Purdue CMSC, in collaboration with Purdue Silicon Detector Laboratory (PSDL), is designing, prototyping, testing, and fabricating composite support structures for CERN’s Large Hadron Collider (LHC) CMS and ATLAS experiments. This is part of the particle collider’s High Luminosity upgrade, with the installation of final components in 2026-27. The Thermwood LSAM 105 Additive Printer and five-axis LSAM Trim router at the Purdue LSAM Research Laboratory have enabled rapid large-scale printing and machining of trimming fixtures for the high precision composite tube structures. The 1m long, 208mm radius trimming fixture was printed on the LSAM with Acrylonitrile Butadiene Styrene (ABS) reinforced with 20% by weight of carbon fiber.
This 914mm long prototype of the CMS upgrade inner tracker support tube will allow project partners at national labs, universities around the world, and CERN to begin installation tests of their structural and detection components. Individual components installed into this support tube are expected to be positioned within +/- 0.5mm or less, so accurate machining of interface features is critical. The kind of precision necessary for the particle collider, at a large scale, is made possible, economical, and convenient with the aid of systems like LSAM.
Since critical surfaces would be machined later, and to increase production speed for the prismatic geometry, the tool was split into two vertically-printed segments. The halves were bonded with adhesive and dowel pins for joint strength and stability.
The faces that would become the trimming fixture base were machined to the flatness required for fixturing later. The printed, bonded fixture was then mounted on pedestals in the LSAM Additive Trimmer and the surface was machined to fit the nominal inner surface shape of the composites half-cylinders to be trimmed. Edge finding and reference features were machined into the trimming fixture to allow proper centering of the cured composite part.
Using this printed and machined fixture, the composite part edges were trimmed, interface holes drilled, mating surfaces machined flat and a scarf joint for joining the two half-cylinders was created. The precision trimmed composite halves were then able to be bonded together.
The final tube, 3.2m long, has to support 140kg of mass while only allowing sub-millimeter deflections to occur. Purdue CMSC and PSDL will also be designing, fabricating, or testing other composite support structures for the CERN LHC upgrade as small as 0.5mm sheet goods and as large as 2.4m x 5m sandwich panel tubes. It is planned for the LSAM system to be utilized to create tooling and some final components for these other structures.