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In 1994, Mok and Cheung [1] presented work on the development of an injection mould design application based on Unigraphics. In 1997, Shah [2] proposed a 3-tier architecture for standardising communications between geometric modeling kernels and applications that require geometric modelling services. His objective is to achieve plug compatibility between 3D applications that are based on Parasolid [3] (a 3D kernel,developed at the University of Cambridge) and ACIS. This,however, involved an extensively developed 3-tier modeling husk. In this paper, the author attempts to develop a lightweight injection mould design application using a low-level 3D kernel directly. The focus is on the flexibility and speed of the software development. Design concepts and procedures were taken from IMOLD [4,5], a complete mould design and assembly 3D application. Although the discussion is limited to injection mould design only, the methodology applied can easily be applied in other 3D-based applications that are of a similar nature.
A combination of developer tools was chosen for this purpose. Before the methodology is discussed, brief introductions to some of these tools are first presented. They are, IMOLD,Parasolid version 10.1, Visual C++ version 6.0, and the Microsoft Foundation Classes.
2. IMOLD as a Mould Design Application
IMOLD (Intelligent Mold Design and Assembly) is an established 3D-based application that is dedicated to injection mould design. It is developed on top of an advanced CAD system called Unigraphics. The development is carried out using the applications programming interface (API) provided. The software enables mould designers to create a design rapidly by providing the tools that are commonly needed. Standard components parts, that are often required in the design, have been pre-created in the software and can be readily used by the designer. This reduces the design time significantly. The mould design process is pided into several stages, providing the designer with a consistent method of creating the mould design. They are, namely:
1. Data preparation.
2. Filling system design.
3. Mould base design.
4. Inserts and parting design.
5. Cooling system design.
6. Slider and lifter design.
7. Ejection system design.
8. Standard parts library.
Each stage can be considered as an independent module of the program. The 3D-based requirements for each module vary only slightly. The success in developing the mould base module implies feasibility in developing all the other modules.
3. Parasolid as a 3D Kernel
Parasolid is designed to be the centre or “kernel” of any system that is based on 3D model data. It is essentially a solid modeller, which can be used to:
1. Build and manipulate solid objects.
2. Calculate mass and moments of inertia, and perform clash detection.
3. Output the objects in various ways, including pictorially.
4. Store the objects in some sort of database or archive, and retrieve them later.
Parasolid is one of the most advanced 3D kernels among CAD applications. It is the 3D kernel of Unigraphics and SolidWorks. Its unique tolerant modelling functionality enables it to accept data stored in other modeller formats. Parasolid model files are thus very potable. It is, therefore, a superior platform for the development of stand-alone applications. The 3D-based application interacts with Parasolid through one of its three interfaces (see Fig. 1). These are called the Parasolid kernel (PK) interface, the kernel interface (KI) and the downward interface. The PK interface and the kernel interface sit “on top” of the modeller (side-by-side), and are the means by which the application models and manipulates the objects, as well as controls the functioning of the modeller. The downward interface lies “beneath” the modeller, and is called by the modeller when it needs to perform data-intensive or system type operations. It consists of three parts: frustrum; graphical output (GO); and foreign geometry. These are briefly explained below.