CAD Data Exhange and CAD Standards

CAD Data Exhange and CAD Standards

Xun Xu
DOI: 10.4018/978-1-59904-714-0.ch002
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Today, more companies than ever before are involved in manufacturing various parts of their end products using different subcontractors, many of whom are often geographically diverse. The rise of such global efforts has created the need for sharing information among vendors involved in multi-disciplinary projects. Transfer of data is necessary so that, for example, one organization can be developing a CAD model, while another performs analysis work on the same model; at the same time a third organization is responsible for manufacturing the product. Data transfer fills the need to satisfy each of these functions in a specific way. Accurate transmission is of paramount importance. Thus, a mechanism for good data transfer is needed. The CAD interoperability issue - using one CAD system in-house, yet needing to deliver designs to, or receive designs from, another system, poses a challenge to industries such as automotive, aerospace, shipbuilding, heavy equipment, and high-tech original equipment manufacturers and their suppliers. It is worth studying the issue and determining how engineering model data is delivered today to manufacturers and suppliers, how CAD conversion, geometric translation, and/or feature-based CAD interoperability are handled, at what expense, and under whose authority. This chapter explores the various ways to make this vital transfer possible. The attention will be directed towards data exchange and standards for 3-D CAD systems. Since CAD data formats have a lot to do with CAD kernels that govern the data structure and therefore the data formats, some popular CAD kernels are discussed. The data interoperability section covers different types of data translations and conversions. The use of neutral or standardized data exchange protocols is one of the natural methods for data exchange and sharing. This topic is covered at the end of this chapter.
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Cad Kernels

CAD data formats are governed by the (solid) modelling kernels that the CAD systems were built upon. This is true with both history-based and history-free CAD systems as discussed in Chapter I. A modelling kernel is a collection of classes and components comprised of mathematical functions that perform specific modelling tasks. A modelling kernel may support solid modelling, generalized cellular modelling and freeform surface/sheet modelling. It may contain functions such as model creation and editing (e.g. Boolean modelling operators), feature modelling support, advanced surfacing, thickening and hollowing, blending and filleting and sheet modelling. Most of the kernels also provide graphical and rendering support, including hidden-line, wire-frame and drafting, as well as tessellation functionality and a suite of model data inquiries. The CAD graphic user interface (GUI) interfaces with the kernel’s functions through so-called application user interface. Take Parasolid® modelling kernel as an example, which provides 3D digital representation capabilities for NX™, Solid Edge, Femap and Teamcenter solutions. The 3D-based application interacts with Parasolid® through one of its three interfaces as shown in Figure 1: Parasolid® Kernel (PK) interface, Kernel Interface (KI) and Downward Interface (DI).

Figure 1.

Kernel working diagram


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