Studies Of High-Power Laser Heat Effect Simulation And Laser Beam Description

With the advent of intensive laser in 1960s, the technology of laser heat treatment has been widely applied in industry. However, so far, the technology of laser heat treatment has depended on summarizing experimental laws. So in order to exactly indicates the heat effect of laser on substance and to realize optimizing control of the technology have been always the tasks which overseas and domestic technician have actively undertaken. In the course of non-melting heat treatment, as a rule, the heat effect of laser can be concisely indicated because the extent of heat effect is limited to laser radiation area as a result of the shorter effect time of laser to materials, and the treated materials is regarded as semi-infinite continuous medium with the constant of physical properties. On the basis of approximate effect, the calculation formula of temperature field with elliptic Gaussian beam radiation has been deduced and widely applied. Because of the complexity of distribution of laser intensity in practical, the international standardization organization has stipulated the width and radius of laser beam in order to describe canonically laser beam. Thus the laser beam is ordinarily described by laser power, radius of laser beam and distance of defocus in the technics of heat treatment. Formally speaking, if the parameters such as scanning speed, physical properties are given, the calculation result of heat effect of laser on temperature field can be wholly confirmed. However, there are usually some trouble in replanting and recurring the technics of heat treatment with laser in practical research in accordance with these parameters. In my dissertation, via strictly theoretical calculation and experimental investigation, laser parameters described above and the feasibility of calculative formula in heat effect are reviewed by using calculative methods, and major factors which affects the result of heat treatment are discussed in detailed, in addition, some conclusions are obtained as follows:1. If the distribution of laser beam has maximum at the center of beam and is similar with the distribution of Gaussian beam in formal, it is feasible that heat effect is calculated by thinking the model of laser beams as Gaussian beam (e.g., the average error, which comes from the calculation of strip of hardening for phasechange by outputting beam of light from YAG laser, is about percent 20). The error of the theoretical value with that measured by experiments will be much more reduced if the beam of light outputted by YAG laser is regarded as TEMoo+TEM01, the pattern of intension superposition according to some proposition.2.When the distribution laser beam presents complicated high-rank model, there will be a bigger error between the result calculated by temperature area of laser heat treatment arid practical outcome by using the method of percent 86.5 power which regards the beam of light as Gaussian beam (e.g., the average error, which comes from the calculation of strip of hardening for phase change by outputting beam of light from HJ-3 laser, is about 46%).3. According to the definition of beam width stipulated by the international standardization organization, if practical beams of light is thought as Gaussian elliptical beam, a result, which is much closer to practical outcome. However, it cannot satisfy the need of quantificational calculation.4. The theoretical knowledge and experimental research shown that different laser equipments, even the same equipment with different modulation status, such as the light maladjustment of laser cavity, have much difference in distribution of power density of outputting beam. Therefore, a bigger error is brought when all practical beams are regarded as Gaussian beam and heat effect is researched by using briefly calculative formula of temperature field with ideal Gaussian beam.5. In the practical research of laser heat treatment, it is inadequate that practical beams of laser heat treatment are merely described by radius of beam, distance of defocus and laser power...