Final Report Summary - GEOVAR (Non-rigid geometry variation for fabricated aero structure)
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 defines variation in geometrical input parameters giving rise to geometrical variation in the subassembly after welding. Physical parts are measured before and after welding. A strong correlation between deviations before and after welding was found.
Measured geometrical variation after welding was then compared to simulated geometrical variation after welding. Also here, good correlation was obtained for the non-nominal setups.
The project has basically been in line with the project plan. WP4 (physical test) was however a little ahead of plan. This was due to the fact that this work-package was identified as a risk for the project and therefore got extra attention. The work in the project started with a literature study on non-rigid variation simulation and welding simulation followed by a problem definition defining the two test cases, a small and a large, and all parameters needed for simulation. The smaller test case consists of two sheet metal parts that are to be welded together in a fixture. This case was used later on for verification of the simulation procedures with real physical parts and a fixture developed in the project. The large test case is an industrial case, basically with the same parameters and focus as the small one but consisting of more parts to be welded together. For this case, no physical verifications were performed due to time and budget limitations but the outcome was simulated using the methods developed and verified on the small test case. After problem definition and case specification, the virtual demonstrator, combining non-rigid variation and welding simulation was set up and simulation models were built. Variation and welding simulations for the small case and the large case has been carried out. Physical welding has been conducted.
The following work has been conducted:
• The two test cases are specified, including CAD models and specification of the joining fixture.
• Meshes of part geometries for simulation are created.
• Welding parameters and material data for both cases are specified.
• Welding simulations models are built and simulations are performed for some disturbances/instances. The simulation procedure is verified for the small case.
• Basic variation simulation models are set up and variation simulations including clamping forces are performed for the small case.
• Welding and variation simulation is performed for the large case.
• Production of parts for the small case is conducted.
• The physical fixture to be used during welding is built.
• Inspection plan for the final assembly is defined for the small case.
• A test plan with welding parameters and locators disturbances is defined.
• Welding according to defined test plan is carried out without problems.
• Inspection of welded assemblies is carried out without problems.
• Comparison between inspected physical assemblies and simulated results have been conducted successfully.
• Heat treatment of physical assemblies have been conducted to investigate its importance. This was outside the project scope, but will provide useful knowledge for future research.
The methods and simulation tools developed in the project has a great potential to make large direct industrial impact as well as long term technological and environmental impact.
1. The concept of “fabrication”, were small parts (“sub-components”) are welded together to form subassemblies or “components” has a great potential in saving weight but adds a large complexity when it comes to managing geometrical variation and tolerances. Variation in sub-components and fixtures, together with variation added from the welding process will accumulate and may jeopardize the fulfilment of geometrical requirements on component level that in turn may affect requirements on aerodynamics, life etc. The ability to simulate and predict the effect of variation propagation in non-rigid structures and what variation that can be accepted to secure the quality of the weld will reduce risk and number of testing loops required and increase quality in the final components delivered to the customer. The result have been spread to industry through the topic manager and the use of the research results. RD&T Technology has further strengthen its ability to simulate and predict the effect of welding in combination with geometrical variation which will be used in other business areas.
2. Through this project, FEA-based simulation tools for non-rigid variation simulation and welding simulation has been further developed and also used together in a novel way. Increased accuracy in non-rigid variation simulation as well as in welding simulation has by itself lead to better understanding and better quality in early design predictions. Using the two technologies together will allow new design and manufacturing solutions to be verified with better accuracy and thereby reducing risk, time and cost. The simulation environment developed was in this project used to evaluate novel concept for aero engine structures but the simulations are generic and can easily be transferred to other business areas with other geometries, materials, and welding strategies. This generic knowledge will open doors to other research projects for different products or market areas.
3. The systematic increase in air traffic and number of flights introduce a huge challenge in reducing the absolute emissions from air transport. Therefore, in order to fulfil the European aviation environmental objectives the aero industry needs to reduce CO2 emission by 50% until 2020 and 75% until 2050. 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. Fabrication of structural components increases the need for accurate methods and tools for variation and welding simulation to reduce the number of testing loops without increasing risk, time and cost. The ability to simulate and predict the combined effects of geometrical variation, fixture force and welding on the performance parameters of an aero engine component is crucial for the whole fabrication concept and the fulfilment of the goals on reduced weight.
Hence, this project’s main impacts are industrial, technological and environmental. All of them give Europe a clear competitiveness when environmental aspects are so related to European policies, and so, European future minimum specifications for aeronautics.
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