Technical Report Plastic strain distribution during splined-mandrel flow forming M. Haghshenas ⇑ , M. Jhaver, R.J. Klassen, J.T. Wood Department of Mechanical and Materials Engineering, University of Western Ontario, London, Ontario, Canada N6A 5B9 article info Article history: Received 22 November 2010 Accepted 4 February 2011 Available online 24 February 2011 abstract 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 inter- face 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. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Splined-mandrel flow forming is a manufacturing process that uses rollers to form a spinning metal disc over a cylindrical mandrel containing longitudinal splines (Fig. 1). This allows for an internally ribbed thin-walled cylindrical metal part to be created in a single forming process. It is for this reason that splined-mandrel flow form- ing is a very cost effective fabrication method for a wide variety of parts. Although the technique is now used commercially there remains questions about how the magnitude of the local plastic strain near the region of the ribs of these flow formed parts is af- fected by process parameters such as, for example, the work piece thickness reduction ratio. Understanding these dependencies is crit- ical to optimizing the usefulness of the splined-mandrel flow form- ing process. In a previous study Roy et al. [1] measured the distribution of the local von-Mises equivalent plastic true strain through the thickness of a low carbon steel work piece that was flow formed, with different thickness reduction ratios, over a smooth-mandrel. They determined the equivalent plastic strain by performing micro-indentation hardness tests and relating the measured hard- ness to the equivalent true plastic strain through calibration equa- tions developed from similar hardness tests performed on samples, of the same alloy, deformed to known levels of true plastic strain. Roy et al. [1] found that the von-Mises equivalent plastic true strain followed a highly non-linear dependence upon position through the thickness of the flow formed part. The maximum plas- tic strain occurred at the surface of the work piece over which the roller contacted while the minimum strain occurred near the mid-thickness of the work piece. This method of using micro- indentation hardness to determine equivalent plastic strain will be use in this study to assess the through-thickness variation in plastic strain in various regions of an internally ribbed part made by a splined-mandrel flow forming process. There exists to date only a limited amount of published work on the local stress and strain within a work piece that has been flow formed over a splined mandrel. Ma et al. [2] investigated the local stress and strain in an aluminum alloy work piece subjected to spin forming over a conical mandrel containing a circumferential spline. They proposed a range of processing parameters that are suitable for fabricating internally ribbed conical parts from the 3003 alumi- num alloy. Jiang et al. [3–5] have reported the results of experi- ments and finite element simulations of the local plastic strain in an aluminum alloy work piece formed by a ball spinning operation over a longitudinally splined mandrel. They reported significant grain elongation occurring in the work piece as it enters into, and fills, the mandrel splines. It was observed that the extent of grain elongation, and hence the degree of local plastic strain, varied with location within the work piece ribs. No data have yet been reported on the effect of process variables on the magnitude of the local plas- tic strain in various regions of a metal work piece made by splined- mandrel flow forming. Zhang et al. [6] studied folding defect and plastic strain distribution during ball spinning of inner grooved copper tubes using two-dimensional FE simulations. Li et al. [7] conducted the finite element simulation of the cross-section form- ing of axially inner grooved copper tube. They analyzed the stress– strain distribution, metal flow rule, and contact force based on the simulation and experimental results. Their results show that gaps in the groove walls are caused not only by the diametric clearance between the inner wall of the copper tube and the mandrel but also the bending deformation of the copper tube. 0261-3069/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2011.02.014 ⇑ Corresponding author. Fax: +1 519 661 3020. E-mail address: mhaghshe@uwo.ca (M. Haghshenas). Materials and Design 32 (2011) 3629–3636 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes