An Intelligent Cavity Layout Design System for Injection Moulds by Weigang Hu and Syed Masood

An Intelligent Cavity Layout Design System for Injection Moulds by Weigang Hu and Syed Masood

This paper presents the development of an Intelligent Cavity Layout Design System (ICLDS) for multiple cavity injection moulds. The system is intended to assist mould designers in cavity layout design at concept design stage. The complexities and principles of cavity layout design as well as various dependencies in injection mould design are introduced. The knowledge in cavity layout design is summarized and classified. The functionality, the overall structure and general process of ICLDS are explained. The paper also discusses such issues as knowledge representation and case-based reasoning used in the development of the system. The functionality of the system is illustrated with an example of cavity layout design problem.

Cavity Layout Design in Injection Moulds

Current practice for injection mould design, especially cavity layout design, depends largely on designers’ ex- pertinences and knowledge. It would therefore be desirable to use knowledge engineering, artificial intelligence and intelligent design techniques in generating an acceptable cavity layout design in injection mould accurately and efficiently. In mould design, most of patterns of cavity layout and rules and principles of cavity layout design can also be easily represented in the form of knowledge, which can be used in most of knowledge-based design systems.

For example, for the layout patterns shown in Fig, the criteria to select the suitable layout pattern for design are mainly dependent on working environments, conditions and requirements of customer and are mainly based on designer’s skill and experience. To make a choice of contradictory factors will rely obviously on designer’s knowledge and experiences. It is rather suitable for intelligent design techniques to be used in systems designed for such situations, especially for routine or innovation design.

Design of injection mould mainly involves consideration of design of the following elements or sub-systems

(1) Mould type

(2) Number of cavities

(3) Cavity layout
(4) Runner system
(5) Ejector system
(6) Cooling system
(7) Venting
(8) Mounting mechanism
Most of the elements are inter-dependent such that it is virtually impossible to produce a meaningful flow chart covering the whole mould design process. Some of the design activities form a complicated design network as shown in Fig.
Obviously, in injection mould design, it is difficult for designer to monitor all design parameters. Cavity design and layout directly affects most of other activities. The application of advanced knowledge based techniques to assist designer in cavity layout design at concept design stage will greatly assist in the development of a comprehensive computer-aided injection mould design and manufacturing system.

It is noted from Fig a number of different layout patterns are possible with multiple cavities inside a mould. Higher the number of cavities of mould, higher the productivity of the injection mould. But this may lead to difficulties with issues such as balancing the runners or products with the complicated cavity shapes, which in turn may lead to problems of mould manufacturability. It is also possible that the number of cavities and the pattern of cavity layout will influence the determination of parting line, type of gate, position of gate, runner system and cooling system. Most of the main activities of mould design are therefore linked to cavity layout design. Fig. 3.5 shows the relations between cavity layout design and other design activities. The cavity layout design problem therefore depends upon a number of functionalities of the overall mould design system, which includes:

(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, manufacturing
(9) Ability and economic performances
(10) Determination of cooling system
(11) Graphic results display and output


Relationship diagram between cavity layout design and other modules of mould.

Example of Application

An application example, “determination of cavity layout pattern” of the “conceptual design for cavity layout” provided by Intelligent Cavity Layout Design System
(ICLDS) is given below:
If the initial design conditions are:
(1) What type of mould is used? Two plate
(2) What type of runner is used? Cold runner
(3) How many cavities are there in mould?
(4) How long is it required for product to clear the moulding area? Small
(5) What shape of product does moulding make? Rectangle
Then the result is given by: (this is shown in Fig.) Pattern of cavity layout design is:
Y-Rectangular-Layout
The knowledge base is developed using features of ECLIPSE language, such as ‘defrelation’, ‘deftemplate’, ‘defruleset’, and ‘goal’ generation. Part of the program, which describes the overall format of knowledge base development, is listed below:
Conclusion
The problem of design of cavity layout in multiple cavity injection moulds has received relatively little attention in computer aided design support systems for injection moulding. A computer based design system will offer great savings in time and cost in arriving at the best possible layout from a number of alternatives. The development of Intelligent Cavity Layout Design System (ICLDS) is believed to be the first attempt in this direction using knowledge-based approach. The development of ICLDS for injection mould is based on RETE++ in Windows environment on PC. From a practical point of view, ICLDS can be used as a tool for designer to implement cavity layout design of injection mould at concept design stage. It provides a positive step towards the development of a fully automated injection mould design process from product model to mould manufacturing.