3-D solid modeling creates parts and assemblies permitting more accurate modeling. For instance, there is no way to accurately model anything that contains complex surfaces in 2-D because one would need to define an infinite number of cross sections.

3-D modeling also allows feature-based modeling – part features are allowed to intersect each other to automatically create lines and curves that would normally have to be manually created in a 2-D system. Another advantage of 3-D solid modeling includes the ability to check for interferences between solid parts. 3-D solid models also are the best models to use for NC programming because more information about the part is provided; for example, defining what is considered inside and outside the part, thereby making it easier to create an accurate NC toolpath.

It is best to use CAD/CAM systems that support 3-D solid modeling. When designing a mold, one needs to be able to make all of the geometry required. Some molds require the ability to create complex surfaces, complex rounds and drafts. If your CAD/CAM system does not have the ability to handle high-end modeling, you will have to fake the geometry. Faking geometry will inevitably lead to some error either in drawing detailing, NC toolpaths or inspection. This will result in producing a product that is unacceptable to the customer, costing time and money in reworking the mold.