ComputerAided_Design_Engineering_amp_Manufactur.pdf

Before making an attempt to generalize the methodology for developing feature-based systems, it is
necessary to bring out the underlying principles that are applicable to different modeling schemes. The
following points are generally valid to all feature-based systems irrespective of the modeling scheme,
representation method, part range, or development platforms selected for developing a modeling system:
(a) The complete part specification, comprising geometrical, technological and general details, should
be contained in the part model.
(b) Though high-level form features address the issue of CAD-CAPP integration, it is also necessary
to maintain the low-level primitive features simultaneously in order to facilitate the visualization
of the form features and the representation of the technological attributes.
Based on these common concepts, a framework for containing various types of data in a featurebased
model can be given as shown in Figure 5.9, which shows the part model as a set of three types
of data. The steps to be followed for the development of a feature-based system within this framework
are listed below. Note that the following sequence is not prioritized since the steps involved are interdependent.
However, it is felt that the given sequence can serve as a guideline in developing a featurebased
system.
(a) Decide the feature definition based on the part type. More than one feature definition can be
adopted to describe a part.
(b) Catalog the form features (along with the geometrical attributes) identified in the part range.
(c) Decide the representation (wire frame, CSG, B-rep or hybrid) scheme based on factors such as
the complexities involved in the part geometry, feature definition or choice of software and
hardware.
(d) Decide the set of operators (e.g., Boolean operations) using which the part range under
consideration can be modeled as a set of form features.
(e) Study the arrangement of form features in the part range. Some general rules on the arrangement
of the features in the part range can be observed. These rules can form the basis to check the
validity of the model.
(f) Identify the primitive features that can construct the form features. The relationship between the
primitive features and form features must be consistently maintained with suitable indexing.
(g) Decide the set of technological details applicable to the part range. Some general rules on the
application of these details to the individual form features and primitive features can be observed.
Validation rules can be developed at this stage.
(h) Classify the technological data, based on the number of (primitive or form) features involved in
specifying a particular data.
(i) Consider the task-dependent general (or global) data to be added to the feature-based model.
(j) Fix the data structures for representing the geometrical, technological, and global details.
(k) Select the method of realizing the feature-based part model.
(l) Choose the software and hardware platforms for the system development.
(m) Finally, carry out the system development. Flexibility, customization, and user-friendliness are
the guidelines in the development.
The development of a part modeling system based on this methodology is presented in later sections.
5.7 Modeling of Manufacturing Resources for CAPP
Process planning is a data-intensive activity. Preparation of the process plans is always guided by the
availability and status of manufacturing facilities on the shop floor. The information about these should
be made available to the CAPP system to enable it to generate realistic process plans.
As shown in Figure 5.6, MRIR is a collection of information representing manufacturing resources
such as machine tools, cutting tools, materials, jigs, fixtures, accessories, inspection gauges, etc. If the
scope of the CAPP system is limited to a few manufacturing facilities, these can be directly embedded