Introduction to Reverse Engineering
Reverse engineering generally refers to the development of a 3D CAD model from an existing part. Traditional methods of reverse engineering typically involve hand measurements of the part in question using tools such as calipers or tape measures. Larger parts may include the use of cardboard templates and plumb bobs. The manual dimensions are used to dimension hand sketches that are subsequently input into a CAD (Computer Aided Design) program. This is a time consuming and laborious process. It is also fraught with errors, particularly on parts with very complex shapes that cannot be easily measured by hand.
3D scanning significantly improves the process of data collection, easily capturing millions of data points on even the most complex of surfaces. This data is then triangulated into a polygon mesh, or STL file, providing the frame work from which the ultimate 3D CAD model will be developed.
Parametric modeling has been around since the late 1980’s. The technology was a breakthrough, allowing designers to easily edit their 3D models by “rolling back” in history to make changes to sketches and features. The implementation of parametric solid modeling from scanned data was pioneered by Rapidform in 2006 with the release of Rapidform XOR, now re-branded as Geomagic Design X.
This powerful tool allows for sketches to be developed based upon cross-sections cut through the polygon mesh, or STL file. The sketches can be “perfected” to compensate for issues with the original part or missing or erroneous data. These sketches are then used to create traditional solid modeling features such as extrudes, lofts and sweeps. Since the modeling method is parametric, a history tree is developed, allowing for future changes to the final CAD model.
This method is ideal for mechanical components, but may be somewhat difficult to accomplish on organic or artistic parts.
Parametric Solid Model
In contrast to parametric modeling, rapid surfacing does not employ traditional modeling techniques. Rather, a network of curves is drawing on the surface of the polygon mesh. These curves then form the boundaries of the resultant NURBS (non-uniform rational B-Spline) surfaces. The final surface body is comprised of a series of smooth, tangent surface patches. A fully closed volume of surfaces will result in a solid body being generated. This method is ideal for organic, or natural geometry such as bones and other body parts.
Rapid Surface Model
Hybrid modeling employs techniques from both rapid surfacing and parametric modeling. It is most useful for CAD modeling parts that contain both highly complex surfaces as well as geometric features. These types of geometry can be see in both manufactured parts such as castings and forgings, as well as in the art world where mechanical features are used to assembly large pieces.
Hybrid Solid Model