Assembly of the Iter reactor is underway. Tokamak components from hundreds of factories on three continents are assembled on the international program's own site. The Iter Organization is responsible for integrating and assembling the components delivered to the site by the seven program members. But assembling these elements is more than just a simple matter of fitting them together - the components are complex and numerous, and the tolerances very tight, in the millimetre range.
An analysis based on digital elements is necessary to ensure that the components can be perfectly integrated. The essential preliminary step is data collection by metrologists. Their aim is to provide reverse engineering specialists with precise data, after measuring each part to check its conformity. PolyWorks software is used in both phases, metrology and reverse engineering.
" I had already used Poly Works Inspector on a major project before arriving at Iter. I wanted to continue using this software, which enables us to acquire large point clouds directly in the software. "says Lionel Poncet, an engineer in Iter's metrology group. " Other software on the market is limited in its ability to analyze large numbers of points. We prefer PolyWorks Inspector, which meets the need for rapid analysis of data containing a large number of points. "adds Hani Gagueche, CAD draftsman in charge of reverse engineering.
The cryostat base was installed in the Tokamak assembly shaft in May 2020: it took teams from Iter and its partners 10 years to design, build, deliver, assemble and weld the cryostat base. Some 6 meters high and 30 meters in diameter, 1,250 tons to move and position: the integration of the cryostat base required measurements and 3D reconstructions to adjust the assembly.
" In the field of metrology, we use PolyWorks directly with our laser scanning equipment. Once the object has been scanned, we have access to a point cloud and a polygonal model that are both highly accurate and of excellent quality, thanks to the tools available at the very moment of acquisition. "explains Lionel Poncet. " Once the data has been received, thanks to reports in our possession indicating critical assembly zones, we launch analyses that take into account the components as built and the components located around them whose dimensions we know, to ensure that they work well together. For the cryostat base, we quickly realized that there were some very critical areas, identified using PolyWorks, and that a tool would be needed to move this component to within a millimeter over a distance of some thirty centimeters. Several tools were developed in-house, and PolyWorks enabled us to choose the most suitable one "adds Hani Gagueche. And Lionel Poncet adds that, in this case, PolyWorks optimized the installation sequence in less than 12 hours.
While the installation of the cryostat base was not easy, even more complex challenges await the metrology and retro engineering specialists: the components to come are certainly smaller, but the area is now crowded and tolerances even tighter. And the deadlines for carrying out the operations are short!
"This summer, the installation of the first sector of the Tokamak's vacuum chamber on its pre-assembly tool was tricky, confirms Hani Gagueche. Magnets, heat shield and vacuum chamber sector had to be assembled with a clearance of just 20 millimeters at the most critical points. To allow for the integration of sensors, we had to reposition these elements in relation to each other using PolyWorks renderings."
" The prestressing rings were also completely scanned.explains Lionel Poncet. A model was created for integration into CAD in preparation for future assembly packages. Correction coils were also scanned using PolyWorks. On the resulting model, we need to design shims to fit future interfaces. We also need to characterize and measure a number of pipes to ensure that there will be no collisions with future components due to arrive. This also enables us to know the interface for future welding and cutting. "
In addition to in-house teams, subcontractors also use PolyWorks to acquire point clouds. " PolyWorks Inspector is a universal module dedicated to metrology, enabling multi-device connection. It is available in standard or premium mode, enabling post-processing of dense point clouds with the possibility of obtaining, in real time, "quality" indications on data acquisition. Beyond the logical metro aspect, the software can also be used, for example, to obtain clearance maps. ", argues Thibaut Hehlen, Sales Manager at PolyWorks Europa, a subsidiary of InnovMetric, the publisher of Poly Works. " Thanks to software such as PolyWorks, we are able to make watches with trucks. "says Hani Gagueche. To make 3D reconstructions of critical cases available, the reverse engineering specialists use PolyWorks Modeler, a modeling and reverse engineering solution. " This module enables us to reconstruct surfaces from very precise meshes, and to provide a CAD file accessible to all, even when users don't have Poly Works or powerful computers. For example, Catia users on the Iter program have access to the files we have produced. "explains Hani Gagueche.
The new PolyWorks Modeler automatic surface calculation algorithm will soon be tested by Iter teams. This algorithm could save a considerable amount of time in terms of reconstruction time!
Front page photo:Positioning the cryostat before lowering it into the Tokamak shaft for final assembly.
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