压铸模具分型线的自动确定方法研究

提出了一种自动确定模具分型线的方法,该方法首先离散铸件的实体造型的边线和面,并把离散点投影到主平面上,然后采用改进后的AIpha Shapes算法计算主平面上离散点的外轮廓线;再根据脱模方向,通过外轮廓点向铸件做射线,求得射线与铸件边线的交点,并连接交点得到铸件上的轮廓线;最后通过优化评价这些轮廓线得到分型线.实例结果显示,该方法具有较好的实用性和较高的效率.     

网格曲面数控加工编程分型线提取算法

针对复杂网格曲面分型线提取精度和效率不高的问题,根据非封闭自由曲面和封闭自由曲面的拓扑信息和几何特点,提出了2种基于投影方法的分型线提取算法. 对非封闭模型,首先将模型投影到平面并重新三角网格化,然后提取投影三角网格的边界,最后以平面三角网格的边界为检索信息在原始网格中检索得到自由曲面的分型线. 对封闭模型,根据模具分模的几何原理,提出通过建立封闭自由曲面凹模和凸模离散几何模型的方法提取封闭自由曲面的分型点,然后通过一环邻域点搜索法对分型点排序,得到分型线. 实验结果和数据分析表明,两种方法可以精确、高效地提取非封闭和封闭自由曲面的分型线,并可以确保分型点都是三角网格曲面的顶点.     

从投影图重建二次曲面

首次定义了二次曲面截交线——位于三维空间的二次曲线的坐标概念,建立了截交线与其投影曲线坐标之间的约束关系,给出了从二次曲面正投影的轮廓线及截交线的投影重建二次曲面和截平面的计算公式,据此建立了从轮廓线和截交线投影重建二次曲面体的方法。     

多自由曲面产品注塑模具分型线的自动确定

为有效地确定多自由曲面产品模具分型线问题,提出了一种将特征识别技术和有限元方法相结合的模具分型线确定方法。在该方法中,首先,提出了基于图的特征识别方法来对产品中的侧凹特征进行识别,并在识别的基础上对产品模型进行简化;然后,提出了基于有限元的离散方法,对简化的产品模型的所有组成面进行离散,并根据网格面的可视性来判别组成面的可视性;最后,将产品中的所有组成面分成可视面组、不可视面组和退化面组,并通过抽取可视面组或不可视面组的最大边环来确定模具的分型线。研究实践表明,通过该方法可以有效地解决多自由曲面产品模具分型线的确定问题,提高模具设计的效率。     

主法向方向单调自由曲面简易骨架图生成算法

利用骨架图进行三维模型的相似性比较研究在工程中有着重要的应用,可以有效地解决检索与重用等问题。本文给出了一种用简易骨架图描述主法向方向单调自由曲面(沿曲面的主法向方向的任一直线与该曲面最多只有一个交点)的方法。首先,求自由曲面的总法向量,按照总法向量的反方向将自由曲面投影到二维平面上,得到投影曲面;然后,求取投影曲面的骨架点和骨架线;最后,将投影曲面的骨架线按照自由曲面的总法向量方向进行柱面拉伸与自由曲面产生交线,该交线就是自由曲面的简易骨架图。并将本文算法与MATLAB中求骨架算法进行比较,实验表明,本文所得的简易骨架图可以更好地描述主法向方向单调自由曲面的几何与拓扑特征,为比较自由曲面的相似性提供了理论技术基础。     

冲裁模具压力中心的确定

均质板料在同一工位冲裁时，冲裁件上所有的冲裁力相互平行，可合成为一个合力。合力的作用点称作模具的压力中心。在冲裁时应保证压力中心与冲床滑块中心相重合，否则会产生偏心弯矩，使冲床和模具加速磨损，降低冲裁件质量，甚至发生事故。所以压力中心的确定是模具生产中的重要一环。本文就教学中的体会和实践，对冲裁件压力中心的确定，介绍以下３种方法供参考。一、几何作图法１．内、外轮廓有十字对称线的制件该件的十字线交点即为压力中心。如图１和图２所示：交点Ｏ为制件的压力中心。２．圆弧线轮廓（切口）制件按弧长用２原则等分…     

基于主元分析的空间手写平面化预处理技术

为了将空间手写识别回归为平面手写识别问题,提出了一种新型的空间手写识别平面化预处理技术,采用基于主元分析（PCA）的投影算法对空间手写字符轨迹进行了平面化处理。该算法中,投影平面的确定仅依赖于手写字符轨迹采样点集本身的统计特征,故当书写角度发生变化时,投影平面也会随之产生适应性变化,以产生最佳的投影效果;最后在实验中,对比了指定初始平面投影法和主元分析投影法在不同书写角度下的投影效果,实验结果直观地证明了该投影算法的有效性。     

基于UG MoldWizard软件注塑模分型面设计初探

注塑模具分型面设计是模具设计中的重要部分,首先介绍模具分型面的选择原则,通过典型案例介绍UGMoldWizard四种分型面的创建方法.提出注塑模分型面设计的关键是判斯创建的分型线是否在同一个平面或是曲面内,再采用相应创建曲面的方法创建分型面.目的是为类似注塑件分型面的创建提供参考.     

基于Offset技术的汽车覆盖件边界光顺方法

针对模具型面设计过程中处理零件外边界凹入部分的工艺补充的问题,提出一种基于平面多段线Offset技术的零件边界光顺算法。在冲压方向上对零件外边界进行投影,基于滚柱法的原理,给出分段投影轮廓线的距离为R的Offset曲线并以圆弧相连。根据闭合的Offset曲线的自交点判断零件投影轮廓光顺区域,得到的光顺区域端点与空间零件外边界的真实光顺区域端点一一对应。结合零件外边界的几何信息,用NURBS曲线及蒙皮法在已判定的光顺区域构建光顺曲线及光顺曲面。采用Offset技术可以精确找出所有需要光顺的区域,可避免出现细小误差和修正问题,具有一定的鲁棒性。将算法集成到自主开发的冲压成形分析软件KMAS模具型面设计模块,并与Dynaform软件和Pam-Stamp软件的光顺结果相比较,试验表明该算法具有很好的有效性和可靠性。     

3D打印制件外轮廓线的自适应分层算法研究

针对3D打印三维模型直接转换成STL文件进行切片分层处理过程中,存在模型表面信息缺失、打印精度不高等问题,提出了面向3D打印制件外轮廓线的自适应分层算法。该算法利用Z轴方向特征曲线的方法得到打印制件外轮廓曲线,采用微元思想对模型分段处理,确定打印方向与外轮廓切线夹角的关系,运用概率统计、叠加求和等数学理论求出每一层切片的自适应分层方法。通过实例打印表明,该算法减少了转换成STL文件时的信息缺失,提高了3D打印的精度与效率。     

Feature extraction from freeform molded parts for moldability analysis

In the design of plastic injection molds, the depressions and protrusions (DP) preventing the removal of molded part from mold are referred to as undercuts. This paper describes an approach to recognize DP feature within the curvature region representation based on the curvature properties of entities in B-rep model. The recognized depression features and the concave transitions between protrusion features are potential undercuts which affect the choice of parting directions of the molded part. The possible withdrawal directions of the potential undercuts are derived by geometric reasoning and visibility map computation. This method can recognize isolated and intersecting features with planar, quadric, and freeform surfaces. The identified potential undercuts with their possible withdrawal directions can provide decision support information for mold design such as selecting parting direction, parting lines and surfaces, etc. The case study is presented to verify the feasibility of the developed method.     

Algorithm for automatic parting surface extension in the mold design navigating process

This study focused on the planning and development of an algorithm and process for automatic parting surface design under the CAD software architecture. Relating to the smooth opening of a mold, the parting surface is an important step of mold design. The parting surface can be categorized into the main parting surface and the shut-off parting surface. This study developed an algorithm of extension rules for the main parting surface and determined the contour vector and geometric relationship via computer software. It can realize the main parting surface automatic extension and can be embedded into a web-based mold design navigating process. Through a standardized design process, it can reduce the number of mouse clicks by 90%, enabling users to rapidly complete mold designs, reduce design errors, and improve efficiency.     

DISCRETIZATION APPROACH USING RAY-TESTING MODEL IN PARTING LINE AND PARTING SURFACE GENERATION

Surface classification, 3D parting line, parting surface generation and demoldability analysis which is helpful to select optimal parting direction and optimal parting line are involved in automatic cavity design based on the ray-testing model. A new ray-testing approach is presented to classify the part surfaces to core/cavity surfaces and undercut surfaces by automatic identifying the visibility of surfaces. A simple, direct and efficient algorithm to identify surface visibility is developed. The algorithm is robust and adapted to rather complicated geometry, so it is valuable in computer-aided mold design systems. To validate the efficiency of the approach, an experimental program is implemented. Case studies show that the approach is practical and valuable in automatic parting line and parting surface generation.     

一种模具脱模方向自动判定及优选算法

提出一种自动判别模具脱模方向的算法。该算法以基于图的特征识别所获得的特征作为研究对象,通过特征间可视性分析运算来判断零件潜在的脱模方向,引入脱模方向判定原则,最终确定出脱模方向。该算法可解决存在多特征复杂零件脱模方向的判定问题,不但可以获得最优脱模方向,还可得到侧凹特征的相关信息。在UG平台上开发的自动脱模方向判别系统,提高了模具设计中该环节计算的效率和精度,为模具设计后续工作提供可靠保障。     

基于事例推理的模具分型面设计方法研究

在全面分析分型面自动设计方法的基础上，提出了基于事例推理的注塑模分型面设计方法，给出了基于事例推理的分型面设计总体框架。运用特征造型技术进行塑件三维建模，以主形状特征为索引构建了含有分型面信息的塑件事例知识库。采用正向推理策略与相似性求解相结合的方法，实现了模具分型面的自动推理设计，给出了分型面位置设计的推理方法与流程，提高了模具设计的质量和效率。     

CAD APPROACH FOR PLASTIC MOULD PARTING DIRECTIONS OPTIMIZATION

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Experimental Study of Shrinkage Displacements of Points on Injection Molded Parts

The existing research on shrinkage of the injection molded plastic part mainly focuses on various shrinkage ratios of the part dimensions,and the relevant experimental studies belong to mere dimension measurement after demoulding.Obviously,measuring after the plastic part is demoulded from the cavity can not offer shrinkage displacements of points on the plastic part.However,shrinkage displacements of points on an injection molded plastic part are essential for exposing the inner relation among shrinkage ratios of various dimensions of the part.So visualization of the in-mold plastic part which can indicate the location relationship between the part and the cavity is needed.In this paper,a visual injection mold was fabricated by adopting the half mold structure and light transmission manner.With the visual mold,in-mold shrinkage images of injection molded plastic parts were photographed after the plastic part stayed in the injection mold for 24 h.By means of digital image processing of the in-mold shrinkage images,the experimental data of shrinkage displacements of points on injection molded parts were researched.From the experimental data,it is found that shrinkage directions of points on an injection molded part are related with both positions of the gate and of the part centroid,and either the gate or the centroid will exert more influence on the shrinkage direction of some point which is closer.Furthermore,some point at the later filled area has more shrinkage distance than the point at the earlier filled area.Combination of shrinkage directions and shrinkage distances of points on an injection molded part determine shrinkage ratios for various dimensions of the part,and shrinkage directions are more influential to shrinkage ratios of dimensions.This experimental research of shrinkage displacements offers a unique approach to understand the shrinkage principles of injection molded parts.     

线壳盖塑料模具设计

介绍了在CAD和Pro/E环境下一副单分型面注塑模具的设计过程。本设计着重介绍了模具设计的整个流程,包括塑件及材料分析、分型面与排气系统设计、浇注系统的设计、成型零件设计、冷却系统等部件的设计,同时分析了该模具的注射过程。模具结构紧凑,工作可靠,操作方便,生产效率高。