base of mould feature geometry through the autographic routine。 In the knowledge base of mould feature geometry, the detailed dimensions of the geometry 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。 Afterwards the designer then proceeds to the design of another functional design through similar procedure as mentioned above。 When all the functional designs have been completed, a complete drawing would be generated。 Finally all the designer has to do is to review and modify the mould drawing if necessary。

5。1。 The coding system

The code is a coded representation of all necessary information about the plastic part such as shape, undercut features, material and other specifications。 In designing the coding system considerations have been made to the characteristics of most injection moulded parts  and moulds。 The design of injection moulds depends critically on the shape and features of the product。 It is almost impossible to develop a unique definition for all the shapes of plastic parts as their shapes can vary indefinitely。 Nevertheless, in real life the shapes of a large percentage of commonly encountered plastic parts can be approximated as either rectangular or circular。 For example most of the plastic housings and casings are basically rectangular in shape; and most of the knobs, buckets and cups are basically circular in shape。 The Opitz system [19] which is the popular classification system for mechanical parts, has also been referred to in developing part of the coding system。

The code is pided into three sections and has a total of 12 digits。 The first section which describes the plastic part contains the first four digits。 The second section which describes the relation between the part and the mould includes the fifth digit。 The third section which describes the mould contains the last seven   digits。

5。1。1。 The first section: part   description

This section includes the first four digits。 They represent the part class, part external shape, undercut features and material class, respectively。

5。1。1。1。 Part class。   The first digit distinguishes the part as a circular part or a non-circular part。 There are seven numeric positions for this digit as shown   below。

(1) Circular part with  H/Dp0。5。

(2) Circular part with 0。5oH/Do3。

(3) Circular part with H/DX3。

(4) Variational circular part。

(5) Non-circular part with H/Dep0。5。

(6) Non-circular part with 0。5oH/De o3。

(7) Non-circular part with H/DeX3。

Here H is the height of the part measured from the parting line。 D is the diameter of a circular part。 De is the equivalent diameter of a non-circular part  with  length L and width W (De ¼ O(4LW/p))。 Parts belong to Class 1 and Class 3 are like flat discs and long cylinders respectively。 Parts belonging to Class 5 and Class  7  are like flats and long prisms,  respectively。

5。1。1。2。 Part external shape。 The second digit depends on which class the part belongs and the classification rules are as follows:

Class 1–3

The undercut feature is represented by the third digit which has the following positions。

(1) External  undercut only。