18 th Annual International Conference on Mechanical Engineering-ISME2010 11-13 May, 2010, Sharif University of Technology, Tehran, Iran 1 ISME2010-XXXX Laser welding process optimization using statistical design of experiments M. Moradi 1 M. Ghoreishi 2 , Y. Javid 3 1 Mahmood Moradi, PhD candidate, Mechanical engineering department, K.N.Toosi University of technology; mahmoodmoradi@dena.kntu.ac.ir 2 Majid Ghoreishi, associate professor, Mechanical engineering department, K.N.Toosi University of technology; ghoreishi@kntu.ac.ir 3 Youness Javid, MS student, Mechanical engineering department, K.N.Toosi University of technology; yoones_javid@yahoo.com Abstract Laser welding is a keyhole fusion welding which is carried out through using high energy density which is caused by focusing the laser beam on the small spot point. The present study was aimed at the statistical optimization of CO 2 laser butt joint welding of Ni-base super alloy Rene 80. In fact, the proper weld geometry is comprised of welding surface width (W 1 ), welding pool area (A) and welding width of weld zone (W 2 ) process optimization. Moreover, the optimal input parameters consist of laser power, welding speed, laser beam focal point position and inert gas pressure. In order to achieve the proper weld geometry as well as find out the optimal input parameters, the response surface methodology (RSM) was considered as one of the designs of experiments methods (DOE) benefiting from the desirability approach. RSM is a set of mathematical and statistical techniques that are useful for modelling and predicting the response of interest affected by a number of input variables with the aim of optimizing this response. Solving multiple response optimization problems employing this technique involves using a technique for combining multiple responses into a dimensionless measure of performance called the overall desirability function. Minitab V.15 software was used analyzing this multiple response problem. Verification experiments were carried out in order to analyse the results obtained via software. In this study, the optimum laser welding condition was obtained in an attempt to achieving minimum welding geometric. Keywords: laser beam welding, optimization, designs of experiments, response surface methodology, desirability approach. Introduction Laser have been used as a tool for precise materials processing in manufacturing operations due to non- contact nature and the high intensity resulting from the ability to focus it to a small diameter [1]. Among welding methods, laser beam is successfully used for welding metals and different alloys [2]. A very narrow zone under the laser beam is suddenly heated and consequently, vaporized after a few milliseconds of radiation [3]. During last decades, the use of design of experiments (DOE) has significantly increased in different fields, such as physics, engineering and chemistry in order to modeling and optimization [4, 5]. Response Surface Methodology (RSM) is one of the proper statistical and mathematical optimization techniques used widely in describing the performance of the welding processes and finding the optimum settings of the parameters to achieve responses of interest. Wang and Rasmussen [6] investigated and optimized the inertia welding process of low-carbon steels using RSM. Benyounis et.al [7] applied response surface method to identify the optimal welding conditions in order to increase the productivity and minimize the total operating cost. Moradi and Ghoreishi [8] have developed mathematical models to study the effect of the laser welding parameters of Ni-Base Super Alloy Rene80 on weld-bead profile using RSM method. Anawa and Olabi [9] have optimized tensile strength of CW CO2 laser welding by using a matrix design of Taguchi method. Comparison between numerical algorithm and DOE methods of optimization was performed by Olabi et.al in order to gain minimum residual stress of laser butt-joint welding [10]. In the present study, optimization of the laser welding parameters were carried out for the purpose of access minimum geometrical dimensions of weld-bead profile according to achieved mathematical models by authors’ previous works [5, 8]. In order to validate the results of optimization, three welding experiments were carried out at optimum settings and compared with the optimization results. Response Surface Methodology Response surface methodology, one of the optimizing techniques, is widely used in describing different processes and suggestion of optimum answers [11]. Response surface method is a set of statistical and mathematical edicts which are used for modeling and predicting results, affected by input parameters. Response surface method clarifies relations between answers and input under control parameters [12]. When all independent variable parameters during experiment are measurable and controllable, the response surface will be represented by: Y= f(x 1 , x 2 , x 3 , ….., x k ) ) ١ (