(3) Ejector sleeves。

(4) Air ejection。

It can be seen that this coding system has catered for very complicated parts。 For example, a non-circular part which has varying cross-section along its entire height and both external undercuts and internal undercuts/thread can be coded by this system。 The coded representation of all necessary information about a plastic part together with its respective plastic mould is illustrated in Fig。 4。

5。2。  The  knowledge base

The knowledge base in this system was acquired from a literature search and from a number of mould making companies。 There are a number of useful injection mould design and mould-making rules as well as technical data in the technical papers, handbooks and trade standards。 The expert knowledge and empirical rules were also collected through interviews and case discussions with the experts of some local companies。 The scope of knowledge covers the most widely used methods and elements of mould features for the main functional design modules for standard two- plate moulds, stripper moulds, split moulds and three-plate moulds。

The internal structure of the knowledge base consists of three parts namely the methods file, the alternative mould features by method database and mould feature    geometry

database。 The methods file contains a long list of methods of achieving the various functional designs of an injection mould。 The method screening routine (block 8 in Fig。 3) uses the part code to select the recommended list of methods。 Once method has been selected a code associated with each chosen method would be generated and is then used to access the alternative mould features of the chosen method through the mould feature screening routine (block

9 in Fig。 3)。 When particular mould feature of chosen method has been selected, a code associated with each mould feature would be produced and is then used  to access and prompt the designer to input information concerning inpidual dimensions, position and orientation from the mould feature geometry database through the autographic routine (Fig。 3)。 In the  mould  feature geometry database, the detailed dimensions of the geome- try of all the mould features are stored in terms of parameters。 Once the graphic information has been inputted, the geometry of the chosen mould feature would be drawn。 The schematic representation of the internal structure of the KB is illustrated in Fig。    5。

A rule-based knowledge-representation method was used to develop the knowledge base。 This method is the most popular and versatile of all the representation schemes。 Knowledge is represented in the form of production rules。 Rules are written as IF-THEN statements to provide a formal way of representing strategies, directives and recommendations。 This scheme is appropriate for a variety of KB systems problem domains。 More than 500 rules have been established in this work。 The various functional designs of injection moulds are related to part information and mould specifications by rules developed in the knowl- edge base。 For example, the rules  for  the  cavity layout and part of the rules for the cooling system are shown in Tables 1 and 2, respectively。

The JESS 4。4 expert system shell [22–24] was selected to develop the knowledge base of the Internet-based mould design system。 JESS is a forward chaining production system implemented in the Java programming language。 Rules are written in CLIPS/JESS language, which can easily call and be called by Java programs。 The programme for the knowledge base was written in modular structure consisting of the five basic functional systems of injection mould design, namely cavity layout, feed system, mould construction, cooling system, and ejection system。 The capability of the knowledge base can be further expanded through continual refinements in the rules and databases of the system。 Using the system’s editing facilities, it is fairly easy to add and delete rules in the knowledge base。 In addition, the assignments and combinations of certainty factors can be added, and user queries can also be added or deleted where it seems  appropriate。