Using CAD
Image rendered with computer aided design.
Computer-Aided Design is one of the many tools used by engineers and designers and is used in many ways depending on the profession of the user and the type of software in question. There are several different types of CAD. Each of these different types of CAD systems require the operator to think differently about how he or she will use them and he or she must design their virtual components in a different manner for each.
There are many producers of the lower-end 2D systems, including a number of free and open source programs. These provide an approach to the drawing process without all the fuss over scale and placement on the drawing sheet that accompanied hand drafting, since these can be adjusted as required during the creation of the final draft.
3D wireframe is basically an extension of 2D drafting. Each line has to be manually inserted into the drawing. The final product has no mass properties associated with it and cannot have features directly added to it, such as holes. The operator approaches these in a similar fashion to the 2D systems, although many 3D systems allow using the wireframe model to make the final engineering drawing views.
3D “dumb” solids (programs incorporating this technology include AutoCAD and Cadkey 19) are created in a way analogous to manipulations of real world objects. Basic three-dimensional geometric forms (prisms, cylinders, spheres, and so on) have solid volumes added or subtracted from them, as if assembling or cutting real-world objects. Two-dimensional projected views can easily be generated from the models. Basic 3D solids don’t usually include tools to easily allow motion of components, set limits to their motion, or identify interference between components.
3D parametric solid modeling require the operator to use what is referred to as “design intent”. The objects and features created are adjustable. Any future modifications will be simple, difficult, or nearly impossible, depending on how the original part was created. One must think of this as being a “perfect world” representation of the component. If a feature was intended to be located from the center of the part, the operator needs to locate it from the center of the model, not, perhaps, from a more convenient edge or an arbitrary point, as he could when using “dumb” solids. Parametric solids require the operator to consider the consequences of his actions carefully.
Some software packages provide the ability to edit parametric and non-parametric geometry without the need to understand or undo the design intent history of the geometry by use of direct modeling functionality. This ability may also include the additional ability to infer the correct relationships between selected geometry (e.g., tangency, concentricity) which makes the editing process less time and labor intensive while still freeing the engineer from the burden of understanding the model’s design intent history. These kind of non history based systems are called Explicit Modellers. The first Explicit Modeling system was introduced to the world at the end of 80′s by Hewlett-Packard under the name SolidDesigner. This CAD solution, which released many later versions, is now sold by PTC as “CoCreate Modeling”
Draft views are able to be generated easily from the models. Assemblies usually incorporate tools to represent the motions of components, set their limits, and identify interference. The tool kits available for these systems are ever increasing; including 3D piping and injection mold designing packages.
Mid range software are integrating parametric solids more easily to the end user: integrating more intuitive functions (SketchUp), using the best of both 3D dumb solids and parametric characteristics (VectorWorks), making very real-view scenes in relative few steps (Cinema4D) or offering all-in-one (form•Z).
Top end systems offer the capabilities to incorporate more organic, aesthetics and ergonomic features into designs (Catia, GenerativeComponents). Freeform surface modelling is often combined with solids to allow the designer to create products that fit the human form and visual requirements as well as they interface with the machine.
