Post-machining distortion of formed fuselage frame segments

Process development work was conducted to develop a machined fuselage frame concept for a small (5 abreast) commercial airplane. To minimize detail fabrication cost and to facilitate lean manufacturing, roll forming was identified as the preferred forming process. To reduce assembly costs, long frame segments were desired to minimize the number of frame splices. Since plate stock is limited to lengths of approximately 3.66 meters (12 feet), formed aluminum extrusions were selected as the raw material form. Roll forming and stretch forming process paths were screened for both J section and rectangular bar extrusions. The post machining distortion produced in formed extrusion and plate hog-out frame segments was compared to each other and to process standards governing allowable fit-up forces. As a result of this process development activity, a producible roll forming process path was developed. The direction as well as the magnitude of the distortion for the selected and alternate forming process paths will be discussed in detail.