4.1 Dimensional entity
The size entity mainly describes the size composition, the size association between the entities, and the like, including the length size, the degree size, the length associated size, and the angle-related size.
In size entities, you should first define an abstract superclass. The so-called abstract superclass refers to the parent class that is not instantiated by itself. It can itself contain attributes, and the keywords after the attributes indicate the type of data they belong to, and the attributes will be inherited by all of their subclasses. Secondly, based on the abstract superclass, define a subclass model of the size entity.
4.2 Geometric Element Entity
Geometric elements are the basic elements that form the feature geometry of a CAPP part. Geometric element entities include axes such as coordinate axes, vector directions, points, curves (mainly cam profile curves), and faces.
4.3 Processing entity
As previously mentioned, the processing entity corresponds to the features processed by the Generative CAPP. These features consist of defined size entities and geometric element entities as well as a number of attributes and constraints that they carry.
Like the first two types of entities, a processing entity also defines its abstract superclass. There are three categories of basic features, composite features and distribution features. We refer to CAPP features composed of size entities, geometric element entities, and their own properties as basic features, such as light holes, U-shaped grooves, and so on. A number of basic feature entities can be combined into a composite feature, such as a stepped hole that can be considered to be a composite of several light-passing features. The basic features form a distribution feature in a rectangular or circumferential distribution.
5 Conclusion
PDM is an integration platform built on a relational database. It is centered on a shared database and can span the operating system platform and application software platform, enabling multi-platform information integration. The CAD/CAPP/CAM integration system built on PDM makes full use of its characteristics of data and software integration. Guided by the STEP standard, the EXPRESS description language is used to establish an information model covering all integrated interfaces. Therefore, the combination of CAD files based on STEP standard and shared database is used to realize the information integration of CAD/CAPP/CAM in CIMS environment based on PDM.
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