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Non-rigid geometry variation for fabricated aero structure

Final Report Summary - GEOVAR (Non-rigid geometry variation for fabricated aero structure)

Executive Summary:
Green and sustainable aero engines require weight reduction. For the open rotor technology, with rotating Ni-based superalloy components this is enabled by fabrication (welding) methods where a number of small parts, often in different materials, are welded together. In this type of fabricated structures, variation from manufacturing of the individual parts, from the fixturing and assembly process and from the welding process itself accumulates and propagates through the structure and creates geometrical variation in the final subsystem. This in turn has an influence on the ability to meet requirements on aerodynamics and life. It is therefore extremely important to have a reliable process to control how variation affects the final welded geometries. Therefore, the GeoVar project combines state of the art variation simulation with welding metallurgy, welding simulation and fixture design.

The main result in the project is a novel approach on how to combine variation simulation and welding simulation to optimize fixture design and tolerances to meet geometrical requirements. The method will contribute to decreased development time and cost and increased product quality for welded areo-stucture components.
Project Context and Objectives:
The systematic increase in air traffic and number of flights introduce a huge challenge in reducing the absolute emissions from air transport. The challenge for engine structures is to reduce weight by 10-20%. The way to reduce weight is by using novel material combinations and optimized (fabricated) structures where small parts are manufactured individually and welded together to form a subassembly. Since this way of manufacturing is new to aerospace industry, more knowledge about the effects of geometrical variation and of welding is needed to design robust manufacturing systems to secure geometrical quality and production throughput.
This project proposes new and more accurate methods and tools for variation and welding simulation to reduce the number of testing loops without increasing risk, time and cost. The project propose a novel way to combine variation and welding simulation to support the design of future welding fixtures for aircraft engine components. Specifically, non-rigid geometrical variation simulation is further developed to be able to optimize locator and support positions in order to minimize geometrical variation in the weld gap and also to take fixturing forces into consideration. Computational welding mechanics simulations with integrated control functions is further developed to prescribe fixturing forces for maintaining specific tolerances ahead of the weld for a stable weld process. The two simulation areas are then combined and integrated to support the design of a physical welding fixture suitable for fabrication of aircraft engine components. Here, variation simulation and force estimation will give input to the welding simulation were the effect of variation in the gap, as well as fixturing forces is evaluated. The welding simulation then generates input back to the variation simulation and virtual fixture design. The loop can be repeated until a good combination of part tolerances, fixture design (position of locators and supports, fixturing force), and welding parameters is found. The virtual development is supported and finally verified in a physical demonstrator (a physical fixture) were the most critical combinations of design parameters are tested. The physical demonstrator is a simplified example of a real production fixture but will illustrate typical situations and problems that can occur in real production.
A large part of the project is to build the virtual demonstrator, combining and iterating non-rigid variation simulation and welding simulation to optimize fixture and welding parameters. A small (simplified) and a large simulation case is used to exemplify how optimal locating points, clamp positions, clamp forces and tolerances can be found to meet geometrical requirement on assembly level. In the demonstrator, the RD&T software for variation simulation was chosen since it has the basic functionality needed in the project and because it is used industrially within the aerospace industry. Welding simulation is in the demonstrator performed in the MSC.Marc software, also with the necessary capability and widely used within the aerospace industry. Both software packages are also open to development for the research groups.
To verify the proposed working procedure and simulations preformed, physical tests are carried out. Due to budget and time limitations, only the small test case is verified physically. The small case is however chosen to represent the large case and the results are most likely transferrable. In the physical verification, a physical fixture is built and real welding tests are performed according to a well-defined test plan. The test plan