Metal Fatigue Failure of Rubber Mixing Machine Rotor
3DWORX, a service bureau in South Africa, was tasked with quite the job. A truck tire manufacturer wanted to recreate a 900kg hardened steel rotor for a rubber mixing machine. The rotor had snapped like a toothpick from very high torque and metal fatigue.
The machine had been imported many decades ago, so replacement parts were not available, and even if they could be sourced, it could easily take a year or two for parts to land in South Africa.
The broken rotor showed signs of welding repairs and machining, and nobody knew what the original bearing and keyway sizes were. So again, if a part could be sourced, it may not even match due to repairs and modifications done over time.
Decision to 3D Scan, Design 3D CAD Models, and Manufacture New Parts
A solution had to be found quickly to manufacture a replacement rotor in South Africa, but no schematics or CAD models existed.
The rotor had precision-machined bearing surfaces and keyways on each end, but the central section consisted of two organic-shaped “wings” that mixed tons of rubber as it passed through the mixer. These central sections could not be sketched in CAD easily, so generating a 3D model was not as simple as designing it in a conventional CAD program.
The hardened surfaces on the “wings” were severely worn, with significant abrasion and pitting. So 3DWORX proposed to their client that the unbroken rotor in the pair should be 3D scanned in order to create a 3D CAD model that could be built from the 3D scan data.
The rotors in the pair had some mirrored features, but the two rotors weren’t simply complete mirrors of one another. This was going to be a tricky reverse-engineering project, requiring some state-of-the art hardware, software, and techniques.
3D Scanning
The project was approved and 3D scanning was done on-site with an eviXscan HD Optima 3D scanner. It’s a metrology-grade, professional 3D scanner that uses structured blue light to measure parts to an accuracy of 20 microns, for which the scanner has a VDI/VDE calibration certificate. The eviXscan HD Optima is portable and yet extremely stable as it is mounted on a very sturdy Manfrotto tripod, with which it ships.
A white contrast spray was applied, then eviXscan’s unique-code magnetic markers were used to automatically align the 3D scans – a huge time-saver.
The eviXscan Suite software was used to reconstruct the 3D scans into a mesh model that was then exported. From there, a 3D CAD model was created and two new rotors were manufactured.
Analysis with Geomagic Design X
Initial analysis with Geomagic Design X after 3D scanning revealed that the unbroken rotor was bent along its longitudinal axis. It was likely that it would fail if put back into use, so two CAD models would be needed.
eviXscan unique-code magnetic markers to automate scan alignment.
Hybrid CAD Modeling Using Geomagic Design X
A hybrid 3D CAD modelling technique using typical geometric CAD features combined with splines would have to be used to create the 3D models.
3DWORX knew that Geomagic Design X Pro was the right solution for them. With its ability to quickly generate a surface model of the organic-shaped “wings” from 3D scan data and to sketch the more conventional shaft end detail. Geomagic Design X was able to effortlessly manipulate the huge mesh model, while the 3D CAD model was sketched from the scan data.
eviXscan Suite 2.9 used to control the 3D scanner and assemble the 3D scans into a mesh model.
Geomagic Design X Pro “Auto Sketch” used to accelerate sketching the core shaft.
Modeling the organic-shaped “wings” was going to be tricky. First the manual “feature following” technique was used, but then it was quickly discovered that Geomagic Design X Pro could do this automatically using “Auto Surfacing.” This saved them days of modeling time!
Geomagic Design X Pro “Auto Surfacing”
Completed 3D CAD models in Geomagic Design X Pro.
Comparing 3D CAD Model with 3D Scan
After the first 3D CAD model was completed, it was compared with the eviXscan 3D scan data using the “Accuracy Analyzer” in Geomagic Design X. The result was simply outstanding, considering the significant amount of damage to the rotor.
Accuracy Analyzer in Geomagic Design X Pro.
Some Reflections on the Project and Tools
The above real-world example illustrates how engineers can rapidly create solutions for complex manufacturing and production problems when they have access to the best toolset and skills.
3D scanning would have been even quicker using eviXscan’s newest 3D scanners, specifically the eviXscan WideRange 65 with its very large field-of-view, or the eviXscan 3D Quadro with its four cameras and dual field-of-view for both small and large objects.
Both of these new eviXscan models can 3D scan larger areas using their significantly faster, higher-resolution cameras that deliver more precise results at an affordable cost.
The combination of eviXscan’s various 3D scanners, the eviXscan Suite of software (included with scanners), and Oqton Geomagic Design X, offers a great ROI for reverse engineering and quality control.
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