Plastic strain distribution during splined-mandrel flow forming

The local variation in the von-Mises equivalent plastic true strain within an AISI 1020 steel work piece that was fabricated by single-roller flow forming over a splined-mandrel was assessed using micro-indentation hardness. The largest equivalent plastic true strain occurs near the work piece/mandrel interface directly in front of the nose of the internal ribs and reaches approximately 170% when the work piece thickness reduction is 51%. This represents the forming limit for AISI 1020 steel when subjected to the flow forming parameters used in this study. High levels of grain elongation were also observed in the work piece at the work piece/mandrel interface near the nose of the internal ribs and along the leading and trailing edges of the ribs.

► Sharper dependence to the thickness reduction in the grains aspect ratio in the mandrel side compared with the roller side.
► Highest strain on the mandrel/work piece interface directly in front of the nose of internal ribs with highly elongated grains.
► Very high strain close to mandrel side represents the forming limit for flow formed AISI 1020 steel.