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Reverse Engineering to A CAD Model

Capture every detail of your machine part. Convert physical objects into precise digital models quickly and accurately.

What is Reverse Modeling or Engineering?

Reverse modeling refers to the process of analyzing the construction of a product when there are no design documents available from its original production. Reverse modeling serves many purposes including:

  • developing a similar or improved product/design
  • creating adapters or enclosures to the original product
  • reproducing an existing part

The process involves taking measurements of the object with the use of a 3D scanner and then using the 3D data to create a 3D CAD (computer-aided drawing) model. A CAD model is the standard format for manufacturing

Does 3D scanning an object produce a CAD Model?

A common misunderstanding of the 3D scanning process is that the direct output is a CAD model that can imported into any CAD system. Unfortunately, this is not the case. The direct output of all optical scanners is point cloud or polygon mesh data. A CAD modelling stage is needed if a geometric solid model is required.

If you have the right software and experience, point cloud data tells you everything you need to know in order to reconstruct a part in CAD. Unfortunately most mainstream CAD packages (example: AutoCAD, Rhino3D, Solidworks) are not particularly good at working with this type of data. 3D scan data processing software (example: Geomagic, Rapidform XOR and Polyworks) are great at converting point cloud data into CAD models.

Why use 3D scanning for this process?

It is difficult to take measurements of objects with organic or complex shapes. It is easy and fast to achieve this task using a 3D scanner since we can get measurements of an object from 3D scans rather quickly. A Coordinate Measuring Machine (CMM) only provides a discrete number of points, and although very accurate, it doesn’t compare to the information acquired by scanning, which shows how the surfaces flow.

What do you model?

When 3D scanning an object, all surface geometry is captured, including imperfections caused by the manufacturing process and any damage the part may have suffered. Typically the part will be remodelled to capture the design intent and to disregard imperfections. There are some good reasons for this. Firstly, modelling in every single defect could be time consuming and therefore expensive. Secondly, one of the main reasons for reverse engineering is to remake the part. Therefore the requirement is to create a ‘perfect’ part representing true design intent. This may require a detailed understanding of the function (depending on the part being modelled) because only then can the design intent be correctly interpreted.

File Types and Characteristics

3D scanners produce what is know as a point cloud these files are the bases of 3d scanning and are used to generate the three different file types, surface wrap, hybrid surface model, and parametric model.

Point Cloud

Scan data produces point clouds which are converted into a mesh or polygon file. These files can be used for inspection, animation gaming and are the base data for reverse engineering.

Characteristics

  • Captures points of the as built component
  • Includes manufacturing defects
  • More points = more definition
  • Used in gaming
  • Most cad programs do not support
  • STL, OBJ, 3DS, PLY

Surface Wrap

Refers to the way in which 3D scanning software like Geomagic, RapidForm, fit mathematical IGES surfaces to a “physical” scan. Similar to how plastic shrinkwrap “shrinks” down onto a part being “wrapped”.

Characteristics

  • Captures as-built state
  • Includes manufacturing defects
  • Patch-work of small surfaces
  • Non Class A surface finish
  • Requires STL file

Hybrid Surface Model

An IGES or STEP surface that usually combines auto-surfaced features with typical 3D modeling operations. Hybrid models are “dumb” because the data contains no parametric history of the model; it is simply a surface that cannot be intelligently edited. Such models have areas that are not ideally mathematical in nature, and instead are composed of NURBS surface estimates of the scan data

Characteristics

  • Ideal data converted from scan data
  • Can ignore or incorporate manufacturing defects
  • “Dumb” IGES surfaces or solid
  • Modifications require re-trimming
  • Can be Class A surfaced

Design Intent Model

Data set that retains the history of how it was designed, so that modifications update all downstream features. Exchange of such models is supported by IGES. SolidWorks is a software program that is popular for creating and modifying parametric models.

Characteristics

  • Ideal data converted from scan data
  • Can ignore or incorporate manufacturing defects
  • Parametric solid model
  • Modify model parametrically
  • Can be Class A surfaced

3D MODELING PROJECTS

Combing scan data to derive new parts

 

Expediting Prototypes to Manufacturing

 

Modeling Large Parts

 

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