1. Getting Started with 3-D CAD by Solid Modeling
Goals
3-D CAD models developed from primitive solids
Reference –
Chap 11 – 3-D Geometry Concepts BTG
CADKEY 99 – Chapter 6
AutoCAD 2002 Tutorial – 3-D Modeling – Chapter 6
3-D CAD with Solid Modeling

2. Agenda Understand basic ways to generate 3-D solid models
Create solid models from primitive shapes – usage of Solids99 or AutoCAD functions and features
Derive shapes using Boolean functions
Modify solids using fillets and chamfer
Use Drawing Layout Mode
3-D CAD with Solid Modeling

3. Review of important concepts in CAD
CAD model is a “virtual” part
A 3-D CAD model stores the entire 3-D shape of the object
3-D models can be generated from 2-D profiles by using CAD programs
Encourage students to revisit the slides in Basics 12
3-D CAD with Solid Modeling

4. Approaches to developing a solid model
Constructive solid or primitive modeling
Constraint-based modeling
Feature-based modeling

5. Primitive Modeling - combine simple shapes
The first attempt at solids modeling was a technique known as constructive solid geometry or primitive modeling, which is based on the combination of geometric primitives such as right rectangular prisms (blocks), right triangular prisms (wedges), spheres, cones, and cylinders. Each primitive could be scaled to the desired size, translated to the desired position, and rotated to the desired orientation. Then one primitive could be added to or subtracted from other primitives to make up a complex object. It is easy to see how two blocks plus a negative cylinder (hole), as shown in figure , could represent an object similar to the one shown in Figure 4.4. (The rounded surface, or fillet, at the comer between the horizontal and vertical surfaces has been omitted.) The problem with constructive solid geometry was that the mental process of creating a solid model based on geometric primitives was much more abstract than the mental processes required for designing real world objects.
3-D CAD with Solid Modeling

6. Constraint-based solids modeling
Part roughed in
Constrained or detailed by adding dimensions
3-D Objects created by revolving or extruding
Constraint-based solids modeling overcomes the weakness of constructive solid geometry modeling by making the modeling process more intuitive. Instead of piecing together geometric primitives, the constraint-based modeling process begins with the creation of a 2-D sketch of the profile for the cross-section of the part. Here, "sketch" is the operative word. The sketch of the cross-section begins much like the freehand sketch of the face of an object in an oblique view. The only difference is that CAD soft- ware draws straight lines and perfect arcs. The initial sketch need not be particularly accurate; it need only reflect the basic geometry of the part's cross-sectional shape. Details of the cross-section are added later. The next step is to constrain the 2-D sketch by adding enough dimensions and parameters to completely define the shape and size of the 2-D profile. The name constraint-based modeling arises because the shape of the initial 2-D sketch is "constrained" by adding dimensions to the sketch. Finally. a three-dimensional object is created by revolving or extruding the 2-D sketched profile. Figure in next slide shows the result of revolving a simple L-shaped cross-section by 270° about an axis and extruding the same L-shaped cross-section along an axis. In either case, these solid bodies form the basic geometric solid shapes of the part. Other features can be subsequently added to modify the basic solid shape.
3-D CAD with Solid Modeling

7. Constraint-based solids modeling – by revolving
More exercises and dedicated sessions on transforming 2-D profiles to 3-D solids
3-D CAD with Solid Modeling

8. Constraint-based solids modeling – by extruding

9. Feature-based Modeling
Creating and modifying geometric features of a solid model like a manufacturing process.
Feature-based modeling attempts to make the modeling process more efficient by creating and modifying geometric features of a solid model in a way that represents how geometries are created using common manufacturing processes. Features in a part have a direct analogy to geometries that can be manufactured or machined. A base feature is a solid model that is roughly the size and shape of the part that is to be modeled. The base feature is the 3- D solid created by revolving or extruding a cross-section. It can be thought of as the initial work block. All subsequent features reference the base feature either directly or indirectly. Additional features shape or refine the base feature. Examples of additional features include holes or cuts in the initial work block.
3-D CAD with Solid Modeling

10. Example of Feature-base process
The analogy between feature-based modeling and common manufacturing processes is demonstrated in figure - for making a handle for a pizza cutter. Beginning at the top of the figure we follow the steps that an engineer would use to create a solid model, or virtual part, on the left and the steps that a machinist would take to create the same physical part in a machine shop on the right. The engineer using solids modeling software begins by creating a two-dimensional profile, or cross-section, of a part, in this case a circle {shown in isometric projection). The analogous step by a machinist is to choose a circular bar stock of material with the correct diameter. N ext the engineer extrudes, or stretches, the circular cross-section along the axis perpendicular to the plane of the circle to create a three-dimensional base feature {a cylinder in this case). The equivalent action by a machinist is to cut off a length of bar stock to create an initial work block. Now the engineer adds features by cutting away material on the left end to reduce the diameter and by rounding the right end of the cylinder. The machinist performs similar operations on a lathe to remove material from the cylinder. N ext the engineer creates a circular cut to form a hole through the cylinder on the right end. The machinist drills a hole in the right end of the cylinder. Finally, the engineer creates a pattern of groove cuts around the handle. Likewise the machinist cuts a series of grooves using a lathe. In similar fashion a geometric shape could be added to the base feature in the solids model, analogous to a machinist welding apiece of metal to the work block. Feature-based techniques give the engineer the ability to easily create and modify common manufactured features. As a result, planning the manufacture of a part is facilitated by the correspondence between the features and the processes required to make them.
3-D CAD with Solid Modeling

11. How Solids Models Can Be Used
Improve efficiency in design by visualization and virtual assembly
Link to Numerical Analysis
Stress
Heat Transfer Analysis
Fluid Flow
Link to Computer-aided Manufacturing

12. Using CADKEY 99 and AutoCAD 2002 as 3-D Programs
Chapter 6 introduces some of the basic techniques for creating 3-D geometry
Basic models are initially built from primitive shapes – modified to create more complex objects
A CADKEY 3-D blank seed drawing or AutoCAD 4-viewport template would serve as the basis for 3-D solids modeling
3-D CAD with Solid Modeling

13. Creating Layout Mode drawings
Even if the model is built with a 3D construction approach, conventional orthographic views with dimensioning and in some cases sectioning will be needed.
CADKEY Chapter 6 demonstrates how to create layout mode drawings, starting with a 3D model.
AutoCAD Chapters 6 and 7 show modeling, Chapter 8 shows the layout.
Procedures and conventions for dimensioning will be covered later
Note for students that they will first build a three-dimensional model of by rotation of a figure.
This is done in what is called MODEL MODE.
Creating a LAYOUT or going to LAYOUT MODE is next. In layout CADKEY can automatically produce a number of different views (Top, Front, Right, Left, ISO., Etc.)
Sectioning are done tin the LAYOUT mode. This will be done in the Part II(Session20) or in 182. Dimensioning is done as a part of ENG182
Title block in IMPORTED to LAYOUT mode.
3-D CAD with Solid Modeling

14. Creating Layout Mode drawings
CADKEY and AutoCAD have two system modes - Model mode and Layout mode.
CADKEY and AutoCAD distinguish between the two so that you can create part files in Model mode, then switch to Layout mode to create different layouts of the part file and detail them for drafting purposes.
In Model mode you can take advantage of all the CADKEY and AutoCAD functions to create and edit part files. Model mode is the default system mode that you enter when you start CADKEY and AutoCAD.
Layout mode is a drafting tool that you use to create, dimension and then print or plot
Note that dimensioning and sectioning will be handled later – in Session19/20 if time permits and in Eng182.
3-D CAD with Solid Modeling

15. Example Problem from CADKEY
3-D CAD with Solid Modeling

16. Review Questions
What are the views listed in the four view port option?
What is the difference between View and WLD coordinates?
Answers:
Top/Front/Right and Isometric
View: Constructs an entity in view coordinates; with the display axes representing X as horizontal, Y vertical, and the positive Z axis pointing out of the screen. View Coordinates are the same as what appears on your screen. When you choose View from the View, View/World Coordinates options, the coordinates system is automatically assigned to view coordinates.
World: Constructs the entity in world coordinates, relative to View 1, top view. World Coordinates are always relative to View 1 and represent real model space. The directions of X, Y, and Z axes are independent of the current working view.
2 corner points in the base and height
A circle in any of the views created using CADKEY99 and the height of the cylinder
3-D CAD with Solid Modeling