Faster to the ideal CAD model – Engineers are familiar with the challenge: In reverse engineering, surface reconstruction often becomes a bottleneck when building a CAD model. That’s why the Swiss company units OST has optimized and accelerated the process using Siemens NX – supported by a CAD/CAM partner network including Janus Engineering and Marenco.
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When engineers and designers visit Lake Greifensee in Switzerland, they can take a cruise aboard the Greif – the only coal-powered steamship still operating in public passenger service in Switzerland today. That this relic from the late 19th century is still running is thanks to the “Foundation for the Operation of the Steamship Greif.” The foundation meticulously overhauled the steam engine as recently as 2021 – a complex undertaking, as replacement parts for many components of the 450-kilogram engine no longer exist. Therefore, modern CNC machines and injection molding systems are used to replicate them. The challenge: these devices are fully digital and require CAD models of the components – 3D blueprints that simply don’t exist for the old parts. The foundation therefore commissioned units OST. The company is a full-service partner for simulation, engineering, and industrial metrology, as well as a specialist in so-called reverse engineering.
Reverse Engineering: Creating a Surface Model as the Supreme Discipline
Here’s how reverse engineering works: In the first step, a GOM system from the Zeiss Group was used to scan system-relevant engine components – including slide rods, low-pressure connecting rod base plates, and eccentric rods. In the strip projection process, the camera system captures the surfaces of engine components in a short time with up to 500,000 measurement points. This made it possible, for example, to digitize the connecting rod of the steam engine from 27 angles with an accuracy of 0.01 millimeters. But building a point cloud of up to half a million points is only half the battle. Once these points are polygonized into a faceted body – a mesh of tiny triangles – and saved as an STL file, the real challenge begins: generating a CAD surface model. Such a model is essential for manufacturing replacement parts using CNC machines.
The most time-consuming part of creating a 3D volume model through reverse engineering is surface reconstruction – converting the polygon mesh into closed surfaces. All the more frustrating, says Roger Eggenberger, Managing Director of units OST, that for a long time no software reliably supported this process. “There are many vendors that promote their solutions. But most programs still struggle, for example, to recognize where a curve begins. They didn’t meet our high quality standards,” says Eggenberger. “That’s why a lot of manual post-processing was previously required – which we wanted to reduce in order to save time and lower costs.”
Eggenberger was accordingly pleased when Janus Engineering – a CAD/CAM/PLM process chain specialist for over 30 years – presented a promising solution. “Most of our customers know us as a CAM service provider,” says Bernhard Maurer, Chairman of the Board at Janus Engineering Switzerland and Austria. “We’ve evolved into a systems integrator and built a strong partner network. This allows us to manage all processes from CAD to CAM from a single source, ensuring maximum security and productivity.” In this case, also on board: Swiss company Marenco – a Janus partner, CAD specialist, and NX service provider.
Surface Reconstruction Optimized
Janus Engineering and Marenco jointly supported units OST in optimizing the surface reconstruction process. The core of the solution: Siemens NX, an interactive CAD/CAM/CAE system that supports all aspects of digital product development – from concept to design to manufacturing. The system includes a tool that generates a surface model from the polygon mesh of an STL file. The software can automatically recognize geometries like cylinders, producing a clean surface model that accurately reflects the component’s actual condition in a short time.
However, since most parts are damaged or worn – for example with a curvature – Eggenberger still has to reconstruct them digitally. Siemens NX assists with this as well. Using the software, he can quickly generate freeform surfaces from recognized geometries, trim and merge them into a solid body, and add interior contours. “Siemens NX has become much more intuitive in recent years. Commands like union and subtraction work reliably, and trim functions are mature,” says Raffael Heierli, Head of Mechanical Engineering at Marenco. This makes it possible to create a perfect CAD model in relatively little time. “Without NX software, this work used to take about 18 hours,” confirms Eggenberger. “Thanks to the optimization, generating the 3D model now takes just six hours. We‘ve significantly accelerated the process.”
The next step is seamlessly transferring the CAD model into the CAM system – without time-consuming and error-prone conversion. There, employees can develop high-quality tool paths in an automated way and simulate the resulting G-code execution.
“The collaboration with Janus Engineering and Marenco was productive. We were able to discuss everything on equal footing and find the perfect solution for economically viable reverse engineering,” Eggenberger concludes. “The investment in the software has paid for itself very quickly.”