Laser Beam Processing Research Articles

Characterization and simulation of AlSi10Mg reinforcement structures by direct energy deposition by means of laser beam and powder

Among metal additive manufacturing technologies, direct energy deposition (DED) processes have the advantage to be easily integrable in a manufacturing chain with other conventional technologies. This characteristic can be exploited by designing reinforcement structures to be added by DED onto pre-existing subcomponents to tailor the part’s mechanical properties while keeping the part lightweight. This study focuses on DED by means of laser beam and powder process optimization to improve material quality and geometrical accuracy of AlSi10Mg reinforcement structures while preventing excessive thermal deformations and material dilution into the substrate. These results are compared with finite elements numerical simulations of the deposition process, comprising thermo-elastic deformation and material deposition, to predict the bending and reinforcement of the processed substrate. In particular, the model includes the deterministic prediction of the deposition profile as a function of the process parameters and a few condition-specific coefficients: once calibrated, the model was used to compare the numerical and experimental residual deformation of the reinforced sample, obtaining promising agreement. The reinforcement provided to a 1.5 mm thick substrate by a single wall of deposited materials, with cross-sectional dimensions of 2 mm in width and 2.5 mm in height, was evaluated by three points bending. With the reinforcement on the tensile side of the stresses, the energy absorbed by the material plastic deformation increased by 2.4% as compared to the substrate alone, while with the reinforcement on the compression side of the stresses the energy absorption increased by 75.8% on average.

Influence of microstructure and surface topography on material removal by the Hirtisation® process

ABSTRACT The Hirtisation® process is an electro-chemical process, wherein the electrolyte can easily access both external and internal surfaces. The process shows promising results in both support structure removal and reduction of surface roughness, and has the potential to solve the productivity and quality trade-off in powder bed fusion – laser beam (PBF-LB) processing. In this study, the role of the microstructure and surface topography on the capability of the Hirtisation® process to lower the PBF-LB produced surface roughness, has been investigated. A detailed microstructure analysis by SEM was used to determine the effect of the Hirtisation® process on removal of sintered powder, the effects on melt pool boundaries and grain boundaries, and thus the final surface quality. The Hirtisation® process significantly reduced surface roughness thanks to the complete removal of sintering powder from the as-built surface. Additionally, preferential material removal was detected along melt pool boundaries, leading to creation of notches of up to 10 µm in depth.

Investigation of the impact of process parameters and thermal treatments on mechanical properties and microstructure of ScanCromAl ® manufactured via powder bed fusion laser beam process

This study explores the processability window of a newly developed aluminium alloy for laser beam powder bed fusion (PBF-LB/M). The impact of the volumetric energy density on the melt pool shape, microstructure, and mechanical properties of manufactured parts are evaluated. Additionally, thermal treatments are optimized to tailor precipitation hardening mechanisms. The results demonstrate the promising potential of this material, exhibiting high relative density (>99.90%) and competitive mechanical properties for the thermally treated samples (UTS ranging from 486 MPa to 514 MPa with elongation of 11–30%). EBSD analysis reveals a characteristic bimodal microstructure of fine equiaxed grains at grain boundaries and elongated coarse grains aligned along the melt pool direction. This work provides valuable insights for tailoring the processing parameters and optimizing the performance of this novel material for diverse applications.

AscentAM: A Software Tool for the Thermo-Mechanical Process Simulation of Form Deviations and Residual Stresses in Powder Bed Fusion of Metals Using a Laser Beam

Due to the tool-less fabrication of parts and the high degree of geometric design freedom, additive manufacturing is experiencing increasing relevance for various industrial applications. In particular, the powder bed fusion of metals using a laser beam (PBF-LB/M) process allows for the metal-based manufacturing of complex parts with high mechanical properties. However, residual stresses form during PBF-LB/M due to high thermal gradients and a non-uniform cooling. These lead to a distortion of the parts, which reduces the dimensional accuracy and increases the amount of post-processing necessary to meet the defined requirements. To predict the resulting residual stress state and distortion prior to the actual PBF-LB/M process, this paper presents the finite-element-based simulation tool AscentAM with its core module and several sub-modules. The tool is based on open-source programs and utilizes a sequentially coupled thermo-mechanical simulation, in which the significant influences of the manufacturing process are considered by their physical relations. The simulation entirely emulates the PBF-LB/M process chain including the heat treatment. In addition, algorithms for the part pre-deformation and the export of a machine-specific file format were implemented. The simulation results were verified, and an experimental validation was performed for two benchmark geometries with regard to their distortion. The application of the optimization sub-module significantly minimized the form deviation from the nominal geometry. A high level of accuracy was observed for the prediction of the distortion at different manufacturing states. The process simulation provides an important contribution to the first-time-right manufacturing of parts fabricated by the PBF-LB/M process.

Design and Analysis of 5-DOF Compact Electromagnetic Levitation Actuator for Lens Control of Laser Cutting Machine.

In laser beam processing, the angle or offset between the auxiliary gas and the laser beam axis have been proved to be two new process optimization parameters for improving cutting speed and quality. However, a traditional electromechanical actuator cannot achieve high-speed and high-precision motion control with a compact structure. This paper proposes a magnetic levitation actuator which could realize the 5-DOF motion control of a lens using six groups of differential electromagnets. At first, the nonlinear characteristic of a magnetic driving force was analyzed by establishing an analytical model and finite element calculation. Then, the dynamic model of the magnetic levitation actuator was established using the Taylor series. And the mathematical relationship between the detected distance and five-degree-of-freedom was determined. Next, the centralized control system based on PID control was designed. Finally, a driving test was carried out to verify the five-degrees-of-freedom motion of the proposed electromagnetic levitation actuator. The results show it can achieve a stable levitation and precision positioning with a desired command motion. It also proves that the proposed magnetic levitation actuator has the potential application in an off-axis laser cutting machine tool.

Microstructural and Hall–Petch Analysis of Additively Manufactured Ferritic Alloy Using 2507 Duplex Stainless Steel Powder

The powder bed fusion–laser beam (PBF-LB) process, a method of additive manufacturing (AM), was used to print duplex stainless steel (DSS) using commercial-grade 2507 powders. While conventionally processed DSS has a two-phase microstructure consisting of 50% austenite and 50% ferrite, the PBF-LB-printed 2507 alloy was nearly 100% ferrite. Optimal processing conditions that minimized porosity were determined to be 290 W laser power and 1000 mm/s scan speed, and grain size, texture, and phases were characterized as a function of laser power and scan speed. Grain size increased with increasing laser power but decreased with increasing scan speed. A <100> texture diminished with increasing scan speed from 1000 mm/s to 1400 mm/s. No austenite phase was detected. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) characterization revealed nanoscale chromium nitride precipitates in the ferritic matrix (incoherent hexagonal close-packed (HCP) precipitates at grain boundaries and coherent body-centered cubic (BCC) precipitates within the grains) and a high density of tangled dislocations. Tensile tests of as-printed alloys showed a yield strength of 570 MPa, an ultimate tensile strength of 756 MPa, and an elongation to failure of 10%. The tensile properties were analyzed based on the observed microstructure considering grain size, nanoscale precipitates, and the high density of dislocations.

Review on Recent Laser Welding Trend in Electric Powered Vehicle Production

In this study, we summarize the state-of-the-art laser welding used for welding copper and aluminum alloys, which are key materials for electrified powertrain components. Extensive research on laser beam modulation, power control, beam control, and process monitoring to improve welding reliability and to solve the challenges of dissimilar welds are reviewed and summarized. Furthermore, various techniques for real-time behavior of the weld pool and weld quality monitoring are presented. Along with various techniques to improve spatter and weld pool instability during welding, we have also included research results on process monitoring using artificial intelligence and deep learning techniques. Moreover, computer simulation helps understand various welding phenomena. The research results on improving the quality of welded products through laser beam dynamic control are also included.

Development of a rapid solidification model for additive manufacturing process and application to Al-Si alloy

Accurate prediction of the solidification microstructure produced by additive manufacturing (AM) process is indispensable for the precise manufacturing process control. In the present study, a simple solidification model that can be applied to the powder bed fusion – laser beam (PBF-LB) process has been developed by integrating conventional and rapid solidification theories in literature. Based on the solidification parameters calculated by Rosenthal equation, the present solidification model can predict the primary dendrite arm spacing (PDAS), primary cell fraction, and solute profile using solute trapping, dendrite tip undercooling, and eutectic undercooling. Single track experiments for Al-12Si binary alloy were also performed to validate the accuracy of the model.

Engineering of heat sources in laser precision machining

Requirement towards the enhancement of the results of technological operations of laser processing, their transformation into precise technological operations is solved, in general, by the choice of optimal technological schemes of laser processing and characteristics of a tool that is formed from laser beam characteristics. The main goal of these attempts is to minimize portions of energy that destroys and removes the material from the cavity of element being formed utilizing ultra-short pulses of electro-magnetic energy with high intensity that can bring balance to the instability of technological process, manage it outcome and maintain the quality of processing. On the other hand, it leads to a decrease in the efficiency of technological operations of laser processing. For example, linear speed of laser cutting of stent with nanosecond pulses are used is within the range of 25 to 30 millimeters per minute, whereas in the case of microsecond pulses - the processing speed can reach up to 250 mm/min and slight striation of side surface of the cutting kerf could be eliminated by means of post processing. Since the process of material destruction at laser beam processing is of a thermal nature in terms of heat dissipation and its propagation into the body of the work piece (especially the metal one), it is possible to control and modify the absorption of radiation by the surface of the work piece, the spatial shape of the heat source and thermal an physical properties of the work piece. This paper discusses perspective solutions for the successful engineering of laser beam irradiation process.

Influence of Different Build Orientations and Heat Treatments on the Creep Properties of Inconel 718 Produced by PBF-LB.

Inconel 718 is a nickel-based superalloy with excellent creep properties and good tensile and fatigue strength. In the field of additive manufacturing, it is a versatile and widely used alloy due to its good processability in the powder bed fusion with laser beam (PBF-LB) process. The microstructure and mechanical properties of the alloy produced by PBF-LB have already been studied in detail. However, there are fewer studies on the creep resistance of additively manufactured Inconel 718, especially when the focus is on the build direction dependence and post-treatment by hot isostatic pressing (HIP). Creep resistance is a crucial mechanical property for high-temperature applications. In this study, the creep behavior of additively manufactured Inconel 718 was investigated in different build orientations and after two different heat treatments. The two heat treatment conditions are, first, solution annealing at 980 °C followed by aging and, second, HIP with rapid cooling followed by aging. The creep tests were performed at 760 °C and at four different stress levels between 130 MPa and 250 MPa. A slight influence of the build direction on the creep properties was detected, but a more significant influence was shown for the different heat treatments. The specimens after HIP heat treatment show much better creep resistance than the specimens subjected to solution annealing at 980 °C with subsequent aging.

On the Thermal Behavior during Spatial Anisotropic Femtoseconds Laser-DNA Interaction: The Crucial Role of Hermite Polynomials.

A novel analytical formalism based on the quantum heat transport equation is proposed for the interaction of fs-laser pulses with deoxyribonucleic acid (DNA) strands. The formalism has the intensity of the laser beam and the interaction time between the laser and the DNA as input parameters. To this end, the thermal distribution generated in the irradiated DNA strands was introduced by splitting the laser beam into transverse Hermite-Gauss modes. To achieve this goal, a new powerful mathematical model was developed and applied. Fluctuations in laser intensity were taken into account by modeling them as superpositions of Hermite-Gauss laser modes. These analyses were carried out for a laser pulse duration of 100 fs, where a tiny heat-affected zone is expected, with positive predicted effects on the stability and repeatability of this technology. The main conclusion is that the laser beam spatial distribution intensity plays an essential role in the generation of the shape and magnitude of the thermal field at the junction of the irradiated DNA strands. The model may prove useful in modeling laser beam processing under significant intensity fluctuations. There are at least two main areas of application for the present model of heat transfer from laser to DNA: (i) the study of DNA elongation without destroying the target information (for a sample temperature variation lower than 10 K; in the case of H[1,y]); and (ii) cancer treatment (especially of skin tissue), where we should obtain a temperature variation higher than 10 K (but lower than 30 K; in the case of H[2,y], H[4,y]), in order to eradicate the diseased cells.

Concrete Crack Width Measurement Using a Laser Beam and Image Processing Algorithms

The presence of concrete cracks in structures indicates possible structural deterioration, but it is quite difficult to measure crack width accurately. While much research has been conducted on crack detection using image processing, there is a gap in the accurate quantification of crack width in millimeters. Current methods either measure in pixels or require the attachment of scales or markers onto a measured surface, which can pose safety hazards in hard-to-reach areas. This paper addresses these issues by proposing a novel image-based method for measuring concrete crack width in millimeters using a laser beam and image processing. The proposed method was validated in the laboratory by capturing images of concrete cracks with two cameras of different resolutions, each attached with lasers. The lasers projected a circular laser beam onto the surface of the concrete under inspection. The images were then pre-processed, segmented, and skeletonized for crack width measurement in pixels. The relationship between the laser diameter and camera distance from the surface was used to convert the measured crack width from pixels to millimeters. The method was performed with high accuracy, as indicated by the absolute error. The largest absolute error was 0.57 mm, while the smallest absolute error was 0.02 mm. The proposed method allows real-world interpretation of results in millimeters. As a result, measured crack widths can easily be compared to allowable limits in international standards, which are typically expressed in metric or SI units. The proposed method can also promote safer inspections in areas of low accessibility by attaching the laser to devices such as drones.

High frequency beam oscillation keyhole dynamics in laser melting revealed by in-situ x-ray imaging

The metal additive manufacturing industry is actively developing instruments and strategies to enable higher productivity, optimal build quality, and controllable as-built microstructure. A beam controlling technique, laser oscillation has shown potential in all these aspects in laser welding; however, few attempts have been made to understand the underlying physics of the oscillating keyholes/melt pools which are the prerequisites for these strategies to become a useful tool for laser-based additive manufacturing processes. Here, to address this gap, we utilized a synchrotron-based X-ray operando technique to image the dynamic keyhole oscillation in Ti-6Al-4V using a miniature powder bed fusion setup. We found good agreement between the experimental observations and simulations performed with a validated Lattice Boltzmann multiphysics model. The study revealed the continuous and periodic fluctuations in the characteristic keyhole parameters that are unique to the oscillating laser beam processing and responsible for the chevron pattern formation at solidification. In particular, despite the intrinsic longer-range fluctuation, the oscillating technique displayed potential for reducing keyhole instability, mitigating porosity formation, and altering surface topology. These insights on the oscillating keyhole dynamics can be useful for the future development and application of this technique.

Microstructure, mechanical properties and fracture mechanisms in a 7017 aluminium alloy tailored for powder bed fusion – laser beam

This study addressed a 7017 Al-alloy tailored for powder bed fusion – laser beam (PBF-LB) process. The alloy was prepared by mixing 3 wt% Zr and 0.5 wt% TiC powder to standard pre-alloyed 7017 grade aluminium powder. This made printing of the alloys possible avoiding solidification cracking in the bulk and achieving high relative density (99.8 %). Such advanced alloys have significantly higher Young’s modulus (>80 GPa) than conventional Al-alloys (70–75 GPa), thus making them attractive for applications requiring high stiffness. The resulting microstructure in as-printed condition was rich in particles originating from admixed powders and primary precipitates/inclusions originating from the PBF-LB process. After performing a T6-like heat treatment designed for the PBF-LB process, the microstructure changed: Zr-nanoparticles and Fe- or Mg/Zn- containing precipitates formed thus providing 75 % increase in yield strength (from 254 MPa to 444 MPa) at the cost of decreasing ductility (∼20 % to ∼9 %). In-situ tensile testing combined with SXCT, and ex-situ tensile testing combined with fracture analysis confirmed that the fracture initiation in both conditions is highly dependent on defects originated during printing. However, cracks are deflected from decohesion around Zr-containing inclusions/precipitates embedded in the Al-matrix. This deflection is seen to improve the ductility of the material.

Laser gas-powder surfacing with beam scanning

The proposals and possibilities of technological laser heads for additive technologies and surfacing are considered. The advantages of laser beam processing using a scanning system for gas-powder laser surfacing, its capabilities and modifications are shown. Experiments are carried out to study the effect of the scanning frequency of the laser beam and the scanning trajectory on the geometric characteristics of the deposited layers. The experiments are carried out using carbon dioxide and fiber laser. A multifunctional scanning unit which makes it possible to significantly increase the efficiency of the gas powder laser surfacing process and a powder dosing device designed specifically for additive laser technology are proposed. Their advantages and the possibility of using them as part of laser processing complexes are considered.

The effect of powder reuse on the surface chemical composition of the Scalmalloy powder in Powder Bed Fusion – Laser Beam process

The powder quality is one of the main factors to be considered in laser powder bed fusion (PBF‐LB/M) production closely connected with the performance of the final component. Only powders with spherical particles, a low percentage of satellites, a narrow particle size distribution, controlled internal defects and a strongly limited surface oxide layer are acceptable for PBF‐LB/M production. Gas atomisation is the main production method that permits to achieve the restrictive standards of the PBF‐LB/M powder; however, it is energy‐intensive and characterised by limited productivity. These considerations justify the key role of the reuse of the unmelted metal powder in obtaining a more sustainable PBF‐LB/M process. Nevertheless, the reuse of the powder leads to significant changes in the particle morphology, particle size distribution and surface chemical composition, which can compromise the bulk properties. Powder surface oxide is one of the most impactful problems for the PBF‐LB/M production, and Al‐based alloys are particularly prone to this phenomenon. With the aim to study the effect of the powder reuse, a surface chemical analysis on gas atomised Scalmalloy powder was performed through the X‐ray photoelectron spectroscopy investigation before and after seven jobs with 32 h as overall build time. Results obtained for virgin and recycled Scalmalloy powders revealed remarkable differences in depth and composition of the surface oxide layer. The 57% increase in the oxide layer thickness and the formation of carbides during PBF‐LB/M production can have harmful effects on bulk properties.

Influence of working pressure on laser beam welding in vacuum of electrical steel sheets

In a recent research project of RWTH Aachen University it is shown, that laser beam spot welding is advantageous over line welds with respect to the magnetic properties of an iron core and can therefore increase the efficiency of electric motors. In this case laser beam welding in vacuum is used to join these iron cores. A pulsed laser beam process was used to generate individual weld spots. The influences of a reduced working pressure on the welding result in the range of 1 mbar–1000 mbar occurring in this process are presented in this paper.

Effect of precipitation kinetics on microstructure and properties of novel Al-Mn-Cr-Zr based alloys developed for powder bed fusion – laser beam process

This study investigates the precipitation kinetics and resulting effect on microstructure and property of a family of novel high strength Al-Mn-Cr-Zr alloys designed for powder bed fusion – laser beam process. The alloys have been shown to be printable without solidification cracking along with high supersaturation of solutes in as-printed state. Upon direct ageing, two families of precipitates namely Al-Mn and Al-Zr are observed. Al-Mn containing precipitates, which are observed in as-printed condition as nanometric precipitates decorating special regions are seen to grow preferentially at grain boundaries, which is followed by growth in bulk of the sample. A possible explanation is suggested to be a higher diffusivity at grain boundaries leading to faster growth while depleting solutes around grain boundary region quickly. The Al-Zr precipitation, which normally follows bulk precipitation is observed to co-precipitate with Al-Mn precipitates. Optimised heat treatments are seen to achieve peak hardness of 143 HV at 623 K for 24 h and 142 HV at 648 K for 14 h as compared to 102 HV in as-printed condition for one of the alloys. This overall hardening effect is attributed majorly to Al 3 Zr nanoprecipitates along with semi-coherent Al 12 Mn precipitates. • Alloy design tailored for PBF-LB process created Al-Mn-Cr-Zr family of Al alloys. • Alloying elements are supersaturated in solid solution after printing. • On direct ageing, two novel precipitation phenomenon observed. • Feature analysis enabled quantitative precipitation analysis with chemical data.

Development of powder bed fusion – laser beam process for AISI 4140, 4340 and 8620 low-alloy steel

ABSTRACT This study focuses on process development and mechanical property evaluation of AISI 4140, 4340 and 8620 low-alloy steel produced by powder bed fusion – laser beam (PBF-LB). Process development found that increasing the build plate preheating temperature to 180°C improved processability, as it mitigated lack of fusion and cold cracking defects. Subsequent mechanical testing found that the low-alloy steels achieved a high ultimate tensile strength (4140:∼1400 MPa, 4340:∼1500 MPa, 8620:∼1100 MPa), impact toughness (4140:∼90–100 J, 4340:∼60–70 J, 8620:∼150–175 J) and elongation (4140:∼14%, 4340:∼14%, 8620:∼14–15%) that met or exceeded the ASTM standards. Mechanical testing also revealed limited directional anisotropy that was attributed to low levels of internal defects (< 0.1%), small grains with weak crystallographic texture and improved tempering due to build plate preheating and post PBF-LB stress relief. This indicates that with adequate process development, low-alloy steels produced by PBF-LB can meet or exceed the performance of conventionally produced alloys.

Status and Perspective of High-Energy Beam Surface Strengthening: High-Speed Steel.

High-speed steel (HSS) is primarily used to manufacture cutting tools and roll materials for various machine tools. Improving the hardness, wear resistance, and corrosion resistance of HSS is of great significance to the development of the manufacturing and tool industries. The high-energy beams, consisting of laser, plasma beam, and electron beam processing (e.g., surface remelting, cladding, and alloying), have the advantageous characteristics of high heat source energy and good surface processing effect. The research status and perspective of the above three processing techniques on the surface properties (in particular, hardness, wear resistance, and corrosion resistance) of HSS is reviewed, and the principles, advantages, and disadvantages of the three strengthening methods are discussed. High-energy beam surface alloying appears to be the most cost-effective of HSS surface strengthening methods and is promising to receive increasing research attentions in the future.