KP3213 CAD/CAM

1. KP3213 CAD/CAM • Snapshot Lecture 5 • Objective of Lecture 6 • Understand constraint modeling • Learn CAD Standard • Lecture 6

2. Constraints and Variational Modelling

3. Constraint-based Modelling • User constrains geometry based on Design Intent • Design variations can be generated by changing a few key dimensions • Geometry is automatically regenerated based on constraints

4. D5 D1 D2 D4 D3 Example

5. Design Intent • The part should be twice as long as it is wide • The hole should be centred in both directions • The hole diameter should be 50mm

6. Parametric and Variational Modelling • Parametric modelling • constraints defined sequentially • each constraint calculated based on previously defined constraints • order of constraint specification is important • Variational modelling • constraints solved simultaneously • order of constraint specification doesn’t matter

7. Parametric Definition User specifies dimension D1, other dimensions calculated sequentially

8. Variational Definition Solve system of simultaneous equations:

9. Constraint Types • Ground constraints • Dimensional constraints • Geometric constraints

10. Ground Constraints • Horizontal • Vertical • Both ends fixed • Point location • X of point • Y of point • Angle of line

11. Dimensional Constraints • Horizontal dimension • Vertical dimension • Linear dimension • Angular dimension • Radial dimension

12. Geometric Constraints • Parallel • Perpendicular • Tangent • Collinear, coincident, coplanar

13. Modelling Approach • Sketch approximate geometry • Generate solids and features • Add constraints and dimensions afterwards

14. Smart Sketching • Most CAD systems use “smart” sketching tools • Design intent is inferred, and constraints added automatically • For example, two lines that are nearly perpendicular “snap” perpendicular, with a constraint

15. CAD Standard

16. CAD Standard • Too many ways, need for standardization • Understand the graphic kernel system and its extension for developing graphic software system • Understand IGES, DXF and STEP • Dimensional measurement interface specs for communication between coordinate measuring machine and CAD data

17. Standardization • GKS Graphical Kernel System • PHIGS Programmer’s Hierarchical Interface for Graphics • IGES Initial Graphics Exchange Specification • DXF Drawing Exchange Format • STEP Standard for the Exchange of Product Model Data • DMIS dimensional Measurement Interface Specification • VDI Virtual Device Interface • VDM Virtual Device Metafile • GKSM GKS Metafile • NAPLPS North American Presentation Level Protocol Syntex

18. GKS Graphical Kernel System • It is very difficult for a program developed for a particular system to run on different system • However, substantial portions of it is similar • Same codes are rewritten many times • Program interchangeable is created • ISO has standardized GKS for 2D in 1982 with objectives: • Complete range of 2D facilities including interactive • Control graphics devices such as plotter and display devices • Small enough for variety of program • GKS 3D standards developed to cover which were not covered by GKS • GKS has been enhanced to provide separate stand for 3D

19. PHIGS Programmer’s Hierarchical Interface for Graphics • Accepted by CAD vendors as system capable of 3D • Features in PHIGS not covered by GKS is as follows: • Very high interactivity • Hierarchical structuring of data • Real time modification pf graphics data • Support of geometry animation • Adaptability to distributed user environment

20. NAPLPS North American Presentation Level Protocol Syntex • Presentation standard developed by the Canadian government with AT&T and other telcos • Basis of transferring data from computer to video displays systems such as tele-text and other video presentations systems • Is a means of encoding graphic data and text in electronically transferable format (ASCII) • Features: • Very compact (10% more compared with other format) • Resolution will be clearer • Integrated with communication networks • Large range of colors

21. IGES Initial Graphics Exchange Specification • Most comprehensive standards and is designed to transmit the entire product definition including that of manufacturing and any other associated information • IGES file contains 6 sub-sections • Flag Section – ASCII format. Version 3 onward standardized as follows (ASCII default, binary form and compressed ASCII) • Start Section – man-readable prologue. Information contain is essentially for the person who would be processing this for other application. • Global Section – Contains info. about detail of the product, originator, company , date, drafting standards etc. • Directory Entry Section – Each entiry present is fixed in size contains 20 fields and 8 character each. To provide an index for the file and to contain attribute information such as color, line type transformation matrix etc. • Parameter Data Section – contains data associated with entities. A free format is allowed for maximum convenience. Also contains pointers. • Terminate Section – Contains the sub-totals of the records present. This would always contains a single records. It is possible that some design technique is lost.

22. STEP Standard for the Exchange of Product Model Data • ISO standard 10303 (Product Data Representation and Exchange) • Able to share data across application, vendor platform between contractor, suppliers and customers • Scope: • Standard method representing info. Necessary for completely defining a product throughout the entire life cycle • Standard method for exchanging data electronically between two different systems • Overview – general introduction and overview part one of standard 10303 • Description methods - the application protocols planned in STEP are far-reaching compared to existing standards • Implementation methods – Specifications how STEP information physically represented for exchange environment. Refer to actual implementation levels.

23. STEP Standard for the Exchange of Product Model Data • Conformance and tools – Provide specifications and conformance testing of the processors used for STEP information. • Integrated generic resources – Contains the specifications of the information models that support various application areas. Includes geometric and topological representation, product structure organization, material, visual representation, etc. • Application information models – These specify the information models to be used for specific application • Application protocols – Defines the context for the use of product data for a specific industrial needs.

24. DXF Drawing Exchange Format • DXF has been developed and and supported by AutoDesk for use with the AutoCAD files • The drawing interchange file is ASCII • Overall organization: • HEADER section – contains general information about the drawing similar to the global section of IGES. Consists of AutoCAD database version number of system variables. • CLASSES section – Holds information for the application-defines classes. • TABLES section – contains definition of symbol tables such as line-tables, layer table text style table etc. • BLOCK section – contains symbols • ENTITIES section – contains graphical objects • OBJECTS section – Contains non-graphical. Examples are dictionaries that contain mline (multiple line styles and groups.

25. Book Review for Week 3 • CAD/CAM Principles and Application 2nd edition by PN Rao Published by Mc Graw Hill • Chapter 8 Finite Element Analysis. Find other books that is relevant to FEM because we will do some detailed calculation