Efficient shaping or reshaping of complex 3D parts using engineered residual stress

ABSTRACT: Due to their excellent strength-to-weight characteristics, integral components (i.e., thin-walled components machined from a single piece of material, which typically consist of a series of pockets, ribs, and stiffeners, have become commonplace on modern aircraft structure. The fabrication of integral components is a machining-intensive process that employs non-conventional machining at high material removal rates. One of the biggest limitations of high speed milling of integral structures is distortion, which results from changes in the residual stress state within the machined component. Excessive distortion can lead to the introduction of excessive fit-up stresses during assembly, can result in improper joints/connections, and can result in parts being scrapped. In certain instances, shops are allowed to use mechanical means (e.g., plastic bending over a fixture) to rectify some of the distortion. This can be effective, but is limited to use on simple geometry and this approach is lacking in quality and traceability. The proposed work plan will develop improved technology for correcting distortion (i.e., reshaping back within drawing tolerance) in complex aerospace parts. BENEFIT: The proposed shape correction technology would provide significant improvements to the efficiency of high speed machining processes. Currently, significant losses result from machined parts that are scrapped due to excessive distortion. Generally, significant machining has been performed on these parts prior to scrapping so the scrapped parts have considerable value. A process to efficiently and effectively correct the shape of these distorted parts and return them into the production supply offers the potential for significant cost savings relative to the current approach (scrapping these distorted parts). This technology is important to the aerospace community and is applicable to many other industries as well. For example, ships and space vehicles use similar integral components that have distortion related issues. Large welded structures like pressure vessels and industrial facilities are often adversely affected by distortion due to residual stresses from welding. As this technology becomes more mature there is an opportunity to apply it for benefit in other industries.