Characterising material and process variation effects on springback robustness for a semi-cylindrical sheet metal forming process T. de Souza a,n , B.F. Rolfe b a Institute for Technology Research and Innovation, Geelong Technology Precinct, Deakin University, Waurn Ponds, Victoria 3217, Australia b School of Engineering, Faculty of Science and Technology, Deakin University, Waurn Ponds, Victoria 3217, Australia article info Article history: Received 15 September 2009 Received in revised form 29 April 2010 Accepted 15 September 2010 Available online 19 September 2010 Keywords: Springback Sheet metal forming Stochastic modelling Robustness abstract Variation in the incoming sheet material and fluctuations in the press setup is unavoidable in many stamping plants. The effect of these variations can have a large influence on the quality of the final stamping, in particular, unpredictable springback of the sheet when the tooling is removed. While stochastic simulation techniques have been developed to simulate this problem, there has been little research that connects the influence of the noise sources to springback. This paper characterises the effect of material and process variation on the robustness of springback for a semi-cylindrical channel forming operation, which shares a similar cross-section profile as many automotive structural components. The study was conducted using the specialised sheet metal forming package AutoForm TM Sigma, for which a series of stochastic simulations were performed with each of the noise sources incrementally introduced. The effective stress and effective strain scatter in a critical location of the part was examined and a response window, which indicates the respective process robustness, was defined. The incremental introduction of the noise sources allows the change in size of the stress–strain response window to be tracked. The results showed that changes to process variation parameters, such as BHP and friction coefficient, directly affect the strain component of the stress–strain response window by altering the magnitude of external work applied to forming system. Material variation, on the other hand, directly affected the stress component of the response window. A relationship between the effective stress–strain response window and the variation in springback was also established. Crown Copyright & 2010 Published by Elsevier Ltd. All rights reserved. 1. Introduction A major obstacle in improving quality for any manufacturing process is the variation in the inputs and the changing conditions over time. The sheet metal forming industry is plagued by this. Col [1] summarised the potential sources of scatter for a stamping process into the following categories:  Material variability: despite recent advances, material proper- ties, surface roughness and thickness vary from coil to coil and also from head to tail of a coil.  Tooling variability: geometric changes in the tooling occur due to wear over time. Further fluctuations in surface characteristics, clearances, tool material properties and tool temperature exist.  Process variability: variation in blank holder pressure, punch velocity, press stiffness, tooling location.  Lubrication: a key parameter in a successful forming opera- tion; that is difficult to control. Lubrication conditions can change globally and locally on the sheet due to temperature or surface roughness.  Random variability: arises from incorrect tool or sheet positioning, or malfunction of mechanical devices. These noise sources can affect the quality of the final stamped component and can lead to reject parts in production if not accounted for. Rejection criteria can include [2]:  splitting or fracture of the sheet within the trim line,  wrinkling or buckling (due to large compressive stresses),  loose metal (due to insufficient straining), and  unsatisfactory shape (caused by springback). In particular, springback, the elastically driven shape change when the sheet is removed from the tooling, is a growing concern in the automotive industry. This problem is compounded by the introduction of advanced high-strength steels (AHSS) in many vehicle body structures. AHSS cause an increase in springback [3–5] and, perhaps, more concerning is the increased variation in springback from stamping to stamping that has been noted [6–9]. The increased magnitudes in springback can be compensated for Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ijmecsci International Journal of Mechanical Sciences 0020-7403/$ - see front matter Crown Copyright & 2010 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijmecsci.2010.09.009 n Corresponding author. E-mail address: timothy.desouza@deakin.edu.au (T. de Souza). International Journal of Mechanical Sciences 52 (2010) 1756–1766