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A 3D CAD knowledge-based assisted injection mould design system1 IntroductionIn recent years the plastic product manufacturing industry has been growing rapidly. A very popular moulding process for making plastic parts is injection moulding. The injection mould design is critically important to product quality and efficient product processing. Mould-making companies, who wish to maintain the competitive edge, desire to shorten both design and manufacturing leading times by automating the design process. Thus, the development of a computeraided injection mould design system (CAIMDS) is becoming a focus of research in both industry and academia.Recently published papers show that research in automatic mould design focuses on individual components of the mould process. For example Ong et al. and Ravi focused their research on the feeding system. Wang et al. focused their research on the ejection system. Others focus their research on the general design. Most research done on the general injection mould system can be classified into two areas:(a) functional, conceptual and initial mould designs;and (b) algorithms to automate mould generation.Functional, conceptual and initial designs of the injection mould are applied mainly to the pre-mould design. Such design involves selecting a suitable mould base, arranging the cavity layout, designing the runner and designing the gate. The objective is to come up with a large number of very different product ideas for a certain requirement. Britton et al. addressed injection mould design from a functional perspective by presenting the Function-Environment-Behaviour-Structure (FEBS) model.The study fostered a wide range of design alternatives. Costa and Young proposed a product range model (PRM) to support the reuse of design information in variant design cases. The general structure of a PRM is defined in terms of design functions linked with sets of design solutions, interactions between potential solutions and knowledge links. Ye et al. presented an approach to automatic initial design with algorithms that calculate the cavity number and automatically lay out the cavity. The initial injection mould design involves extensive empirical knowledge of the structure and functions of the mould components. Thus, a lot of researchers adopt a knowledge-based approach. Several knowledge-based systems (KBSs) were developed to advise plastic material selection, capture injection mould part design features, analyse mouldability, automate the mould design process and develop mould design for manufacture. Examples of such systems are GERES (Nielsen), PLASSEX(Agrawal and Vasudevan), EIMPPLAN-1 (Chin and Wong), CADFEED ( Ong et al.), ICAD (Cinquegrana), IKMOULD (Mok et al. ) and KBS of Drexel University (Tseng et al.). However, these KBSs consider only certain aspects of the total design.As for the automatic generation of an injection mould, a number of theoretical research works were conducted to automatically determine the parting direction, to determine the parting line, to generate the parting surface, to recognise undercut features and to generate the core/cavity. Ravi and Srinivasan presented nine rules that can be used by the mould design engineer to develop a suitable parting line in the product. These rules are projected area, flatness, draw, draft, undercuts, dimensional stability, flash, machined surfaces and directional solidification. Hui and Tan proposed the sweep method to form the cavity and core. The cavity and core are generated in a number of steps. Sweeping the mould part in the draw direction generates a solid. One end of the swept solid is subtracted from the first mould block. The other end of the mould block is subtracted from the mould part. The results of the above steps are subtracted with the part at the closed position to obtain the cavity and core. Shin and Lee proposed a method of core and cavity development so that the side cores and corresponding core and cavity plates can be generated. This method is composed of 3 steps. The designer determines the parting line that separates the product into 2 groups of faces. Each group face has the parting surface attached to it. Then external faces are added to each group face. Shin added that a mould could be made up of many pieces in addition to the cavity, core and side cores. Hui studied the mouldability of an injection mould based on an external and internal undercut analysis only for polyhedral solids. A blockage concept is presented to determine the main parting direction and a subdivision technique is developed to evaluate the geometry of an undercut. Chen et al. introduced the concept of visibility maps (V-maps) of the pockets to determine the parting direction. The method did not take into account internal undercuts. Fu et al. and Nee et al. gave a new classification of undercuts according to the external loops and the internal loops of a moulded part. The parting direction is then determined based on the proposed parting direction criteria considering the directions, location, number and volumes of undercut features. Fu et al. proposed an approach to generate the parting surface by extruding the parting line edges and create the core/cavity block using the Boolean regularised difference operation (BRDO). A methodology that generates non-planar parting lines and surfaces is presented by Nee et al. Wong et al. proposed a method to determine the cutting plane of a complex shaped product. Their method uses an algorithm that slices the product. The parting line and surfacesformed by this method are planar.Current research on automatic mould design is on going. However, some methods can be quite theoretical and the mould design can have a complicated product geometry. Most mould development activities involve a high level of skill, a wide variety of design expertise and knowledge. Due to the fact that automatic mould development is still far beyond the current technology, it is more reasonable to provide intelligentrules or guidelines that prevent the design from conflicting with design constraints. These rules also provide interactive tools in the detailed mould design environment. This paper presents an interactive knowledge based injection mould design system (IKB-MOULD).This system integrates the initial mould design and detailed mould design with both knowledge base and interactive commercial CAD/CAM software.The next section of this paper outlines an analysis of the injection mould design process based on the mould designers point of view. A later section introduces the basic structure of our IKB-MOULD for injection mould design. A case study of the injection mould design for a plastic product in IKB-MOULD is then presented. The conclusion and future work is located in the last section.2 The injection mould design process requirement analysisAn injection mould design is composed of two steps: the initial design and the detailed design. The initial design is composed of decisions made at the early stage of the mould design, such as the type of mould configuration, the number of cavities, the type of runner, the type of gate and the type of mould base. The detailed design is composed of the insert (core/cavity) design, the ejection system design, the cooling and venting component design, the assembly analysis and the final drafting. To develop a good CAIMDS, an analysis of what they have and what they want needs to be performed.What they have: The customers requirements for the product. This includes the detailed geometry and dimension requirements of the product. An existing mould design library. This library covers the standard or previously designed components and assemblies of the mould design, for example, the mould base (the fixed half and the moving half) and the pocket (the fixed half and the moving half). An expert knowledge in injection mould design. Expert knowledge of both initial and detailed designs for the injection mould is obtained mainly from experienced mould designers. Such knowledge includes material selection, shrinkage suggestion, cavity layout suggestion and others.What they want: An intelligent and interactive mould design environment. Mould design is often composed of a series of design procedures. These procedures usually require certain mould parts to be created and existing mould parts to be assembled. Such a mould design environment need not be fully automatic, especially for complicated products with many undercuts. An intelligent and interactive environment will be a good choice to integrate some useful automation algorithms, heuristic knowledge and on-line interaction by the experienced mould designer. Standard/previous designed components/ assemblies(product-independent parts) management. Apart from the core and cavity, an injection mould has many other parts that are similar in structure and geometrical shape that can be used in other injection mould designs. These parts are independent of the plastic mould products. They are mostly standard components that can be reused in different moulddesigns and mould sets. Useful tools (including solid design and analysis calculation) in the core and the cavity (product dependent parts) design. Geometrical shapes and the sizes of the core and cavity system are determined directly by the mould product. All components in such a system are product dependent. Also, these parts are the critical components in the mould design. Their geometrical requirements may be complicated. Thus, some tools developed to design the core and the cavity based on partial automation and partial interaction can be quite useful. Design for assembly. In conventional CAD/CAM systems, moulds are represented and stored as a complete geometric and topological solid model. This model is composed of faces, edges and vertices in a three dimensional (3D) Euclidean space. Such a representation is suitable for visual display and performing geometrically computation-intensive taskssuch as engineering analysis and simulation. However, this form is not appropriate for tasks that require decision-making based on high-level information about product geometric entities and their relationships. Mould designers prefer a design for assembly environment instead of a simple solid model environment. This idea is also presented in Ye et al.swork. A design for manufacture. A complete injection mould design development cycle can be composed of the mould design and mould manufacturing process. To integrate CAD/CAM into the mould design, the manufacturing features on the mould should be abstracted and analysed for the specific NC machine.Both the process plan and the NC code should be automatically generated to enable the final designed mould to be manufactured. A design for engineering drawings. For many companies, the injection mould design has to be represented in the form of engineering drawingswith detailed dimensions. CAD/CAM tools that are able to automatically generate these engineering drawings from the final injection mould design will be useful.Based on the above analysis, our research focus is to develop techniques to represent what they have and what they want.Representing what they want is actually the representation of the knowledge and injection mould object. Developing what they want means to integrate the representation with intelligent and interactive tools for the injection mould design into a completed design environment. Therefore, an IKB-MOULD is proposed for mould designers to realise the above two requirements.三维CAD知识付诸注射模具设计系统一、介绍近年来，塑料制品制造行业迅猛发展。注塑成型是一种非常受欢迎的塑料零件成型方法，注塑模具对于产品质量和高效的制品加工有着十分重要的意义。想要保持竞争优势的模具制造公司，希望通过实现设计过程的自动化来缩短模具设计和制造的周期。因此，计算机辅助注塑模具设计系统（CAIMDS）的发展正逐渐成文工业界和学术界研究的焦点。最近发表的论文表明，自动化模具设计的研究主要集中于单个组件的模具工艺。例如，翁等人以及拉维集中研究送料系统；王等人主要研究喷射系统；其他人研究的重点是总体设计。一般注塑模具系统的研究大多数可以分为两个领域：功能、概念和初步模具设计以及自动化模具生成算法。注塑模具的功能、概念和初步设计主要用于前模设计。此类设计包括选择一个合适的模架、安排型腔布局、设计分流道以及设计浇口，目的是为了对于一个特定的要求提出大量不同的产品理念。布里顿等人通过提出功能-环境-行为-结构模型，从功能的角度解决了注塑模具设计的问题。这项研究制造出了很多设计的互换件。科斯塔和杨提出了产品范围模型，以支持不同设计案例中设计信息的再利用。产品范围模型的总体结构大致是从设计功能方面定义的，该功能的设计与各系列设计方案以及潜在方案与知识链之间的内在联系息息相关。叶等人提出了一种自动化初始设计的算法，能够计算出型腔数并自动化地设计出型腔。注塑模具的初始设计涉及对模具组件广泛的实验知识。因此，许多研究人员采用以实验知识为基础的方法。他们开发了一些以实验知识为基础的系统，用来建议塑料材料的选择、捕获注塑模具零件的设计特征、分析可塑性、自动生成模具设计工艺以及开发产品的模具设计。这样的系统有诸如GERES (尼尔森), PLASSEX（阿格拉沃尔和瓦苏德万),EIMPPLAN-1（秦和王),CADFEED(翁等人),ICAD (辛魁格兰那),IKMOULD(莫克等人)以及卓克索大学的知识库系统(曾等人)。但是，这些知识库系统只考虑吧了总体设计的某些方面，作为一个注塑模具的自动生成系统，需要做大量的理论研究工作，以自动地确定分型方向和分型面、生成分型面、识别削弱特征以及生成型腔。拉维和斯利瓦尼桑提出了九个规则，工程师可以用它们在制品中开发合适的分型面。这些规则分别是投影面积、平整度、收缩力、同轴度、削弱力、尺寸稳定性、流动率、加工表面和定向凝固。惠和谭提出了行程型腔和型芯的扫描方法。型腔和型芯是经过一系列的步骤生成的，在拉伸方向扫描生成一个实体，这个实体的一端是从第一个模块中去除得到的，模块的另一端是从模具中减去的。上述步骤的结果被去除的部分在闭合位置得到型腔和型芯。信和李提出了一种型芯和型腔发展的方法，因此可以生成侧型芯以及相应的型芯和型腔板。该方法由三个步骤组成，设计者确定分型线，它把制品分为两组表面，每组表面都有分型面连接到它，然后，外部的表面再与每组的表面接触。信说，一个模具由多个型腔、型芯和侧芯组成。惠基于多面体外部和内部的削弱分析，研究了注塑模具的的可塑性。堵塞概念的提出确定了主脱模方向，而且，细分技术被开发用来评估几何方法削弱。陈等人引入了可视映射的概念，确定了分型的方向。但这个方法没有考虑到内部削弱力。付等人和倪等人根据外环槽和成型件的内环槽，提出了一种削弱力的新分类。考虑到方向、位置、数量和削弱力特征量，他们提出了分型方向的标准，而分型方向正是基于此确定的。付等人通过挤压分型线边缘和使用布尔查运算创造型芯/型腔块，提出了一种生成分型面的方法。倪等人还提出了生成非平面的分型线和分型线的方法论。王等人提出了一种确定复杂形状制品的分割面的方法，他们的方法是，使用一种算法分开制品。通过这种方法形成的分型线和分型面是平面内的。目前，对于自动化模具设计的研究还仍然在进行中。然而，有一些方法是相当的理论化的，而模具设计却可能有着相当复杂的制品几何形状。大多数模具开发活动要有很高的技术水平，以及各种专业设计经验和知识。由于自动化模具设计技术的发展仍然远远超出了当前的技术，所以它更适合用于提供只能规则或指导方针，防止设计过程中与约束产生冲突。这些规则在具体的模具设计环境中，还提供交换工具。本文阐述了一种交互式的注塑模具设计系统，该系统集成了初始模具设计、具体的模具设计知识库和交互式计算机辅助设计/计算机辅助制造软件。本文的第二部分，从设计师的角度，概述了注塑模具设计过程的分析。二、注塑模设计过程要求分析注塑模具设计由两个步骤组成：初始设计和详细设计。初始设计由前期阶段的模具设计作出的决定组成，如模具结构类型、型腔数、流道类型、浇口类型和模架类型。详细设计由内嵌（型芯/型腔）设计、弹射系统设计、冷却和排气组件设计、装配分析和最终的起早组成。为了开发一种好的计算机辅助注塑模具设计系统，需要执行“他们有什么”和“他们想要什么”的分析。他们有什么：-客户对该制品的要求。这包括制品详细的几何形状和尺寸要求。-现有模具设计库。这个设计库涵盖了设计标准或预先设计的部件及其装配，例如，模架（定模架和半动模架）和模腔（定模腔和半动模腔）。-注塑模具设计中的专用知识。注塑模具的初始设计和详细设计的专用知识，主要是从有经验的模具设计师那里获得的。这些知识包括材料的选择、收缩建议、型腔布局的建议等等。他们想要什么：-一个智能并且交互式的模具设计环境。模具的设计往往是由一系列的设计程序组成的，这些程序通常需要创建一定的模具零件，并且装配现有的模具零件。这种模具设计环境不需要是完全自动化的，尤其是对于许多复杂的制品。智能并且交互式的设计环境将是使一些有用的自动化算法、启发性知识和经验丰富的模具设计师的在线互动相结合的一个很好的选择。-设计标准或预先设计的部件及其装配（独立的制品零件）管理。除了型芯和型腔，注塑模具有很多其他的零件，他们在结构和几何形状上是相似的，而这可以用于其他注塑模具的设计。这些零件与塑料模具制品是相互独立的，他们大多是标准件，可以在不同的模具设计和模具组中重新使用。-型芯和型腔设计中有用的方法（包括实体设计与分析算法）。型芯、型腔系统的几何形状和尺寸的确定是由模具制品直接决定的。这样一个系统中的所有组件都对制品有依赖性。同时，这些零件是模具设计中的关键部件，他们的几何要求可能是非常复杂的。因此，一些用于设计基于半自动和半相互作用的型芯和型腔的工具是非常有用的。-装配设计。在传统的计算机辅助设计/计算机辅助制造系统中，模具被表示为一个完整的几何和拓扑实体模型，这个模型是由一个三围欧式空间中面、边、顶点组成。这样的表示适用于视觉显示和执行几何计算密集型任务，例如工程分析与仿真。但是，对于基于制品几何实体及其关系的高层信息的要求决策的任务，这种形式是不适用的。模具设计师喜欢装配环境的设计，而不是简单实体模型的环境。这个理念也是由Ye等人提出来的。-设计制造。一个完整的注塑模具设计开发周记是由模具设计和模具制造工艺组成的。为了使计算机辅助设计/计算机辅助制造应用于模具设计，模具的制造特点应是由特定的数控机床抽象出来并分析的。无论是工艺规划还是数控代码都应该是自动化生成，使最终设计的模具得以制造。-设计图纸。对于许多公司来说，注塑模具的设计必须表示有着详细尺寸的工程制图。能够从最终的注塑模具设计中自动生成这些图纸的计算机辅助设计/计算机辅助制造工具将是有用的。基于上述分析，我们研究的重点是开发代表“他们有什么”和“他们想要什么”的技术。代表“他们想要什么”实际上是知识和注塑模具对象的表示。开发“他们有什么”意味着将为注塑模具设计的智能、交互式的工具，结合到一个完整的设计环境中。因此，为模具设计师提出的IKB-MOULD实现了上述的两个要求。
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