Main challenges in the development of a serial kinematic portable machine for the ITER vacuum vessel

• A portable machine is presented for machining, post welding operations and NDT tests of the vacuum vessel of ITER.
• It shows stiffness values above 10 N/μm in all XYZ axes and 860 kg, a remarkable stiffness/weight ratio.
• The machine references itself with respect to features and automatically adapts part programmes.
• Said process is fully automatic and the operation of the machine is simple and straightforward.

Last years have seen an increasing demand for large and precise parts following the growth of several sectors, such as conventional and nuclear power plants, shipbuilding industry, etc. The vacuum vessel of ITER is a paradigmatic example of one of those enormous systems that can only be processed in situ and from the inside. This paper reports on the development of a portable machine with serial kinematics to perform the machining, welding and post welding repair, finishing and NDT operations of the assembly procedure of the vacuum vessel of ITER. By applying the topology optimization method on the structure of the machine, a maximized stiffness–weight ratio and homogeneous stiffness figures in the different directions are achieved, thus reaching the goals of the machine with a minimum mass. Moreover, the machine avoids a constant monitoring by a human operator located in the nearby by being able to reference itself with respect to the existing geometry, inform about its position and orientation and automatically adapt its part programmes to perform its duty. The assessment of the machine performance is performed using FEM calculations. The serial kinematic portable machine developed in this manner is then compared with the existing solutions and its operational limits discussed.