Design and Development of Fixtures for Top-Lid of Cryostat

Abstract

The cryogenic vessel is having a diameter of about 30 meters, height of 30 meters and a weight of around 4000 MT. Hence, it is not feasible to manufacture and transport the entire vessel as a single unit. The complete assembly is divided into sub-assemblies of 54 modules. This cryogenic vessel is a fully welded stainless steel cylindrical chamber with thickness ranging from 50 mm to 250 mm. Later on to be transported for the final assembly at the installation site. The profile of Cryostat is very complex and requires a proper sequence and welding methods to weld it. So looking at the size and complexity of Job, fixtures are required to be designed to ease up the manufacturing processes.

A fixture is used in manufacturing for quick and easy set-up of job, to hold work-piece, position it correctly with respect to a welding SPM and support it during machining/welding. Fixtures have a direct impact upon product quality, productivity and cost and thus are widely used in manufacturing. Thus it is required to design the fixtures to get the effective setup and welding of sub-assemblies. The purpose of this thesis is to design fixtures for setup and welding of different sections of top-lid sector. It is difficult to set-up such profile because of the non-regular profile it follows, besides the C.G of the job is also non-symmetric. Welding of SS plates can cause distortion in it. Hence to avoid such distortion and to have an ease of welding, it is required to design fixtures. Different parameters affecting the fixture design are analysed and optimized.

Various schemes are conceptualized based on parameters such as welding processes and sequence, fixture assembly planning, ease of handling, shop floor height, crane capacity, fixture weight, lifting plan, etc. The fixtures are modelled using CAD software Solid Edge ST6. Manual load calculations are also carried out and are compared with permissible stress limits. Whereas validation is carried out using FEA software NX 7.5. The fixtures are investigated for structural analysis. By studying the results, the best possible design is selected.