Robust design of aircraft skin stretch forming process based on transmitted variance model

Conventional optimization design in skin stretch forming process rarely considers the uncertain factors existing in materials, process conditions and parameters such as modulus, thickness and residual strain, thus causing great fluctuation in forming quality. Aiming at this problem, a robust design approach for aircraft skin stretch forming based on transmitted variance model is proposed, which combines robust design with finite element method. The main quality defects and key design parameters in skin stretch forming process are analyzed, and the fluctuation of design parameters and noise factors are considered. Based on the transitive relationship among the variances of design parameters, noise factors and response, the estimations of response mean and variance are obtained on the basis of the transitive relationship among response variance, design parameter variance and noise factor variance. Robust design of parameters is realized by taking the minimized mean square error as the criterion of robust optimization and by combining with ideal point to carry out multi-objective optimization. The stretch forming process of a certain skin part is taken as an example to verify the proposed method. The result shows that in comparison with the traditional optimization design, this method can effectively reduce the quality fluctuation and improve the robustness of skin stretch forming process.