Chapter 7 Computer-Aided Drafting and Design
167
a part begins by drawing a 2D profi le called a
sketch to create the most basic feature or shape
of the part, called the base feature. Additional
features can be created from sketches or other
modeling methods. Because features form the
basic building blocks of a part, this process is
referred to as feature-based modeling.
Each part is created as a separate electronic
fi le. Several completed parts can then be used to
create an assembly by assembling and mating
the parts together. An assembly is a functional
mechanism made up of multiple components
(parts). An example of an assembly is a set of
gears. An assembly is created as a separate
electronic fi le and contains references of the
individual part fi les. The part fi les are linked
to the assembly fi le so that if a part fi le is
edited, the assembly updates automatically to
refl ect the edit. The completed assembly can
be simulated to determine the effectiveness
of the design and to check for interference
between parts.
Once the modeling process is completed,
working drawings can be generated from
the part and assembly fi les to document the
engineering design process. Drawings are
created as separate electronic fi les. However,
the part and assembly fi les are linked to the
drawing fi les so that if the model is edited, the
corresponding drawing is updated to refl ect
the edit.
The following are typical steps used in
parametric modeling to model parts and
construct an assembly from the parts. These
steps are discussed in more detail in the
following sections.
1. Create a 2D sketch that defi nes the profi le
of the base feature of a part. Make the
sketch on the appropriate plane (front,
top, or side).
2. Add geometric constraints and dimensions
to the sketch. Fully defi ne the sketch.
3. Using the appropriate modeling
tool, create the base feature from the
completed sketch.
4. Create additional features as needed to
complete the part.
Parametric modeling programs that are used
to create solid models are most common in
mechanical engineering applications. This
chapter focuses on the common tools used in
these programs.
Parametric Modeling
Parametric modeling is an advanced form
of 3D modeling in which the model dimensions,
or parameters, are defi ned and modifi ed as
needed throughout the modeling process.
In this type of modeling, parameters control
feature sizes and locations and a change to
one parameter affects the entire model. See
Figure  7-25. Because parameters control the
size and location of features, parametric models
are sometimes referred to as “intelligent”
models.
Parametric modeling programs used in
mechanical design and engineering involve a
different workfl ow in comparison to 2D CAD
drawing programs and other types of CAD
modeling programs. In parametric modeling,
3D models called parts are created to represent
mechanical components. Each part is made
up of the various features that defi ne the part.
An example of a part is a shaft. In many cases,
Model courtesy of SolidWorks Corp.
Figure 7-25. 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.
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