Validation of models for welding and post weld heat treatment in product development of aerospace components

Abstract: It is important to control key dimensions in aero engine components during manufacture. This is achieved by finding a stable process-parameter window for each manufacturing operation and to choose an order of manufacture, which gives an adequate result. Production planning has traditionally been carried out from experience and experiments. However, in order to reduce lead-time and cost, computer based numerical simulations using the finite element method increasingly being used. Simulations can give valuable information about component dimensions, shape, and residual stresses after each manufacturing process. The generated stresses and deformation at each individual manufacturing step affect the subsequent operation. One example is welding where stresses are generated in the structure and the level of stress is dependent on the type of fixture. If the fixture does not allow the component to move dusring the operation, then large residual stresses are generated but the deformations are small. Some of these stresses are released when the component is taken out of the fixture and others are released when it is heat-treated. This is one example why production must consider the whole manufacturing chain. Using combined welding- and heat treatment simulation in the early stages of product development require a tool, which give result of sufficient accuracy and simulations completed within an acceptable time. The necessary conditions to fulfil the accuracy requirement are dealt with in this thesis. Both geometrical- and material simplifications are investigated and conclusions about the effect on full-scale components are drawn. Before the simulation tool with its simplifications is used in product development, the models have to be validated. Validation of tools used for manufacturing simulations on component level must be minimised because of the cost and limited time. A two-stage validation strategy for welding and post weld heat treatment models is presented. It can be performed in the pre- development stage or even before a product is planned, and thereby reduces the the time needed when simulations will be used in later stages. The material model is validated separately using a simple experiment executing the relevant phenomena. In the second validation step, the models for welding and heat treatment are validated on a test plate using the deformation and residual stress as validation parameters.