增材制造中STL模型三角面片法向量自适应分层算法研究

本文提出了增材制造技术中STL模型三角面片法向量自适应分层新算法。该方法寻找与层厚t相交的三角面片的最小法向量,应用三维模型体素中x-y分辨率和STL模型中三角面片法向量与制造方向间夹角变化关系,实现STL模型的自适应分层。用此方法分层,减少了分层参数处理的复杂性,使自适应分层变得更加简单且易实现,得到的分层厚度值更加准确。由于自适应分层是在允许的误差范围内得到的分层厚度,因此在STL模型轮廓变化明显的区域分层更加精细。     

快速成型制造中分层算法的改进

在现有STL模型切片算法的基础之上,提出了一种基于STL模型坐标分层算法,该算法在读入STL模型时,据各三角面片顶点的Z坐标对其分层,然后据三角面片内部边、顶点之间的拓扑关系在层内进行求交,生成CLI片层文件,输入快速成型机.该算法优化了数据结构,减少了切片时间,提高了切片效率.     

Parasolid数据的STL变换研究

为满足CAD软件与快速成形领域的数据交换需要,提出了一种Parasolid数据的STL变换方法。利用Parasolid建模核心的PK-TOPOL-facet()函数将Parasolid模型按STL文件规则进行三角网格化,通过返回的拓扑信息构建三角面片与它的顶点和法向量的拓扑关系,并由此生成了STL文件。应用实例和Solidworks软件诊断表明,采用该方法可以将Parasolid文件变换为STL文件,生成的STL模型中无错误面和缝隙存在。     

金属板料单点渐进成形自适应螺旋线轨迹生成研究

等高线成形轨迹是现行板料渐进成形的主要加工方式。针对等高线成形方式易产生局部凹陷或破裂等问题,提出了一种基于STereo Lithography(STL)三角面片法向矢量的自适应螺旋线轨迹的生成算法。利用顶点偏置法偏置STL三角面片模型,对偏置后的模型采用自适应分层算法求取分层面与模型的交点,得到与XY平面平行的系列轮廓线,并将各层轮廓线离散成等数点,再对相邻轮廓上点的插值得到自适应螺旋线轨迹。算法实例表明,螺旋线成形轨迹能缩短成形时间,可避免等高线成形中刀位点集中造成的质量缺陷等问题。此外,双成角成形件不同区域表面粗糙度的一致性,说明自适应螺旋线轨迹在变成形角成形件上能避免等高线成形件表面粗糙度的多样性,在统一变成形角成形件表面粗糙上具有广阔的运用前景。     

带有装配定位系统的STL模型直接生成算法研究

提出了在分割STL模型上直接添加装配定位系统的方法。分析了分割后各子零件STL文件中三角面片的特点，建立了有效的带有装配定位系统的STL模型直接生成算法，保证了完整原型的尺寸和形状精度。     

基于边界分割的STL模型三维分段

针对分段注射/雕刻复合快速成型工艺的三维分段要求,提出一种STL三角网格模型的三维分段方法。以改进的翼边数据结构为基础,基于边界扩展法将STL模型分解为多个子模型,各子模型只包含相同类型面片或者垂直类型面片;以边对为基础来识别各子模型中的被遮挡边界线,由此生成垂直扫描面来分割子模型,进一步获得Z轴方向上无干涉的子模型。实例证明算法能有效实现STL三角网格模型的三维分段以满足工艺要求。     

三轴与五轴数控渐进复合成形轨迹规划

综合考虑挤压工具对待成形件曲面的可接近性和数控渐进成形效率,提出了三轴与五轴数控渐进复合成形策略及其成形轨迹规划方法。通过识别待成形件STL模型的三角面片各边的凸凹性,以三轴数控渐进成形挤压工具对模型各曲面的可接近性,将模型曲面划分出三轴数控渐进成形与五轴数控渐进成形加工的区域,进而对成形轨迹进行分区规划并在相应的曲面分区内分别生成出三轴数控渐进成形和五轴数控渐进成形加工轨迹。算法应用实例表明,该方法能够实现三轴与五轴数控渐进复合成形所需曲面分区及其成形轨迹规划与生成。     

三维模型的适应性切片方法研究

阐述了一种基于STL文件进行自适应切片的有效方法，以减少台阶效应对成形零件各种性能的影响。利用零件STL文件中小三角片法向量，计算出各小单元层侧表面最大法向量，适应性地计算出在分层方向上每层切片的厚度，确保层与层之间的台阶效应在允许值范围内。利用STL小三角片数据反向求出其切片方向对应小单元层的法向量，提高了计算速度。对该方法在直接切片时的不足进行了分析，提出了精确性修正方案。     

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。     

基于STL文件的实体分割算法研究

由于快速成型机加工尺寸的限制,难于制造尺寸较大的零件。针对这一问题本文提出一种基于STL文件格 式的实体分割算法,对STL文件分割过程中的关键问题进行了详细地论述,包括:截面轮廓的生成,截交三角面片的 处理和截面轮廓的三角化算法;通过对STL文件的分割处理,提高了快速成型系统对大尺寸零件的制造能力。     

Direct slicing and G-code contour for rapid prototyping machine of UV resin spray using PowerSOLUTION macro commands

Rapid prototyping processes produce parts layer by layer directly from 3D CAD models. An important technique is required to slice the geometric model of a part into layers and to generate a motion code of the cross-sectional contour. Several slicing methods are available, such as slicing from sterolithgraphy (STL) files, tolerate-error slicing, adaptive slicing, direct slicing, and, adaptive and direct slicing. This paper proposes direct slicing from 3D CAD models and generating a G-code contour of each layer using PowerSOLUTION software (Delcam International, Birmingham, UK). PowerSOLUTION includes two main modules: PowerSHAPE is used to build 3D CAD models and PowerMILL is used to produce G-Code tool paths. It provides macro language, picture files and cutting paths for secondary development work.The authors used macro commands to write an interface generating direct slicing from 3D CAD models and G-code contours for all layers. Most well-known controllers in the market accept the G-Code. Therefore, it is easier to apply this scheme in a CNC-machining center to produce rapid prototyping such as laminated object manufacturing (LOM) for complex geometries. The interface was successfully applied the interface to the UV resin spray rapid prototyping (UVRS-RP) machine that was developed to produce RP.     

一种经济型精密快速原型制造技术

在分析目前已有的各种快速原形制造技术缺点的基础上,提出了一种新型的基于刀具切线切割轮廓的厚层叠层制造技术。该技术通过改造三坐标钻铣床为五坐标数控铣床,利用现有的三维CAD软件,配置切片软件,达到了降低成本、提高精度和效率的目的。介绍了系统的组成方案以及初步的成形实验。     

硬质合金可转位车刀刀片的力学特性分析

为了深入研究切削过程中可转位刀具的力学特性,以硬质合金可转位车刀刀片为例,采用三维有限元方法对金属的切削加工过程进行模拟计算。考虑实际刀片几何形状及其安装角度,基于三维建模软件SolidWorks,建立了硬质合金可转位刀片三维立体模型;通过切削力试验测得切削力,利用内嵌于SolidWorks之上的COSMOS＼works对该刀片加载求解,进行应力场分析。结果表明,利用有限元方法对硬质合金可转位刀片分析的结论与其实际加工状况较为相符,为可转位刀片的优化设计提供了一定的方法和依据。     

An Effective Error-Tolerance Slicing Algorithm for STL Files

Although the STL (stereo lithography) file format is the de facto standard for the rapid prototyping industries, there are always some defects in STL files, many of which are difficult to correct. Instead of correcting the defects of bad STL files by a manual, interactive and complex approach with an STL file correction program, an error-tolerance slicing algorithm for STL files is proposed in this paper. With the detailed analysis of complex defects such as cracks and non-manifold facets, a complete topological structure for the facets model with defects is built and the layer is sliced effectively. The badly sliced contour is processed by crack-tracking and non-manifold facet travelling methods to obtain a correct contour in a relatively easy 2D way.     

Cutting path generation of linear hotwire cutter for VLM-ST

Most rapid prototyping (RP) processes adopt a solid CAD model, which will be sliced into thin layers of constant thickness in the building direction. Each cross-sectional layer is successively deposited and, simultaneously, bonded onto the previous layer; eventually, the stacked layers form a physical part of the model. A new thick-layered RP process, the transfer-type variable lamination manufacturing process using expandable polystyrene foam sheets (VLM-ST), has been developed to reduce building time by employing thick layers and to improve the surface finish of parts with a sloping surface. This paper describes the method to generate the unit shape layer (USL), the cutting path data of the four-axis hotwire cutter for the VLM-ST process. The USL is the basic unit of cutting and building in the VLM-ST process and it is also the basic unit of cutting path data of each layer. The USL includes data such as layer thickness, positional coordinates, side angles of each layer, and reference shape. The method to generate the USL is as follows: (1) the mid-slice of each layer is generated from the CAD model, (2) each mid-slice is converted into a simply-connected domain, (3) the rotation angle of the hotwire of the cutting system is calculated for each layer, and (4) the reference shape of each layer is generated for manual stacking. The procedure to generate the cutting path data of the linear hotwire cutter for VLM-ST was practically applied and verified for various three-dimensional shapes.     

激光三维内割技术——一种新型的快速原型技术

提出了一种全新的原型加工技术－－激光三维内割技术,将激光聚焦在透明（有机）材料内部,并按照计算机中零件（中部件）三维CAD模型,以控技术引导焦点在材料内部进行扫描和切割,从而使成形的零件与母材分离,达到了真正的无刀具三维切割加工。该项技术可以较大程度地克服现有各种快速原型技术的缺陷,可以用于微型制造、零件原型制造等,具有广阔的应用前景。     

可用于消失模模样制造的EPS快速成型系统

针对目前消失模模样加工发展的要求,研究了EPS快速成型技术,采用CAD/CAM技术、计算机控制技术、数控技术等知识,开发了一种EPS快速成型系统.该系统通过成型软件自动生成加工路径,将其转化成步进电机的输入信号,从而控制机械部分的运动,以电热丝气化EPS的切割方式,切割出一个完整的三维模型.此系统总体分为三大块:机械部...     

基于有效交叉点搜索的PS边界补偿重建算法

研究了快速成形数据处理中封闭PS边界曲线补偿重建算法，分析了快速成形数据处理过程中截面多边形补偿的特点及有效交叉点形成规律。提出了基于有效交叉点搜索的补偿边界重建的新算法。该算法在已开发的RPM数据处理软件中得到成功应用，可提高已有数据处理软件的稳定性，实现了RPM的OFFSET加工轨迹的生成。     

先进制造业中的激光测试与激光加工技术

论述了激光技术在先进制造业中的重要地位及主要特点,对用于制造业的激光测试和激光加工技术的激光视觉三维测量、激光层析成像、激光无损检测技术、激光振动测量、激光快速成型技术、激光焊接技术、激光切割技术、激光打孔技术、激光标记技术、激光热处理技术和激光内腔加工技术等主要技术进行了研究与分析。     

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.