Applications in Reverse Engineering

To Create

Surface Wraps and Parametric Models

A surface wrap requires a scan to work from. This can be achieved by laser or CT scanning an object. A point cloud is generated from the raw scan data.

After scanning and point cloud generation, an .stl mesh is created. An .stl mesh consists of polygons or triangles calculated from the point cloud data.

The Process: Surface “Wrapping”

The next step is post scan processing or “mesh editing”. This step consists of the removal of errors from the mesh created by erroneous points or “noise” from the point cloud. Gaps or irregularities in the mesh can also be detected and healed. This is the most important step in the surface wrapping process. It is crucial to remove or fix all errors prior to surfacing to ensure that the final model does not contain undesirable irregularities or surface anomalies. This step in the process can be the most time consuming. The model also must be water tight or “manifold” before surfacing.

Mesh Editing

The final step in this process is “wrapping” or “surfacing” of the polygonal mesh with solid NURBS surfaces. Specialized algorithms are used to accomplish this through a mostly automated process. A desired surface fitting tolerance range can be applied by the user. However, the tighter tolerances tend to create larger files and can take longer to complete. The final CAD model can then be exported in an .iges or step format.

Wrapping

Not Just for Smurfs

Surface wrapping is suitable for both organic and mechanical shapes. The result is a highly accurate CAD model that can easily be imported by any major CAD package and can be used for a variety of purposes including but not limited to: metrology, CAM applications, design incorporation, and rapid prototyping.

The process begins with a scan using a CMM, laser, or CT scanner.

In this case, CMM measurements were performed directly on the part. Dimensional data obtained from CMM measurement was used to build the part from scratch in Solidworks. This is a traditional approach to reverse engineering.

The Process: Creating a Parametric Model

Creating a Parametric Model Using Scanned Data

This part was scanned in our Metrotom 800 industrial CT scanner. A CT scan was the preferred measurement method to access the interior geometry of the part. This process requires some additional steps.

An .stl file was generated from the CT point cloud data. The next step in the process is mesh editing. Mesh editing is not as crucial to the parametric modeling process as it is for a surface wrap. The mesh just needs to be clean enough to extract dimensional data for feature modeling.

Dimensions are extracted from the scan and parametric features are created.

Accuracy Delivered

The result is a fully parametric solid model with feature design history that can be transferred over to most major CAD packages for further design editing or incorporation into an assembly. This model can also be exported in a step or iges format.

Using the accuracy analyzer. This allows the user to see areas of deviation. This is useful for finding areas that may need to be further processed or to expose areas where the original part may be worn.

Carl Zeiss Industrial Metrology

John HayesSales Manager

Nel PreTech Corporation

8420 183rd Place

Tinley Park, IL. 60487

Office: 708-429-4887

Cell: 630-965-8068

Email: john@nelpretech.com

Web: www.nelpretech.comSpecialists in Contract Dimensional Inspection

A2LA Accredited in Industrial Computed Tomography