Abstract
Single point incremental forming (SPIF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts. In the SPIF process, a ball nose tool moves along a predefined tool path to form the sheet to desired shapes. Due to its unique ability in local deformation of sheet metal, the friction condition between the tool and sheet plays a significant role in material deformation. The effects of friction on surface finish, forming load, material deformation and formability are studied using a newly developed oblique roller ball (ORB) tool. Four grades of aluminum sheet including AA1100, AA2024, AA5052 and AA6111 are employed in the experiments. The material deformation under both the ORB tool and conventional rigid tool are studied by drilling a small hole in the sheet. The experimental results suggest that by reducing the friction resistance using the ORB tool, better surface quality, reduced forming load, smaller through-the-thickness-shear and higher formability can be achieved. To obtain a better understanding of the frictional effect, an analytical model is developed based on the analysis of the stress state in the SPIF deformation zone. Using the developed model, an explicit relationship between the stress state and forming parameters is established. The experimental observations are in good agreement with the developed model. The model can also be used to explain two contrary effects of friction and corresponding through-the-thickness-shear: increase of friction would potentially enhance the forming stability and suppress the necking; however, increase of friction would also increase the stress triaxiality and decrease the formability. The final role of the friction effect depends on the significance of each effect in SPIF process.
Highlights
Single point incremental forming (SPIF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts
The fracture depths of AA2024, AA5052 and AA6111 using the oblique roller ball (ORB) tool are much deeper than those made by the rigid tool, indicating that the ORB tool achieves better Incremental sheet forming (ISF) formability
The experimental results suggest that ORB tool can increase the ISF formability
Summary
Single point incremental forming (SPIF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts. The effects of friction on surface finish, forming load, material deformation and formability are studied using a newly developed oblique roller ball (ORB) tool. Single point incremental forming (SPIF) process by deforming sheet metal using a ball-nose tool along a path of contour lines. Lu et al / International Journal of Machine Tools & Manufacture 85 (2014) 14–29 introduced laser heating in the SPIF process to increase the formability They extended the process window of the single point incremental forming process using multi-step tool paths [8]. Durante et al [17] calculated the relationship between the roughness and ISF parameters including tool radius, vertical step depth and wall angle of the forming parts with a mathematical method, which did not take the deformation and material properties of the sheet metal into consideration. To develop a new tool configuration is much crucial in potentially improving the surface quality and reducing the lubricant consumption during the SPIF process
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