激光直接制造和再制造技术CAM研究

【作者】 靳晓曙；

【导师】 杨洗陈；

【作者基本信息】 天津工业大学 ， 纺织机械设计及自动化， 2007， 博士

【摘要】 激光直接制造和再制造技术是近几年才兴起的先进制造技术，其实质是利用同轴送粉激光熔覆按照快速原型的理念进行添加式层叠直接制造和再制造的方法。它是一门新的光、机、电、计算机、自动化、材料综合交叉的先进制造技术，无论从基础理论、工艺、设备的开发和研制，还是工业化应用都面临着许多研究课题。本文全面总述了国内外直接制造和再制造技术发展状况，阐述了自主开发的激光直接制造和再制造硬件系统组成，主要研究内容包括：同轴送粉喷嘴的研制、激光直接制造和再制造CAM软件原型系统的研究与开发以及加工实践。载气式同轴送粉喷嘴是激光直接制造和再制造技术的关键部件之一，同轴送粉喷嘴输出的粉末流参数直接影响着制造零件的尺寸精度及形貌等，因此对同轴送粉喷嘴粉末流运动规律的研究对同轴送粉喷嘴的设计和激光直接制造和再制造工艺优化具有重要的意义。本文采用两个共轴的喷嘴来实现同轴送粉，根据气固两相流的双流体模型理论，建立了载气式同轴送粉喷嘴处气一粉两相流的基本守恒方程组，对载气式同轴送粉喷嘴的粉末流场进行数值模拟，研究分析了粉末流场浓度分布规律，粉末流参数——聚焦焦距和聚焦半径的变化规律，并进行了试验研究，计算结果与试验结果吻合较好。同时研制了系列同轴送粉喷嘴。CAD／CAM应用软件系统主要完成零件三维实体造型并将模型转换成数控机床驱动指令的功能，是直接制造和再制造技术的前提和基础，是影响整个加工速度、精度和效率的重要因素。根据直接制造和再制造原理，分析了CAD／CAM应用软件系统的工作流程，将整个软件系统划分为CAD造型(含三维反求)、轨迹生成、轨迹模拟、工艺参数设置和工艺数据库、数控代码生成和数据传输等模块。通过研究通用三维CAD系统的二次开发技术，基于CAD平台规划了直接制造和再制造CAD／CAM系统框架。在分析研究CAD软件平台下CAD模型数据的内部表达方法以及拓扑信息和几何信息提取方法的基础上，提出应用CAD软件应用程序接口(Application Program Interface，API)函数中的曲面一曲面求交函数实现CAD模型曲面与分层平面求交的方法，给出了一系列直接分层算法，包括求交后轮廓交线的提取、排序整理及离散方法和光栅填充扫描算法。开发了相应的程序，用户可以输入激光功率、扫描速度、分层厚度、熔覆宽度、设置不同的容差等参数，沿不同方向进行直接分层提取零件截面轮廓信息，生成光栅填充扫描路径，进行轨迹模拟，可以处理复杂零件。同时自行设计了记录切片数据的文件格式，用直线、圆弧或圆描述分层轮廓，提高了分层的精度。为确切分析直接分层的精度，制作了试件与STL间接分层试件比较，结果表明采用直接分层的试件的精度和表面质量优于STL间接分层。为了进一步提高制作精度，减少台阶效应，研究了自适应直接分层算法，采用法向矢量判别原则，基于CAD平台二次开发实现了这一算法。研究了应用5轴机床直接制造和再制造的特点，通过改变激光束的光轴方向可以减少甚至不需支撑，可叠加制造具有悬边或型腔特征的零件，给出了5轴制造轮廓信息处理及轨迹路径生成算法，通过直接分层提取到轮廓点坐标及其法向矢量和切向矢量，计算得到表示光斑中心位置和光轴矢量的系列点集(x_m，y_m，z_m，i_m，j_m，k_m)(m=1，2，…n)，然后通过后置处理把它转换为机床运动坐标(x，y，z，A，C)用于生成数控代码，为今后开展多轴3D直接制造和再制造打下基础。最后介绍了应用研制的同轴送粉喷嘴和开发的程序，进行激光直接制造和再制造的应用。实践表明，激光直接制造和再制造这项先进的制造技术在今后的发展中必将有更广阔的应用前景。更多还原

【Abstract】 Laser direct manufacturing and re-manufacturing is an advanced manufacturing technology which just rises and has been developed in the last few years. This technology is actually an additive-layered manufacturing technology which applys coaxial powder feeding laser cladding technology according to rapid protyping principle. It is a new advanced manufacturing technology which integrates optics, mechanics, electrics, computer, automation and material science. Therefore, there are many problems need to be studied or solved whether in basic theory, processing technology, equipment developing or industry application. In this paper, the development status of laser direct manufacturing and re-manufacturing was first summarized comprehensively and then the hardware system developed by ourselves were introduced. The studying work mostly includes the research or designing of coaxial nozzle, studing or developing of CAD/CAM prototype system in laser manufacturing and processing practice.Coaxial powder feeding nozzle is one of the key components in laser direct manufacturing and re-manufacturing. The powder parameters from nozzle directly influenced the part precision and face quality and hence it is necessary to study the powder flow movement for coaxial nozzle designing and process optimizing in laser manufacturing. By analyzing the powder feeding technology, the coaxial nozzle was designed to have two coaxial nozzle tips. According to the double-fluid model in gas-particle two-phase theory, the basic governing equations of powder flow out of coaxial nozzle tips was established to simulate the powder flow in coaxial powder feeding with carrying gas. The concentration distributing of powder flow and powder parameters (focus distance to nozzle exit and focus radius of of powder flow) varying are simulated and analyzed. The effect of gas flux and feeding powder rate upon powder parameters was studied. Comparing the result of computer simulation with one of measurement by DPIV(Digital Particle Image Velocimetry), it is shown that a good agreement between theoretical and experimental data can be obtained. Meanwhile, a series of coaxial nozzles have been designed and manufactured.CAD/CAM application software system is used for for parts body modeling and converting three_ dimensional model into NC code to control machine forming movement. It is the premise or base of laser direct manufacturing and re-manufacturing. It is the important factor influencing process velocity, accuracy and efficiency. The software system running procedure was analysed according to principle of laser direct manufacturing and re-manufacturing. The whole system consists of 3D solid modeling module(including 3D reverse engineering), tool path generating module, tool path simulating module, process parameters setting and process data-base module, NC code generating module and data transmitting module. Further developing technology of general CAD software was studied and the CAD/CAM system frame has been laid out.By studying the data structure of CAD solid model and the method for obtaining geometric and topological information from CAD model, a direct slicing approach is proposed in which the surface-surface intersection function of Application Programming Interface (API) functions was called to get the section contours of model surface and slicing plane from CAD solid models. A series of algorithms such as extracting the information of section contours, sorting and discretizing section contours, generating raster filling path have been put forward. The direct slicing program based on above algorithms has been developed in which process parameters including laser power, scanning velocity, slicing thickness, cladding width or discrete tolerance can be set, solid model can be sliced along different directions and tool path for contouring or filling be generated. The slices data are saved in special file in which lines, arcs and circles are used to describe the section contours. The direct slicing result was simulated in software. Part was fabricated with application of direct slicing software. Comparing the part fabricated based on direct slicing format with part based on stereolithography (STL) format ,it is shown that the accuracy and surface finish of direct slicing part was better than STL indirect slicing.For the sake of improving manufacturing accuracy or reducing step effect, an adaptive direct slicing method complete with the algorithm for calculating the thickness of layers is proposed. By adopting the normal vector judge principle, it was programmed based on the commercial CAD software package. The method was shown to be fast and accurate in comparison with direct slicing.Five-axis laser machining system is used to build a part having overhang or pocket features without support structure because of laser beam axis direction changing. An algorithm to extract additional information on surface contours and generate tool path has been developed for 5-axis laser manufacturing. A series of contours points information with position and its unit normal vector or tangent vector information was extracted. The laser beam center point position (x_m,y_m,z_m) and laser axis vector (i_m,j_m,k_m) through the direct slicing can be extracted. Then by post-processing, the geometrical data (x_m,y_m,z_m,i_m,j_m,k_m) (m=1,2,...n) can be transformed into 5-axis machine coordinate for generating CNC code to control tool movement . This work is the basis of 3D Laser direct manufacturing and re-manufacturing.Finaly the application of coaxial nozzle and developed CAM system in Laser direct manufacturing and re-manufacturing are introduced .It shows that the laser manufacturing will have expansive application.更多还原