Reverse Engineering

Reverse Engineering: Which CAD Model Do I Need?


Reverse engineering has become a viable way to create a CAD model now that CAD packages are readily available. Engineers are using reverse engineering to not only help create new parts, but help copy an existing part or recover a damaged or broken part. When looking to reverse engineer one of your parts, how do you know which CAD model do you need? One of the first questions you need to ask is: how am I going to use this part? This will help you to answer which one of the reverse engineering methods you will require. Here is a list of the different reverse engineering methods, and how they apply to your product.

Polygonal Modeling (STL)

With Polygonal Modeling, the data collected on the part (e.g. laser scan) is converted to a polygonal “mesh” surface (STL).  The mesh is comprised of seamlessly connected triangles that accurately replicate the shape of the part.  Polygonal Modeling is best-suite for parts that will be replicated via a 3D printer.  STL models are not usually suitable for importing into a traditional CAD modeling package.

NURBS Modeling

With NURBS modeling, the data collected on the part (e.g. laser scan) is converted to a free-form surface.  The free-form surface (Non Uniform Rational BSpline surface) is seamless and is able to precisely replicate the actual shape of the part.  NURBS modeling is best suited for parts that are very free-form in shape (not prismatic).  The NURBS model can be imported into traditional CAD modeling packages, but cannot be easily edited.

Parametric (Feature-Based) Modeling

With parametric modeling, the data collected on the part (e.g. laser scan, CMM measurements) is converted to “true” geometries.  The features are model with traditional CAD modeling tools (extruding a contour/lofting/fillets/applying draft/etc).  This provides a feature-based model that can be easily edited.  Parametric modeling is best suited for parts that are prismatic in shape (not free-form).

Hybrid Modeling

Sometimes a combination of NURBS and Parametric Modeling is needed.  To accomplish this, a NURBS surface is combined with a feature-based model in a traditional CAD modeling package.  This method allows for reproducing the free-form features of a part accurately and then the rest of the part is modeled with feature-based techniques.