In
the beginning : … there was the Extrusion and Sweep design! This
modeling technique involved drawing or sketching a cross-section on a plane.
After the completion of the drawing part, one had to gently, slowly but
steadily drag or sweep it in a straight or curved fashion. The resultant
cross-section design ended up with inner loops leading to hollow shapes. The
sketching could also be dragged in a circular or ovular manner leading to
straight extruded shapes and solids of revolution. In all cases, the distance to be dragged was to be determined before hand. Usually revolution designs occurred along the complete circle or a part of the plane. Such extrusion modeling techniques can also give way to negative or cut extrusion. Cut extrusion is usually characterized by local features of depression.
Constructive
Solid Geometry : Extrusion modeling techniques later evolved into
polished constructive solid geometry modeling methods. This technique
primarily used the Boolean operations. The Boolean method of function is
characterized by the union, intersection and difference on pairs of simpler
models to create a desired shape and format. The modeling technique was
initiated by using base feature casting to produce solid shapes of cube,
cylinder, sphere, cone and torus. The second stage of the technique involved specifying the details of the various shapes including its dimensions, thickness and orientation. Constructive solid geometry design combines extrusion-modeling methods to create solid intermediate design models.
Features- based modeling technique :
This latest technique imbibes base and local casting features of the hole, pocket, slot, boss, rib and fillet. The technique also uses the Boolean operations method to produce depressions and negative extrusions from the metal surface. This technique enables the technician to select the design after casting. The casting formed is malleable and enables flexible movement. This means that the design can be moved or deleted.
The future :
Modern cast modeling techniques employ a variety of methods signaling a
cross between analytical and parametric modeling. These techniques deploy
the effective methods of lofting and shelling to define cross sections and
join them. Shelling methods are used to form an offset surface. This surface
is created inside out in a shell fashion with the complete annihilation of
the shell interferer. The latter technique of parametric modeling is
beneficial to the user. It allows the user to specify relationships between geometric elements -- distance of a hole from a rib. The technique of parametric modeling employs a software program, which adjusts relevant parameters accordingly. Graphical stimulation along with radiography is used to detect any errors in feature casting.