アルミニウム薄板のＣＮＣインクリメンタル１パス浅底円すい状張出成形時のくぼみ現象

Abstract

Although the process of CNC incremental forming has the advantage of adaptability to small-lot production of thin shell parts, its production rate is relatively low because numerous tool-paths are generally necessary for producing the required profile. The possibility of a single tool-path process, in which a shell is formed from a flat blank by means of stretching on only one stroke of the tool, has been found for deep conical shells, but has not been illuminated previously for shallow conical shells. Here we report the deformation behavior of shallow conical stretching by the single tool-path process. Aluminum and its alloy sheets were stretched to shallow conical shells with several values of half-apex angle α ranging from 60° to 90°, and the deformation behavior was examined. It was found that, when α was larger than about 80°, the depression occurred at the apex in the shallow conical shell; otherwise the shallow conical shells with sharp-pointed apex was formed. The experimental results can be explained on the basis of the mechanism resulting from metal-flow balance between thinning due to stretching and thickening due to ironing-induced excess metal as α approaches 90° the thickening become predominant, so that the piled-up excess metal forms the depression at apex in the shallow conical shell.