Reverse engineering is a powerful method of creating digital designs from physical parts, and along with techniques like 3D scanning and 3D printing, can be an invaluable tool in your prototyping toolkit.
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3D scanners can measure complex objects very quickly and can dramatically speed up your design workflow when real life references are involved. With the ability to capture and modify physical shape, you can design 3D printed parts that fit perfectly into a variety of existing products. 3D printed jigs allow you to repeatedly position a drill or saw, or use adhesives to assemble parts precisely. Make a form-fitting, reusable face shield for sandblasting, painting, or etching.
In this post, we'll walk through the reverse engineering process for aftermarket digital gauges, explain how to scan parts for 3D printing, and provide tips for using the correct reverse engineering tools in CAD software to 3D scanners and 3D printers.
1. From physical to digital: grids and solids
One of the biggest challenges people encounter when converting physical objects to digital objects is the major incompatibility between the two different types of 3D models (meshes and solids).
3D scanners output meshes, not constructive "solid" models. The mesh needs to be reverse engineered to make it editable.
The mesh is the main output of all 3D scanners and is a format commonly understood by 3D printers (STL). A mesh represents a surface in the shape of a large number of triangles connected edge-to-edge. A mesh model does not contain any information about an object other than the position of the triangles that define the shape.
Engineers, on the other hand, are trained to use solid models. A solid model holds information about how to design an object, and this information is explicitly encoded into the model as features in a "stack" of logical steps. In solid CAD, the size of a single feature can be changed and the rest of the model will update to accommodate the change.
Because the mesh lacks information about the object's construction, the ways to change the mesh model are limited - CAD software such as Solidworks and Onshape cannot modify the mesh directly. If you need to make significant modifications to the base design of a scanned part, you need to convert the mesh into a solid CAD drawing: this process is reverse engineering.
2. Reverse engineering workflow
Reverse engineering is important when you want to create new parts that reference or incorporate old designs (where the original CAD design is not accessible).
For example, you can create replacement parts that match the original design of damaged existing parts, or use reverse engineering processes to integrate complex surfaces of existing objects into 3D printable very useful product.
To demonstrate the basic steps of a reverse engineering workflow, let's take a look at the process of creating an assembly jig for an aftermarket digital instrument mounted on a Volkswagen Golf air vent.
2.1 Prepare objects for scanning
Spray temporary matte powder on objects to improve scanning accuracy. Even slightly glossy surfaces can degrade scan quality, while reflective and transparent surfaces cannot be scanned at all without a matte coating.
Using a temporary matte powder can improve the scanning accuracy of objects
2.2 3D scanning objects
Capture important parts of your part with a high-precision 3D scanner. A desktop structured light or laser scanner is the right tool for the job, with an accuracy of ±100 or better.
NOTE: If the object has deep depressions, you may need to orient and rescan the object several times.
2.3 Refining the grid
Some scanners generate very large mesh files, which bog down subsequent steps.
Scanner software fixes small gaps and simplifies scanning, making the data more manageable in CAD. Try to make the model as small as possible without destroying important details.
Tip: If you need more control, Meshmixer is an excellent choice for refining the scanned mesh.
2.4 Import mesh into CAD
Import the mesh into CAD software equipped with reverse engineering tools. Geomagic for Solidworks is a powerful choice for resurfacing complex organic shapes.
If you're reverse engineering parts with simpler planes, Xtract3D is a cheaper, lightweight alternative.
In this step, the scan grid is moved and rotated so that it aligns with any existing design components.
Tip: Make drawing easier by rotating and aligning your scans to face the orthogonal view orientation.
2.5 Extract important surfaces
There are three approaches to extracting scanned shapes to create solid models that can be edited with CAD tools: semi-automatic surfacing, automatic surfacing, and manual redrawing.
- semi-automatic surface construction
Complex surfaces are difficult to draw by hand, so semi-automatic surface drawing is an option. This function generates a surface suitable for scanning the detection area. By varying the sensitivity of the surface detection function, different surfaces will be found.
Tip: Geomagic for Solidworks detects surfaces on the scan to fit 3D curves. Use the Paintbrush to manually add or subtract to the scan area for each area.
You may need to repeat this process several times with different sensitivity settings to detect all surfaces. These surfaces can then be trimmed and woven together to create editable solids.
Semi-automatic surfacing can be used to recreate curved shapes later when maximum editability is required and sharp-edged accuracy is important.
- Automatic Surface Texture
Autosurfacing generates solid models from any waterproofing scan. You can subtract and add to this autosurface body using standard CAD tools, but it's more difficult to move the base features on the body itself.
You probably don't need control over edge placement. For example, if you are scanning parts of the human body to create custom ergonomically shaped products, or want to create jigs to precisely or repeatably modify handcrafted objects. In these cases, automatic surfacing is a great way to save modeling time.
Note: Comparing the results of automatic surfacing with semi-automatic surfacing: some precision is lost, especially around sharp edges.
- manual redraw
For simple features such as bosses, holes, and recesses, it is usually fastest and most accurate to redraw the feature using the scanned model as a reference. Reverse engineering software allows you to create sketch planes that align to the planes on the scan and extract cross-sections from the scan mesh, which helps you match the shape of the original object.
2.6 Integrating new objects
Once the scan has been converted to a solid, it can be subtracted from another solid to create a fixture that firmly holds the original part.
The design of the new gauge components was also referenced to scanned dimensions, using semi-automatic surface extraction of curves.
2.7 3D printing new design
Printing fixtures on Formlabs Stereolithography (SLA) 3D Printers gives you high precision comparable to the output of engineering-grade 3D scanners. Use the strength and precision of Formlabs Rigid 4000 Resin.
Once these steps are complete, the 3D printed jig can be used to assemble the new gauge to the OEM vent.
Original Link: 3D Reverse Engineering Combat—BimAnt