Solid Modeling has grown to become the preeminent CAD modeling technology. It is the modeling method of choice for CATIA, Pro/ENGINEER, Unigraphics, Autodesk Inventor, Solid Edge, and SolidWorks, along with just about any other CAD system you can name. In the past, this solid modeling technology had been reserved for large, expensive, Unix-based workstations. Recently, however, enhanced hardware and new products have brought solid modeling to personal computers (PC's). Of special interest to NC shops are CAD/CAM products that will machine solid models created by their customers, as well as greatly simplify their own creation of complex multi-surface part models for machining.

CAD Modeling

CAD (Computer-Aided Design) modeling is any method of defining a part's shape and dimensions using a computer. CAM (Computer-Aided Manufacturing) is the process of creating an NC part program for a specific part model. Design CAD software is intended for an engineer to use in the creation of new designs. NC programming software usually includes manufacturing modeling and CAM capabilities. There are several different types of modeling currently used for NC programming. They have developed and evolved over the past forty years from simple 2D wireframe modeling, to surface modeling, to today's 3D solid modeling.

This type of modeling consists of a collection of shapes or outlines of a part, usually built from lines and arcs, constrained to a single plane or two dimensions (X,Y). It is probably the most popular way to program simple parts. You can import the geometry for a part from other CAD systems using IGES or DXF files, or you can use your CAD/CAM system to create the required shapes from blueprint information.

2D wireframe modeling has several advantages for NC programming. It is simple and easy to understand. It is well suited for turning parts and mill parts with straight walls and flat floors. Most NC programming systems have 2D wireframe CAD capabilities built in. This means you don't need to buy separate CAD software in order to program simple parts.

The biggest disadvantage to 2D wireframe modeling is the inability to define more complex 3D mill part shapes for machining.

3D Wireframe Modeling

This type of modeling is similar to 2D wireframe modeling, except that it works in three dimensions (X,Y,Z). It produces a line drawing of the part that can be viewed from various orientations.

One advantage of 3D modeling is the ability to produce a complete 3D image of the part. It is not a collection of different 2D part views, as in a typical 2D blueprint style drawing.

The disadvantage of 3D wireframe modeling is that it does not define the complete interior surfaces for machining. In fact, it cannot define parts significantly more complex than those created with 2D modeling.

This type of modeling creates surfaces representing the area of the part where every position on the surface is defined from a mathematical method. Mathematical methods to define surfaces include Bezier, B-Spline, NURBS, Coons Patch, etc. A surface may be flat (as with a plane), or very complex and curved (as with NURBS). Surface modeling is best used to describe more complex part shapes, such as parts that are not flat-bottomed with straight walls. A good example of such a part is a telephone handset. Modeling a handset would require defining a number of surfaces. A finished handset surface model would be a collection of surfaces, defining the skin of the handset. Surface modeling was the first technology that allowed models of complex 3D shapes to be defined and machined. It is still widely used in PC-based CAD/CAM systems.