One novel method to improve surface quality in incremental sheet forming

摘要

Incremental sheet forming receives widespread study with its advantages of economy and flexibility in low-volume sheet metal parts. However, local loading leads to poor surface quality in formed parts, such as friction trace caused by direct contact between blank and forming tool, and waved impression caused by forming instability or local bending of blank. The formed parts with above surface problems cannot be used as outer panels of one car or aircraft. For this reason, one novel method is proposed that a sheet, namely interpolater, is placed between blank and forming tool to increase the contact area of blank. In this paper, a shallow dome specimen, showing poor surface quality in traditional incremental sheet forming, is selected to analyze the influence of interpolater on surface quality. The specimen is made of aluminum AA2024 which is widely used for aircraft skins. Meanwhile, the interpolater is made of deep drawing steel DC04. Then, a Box-Behnken design is provided and the specimens are formed with various process parameters, such as thickness of interpolaters, tool diameter and step size. With measurement of surface roughness horizontally and perpendicular to the tool path through application of roughness tester, arithmetic mean surface roughness (Ra) and maximum peak to valley height (Rz) are obtained. Then, the specimens formed with interpolaters show better surface roughness compared with those formed without interpolaters. Furthermore, comparing surface roughness of specimens formed with different process parameters, the influence of process parameters on surface roughness is obtained. Finally, the best combination of process parameters with minimum surface roughness is obtained with mathematical analysis.