Springback control in sheet metal bending by laser-assisted bending: Experimental analysis, empirical and neural network modelling A. Gisario a , M. Barletta b,n , C. Conti b , S. Guarino b a Dipartimento di Meccanica ed Aerospaziale, ‘La Sapienza’ Universit  a degli Studi di Roma, Via Eudossiana, 18 – 00184 Roma, Italy b Dipartimento di Ingegneria Meccanica, Universit  a degli Studi di Roma Tor Vergata, Via del Politecnico, 1 – 00133 Roma, Italy article info Article history: Received 6 May 2011 Received in revised form 15 July 2011 Accepted 18 July 2011 Available online 30 July 2011 Keywords: Neural network Modelling Springback Bending Laser abstract The present investigation deals with the control of springback phenomena in the bending process of aluminium sheets by hybrid forming process. Metal substrates were pre-bent to nominal shapes on a built-ad-hoc mould after being constrained on it. Then, they were post-treated by high power diode laser to prevent the deformation of the pre-bent sheets after the release of the constraints. The extent of springback phenomena were estimated by measuring the difference between the nominal bending angles and those achieved on the unconstrained substrates after laser post-treatments. Analytical models, aimed at predicting the springback by varying the setting of the operational parameters of the forming process, were developed. Neural network solutions were also proposed to improve the matching between experimental and numerical data, with the Multi-Layer Perceptrons trained by Back-Propagation algorithm being the fittest one. On this basis, a control modulus very useful to practitioners for automation and simulation purposes was built-on. & 2011 Elsevier Ltd. All rights reserved. 1. Introduction Bending processes are widely used in several manufacturing segments to achieve a large variety of geometrical shape, even complex, starting from raw materials or components [1]. According to Tekiner [2], bending is the uniform straining of material, usually flat sheet or strip metal, around a straight axis, which lies in the neutral plane and normal to the lengthwise direction of the sheet or strip. It is therefore used to achieve very simple shape (i.e., V-shape and U-shape) bending flat sheets on basic moulds [3]. The main drawback of the bending process is the springback phenomenon which, if not properly managed, can cause serious error in the final shape of the workpiece, thus compromising the process performance [4]. The springback phenomenon is the result of the energy stored inside the processed workpiece when plastically deformed during the bending process [5,6]. The bent materials can see their elasticity limits exceeded, whilst they keep a residual elastic inside. When the constraints are removed at the end of the bending process, the energy stored inside the material can be immediately released. This can lead to an unexpected change in the final shape of the workpiece due to residual elasticity kept inside the bent material, which can cause the lack of the closest shape and dimensional tolerances [5,7,8]. Several studies in the literature deal with the analysis of the springback in metal sheet forming and its compensation [2,9–11]. Many expe- dients have been described to compensate springback. Overbend- ing the workpiece is by far one of the most common solution employed in the industrial practise [1,3]. The technique is usually based on the design of built-ad-hoc moulds, which must account for the extent of the springback of the bent workpiece once the constraints are removed at the end of the bending process. Other alternatives include the stretch bending, in which the workpiece is submitted to high stretch tension during the bending process [12,13], and the high pressure coining, in which the bent area is submitted to high-localised compressive stresses between the tip of the forming punch and the die surface. Unfortunately, the overbending as well as the aforementioned alternative techniques can occasionally cause the overload of the bent workpieces, with the onset of severe fractures inside the processed materials. Another widespread solution in several manufacturing segments involve the usage of pre-heated moulds and tools or, alternatively, the running of the bending process at elevated temperatures with the final purpose of increasing the formability of the materials being bent [14–19] or modifying the stress distribution in the formed parts to decrease the springback [20,21]. The increase in temperature of the formed alloy can increase the formability and decrease the strength of the metals, thus simplifying the bending by reduction in the maximum force needed for the operations. In particular, in aluminium alloys, even a small increase in temperature can lead to a substantial decrease in Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/optlaseng Optics and Lasers in Engineering 0143-8166/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.optlaseng.2011.07.010 n Corresponding author. E-mail address: barletta@ing.uniroma2.it (M. Barletta). Optics and Lasers in Engineering 49 (2011) 1372–1383