Laser-assisted Milling Research Articles

Surface roughness modeling in Laser-assisted End Milling of Inconel 718

Inconel 718 is a difficult-to-machine material while products of this material require good surface finish. Therefore, it is essential for the evaluation and prediction of surface roughness of machined Inconel 718 workpiece to be developed. An analytical model for the prediction of surface roughness under laser-assisted end milling of Inconel 718 is proposed based on kinematics of tool movement and elastic response of workpiece. The actual tool trajectory is first predicted with the consideration of overall tool movement, elastic deformation of tool, and the tool tip profile. The tool movements include the translation in feed direction and the rotation along its axis. The elastic deformation is calculated based on the previously established milling force prediction model. The tool tip profile is predicted based on the tool tip radius and angle. The machined surface profile is simulated based on the tool trajectory with elastic recovery, which is considered through the comparison between the minimum thickness and actual cutting thickness. Experiments are conducted in both conventional and laser-assisted milling under seven different sets of cutting parameters. Through the comparison between the analytical predictions and experimental measurements, the proposed model has high accuracy with the maximum error less than 27%, which is more accurate for lower feed rate with error less than 3%. The proposed analytical model is valuable for providing a fast, credible, and physics-based method for the prediction of surface roughness in milling process.

Residual stress prediction in laser-assisted milling considering recrystallization effects

An analytical predictive model for residual stress in laser-assisted milling considering material recrystallization caused by laser preheating is proposed. The laser preheating temperature field is predicted by treating the laser beam as a heat source on top surface following Gaussian distribution. Heat convection between top surface and the environment is factored into account. Isothermal boundary conditions are assumed for the area of interest with conduction within the material. Next, the milling configuration is treated as orthogonal cutting at each instance. All process parameters including cutting depth, cutting speed, and tool geometry are therefore transferred. The recrystallization effect and thus the grain growth are considered through calibrated models describing the dependency of strain rate, strain, and temperature on dynamic recrystallization process for specific alloys using exponent functions. The residual stress is then predicted through the calculation of elastic stress distribution in loading process, actual stress with kinematic hardening, and the stress change during relaxation. The proposed model is validated through experimental measurements on the laser-assisted milling of Si3N4 and Ti-6Al-4V. The predictive model matches the trends of experimental measurements with agreement to an average error less than 30% in all cases. The proposed analytical model is valuable for providing a fast, credible, and physics-based method for the prediction of residual stress in laser-assisted milling of various materials.

A Study on the Machining Characteristics of Curved Workpiece Using Laser-Assisted Milling with Different Tool Paths in Inconel 718

Difficult-to-cut materials are being increasingly used in many industries because of their superior properties, including high corrosion resistance, heat resistance and specific strength. However, these same properties make the materials difficult to machine using conventional machining techniques. Laser-assisted milling (LAM) is one of the effective method for machining difficult-to-cut materials. In laser-assisted milling, the machining occur after the workpiece is locally preheated using a laser heat source. Laser-assisted milling has been studied by many researchers on flat workpiece or micro end-milling. However, there is no research on the curved shape using laser assisted milling. This study investigated the use of laser-assisted milling to machine a three-dimensional curved shape workpiece based on NURBS (Non-uniform rational b-spline). A machining experiment was performed on Inconel 718 using different tool paths (ramping, contouring) under various machining conditions. Finite elements analysis was conducted to determine the depth of cut. Cutting force, specific cutting energy and surface roughness characteristics were measured, analyzed and compared for conventional and LAM machining. LAM significantly improved these machining characteristics, compared to conventional machining. There results can be applied to the laser-assisted milling of various three-dimensional shapes.

Inverse Analysis of Inconel 718 Laser-Assisted Milling to Achieve Machined Surface Roughness

This manuscript proposes an inverse analysis method for the machined surface roughness in laser-assisted milling on Inconel 718. The method solves the forward problem considering the tool profile and the elastic recovery of machined surface and applies the variance-based recursive method to guide the updating mechanism of process parameters to match the measurements. Subsequently, the inverse analysis identifies four process parameters of feed per tooth, tool tip radius, minimum cutting thickness, and tool tip angle, and finds the optimal solution for target performance, the surface roughness. The measurements are collected under the single beam coaxial laser-assisted milling spindle. The proposed modified Kalman filter algorithm introduces the gain coefficient G when updating the process parameters to improve robustness and accuracy. The inverse analysis is conducted on all measurements, and the average error of target performance is 0.460% when the laser is on and 0.394% when the laser is off. The average difference of process parameters is less than 5%, and the selection process is done in 50 loops within a minute. Therefore, the proposed inverse analysis model is robust, adaptive to different initial guesses and measurements, highly accurate, and saves computation time.

Analytical prediction of temperature in laser-assisted milling with laser preheating and machining effects

An analytical predictive model for temperature in laser-assisted milling considering both laser preheating temperature and machining induced temperature rise is proposed. The preheating temperature at top surface is predicted first by considering the heat generation from laser and convection. The heat generation rate is described by Gaussian equation. Within the material, heat conduction is considered with isothermal boundary conditions at side and bottom surfaces. The machining temperature is considered by transferring the milling configuration to orthogonal cutting at each instance. The shearing heat source and secondary rubbing heat source are included for machining temperature prediction. The heat source is calculated from the cutting or plowing forces, and a mirror heat source method is applied to predict temperature rise through integration. The proposed model is validated through experimental measurements on silicon nitride ceramics and Ti-6Al-4V alloy. The proposed predictive model matches the experimental measurements with less than 7.1% difference at laser spot and 5.2% difference in front of the cutting zone with computation time less than 15 s. The model is valuable for providing a fast, credible, and physics-based method for the prediction of temperature in laser-assisted milling of various materials. The overall temperature distribution is accurately calculated by predicting laser preheating temperature and machining induced temperature rise.

A Study on the Optimum Machining Conditions and Energy Efficiency of a Laser-Assisted Fillet Milling

Laser-assisted machining (LAM) is known to be an effective and economical technique for improving the machinability of difficult-to-machine materials. In the LAM method, material is preheated using a laser heat source and then the preheated area is removed by following cutting tool. For laser-assisted turning (LAT), the configuration of the system is not complicated because laser irradiates from a fixed position. In contrast, laser-assisted milling (LAMill) system is not only complicated but also difficult to control because laser heat source must always move ahead of the cutting tool along a three dimensional (3D) tool path. LAMill is still early stage and cannot yet be used to machine finished products with 3D shapes. In this study, a laser-assisted fillet milling process was developed for machining 3D shapes. There are no prior studies combining fillet milling and LAMill. Laser-assisted fillet milling strategy was proposed, and effective depth of cut (EDOC) was obtained using thermal analysis. Experiments were designed using response surface method and cutting force prediction equations were developed using statistical analysis and regression analysis. The optimum machining conditions were also proposed, and energy efficiency of the LAMill was analyzed by comparing the specific cutting energy of conventional machining (CM) and LAMill.

The temperature process analysis and control on laser-assisted milling of nickel-based superalloy

Nickel-based alloys of Inconel 718 are well-known for their excellent properties of high-temperature hardness, mechanical strength, and wear resistance and are currently popular and applied in aerospace industry, such as the manufacturing of aero-engine turbine disks and compressor disk. Laser-assisted milling (LAML), which uses laser to locally heat the workpiece to improve the machinability of the material, has the advantage of increasing machining efficiency, reducing tool wear, and improving machining quality. In LAML, laser preheating temperature is the most important parameter influencing laser heating effect; however, constant laser energy commonly used in experiments cannot provide a stable preheating temperature. Therefore, temperature feedback control method is used in LAML and composite simulation models are established to simulate the temperature field and cutting process. The composite simulation models contain laser preheating temperature model, temperature feedback model, temperature difference prediction model, and cutting process model. Finite element method and neural network calculation method are used in building the model, which can be used to get the temperature difference, and then through monitoring to control the temperature of the laser heating. The simulation results show that the laser energy and the laser moving speed are the main factors affecting the laser preheating temperature, the difference between cutting area temperature and monitor temperature. A LAML experiment system is set up; cutting force and cutting chips are obtained through experiments. The simulation results express a good agreement with the experimental results, thus demonstrating the feasibility of the temperature-monitoring laser heating system and capabilities of LAML in fabricating difficult-to-machine parts for industrial implementation.

Inverse analysis of the cutting force in laser-assisted milling on Inconel 718

Inverse analysis is of value identifying viable solutions of process parameters that can achieve specified process performance. In this study, an inverse analysis method is proposed for the cutting force in laser-assisted milling on Inconel 718. The method uses the analytical model to solve the direct problem and applies a variance-based recursive method to guide the inverse analysis. The half-slot milling is simplified as an orthogonal cutting at each instant, forces in cutting and radial directions are calculated under microstructure evolution, and the axial force is predicted according to tool geometry and coordinates transformation. The inverse analysis identifies five process parameters including feed rate, axial depth of milling, laser preheating temperature, spindle speed, and rake angle, and finds the optimal solution for target performance, the resultant cutting force. Four experiments verified the effectiveness of the proposed method because of a maximum error less than 8% between predicted forces and experimental measurements. The proposed method is valuable in terms of providing a reference for the selection of process parameters under certain cutting force requirements.

A study on the edge chipping according to spindle speed and inclination angle of workpiece in laser-assisted milling of silicon nitride

Ceramics are difficult to machine due to their high hardness and brittleness. As an effective method for machining ceramics, laser-assisted machining (LAM) has been studied by many researchers. In particular, many studies of methods to improve the machinability of silicon nitride using LAM have been performed. However, there is little research on the effect of the inclination angle of the workpiece, because varying the angle increases the difficulty of controlling the laser preheating and tool path. This paper investigates the effect of preheating temperature, spindle speed and inclination angle of the workpiece on edge chipping of silicon nitride in an effort to obtain an enhanced surface finish using laser-assisted milling (LAMill). The machining conditions were determined by considering the parameters that can reduce edge chipping using related theory. Experimental results showed a reduction in edge chipping based on increases in preheating temperature, spindle speed and inclination angle of the workpiece. Also, by increasing the spindle speed and the inclination angle of the workpiece, surface roughness was decreased due to reduction in the cutting force. The energy efficiency of LAMill by comparing the specific cutting energy according to the machining conditions is analyzed.

Heat affected zone in the laser-assisted milling of Inconel 718

The melting zone shape is experimentally characterized in the laser-assisted milling process of Inconel 718. A three-dimensional finite element model is proposed for the temperature field distribution prediction. A good agreement is found between the experimental characterized melting zone shape and predicted melting zone shape. The material absorption ratio is determined by matching the melting zone shape from experiment with simulation model. The material absorption ratio is found to be a weak function of laser scanning speed. With the increase of laser power input, the absorption ratio monotonically decreases. The effects of laser scanning speed and power input on the melting zone shape are investigated. The melting zone depth, width and cross section area decrease with the increasing of laser scanning speed and increase with increasing power input.

Investigation into the machining characteristics of AISI 1045 steel and Inconel 718 for an ellipsoidal shape using laser-assisted contouring and ramping machining

Laser assisted machining (LAM) is a thermally assisted machining (TAM) method that softens difficult-to-cut materials by laser preheating. Laser assisted turning (LAT) is easy to keep the shape of the laser heat source to be circle because the laser heat source is irradiated to the workpiece surface at a fixed position. So, commercial LAT devices have been developed in some countries. However, it is difficult to apply laser assisted milling (LAMill) to three-dimensionally shaped workpieces, because it is not easy to control laser preheating according to the change of workpiece shape. In this study, LAMill was newly applied to two materials having an ellipsoidal shape as a curved 3D example. Effective depth of cut and the optimum preheating temperature were obtained by a transient thermal analysis. Contouring and ramping machining were employed in the experiments. Machining characteristics were investigated by analyzing the cutting force, surface roughness and tool condition, and it has been found that they are enhanced by LAMill. The research results can be used further to processing of other difficult-to-cut materials.

Microstructure-sensitive flow stress modeling for force prediction in laser assisted milling of Inconel 718

Inconel 718 is a typical hard-to-machine material that requires thermally enhanced machining technology such as laser-assisted milling. Based upon finite element analysis, this study simulates the forces in the laser-assisted milling process of Inconel 718 considering the effects of grain growth due to γ' and γ phases. The γ phase is unstable and becomes the δ phase, which is likely to precipitate at a temperature over 750 °C. The temperature around the center of spot in the experiments is 850 °C, so the phase transformation and grain growth happen throughout the milling process. In the analysis, this study includes the microstructure evolution while accounting for the effects of dynamic recrystallization and grain growth through the Avrami model. The grain growth reduces the yield stress and flow stress, which improves the machinability. In finite element analysis (FEA), several boundary conditions of temperature varying with time are defined to simulate the movement of laser spot, and the constitutive model is described by Johnson-Cook equation. In experiments, this study collects three sets of cutting forces and finds that the predicted values are in close agreements with measurements especially in feed direction, in which the smallest error is around 5%. In another three simulations, this study also examines the effect of laser preheating on the cutting forces by comparison with a traditional milling process without laser assist. When the laser is off, the forces increase in all cases, which prove the softening effect of laser-assisted milling. In addition, when the axial depth of milling increases, the laser has a more significant influence, especially in axial direction, in which the force with laser is more than 18% smaller than the one without laser. Overall, this study validates the influence of laser-assisted milling on Inconel 718 by predicting the cutting forces in FEA.

Case study of virtual reality in CNC machine tool exhibition

Exhibition and demonstration are generally used in the promotion and sale-assistance of manufactured products. However, the transportation cost of the real goods from the vender factory to the exposition venue is generally expensive for huge and heavy commodity. With the advancement of computing, graphics, mobile apps, and mobile hardware the 3D visibility technology is getting more and more popular to be adopted in visual-assisted communication such as amusement games. Virtual reality (VR) technology has therefore being paid great attention in emulating expensive small and/or huge and heavy equipment. Virtual reality can be characterized as 3D extension with Immersion, Interaction and Imagination. This paper was then be focused on the study of virtual reality in the assistance of CNC machine tool demonstration and exhibition. A commercial CNC machine tool was used in this study to illustrate the effectiveness and usability of using virtual reality for an exhibition. The adopted CNC machine tool is a large and heavy mill-turn machine with the width up to eleven meters and weighted about 35 tons. A head-mounted display (HMD) was attached to the developed VR CNC machine tool for the immersion viewing. A user can see around the 3D scene of the large mill-turn machine and the operation of the virtual CNC machine can be actuated by bare hand. Coolant was added to demonstrate more realistic operation while collision detection function was also added to remind the operator. The developed VR demonstration system has been presented in the 2017 Taipei International Machine Tool Show (TIMTOS 2017). This case study has shown that young engineers and/or students are very impressed by the VR-based demonstration while elder persons could not adapt themselves easily to the VR-based scene because of eyesight issues. However, virtual reality has successfully being adopted and integrated with the CNC machine tool in an international show. Another machine tool on laser-assisted milling machine motion simulation has also been successfully conducted to show the expandability of the VR based technology. One can conclude that VR will be adopted and paid more and more attention in the future in helping CNC machine tool promotion. Further study could be extended to education and training system, and also for the maintenance system, too.

Precision Cutting of Glass by Laser-assisted Machining

Precision machining of glass has been receiving attention in various applications because of the use of glass interposers in layered semiconductors or glass substrates for microfluidic chips. These applications require complicated and three-dimensional machining for further product functionality. Etching is conventionally used for precision machining of glass. However, applying etching for three-dimensional machining is difficult, and thus, a method which is applicable to three-dimensional machining of glass is needed. Cutting is a method applicable to three-dimensional machining. However, precision cutting of glass is difficult because glass is a hard and brittle material. In this research, we applied laser-assisted machining for cutting of glass. We first conducted laser-assisted milling for plane surface cutting. We then proposed laser-assisted drilling for glass drilling to perform the three-dimensional cutting of glass by laser-assisted machining. Through the experimental analyses, we demonstrated the feasibility of the precision and three-dimensional cutting of glass.

Analytical model for force prediction in laser-assisted milling of IN718

Laser-assisted machining (LAM) could help to significantly reduce the machining forces and improve machinability of hard to machine materials. The physical ground explanation for machinability improvement of the LAM stay largely unknown. In the current study, a 3D model is developed for the temperature field calculation induced by laser preheating. Taking preheating temperature field as initial input, an analytical milling force model is developed based on Oxley’s contact mechanics. Model validations are conducted by comparing the milling forces between the model predictions and experimental measurements in the LAM of Inconel 718 (IN 718). A good agreement is found. Also, the LAM forces are compared with traditional milling. The reduced specific cutting energy and reduced milling forces in LAM show the improved machinability of IN 718. The proposed analytical model provides a new method for the LAM process optimization.

High-efficiency and precision cutting of glass by selective laser-assisted milling

As a hard and brittle material, glass is difficult to precisely cut with high efficiency. Although various attempts at ductile cutting of glass with high cutting depth have been reported, the low efficiency of the cutting process remains problematic. In order to achieve high-efficiency and precision cutting of glass, this paper proposes selective laser-assisted milling (SLAM). In this method, a fiber laser that has a wavelength out of the absorption band of glass is absorbed only into the small area where the black-body coating is put, and the selectively heated area is removed with a cutting tool. The experimental results of this study have demonstrated that SLAM reduces the arithmetic average of the roughness profile by 74% compared with conventional cutting. An observational analysis of the generated chips revealed that the application of SLAM changed the morphology of the chips from the crack type to the quasi-continuous type. These results demonstrate the feasibility of the high-efficiency and precision cutting of glass.

Design and implementation of a system for laser assisted milling of advanced materials

Laser assisted machining is an effective method to machine advanced materials with the added benefits of longer tool life and increased material removal rates. While extensive studies have investigated the machining properties for laser assisted milling(LAML), few attempts have been made to extend LAML to machining parts with complex geometric features. A methodology for continuous path machining for LAML is developed by integration of a rotary and movable table into an ordinary milling machine with a laser beam system. The machining strategy and processing path are investigated to determine alignment of the machining path with the laser spot. In order to keep the material removal temperatures above the softening temperature of silicon nitride, the transformation is coordinated and the temperature interpolated, establishing a transient thermal model. The temperatures of the laser center and cutting zone are also carefully controlled to achieve optimal machining results and avoid thermal damage. These experiments indicate that the system results in no surface damage as well as good surface roughness, validating the application of this machining strategy and thermal model in the development of a new LAML system for continuous path processing of silicon nitride. The proposed approach can be easily applied in LAML system to achieve continuous processing and improve efficiency in laser assisted machining.

Laser assisted milling device: A review

Laser-Assisted milling is a type of thermally-assisted machining process in which a workpiece is locally softened by a laser heat source before machining. This method is effective solution for machining materials such as Inconel series alloys, titanium alloy, and ceramics, which are more difficult to machine compared with conventional materials. It is also a green machining process, because it saves energy by reducing the cutting force. Laser-Assisted milling has only been used in limited fields including single-direction machining of flat surfaces. When the laser-assisted milling has a complex tool-path, it is difficult to control the heat source and cutting tool simultaneously. To apply the process in industrial field studies of workpieces having various shapes are needed. This paper provides a review of current laser-assisted milling devices, and then develops a three-dimensional laser-assisted milling device for complex tool-path machining. A high-power diode laser with additional axes was retrofit to the spindle of a five-axis machining center. The device could be used in industrial fields whose machined products have complicated shapes.

A study of preheating characteristics according to various preheating methods for laser-assisted machining

Laser-assisted machining (LAM) is being actively studied as a new method for machining difficult-to-cut materials. In LAM, machining is performed after preheating the material using a laser. Among difficult-to-cut materials, silicon nitride, a type of ceramic material, is difficult to machine due to its high strength at high temperature and high thermal conductivity. Although machining of silicon nitride using laser-assisted turning has been performed, there are few studies and results using laser-assisted milling because it is difficult to maintain the proper preheating temperature of silicon nitride. So, in this study, three preheating methods, one-way, zig-zag, and back-and-forth, are proposed for machining silicon nitride using laser-assisted milling. The preheating effect according to the three preheating methods is analyzed by finite element analyses and experiments. And, the back-and-forth method is verified to be the most effective method.

A study on the laser-assisted ball-end milling of difficult-to-cut materials using a new back-and-forth preheating method

Laser-assisted machining is an effective process to facilitate the material removal processes of difficult-to-cut materials by laser preheating. Machinability of several difficult-to-cut materials, such as Inconel 718, zirconia, and silicon nitride, was studied including a newly developed back-and-forth preheating method used as an enhanced method to heat the workpiece effectively. Experiments were performed according to the inclination angle of the workpiece, for three-dimensional machining using a computed laser power and feed, on a 5-axes machining center with an additional axis for a laser module. The characteristics of the cutting force and surface roughness of the machined workpiece and the wear of the cutting tool were measured and discussed. Decreases in the cutting force and the enhancement of the surface quality were confirmed using the proposed back-and-forth preheating method in laser-assisted milling on Inconel 718, zirconia, and silicon nitride.