【作者】 王成；

【导师】 曾晓雁；

【作者基本信息】 华中科技大学 ， 物理电子学， 2007， 博士

【摘要】 作为一种先进制造技术,激光雕刻成形加工目前已在许多领域得到应用。综观现有的几种激光立体雕刻工艺,主要局限在高分子聚合物和几种透明材料,很少见到能在陶瓷、钢铁等硬质材料表面直接加工三维图形的激光雕刻技术的相关报道。本文提出了一种可以用激光在材料表面雕刻真正三维图形的新工艺、新技术——采用分层制造原理的激光三维雕刻技术,并从三维雕刻软件开发、控制系统设计、雕刻工艺实践与探索等方面入手,系统研究了激光三维雕刻的若干关键技术问题。主要研究结果总结如下:采用STL文件作为该系统与通用CAD造型软件之间的模型数据接口,实现了STL模型的拓扑重建、实时切片、区域扫描填充、加工仿真、过程控制、人机交互等模块,并从提高数据处理速度的角度对切片算法和扫描填充算法进行了深入研究。根据STL文件几何信息有余、拓扑信息不足的特点,通过对各几何元素先排序、再归并、然后建立邻接边表的策略来为切片赢得时间。为保证切片时对邻接三角形的顺利追踪,将切平面与三角形相交出现的5种位置关系统一成切平面与三角形两条边相交的情形。在扫描算法中,充分利用边连贯性和扫描线连贯性来建立活性边表,以减少求交量和提高排序效率,从而提高扫描线的生成速度。针对带有岛屿的轮廓截面,提出并实现分区直线扫描算法以优化扫描路径。通过对现有三维工作台进行改造,建立起激光三维雕刻硬质材料的硬件平台。在研究分析现有的几种计算机控制模式和操作系统实时性的基础上,确定以Windows2000作为软件平台、采用PC+智能控制卡的开放式数控系统作为激光三维雕刻系统的总体控制方案。重点分析控制系统的硬件结构、电机回路及系统性能,并详细阐述了设备驱动程序及控制接口类的设计思想和实现过程。建立激光三维雕刻工艺,并利用该系统进行激光三维雕刻。主要以陶瓷作为雕刻材料,研究探索雕刻深度随激光功率、扫描速度、脉冲重复频率的变化规律以及工艺参数对雕刻质量的影响。通过分析激光雕刻的物理过程,揭示激光雕刻过程中多余物质的转移规律。建立雕刻深度数学模型,揭示雕刻深度和激光功率、扫描速度、脉冲重复频率三个主要工艺参数之间的数学关系,为快速获得加工参数数据提供理论上的指导。为便于仿真雕刻深度数学模型,采用平均值估算法替代积分精确计算法来计算数学模型中单个激光光斑区域内的能量。雕刻深度的数学模型为:此外,利用BP人工神经网络构建雕刻深度和工艺参数之间的非线性映射关系,通过神经网络模型将试验获取的有限数据泛化扩展到各参数取值的全局范围,以提高雕刻试验中参数设置的命中率,并为激光三维雕刻建立优化工艺参数数据库。从原理、设备及工艺等方面分析激光三维雕刻的成形误差,为激光三维雕刻建立完整的误差评价体系。通过分析CAD模型误差、切片误差、扫描机构的运动误差、扫描方式误差、雕刻面粗糙度及断面垂直度误差的形成机理,为提高雕刻精度和质量探索行之有效的途径。通过建立雕刻平面粗糙度理想模型和雕刻断面粗糙度理想模型揭示雕刻参数对表面粗糙度的影响规律,为加工参数的优选提供理论指导。以现有瞬间点热源温度场模型和热应力计算方法为基础,根据激光三维雕刻去除材料的特点,通过一系列近似假设,初步建立激光雕刻过程中的温度场和热应力场理论模型,并对其分布和变化情况进行数值仿真。本文研究开发的硬质材料激光三维雕刻工艺与装备开辟了一门崭新的激光加工技术,具有快速、柔性、高精度、雕刻成本与模型复杂程度无关等优点,不仅可以雕刻微细图形,也可以雕刻常规方法难以加工的硬脆性材料,在模具、工艺品制作、立体标刻、防伪、MEMS/MEOMS等领域具有广阔的发展空间和应用前景。更多还原

【Abstract】 As an advanced manufacturing technology, laser machining has already been applied in many fields. Different kinds of laser forming techniques have been developed. Among the existing laser carving techniques, there seems not the laser carving technology that can fabricate three-dimensional (3D) graphics directly on the surface of hard materials. In this dissertation, a new technology, namely 3D laser carving that can fabricate the true 3D graphics on the surface of hard materials was presented, and some concerned fundamental scientific problems such as software development, control system design and carving process exploration of the 3D laser carving system were studied based on the principle of layered manufacturing. Following are the main results on the subject:STL (StereoLithography) file was used as the data interface between CAD modeling software and the 3D laser carving software. The concerned software functional modules such as topologic reconstruction, on-line slicing, regional filling, processing simulation, process control and human-machine interaction were developed, and the slicing algorithm and scanning algorithm were studied further with a view to improve the speed of data processing. Due to the redundancy of geometric information and the lack of topological information, the geometric elements of STL model should be sorted and merged firstly, and then the adjacent-side lists were built to gain time for slicing. In order to track the adjacent triangles successfully during slicing STL model , the five intersection relationships among slicing planes and triangle facets were converted into the intersection relationship among slicing plane and two sides of the triangle facet. To reduce the times of intersection and improve the sorting efficiency, the active-side list was established to make full use of the consistency of the side and the scanning line. In view of the profile with islands, the divisional linear scanning algorithm was put forward and implemented to optimize the scanning paths.The hardware platform for 3D laser carving system was established by upgrading an existing 3D working table. Based on the study of several existing computer-controlled modes and the real-time ability of operating system, the open NC systemic architecture of PC + intelligent control cards was used in the control system of 3D laser carving, in which Windows2000 was chosen as the software platform. The hardware architecture of control system, electrical circuit and systemic performance were analyzed specially, in addition, the framework and the calling mechanism of the device driver in Windows2000 were studied and the details of the development of device driver and interface were given.The technological process, namely doing laser carving experiments to obtain the optimum parameters related to one single-layer carving depth firstly and then carrying out 3D laser carving based on these data, was laid down for 3D laser carving. Laser carving on Al2O3 ceramic plate with different processing parameters was done to study the effects of laser processing parameters on single-layer carving depth and carving quality, and in the mean time to analyze the physical process of laser carving, and to uncover the removing rules of redundant materials in the course of laser carving. In the experiments on ceramics, the main mechanism that contributes the laser carving mechanisms is that laser beam with high peak power ablate the ceramic surface which induced the pit spallation. By establishing the mathematical model for carving depth, the relationships between carving depth and the main processing parameters such as laser power, scanning speed and repetition rate were disclosed mathematically, which can give the theoretical guidance to rapidly get the process parameter data. In order to simulate the mathematical model conveniently, the laser beam energy within one single laser pulse was calculated by the average estimate method. The mathematical model for carving depth is as follows: In addition, the nonlinear mapping relationship between carving depth and the process parameters was established by ANN (artificial neural network). The BP was trained by using the existing data obtained by laser carving experiments, and the ANN model was built based on the training results. By ANN model, the finite data from experiments can be generalized to the overall range, which effectively improved the optimizing rate of process parameters and was very helpful to build the parameter database for 3D laser carving. On the basis of making full analysis of the carving errors in aspect of carving principle, equipment and technology, the complete error-evaluation system was established for 3D laser carving. By analyzing the CAD model error, slicing error, motion error, scanning error, carving surface roughness error, carving vertical error and their forming mechanisms, many effective ways were explored to improve the carving precision and quality. The ideal model for carving surface roughness of horizontal plane is And the ideal model for carving surface roughness of vertical plane isAccording to the characteristics of 3D laser carving, the temperature-field model and the thermal-stress model for 3D laser carving were established and simulated tentatively on the basis of the existing temperature filed model of the instantaneous point heat source, the existing calculation method of thermal stress and a series of assumptions.Summing up above mentioned, the technology and equipment of 3D laser carving have created a new laser processing technology with fast, flexible, high efficiency and low cost, as well as the ability to fabricate 3D micro-graphics and carve the hard and/or brittle materials. 3D laser carving technology has a great potential industrial application prospect in the field of mould/die, craft production, 3D mark, security and MEMS/MEOMS.更多还原