity, increased accuracy, saving of labour, greater production reliability, longer production hours, better working conditions for the human staff, increased flexibility of production to meet the needs of changing markets and improved quality. This list is a formidable argument for automation but it is only justified for certain production volumes. Figure 10.1 gives an idea of the stages which are most economical in setting up an automatic production facility. If very few pieces are needed then it is cheapest to make them by hand. If a very large number of pieces are needed then it is cheapest to make them on a purposebuilt production line — “hard automation”.
William M. Steen

11. Laser Safety

Abstract
All energy is dangerous, even gaining potential energy walking up stairs is dangerous! The laser is no exception, but it poses an unfamiliar hazard in the form of an optical beam. Fortunately, to date, the accident record for lasers is very good, but there have been accidents. The risk is reduced if the danger is perceived.
William M. Steen

Epilogue

Abstract
This book started with the extravagant claim that optical energy was a new form of energy and therefore should lead to a major advance i n our quality of life, as has been the case with the mastery of other forms of energy. Thus the expectation was high. Hopefully the patient reader has seen in the chapters of this book that some of this expectation is beginning to shape up. It seems appropriate, therefore, to finish with a little thoughtful wander through the future possibilities for laser material processing, which it must be remembered is only one small part of the impact of optical energy.
William M. Steen

Backmatter

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