Assembly tool design
A daunting task for a young engineer
Like so many visitors before him, a youthful-looking, middle-aged Korean man posed for a picture a few weeks ago at the foot of one of the 22-metre-tall sector sub-assembly tools (SSAT) in the ITER Assembly Hall. Something however set this visitor apart from the others. Back in 2006 as the Chief Engineer at SFA Engineering Corp., one of Korea's leading industrial automation companies, Kyoung Kyu Kim had been entrusted with a daunting task—to design the very sector sub-assembly tools now towering above him. After years of working with CAD designs, building a functional 1:5-scale mockup, and eventually overseeing the manufacturing of the actual tools at Taekyung Heavy Industries, Kyoung Kyu was seeing them for the first time in their natural environment. And although he knew them well, he was utterly impressed.
Assembly tool design | A daunting task for a young engineer
Trained as a mechanical engineer at the prestigious Gyeongsang National University, Kyoung Kyu Kim had already accumulated, at age 31, significant experience in structural design and factory automation. The challenge he faced in 2006, however, was beyond anything he had ever anticipated. Of course, he was not starting from scratch—international ITER teams had been working on sector sub-assembly tooling since the mid-1990s as part of the Engineering Design Activities phase (EDA), with Russia leading the effort. When Korea joined the project in 2003, ITER Korea expressed a strong interest in ITER tool manufacturing and, together with the ITER Joint Central Team, soon produced conceptual design documents.
In 2006, as a young engineer, Kyoung Kyu Kim was entrusted with a daunting task—to design the giant tools (SSAT) that would assemble the ''modules'' of the ITER vacuum vessel. On a recent visit to ITER he saw them for the time in their natural environment.
A conceptual document, however, is not a "nuts and bolts" blueprint. "It's more of a concept for how the tool is supposed to operate," explains Robert Shaw, presently in charge of coordinating ITER machine assembly and at the time closely associated with SSAT conceptual development. "A conceptual document shows the geometry, the kinematics (the geometry of motion), the specifics for the weight to be supported and the precision to be obtained. But conceptual designs require quite a bit of fleshing out before you have an actual design document." And that is precisely the job that was passed on by ITER Korea to SFA Engineering in 2006.
"No one had ever manufactured a tool like this, capable of handling and assembling with millimetric precision components that are up to 17 metres tall and weigh in excess of 400 tonnes," says Kyoung Kyu Kim. "The kinematics were extraordinarily subtle and complex. In order to position the vacuum vessel sector and the toroidal field coils, the moving parts of the tool needed to handle six degrees of freedom: up and down, side to side, forward and backward, plus rotational directions (swivel, tilt, pivot) relative to the axes..."
Although far from being as sophisticated as the projected SSAT tools for ITER, the assembly tools used to assemble the Korean tokamak KSTAR, and to a lesser extent the European JET, had faced similar challenges. What was different here was the sheer mass of the components to be handled. "A vacuum vessel sector alone weighs as much as a fully-loaded Boeing 747. This translates to an enormous stress on the structures." From calculations and 3D models, a monster emerged: 22 metres tall (the equivalent of a six-storey building), 800 tonnes (the weight of a Union Pacific steam locomotive), with legs as thick as a sequoia tree and "arms" so sturdy and powerful they have to move on rails.
We have grown so used to the actual size of the sector sub-assembly tools that this image feels unreal: dated 2010, it shows the model, one-fifth of the tool's actual size, that was manufactured to perform structural and functional tests, and to demonstrate the global kinematics of the system.
No tool this size, not even in the shipbuilding world, and with such complexity had ever been manufactured. The challenge was both structural and functional and Kyoung Kyu Kim, ITER Korea, and SFA agreed that it was safer to build and test a model, one-fifth of the tool's actual size. By 2010, the mockup was ready and operational, and it demonstrated kinematics "with no real feasibility issue."
The rest of the story has been chronicled in the ITER Newsline—from the progress of manufacturing at Taekyung Heavy Industries in the port city of Changwon, to the arrival of the first SSAT elements on the ITER site and the subsequent assembly of the two identical twins beginning in late 2017.
Five years later, the SSATs have succeeded in the first steps of their immense task: a first "module" was assembled in 2021-2022 and installed in the Tokamak pit last May; a second one has recently entered the same process and should be ready by the end of the year. Seven others will follow the same path in order to complete the machine torus.
For Kyoung Kyu Kim, designing the ITER sector sub-assembly tools was a defining experience and a lesson in determination that oriented his subsequent career. Through the company he later founded and heads—Mecha T&S Inc. (Mechanical Total Engineering Solution)—the 31-year old engineer of 2006 now works for Korea's nascent space industry, another way to contribute to the future of humankind.
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