Chapter 7 Computer-Aided Drafting and Design 175
modeling, parameters defi ne the dimensions
of the model and a change to one param-
eter affects the entire model. See Figure 7-22.
Parametric modeling programs are avail-
able for both solid modeling and surface
modeling.
Parametric modeling programs designed
for mechanical drafting are typically used to
model assemblies. An assembly is a functional
mechanism made up of multiple components,
referred to as parts. In assembly modeling,
models representing the assembly compo-
nents are constructed as part models. Then,
the part models are used to construct the
assembly. In this type of modeling, tools in the
software can simulate how a part will “work”
with other parts in the assembly. This enables
the engineer to determine whether possible
conflicts exist (for example, if two parts are fl
in the same place at the same time). The engi-
neer can check for proper fi t and tolerances,
design functionality and effi ciency, and usage
of proper materials. The software can also be
used to generate two-dimensional drawings
of the assembly and part models for use in
manufacturing.
Most CAD modeling programs typically
include rendering capability. In CAD terms, a
rendering is a highly realistic representation g
of a model with lighting, shadows, and other
visual effects applied. Renderings are com-
mon in mechanical and architectural drafting,
because a mechanical assembly or an interior
room can be shown in great detail to a poten-
tial client. The models shown in Figures 7-20,
7-21, and 7-22 are rendered models.
CAD/CAM
Computer-aided design/computer-aided
manufacturing (CAD/CAM) combines CAD
with automated manufacturing operations.
In this type of manufacturing, computer
numerical control (CNC) machines control
the manufacturing processes. Computer data
that is input to the machine is used to control
the movement of machine tools. After a part
is drawn in the CAD program, the mathemat-
ical shape and size description of the part, or
design data, is calculated by the program for
manufacturing. The data is used to cut the
material and make the part, Figure 7-23.
Advanced Rendering and
Animation Programs
In high-end CAD applications, advanced
rendering programs are used to create
very realistic displays of complex models.
See Figure 7-24. These programs provide
lighting, materials, and environmental effects
to greatly enhance the appearance of a model.
A model set up for rendering in this manner is
known as a scene. When the scene is rendered,
material fi nishes and other effects are calcu-
lated based on the lighting used. Computer
rendering programs require greater amounts
of resources in order to perform the calcu-
lations needed. The original model may be
created within the program, or it may be
imported from a different modeling program
with less powerful rendering capability.
Figure 7-22 Parametric modeling programs provide
powerful modeling tools that allow object dimensions
to be changed throughout the modeling process. Any
changes made affect the entire model. (Designed
with Solid Edge from Siemens PLM Software)