【作者】 梅丽芳；

【导师】 陈根余；

【作者基本信息】 湖南大学 ， 机械工程， 2008， 硕士

【摘要】 激光加工的本质是利用材料吸收激光能量改变材料的物理化学结构,因此,研究确定材料对激光的吸收系数是研究激光加工的基础,具有重要的理论意义和实际应用价值。激光修整超硬磨料砂轮作为一种新型的修整技术,正显示出广阔的应用前景。照射到砂轮上的激光一部分被磨料和结合剂吸收,另一部分则被反射或透过超硬磨料作用于结合剂上。激光修整的本质是利用磨粒与结合剂吸收激光能量对砂轮进行深度的整形或轻度的修锐,使砂轮达到所要求的几何形状误差和地形地貌。迄今,针对不断出现的各种超硬磨料对YAG激光的吸收系数测量研究未见报道。如何准确的测定超硬磨料对激光的吸收系数,对激光修整超硬磨料砂轮的理论研究和实际推广应用具有关键作用。本文以试验研究与数值模拟计算相结合,以传热学为理论基础,基于集总参数分析法,设计了超硬磨料对YAG激光吸收系数的测量装置,利用热电偶传感器经数据采集系统测定出超硬磨料试样在YAG激光辐照和冷却过程中的热电势,将热电势值转换成相应的温度值代入吸收系数计算模型,可得出MBD系列人造金刚石和CBN系列立方氮化硼超硬磨料对YAG激光的吸收系数。同时对激光平均功率、激光光斑直径大小、激光连续辐照频率、热电偶传感器放置位置、试样本身质量以及绝热盒的性能等因素对吸收系数的影响情况进行分析,找出其中的影响规律及原因。根据传热学原理分析试验过程中试样的热量传递方式及对流换热形式,同时采用集总参数分析法计算对流换热系数,这是一种针对特殊场合求解对流换热系数的方法。对整个试验过程建立相应的三维非稳态传热物理和数学模型,对传热模型进行离散处理,将由试验测定的试样吸收系数值及对应激光参数代入模型,并采用APDL编程语言编制程序在ANSYS有限元分析软件中进行整个试验过程的数值模拟计算。并将数值模拟计算所得的温度与试验测定的温度进行比较,通过对两者结果的比较分析来验证试样测定结果的准确性以及整个试验方案的可行性。更多还原

【Abstract】 The laser processing essence is to change the material physical or chemical structure by absorbed laser energy, thus fulfills a certain processing purpose. Therefore, research on measuring method of the absorption coefficient is the foundation to the laser processing, and it has important significance in practical application.Laser truing and dressing of superabrasive grinding wheel as one kind new technology is demonstrating powerful prospect in development day by day. In the process of laser truing and dressing superabrasive grinding wheel, a part of laser radiating to grinding wheel is absorbed by abrasives and bond, another part is reflected or penetrates through the abrasives to act on bond. The essence of laser truing and dressing is using the abrasive and bond absorbed laser energy to change the grinding wheel structure, thus to satisfy the request of grinding wheel geometric deviation. The laser absorption of superabrasive is an extremely important problem to laser truing and dressing of superabrasive grinding wheel. How to measure the laser absorption of superabrasive conveniently and economically is one of the rationale researches of laser truing and dressing superabrasives grinding wheel.This paper combines the experimental study with the numerical simulation, embarks from the heat transfer theory, bases on the lumped parameter method, then adopts the thermocouple sensor and data acquisition system to measure the superabrasive specimen thermoelectric potential before and after laser irradiating, afterwards transforms the thermoelectric potential into corresponding temperature and substitutes the temperature into absorption coefficient computation model, finally obtains the YAG laser absorption coefficient of MBD series artificial diamond and CBN series cubic boron nitride superabrasive. Analyzes the influence of laser average power、laser facual、heat-insulating material、laser irradiating frequency and so on to absorption coefficient, and discovers the influence rule and reason.Analysis the specimen’s heat transfer way and heat convection form according to heat conduction theory, simultaneously, uses the lumped parameter method to measure the coefficient of heat convection, which is a new method for measuring the heat convection coefficient under special occasion. Establishes the three dimensional unstable heat transfer physical and mathematical model corresponded to entire experiment, carries on discretization to heat transfer model, substitutes the specimen absorption coefficient measured by experiment and its corresponding laser parameter into computational model, and makes program by APDL programming language and calculates the program in ANSYS software. Compares the calculated results with the experimental results, and examines and verifies the accuracy of measured results by analyzing the two results.更多还原