Multi-objective Optimization of Nd:YAG Laser Drilling of optical-grade Acrylic Plate by using Taguchi-Grey Relational Analysis

Abstract This study proposes an effective method for optimizing laser drilling processing (LDP) by using grey relational analysis (GRA) for multiple performance characteristic requirements. First, We developed a system using a Quantel Brilliant neodymium-doped yttrium aluminum garnet (Nd:YAG) laser with pulse width of 5–6 ns and an F-theta lens to obtain a focused laser beam with a diameter of 0.2 mm. The developed system was employed to drill holes in a 3-mm-thick optical-grade acrylic polymethyl methacrylate (PMMA) plate on a safe window with high optical density and grade of OD 7+ @950 ~ 1085nm. Four major control factors include laser pulse energy, repetition rate, focusing position offset, and drill time. Then, 9 sets of experiments were performed using Taguchi method with orthogonal arrays in L9(34). The experimental results with multiple quality characteristics are measured and used to optimize the control parameters by using Grey relational analysis (GRA) with equal weighting and different weighting factors of four qualities (Roundness, Hillock ratio taper, HAZ and taper). From the experimental results with equal weighting factors, the combination of the laser energy at level 2, focusing position offset at level 3, drill time at level 1, and repetition rate at level 2 can achieve the optimal results. The combination is implemented in Run 6 of the orthogonal arrays of L9(34). It is found that models predicted by the grey correlation analysis (GRA) are in close agreement with the experimental values. Hence, the models may be further used for optimization of process parameters using evolutionary algorithms. From the experimental results, it was found that HAZ has less effect on this experimental method design, and the focusing position offset affects the Taper. When the average laser energy increases, the drill hole and shallow cracks in the Hillock hole will also increase.