Laser Heat Source Research Articles

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.

Management and storage of energy converted via a pyroelectric heat engine

Heat is a ubiquitous energy resource, which is easily accessible from the environment. The pyroelectric effect, a phenomenon that converts temperature variation into electricity, enables a material to be operated like a heat engine between high and low temperatures and electric fields, producing electrical work. However, current literature focuses on material performances, with no energy stored by operating in such conversion cycles. This work presents a complete pyroelectric management system that both realized cycled energy conversion and a maximum harvested power up to 13.1 μW. We achieved this by integrating a laser heat source, an advanced pyroelectric device, a practical power interface, and an energy storage component together. A thin film Lead Zirconate Titanate device was fabricated to achieve very fast temperature response (∼0.1 ms). Thus, the energy conversion can be achieved in a much higher thermodynamic frequency (1 kHz), leading to a larger power density. The proposed power interface manages an optimized pyroelectric conversion cycle while recharging a battery, or a storage capacitor (up to 2.1 V). The results provide a promising method to harvest energy from waste-heat and have shown great potential to supply power to small-scale, distributed devices. In addition, the application of the laser source has also enabled the system to achieve wireless power transmission, which would enable a more flexible way to supply power to multiple devices.

Combination of Laser Material Deposition and Laser Surface Processes for the Holistic Manufacture of Inconel 718 Components.

The present work proposes a novel manufacturing technique based on the combination of Laser Metal Deposition, Laser Beam Machining, and laser polishing processes for the complete manufacturing of complex parts. Therefore, the complete process is based on the application of a laser heat source both for the building of the preform shape of the part by additive manufacturing and for the finishing operations. Their combination enables the manufacture of near-net-shape parts and afterwards removes the excess material via laser machining, which has proved to be capable of eliminating the waviness resulting from the additive process. Besides, surface quality is improved via laser polishing so that the roughness of the final part is reduced. Therefore, conventional machining operations are eliminated, which results in a much cleaner process. To validate the capability of this new approach, the dimensional accuracy and surface quality as well as the microstructure of the resulting parts are evaluated. The process has been validated on an Inconel 718 test part, where a previously additively built-up part has been finished by means of laser machining and laser polishing.

A new approach to control and optimize the laser surface heat treatment of materials

Laser heating is often used to perform the surface treatment by modifying local microstructural and mechanical properties of components having complex geometries. In this study, the laser surface heat treatment of a rotating cylindrical work-piece was investigated using both experimental and numerical modeling approaches, with an aim to correlate and predict the temperature distribution during the process. The depth of the laser affected zone was predicted by solving the transient heat transfer with a moving laser heat source, using finite element analysis. The temperatures derived from the microstructural examination of the experimental specimen were found to closely agree with the predicted results from the numerical simulations. The numerical and experimental results have also led to a new observation, indicating a linear variation of the absorptivity with the laser scan speed. The prediction of the cooling curves from simulation suggested the β→αʺphase transformation and the recovery of the β phase, and the existence of new phases were confirmed through electron microscopy. The rapid cooling during the laser surface treatment was found to induce a flake-structure that consisted of both martensite (αʺ) and regained bcc (β) phase. A new polynomial input power function has been proposed to achieve uniform distribution of the heat penetration along the cylinder axis, saving about 10% of the material wastage.

Thermal characteristics of silicon wafer-based TVCs (thin vapor chambers) with disk-shape using DI water

This paper analytically and experimentally investigates the thermal characteristics of disk-shaped, silicon wafer-based thin vapor chamber (TVC) using de-ionized water as the working fluid. The maximum heat transfer rate, the maximum temperature, and the thermal resistances of the TVCs were measured experimentally. An analytical model based on the modified liquid pressure drop through a micro-pin–fin wick and the capillary limit was developed to determine the maximum heat transfer rate. In addition, a thermal resistance model was developed for the TVC that was used to calculate the maximum temperature from the maximum heat transfer rate. The maximum temperature of TVCs is ensured to not exceed the maximum allowable temperature of the electronic components. The silicon wafer-based TVCs, which have an overall thickness of 1 mm and radii of 5 mm, 7.5 mm, and 10 mm, were manufactured by using both deep reactive ion etching (DRIE) and Ionic bonding. A laser heat source and an IR camera were used not only to eliminate the effect of a thermal contact resistance between the heat source and the TVCs, but they were also used to observe the burn-out phenomena in the TVCs directly. The analytical model was shown to predict most of the measured data within ±10%. The effect that key TVC design parameters, such as the TVCs’ radius, the fin diameter, and the wick height, had on its maximum temperature and its thermal resistance were illustrated with the model and the measurements.

A study on the machining characteristics of induction and laser-induction assisted machining of AISI 1045 steel and Inconel 718

Difficult-to-machine materials are being widely used in various industries. However, these materials are much more difficult to machine using conventional machining (CM) methods than other common materials, because of their superior material properties such as high strength, stiffness and brittleness. Thermally assisted machining (TAM) methods have been developed to address this problem. Laser assisted machining (LAM) is a type of TAM process in which a workpiece is locally softened by a laser heat source in front of the cutting tool. The method is an effective way to enhance machinability when processing various difficult-to-cut materials. Two other approaches, induction assisted machining (IAM) and laser-induction assisted machining (LIAM), were analyzed and experimentally investigated in this study to compare their efficiency with that of CM for two materials, AISI 1045 steel and Inconel 718. It was found that cutting force was decreased and surface quality was improved when the IAM and LIAM were used.

A study on the machining characteristics using plasma assisted machining of AISI 1045 steel and Inconel 718

Difficult-to-cut materials such as titanium, Inconel and nickel alloys are being increasingly used in aerospace, automobile and medical equipment. However, these materials are difficult to machine using conventional machining (CM) methods, because of their superior material properties. New machining methods are being studied and developed for these materials. One of these machining methods, Thermal assisted machining (TAM,) applies a heat source to enhance the machinability of the materials. Laser assisted milling (LAMill) is a widely used type of TAM. In the LAMill process, a laser heat source softens the materials in front of the cutting tool. However, LAMill is expensive. A plasma heat source has been widely used for welding, melting, preheating, etc., and at a cost of about one tenth that of a laser heat source. But few studies on Plasma assisted machining (PAM) have been conducted. In this study, a PAM process was developed and investigated, and its performance compared with LAMill and CM. The proper preheating temperature and depth of cut (DOC) were determined by thermal analysis. Experiments were carried out with the PAM system on AISI 1045 steel and Inconel 718 using the determined preheating temperature and DOC. It was found that PAM reduced cutting force and improved the surface quality.

Evaluation of interlaminar delaminations in titanium-graphite fibre metal laminates by infrared NDT techniques

Fibre Metal Laminates (FMLs) describe a number of aerospace-grade layered structural materials where thin metal alloy foils are interleaved with Fibre Reinforced Polymer (FRP) plies. Such material hybridisation at the layer meso-scale poses a challenge for non-destructive testing (NDT). On the other hand, the need for NDT inspection of FMLs arises due to the potential development of interlayers disbonds, both during fabrication or in-service. This work describes the successful implementation of two Infrared-NDT approaches to evaluate a defected FML panel made of Titanium/Graphite (Ti-Gr). One technique is based on the modulation of the deployed heat from a low-cost halogen lamp, to retrieve defects as phase-contrast signatures from harmonics in the frequency domain. The second technique uses a flying laser heat-source, raster scanning the surface, searching for defect signatures on the heat distribution trail of the moving laser. The work explores also the opportunity to collimate the laser heat source as a round spot or a linear distribution. The proposed non-conventional IR-NDT approaches are also compared with a well-established Pulsed Phase Thermography (PPT) algorithm, demonstrating a similar ability of defects evaluation, but offering some favourable features, which are highlighted in the work.

Finite element simulation and microstructure analysis of nickel based alloy for additive manufacturing

In this paper, the finite element simulation of GH4169 high temperature alloy by selective laser melting was carried out, and the microstructure was analyzed by experiments. The results show that the shape of the temperature field cloud formed by the laser heat source is different from the shape of the theoretical model, but is in the shape of the ellipse. The temperature gradient at the front end of the molten pool is larger than that of the back end of the molten pool, and the isotherm of the front end of the molten pool is more intensive. The temperature of the substrate is less affected by the temperature gradient. The temperature gradient of the front end of the melting pool is larger than the back end of the molten pool, and the temperature field of selective laser melting is like a meteor with trailing tail. In the laser heat source, the temperature isotherm is the most dense and the temperature gradient is maximum. The relative effect of mechanical properties of δ phase is very complex. When the phase is precipitated by widmanstatten structure, it is easy to produce stress concentration as a source of cracks

Mechanical and microstructural characterisation on direct metal laser sintered Inconel 718

Direct metal laser sintering (DMLS) is one of the additive manufacturing technologies which allows the fabrication of complex components in layer by layer technique with melting and solidification of powder raw material by laser heat source. This paper investigates about the mechanical and microstructural characteristics such as bulk density, porosity, micro hardness and surface roughness on Inconel 718, a nickel super alloy made by using DMLS. Bulk density and porosity finds good agreement with the components fabricated by casting. Microhardness and surface roughness along the surface of the component was investigated and also surface roughness along the build direction was inspected. The phases present in the processed Inconel 718 was found by using X-ray diffractometre. Optical microscopy and scanning electron microscopy was used to examine and understand the microstructure of as-built Inconel 718 without post-processing effects.

A study on the machining characteristics and energy efficiency of Ti-6Al-4V in laser-assisted trochoidal milling

Titanium alloys are widely used in high value-added applications such as aerospace and automobile products. However, their superior mechanical properties also make them difficult-to-cut materials. Various machining methods have been developed for machining difficult-to-cut materials. One of these methods, the trochoidal milling method, combines a linear tool movement with a circular movement. It has several advantages, including low cutting force and better tool life, and it can also be applied to high speed machining. Laser-assisted machining (LAM) is another hybrid machining method for difficult-to-cut materials. When the material is locally preheated by a laser heat source prior to machining by the cutting tool, cutting resistance is reduced, and processing efficiency is increased. The purpose of this study is to develop a laser-assisted trochoidal milling process by combining the two machining methods. The processing efficiency of the trochoidal milling method was verified through experiments and comparison with conventional milling. Also, the cutting force and energy efficiency by considering specific cutting energy during the laser-assisted trochoidal milling of Ti-6Al-4V were analyzed for various machining conditions and compared with trochoidal milling.

Experimental and computational study of optically-driven electrothermal vortex

Optically-driven electrothermal vortex flow is one of the most effective ways to induce convection in microscale domains. In this work, side view microscopic imaging is used for qualitative flow visualisation as well as quantitative µPIV measurements of the vortex pattern in microfluidic chips between simple parallel-plate electrodes. The uniform electric field is generated from parallel-plate, indium tin oxide (ITO) electrodes separated by 400 µm. Alternating current (AC) electric fields at a range of frequencies (9-100 kHz) and voltages (5-40 V) are applied to the electrodes to drive the flow. Simultaneously, a near-infrared (1064 nm) laser beam at various intensities is focused on the bottom electrode surface of the microchannel. Strong electrothermal vortices are observed in the flow visualisation experiments and measured by µPIV. A realistic computational model featuring a laser heat source and an applied electrical field is constructed. Computational simulations are performed under the same conditions as the experiments. The simulations and the experiments show the same qualitative behaviours and also agree quantitatively when comparing the maximum velocities.

Hybrid laser/arc welding of thick high-strength steel in different configurations

In this investigation, hybrid laser/arc welding (HLAW) was employed to join 8-mm-thick high-strength quenched and tempered steel (HSQTS) plates in the butt- and T-joint configurations. The influences of welding parameters, such as laser power, welding speed, stand-off distance (SD) between the arc of gas metal arc welding, and the laser heat source on the weld quality and mechanical properties of joints, were studied to obtain non-porous and crack-free fully-penetrated welds. The weld microstructure, cross-section, and mechanical properties were evaluated by an optical microscope, and microhardness and tensile tests. In addition, a finite element model was developed to investigate the thermal history and molten pool geometry of the HLAW process to join the HSQTS. The numerical study demonstrated that the SD had a paramount role in good synergy between the heat sources and the stability of the keyhole. For the butt-joint configuration, the results showed that, at a higher welding speed (35 mm/s) and optimum SD between the arc and laser, a fully-penetrated sound weld could be achieved. A non-porous weld in the T-joint configuration was obtained at a lower welding speed (10 mm/s). Microstructural evaluations indicated that the formation of residual austenite and the continuous network of martensitic structure along the grain boundary through the heat affected zone were the primary reasons of the softening behavior of this area. This was confirmed by the sharp hardness reduction and failure behavior of the tensile coupons in this area.

Processing of thermoplastic matrix composites through automated fiber placement and tape laying methods

Fiber-reinforced composite materials are replacing metallic components due to their higher specific strength and stiffness. Automation and thermoplastics emerged to overcome the time and labor intensive manual techniques and the long curing cycles associated with processing thermoset-based composites. Thermoplastics are processed through fusion bonding which involves applying heat and pressure at the interface. Together with automated techniques (such as automated fiber placement, and automated tape laying), a fast, clean, out-of-autoclave, and automated process can be obtained. A detailed review of thermoplastic composites processing through automated methods is presented. It sheds the light on the materials used and the different heat sources incorporated with the pros and cons of each, with concentration mainly on hot gas torch, laser, and ultrasonic heating. A thorough illustration of the several mechanisms involved in a tow/tape placement process is tackled such as heat transfer, intimate contact development, molecular interdiffusion, void consolidation and growth, thermal degradation, crystallization, and so on. Few gaps and recommendations are included related to materials, laser heat source, heat transfer model, and the use of silicone rubber rollers. A review of optimization studies for tape placement processes is summarized including the main controllable variables and product quality parameters (or responses), with some of the major findings for laser and hot gas torch systems being presented. Both mechanical and physical characterizations are also reviewed including several testing techniques such as short beam shear, double cantilever beam, lap shear, wedge peel, differential scanning calorimetry, and so on. Challenges, however, still exist, such as achieving the autoclave-level mechanical properties and complying with the porosity levels required by the aerospace industry. More work is still necessary to overcome these challenges as well as increase the throughput of the process before it can be totally commercialized.

Heat and mass transfer effects of laser soldering on growth behavior of interfacial intermetallic compounds in Sn/Cu and Sn-3.5Ag0.5/Cu joints

The magnitudes of input power and scan speed of laser heat source can affect the morphology and size of interfacial Cu6Sn5 intermetallic compound (IMC) formed or grown in Sn/Cu and Sn-3.5Ag-0.5Cu/Cu (SAC/Cu) joints. Experimentally, it has been observed that greater power and smaller scan speed can create temperature field of higher magnitude, thereby enhancing the interfacial reaction. The occurrence of conglomerated, prismatic (faceted) and scalloped IMC morphologies in the specimens corresponding to designated laser processing parameters, has been explained with the help of Jackson parameter. The heat and mass transfer phenomena during laser soldering, is modeled using finite element analysis. Enthalpy method is applied in the FEM based computational model to describe the phase change based heat transfer at the melting regime of the solder. With an attainment of transient temperature profiles at several scan speeds through the numerical analysis, the values of interfacial reaction temperature at solder/substrate interface and diffusion phenomenon based mass transfer of Cu into solder are then utilized to explain the experimental results of IMC size. In comparison to pure Sn solder, SAC solder type is characterized with the formation of thicker IMC at laser power of 50W and scan speeds below 180mm/min.

Numerical analysis of the temperature profile during the laser-assisted automated fiber placement of CFRP tapes with thermoplastic matrix

In this study, a thermodynamic model of a laser-assisted automated thermoplastic fiber placement process is developed and validated. The main focus is on modeling the heat transfer into the composite with a laser heat source, the thermal properties of the tape, and the resulting heat distribution in the part, the mold, and the compaction roller. A new integrated analytical method is presented to calculate the energy input of the laser based on the geometric boundary conditions, including first-order reflection and laser shadow. The carbon fiber/polyethersulphone tape is modeled by combining literature properties of carbon fiber and matrix as well as based on experimental data of the tape itself. Also a thermal contact resistance between the tape layers is modeled based on a literature model and own experimental measurements. The created model is discretized and implemented in a 2-D finite difference code. With the help of this simulation, the temperature distribution is calculated during layup. The influence of a possible thermal contact resistance between the composite layers is investigated. Furthermore, an experiment with a thermoplastic fiber placement machine from Advanced Fibre Placement Technology GmbH (AFPT) was conducted in order to evaluate the simulation. The simulation and the experiment show a good agreement and prove that thermal contact resistance between the layers is negligible for the investigation process.

On thermal modeling of Additive Manufacturing processes

A two-dimensional Finite Difference (FD) model of the thermal history of parts manufactured in powder bed fusion Additive Manufacturing (AM) processes is presented. The temperature of the part is calculated in each time-step taking into account the moving laser heat source, the melting phase change and functions of both temperature and porosity are used for the material thermal properties. Also, an algorithm for node birth and distance adaptation over time is utilized, minimizing computational time and memory. A validation of the results of the model is included.

High Power Diode Laser (HPDL) for Fatigue Life Improvement of Steel: Numerical Modelling

This paper deals with the improvement of fatigue life of AISI 1040 steel components by using a High Power Diode Laser (HPDL). First, the meaningfulness of each operational parameter was assessed by varying the experimental laser power and scan speed. After laser treatment, fatigue tests were performed to investigate the influence of laser processing parameters on the material resistance. The fatigue tests were carried out by using a rotating bending machine. Wöhler curves were obtained from the analysis of experimental results. Second, in the light of experimental findings, a 3D transient finite element method for a laser heat source, with Gaussian energy distribution, was developed to predict the temperature and the depth of the heat affected zone on the workpiece. The model allows us to understand the relationship between the laser treatment parameters and the fatigue enhancement of the components. HPDL was found to significantly increase the fatigue life of the irradiated workpieces, thus revealing its suitability for industrial applications.

Numerical and experimental study of laser aided additive manufacturing for melt-pool profile and grain orientation analysis

Laser aided additive manufacturing (LAAM), a blown powder additive manufacturing process, can be widely adopted for surface modification, repair and 3D printing. A robust numerical model was developed to simulate convective fluid flow and balancing of surface tension forces at the air-fluid interface to predict melt-pool free surface curvature and solidified clad dimensions. The free surface physical interface was calculated using the Arbitrary Lagrangian Eulerian (ALE) moving mesh approach. Powder deposition efficiency was considered by activating mesh normal velocity at melted regions based on localized powder mass flux intensity from the discrete coaxial powder nozzles. The heat flux equation used for representing the laser heat source considered attenuation effect from the interaction between the powder jets and laser as well as heat sink effects of un-melted powder particles entering the melt-pool. The predicted thermal gradient directions agree well with grain growth orientations obtained from electron backscatter diffraction (ESBD) analysis in three different cross-sectional orientations. Experimental validation of clad width, height and melt-pool depth shows a maximum error of 10% for a wide range of processing parameters which consider the effects of varying laser power, laser scanning speed and powder feeding rate.

Elastodynamic interactions of laser pulse in microstretch thermoelastic mass diffusion medium with dual phase lag

The aim of the present investigation is to study the effects of laser heat source and phase lags on a microstretch thermoelastic mass diffusion medium including dual phase lag model. The normal mode analysis technique has been adopted to obtain the components of displacement, microrotation, microstress, mass concentration and temperature distribution due to the presence of ultra-laser heat source. The numerical computation has been performed (using Matlab software) on the resulting quantities. The computed numerical results are shown graphically to depict the effect of laser heat source and diffusion phase-lags. Some particular cases of interest are also deduced from the present investigation.