Image processing-based accessibility analysis method for determining undercut-free parting direction

In injection molding, demoldability of a part without the use of a side core is possible only if all of its surfaces are fully accessible in the parting direction. A mold surface may be fully accessible from some directions, but may not be accessible from other directions. Therefore, to determine the undercut-free parting direction, an algorithm is developed that evaluates the accessibility of each part surface from a set of directions (called as candidate parting directions) by using image processing techniques. In the proposed methodology, the surface accessibility is determined by comparing the projected area of each surface on the image plane in the presence of other part surfaces to that of the same surface in the absence of other part surfaces. The algorithm can be used to determine the accessibility of planar, ruled, and free-form surfaces without tessellating the part surfaces. The algorithm includes a method that can also successfully classify surfaces that are oriented perpendicular to the parting direction. The surface classification can be used to identify the undercut-free parting direction, recognize the various undercut features, and form the visibility maps. The accuracy of the algorithm depends upon the number of pixels used to represent the part on the computer screen. The method has been successfully implemented, and test results are discussed in this paper.     

注塑模具分型线自动搜索技术研究

提出了一种自动搜索模具分型线的方法。该方法首先依据脱模方向确定与之垂直的平面 ,并将塑料制件向该平面投影 ,得到模具分型线的主轮廓线 ,然后建立主轮廓线与制件表面上的边线和顶点投影映射关系 ,从中可以得到多种候选分型线 ,最后根据分型线的评价因子计算各分型线的优化目标函数值 ,确定最佳的分型线。实例测试表明 ,该方法具有较高的效率和实用性。     

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。     

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。     

Recognition of undercut features and parting surface of moulded parts using polyhedron face adjacency graph

An injection or die-casting mould is an assembly of parts containing an impression into which molten material is injected. In this article, the undercuts present in mould parts are divided into basically two parts: completely visible and partially visible. A graph-based approach is proposed to identify these undercuts even for the free form objects. Unlike conventional graph based methods a new polyhedron face adjacency graph (PFAG) is proposed with the key concept of visibility of undercuts by using Bezier surface. A rule-based approach is also discussed to automatically generate an optimal parting surfaceof irregular moulded parts. Since the generation of parting surface plays an important and effective role in mould – die design, thus it is essential to develop a simple and robust algorithm based on proposed methodology, which can effectively tackle the problem. Different case studies show that the proposed method can recognize various undercut features without much difficulty.     

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。     

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.     

往复式骨架油封模具自动化设计技术研究

针对骨架油封模具设计周期长的问题,通过对往复式骨架油封进行研究,以模具设计为出发点,对模具中关键分型线的确定方法进行了研究,并分析了余胶槽、顶杆和相关壁厚等关键地方的变形规律,建立了数学模型。采用自顶向下的建模方法对模具总体装配及零件进行建模,依据模具设计规则,从油封三维模型的几何特征中提取构成模具型腔的各个零件及其分型线的关键特征,形成封闭的型腔特征曲面,进而利用这些特征曲面切除装配结构中的各个模板零件内侧特征,获得模具型腔结构特征,完成模具详细设计。该设计方法实现了骨架油封模具随油封尺寸自动变形设计,大大提高了设计效率。     

模具自动分型算法研究综述

系统总结几种国内外较流行的模具分型方向求取算法，根据其不同的数学建模方式对其进行分类，并对各种算法的优劣进行了详细的分析、比较，在实例分析的基础上，提出了应进一步研究的方向与重点。     

DESIGN TECHNOLOGY FOR INJECTION MOLD PARTING SURFACE BASED ON CASES AND KNOWLEDGE

On the basis of the comprehensive analysis about the automatic generation of the injection mold parting surface,the parting surface design method which introduces knowledge and case-based reasoning (CBR) into the computer-aided design is described by combining with the actual characteristic in injection mold design,and the design process of case-based reasoning method is also given.A case library including the information of parting surface is built with the index of main shape features.The automatic design of the mold parting surface is realized combined with the forward-reasoning method and the similarity solution procedure.The rule knowledge library is also founded including the knowledge,principles and experiences for parting surface design.An example is used to show the validity of the method,and the quality and the efficiency of the mold design are improved.     

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.     

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.     

Algorithm for automatic undercut recognition and lifter design

When having internal undercut in the ejection direction, the finished plastic product cannot be directly removed from the mold. Through lifter design, during the ejection process, the lifter can eject products in the upward direction and make lateral movements to successfully leave the undercut location to part from the mold. Under the framework of CAD software, this study developed the undercut feature recognition, integrated the mold design, and automated lifter production. Based on the geometric relationship of the internal undercut surface, edge, and point of the product model, this study summarized a set of recognition rules. Through computer programming calculation and judgment, the proposed method can automatically recognize undercuts to reduce the labeling time at the conceptual design stage and record the undercut width and length in feature parameters. At the mold design stage, through the acquisition and calculation of its parameters, it can automatically produce a suitable lifter during the architecture of the web-based mold design navigation process. Through standardized design process, it can reduce 90 % of mouse clicks and design time to guide users to quickly complete the design, while reducing design errors to improve working efficiency by the automatic integration function.     

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.     

面向制造的曲面设计系统

为了支持面向制造的曲面设计,提出了一个基于计算机辅助设计／计算机辅助制造系统的嵌人式计算平台,该计算平台主要包括约束信息建模和可制造性分析2个功能模块。通过对曲面可制造性判据的抽象,建立了应用信息模型,用于从曲面几何形状中提取制造约束信息。应用于曲面加工问题,给出了根据约束信息计算可行刀具方向的具体方法。面向模具零件分型曲面的设计,建立了可制造性分析工具。针对一个雕塑曲面零件设计实例,通过对模具分型方向和加工约束进行分析,给出了可行的分型曲面设计结果,验证了所提出的曲面可制造性分析方法的可行性。     

基于Pro/E的浏阳河酒瓶模具设计

基于Pro/E环境介绍了酒瓶模具的设计方法,玻璃模具有其自身的特点,其中重要的是分型面的建立方法,本文以浏阳河酒瓶为例,提出一种建立酒瓶模具分型面的新方法,即平整和复制方法.该方法易于掌握,在酒瓶模具的设计中有广泛的应用前景.     

基于图的注塑产品侧凹特征识别技术的研究

提出一种基于图的注塑产品侧凹特征识别方法：首先将产品属性面邻接图中的节点和边进行属性扩展，以形成产品的扩展属性面邻接图；在此基础上，应用扩展属性面邻接图对凹、凸及通孔三种类型的侧凹特征进行描述，并采用子图匹配的方式将侧凹特征的子图从产品属性面邻接图中识别出来；对于识别出的侧凹特征，特征方向可采用可视图的方法确定，并通过分析识别出的侧凹特征的特征方向来最终确定产品的优化脱模方向。实例测试表明，该侧凹特征识别方法可以有效地识别注塑产品中的侧凹特征，提高侧凹特征的识别效率。     

Fundamental study on releasability of molded rubber from mold tool surface

In compression or injection molding of rubber products, small pieces of residual rubber often remain on the metal mold surface after releasing the product. This is caused by excessive localized adhesion to the mold surface. Therefore, cleaning of metal mold surface must be often performed, which results in longer molding cycle time, and the lifetime of metal mold is often reduced. In this study, the separation forces between molded rubber and metal mold surfaces are measured with a tensile tester to evaluate the releasability of molded rubber from the metal mold surface. Mold surfaces treated by various surface coatings and surface modification methods including EB polishing were tested and compared. Experimental results show that the separation force between molded rubber and metal mold surfaces depends on the true contact area between them and the chemical composition of the metal mold surface. The separation force decreases with a decrease in contact area. The chromium content at the metal mold surface significantly reduces the separation force. EB polishing is one of the most effective surface treatments for metal molds since the real contact area can be decreased while also decreasing the surface roughness of the tool surface in a short time. Electron beam melting is also shown to be an effective method of distributing chromium uniformly on the metal mold surface.     

Characteristics analysis of cellular bucket brigades with different constraints

Reconfigurable machines are used in various manufacturing processes increasingly, so that the system could be adapted to successive market changes, changes in customer requirements, and competition among manufacturers. This makes necessary designing reconfigurable machines that can get into the market as soon as possible. Injection molding machines are an example of an equipment that requires reconfigurability, and the mold is one of the machine modules requiring further attention. This article provides a design methodology that helps designers to decide which mold configuration is appropriate to produce a molded part family. Proposed methodology brings together classical methodologies and design modern tools, and establishes a sequence of activities during the product architecture. This adjustment provides a useful tool in the conceptual definition of the mold architecture and facilitates the preliminary design of molds. Decisions are based on nature and predominant features of conventional products which are manufactured by injection molding. A characterization of common products obtained by molding is proposed as a support database for developing the methodology. In addition, in this work, a case study is developed in order to illustrate how the methodology can be performed. Benefits and advantages of the model are summarized as well.     

Automated Generation of Lifters for Injection Moulds

An algorithm for automated identification of undercuts and the creation of the lifter subassembly in plastic injection mould design is described. The algorithm is suitable for injection mould design in a 3D mode. The input to the software is a 3D part model, parting direction and lines, and a mould-base. The software then generates the lifter subassembly and places it properly in the mould-base. This is accomplished in four steps. First, the so-called virtual core and cavity are generated without considering any undercuts. Undercut faces on the part are then identified and undercut groups are formed. Secondly, the releasing direction of each undercut group is found. Thirdly, for each undercut group, a lifter head based on its releasing direction is created. Fourthly, other standard components of a lifter assembly are retrieved and attached to the corresponding lifter head within the mould-base at the correct location. A case study is presented that illustrates the efficacy of the technique for the automated design of lifters to fulfil a real industrial requirement.