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ComputerAided_Design_Engineering_amp_Manufactur.pdf

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TABLE 5.2 Data Structure for Representing Internal Features<br />

Feature Code 1 2 3 4<br />

Other Parameters<br />

5 6<br />

Bore 20 Xb Yb Xe Ye<br />

Taper 21 Xb Yb Xe Ye<br />

Face 22 Xb Yb Xe Ye<br />

Arc 23 Xb Yb Xe Ye R D<br />

Fillet 24 Xb Yb Xe Ye R D<br />

Chamfer 25 Xb Yb Xe Ye<br />

Groove 26 Xb Yb Xe Ye Depth Form<br />

Thread 27 Xb Yb Xe Ye Pitch Type<br />

Xe,Ye: end point; Xb,Yb: start point; R: radius; D: direction (CW/CCW); Type: type of<br />

thread/knurl.<br />

It should be noted that in rotational parts, many of the tolerances are controled with respect to the axis<br />

of the part. There will be no special need to model the axis as it is implied. The resultant data structure<br />

for storing the feature information (geometrical � intrafeature data) is shown in Appendix A.<br />

Interfeature tolerances control a feature in relation to another feature. These relational tolerances, as<br />

the name specifies, relate two or more features through a tolerance. Of the related features, one feature<br />

can be named as the reference feature (REF) and the other as the toleranced feature (TOF). REF and<br />

TOF are related by a type of tolerance (relation, REL). The relationship can be denoted by a quantity<br />

(QNT). The quantity QNT may be specified by two values (denoting upper and lower bounds) for some<br />

tolerances.<br />

Thus, the set of<br />

completely describes any type of tolerance which relates more than one feature.<br />

It is important to note here that TOF and REF can be a set of primitive features—an important<br />

observation as it forms the basis for evolving the structures to represent the interfeature data. For<br />

rotational components, runout and concentricity are considered. Length-wise tolerances are also included<br />

in this category. To represent these tolerances, primitive features are to be maintained along with the<br />

form features. The data structure for representing the set (TOF, REF, REL, QNT) evolves based on these<br />

considerations.<br />

Turbo-Model: Implementation<br />

(TOF) Which is the feature to be toleranced?<br />

(REF) To which feature is TOF related?<br />

(REL) How are these (TOF and REF) related?<br />

(QNT) How much is the relation?<br />

The objective of the Turbo-Model is to provide a simple, user-friendly environment in which a rotational<br />

component can be interactively modeled in terms of features and their technological attributes so as to<br />

provide the necessary inputs to the CAPP system (GIFTS). The system-user interaction is designed to<br />

facilitate easy navigation of the user through the system. Many facilities such as hierarchical menus, icons,<br />

mouse interface, help, prompts, etc. are employed in the system.<br />

Modeling Part Data<br />

The system supports an exhaustive set of commands and external utilities to carry out various activities<br />

involved in the modeling process.

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