2. RELATED WORK

In recent highly competitive industrial environment, metal stamping dies for producing sheet metal parts in mass production have been widely applied in various industries such as aerospace, electronics, machine tools, automobiles, refrigeration, etc., resulting in production automation at higher productivity, higher product quality and lower tooling cost. However, it has been well recognized that die design, even after many years of practice, still remains more of an art rather than a science. Historically, the work is mainly carried out manually, based on designers’ trial-and-error experiences, skills and knowledge.

In order to speed up stamping die design, and reduce the experience and skill required, researches on the computer-aided die design have been widely reported since 1970s, providing productivity improvements, cost reductions and design automation. The first generation of CAD systems [e.g., 4, 5] for the design of stamping dies have been characterized by basic computer graphics facilities, standardization of die components, and standardization of design procedures, resulting in reduced design and drafting time. Since late 1980s, significant efforts have been made by worldwide researchers to integrate a wide variety of feature modeling, parametric modeling and knowledge-based approaches to develop intelligent die design systems [e.g., 6-10] aiming at detailed die design automation. However the previous work can only deal with geometric modeling and knowledge-based symbolic reasoning, but not handle more sophisticated functional modeling techniques (e.g., building the functional structure of a design object), which is the basis for supporting the conceptual design stage of die design process.

On the other hand, functional modeling has become a promising and leading technique to model a design and requirements from its functional aspects so as to allow reasoning about its function for general or some domain-specific engineering design researches.

One of the most well-known functional modeling frameworks is that of Pahl & Beitz [2], i.e., systematic approach, which is based on the concept of flow (and sometimes effort) [11]. They model the overall function and decompose it into sub-functions operating on the flows of energy, material, and signals. Based on Pahl & Beitz’s work, many other researchers [12-15, etc.] have made significant contributions to functional modeling frameworks in the general engineering design domain as well. For example, Multilevel Flow Modeling (MFM) [12] models a technical system by expressing it in terms of its goals and in terms of flow functions (source, sink, storage, transport, barrier and balance) that describe the mass, energy and information flows in the system. Functions are linked to goals by two types of means-ends relations: achieve and condition. Instances of flow functions are connected together to build flow structures. Umeda et al. [13] proposed a Function-Behavior-State (FBS) modeler that reasons about function by means of two approaches: causal decomposition and task decomposition. Szykman et al. [14] proposed a standardized set of functions and flows as part of a computable data structure to represent product function and its link to product structure. An analysis-based functional design environment has been proposed by Deng et al. [15] to support the early stage of mechanical product design. In this system, the functional modeling process begins with an initial functional decomposition and ends in a mapping from the fundamental mechanical function to physical structure. The resulting functional model establishes the functional and structural relationships of a product to satisfy the product’s specifications and verifies the realization of the functions.

Mukherjee & Liu [16] presented a sketching abstraction scheme for conceptual design of stamping metal parts, using the function-form relations in a design. The functionally critical part of the geometry is represented using a set of functional features, while the rest of the geometry is abstracted as a set of linkages. Part functionality is correlated with the sketching abstraction using data structures called function-form matrices. Although the work was pioneering and promising in the application domain of sheet metal manufacturing, its usefulness is limited in providing conceptual design support for stamping metal part but not die structure.