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The Theory Of Laser Materials Processing: Heat ... Fixed

The revised edition of this important reference volume presents an expanded overview of the analytical and numerical approaches employed when exploring and developing modern laser materials processing techniques. The book shows how general principles can be used to obtain insight into laser processes, whether derived from fundamental physical theory or from direct observation of experimental results. The book gives readers an understanding of the strengths and limitations of simple numerical and analytical models that can then be used as the starting-point for more elaborate models of specific practical, theoretical or commercial value.

The Theory of Laser Materials Processing: Heat ...

Although the book focuses on laser interactions with materials, many of the principles and methods explored can be applied to thermal modelling in a variety of different fields and at different power levels. It is aimed principally however at academic and industrial researchers and developers in the field of laser technology.

The purpose of the book is to show how general principles can be used to obtain insight into laser processes. The principles used may come from fundamental physical theory or from direct observation of experimental results, but an understanding of the general characteristics of the behaviour of a process is essential for intelligent investigation and implementation, whether the approach is experimental, observational, numerical or analytical. The last two have a special value since the associated costs can be relatively low and may be used as a starting point for more expensive techniques. The construction of simple models whose underlying principles are easy to see is therefore of special value, and an understanding of their strengths and limitations is essential. The applications considered in detail are cutting, keyhole welding, drilling, arc and hybrid laser-arc welding, hardening, cladding, forming and cutting, but the general principles have a very wide application; metallurgical aspects are considered, as are femtosecond interactions with metals. The book begins with a discussion of the mathematical formulation of some relevant classes of physical ideas, and ends with an introduction to comprehensive numerical simulation. Although all the examples considered have the common feature that the source of power is a laser, many of the principles and methods apply to thermal modelling in a variety of different fields and at many different levels of power.

Laser material processing is one of the main areas of laser applications (and more generally of harnessing laser light), having a particularly strong economical impact.It is nowadays used in a very wide and diverse range of industrial fabrication techniques, involving mass production of common goods as well as very specialized applications.Such processes can be applied to a wide range of materials, including many different metals (from thin foils to thick sheets), ceramics, glasses, polymers (plastics), textiles, leather, paper and wood.A wide range of laser sources and processing methods is employed, adapted to the strong differences concerning various material properties (e.g. strength of light absorption, hardness, melting and evaporation temperature, thermal conductivity, tendency to oxidize, etc.) and the intended processing results.

Processes based on ultrashort laser pulses (with picosecond or even femtosecond durations) have the advantage that energy losses by heat conduction and heat radiation are largely eliminated.On the other hand, the vaporization and ionization consumes a lot of energy.Therefore and because of the tentatively more limited available laser average power, the processing speed and efficiency are often not that high.Also considering the substantially higher cost per watt of average power, one finds that ultrafast laser processing is problematic in competition with alternative processes with longer pulses, as far as those are available and working well enough.However, there many cases where the required processing results (e.g. in terms of quality) are only possible with ultrafast laser methods.

Various kinds of materials which are important in industrial fabrication can be ablated, mostly using short or ultrashort laser pulses.A large number of pulses is applied, while moving the laser processing head (or the workpiece), often systematically along a predefined pattern with a certain overlap of the zones affected by single pulses.

Here, the most important parameter is the very high intensity level, as can be achieved in conjunction with very short pulse durations; of lower importance is the wavelength of the radiation.Methods of thermal laser ablation require nanosecond pulses in the case of metals, while much longer pulse durations are suitable for ceramic materials, for example, because those exhibit a lower thermal conductivity.

Laser cutting is in some respects similar to drilling, but aimed at separating parts over some length.It often begins with drilling (piercing) to get some initial hole, from where the cutting process can continue by the smooth movement of the laser processing head and/or the workpiece.A defined gap (kerf) needs to be obtained in order to achieve the separation.For that, some amount of material has to be removed, either in liquid form (as melt) or by vaporization.The latter generally leads to higher processing quality, but also to a lower process efficiency.In some cases, a substantial part of the process heat is generated by oxidation of the metal, achieved by injecting purified oxygen.In other cases, an inert process gas is applied for improved quality.

Efficient laser cutting methods and machine systems have been developed for a wide range of industrial applications, ranging from the cutting of metal sheets in shipbuilding to precision machining, even micro-machining.Various types of metals can be cut, from thin foils to thick sheets, also a wide range of polymers (plastics), and even brittle materials such as ceramics, glasses and semiconductors.

Lasers can be used in various ways to mark materials.One possibility is laser engraving, i.e., removing some depth of material from a homogeneous surface.In other cases, one removes a thin coating, e.g. an anodized layer from an aluminum part, or some paint layer; in such cases, removal of only a thin layer can be sufficient for obtaining a strong visual contrast.Other methods are based on surface modifications, which can again result from a variety of physical effects of thermal or non-thermal origin.

With moderately focused laser beams (spot diameter well below 1 mm), very controlled heating can be achieved, so that soldering of very fine structures is possible.That is used for attaching mainsprings in mechanical watches, and in many other areas with fine mechanical parts.

Various kinds of unwanted materials can be removed from surfaces by applying sufficiently intense laser light.For example, artworks exposed to polluted air, which created dark depositions, can be cleaned with lasers while preserving the original material.More frequently, such methods are applied to efficiently cleaning parts in industrial manufacturing processes.

Note that there can be many different reasons for degradation of performance, for example aging of the laser system, contamination of critical optical components, misalignment due to vibrations or mechanical shocks, overheating of optics, a lack of gas supply or variable properties of workpieces.Therefore, it could be rather hard and time-consuming to identify problems without extensive monitoring of various details.

The use of lasers for various applications in materials processing has grown rapidly in recent years. Lasers are by nature particularly well suited to automation, but to ensure repeatability and reliability, the engineers employing them must not simply rely on numerical analysis software. They must have a firm grasp on the physical principles involved. Mathematics of Thermal Modelling: An Introduction to the Theory of Laser Material Processing introduces the mathematics needed to formulate and exploit the physical principles important to modelling various aspects of laser material processing. The author shows how to gain insight by constructing and analyzing simple models. He demonstrates how to extract qualitative information from the models, how the underlying principles can be extended to more complex modelling, and how these principles can be applied to processes such as laser welding, surface treatment, drilling, and cutting. Written at a level accessible to graduate students, this book shows that simple mathematical investigation-- based primarily on analytical methods backed by relatively simple numerical methods--can greatly illuminate the processes being studied. Regardless of the stage of your career development, if you are confronting the modelling of thermal process in this field for the first time, Mathematics of Thermal Modelling will build the foundation you need.

Prerequisite: MECHENG 211, Math 216. (3 credits) Introduction to theory and practice of the finite element method. One-dimensional, two-dimensional and three dimensional elements is studied, including structural elements. Primary fields of applications are strength of materials (deformation and stress analysis) and dynamics and vibrations. Extensive use of commercial finite element software packages, through computer labs and graded assignments. Two hour lecture and one hour lab. (Course Profile)

Prerequisite: MECHENG 350, MECHENG 360, MECHENG 395, preceded or accompanied by MECHENG 335. May not elect MECHENG 450 concurrently. Student must be declared in Mechanical Engineering. Not open to graduate students. (4 credits).Weekly lectures and extended experimental projects designed to demonstrate experimental and analytical methods as applied to complex mechanical systems. Topics will include controls, heat transfer, fluid mechanics, thermodynamics, mechanics, materials and dynamical systems. Emphasis on laboratory report writing, oral presentations and team-building skills, and the design of experiments (Course Profile) 041b061a72

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