Experimental investigations and statistical analysis of pulsed laser bending of AISI 304 stainless steel sheet Kuntal Maji, D.K. Pratihar n , A.K. Nath Department of Mechanical Engineering, Indian Institute of Technology, Kharagpur, Kharagpur 721302, India article info Article history: Received 23 August 2012 Received in revised form 21 November 2012 Accepted 7 December 2012 Keywords: Pulsed laser bending Response surface methodology Optimization abstract This paper presents experimental investigations on pulsed laser bending of sheet metal and statistical analysis to study the effects of process parameters. Laser power, scan speed, spot diameter and pulsed duration were taken as input variables and bending angle was considered as the output. Response surface methodology was used for modeling and optimization of the pulsed laser bending process. The performance of the developed model was validated through the experiments. All the input variables were found to have significant influence on the bending angle. Bending angle increased with the increase of laser power and pulse duration and decreased with the increase of scan speed and spot diameter. The optimum process parameters for the maximum bending angle were also found and verified with experimental data. The effects of pulse frequency, pulse width and pulse energy on bending angle were also investigated through experiments. Bending angle was found to be the maximum for a certain value of pulse frequency. With the increase of pulse width, bending angle increased at constant laser power but decreased at constant pulse energy. Bending angle was seen to increase with the increase of spatial overlapping and decrease with the increase of gap at constant laser power, but it showed optimal values for both the cases at constant line energy. A comparative study between continuous and pulsed laser bending was carried out to study the process efficiency in terms of energy input and produced deformation. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction Laser forming is a non-contact flexible thermal forming pro- cess, which deforms the sheet metals by thermal residual stresses instead of external forces. It has potential applications in both macro- and micro-scale manufacturing for rapid prototyping and precision adjustment in ship building, aerospace, automobile, microelectronics industries, and others. Extensive studies had been carried out by various researchers [1] to model the contin- uous laser bending process. Sheet metal forming using pulsed laser was also investigated by a few researchers to study the effects of process parameters on the deformation and properties of the laser formed samples. Both empirical and finite element methods were used to model the pulsed laser bending process. Numerical and experimental investigations were carried out by various researchers [2–4] to determine the temperature field, deformation pattern, stress–strain states, residual stress distribu- tions, and others in pulsed laser bending considering various process parameters, such as laser parameters, laser beam shapes, single and multiple pulses. Good correlations were found between the numerical and experimental results of bending angle in their works. Transient nonlinear 3-D finite element simulation of pulsed laser forming process takes a long computational time because of finer mesh sizes at the laser irradiated zone and the small time steps required for the convergence and accuracy of prediction. Zhang et al. [5] presented an efficient method to reduce the computational time in calculating bending angle numerically in pulsed laser bending of thin stainless steel sheet considering only a few laser pulses. Experimental study and empirical modeling were carried out by Gollo et al. [6] in laser bending of sheet metal with a Nd:YAG pulsed laser using Taguchi experimental design. Regression analysis was carried out con- sidering the different factors, that is, laser power, beam diameter, scan speed and pulse duration to establish the relationship between the factors and bending angle and a first order poly- nomial equation was obtained to predict the bending angle. Yang et al. [7] investigated the metallurgical changes of surface proper- ties of stainless steel due to pulsed laser forming. The relationship between the surface properties of heat affected zone (HAZ) and the laser pulse parameters was also studied. The microstructure, micro-hardness and anticorrosion in the HAZ generated by laser forming were tested with the metallographic microscope, scan- ning electron microscope (SEM) and micro-hardness testing Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/optlastec Optics & Laser Technology 0030-3992/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.optlastec.2012.12.006 n Corresponding author. Tel.: þ91 3222 282992; fax: þ91 3222 282278. E-mail addresses: kuntalmajiiitkgp@gmail.com (K. Maji), dkpra@mech.iitkgp.ernet.in (D.K. Pratihar), aknath@mech.iitkgp.ernet.in (A.K. Nath). Optics & Laser Technology 49 (2013) 18–27