3D scanning for reverse engineering: from physical part to CAD model

Start with the decision, not the scanner

3D scanning serves several different purposes: documenting a part, reproducing it, comparing it with its design or measuring how much it has worn. Each goal calls for a different deliverable, and defining it at the start avoids paying for a more elaborate model than needed or, worse, receiving one that cannot be used for manufacturing.

Before scanning, answer one question: what decision will be made with the result? If it is manufacturing a spare part, you need a CAD model with functional dimensions. If it is deciding whether to repair or replace a mold, a comparison against a reference is enough.

From scan to CAD model

The process has four stages. First, the part is prepared: cleaning, stability and, if needed, targets or treatment of shiny surfaces. Then comes capture, where the scanner records millions of points on the surface. Next, processing: noise is removed, the captures are merged and a mesh is obtained. Finally, depending on the goal, the mesh is aligned with a reference CAD model or used as the basis for rebuilding the model.

At Fundimoldes we work with a HandySCAN 3D Silver, with a stated accuracy of 0.040 mm and a stated mesh resolution of 0.200 mm, on parts within a recommended range of 0.05 m to 4 m. The real feasibility of each project depends on the geometry, access and finish of the part.

Mesh, surfaces and parametric solid

A mesh is not a drawing. To manufacture a spare part with fits, holes and tolerances, the model must be rebuilt with engineering judgment: deciding what is a perfect cylinder, which face is flat and which dimension is nominal, instead of copying the imperfections of the scanned part.

Limits worth knowing

The scanner records what it can see. Deep holes, internal cavities, narrow slots and very shiny or transparent surfaces are hard to capture and sometimes require preparation or complementary measurement. Threads and fine fits are usually defined by standard or drawing, not by scanning.

Inspection against CAD

When a design model does exist, scanning makes it possible to compare the real part against it. The result is a color map showing where the part sits above or below the nominal geometry and by how much. It is useful for approving the first parts from a new mold, finding the cause of a warped part or measuring cavity wear.

In maintenance, comparing successive scans of the same mold shows how wear progresses and helps plan the repair before rejected parts appear. For what to check, see the guide to mold component wear.

Checklist before scanning

Common questions.