Datasheet

UNDERSTANDING SOLIDS VS. SURFACE MODELING 21
3D modeling began because of the desire to create a 3D wireframe representation of a part.
This representation provided early users with the ability to visualize and measure the limits or
boundaries of parts they were designing. Wireframes provided a minimal amount of information
needed to create a part.
It soon became apparent that much more was needed in a 3D model. Software engineers
devised objects called surfaces that could be created from the 3D wireframe model. Creating sur-
faces permitted the accurate definition of the faces or shapes that would be required in order to
machine the design.
This new model description technology revolutionized the manufacturing industry. With sur-
faces, shapes could be programmed into CNC machines, producing accurate geometry to be used
for creating precision parts. Surface modelers quickly jumped into the forefront of leading-edge
technology. With surfaces, virtually anything could be designed or created.
However, surface modeling had some shortcomings. Creators of surface models had great diffi-
culty calculating volumes, centroids, and mass. The development of surface modeling technology
evolved into the ability to create a collection of watertight surfaces. Modeling kernels were further
developed to allow the representation of the watertight collection of surfaces as a solid model
composed of faces (surfaces).
Solid modeling got off to a good start in the mid-1980s. The first iteration of solid modeling was
the ability to create static, base solids. Like surfaces, base solids were difficult to impossible to edit
once created. If a mistake was made in the model, the user started over.
The second generation of solid modeling introduced parametric, history-based model creation
with the ability to parametrically modify dimensions and constraints within the model to edit or
modify the size or shape of the part. If an error was made in creating the part, users could access
the history tree and retrace their steps toward the beginning of the part creation process, selecting
the point to rebuild the rest of the model. Unfortunately, with history-based modeling, anything
that was previously created from that point forward would be deleted and have to be re-created.
The current generation of solid modelers provides dynamic feature-based parametric model-
ing, where powerful features can be added, modified, suppressed, deleted, or reordered within
the model without having to re-create good geometry. With the introduction of feature-based
modeling, 3D became a must-have within the engineering community. Now, complex designs can
be quickly created and modified to create virtual prototypes of complex machines without having
to cut metal to prove the design.
The following are frequent questions among 3D users: Which is better? Should I use surface or
solid modeling? Which should I use? The answer is that you should become proficient at using
both and never have to limit your abilities. Both surface and solid modeling have a place in today’s
engineering environment. Learning to use both proficiently should be on the agenda of every
aspiring modeler.
Although solid modeling is preferred by more users, primarily because it is a simpler approach
to design, the ability to add surfaces to sculpt or modify a solid model or to add faces that would
be difficult to impossible to create using solid model features adds a new dimension to creating a
quality model. It’s a little thing, but it differentiates an expert user from the rest of the pack.
Let’s look at definitions of some of the aspects of solid and surface modeling:
Wireframe A collection of curves and lines and other geometry is connected into a 3D (XYZ)
construction representing the outer boundaries and features of a 3D part. See Figure 1.16 for an
example of a wireframe model.
Surface A 3D mesh is composed of U and V directional wires or vectors representing a
3D face. Surfaces are generally described by a few different types: polyface meshes (typical in