Laser-assisted Machining Process Research Articles

A fully-coupled FEM-based 2D metallo-thermo-mechanical model of laser-assisted machining of Ti-6Al-4V - a focus on residual stresses

The complex interaction between the laser beam, the workpiece, and the cutting tool during laser-assisted machining (LAM) can result in considerable thermal gradients, variational strains and microstructural phase transformations, ultimately leading to residual stresses. This study presents a finite element-based model for the LAM of Ti-6Al-4V alloy, integrating the material’s metallurgical transformations and thermo-mechanical behaviour to predict residual stresses. The thermal, mechanical, and metallurgical aspects of the LAM process are fully-coupled in the model, accurately capturing chip formation and serration, while also accommodating strains induced by metallurgical transformations. Implemented within the finite element software, ABAQUS, the model’s predictions for surface residual stresses align closely (¿90%) with experimental data from literature. Notably, the model elucidates the transition of surface residual stresses towards tensile nature due to laser heating in LAM. The results reveal that the metallurgical transformation exerts a more pronounced influence at lower cutting speeds. Moreover, surface residual stresses tend towards tensile nature with increased laser power but shift towards compressive nature with higher laser-tool gap, cutting speed, and feed. Depth-wise residual stress distributions underscore the significant impact of laser power, speed, and feed compared to laser-tool gap. The proposed model can be used to optimise the LAM process and improve the quality and reliability of the finished products.

Modeling of laser-assisted micro-milling

The difficulties in the mechanical micro-machining process regarding the tool deflection, size effect and tool wear are much more pronounced than those in mechanical macro-machining. However, the role of mechanical micro-machining cannot be overestimated as an alternative against the non-traditional machining methods in manufacturing complex micro-parts with high dimensional and geometrical accuracies. Laser-Assisted Machining (LAM) can be used as a promising method by reducing the cutting forces and providing the possibility of increasing the Material Removal Rate (MRR) to enhance the productivity of mechanical micro-machining of difficult-to-cut material. Unlike common LAM, the parts are structured before machining using the ultra-short pulsed laser, followed by removing some parts of the material and consequently changing uncut chip thicknesses at the machining process. A model has been developed to understand how the structuring of the parts before micro-milling affects the uncut chip thicknesses at the micro-milling process. The model includes a variety of input parameters in terms of structure, tool, and process parameters to investigate this novel LAM comprehensively. Based on model results, the uncut chip thicknesses are reduced through the structuring of the part. The structure density was found as the most crucial parameter in uncut chip thickness reduction. The influence of structure density on cutting force reduction was also studied in the experiment. Workpieces made of titanium alloy (Ti6Al4V) were structured using a pico-second laser at different structure densities. The structured parts were machined at two feeds of 10 and 50 µm/tooth with a 35 m/min constant cutting speed. Structure density's role in reducing cutting force was also considerable. In addition, the contribution of different factors affecting cutting force reduction in this novel LAM process is discussed.

A comparative study on modeling approaches towards laser-assisted machining

Finite element method (FEM) is widely used in machining processes as it can efficiently respond to the thermomechanical deformation and removal processes of materials. In this paper, FEM simulation analysis for laser-assisted machining (LAM) of Ti6Al4V alloy is carried out using two different modeling approaches: the sequentially coupled simulation (SCS) and the predefined fields coupled simulation (PFCS). The results of temperature, cutting force and chip morphology are obtained by these different approaches and verified by experiments. By analyzing the errors of the two approaches, the results show that the cutting force and chip morphology errors of the SCS method are 16.14% and 11.11%, respectively, while the errors of the PFCS method are 7.58% and 16.67%. However, neither of these approaches can fully simulate the complete LAM process. Therefore, a fully coupled simulation (FCS) approach needs to be developed to overcome the shortcomings of the above two methods.

Influence of cutting parameters on laser assisted machining of C103 Nb alloy

ABSTRACTC103 Nb alloy shows the good consistent microstructure that leads to better controlled properties of the material such as high strength, stress resistance, fabricability, and high temperature resistance. C103 Nb alloy shows the unique properties for challenging the aerospace, orbital rocket nozzles or chambers, and jet engine applications but they are costly and difficult to machine through traditional technique like single point cutting operation. Laser assisted heating plays a significant role in machining process due to easy and to develop very high intense heat energy in a precise region The generated energy leads to soften sample and smooth machining surfaces with crack free and superior quality. The present work deals with the influence of cutting parameters (laser power (LP) and depth of cut (DoC)) on the responses (surface roughness and cutting force (CF)) of C103 Nb alloy through laser assisted machining process at constant feed rate (0.02 mm/rev) and constant cutting speed (500 rpm). Based on the experimental results, LP shown the significance influence on surface roughness, CFs and decreases with increase of LP and increases with increase of DoC.

Study on machining characteristics of SiC–Al2O3 reinforced aluminum hybrid nanocomposite in conventional and laser-assisted turning

In the present paper, the laser-assisted machining (LAM) of aluminum nanocomposite reinforced with SiC–Al2O3 nanoparticles was carried out using turning process. The laser power, depth of cut and cutting speed were considered as control factors. The optimization of factors was performed using Taguchi method by seeking the smallest surface roughness and cutting force. The results were compared with conventional machining (CM) process. According to the results, depth of cut had maximum influence on the cutting force in the LAM and CM processes. However, for surface roughness, the cutting speed and feed exhibited the major effect in LAM and CM processes, respectively. Moreover, the LAM had a reduction of 26% in the cutting force in comparison with CM process at optimal conditions. The lower cutting force resulted in a reduction of 51% in the surface roughness during LAM in comparison with CM process.

Numerical Modeling and Experimental Study of Laser Assisted Machining of Fused Silica

Fused silica is a kind of high-strength optical material, which is widely used in industry. It is slow and inefficient to process hard and brittle materials by conventional machining (CM) methods, while laser-assisted machining (LAM) technology can improve the plastic cutting ability of materials by local heating and softening, despite its application was not yet carried out in the case of fused silica. In this paper, the smoothed particle hydrodynamics (SPH) method is used to simulate the LAM process of fused silica. The result of LAM simulations show that the chips consist of continuous and discontinuous regions, which is significantly different from the CM in which the crack propagates and breaks in the initial deformation region. This indicates that the material removal mechanism takes place in a hybrid mode, which is a mixture of a brittle fracture and a plastic deformation. And the effect of process parameters on machining surface integrity, tool stress and tool wear were studied by numerical model. Both the simulations and the experimental results demonstrate that LAM significantly improves the machinability of fused silica by reducing the cutting force, improving the machining quality and decreasing the tool wear.

A study on the process efficiency of laser-assisted machining investigating energy consumption

Laser-assisted machining (LAM) has emerged as an effective process to facilitate the machining of several difficult-to-cut materials, including ceramics, titanium alloys, and nickel alloys. During LAM, the material is preheated by a laser beam, which leads to thermal softening. The softened material is removed by the cutting tool. Methods of improving LAM, by reducing cutting force, increasing tool life, and improving surface roughness, have been studied. While LAM effectiveness has been proven, there are few studies about LAM efficiency. In this study, the energy consumption of LAM laser power and depth of cut was analyzed for Ti-6Al-4V alloy. In addition, LAM process efficiency compared with conventional machining (CM) was experimentally analyzed, and optimized conditions were obtained. Under optimal conditions, LAM machining efficiency and process efficiency were improved by 230% and 104%, respectively, compared with CM.

Unconventional Machining of ceramic matrix Composites – A review

With an increase in demand for materials that are lightweight, thermally stable, and can sustain higher temperatures, ceramic matrix composites or CMC’s turned out to be potential candidates however, the major challenge with these materials was the manufacturing aspect and so, there was a demand for machining methods which could easily machine these materials without having much tool wear, provide higher material removal rate (MRR), and produce low surface roughness. Conventional machining (CM) processes like milling, grinding, drilling, and so on were turning out to be disadvantageous as the hardness of these materials is high and it results in excessive tool wear, high surface roughness, and low MRR. Recent researches in unconventional machining processes such as laser machining, plasma machining, electric discharge machining, and abrasive water jet machining, etc. are showing positive results when compared with CM. The current work presents a review of the unconventional machining process of these difficult to machine materials. The unconventional machining processes considered here are the laser-assisted machining process, rotatory ultrasonic machining process, and abrasive water jet machining process. Furthermore, it also discusses how these machining processes are better than conventional machining processes and it compares their MRR, surface roughness (SR), change in the properties, and also discusses the effect of these machining processes on the same parameters.

Comparative investigation of surface integrity in laser assisted and conventional machining of Ti-6Al-4 V alloy

Titanium alloys have numerous applications in the aerospace and medical industry due to their high strength and low weight. In the manufacturing of aerospace parts, surface integrity plays a key role due to its strong relationship with fatigue life and performance of the components. Since titanium alloys are difficult-to-machine, their Conventional Machining (CM) provides some technical limitations. As an alternative method, Laser-Assisted Machining (LAM) can be employed for this purpose and it is recommended for machining of hard materials. Laser Machining is the hybrid machining technique in which laser radiation is localized in front of cutting zone. However, surface integrity of the machined part should be controlled in LAM process due to the thermal effects of laser beam in to the workpiece material. Therefore, at the present study, experimental investigations were performed for both conventional and laser-assisted machining of Ti-6Al-4 V alloy and their results on surface integrity were compared and discussed together. In this regard, important indications of surface integrity including microhardness, grain size, surface roughness as well as thermal loads generated during the removal process were evaluated at different machining parameters. The results demonstrated that the use of laser-assisted machining under controlled process conditions can be significantly useful for improvement of surface integrity indications in machining of Ti-6Al-4 V superalloy.

Surface integrity in laser-assisted machining of Ti6Al4V

In laser-assisted machining (LAM), the laser source is focused on the workpiece as a thermal source and locally increases the workpiece temperature and makes the material soft ahead of the cutting tool so using this method, the machining forces are reduced, which causes improving the surface quality and cutting tool life. Machinability of advanced hard materials is significantly low and conventional methods do not work effectively. Therefore, utilizing an advanced method is inevitable. The product life and performance of complex parts of the leading industry depends on surface integrity. In this work, the surface integrity features including microhardness, grain size and surface roughness (Ra) and also the maximum cutting temperature were investigated experimentally in LAM of Ti-6Al-4V. According to the results, cutting speed has inverse effect on the effectiveness of LAM process because with increasing speed (15 to 63 m/min), temperature decreases (524 °C to 359 °C) and surface roughness increases (0.57 to 0.71 μm). Enhancing depth of cut and feed has direct effect on the process temperature, grain size, microhardness and surface roughness.

Reverse identification of high-temperature constitutive parameters of fused silica based on orthogonal cutting theory

<p indent=0mm>Laser-assisted machining (LAM) is a new type of thermomechanical processing technology that provides high-efficiency, low-cost, and high-quality processing of fused silica and other hard, brittle materials. However, the LAM process usually involves large strains, large strain rates, and high temperatures, which are difficult to observe in experiments. Finite element cutting simulations are effective for predicting the cutting mechanism of the cutting process, but an accurate material constitutive equation must be used for an accurate simulation. To obtain more accurate simulation results, this paper proposes a method for constructing the constitutive relationship of materials based on orthogonal cutting theory to compensate for the lack of a constitutive model for fused silica. According to the Oxley cutting theory, a mathematical model of the field distribution of parameters, such as stress, strain, strain rate, and temperature, in the main shear zone was established. An orthogonal cutting test platform was established, and the equivalent flow stress was calculated according to the test results. Then, a high-temperature constitutive equation for fused silica was determined by the genetic algorithm (GA) and applied to the simulation. Finally, the cutting simulation model was verified by experiments. The results showed that the simulation can better reflect the cutting force and chip morphology during an actual cutting test, which confirms the accuracy of the constitutive parameters and the reliability of the GA identification method.

Laser-Assisted Machining of Ti-6Al-4V Fabricated by DED Additive Manufacturing

Recently, the commercialization of hybrid machine tools that combine directed energy deposition (DED) additive manufacturing (AM) technology and subtractive manufacturing (SM) has rapidly progressed. This technology trend has been developed to meet the market demand for processing quality (precision) and productivity, and to produce products such as lightweight parts, and complex and special functional parts, as well as to facilitate mold production and part repair. Compared to SM technology, metal AM technology has limitations in terms of surface quality and shape accuracy. Therefore, post-processing is necessary for the AM output. Laser-assisted machining (LAM) is an innovative hybrid technique in which surface quality and productivity can be improved by enhancing the machinability of difficult-to-cut materials. LAM studies have mainly been performed on titanium alloys, nickel based alloys and ceramic materials. However, except for ceramics, no high-strength material studies have been conducted to analyze the LAM process machining characteristics of workpieces fabricated by AM process. Therefore, in this study, LAM is applied to post-processing of output fabricated by AM of Ti-6Al-4V. DED device was developed using metal powder feeder and a laser. The Ti-6Al-4V workpieces were successfully fabricated through many tests. The cutting depth for LAM was selected through thermal analysis for LAM of the fabricated workpiece. Compared to the case of traditional machining without preheating, machining characteristics in LAM experiments were analyzed and property testing was performed.

SPH/FEM modeling for laser-assisted machining of fused silica

Laser-assisted machining (LAM) is a promising technology for the machining of difficult-to-cut materials with reduced cutting forces, improved surface finishing, and enhanced tool life. Smoothed particle hydrodynamics (SPH) method is used to study the cutting mechanism during the laser-assisted machining of fused silica. In the present study, a 3-D transient thermal model is initially proposed to predict the temperature field distribution in the cutting zone of the fused silica. A Fortran subroutine is developed to simulate the moving laser with the Gaussian distribution. Both simulation and experiment results indicate that the thermal model produces an accurate prediction of the temperature in the workpiece. Then, temperature distributions are taken as the initial condition to establish the thermo-mechanical coupled cutting model. The dynamic cutting process is visualized in the cutting model. Moreover, discontinuous and continuous chips are found in both simulation and experiment. It implies that the cutting mechanism works under a hybrid mode of brittle fracture and plastic deformation in the LAM process. The variation of effective stress and plastic strain with temperature is analyzed in the cutting process. It is found that the application of the laser heating remarkably reduces fluctuations of the cutting force. Then, simulated cutting forces are evaluated experimentally. Comparisons show that simulated forces have excellent agreement with those from the experiment. It is concluded that localized high temperature originating from the laser significantly improves the machined surface quality.

Modeling of Laser assisted machining process using Artificial Neural Network

Recently machining with the assistance of laser is the cost effective proven technique to process high temperature alloys in aerospace industries. The challenge in laser assisted machining is to optimize the process parameters to get good surface integrity without changing the metallurgical and mechanical properties. As several input parameters such as feed rate, pulsed frequency, depth of cut, laser power and cutting velocity are involved in LAM, experimental studies are not an effective solution. So the main aim of this work is to develop an Artificial Intelligence model to understand the process mechanics and for the prediction of surface roughness, specific cutting energy and cutting zone temperature during laser assisted machining. ANN model has been developed by considering the topology of the network, selection of algorithm and selection of number of neurons. ANN model is developed by considering Levenberg-Marquardt algorithm and error is minimized by root mean square method. There is a better agreement between experimental and ANN model. The proposed model predicts the surface finish and specific energy with an prediction accuracy of 95.94 and 99.618% respectively during machining of hardened steel.

Multiresponse Optimization for Laser-Assisted Machining of Fused Silica Using Response Surface Methodology

Fused silica is difficult to machine using conventional machining methods mainly owing to its high brittleness and strength. Laser-assisted machining (LAM) provides desirable process for machining of fused silica. It was necessary to find the optimal machining condition during the LAM process. In this study, the regression models of the surface roughness and cutting force have been developed using Response Surface Methodology (RSM). Multiresponse optimization and composite desirability method were used to determine the optimum machining parameters. The experimental confirmed that the percentage errors of the regression models were within the permissible limits. It was also found that the high value of pulse duty ratio of laser corresponding to a better machining performance in the LAM of fused silica.

On modelling of laser assisted machining: Forward and inverse problems for heat placement control

Abstract Laser assisted machining (LAM) is one of the most efficient ways to improve the machinability of difficult-to-cut materials (e.g. Nickel-based superalloys). In the conventional LAM process, the laser beam is focused ahead of the cutting area at a fixed location, which leads to a series of restrictions, e.g. small heating area and non-uniform heat distribution due to the limitation of beam size and energy distribution. In this paper, a novel spatially and temporally (S&T) controlled laser heating method was proposed, in which a large area can be heated up with a small laser spot by controlling the beam scanning, i.e., laser power, path and speed of scanning. The laser configuration for the prescribed HAZ (heat affected zone) was achieved by solving the inverse heat conduction problem where the laser power together with either laser path or laser speed were optimised to achieve a particular temperature distribution in the chip to be removed by the following milling cutter. The proposed S&T laser heating method was thoroughly validated both for the direct and, the more important, inverse heating models by performing extensive temperature experiments by both infrared thermal camera and thermocouple array and further verified by laser assisted milling (LAMill) tests of Inconel 718 for large widths of cuts. The results showed that by applying path-optimised LAMill based on the inverse solution of the thermal problem, the peak and mean principal cutting forces were reduced by 55% and 47.8% respectively compared with the conventional dry milling process while the surface roughness improved by at least 14%. Moreover, after controlling the HAZ using the inverse thermal problem, a microstructure analysis of the machined surface showed that the proposed laser heating method avoids overheating of the workpiece below the planned depth of cut for the milling operation.

Experimental and numerical study of low frequency pulsed Nd:YAG laser heating of slip cast fused silica ceramics for laser assisted turning process considering laser beam overlapping

Machining of ceramics often involves many challenges due to their high hardness, brittleness, and low thermal conductivity. Laser assisted machining (LAM) is a promising technology for improving the machinability of hard-to-cut materials. In this work, the effect of laser heating in the LAM process on slip cast fused silica (SCFS) ceramics is investigated by presenting a numerical thermal analysis of laser effects on material behavior. A transient three-dimensional heat transfer analysis for laser assisted turning (LAT) of SCFS is performed using finite element method. Temperature distributions in SCFS cylindrical specimens are obtained. Moreover, the influence of laser parameters such as power, translational speed, and feed rate on the temperature field are studied. To increase the absorptivity of the ceramic surface, a coating is applied, and the absorptivity of the coated surface is determined by carrying out a series of experiments. Experiments are performed to validate the numerical transient heat transfer finite element model. In addition, the effects of spot overlapping of pulsed laser on temperature distribution and absorptivity of SCFS workpiece are studied. It is for the first time that effect of laser beam overlapping on low frequency pulsed laser heating in LAT is formulated and completely investigated.

Nd:YAG Pulsed Laser Assisted Machining of AMS 5708 Waspaloy Alloy

Due to very high strenght, low thermal conductivity, and high work hardening rate, the machinability of nickel-based superalloys is poor at room temperature. Laser-assisted machining (LAM) can provide a better aspect of machining such alloys. Since the wavelength of Nd:YAG laser is about 1/10th of that of CO2 laser, absorption and heating efficiency of Nd:YAG laser is much higher on metals and especially superalloys. Transmission of Nd:YAG laser through fiber optics to the heating point on the workpiece is a simple task during machining. This makes the LAM process more convenient and practical than the CM process. In this study a model is introduced for LAM of waspaloy, and its machinability is evaluated in terms of ease of material removal. Also, a temperature generation model is introduced for the Nd:YAG laser beam. Furthemore, wear behavior of an uncoated tungsten carbide and the formed chips were compared during the LAM and the CM of waspolay. To study the wear mechanism, the worn cutting tool was studied via scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). The formed chips were also evaluated via SEM and optical microscopy. Based on the results, the optimum LAM conditions were obtained at a cutting speed of 24 m/min and a feed rate of 0.06 mm/rev when a 400 W laser mean power and 80 Hz frequency are applied. Under these conditions, the temperature ahead of the cutting tool edge on the surface of workpiece was estimated to be 524°C. In comparison with CM, a significant improvement in tool wear and a better chip morphology were achieved through LAM, and also specific cutting energy and surface roughness were reduced by 25 and 20%, respectively.

A case-study on the mechanism of flank wear during laser-assisted machining of a titanium alloy

In recent years, researchers have been investigating various technologies including laser-assisted machining (LAM) to improve the machinability of titanium alloys which is considered to be one of the difficult-to-cut materials. The LAM process involves heating the titanium workpiece with a laser beam of sufficient power to soften the material before it engages with the cutting tool. Benefits of LAM include significant reduction in cutting forces as well as better surface finish. However, as diffusion wear is the most dominant tool wear mechanism associated when machining titanium alloys, the effect of the additional heat from laser preheating on the cutting tool life is not clearly understood. Therefore, this paper aims at investigating the tool life of an uncoated carbide tool during LAM of Ti-6Al-4V alloy, as well as identifying the principal flank wear mechanisms involved during the cutting process. It was found that the tool life was reduced by about 8% when machining the workpiece with laser preheating. Moreover, it was found that the carbon from the cutting tool diffused into the titanium built-up edge formed in the vicinity of the cutting zone from where it was carried out through the chips. This considerably weakened the cutting edge of the tool resulting in accelerated tool wear.

A case-study on the mechanism of flank wear during laser-assisted machining of a titanium alloy

In recent years, researchers have been investigating various technologies including laser-assisted machining (LAM) to improve the machinability of titanium alloys which is considered to be one of the difficult-to-cut materials. The LAM process involves heating the titanium workpiece with a laser beam of sufficient power to soften the material before it engages with the cutting tool. Benefits of LAM include significant reduction in cutting forces as well as better surface finish. However, as diffusion wear is the most dominant tool wear mechanism associated when machining titanium alloys, the effect of the additional heat from laser preheating on the cutting tool life is not clearly understood. Therefore, this paper aims at investigating the tool life of an uncoated carbide tool during LAM of Ti-6Al-4V alloy, as well as identifying the principal flank wear mechanisms involved during the cutting process. It was found that the tool life was reduced by about 8% when machining the workpiece with laser preheating. Moreover, it was found that the carbon from the cutting tool diffused into the titanium built-up edge formed in the vicinity of the cutting zone from where it was carried out through the chips. This considerably weakened the cutting edge of the tool resulting in accelerated tool wear.