A. Requirements of Geometric Modelling
Total product cycle in a manufacturing environment involves a large no. of
interconnected functions.
Designer’s mind to be translated into reality.
ƒns. expected of geometric modeling are:
Design analysis:
Evaluation of areas & volumes, Mass & Inertia, Interference checking,
tolerance analysis, Kinematics, Auto Mesh props. given.
Drafting:
Automatic planar cross section, hidden line & surface manual, shaded images,
Automatic dimensioning, exploded views.
Manufacturing:
Parts classification, process planning, NC data generation & verification,
Robot program generation.
Production Engineering:
BOM, material requirements, MRP, Scheduling.
Inspection & Quality:
Program generation for inspection m/c comparison of production part with
design.
B. Geometric Model:
1. 2D
2. 3D a. Line Model
b. Surface Model, planar/ complex
- Analytical / Non-analytical (sculptured)
c. Solid or Volume model
C. Geometric Construction Methods:
a. Sweep or Extrusion
D. Solid Modelling:
Best is Primitive Instancing or Constructive Solid Geometry (CSG)
Boolean operation for complex solids
Storage data: a) Construction tree b) relevant dimensions of primitives
CSG good for modeling, but for other ƒns. computationally not suitable.
Hence alongwith CSG also B-REP.
Most common method of storage is NURBS
Non-analytical surfaces cannot be modeled with CSG.
E. Free Form Surfaces:
e.g. Car bodies, Ship hulls, die cavity surfaces etc.
Types of Surfaces:
1. Planar Surfaces
2. Curved Surfaces
Single curved surface
Double curved surface
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