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(1) definition of design specifications including analysis and description of characteristics of design problem
(2) determination of mould type
(3) determination of number of cavities
(4) determination of orientation of product
(5) determination of runner type and runner configuration
(6) determination of type and position of gate
(7) cavity layout conceptual design
(8) evaluation of ejection ability, manufacturingability and economic performances
(9) determination of cooling system
(10) graphic results display and output
3. Structure of ICLDS and the Design Process
The structure of the Intelligent Cavity Layout Design System (ICLDS) is based on case-based reasoning and ruled-based reasoning designed around the RETE++software system. Fig. 4 shows the overall structure of ICLDS schematically. Fig. 5 shows the general design process of ICLDS. The design process starts with the definition of design specifications. The ICLDS system retrieves similar cases from case base by computing the similarity between the cases and the new case. If the solution is satisfactory, then results are displayed graphically. If the solution is not satisfactory, then ICLDS will use rule-based reasoning with forward or backward chaining or a mixture of both to arrive at a solution. If the solution is still unsatisfactory, then the user has to modify some of the initial design specifications. The use of case-based technology in the design process in ICLDS allows the user to obtain the solution(s) of design problem more quickly and flexibly.
The structure of knowledge base and database used in the development of ICLDS is based on the underlying knowledge base and database structure from the RETE++ software system, which is a commercially available software development platform.
4. Development of ICLDS
4.1. Classifications of Knowledge
For various logic and steps involved in layout design, there are different kinds of knowledge that needs to be described and represented in cavity layout design. The types of knowledge can be classified into five kinds based on object oriented (OO) concept as described below:
(1) Design instance/case: previous design cases and current design instances
(2) Relation: superclass-class-subclass relation, classin stance relation
(3) Attribute: design variables, features, attributes of design problem
(4) Rule: general design rules, design experiences
(5) Procedure and/or model: numeric calculation, mathematical modeling, analysis, evaluation and procedures.
4.2. Knowledge Representations
To describe each of these types of knowledge, the internal data structures of the ECLIPSE language, included in RETE++ inherently, can be used to make the object orientated representation of the design process as explained earlier.
4.3. Case-based Reasoning
Case-Based Reasoning (CBR) is dependent firstly on case retrieved. Case-based retrieval is based on “Similarity Metric”. Therefore, how to calculate the similarity is obviously the key technique in CBR, and it is described in detail as below. which, since dij must range between 0 and 1, must also range between 0 and 1. which, since Wj and dij must range between 0 and 1, must also range between 0 and 1.
4.4. Validation of Case
Validation of case is to check up whether each acceptable case is suitable for current problem and to find out the most suitable one, so each case should be associated with testing methods and tested results on it. Only the case, under the given conditions, for which all tested results on it match those of the current design problem, can be considered as the solution prototype for further refining.
4.5. Criteria for Validity of Cost Reduction
With the application of ICLDS for cavity layout, two kinds of cost reduction can be expected. One is the overall theoretical cost reduction achieved in using the system to carry out the conceptual design of injection moulds. The other is the practical cost reduction value recorded in the case base which may be used to do the case-base reasoning if the case has the “cost reduction” attribute. For the theoretical one, there is no need of any criteria for validity of cost reduction because the cost savings will obviously come out through lead time saving, improvement in design quality and quick response to customers. For the validity of practical cost reduction the criterion of comparison can be used.