Multi-objective optimization of Nd:YAG laser cutting of nickel-based superalloy sheet using orthogonal array with principal component analysis

Laser cutting of nickel-based superalloy sheets, having wide applications in aircraft and rocket industries, is important from the quality of cut point of view. Keeping this in view, a hybrid approach of Taguchi method (TM) and principal component analysis (PCA) has been applied for multi-objective optimization (MOO) of pulsed Nd:YAG laser beam cutting (LBC) of nickel-based superalloy (SUPERNI 718) sheet to achieve better cut qualities within existing resources. The three-quality characteristics kerf width, kerf deviation (along the length of cut), and kerf taper have been considered for simultaneous optimization. The input parameters considered are assist gas pressure, pulse width, pulse frequency, and cutting speed. Initially, single-objective optimization has been performed using TM and then the signal-to-noise (S/N) ratios obtained from TM have been further used in PCA for multi-objective optimization. The results of MOO include the prediction of optimum input parameter level and their relative significance on multiple quality characteristics (MQC). The responses at predicted optimum parameter level are in good agreement with the results of confirmation experiments conducted for verification tests.     

Use of the grey relational analysis to determine optimum laser cutting parameters with multi-performance characteristics

This paper presents an effective approach for the optimization of laser cutting process of St-37 steel with multiple performance characteristics based on the grey relational analysis. Sixteen experimental runs based on the Taguchi method of orthogonal arrays were performed to determine the best factor level condition. The response table and response graph for each level of the machining parameters were obtained from the grey relational grade. In this study, the laser cutting parameters such as laser power and cutting speed are optimized with consideration of multiple-performance characteristics, such as workpiece surface roughness, top kerf width and width of heat affected zone (HAZ). By analyzing the grey relational grade, it is observed that the laser power has more effect on responses rather than cutting speed. It is clearly shown that the above performance characteristics in laser cutting process can be improved effectively through this approach.     

The use of grey relational analysis to determine laser cutting parameters for QFN packages with multiple performance characteristics

This paper reports an application of the grey relational analysis (GRA) to directly optimize laser cutting of a quad flat non-lead (QFN) strip using six performance characteristics. The most important performance characteristics include the cutting depth, the width of heat affected zone (HAZ), and the width of cutting line for both epoxy and Cu+epoxy materials along the cutting path. During the GRA, higher grades are obtained from any of the deeper (more complete) cutting depth, reduced widths of the HAZ and reduced widths of the cutting line. From nine experiments based on the orthogonal array of L9(3⁴), a current of 29 A, a frequency of 2 kHz, and a cutting speed of 2 mm/s were found to be the best parameters for laser cutting of a QFN strip with a thickness of 0.9 mm. Moreover, the analysis of variance (ANOVA) is also employed to determine the contribution of each control parameter on the cutting quality characteristics. The three largest measured contributions on the cutting quality in decreasing order are the frequency, the current, and the cutting speed. Compared with the Taguchi optimization method, the GRA approach is significantly simpler because it directly assigns appropriate weighting factors to the required qualities. Finally, confirmation experiments are performed to ensure the robustness of the GRA predicted optimal configuration for laser cutting a QFN strip.     

Optimized laser cutting on light guide plates using grey relational analysis

This paper present the optimum conditions for direct CO₂ laser cutting of 6-mm-thick polymethylmethacrylate (PMMA) for backlit module applications. The influence of the major processing parameters on the optical transmittance ratio and surface roughness of cut samples material have been discussed. In order to assess the effects of several operational parameters on multiple-performance characteristics, we applied the grey relational analysis method. In this paper, we studied the effects of several laser direct cut parameters, such as assisted gas-flow rate, pulse repetition frequency, cutting speed, and focus position to achieve optimum characteristics for two product characteristics, optical transmittance ratio and work-piece surface roughness. The study involved nine experiments based on an orthogonal array, and results indicate the optimal process parameters as 20 NL/min for assisted-gas flow rate, 5 kHz for pulse repetition frequency, 2 mm/s for cutting speed, and 0 mm for laser focusing position. Additionally, by analyzing the grey relational grade, we found that the assisted-gas flow rate has more influence than any other single parameter.     

Multiple-objective optimization in precision laser cutting of different thermoplastics

Thermoplastics are increasingly being used in biomedical, automotive and electronics industries due to their excellent physical and chemical properties. Due to the localized and non-contact process, use of lasers for cutting could result in precise cut with small heat-affected zone (HAZ). Precision laser cutting involving various materials is important in high-volume manufacturing processes to minimize operational cost, error reduction and improve product quality. This study uses grey relational analysis to determine a single optimized set of cutting parameters for three different thermoplastics. The set of the optimized processing parameters is determined based on the highest relational grade and was found at low laser power (200 W), high cutting speed (0.4 m/min) and low compressed air pressure (2.5 bar). The result matches with the objective set in the present study. Analysis of variance (ANOVA) is then carried out to ascertain the relative influence of process parameters on the cutting characteristics. It was found that the laser power has dominant effect on HAZ for all thermoplastics.     

Multi-objective optimization of laser cutting for flash memory modules with special shapes using grey relational analysis

This paper presents a novel effective method for optimizing laser cutting of specially shaped electronic printed circuit board (PCB) carrier substrates of advanced integrated circuit (IC) back-end packages that have multiple performance characteristics identified using grey relational analysis (GRA). Laser cutting parameters, including laser beam parameters (average laser power and Q-switch frequency), focusing parameters (laser beam focusing spot size), and machine parameters (laser cutting speed), were optimized based on multiple performance characteristics. Some characteristics of the specially shaped flash memory module for IC packages, such as smart disk (SD) cards are verified. The characteristics of interest are the average surface roughness on a PCB substrate cross-section, and the maximum width of the heat-affected zone (HAZ). Eight experiments were conducted using GRA to optimize the settings for laser beam cutting parameters to generate various quality characteristics. Analysis of the grey relational grade indicates that parameter significance and the optimal parameter combination for the laser cutting process are identified. The analytical results from two confirmation experiments using the optimal parameters confirm that laser cutting technology can be effectively applied to cut substrates into special shapes.     

Cutting of nonmetallic materials using Nd:YAG laser beam

This study deals with Nd:YAG laser cutting nonmetallic materials, which is one of the most important and popular industrial applications of laser. The main theme is to evaluate the effects of Nd:YAG laser beam power besides work piece scanning speed. For approximate cutting depth, a theoretical study is conducted in terms of material property and cutting speed. Results show a nonlinear relation between the cutting depth and input energy. There is no significant effect of speed on cutting depth with the speed being larger than 30 mm/s. An extra energy is utilized in the deep cutting. It is inferred that as the laser power increases, cutting depth increases. The experimental outcomes are in good agreement with theoretical results. This analysis will provide a guideline for laser-based industry to select a suitable laser for cutting, scribing, trimming, engraving, and marking nonmetallic materials.     

Laser cutting of thick sheet metals: Residual stress analysis

Laser cutting of tailored blanks from a thick mild steel sheet is considered. Temperature and stress field in the cutting sections are modeled using the finite element method. The residual stress developed in the cutting section is determined using the X-ray diffraction (XRD) technique and is compared with the predictions. The structural and morphological changes in the cut section are examined using the optical microscopy and scanning electron microscopy (SEM). It is found that temperature and von Mises stress increase sharply in the cutting section, particularly in the direction normal to the cutting direction. The residual stress remains high in the region close to the cutting section.     

Modelling and optimization of cut quality during pulsed Nd:YAG laser cutting of thin Al-alloy sheet for straight profile

Thin sheets of aluminium alloys are widely used in aerospace and automotive industries for specific applications. Nd:YAG laser beam cutting is one of the most promising sheetmetal cutting process for cutting sheets for any profile. Al-alloy sheets are difficult to cut by laser beam because of its highly reflective nature. This paper presents modelling and optimization of cut quality during pulsed Nd:YAG laser cutting of thin Al-alloy sheet for straight profile. In the present study, four input process parameters such as oxygen pressure, pulse width, pulse frequency, and cutting speed and two output parameters such as average kerf taper (T_a) and average surface roughness (R_a) are considered. The hybrid approach comprising of Taguchi methodology (TM) and response surface methodology (RSM) is used for modelling whereas multi-objective optimization is performed using hybrid approach of TM and grey relational analysis (GRA) coupled with entropy measurement methodology. The entropy measurement methodology is employed for the calculation of weight corresponding to each quality characteristic. The results indicate that the hybrid approaches applied for modelling and optimization of the LBC process are reasonable.     

Pulsed laser deposition process of PLZT thin films using an infrared Nd:YAG laser

Pulsed laser depositions of PLZT thin films were performed using an Nd:YAG (1064 nm) laser. The growths took place in vacuum or in an oxygen background. Room temperature and 500 °C were the used substrate temperatures. The X-ray diffraction analysis revealed a preferential crystallographic orientation in the films grown at room temperature in vacuum. Such result is discussed. The velocity distribution functions of the species in the plasma plume were obtained from a time of flight study using optical emission spectroscopy. The maximums of these distributions functions fall around 10⁶ cm/s, equivalent to an energy range of 18-344 eV. Ionic species of heavy elements (like lead) achieved higher velocities than other lighter species. This result is linked to the creation of an accelerating spatial charge and to the thermal nature of the target material extraction that allows some elements to be released first than others. Chemical state variations of the elements present in the films were analyzed. Under these different growing conditions, lead chemical states varied the most.     

Inert gas cutting of titanium sheet with pulsed mode CO2 laser

The present work aimed at studying the dynamic behavior of melt ejection in laser cutting of 1 mm thick titanium sheet and to obtain dross-free cuts with minimum heat affected zone (HAZ). CO₂ laser cutting of titanium sheet was carried out with continuous wave (CW) and pulsed mode laser operation with different shear gases namely argon, helium and nitrogen. Laser cutting with high frequency and low-duty cycle pulse mode operation produced dross-free cuts with no noticeable HAZ. Helium, because of its high heat convection and ability to generate high shear stress, produced laser-cuts with narrow HAZ and low dross, as compared to those produced with argon as the shear gas. Microscopic features of laser cut surfaces were analyzed and correlated with dynamic mechanism involved in laser cutting process. Process parameters for laser piercing, required for the initiation of fusion cut within the sheet, were also studied. Laser piercing requires either CW or high-duty cycle (>80%) pulse mode operation.     

Taguchi based fuzzy logic optimization of multiple quality characteristics in laser cutting of Duralumin sheet

Capability of laser cutting mainly depends on optical and thermal properties of work material. Highly reflective and thermally conductive Duralumin sheets are difficult-to-laser-cut. Application of Duralumin sheets in aeronautic and automotive industries due to its high strength to weight ratio demand narrow and complex cuts with high geometrical accuracy. The present paper experimentally investigates the laser cutting of Duralumin sheet with the aim to improve geometrical accuracy by simultaneously minimizing the kerf width and kerf deviations at top and bottom sides. A hybrid approach, obtained by combining robust parameter design methodology and Fuzzy logic theory has been applied to compute the fuzzy multi-response performance index. This performance index is further used for multi-objective optimization. The predicted optimum results have been verified by performing the confirmation tests. The confirmation tests show considerable reduction in kerf deviations at top and bottom sides.     

Nd:YAG激光器光栅式扫描预处理的计算模拟与优化分析

 采用计算模拟的方法,研究了光栅式扫描预处理的扫描方式以及脉冲能量波动、定位误差对预处理效率的影响。研究发现,脉冲能量波动及其定位误差使预处理效率降低,同时其影响与扫描方式之间存在相互调制作用,因此可以通过选择合适的扫描方式以及扫描间隔来优化预处理流程,提高预处理效率。此外发现,光斑呈等边三角形排列时的预处理效率优于正方形。     

Multi-criteria optimization in CO2 laser ablation of multimode polymer waveguides

High interconnection density associated with current electronics products poses certain challenges in designing circuit boards. Methods, including laser-assisted microvia drilling and surface mount technologies for example, are being used to minimize the impacts of the problems. However, the bottleneck is significantly pronounced at bit data rates above 10 Gbit/s where losses, especially those due to crosstalk, become high. One solution is optical interconnections (OI) based on polymer waveguides. Laser ablation of the optical waveguides is viewed as a very compatible technique with ultraviolet laser sources, such as excimer and UV Nd:YAG lasers, being used due to their photochemical nature and minimal thermal effect when they interact with optical materials. In this paper, the authors demonstrate the application of grey relational analysis to determine the optimized processing parameters concerning fabrication of multimode optical polymer waveguides by using infra-red 10.6 µm CO₂ laser micromachining to etch acrylate-based photopolymer (Truemode^™). CO₂ laser micromachining offers a low cost and high speed fabrication route needed for high volume productions as the wavelength of CO₂ lasers can couple well with a variety of polymer substrates. Based on the highest grey relational grade, the optimized processing parameters are determined at laser power of 3 W and scanning speed of 100 mm/s.     

Moving perforation of rocks using long pulse Nd:YAG laser

Laser perforating is a new method in oil and gas wells where researchers look for an alternative to explosive methods. One of the important problems with this method is the generation of uniform and cylindrical holes at a selected pitch for enhancing the permeability of rocks. In non-moving laser perforation, the nozzle of the laser and the rock do not approach each other and due to laser convergence in a point, uniform and cylindrical holes are not created. For this reason, moving laser perforation is suggested in this research. One of the important parameters in moving laser perforation is the power of the laser that can be perforated at a specific rate. In this article we predicted the laser power for a definite rate of perforation (ROP) and then the accuracy of this prediction was evaluated to support the experiments. A pulsed Nd: YAG laser, with a pulse energy around 5.5 J, pulse repetition rate of 30 Hz and pulse duration of 2 ms were used for rock perforation in this study. The results shows that the presented relation for perforation could reliably be used in practice. Furthermore, by knowing the rate of perforation, the required laser power for consistent drilling could be calculated.     

Laser welding of glasses using a nanosecond pulsed Nd:YAG laser

This work reports on laser welding of two 1 mm thickness borosilicate glasses through the irradiation with a nanosecond pulsed laser, as a novel alternative to the use of ultrashort pulsed lasers for welding of transparent materials. Two different methodologies were investigated and compared in terms of interface quality. In a first approach, the glasses were joined without any absorbing intermediate layer. However, the bond interface possesses defects. To improve the resulting bond interface, the use of a titanium ultrathin intermediate layer was proposed to weld the glasses substrates, acting as a sealant between them. The laser parameters were optimized to achieve the best joining conditions of the Ti film. The use of the Ti layer gives rise to a bond interface more homogeneous and free of damages. As a further step, thin glasses of 86 µm thickness, of great technological value, were joined through the Ti film as well. The joined interfaces were inspected through optical microscopy and scanning electron microscopy (SEM) while the bond quality was evaluated by Scanning Acoustic Microscopy (SAM).     

Removal of graffiti from the mortar by using Q-switched Nd:YAG laser

This paper presents part of the larger study on microstructural features of mortars and it's effects on laser cleaning process. It focuses on the influence of surface roughness, porosity and moisture content of mortars on the removal of graffiti by Nd:YAG laser. The properties of this laser are as follows: wavelength (λ) 1.06 μm, energy: 500 mJ per pulse, pulse duration: 10 ns. The investigation shows that the variation of laser fluence with the number of pulses required for the laser cleaning can be divided into two zones, namely effective zone and ineffective zone. There is a linear relationship observed between number of pulses required for laser cleaning and the laser fluence in the effective zone, while the number of pulses required for the laser cleaning is almost constant even though the laser fluence increases in the ineffective zone. Moreover, surface roughness, porosity and moisture content of mortar samples have influence on the laser cleaning process. The effect of these parameters become however negligible at the high level of laser fluence. The number of pulses required for the laser cleaning is low for smooth surface or less porous mortar. Furthermore, the wetness of the samples facilitates the cleaning process.     

Dissimilar autogenous full penetration welding of superalloy K418 and 42CrMo steel by a high power CW Nd:YAG laser

Experiments of autogenous laser full penetration welding between dissimilar cast Ni-based superalloy K418 and alloy steel 42CrMo flat plates with 3.5 mm thickness were conducted using a 3 kW continuous wave (CW) Nd:YAG laser. The influences of laser welding velocity, flow rate of side-blow shielding gas, defocusing distance were investigated. Microstructure of the welded seam was characterized by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). Mechanical properties of the welded seam were evaluated by microhardness and tensile strength testing. Results show that high quality full penetration laser-welded joint can be obtained by optimizing the welding velocity, flow rate of shielding gas and defocusing distance. The laser-welded seam have non-equilibrium solidified microstructures consisting of γ-FeCr_0.29Ni_0.16C_0.06 austenite solid solution dendrites as the dominant and very small amount of super-fine dispersed Ni₃Al γ′ phase and Laves particles as well as MC needle-like carbides distributed in the interdendritic regions. Although the microhardness of the laser-welded seam was lower than that of the base metal, the strength of the joint was equal to that of the base metal and the fracture mechanism showed fine ductility.     

Low repetition rate of a mode locked Nd:YAG laser using quadratic polarization switching

We present the performances of a low repetition rate (4.5 MHz) mode locked Nd:YAG laser using a nonlinear polarization rotation effect in a type II crystal cut for second harmonic generation. We compared their performances in term of peak power, pulse duration and cavity losses with a standard resonator operating at high repetition rate (125 MHz). A gain of 10.8 and 7.3 was obtained on the energy per pulse and on the output peak power between the two lasers.     

Indium tin oxide sol-gel precursor conversion process using the third harmonics of Nd:YAG laser

We use the third harmonics of Nd:YAG laser (λ = 355 nm) for simultaneous precursor conversion and dopant activation on sol-gel ITO thin films at a laser fluence range of 700-1000 mJ/cm². A minimum resistivity of 5.37 × 10⁻² Ω-cm with a corresponding carrier concentration of 6 × 10¹⁹ cm⁻³ is achieved at laser irradiation fluence of 900 mJ/cm². X-ray photoelectron analysis reveals that extremely high tin concentration of 19.4 at.% and above is presented in the laser-cured ITO thin films compared with 8.7 at.% in the 500 °C thermally cured counterpart. These excess tin-ions form complex defects, which contribute no free carriers but act as scattering centers, causing inferior electrical properties of the laser-cured films in comparison with the thermally cured ones.