Engineering drawing

Recap

• Lec 1: Introduction of engineering drawing• Lec 2: Sketching, texting, lettering and

dimensioning• Lec 3: Engineering geometry• Lec 4: Multi-view and visualization

Lecture 5

3-D solid modeling

Model Definition

• A solid model consists of volumetric information, that is, what is on the inside of the 3-D model, as well as information about the surface of an object.

Solid model of a snow ski binding

Primitive modeling

• Modelers are designed to support a set of geometric primitives, such as cubes, right rectilinear prisms (i.e., blocks), right triangular prisms (i.e., wedges), spheres, cones and cylinders.

• A primitive modeler uses only a limited set of geometric primitives; therefore, only certain topologies can be created. This is called primitive instancing.

Primitive modeling

Constructive Solid Geometry(CSG) Modeling

• Constructive solid geometry (CSG) modeling is more flexible than primitive instancing.

• The relationships between primitives are defined with Boolean operations.– union (U)– difference(-)– intersection (∩)

Constructive Solid Geometry(CSG) Modeling

Boolean operations: Union

Boolean operations: Difference

Boolean operations: Intersection

Boolean operations: Difference (A-B)

What would be the Boolean operation of difference for (B-A)????

Boolean operations: Difference (B-A)

Boolean operations on adjoining primitives

Boolean operations: Union

Boolean operations: Difference

What will be the result of B-A???

What will be the result of B∩A???

Boolean operations: Intersection

Boundary Representation(B-Rep) Modeling

• Boundary representation (B-rep) modeling, the surfaces, or faces, are themselves the basis for defining the solid.

• The shape of a B-rep model is created using Euler operations.

Constraint-Based Modeling

• 3-D solid modeling is the idea of having the model defined as a series of modifiable features.

• For example, a feature might be a hole bored through the model

• The geometry of each of these features is controlled through modifiable constraints

Constraint-Based Modeling: Planning

• Careful planning is required so that the model can be modified later by the person who created it or by others into a new design with a minimum of effort.

Constraint-Based Modeling: Sources of data

• If the model is of a brand-new design, then all the model data that exists may be rough sketches created by the modeler or another designer.

• 2-D CAD drawings may be the source of model building data.

• The reuse of existing models is an important benefit to using a constraint-based modeler.

Constraint-Based Modeling: Modeling Standards

• Standards for modeling may include – what geometry should be grouped together to

define a feature– in what order features should be created– How the features should be linked together– how automation features should be documented

Feature analysis

Feature analysis

Feature analysis

Feature Definition

• Features from Generalized Sweeps– sweeping operations– In a sweeping operation, a closed polygon, called a

profile, is drawn on a plane and is moved or swept along a defined path for a defined length

Feature Definition: Linear sweeping

Feature Definition: Linear sweeping

Feature Definition: Linear sweeping

Feature Definition: Revolved sweeping

What shapes can be produced used revolved sweeping??????

Doughnut???

Feature Definition: Revolved sweeping

Feature Definition: Revolved sweeping

Construction Geometry : Workplane

Profile sketching

• It consists of a series of line elements such as straight lines, arcs or circles.

• Closed loop– A closed loop sketch has its last element

connected with its first element to create a sealed path

– It implies an inside and outisde• Open loop

Profile sketching

Closed loop Open loop

Profile sketching