# What is 3D Solid Modelling | Solid Modeling Methods

## 3D SOLID MODELING

To eliminate all kinds of ambiguities in representation and manipulations of the objects, the solid modeller was developed. Out of the various approaches developed, one of them was an approach to the design of mechanical parts by treating them as combinations of simple building blocks like cylinders and cuboids. Such solid modelers or volume modelers can hold complete unambiguous representations of the geometry of a wide range of solid objects. The completeness images of a shape and automation of the process of interference checking. The model can also serve as means of geometric input for finite element analysis or even manufacturing tasks such as the generation of instructions for numerically controlled machining.

### Definition of a Solid Model

A solid model of an object is a more complete representation than its surface (wireframe) model. It provides more topological information in addition to the geometrical information which helps to represent the solid unambiguously.

### Application of Solid Models

1. Graphics: generating drawings, surface and solid models
2. Design: Mass property calculation, interference analysis, finite element modeling, kinematics and mechanism analysis, animation, etc.
3. Manufacturing: Tool path generation and verification, process planning, dimension inspection, tolerance and surface finish.
4. Component Assembly: Application to robotics and flexible manufacturing: Assembly planning, vision algorithm, kinematics and dynamics driven by solid models.

Difference between 2-D and 3-D model

## Solid Modeling Methods

Constructive Solid Geometry (CSG or C-Rep)

• Constructive Solid geometry is one of the two most popular and widely used approaches to create the solid models of the objects.
• In a constructive solid geometry approach, a solid model of an object is created by using the three-dimensional geometric entities, known as primitives.
• These primitives can be combined by a mathematical set of Boolean operations to create the solid.
• In a constructive solid geometry (CSG) approach, two or more primitives are combined by a Boolean operations to create a desired model.
• The Boolean operations are used are: union (ᴜ or +), intersection (I) and difference (-)

Pure Primitives

• In a primitive intancing approach, all the objects that have the same topology but different geometry are grouped into a family called generic primitive.
• The primitives are defined in terms of a parameter group. For example, a block primitive is defined by parameters: height(H), width(W) and depth(D).
• By inputting the values of parameters defining the primitive, the model can be generated.
• In addition to the basic primitives, the library of generic primitives(shapes) which are commonly used is created.
The generic primitive can be called from the library by its assigned name and it can be created by inputting the values of parameters

Boundary Representation(B-Rep)

In addition to the CSG approach, the boundary representation(B-rep) is the another popular and widely used approach to create the solid models of the objects.

Any physical object can be considered to be bounded by a set of faces. In a boundary representation(B-rep) approach, a solid model of an object is created by using a set of faces. Each face is bounded by the edges and each edge is bounded by the vertices.