基于CCD的激光再制造熔池温度场检测研究

【作者】 雷剑波；

【导师】 杨洗陈；

【作者基本信息】 天津工业大学 ， 机械设计及理论， 2007， 博士

【摘要】 激光再制造技术近年来在国内外已受到广泛关注,成为先进制造技术研究领域一个新的分支。该技术尚处在发展之中,目前的研究多限于设备、工艺和材料等方面,其中许多基础理论和技术问题尚需深入开展研究,如高功率激光与粉末流相互作用机理及粉末流状态的检测技术研究,激光熔池内外传热、传质与对流理论及对冶金组织性能的影响,激光再制造的CAD/CAM软件研究开发,激光再制造过程中温度及尺寸精度检测控制等。这些问题使其应用受到很大限制。激光再制造过程中,激光熔池内存在着强烈的能量、动量和质量传输过程,从而产生传热、对流和传质等现象。激光熔池的温度场分布强烈影响能量、动量和质量传输过程,它直接影响激光再制造的冶金性能和表面质量。从理论和试验上开展激光再制造熔池温度场检测研究对激光再制造技术的发展和应用具有重要指导作用。本文旨在研究激光再制造过程中激光熔池的温度场分布,为该技术的发展作进一步研究。针对激光再制造熔池温度场的检测研究,本文详细说明了激光再制造技术的原理,综述了激光熔池温度检测国内外发展现状,提出采用CCD进行激光熔池温度场检测,主要做了以下创新工作:1)基于热辐射机理和金属对激光的反射与吸收特性,研究了激光再制造熔池热辐射的一些特性,选择激光熔池在可见光波段的热辐射进行温度检测,分析了激光再制造常用材料在不同波长、温度和表面状况的表面发射率变化规律,为CCD检测激光再制造熔池温度场模型建立与分析奠定基础。2)确定CCD检测激光再制造熔池温度场系统的结构方案,基于普朗克辐射定律和比色测温原理,建立CCD检测激光熔池温度场模型和一套CCD测温装置,根据模型和CCD的实际光谱响应曲线,进行系统响应、灵敏度和测温误差分析,对比色测温波长选择进行了分析研究。3)进行激光熔池测温专用软件需求和可行性分析,描述了激光熔池热辐射图像的数据流程,采用模块化思想进行软件设计,基于数字图像处理技术,开发出一套激光再制造熔池测温专用软件,详细介绍了热辐射图像的数据采集、输入/输出、图像处理、温度计算模块及程序设计开发。4)介绍了常用黑体辐射源的结构、加热控温方式和性能评价方式,对不同类型的黑体辐射源进行了详细描述,选择中国计量科学研究院的标准高温黑体辐射源进行温度标定,建立了热辐射图像比色值与温度之间的对应关系。5)进行大量运动过程中的激光熔凝、激光熔覆等工艺试验,得到不同工艺情况下的激光熔池温度场分布;进行了激光再制造工业应用试验,通过所建立的CCD测温系统对激光再制造过程进行实时监测。更多还原

【Abstract】 Laser remanufacturing technology has been widely concentrated in the world recent years, which has become a new branch of advanced manufacturing technology. At present, research on it mainly concentrates on equipment, processing parameter and material. In order to solve problems in its industry application, the basic theory and technology on it need to be studied further, such as interaction mechanism between high power laser beam and powder stream, measurement of powder stream feeding, special CAD/CAM software, measurement and control of temperature, size and precision, and so on.There is transmission of energy, momentum and mass in laser molten pool, which would induce some phenomenon, such as heat exchange, convection and mass exchange. Temperature distribution in laser molten pool would strongly affect the transmission, and then influence its metallurgy performance and surface quality. It is important to study it on theory and experiment, which would improve laser remanufacturing technology.In order to study it further, the principle of laser remanufacturing technology was discussed in this paper. Development status of temperature measurement on it in the world was summarized in detail. The method of CCD measurement was proposed. The research mainly includes:1) Based on thermal radiation theory and properties of reflecting and absorbing between metal material and laser, characteristics of thermal radiation in laser molten pool were analyzed. The thermal radiation in visible wavelength could be detected in order to analyse temperature. In order to establish and analyse mathematics model on CCD measurement, surface emissivity variety of common materials at different wavelength, temperature and surface status was analyzed.2) Structure design of the system was developed. Based on Plank radiation law and temperature measurement colorimetry principle, CCD measurement model and CCD measurement device were set up. Based on CCD spectrum quantum efficiency curve, analysis on its response, sensitivity and temperature measurement error was developed. Choice of thermal radiation wavelength for temperature colormetry was analyzed. 3) Function demand and feasibility of its special software were analysed. Data stream of thermal radiation image in temperature measurement was described. Based on digital image processing technology and modularization design method, special software for laser remanufacturing was developed, which was discussed in detail, such as data acquisition, input/output, image processing, temperature computing module and program design.4) Different blackbody structure, temperature control and performance evaluation were analysed in detail. Temperature calibration experiments were developed by high temperature standard blackbody of National Institute of Metrology P.R.China. Relation equation between blackbody temperature and two color gray ratio of thermal radiation image was set up.5) Experiments on laser quenching and laser cladding at moving state were developed. Temperature field distributions at different processing parameters were analyzed. Experiments on laser remanufacturing industry application were developed. It was shown the process of laser remanufacturing could be supervised by the CCD temperature measurement system in real time.更多还原