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Information Requirements


This approach to design evaluation and partner selection requires three general types of data: product design data, manufacturing process data, and manufacturing resource data. We identify and manage the necessary data by constructing appropriate information models.

Product design models. The product design data must include all manufacturing-relevant design information, follow data exchange standards, and provide multiple views to support different design processing functions. This approach employs two data models that support these requirements.

The first product design model is an integrated product information model (see Figure) that includes the following representations:

  1. A geometric and topological boundary representation of the product's nominal shape.
  2. A feature-based model of the design that describes manufacturing features by such parameters as location and size and by the faces forming the feature.
  3. An electrical representation that describes the artwork, components, and electrical characteristics of the product (if any).
Additional tolerance information is associated with the product envelope, the features, and the electrical components.

Figure: Product Model Architecture

The product model integrates existing schemas defined in the STEP (Standard for Exchange of Product Data) international standard. Specifically the data model is defined using STEP resources for Geometry and Topology [21], Form Features [23], Representation Structures [22], and Product Description and Support [20]. Since no STEP standard has been accepted for electrical products, the product model uses the IEEE/Cal-Poly model [17] for describing layered electrical products. The application features in the product model are parametric descriptions of common manufacturing features and comprise the STEP form feature representations, which support application feature definitions, and the STEP face surfaces that compose the features. This product model includes the application features (holes, pockets, cutouts, grooves, and chamfers) relevant to the mechanical and electromechanical product types under consideration. Candadai et al. [3,4,5] describe additional details of the STEP resources in the model and the application feature definitions. For electrical products, the Integration model extends the STEP Product Description schema and defines the product in terms of its feature-based shape representation and its electrical characteristics. If a product has no electrical characteristics, the models within the dashed line of Figure can sufficiently define the product.

The second product information model is a more abstract manufacturing view of the product design. Group Technology (GT) is the standard classification of products on a set of important product attributes. A GT coding scheme describes the product using a number for each attribute. Because of this simple data structure, comparing two product designs by comparing their GT codes is a straightforward procedure. This approach employs two GT codes. The first GT code is the MICLASS [29] coding scheme, which describes the mechanical aspects of the product, including main shape, dimensions, material, and features. The second code describes the electrical attributes of an MWM such as electrical classification, components, hardware, and electrical dimensions [4,13] However, the GT codes are abstract representations of the product design and lack information needed for more accurate design evaluation functions. To address these needs we developed a new abstract product information model that uses the power of Group Technology. This model enhances the GT code attributes to satisfy the information requirements of several concurrent engineering applications, including design evaluation. The new Object-Oriented Group Technology (OOGT) information model is shown in Figure. This model describes the product material, the production quantity, the product envelope, the feature parameters, and the electrical characteristics. (If the product has no electrical characteristics, the electrical information is null.) Moreover, the OOGT model includes additional information critical to evaluating the manufacturability of the design: feature accessibility, feature volume, thin sections, cross section ratios, and undercuts. Candadai et al. [4] provide details of the model.

Figure: OOGT Information Model

Manufacturing plant data. Corresponding to the two types of design evaluation methods (design retrieval and high-level process planning) are two ways of describing the capabilities and performance of a manufacturing facility. The first is the set of products that the plant manufactures. The second is the set of processes that the plant performs. We have defined a manufacturing plant model that contains, for each candidate partner, these two sets and additional information about the plant operations and the corporation that owns the facility.

The set of fabricated products is described by the OOGT product models that facilitate quick and efficient searches for similar products and performance measures that describe the cost, quality, and lead time of the product.

The set of available processes allows the designer to determine what products the plant could manufacture in the future. The model describes the manufacturing processes and the corresponding equipment by their capabilities and performance. For example, machine tool capabilities includes the number of axes, the axis travel, the achievable accuracy, repeatability, and spindle motor power. Process performance comprises cost, queue time, and yield (or variance). This process information is required for the feasibility and manufacturability evaluation of a product design.

The manufacturing plant model also describes the manufacturing management and design functions of the plant and the financial health of the corporate parent. Such information is useful for prequalifying a plant to participate in a virtual enterprise. Figure describes the structure of the manufacturing plant model. An in-depth description can be found in Candadai et al. [5] and Herrmann et al. [15]. The plant model development included the input of manufacturing firms, who suggested important prequalification criteria and process capability attributes. The ISO 9000 standard [18] and military specifications [34,35] provided parameters for the the quality organization. The model also includes attributes identified in previous work on vendor selection (see, for example, [10,26,27,36]).

Figure: Manufacturing Plant Model

Process knowledge. The term ``process model'' generally refers to a mathematical, statistical, or simulation model of a specific process used to analyze a process behavior. A process information model, however, is a database that contains plant independent process information critical for process planning. Such information, typically found in manufacturing handbooks, describes universal process capabilities, material-process compatibilities, and recommended production quantities. We developed such process information models based on data from various sources including design handbooks [2,6,32], manufacturing handbooks [8,14], and material handbooks [9]. This model must be updated regularly in order to describe the most up-to-date process information. These models are used for assessing the feasibility and manufacturability of a product design.

next up previous
Next: Design Processing and Up: Design Evaluation and Partner Previous: Background

Edward Lin
Fri Oct 27 15:01:45 EDT 1995