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A mould is normally constructedby stacking several metal plates to form a rigid body.It has to house various mould components in the correctpositions for the proper functioning of the mould.Major components include: register ring (1) for locationof mould with machine; core/cavity inserts (17, 21) forshaping of the material; guide pins (6) and guide bushes(8) for mould alignment; and clamping plates (12, 22)for mould mounting. For complicated plastic parts,some other mechanisms such as slides, unscrewingdevices, etc., might also be involved in the wholemould structure.3. Knowledge-Based ApproachA knowledge-based approach broadly means to build up asystem, usually called a knowledge-based system (KBS), forsolving complex decision problems in a specific domain. AKBS, normally in the form of an intelligent computer pro-gram, uses knowledge and inference procedures to solveproblems that are difficult enough to require significanthuman expertise for their solution. The knowledge of aknowledge-based system consists of facts and heuristics. The“facts” constitute a body of information that is widely shared,publicly available, and generally agreed upon by experts ina field. The “heuristics” are mostly private, little-discussedrules of good judgement (rules of plausible reasoning, rulesof good guessing) that characterise expert-level decision-making in the field.The typical structure of a knowledge-based system is shownin Fig. 2. It comprises the knowledge base, containing encodedexpertise from the domain expert. The inference engine onthe other hand provides strategies for processing the encodedknowledge in order to reach KB solutions. The KB systemalso provides a user interface for KB system/user interaction,and, possibly, sensors for the collection of data from monitoringdevices. Finally, links to a traditional database provide the KBsystem with the opportunity to import and use data in theinferencing or reasoning process.4. Development of Computer/KBSTechniques in Mould DesignPrevious work in applying computer technologies in the fieldof injection moulding covered many aspects of injection mould-ing and mould design activities. Bezier [3], Goult [4], andKishinami et al. [5] defined sculptured surfaces and mouldcavities with complex shapes; and generated offset surfaces,i.e. generating the inner wall of a mould cavity at a constantthickness. Zwigel [6] and Abrahams [7] calculated the surfacearea and volume of the mould and strength and deformationof the mould by means of finite-element analysis programs.Schumacher [8] and Wubken and Bangert [9] simulated thecavity filling and cooling of the mould. Hui and Tan [10]presented a heuristic search approach based on sweep oper-ations to develop automated mould design systems for determining parting direction, parting line, side core, etc. Lyeand Yeong [11] established a computer-aided tool for theselection of injection machines, the size and position of injec-tion guns, the ejectors, and the steam vents. Huang et al. [12]used solid-modelling techniques to build mould plates and alibrary of standard mould components. Computer-aided engin-eering techniques have been used to represent the injectionmoulding process mathematically and to assist the mould designby simulation analysis. MOULDFLOW from Mouldflow Aus-tralia,
FLOW ANALYSIS from Plastics & Computer Inc., C-FLOW from Advanced CAE Technology Inc., POLYCOOLfrom Structural Dynamics Research Corporation, and MOULD-COOL from Application Engineering Corp., are typical com-mercially available packages for modelling the mould fillingprocess and/or cooling analysis. Researchers have started to adopt a knowledge-basedapproach to solving the injection moulding and mould designproblems in recent years. IMPARD [13] is an expert systemdeveloped for injection moulded part design. IMES [14,15]solved injection moulding part-quality problems. GERES [16],FIT [17], CIMP [18], HyperQ/Plastic [19], PLAssex [20],etc., were developed for the selection of plastic materials.DTMOULD-1 [21] is a KBS for injection mould cost esti-mation. MOULDX [22] and EIMPPLAN-1 [23] incorporatedmouldability considerations into part designs and addressed theconceptual design development of injection moulded parts.ICAD [24], the KBS of Drexel University [25], the KBS ofthe University of Massachusetts at Lowell [26], CADFEED[27], etc., were developed for injection mould design. Theyare, however, limited to specific design areas or simple parts,and are not mature and practical enough to cover generalmould design.From the above review, it can be seen that most of theprevious work considers only certain aspects of the total designand some is too theoretical to be applied to practical moulddesign which involves a substantial practical knowledge compo-nent about functions and structure of a mould, human heuristicknowledge and empirical knowledge. The KB system hasdemonstrated great potential to assist designers in interactingwith a CAD system for conceptualised design as well as forthe final engineering design of a mould by using engineeringrules of thumb with extensive analytical procedures. In general,the major advantage of a KB system for mould design overconventional computer-aided design systems is the explicitrepresentation and manipulation of a body of knowledge, rep-resenting human expertise. 30 C. K. Mok et al.5. System Structure and Development5.1 System RequirementsMould design does not result from a quantitative analysis butcomes within a range of design procedures which are partlycreative and partly require existing items to be brought togetheras assemblies. Inpidual elements of the design may be sub-jected to quantitative analysis but these do not help the designerto establish the overall form of the assembly. Thus, it wouldnot be practical to automate the design procedure completelyas mould design lacks a quantitative and structured approach.An alternative approach was decided upon to structure as muchof the procedure and methodology of mould design as couldbe structured; and to establish and appropriately configure aknowledge base which would incorporate the methods andelements of the mould features. This knowledge base will beaccessed by designers through interactive programs so thattheir intelligence and experience can also be incorporatedwithin this total CAD integrated design procedure.The further requirement is to computerise as much of theprocedure as possible in a way which will ensure that cost-effective and functional mould designs are produced. Thismeans that a minimum number of simple parts should be usedin the design of a mould and that standard parts should beused as far as possible. The system also has to be “userfriendly” and has to be practically applicable in the localplastic industry. If it can make use of the mould designers’skill and experience and provide some challenge to them thenthis is likely to enhance its acceptability. As it is impossiblefor any design procedure developed to consider beforehandevery requirement of mould design, the procedure, its softwareand the knowledge base have to be designed so that it can beeasily developed and extended as experience is gained inusing it.5.2 System Structure and the Interactive DesignProcedureFigure 3 shows a block diagram of the whole structure ofthe system. The modular system structure facilitates furtherdevelopment and extension and it also makes the switching ofthe program from one CAD platform to another relativelysimple. The operation of the system is described in the follow-ing paragraphs.