快速成型中粗糙STL模型细分算法

快速成型过程中STL模型精度直接影响成型零件的成型精度,当面对粗糙的STL模型并且没有原始模型进行重新生成或者生成精度不高时,以及逆向工程三维重建得到的STL模型精度不能满足要求时,需要对STL模型进行细分以提高其表面精度,进而提高成型零件精度。为此,提出一种新的STL模型面边点拓扑信息结构,解决了两三角形面片共享边空间插值两次带来的精度误差问题;在此基础上,应用Hermite空间插值方法近似表示三角形面片三边所对应的空间曲线段,之后依据设定的规律连接空间曲线段的中点,实现对粗糙STL模型三角形面片的细分。试验结果表明:细分算法适用于形面较为复杂以及大尺寸多三角面片的STL模型,其效率可达4~n(n是细分次数),可以快速提高给定STL三维网格模型的表面精度。     

一种复杂曲面类增材制造零件分层截面生成算法

针对传统增材制造分层方法对复杂曲面类零件STL模型分层易造成部分层面轮廓线失真的问题,提出一种基于NURBS曲线的复杂曲面类零件分层截面轮廓生成算法。针对STL模型数据量大和分层速度慢的特点,采用了分组排序的求交算法进行分层,生成截面轮廓点云数据。以切平面与STL模型三角面片的交点作为NURBS曲线的型值点,设定型值点的权值,利用矩阵形式和切失边界条件确定了NURBS曲线的权因子,求解NURBS曲线的控制顶点,采用矩阵形式建立了各切片层的截面轮廓所对应的NURBS曲线方程,绘制了基于NURBS曲线的各层层面轮廓。采用基于NURBS曲线的复杂曲面类零件分层截面生成算法对燃气轮机中压缸动叶片和Ganesha模型进行了分层试验仿真和误差分析。进行了燃气轮机中压缸动叶片的打印试验,通过测量表明:采用本算法打印叶片的轮廓度偏差值符合要求,相比传统算法打印的叶片精度更高,从而验证了所提出的基于NURBS曲线的复杂曲面类零件分层截面生成算法的可行性和准确性。     

SLM快速成型中的支撑结构设计研究

在选择性激光熔融成型中,添加合理的支撑结构对保证具有复杂曲面零件的完整制造有着重要的作用。以最终成型零件的可行性及成型精度为目标,以相关实验验证为依据,对选择性熔融成型中支撑结构设计进行了研究。在STL模型的基础上,针对具有不同复杂曲面的零件,设计了按不同密集度分布的支撑,进行了系统的实验,并对不同参数支撑结构的实验结果进行了分析,得出了支撑密度、支撑当量半径、支撑半径补偿与零件表面倾斜角度间的关系,为选择性激光熔融成型中支撑结构的研究与运用提供理论依据。     

自适应细分曲面算法及在快速成型

为提高快速成型制造中STL模型切片轮廓的光滑性,提出了一种基于Loop模式的自适应曲面细分算法,首先分割出网格模型中的曲面和平面,对和尖锐边相邻的曲面三角面设计了特殊的细分规则.通过三角面顶点的平坦度和容差平坦度决定三角面是否做进一步细分,以达到自适应细分的目的.该算法在保留零件模型上尖锐特征的同时,提高了模型上曲面部分的光顺性,从而可以利用模型的全局信息获得光滑的2维切片数据.     

基于体素的机械臂连续碳纤维3D打印路径规划

碳纤维长纤3D打印对路径的连续性和复杂构型的无支撑成型均提出了需求。传统三轴熔融沉积3D打印采用平面切片和基于轮廓的路径规划方法，由于成型方向的单一性，悬空结构无法避免支撑的产生；由于采用基于轮廓的路径规划，缺少内部几何信息，无法扩展到曲面空间。针对以上问题，提出了基于机械臂的连续碳纤维3D打印曲面切片和曲面连续路径规划方法。通过三维模型的体素化处理，保证空间信息的完整性；在无支撑无碰撞约束下，分解成系列体素曲面层，保证无支撑成型；采用Fast Marching网格测地线算法，形成曲面空间的连续等距螺旋偏置路径，并对路径进行平滑优化，保证路径的连续性；最后生成用于机械臂3D打印的Gcode路径文件。通过多种三维模型路径规划仿真对比和打印实验，证明了该方法的可行性，实现了曲面分层的无支撑连续路径规划。     

基于熔融沉积成型技术的支撑算法设计

针对现有的熔融沉积成型支撑结构生成算法中耗材量大和结构不合理的缺陷,提出了一种支撑结构的生成算法。试验结果表明,该算法基于熔丝能够悬空的最大长度为判断标准来选择模型上的待支撑区域,能够减少打印耗材和打印时间。     

复杂曲面薄壁零件手板模型的快速成型研究

针对复杂曲面薄壁零件手板模型制作的问题,对手板模型的3种常用制作方法进行了对比,研究了快速成型过程的关键技术,包括:STL格式文件转换的格式设置参数设置和快速成型关键参数设置,对普通手板模型及复杂曲面薄壁零件手板模型的关键问题进行了讨论和对比。通过壁厚为0.5 mm的曲面零件设计和模型制作,给出了适合普通零件及曲面薄壁零件快速成型零件的合理工艺参数。研究结果表明,只要正确合理的选取关键工艺参数,可以避免曲面薄壁零件快速成型易出现的断壁、多毛刺的问题,能高效、高精度地制造手板模型,能满足手板模型的各项特性需求。     

快速成型技术中分层算法的研究与进展

根据对零件制造精度和效率的关注程度的不同,开发出了多种分层算法.在同等加工时间的情况下,根据加工精度的不同,将这些分层算法分为等层厚分层算法和适应性分层算法两类.通过对STL模型、原始CAD模型和点云数据的分析,讨论了两类分层算法的研究和发展,然后介绍了斜边分层算法和曲面分层算法等先进分层算法的原理和成果,最后讨论了快速成型分层算法的研究方向和趋势.     

SDI算法在成型铣刀后刀面数控磨削加工中的应用

针对成型铣刀后刀面为螺旋曲面，其数控磨削加工轨迹插补的特点，采用曲面直接插补(SDI)算法，提出了一种适合于复杂曲面类零件加工轨迹的CNC轨迹直接插补模式，为其他类多坐标复杂曲面零件精密高效加工轨迹控制提供了分析方法和借鉴。     

快速成型技术中分层算法的研究综述

作为快速成型技术中必不可少的环节,根据对零件制造精度和装配要求及效率的侧重不同,多年来多种分层算法已被国内外学者开发出来。在同等加工条件下,根据加工精度要求和层厚变化的不同,将分层算法大致分为等层厚分层算法和适应性分层算法两类。从常用的立体光刻(STL)模型、原始计算机辅助设计(CAD)模型和点云数据3种数据模型入手,简述了两类分层算法的研究和发展;介绍了采用斜边的分层算法、基于区域划分的混合算法、曲面分层算法等先进分层算法;讨论了分层算法中待解决的问题:直接分层算法的文件格式标准和轮廓的精确拟合等问题。最后,总结得出了分层算法未来的研究方向和趋势。     

Nonplanar slicing and path generation methods for robotic additive manufacturing

Additive manufacturing (AM, generally called 3D printing) has attracted great research interests due to its ability to build complex shapes. It transforms design files to functional products through slicing and material accumulation. Typically, the planar slicing strategy is used in AM to convert CAD model into accumulating layers. However, when building overhang structures and curved parts, it often needs support structures and generates a large number of planar layers, which lead to the fact that it spends more time in manufacturing. To reduce the need for support structures and decrease the number of layers, this paper presents two nonplanar slicing approaches: a decomposition-based curved surface slicing strategy and a transformation-based cylinder surface slicing method. The former is implemented based on STEP models and the latter is capable of slicing mesh models. The feasibility of the proposed methods are validated by printing two parts with a robotic fused deposition modelling system.     

Explicit correlation model of multi-source constraints for Re-design parts with complex curved surface

In precision machining of complex curved surface parts with high performance, geometry accuracy is not the only constraint, but the performance should also be met. Performance of this kind of parts is closely related to the geometrical and physical parameters, so the final actual size and shape are affected by multiple source constraints, such as geometry, physics, and performance. These parts are rather difficult to be manufactured and new manufacturing method according to performance requirement is urgently needed. Based on performance and manufacturing requirements for complex curved surface parts, a new classification method is proposed, which divided the complex curved surface parts into two categories： surface re-design complex curved surface parts with multi-source constraints（PRCS） and surface unique complex curved surface parts with pure geometric constraints（PUCS）. A correlation model is constructed between the performance and multi-source constraints for PRCS, which reveals the correlation between the performance and multi-source constraints. A re-design method is also developed. Through solving the correlation model of the typical paws performance-associated surface, the mapping relation between the performance-associated surface and the related removal amount is obtained. The explicit correlation model and the method for the corresponding related removal amount of the performance-associated surface are built based on the classification of surface re-design complex curved surface parts with multi-source constraints. Research results have been used in the actual processing of the typical parts such as radome, common bottom components, nozzle, et al., which shows improved efficiency and accuracy of the precision machining for the surface re-design parts with complex curved surface.     

DIRECT AND ADAPTIVE SLICING ON CAD MODEL OF IDEAL FUNCTIONAL MATERIAL COMPONENTS （IFMC）

A brand new direct and adaptive slicing approach is proposed, which can apparently improve the part accuracy and reduce the building time. At least two stages are included in this operation: getting the crossing contour of the cutting plane with the solid part and determining the layer thickness. Apart from usual SPI algorithm, slicing of the solid model has its special requirements. Enabling the contour line segments of the cross-section as long as possible is one of them, which is for improving manufacturing efficiency and is reached by adaptively adjusting the step direction and the step size at every crossing point to obtain optimized secant height. The layer thickness determination can be divided into two phases: the geometry-based thickness estimation and the material-based thickness verifying. During the former phase, the geometry tolerance is divided into two parts: a variety of curves are approximated by a circular arc, which introduces the first part, and the deviation error between the contour     

Direct Slicing from PowerSHAPE Models for Rapid Prototyping

Rapid prototyping processes produce parts layer by layer directly from CAD models. An efficient method is required to slice the geometric model of a part into layers. Several slicing methods are introduced in this paper: slicing from STL files; tolerate-errors slicing; adaptive slicing; direct slicing; adaptive and direct slicing. PowerSHAPE is a powerful package for building models, and it provided macro language and picture files for its secondary development work. To meet rapid proto-typing slicing demands, the author proposes a direct slicing approach based on PowerSHAPE models. In this method, lines, arcs and Bezier curves are used to describe the section contours. This approach can be used in stereolithography, selective laser sintering, fused deposition modelling, and other rapid prototyping processes, e.g. laminated object manufacturing. It may be the future solution to existing slicing problems.     

数控线切割加工空间曲面CAD/CAM技术研究

目前国内加工空间曲面零件通过采用锥度切割装置使电极丝倾斜一定角度来实现锥度切割,这种方法易产生的加工误差较大.论文在五轴联动数控线切割加工系统的运动分析的基础上,建立了直角坐标下空间曲面零件线切割加工成型的数控模型,阐述了利用G代码合成空间曲面的方法,提出了运用模块化技术设计空间曲面线切割五轴联动数控系统上位机软件设计方案,为空间曲面线切割CAD/CAM系统的研究提供了依据.     

Surface accuracy optimization of mechanical parts with multiple circular holes for additive manufacturing based on triangular fuzzy number

Surface accuracy directly affects the surface quality and performance of mechanical parts. Circular hole, especially spatial non-planar hole set is the typical feature and working surface of mechanical parts. Compared with traditional machining methods, additive manufacturing (AM) technology can decrease the surface accuracy errors of circular holes during fabrication. However, an accuracy error may still exist on the surface of circular holes fabricated by AM due to the influence of staircase effect. This study proposes a surface accuracy optimization approach for mechanical parts with multiple circular holes for AM based on triangular fuzzy number (TFN). First, the feature lines on the manifold mesh are extracted using the dihedral angle method and normal tensor voting to detect the circular holes. Second, the optimal AM part build orientation is determined using the genetic algorithm to optimize the surface accuracy of the circular holes by minimizing the weighted volumetric error of the part. Third, the corresponding weights of the circular holes are calculated with the TFN analytic hierarchy process in accordance with the surface accuracy requirements. Lastly, an improved adaptive slicing algorithm is utilized to reduce the entire build time while maintaining the forming surface accuracy of the circular holes using digital twins via virtual printing. The effectiveness of the proposed approach is experimentally validated using two mechanical models.     

多点闭环成形中基本体群曲面描述方法的研究

探讨了在多点闭环成形中，基本体群曲面的数值矩阵描述和离散傅里叶变换描述方法；通过实例验证了离散傅里叶变换描述方法的有效性和对随机测量误差的鲁棒性；从闭环成形的实验结果可以看出，应用离散傅里叶变换描述能够体现板材多点成形时各基本体之间的相互耦合关系，提高了多点成形工件的精度。     

High-precision detection of focal position on a curved surface for laser processing

A new technique for detecting the focal position of a curved surface provides several advantages both in research and industrial applications. The quality of patterns lasered on a roll surface is determined by the precision of the focus detection, and surfaces of the massive rolls used in laser fabrication can be difficult to adjust properly using conventional technologies. Here, a unique method for detecting the focal position of a curved surface based on the reflected profile of a laser beam is presented. The versatility of the proposed technique results from being able to adjust the laser beam based on changes in the shape and diameter of the beam spot when the specimen surface deviates from the focal plane. A theoretical model based on three-axis movement is proposed, and experimental setups are developed based on the model. Analysis of the obtained results enables high precision positioning of the specimen and identification of the focal point. Furthermore, the presented technique can be used to locate the focal point on any curved surface. Therefore, the theoretical model, analysis results, and focal detection method can be combined in an algorithm for a novel auto-focusing system that can be applied to laser processing of curved surfaces, such as fabricating microgrooves, or engraving roll surfaces in printed electronics.     

Recommended slicing positions for adaptive direct slicing by image processing technique

Build time and accuracy are two contradicting issues that have been a major concern in rapid prototyping, and have led to the development of many slicing approaches including those applying adaptive slicing, direct slicing, and adaptive direct slicing concepts. Presented in this paper is an approach for adaptive direct slicing that applies image processing technique to determine appropriate thickness for each sliced layer and to recommend slicing positions on a 3D CAD model. Two orthogonal views of a model are captured and converted to be edge images before being analyzed, and based on the surface complexity on the two edge images, slicing positions are recommended. These positions are passed to the CAD software for slicing activities. This adaptive direct slicing approach has been implemented on LabVIEW platform and compared with uniform direct slicing approach and uniform cusp height approach. The results show that this slicing approach improved slicing performance by reducing the number of layer which has a direct impact on build time while maintaining surface quality at the same level as the thin uniform direct slicing. Since its inputs are the images of a CAD model instead of the model itself, this adaptive direct slicing supports any CAD software.