Effect of toolpath on the springback of 2024-t3 aluminum during single point incremental forming

Incremental forming is a nontraditional forming method in which a spherical tool is used to asymmetrically deform sheet metal without the need for expensive allocated dies. Incremental forming employs a tool path similar to that used when CNC milling. Hence, when forming a part, the forming tool makes a series of passes circumferentially around the workpiece, gradually spirally stepping down in the z-axis on each sequential pass. This tool path deforms the sheet metal stock into the final, desired shape. These passes can start from the outer radius of the part and work in (Out to In, OI forming) or they can start from the center of the shape and work outward (In to Out, IO forming). As with many sheet metal operations, springback is a big concern during the incremental forming process. During the deformation process, residual stresses are created within the workpiece causing the final formed shape to springback when it is unclamped, sometimes very significantly. The more complex the geometry of the final part and the more total deformation that occurs when forming the geometry, the greater the residual stresses that are generated within the part. The residual stresses that have built up in the piece cause more significant distortion to the part when it is released from the retaining fixturing. This paper examines how the step size (in the z direction), OI vs. IO forming, and final part geometry affect the total springback in a finished piece. For all of these tests 0.5 mm thick sheets of 2024-T3 aluminum were used to form both the truncated pyramid and truncated cone shape. From this investigation it was found that smaller step sizes result in greater springback, IO is significantly less effective in forming the part (due to workpiece tearing), and final part geometry plays an important role due to the creation of residual stresses that exist in corners.