Experimental analysis on Nd:YAG laser micro-turning of alumina ceramic

Laser micro-turning is a micro-machining strategy to machine cylindrical workpiece of hard-to-process materials such as ceramics. Laser micro-turning method is in high demand in the present high-precision manufacturing industries because of its wide and potential uses in various engineering fields such as automobile, electronics, aerospace, and biomedical applications, etc. In the present research, the experimental analysis of Nd:YAG laser micro-turning of cylindrical-shaped ceramic material has been made to explore the desired laser output responses, i.e., depth of cut and surface roughness by varying laser micro-turning process parameters such as lamp current, pulse frequency, and laser beam scanning speed. Single laser beam has been utilized for successful micro-turning operation. Experimental results revealed that the laser machining process parameters have great influences for achieving desired laser micro-turned depth and surface roughness characteristics during laser micro-turning of alumina ceramics. SEM and optical photographs have also been analyzed for better understanding of the laser micro-turning process for different parametric settings.     

Parametric analysis and optimization of Nd:YAG laser micro-grooving of aluminum titanate (Al2TiO5) ceramics

Pulsed Nd:YAG Laser offers an excellent role for various micro-machining operations of a wide range of engineering materials such as ceramics, composites, diamond etc. The micro-machining of ceramics are highly demanded in the present industry because of its wide and potential uses in various field such as automobile, electronic, aero-space, and bio-medical engineering applications etc. Aluminum titanate (Al₂TiO₅) has tremendous application in automobile and aero engine industry due to its excellent thermal property. The present research paper deals with the response surface methodology based mathematical modeling and analysis on machining characteristics of pulsed Nd:YAG laser during micro-grooving operation on a work piece of aluminum titanate. In this present study, lamp current, pulse frequency, pulse width, assist air pressure and cutting speed of laser beam are considered as machining process parameters during pulsed Nd:YAG laser micro-grooving operation. The response criteria selected for analysis are deviation of taper and deviation of depth characteristics of micro-groove produced on a work piece made of aluminum titanate (Al₂TiO₅). The analysis of variance test has also been carried out to check the adequacy of the developed regression mathematical models. The optimal process parameter settings are assist air pressure of 1.3 kgf/cm², lamp current of 20.44 amp, pulse frequency of 1.0 kHz, pulse width of 10% of duty cycle, and cutting speed of 10 mm/s for achieving the predicted minimum deviation of taper and deviation of depth of laser micro-groove. From the analysis, it is evident that the deviation of taper angle and deviation of depth of the micro-groove can be reduced by a great extent by proper control of laser machining process parameters during micro-grooving on aluminum titanate (Al₂TiO₅).     

Experimental investigation of laser transformation hardening of low alloy steel using response surface methodology

In this research, a systematic investigation on laser transformation hardening (LTH) process is carried out on high-strength low-alloy medium carbon steel, EN25 using design of experiments (DOE). The effect of input process parameters like laser power, travel speed over the response hardened width (HW), hardened depth (HD), and hardened area (HA) are analyzed. The experimental trials are conducted based on the design matrix obtained from the 3^k full factorial design (FFD) using a 2 kW continuous wave Nd:YAG laser power system. A quadratic regression model is developed to predict the responses using response surface methodology (RSM). Based on the developed mathematical models, the direct and interaction effects of the process parameters on LTH are investigated. The optimal hardening conditions are identified to maximize the HW and minimize the HD and HA. The results of the validation test show that the experimental values quite satisfactorily agree with the predicted values of the mathematical models and hence, the models can predict the response adequately.     

Characterization of hole circularity in pulsed Nd:YAG laser micro-drilling of TiN–Al2O3 composites

In micro-manufacturing, circularity of a drilled hole at entry and exit are important attributes which greatly influence the quality of a drilled hole. This study investigates the effect of five parameters in the circularity of drilled holes in pulsed Nd:YAG laser micro-drilling process. The drilling operation has been carried out on titanium nitride–alumina (TiN–Al₂O₃) composite, an important electroconductive ceramics suitable for wear and heating applications. The effect of various process parameters like lamp current, pulse frequency, pulse width, air pressure, and focal length of Nd:YAG laser micro-drilling on hole circularity at entry and exit has been investigated through response-surface-methodology-based experimental study. The parametric combination for optimal hole circularity at entry and exit has also been evaluated.     

Modeling and optimization of Nd:YAG laser micro-weld process using Taguchi Method and a neural network

The use of a pulsed Nd:YAG laser in the 0.1 mm- thick aluminum alloy lap micro-weld process was optimized. The welding parameters that influence the quality of the pulsed Nd:YAG laser lap micro-weld were evaluated by measuring of the tensile-shear strength. In this work, the Taguchi method was adopted to perform the initial optimization of the pulsed Nd:YAG laser micro-weld process parameters. A neural network with a Levenberg-Marquardt back-propagation (LMBP) algorithm was then adopted to develop the relationships between the welding process parameters and the tensile-shear strength of each weldment. The optimal parameters of the pulsed Nd:YAG laser micro-weld process were determined by simulating parameters using a well-trained back-propagation neural network model. Experimental results illustrate the proposed approach.     

Multiresponse optimization of laser welding of stainless steels in a constrained fillet joint configuration using RSM

This paper presents experimental design approach to process parameter optimization for CW Nd/YAG laser welding of ferritic/austenitic stainless steels in a constrained fillet configuration. To determine the optimal welding parameters, response surface methodology was used to develop a set of mathematical models relating the welding parameters to each of the weld characteristics. The quality criteria considered to determine the optimal settings were the maximization of weld resistance length and shearing force, and the minimization of weld radial penetration. Laser power, welding speed, and incident angle are the factors that affect the weld bead characteristics significantly. A rapid decrease in weld shape factor and increase in shearing force with the line energy input in the range of 15–17 kJ/m depicts the establishment of a keyhole regime. A focused beam with laser power and welding speed respectively in the range of 860–875 W and 3.4–4.0 m/min and an incident angle of around 12° were identified as the optimal set of laser welding parameters to obtain stronger and better welds.     

Computational approach to photonic drilling of silicon carbide

The ability of lasers to carry out drilling processes in silicon carbide ceramic was investigated in this study. A JK 701 pulsed Nd:YAG laser was used for drilling through the entire depth of silicon carbide plates of different thicknesses. The laser parameters were varied in different combinations for a well-controlled drilling through the entire thickness of the SiC plates. A drilling model incorporating effects of various physical phenomena such as decomposition, evaporation-induced recoil pressure, and surface tension was developed. Such comprehensive model was capable of advance prediction of the energy and time required for drilling a hole through any desired depth of material.     

Development of controlled Nd:YAG laser for medical applications

Several medical fields are concerned with applications of thermal lasers such as neodymium-doped, yttrium aluminum garnet (Nd:YAG), argon, and CO2. However, quantification of the necrotic volume of Nd:YAG laser-induced damage is not possible at the time of treatment. Mathematic models and feedback control can help to optimize Nd:YAG laser treatments. We therefore formulated mathematic models for coagulation processes and developed an intelligent Nd:YAG laser system with closed-loop feedback control. Surface temperature evolution proved to be valuable data for real-time control of coagulation and ablation. Infrared thermometry provided the noncontact measurement of temperature. A computer stored the temperature data calculated by the mathematic model. Deviations of surface temperature during the treatment beyond established tolerances causes the Nd:YAG laser system to adjust the laser power automatically.     

Development of RSM- and ANN-based models to predict and analyze the effects of process parameters of laser-hardened commercially pure titanium on heat input and tensile strength

Laser transformation hardening (LTH) is an innovative and advanced laser surface modification technique as compared to conventional transformation hardening processes and has been employed in aerospace, marine, chemical applications, heat exchangers, cryogenic vessels, components for chemical processing and desalination equipment, condenser tubing, airframe skin, and nonstructural components which introduces the advantageous residual stresses into the surface, improving the mechanical properties like wear, resistance to corrosion, tensile strength, and fatigue strength. In the present study, LTH of commercially pure titanium, nearer to ASTM grade 3 of chemical composition was investigated using continuous wave 2 kW, Nd: YAG laser. The effect of laser process variables such as laser power, scanning speed, and focused position was investigated using response surface methodology (RSM) and artificial neural network (ANN) keeping argon gas flow rate of 10 lpm as fixed input parameter. This paper describes the comparison of the heat input (HI) and ultimate tensile strength (σ) (simply called as tensile strength) predictive models based on ANN and RSM. The paper also presents the effect of laser process variables on the HI and ultimate σ. The research work also emphasizes on the effect of HI on σ. The experiments were conducted based on a three-factor, three-level Box–Behnken surface statistical design. Quadratic polynomial equations were developed for proper process parametric study for its optimal performance characteristics. The experimental results under optimum conditions were compared with the simulated values obtained from the RSM and ANN model. Adequacy of the developed models was tested by analysis of variance technique. A multilayer feed-forward neural network with a Levenberg–Marquardt back-propagation algorithm was adopted to develop the relationships between the laser hardening process parameters, HI, and ultimate σ. The performance of the developed ANN models were compared with the second-order RSM mathematical models of HI and σ. There was good agreement between the experimental and simulated values of RSM and ANN. The comparison clearly indicates that the ANN models provide more accurate prediction compared to the RSM models. It has been found that there is a trend of increased tensile strength with the decrease of hardening heat input and a trend of increased tensile strength with the increase of hardening cooling rate. As heat input decreases, there will be a faster cooling rate. Considering the effect of HI on ultimate σ, it was found that the lower the heat input, the faster cooling rate. The details of experimentation, model development, testing, validation of models, effect of laser process variables on heat input and ultimate σ, effect of HI on σ, and performance comparison of RSM and ANN models are presented in the paper. The results of Box–Behnken design of RSM and ANN models also indicate that the proposed models predict the responses adequately within the limits of input parameters being used. It is suggested that regression equations can be used to find optimum conditions for HI and σ of laser-hardened commercially pure titanium material.     

Robust parameter design and multi-objective optimization of laser beam cutting for aluminium alloy sheet

The application of laser beam for precise cutting of sheet metals, in general, and reflective sheet metals, like aluminium, in particular, has become of interest in the recent past. The optimum choice of the cutting parameters is essential for the economic and efficient cutting of difficult to cut materials with laser beams. In this paper, a robust design and quality optimization tool called the Taguchi methodology has been applied to find the optimal cutting parameters for cutting of a reflective sheet made of aluminium alloy with a Nd:YAG laser beam. All the steps of the Taguchi method, such as a selection of orthogonal array, computation of signal-to-noise ratio, decision of optimum setting of parameters, and the analysis of variance (ANOVA), have been done by a self-developed software called computer aided robust parameter design (CARPD). A considerable improvement in the kerf taper (KT) and material removal rate (MRR) has been found by using Taguchi method-based predicted results. Confirmatory experimental results have shown good agreement with predicted results. Further, the Taguchi quality loss function has also been used for multi-objective optimization of laser beam cutting of Al-alloy sheet. The results of multi-objective optimization are compared with the single-objective optimization and it has been found that the kerf taper was increased by 1.60% in multi-objective optimization while the MRR was same in both cases.     

Modelling and analysis of hybrid electrochemical turning-magnetic abrasive finishing of 6061 Al/Al2O3 composite

This paper integrates the electrochemical turning (ECT) process and magnetic abrasive finishing (MAF) to produce a combined process that improves the material removal rate (MRR) and reduces surface roughness (SR). The present study emphasizes the features of the development of comprehensive mathematical models based on response surface methodology (RSM) for correlating the interactive and higher-order influences of major machining parameters, i.e. magnetic flux density, applied voltage, tool feed rate and workpiece rotational speed on MRR and SR of 6061 Al/Al₂O₃ (10% wt) composite. The paper also highlights the various test results that also confirm the validity and correctness of the established mathematical models for in-depth analysis of the effects of hybrid ECT- MAF process parameters on metal removal rate and surface roughness. Further, optimal combination of these parameters has been evaluated and it can be used in order to maximize MRR and minimize SR. The results demonstrate that assisting ECT with MAF leads to an increase machining efficiency and resultant surface quality significantly, as compared to that achieved with the traditional ECT of some 147.6% and 33%, respectively.     

Wavelength optimization for machining metals with the harmonic generations of a short pulsed Nd:YAG laser

The wavelength conversion for a short pulsed Nd:YAG laser has been implemented from infrared to visible and to ultraviolet spectra by using nonlinear optical crystals. The analytical method of wavelength optimization for machining metals with various harmonic generations of a Nd:YAG laser is presented in this paper. Combining the absorptivity of metal and the conversion efficiency of laser apparatus, the absorption efficiency is proposed to select an optimum machining wavelength. Various metals have different optimum machining wavelengths. The optimum machining wavelengths for gold, silver, and copper are in the third-, fourth- and second-harmonic generations of a Nd:YAG laser, respectively. For other metals, such as nickel, their optimum machining wavelengths are all in the fundamental wavelength of a Nd:YAG laser.     

Experimental investigation on submerged arc welding of Cr–Mo–V steel

Welding aspects of a high-quality Cr–Mo–V steel are investigated in the present work. Cr–Mo–V steel can be suggested as a best choice for fabrication of pressure vessels to be operated in high-temperature operating conditions. Welding of this group of steel demands very critical attention on the parameters setting of chosen welding process. Only a few researchers had carried out research on the optimization aspects of the submerged arc welding of Cr–Mo–V steel. In the present work, complete experimental analysis is carried out on the submerged arc welding of Cr–Mo–V steel. The important input process parameters considered are welding current, voltage, welding speed, and wire feed. The effect of these input parameters is studied on various responses related to weld bead geometry and few mechanical properties. Taguchi’s L₉ orthogonal array is used for design of experiment and the mathematical models are developed for the responses using MINITAB 15 software. The models developed are validated by conducting more experiments. Optimised parameter setting is also obtained by using a recently developed teaching–learning-based optimization algorithm.     

Application of Taguchi-based gray relational analysis for evaluating the optimal laser cladding parameters for AISI1040 steel plane surface

The effect of various laser cladding process parameters like laser power, scan speed, and powder feed rate on clad bead quality characteristics (or clad bead geometry) for AISI 1040 steel substrate have been studied by performing a number of experiments with L ₉ orthogonal array. In order to find the process parametric setting for best quality clad bead based on experimental results, a multiresponse optimization technique using gray relational analysis (GRA) is presented in this paper. The GRA is applied on laser cladding process to find out the gray relational grade for each experiment. On optimization, power of 1.25 kW, scan speed of 0.8 m/min, and a powder feed rate of 11 gm/min have been found to be the best parametric setting for laser cladding operation of AISI 1040 steel substrate. Moreover, the analysis of variance is also performed to determine the contribution of each control factor on the clad quality characteristics. Finally, to ensure the robustness of GRA, a confirmatory test is performed at selected optimal parametric setting.     

钢-铝异种合金脉冲激光焊焊缝表征分析

采用Nd:YAG激光焊对304不锈钢和5052铝合金进行异种金属焊接,分别以峰值功率、焊接速度、离焦量和脉冲频率等工艺参数设计24组工艺试验,并对比分析未熔合、熔合和焊穿3种焊缝表面表征。运用激光点位移传感器测量焊缝高度,探索焊缝高度随激光功率等工艺参数的变化趋势,得出钢-铝焊缝3种表面形貌的工艺参数区间。分析结果表明,焊缝的表面形貌是由激光单点能量、离焦量和脉冲频率等因素共同决定,焊缝高度与峰值功率、焊接速度、离焦量和脉冲频率等工艺参数有一定的变化规律。     

Using a Nd:YAG laser and six axes robot to cut zinc-coated steel

Zinc-coated steel sheets are important materials in the automobile and home appliance industries. Currently, lasers are the preferred tools for metal cutting because of their good cutting quality, flexibility and excellent features and results, as compared to traditional tools. The solid-state Nd:YAG laser has successfully replaced the gaseous CO₂ laser for metal cutting; its small size and short wavelength makes it suitable for cutting bright and metal-coated materials, as well as being able to be transmitted via optical fibers and robots to cut complicated three dimensional and curved shapes. In this work, the Nd:YAG laser is used to cut 1 mm zinc coated steel sheets. We demonstrate the effects of different cutting parameters such as laser power, cutting speed, different gas types and pressures, and focus position on the cutting quality characteristics of attached dross, kerf width and cut surface roughness. Using a six axes robot, cutting speed was limited to 6 m/min because of the noticeable vibration at higher speeds. Results showed that the cutting surfaces achieved were very sharp and smooth. In cutting, Nd:YAG required less power and attained higher speeds than the published results of a CO₂ laser, which makes Nd:YAG an economical alternative to cut zinc and metal-coated materials. In addition, laser cutting using robots provided efficient and consistent cutting quality, especially in the case of 3D and countered cutting. Apart from using low speed, robots proved to be more economical than costly, specially designed CNC tables.     

A statistical analysis of rotary friction welding of steel with varying carbon in workpieces

Laser drilling is increasingly becoming the method of choice for precision drilling for variety of components. However, a number of defects such as spatter, recast, heat-affected zone (HAZ), and taper limit the application. Elimination of these defects is the subject of intense research. This paper presents a grey relational optimization approach for the determination of the optimum process parameters which minimize the HAZ and hole circularity and maximize material removal rate in a Pulsed Nd:YAG laser micro-drilling in high carbon steel within existing resources. The input process parameters considered are pulse width, number of pulses, assist gas (oxygen) flow rate, and its supply pressure. A higher resolution-based L₂₅ orthogonal array has been used for conducting the experiments. The designed experimental results are used in grey relational analysis and the weights of the quality characteristics are determined optimizing the parameters. On the basis of optimization results, it has been found that the optimal parameter level gives a small HAZ, fine hole, and maximum material removal rate. Subsequently, the results are also verified and found appropriate by running confirmation tests.     

Investigation into electrochemical micromachining (EMM) through response surface methodology based approach

Electrochemical micromachining (EMM) could be used as one the best micromachining technique for machining electrically conducting, tough and difficult to machine material with appropriate machining parameters combination. This paper attempts to establish a comprehensive mathematical model for correlating the interactive and higher-order influences of various machining parameters, i.e. machining voltage pulse on/off ratio, machining voltage, electrolyte concentration, voltage frequency and tool vibration frequency on the predominant micromachining criteria, i.e. the material removal rate and the radial overcut through response surface methodology (RSM), utilizing relevant experimental data as obtained through experimentation. Validity and correctiveness of the developed mathematical models have also been tested through analysis of variance. Optimal combination of these predominant micromachining process parameters is obtained from these mathematical models for higher machining rate with acuuracy. Considering MRR and ROC simultaneously optimum values of predominant process parameters have been obtained as; pulse on/off ratio, 1.0, machining voltage, 3 V, electrolyte concentration, 15 g/l, voltage frequency of 42.118 Hz and tool vibration frequency as 300 Hz. The effects of various process parameters on the machining rate and radial overcut are also highlighted through different response surface graphs. Condition of machined micro-holes are also exhibited through the SEM micrographs in this paper. Pulse voltage pattern during electrochemical micromachining process has been analyzed with the help of voltage graphs. Irregularities in the nature of pulse voltage pattern during electrochemical micromachining have been observed and the causes of these irregularities are further investigated.     

Modelling and optimisation of laser shock peening using an integrated simulated annealing-based method

Laser shock peening is an innovative surface treatment technique, which has been successfully applied to improve fatigue performance of metallic components. Laser shock peening improves the surface morphology and microstructure of the material. In this paper, three Nd3+:YAG laser process parameters (voltage, focus position and pulse duration) are varied in an experiment, in order to determine the optimal process parameters that could simultaneously meet the specifications for seven correlated responses of processed Nimonic 263 sheets. The modelling and optimisation of a process were performed using the advanced, problem-independent method. First, responses are expressed using Taguchi’s quality loss function, followed by the application of multivariate statistical methods to uncorrelate and synthesise them into a single performance measure. Then, artificial neural networks are used to build the process model, and simulated annealing was utilised to find the optimal process parameters setting in a global continual space of solutions. Effectiveness of the proposed method in the development of a robust laser shock peening was proved in comparison to several commonly used approaches from the literature, resulting in the highest process performance measure, the most favourable response values and the corresponding process parameters optimum. Besides the improved surface characteristics, the optimised laser shock peening (LSP) showed an improvement in terms of microhardness and formation of favourable microstructural transformations.     

Process parameters selection for laser polishing DF2 (AISI O1) by Nd:YAG pulsed laser using orthogonal design

Mechanisms of laser polishing metals in a continuous scanning mode, as envisaged and analyzed in this paper, are rather complex, and experimental optimization of laser polishing metallic material is very time-consuming and difficult. Aiming at shortening the experimental time in achieving a better surface finishing of DF2 (AISI 01) tool steel by pulse Nd:YAG laser, we used the orthogonal experimental design for selecting the laser operational parameters. The results showed that the orthogonal design (OD) allowed the optimum technological parameters for the laser polishing to be obtained quickly and effectively. According to the OD analysis and experimental data, the attainable optimum laser smoothening/polishing parameters from this study are pulse energy (P)?=?1?J, feed rate?=?300–400?mm/min, pulse duration?=?3?ms, and pulse frequency (f)?=?20–25?Hz. The work in this paper demonstrates the relative superiority of orthogonal design in saving experimental times and providing good laser polishing surface in surface texturing and the smoothening process.