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Injection Moulded Cover Reverse Engineering & Deviation Analysis

Other Projects

Recreating an existing part: the steps we take

One of the main benefits of 3D scanning is being able to create different types of digital representations of a part. This may be used for reference, for visual aids or for generating new, fully realised parametric CAD data. 

Reverse engineering follows many of these steps with the crescendo being a reference model or a design intent model. 

A project we were involved in allowed us to show the real benefits of 3D scanning in creating all types of usable data which can be taken and worked into many different stages of a project. Those types are: Point Cloud Mesh; Reference (NURBS) Data; and Parametric Design Intent Data (reverse engineered model). 

The part was an injection moulded cover that made up part of an assembly. It featured holes, a sealing rim and a top surface that profiled around internal components. There was no CAD data for this part so we knew the importance of capturing accurate, reliable data that we could model from and use going forward for tooling, assembly or cataloguing. 

Our scanner was able to capture the accurate data we needed and once we were satisfied we captured all we needed to, it was time to create the mesh.

Different Types of 3D Scanning Data

With this scan, we had the first types of data, a point cloud and the mesh. The most basic, memory-heavy types of 3D scan data. Very little post-processing goes into this (unless required) and this data can be demanding for most computers – even high-spec CAD machines if the dataset is large.

Point Cloud
Mesh

From here, we can use the scan data to, relatively quickly, create the NURBS Reference surface model. This is a much lighter, reference ‘shell’ model of the scan data. It’s made up of a series of splines and vertices and can be handled by computers and CAD programs more readily and in a much more stable way. 

Reference Model (NURBS)

The last type of model we can create from scan data is the most useful but the most time-consuming. A Design Intent model is an editable parametric model that features solid geometry, a model tree and is created to mimic the original design intent of the part. A design intent model may:

  • make surfaces flat again where they may have been distorted;
  • ‘repair’ any damage or wear on the original scanned part; or
  • remove paint, rust buildup or any other surface addition (providing there is some evidence of the original surface somewhere) 
Design Intent Parametric CAD Model

Analysing deviation of the new CAD data

To demonstrate Scan Data vs. Design Intent CAD models, we created a small inspection project of the scanned part and overlaid it on the design intent model. A deviation analysis was created and highlighted by anything other than green that is effectively different to the scan data. This, though, is how the part would have been designed originally. Take a moment to notice the post-mould distortion on the part.

CAD Model
Deviation
CAD Model
Deviation
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