Optimal Laser Power Research Articles

Effect of laser power during laser powder bed fusion on microstructure of joining interface between Tungsten and AISI 316L steel

This study investigates the deposition of tungsten (W) onto a 316L steel substrate by laser powder bed fusion (L-PBF), to optimize process parameters and analyze the interface between W and 316L. To obtain high-density W structure (98.89%), the optimal laser power was 350 W, and scan speed was 500 mm/s, but these parameters cause significant dilution of W in the W-316L interface; as a result, Fe7W6 intermetallics form, despite L-PBF being a non-equilibrium solidification process. These intermetallics which are brittle could degrade joint strength. By reducing laser power below 250 W, the dilution of W can be mitigated, and potentially minimize formation of intermetallics and increase joint stability for advanced manufacturing applications.

Effect of Powder Spreading Parameters on Laser Absorption Behavior and Processability of High‐Strength Aluminum Alloy Fabricated by Laser Powder Bed Fusion

Laser powder bed fusion (LPBF) of rare‐earth‐modified high‐strength aluminum alloys presents a novel approach for manufacturing complex components with enhanced structural performance, particularly in aerospace applications. This study fabricates Al–Mg–Sc–Zr specimens using various powder spreading parameters to explore their impact on laser processability. The investigation reveals that varying the powder layer thickness from 30 to 70 μm yields the smallest irradiation diameter of 135 μm at an optimal thickness of 50 μm, attributable to effective multiple reflections, high laser absorption rates, and stability. With an optimal laser power of 400 W, a scanning speed of 600 mm s−1, and a hatching spacing of 60 μm, the sample produced at 50 μm layer thickness achieves a relative density of 99.23%, a top surface roughness of 15.42 μm, and a refined grain size of 1.67 μm. Following aging at 325 °C for 4 h, this sample exhibits a tensile strength of 518 MPa and an elongation of 15.6%. The findings establish a theoretical basis for controlling the morphology and properties of high‐strength aluminum alloys in laser additive manufacturing.

Optimizing Lasing Parameters for Fabricating an Efficient Flexible Electrothermal Heater Based on Laser-Induced Graphene

This work involved fabrication of an efficient thin film heater from 100 μm thick polyimide (PI) sheet by scribing it using a carbon dioxide lasing machine through optimizing laser power (P), scanning speed (SS), and pulses per inch (PPI). A 15 mm × 15 mm square pattern was designed using CorelDRAW software and scribed in a rastering mode on top of PI with the help of Universal Control Panel (UCP) software of the laser machine. Laser power of 8 %, SS of 4 % and PPI of 1000 were obtained as optimal parameters for producing laser induced graphene (LIG). This LIG exhibited a low sheet resistance of approximately 16.64 Ω/sq and was thermally stable on the PI substrate even after 30 cycles of repeated heating and cooling. The LIG was found to be highly porous with the aid of scanning electron microscope (SEM) and its structure was crystalline from XRD patterns. FTIR was conducted and showed disappearance of functional groups in PI after treatment with the laser beam. Our developed LIG heater showed great electrothermal performance with maximum temperature of approximately 288.7 °C, rate of temperature rise of 107.06 °Cs-1, and time of 1.85 s to reach 63 % of temperature difference at a low input voltage of 6 V with homogeneous temperature distribution seen in the thermal images taken using FLIR camera. This LIG heating element can be placed in confined spaces because of its flexibility, thinness, and lightness. Additionally, its efficient joule heating effect attracts many applications such as seat warmers, anti-fogging equipment, food shelf displays, etc.

Achieving excellent strength and ductility of 24CrNiMoY alloy steel fabricated by high power selective laser melting technology

In order to increase the productivity, new generation of selective laser melting (SLM) machines are evolving towards higher power lasers. In this paper, the microstructure evolution and mechanical properties of 24CrNiMoY alloy steel fabricated by high power selective laser melting (HP-SLM) have been reported. The results show that with the optimized laser power over 400 W, the powder layer thickness can be increased to 60 μm, and the theoretical productivity reaches 7.2 mm3/s, which is more than two times of the normal SLM technology. As the laser energy density increases, the structure of melt pool changes from a thermal conduction mode to a keyhole mode, and the microstructure mainly consists of martensite, bainite and pre-eutectic ferrite, and the phase composition of the specimen is α-Fe phase and a small amount of Fe3C,with fine grain size and irregular orientation. When the laser energy density is 68 J/mm3, the microhardness of the specimen is 410HV0.2, the tensile strength reaches 1121 MPa and the percentage elongation after fracture is 11.5%, which realizes a good match between strength and ductility. The fine tempered martensite and lower bainite in the microstructure is the key to excellent strength and ductility. This research is of guiding significance and serves as a technical reference for understanding the microstructure evolution and mechanical properties of HP-SLM 24CrNiMoY alloy steel.

Achieving strength-ductility synergy of laser powder bed fusion Ti–6.5Al–2Zr–1Mo–1V alloy by regulating laser power

In general, the Ti–6.5Al–2Zr–1Mo–1V (TA15) components fabricated via laser powder bed fusion (L-PBF) exhibit high strength and low ductility. Herein, we report a novel approach to enhance the comprehensive mechanical properties of L-PBF TA15 alloy by adjusting the laser power. Samples processed using the optimal laser power exhibit a grid structure of alternating wide and narrow prior-β grains (PBGs), the inside of which is composed of a fully martensitic microstructure. The paper discusses in detail the alterations in the microstructure of samples processed at both low and high laser powers, clarifying the relationship between microstructure and mechanical properties. Thinner martensite contributes to higher strength, while a homogenous microstructure improves ductility. These findings provide valuable insights for controlling microstructure and achieving strength-ductility synergy in L-PBF additive manufacturing of titanium alloys.

Effect of different powers on microstructure evolution and corrosion behavior of 5SiC-Ni60 coatings by directed energy deposition

The microstructural evolution and corrosion behavior of directed energy deposition (DED) additive manufactured 5SiC-Ni60 composite coatings are investigated, elucidating the impact of fluctuations in power on the coating. The experiment reveals the microstructural characteristics, eutectic evolution, phase-microhardness correlation, and corrosion resistance mechanisms, all influenced by power variation as a crucial factor. Utilizing SEM, EDS, XRD, PDP, EIS, and XPS, the mapping relationship between microstructure reinforcement mechanisms, microhardness region features, corrosion behavior formation mechanisms, and power variation is clarified. The optimal laser power is determined to be 3000 W, facilitating the formation of a dense passivation film, efficiently reducing corrosion contact area and enhancing corrosion resistance. The chemical composition of the passivation film is revealed through XPS. Furthermore, utilizing polarization characteristics, impedance analysis, and corrosion morphology as focal points of discussion, the pitting defects on the corroded surface are explained. Consequently, achieving corrosion protection for the composite coating requires intervention with appropriate power parameters, providing valuable insights for enhancing corrosion resistance based on process parameters.

Towards a digital twin framework in additive manufacturing: Machine learning and bayesian optimization for time series process optimization

Laser directed-energy deposition (DED) offers notable advantages in additive manufacturing (AM) for producing intricate geometries and facilitating material functional grading. However, inherent challenges such as material property inconsistencies and part variability persist, predominantly due to its layer-wise fabrication approach. Critical to these challenges is heat accumulation during DED, influencing the resultant material microstructure and properties. Although closed-loop control methods for managing heat accumulation and temperature regulation are prevalent in DED literature, few approaches integrate real-time monitoring, physics-based modeling, and control simultaneously in a cohesive framework. To address this, we present a digital twin (DT) framework for real-time model predictive control of process parameters of the DED for achieving a specific process design objective. To enable its implementation, we detail the development of a surrogate model utilizing Long Short-Term Memory (LSTM)-based machine learning which uses Bayesian Inference to predict temperatures across various spatial locations of the DED-built part. This model offers real-time predictions of future temperature states. In addition, we introduce a Bayesian Optimization (BO) method for Time Series Process Optimization (BOTSPO). Its foundational principles align with traditional BO, and its novelty lies in our unique time series process profile generator with a reduced dimensional representation. BOTSPO is used for dynamic process optimization in which we deploy BOTSPO to determine the optimal laser power profile, aiming to achieve desired mechanical properties in a DED build. The identified profile establishes a process trajectory that online process optimizations aim to match or exceed in performance. This paper elucidates components of the digital twin framework, advocating its prospective consolidation into a comprehensive digital twin system for AM.

Research on the Process of Laser Cladding Ni60 Coating on High-Nickel Cast Iron Surfaces

In order to achieve high-performance coatings on the surface of electric submersible pump impellers, it is crucial to optimize the laser cladding process parameters. Using Ansys 2021 R1 commercial software, a numerical simulation of laser cladding Ni60 powder on high nickel cast iron was conducted. The simulation utilized a 3D Gaussian heat source, parametric language, and life–death unit technology to replicate the characteristics of synchronous powder delivery laser cladding. The study focused on analyzing the temperature field cloud map and molten pool size under different laser power and scanning speeds, narrowing down the process parameter window, selecting optimized laser power and scanning speed, and assessing the changes in surface morphology, melting height and width, dilution rate, microhardness, and microstructure of the laser cladding coating. Results indicate that the coating width and thickness increase with higher laser power and lower scanning speeds. The microstructure consists primarily of dendritic, block, short rod, and long strip formations, and exhibits a tightly distributed and uniform grain structure. Furthermore, the microhardness of the coating shows a negative correlation with laser power and scanning speed. The optimal process parameters were determined to be a laser power of 1100 W and a scanning speed of 6 mm/s. A comparison with the simulation confirmed the effectiveness of the simulation in effectively guiding actual production.

Effect of laser shock peening on the retention ability of surface roughness in forged Cr5 steel

The roughness retention ability of the work roll surface during the cold rolling process is of great significance, especially in the production of the high-quality rolling section. Laser shock peening (LSP) is an advanced and effective surface treatment technique to improve the fatigue life, wear resistance, and other mechanical characteristics of metal components. Current studies commonly examined the reinforcement effect of single and multiple LSP treatments on Cr5 steel samples through XRD analysis, hardness testing, and residual stress measurements of different parameters. In addition, the abrasion test is widely conducted to determine the wear resistance. Compared to unprocessed samples, LSP could promote grain refinement and thus significantly increase the hardness and residual stress. Furthermore, the slight decrease in surface roughness shows that LSP treatment is an effective approach to slowing down the roughness decline rate and prolonging the roller service life. It is also found that multiple LSP impacts could remarkably improve the surface roughness retention of Cr5 steel, in which the optimal laser power density was around 23 GW/cm2.

Tuning hatch distance to optimize microstructure and mechanical properties of 2205 duplex stainless steel produced by laser powder bed fusion

Laser powder bed fusion (LPBF) of duplex stainless steel is a promising route to fabricate intricate parts with excellent mechanical properties. However, further understanding of build mechanisms is required to improve the process. This paper aims to better understand the influence of hatch distance on the densification behavior and figure out the correlation with microstructure and mechanical properties in LPBF of 2205 stainless steel. With the optimized laser power and scanning speed, the significant influence of hatch distance on the build quality is revealed. A hatch distance of 0.07 mm is selected for an even surface and dense part with a relative density of up to 99.13 %. The hatch distance has a crucial impact on the heat and mass transfer between tracks; hence, poor surface morphologies such as inter-track voids or swelling surfaces occur if an improper hatch distance is adopted. The optimal mechanical properties are also achieved. Specifically, the yield strength (0.2 YS), ultimate tensile strength (UTS), and elongation (EL) values are 896.8 MPa, 1035.13 MPa, and 15.34 %, respectively. The improvement in mechanical properties can be ascribed to the coordination between high dislocation density, fine grain size, high CSL boundaries and LAGBs, and high relative density with few pores. This work can help improve the build quality and expand the application horizon of duplex stainless steel for manufacturing intricate components.

20CrMnTi surface strengthening based on laser-assisted carburizing grinding

Highly wear-resistant 20CrMnTi surfaces with gradient properties are urgently demanded in manufacturing core components such as shafts and gears. However, balancing productivity, production costs, and energy consumption with existing surface machining and strengthening methods are challenging. Therefore, laser-assisted carburizing grinding is proposed, which combines laser micro-carburizing and grinding tempering to realize the integration of processing and strengthening of the 20CrMnTi surface. The optimal laser power is determined to be 300 W by the dynamic thermal-force coupling effect. A 1300 μm thick metamorphic layer is formed on the surface of 20CrMnTi, and its formation mechanism is analyzed based on the microstructural phase transformation. The surface hardness after laser-assisted carburizing grinding can reach 550 HV. The failure form of the carburized surface is mainly abrasive wear, and the wear loss is reduced to 50% compared to uncarburized surfaces. This study developed an efficient, energy-saving, and controllable integrated method of 20CrMnTi surface machining and strengthening. Meanwhile, the surface strengthening mechanism is explained based on laser micro-carburizing and grinding tempering. The findings provide technical references for manufacturing high-performance 20CrMnTi surfaces and theoretical support for carburized grinding strengthening technology.

Bead Characterization for Wire Based Laser Directed Energy Deposition Fabrication Process

A three-dimensional, solid object of almost any shape or design can be created using metal additive manufacturing, often known as metal 3D printing. One of the most popular materials utilized in additive manufacturing is metal. The far more complicated procedure of directed energy deposition (DED) is frequently employed to upgrade or repair existing components. DED fabrication process will be able to construct a 3D metal object with consideration of the weld bead characteristics. Without knowing the weld bead characteristics, the mechanical integrity will not hold as the bead size is not suitable for the product. In the current study, we will study the effect of variation of parameters of the DED machine to be able to print in a continuous deposition and we will also investigate the weld bead characteristics printed by the variation of parameters with the use of DED machine. The variation of parameters of the machine are the laser power with the unit of Watt and the feedrate of the machine with the unit of mm per minute. Nine preliminary samples are printed to check whether the bead can be printed in a continuous line or not. The value of variation of parameters that bring about a continuous deposition will be jotted and continued to be taken to bead characterization for study. Six samples were printed, and the bead width and height are calculated based on the variation of parameters. Based on the result, we found that laser power will increase the bead width, but the bead height needs optimal laser power which is at 473 Watt and optimal feedrate which is on 60 mm per min to reach optimal bead height which is at 2.1162 mm. The effect of the machine feedrate on the other hand is inconsistent, thus more samples need to be gathered.

Multi-layered micro-patterns co-printed with Ag@CuO nano-ink for flexible devices

Abstract Silver (Ag) nano-ink is widely used to fabricate the micro-patterns of flexible electronic devices owing to its excellent conductivity and stability. However, the cost of micro-patterns prepared with silver nano-ink is high. Here, multi-layered, multi-inked (silver@copper oxide) micro-patterns were co-printed layer by layer using an in-house silver nano-ink and commercial copper oxide (CuO) nano-ink. The prepared micro-patterns were solidified by laser sintering. Among the co-printed micro-patterns, the micro-pattern with a top layer of copper (1CuO@2Ag) had the lowest resistance, which was 13.1 Ω cm–1. Additionally, 1CuO@2Ag had the smoothest topography and lowest porosity, which was attributed to effective sintering at the optimal laser power (3 W) for all co-printed micropatterns owing to the high absorptivity and low reflectivity of copper. Moreover, after 500, 1000, and 1500 cycles of fatigue testing, the resistance of 1CuO@2Ag increased by 1.5%, 8.4%, and 13.7%, respectively, indicating good reliability. The proposed method lays the foundation for further studies on Ag@CuO composites for micro-pattern preparation.

The Influence of Laser Process Parameters on the Adhesion Strength between Electroless Copper and Carbon Fiber Composites Determined Using Response Surface Methodology.

Laser process technology provides a feasible method for directly manufacturing surface-metallized carbon fiber composites (CFCs); however, the laser's process parameters strongly influence on the adhesion strength between electroless copper and CFCs. Here, a nanosecond ultraviolet laser was used to fabricate electroless copper on the surface of CFCs. In order to achieve good adhesion strength, four key process parameters, namely, the laser power, scanning line interval, scanning speed, and pulse frequency, were optimized experimentally using response surface methodology, and a central composite design was utilized to design the experiments. An analysis of variance was conducted to evaluate the adequacy and significance of the developed regression model. Also, the effect of the process parameters on the adhesion strength was determined. The numerical analysis indicated that the optimized laser power, scanning line interval, scanning speed, and pulse frequency were 5.5 W, 48.2 μm, 834.0 mm/s, and 69.5 kHz, respectively. A validation test confirmed that the predicted results were consistent with the actual values; thus, the developed mathematical model can adequately predict responses within the limits of the laser process parameters being used.

Enhanced Detection Precision of the Taiji Program by Frequency Setting Strategy Based on a Hierarchical Optimization Algorithm

For space-based gravitational wave detection, a laser interferometric measurement system composed of a three-spacecraft formation offers the most rewarding bandwidth of astrophysical sources. There are no oscillators available that are stable enough so that each spacecraft could use its own reference frequency. The conversion between reference frequencies and their distribution between all spacecrafts for the synchronization of the different metrology systems is the job of the inter-spacecraft frequency setting strategy, which is important for continuously acquiring scientific data and suppressing measurement noise. We propose a hierarchical optimization algorithm to solve the frequency setting strategy. The optimization objectives are minimum total readout displacement noise and maximum beat-note frequency feasible range. Multiple feasible parameter combinations were obtained for the Taiji program. These optimized parameters include lower and upper bounds of the beat note, sampling frequency, pilot tone signal frequency, ultrastable clock frequencies, and modulation depth. Among the 20 Pareto optimal solutions, the minimum total readout displacement noise was 4.12 pm/Hz, and the maximum feasible beat-note frequency range was 23 MHz. By adjusting the upper bound of beat-note frequency and laser power transmitted by the telescope, we explored the effects of these parameters on the minimum total readout displacement noise and optimal local laser power in greater depth. Our results may serve as a reference for the optimal design of laser interferometry system instrument parameters and may ultimately improve the detection performance and continuous detection time of the Taiji program.

Modeling and multiobjective optimization of thermal effects of fiber laser cutting of Inconel 600 sheet by employing the ANN and multi-objective PSO algorithm

In this study, the experimental results of fiber laser cutting of Inconel 600 was modeled and optimized by combining artificial neural networks (ANNs) and particle swarm optimization (PSO). The impact of cutting criteria on the temperature adjacent to the cut kerf and roughness of the cutting edge was experimentally evaluated. The independent variables are the cutting speed, focal length, and laser power. The fiber laser cutting characteristics are modeled at different cutting conditions by the ANN method according to the experimental data. The findings indicated that the ANN is performing reasonably well in dealing with the training and test datasets. Also, the multiobjective PSO has been developed to effectively optimize the laser cutting procedure parameters in order to achieve the maximum temperature (the temperature upper than 370 °C) and minimum roughness (lower than 3 μm) simultaneously in order to improve the laser cutting efficiency. Based on the PSO results, the optimal laser power gained at a laser power of 830 and 1080 W at cutting speed ranges from 2 to 4 m/min and maximum focal length ranges between 0.75 and 0.8 mm where the lowest amount of roughness was created. The optimum temperature ranges were between 370 and 419°C. At a laser power of 1000 W and speed of 4 m/min, the smooth cutting edge at minimum roughness was gained without any defects. Transmission of the focal point up to 1.5 mm below the top surface of the sheet improved the roughness of the cutting edge and the cut quality by producing the smooth surface without slags.

The Research on Ultrasonic Vibration Amplitudes in Ti6Al4V DED Additive Manufacturing

Ultrasonic-assisted Ti6Al4V Directed Energy Deposition (DED) additive manufacturing technology can improve the problem of uneven microstructure caused by laser heating and sudden cooling of the molten pool. In this paper, the numerical analysis and experimental verification methods were adopted. The influencing factors, such as the cavitations’ effect, sound flow enhancement effect, and sound flow thermal effect related to the ultrasonic assistance in the molten pool, were analyzed. After equating the energy of the ultrasound, the model of additive manufacturing was introduced in the form of a heat source. The temperature gradient changes during the solidification process of the molten pool with the addition of ultrasound assistance and the effect of ultrasonic vibration during the manufacturing process on its deposited state and microstructure of solution-aged formed parts were studied. The results showed that when the wire feeding rate is 5 mm/s and the laser scanning speed is 5 mm/s, the optimal laser power is 1000 W~1100 W, corresponding to the optimal ultrasonic amplitude of 120 μm. Then, by comparing the temperature field with the same amplitude of 0 μm (i.e., no ultrasonic vibration) and the microstructure of the formed parts, it was verified that ultrasonic vibration facilitates fluid flow in the molten pool, which could lead to a more uniform temperature distribution. This optimized approach not only enhances the understanding of the process but also contributes significantly to the advancement of related research endeavors.

An Empirical Model and Feedforward Control of Laser Powder Bed Fusion

Abstract Reliable process control for the laser powder bed fusion process, especially at the melt pool scale, remains an open challenge. One of the reasons for this is the lack of suitable control-oriented models and associated control design strategies. To address this issue, this paper (1) identifies an empirical control-oriented model of geometry-dependent melt pool behavior and (2) experimentally demonstrates melt pool regulation with a feedforward controller for laser power based on this model. First, the study establishes that the melt pool signature increases as the scan lines decrease in length. An empirical model of this behavior is developed and validated on different geometries at varying laser power levels. Second, the model is used to design a line-to-line feedforward controller that provides an optimal laser power sequence for a given geometry. Finally, this controller is validated experimentally and is demonstrated to suppress the in-layer geometry-related melt pool signal deviations for different test geometries.

Laser powder bed fusion (LPBF) of commercially pure titanium and alloy development for the LPBF process.

Laser powder bed fusion (LPBF) of titanium or titanium alloys allows fabrication of geometrically more complex and, possibly, individualized implants or osteosynthesis products and could thus improve the outcome of medical treatments considerably. However, insufficient LPBF process parameters can result in substantial porosity, decreasing mechanical properties and requiring post-treatment. Furthermore, texturized parts with anisotropic properties are usually obtained after LPBF processing, limiting their usage in medical applications. The present study addresses both: first, a design of experiments is used in order to establish a set of optimized process parameters and a process window for LPBF printing of small commercially pure (CP) titanium parts with minimized volume porosity. Afterward, the first results on the development of a biocompatible titanium alloy designed for LPBF processing of medical implants with improved solidification and more isotropic properties are presented on the basis of conventionally melted alloys. This development was performed on the basis of Ti-0.44O-0.5Fe-0.08C-0.4Si-0.1Au, a near-α alloy presented by the authors for medical applications and conventional manufacturing, with yttrium and boron additions as additional growth restriction solutes. In terms of LPBF processing of CP titanium grade 1 powder, a high relative density of approximately 99.9% was obtained in the as-printed state of the volume of a small cubical sample by using optimized laser power, scanning speed, and hatch distance in combination with a rotating scanning pattern. Moreover, tensile specimens processed with these volume settings and tested in the as-printed milled state exhibited a high average yield and ultimate tensile strength of approximately 663 and 747N/mm2, respectively, combined with a high average ductility of approximately 24%. X-ray diffraction results suggest anisotropic mechanical properties, which are, however, less pronounced in terms of the tested specimens. Regarding alloy development, the results show that yttrium additions lead to a considerable microstructure refinement but have to be limited due to the occurrence of a large amount of precipitations and a supposed higher propensity for the formation of long columnar prior β-grains. However, phase/texture and microstructure analyses indicate that Ti-0.44O-0.5Fe-0.08C-0.4Si-0.1Au-0.1B-0.1Y is a promising candidate to achieve lower anisotropy during LPBF processing, but further investigations on LPBF printing and Y2O3 formation are necessary.

Optimizing laser power of directed energy deposition process for homogeneous AISI M4 steel microstructure

Optimizing laser power of directed energy deposition process for homogeneous AISI M4 steel microstructure