Process Parameters Including Laser Power Research Articles

Influence of processing parameters on the thermal history, microstructure and tensile properties of Inconel 738 produced by laser directed energy deposition

In this paper, laser directed energy deposition (LDED) technology was applied to produce non-weldable Inconel 738 parts. The influence of processing parameters including laser power, scanning speed and powder feeding rate on the thermal history of molten pool and the morphology of single track was evaluated. Considering the surface quality and deposition efficiency, the appropriate processing parameters for multilayer deposition were selected. Then the impact of laser power on the microstructure evolution and tensile properties of IN738 thin-wall parts was investigated. The research results show that increasing the laser power could increase the peak temperature and molten pool lifetime, but decrease the cooling rate. Increasing the scanning speed significantly increased the cooling rate but had little effect on the peak temperature. The thermal history was hardly affected by the powder feeding rate, but a too high powder feeding rate caused the particle adhesion and decline of surface quality. The microstructure of LDED-manufactured IN738 was composed of dense and fine dendrites. The higher laser powers of 800 W and 1000 W created higher temperature gradient within the molten pool, which promoted the epitaxial growth of dendrites. However, the long dendrites were prone to be torn apart under the transverse tensile stress, which was detrimental to the elongation and ductility. By comparison, when the laser power was 600 W, the growth direction of dendrites between adjacent layers was different and exhibited the best ductility.

Selective laser melting and mechanical behavior of Mo-coated diamond particle reinforced metal matrix composites

Defects, such as pores, microcracks, and thermal damage, pose significant challenges in the selective laser melting (SLM) process of diamond reinforced metal matrix composites. To address these issues, this study utilizes Mo-coated diamond particles prepared via salt bath plating for SLM processing of CoCr-diamond composites. The SLM process parameters including laser power, scanning speed, and hatch spacing were systematically optimized using the response surface method (RSM). Subsequently, the microstructure and mechanical properties of the SLMed CoCr-diamond composites were thoroughly investigated. Notably, a protective layer of Mo2C is formed on the surface of diamond particles during the salt bath plating process. When compared to the SLMed CoCr-15 vol% Mo-uncoated diamond composite, the Mo coating significantly enhances the compressive strength by 69 % and flexural strength by an impressive 345 % for the CoCr-15 vol% Mo-coated diamond composite.

The influence of hatch distance on the surface roughness, microhardness, residual stress, and density of inconel 625 specimens in the laser powder bed fusion process

ABSTRACT The main goal of the laser powder bed fusion process is to produce high-quality parts with the required mechanical properties. Achieving this requires the proper selection of the key process parameters including laser power, scanning speed, layer thickness and hatch distance. In the present article, the effect of hatch distance parameter on the surface integrity issues i.e. surface roughness, residual stress, microhardness, and also density of Inconel 625 specimens has been studied using experimental approach. By using the non-destructive X-ray diffraction technique, residual stresses were measured in the different portion of the samples whose cross section changes. According to the results, as the hatch distance increases the microhardness decreases. The hatch distance has inverse effect on the residual stresses which its effect is less at the lower sections. It can be stated generally that the hatch distance increment reduces the microhardness, residual stress, and surface roughness but increases the specimen’s density.

A Superhydrophobic Surface on a Superalloy Substrate with Properties of High Mechanical Strength and Self-Cleaning of Carbon Deposition.

Laser processing is an efficient method for fabricating a superhydrophobic surface and has attracted much attention due to its multifunctionality. However, excessive laser processing, such as laser beam overlap and multiple scans, generates both a thick, brittle recast layer and a thin material thickness, thereby greatly reducing the mechanical strength of the substrate. In addition, there is no report on fabricating a superhydrophobic surface on a superalloy substrate whose application includes a self-cleaning property. This work proposes the fabrication of a superhydrophobic surface on a superalloy substrate with high mechanical strength by optimizing the laser processing parameters including laser power, scanning speed, line spacing, and number of scans. We found that the microstructures required by superhydrophobicity could be constructed with a single laser scan. which could guarantee a minimal loss of the mechanical strength. The fabricated superhydrophobic surface on the superalloy substrate exhibited excellent self-cleaning of carbon deposition, showing good application potential in the aero engine field.

A comprehensive study on the influence of the scan pattern in two porosity levels and surface roughness on the fatigue behavior of laser powder bed fusion manufactured specimens made of steel H13

As a developing and immature technique, additive manufacturing (AM) shows some limitations: depending on material and process parameters so far, it usually results in parts with residual porosity, high residual stresses and a surface with a certain level of roughness. Due to its weaknesses and high production costs, AM is more preferably used when the fabricated parts have a high geometry complexity, the material used is very expensive, or the parts can offer additional performance. In order to allocate AM further in industry, a better understanding of the not well-investigated fatigue behavior is necessary. This work focuses on the influences of some general process parameters including laser power, scan speed, scan pattern and postmachining on the resulting fatigue properties of H13 tool steel specimens generated through powder bed fusion (PBF) technique. Results reveal that scan patterns influence fatigue properties by affecting the largest porous defect size and microstructure thus matrix strength. The degree of porosity or roughness resulting from the energy input and postmachining has a significant inferior impact on the fatigue strength. Neither porosity nor tensile properties show a single direct mathematic correlation with the fatigue properties.

Study of residual stresses and distortions from the Ti6Al4V based thin-walled geometries built using LPBF process

The current paper focuses on the prediction of residual stresses and distortions in the Laser Powder Bed Fusion (LPBF) built Ti6Al4V thin-walled geometries using Ansys Additive Print (AAP) software which employs a layer-by-layer accumulation of inherent strain to calculate the deformations. Isotropic and anisotropic strain scaling factors were calibrated initially within the APP software for the Ti6Al4V based single cantilever beam geometry. Subsequently, the numerical simulations were performed in APP software and computed the residual stresses and distortions for the varied process parameters including laser power, scan speed and hatch distance while maintaining the layer thickness constant for all the design iterations. The numerical predictions were compared; they were found to match reasonably well with the XRD measurements within the calibrated regime.

Laser powder bed fusion of a non-equiatomic FeNiCoAl-based high-entropy alloy: Printability, microstructure, and mechanical properties

In this work, the laser powder bed fusion (LPBF) process has been applied to fabricate the FeCoNiAlTaB (NCATB) high entropy alloys. The influence of process parameters including laser power and scanning speed on the relative density and microstructure were investigated. A sample with relative density of 99.8% can be achieved by optimal process parameters with laser power of 120 W and scanning speed of 800 mm/s. It can be found that the NCATB alloy maintains the FCC single-phase structure at different parameters, which is consistent with the pre-alloyed powder. According to the tensile test results, samples fabricated with different direction show similarity in strength and anisotropy in plasticity. Therefore, the causes of mechanical property anisotropy are discussed in terms of strengthening mechanism, texture and defects, separately. Compare to the as-cast samples, the printed samples show a substantial improvement in mechanical properties, which was contribute to the grain refinement, fine cellular morphology and high dislocation density.

An Optimization of Manufacturing Process of SS304L Using Direct Energy Deposition Method

The direct energy deposition (DED) method is an emerging manufacturing technique that has been recently highlighted due to its capabilities to coat materials with complex geometry for high temperature and highly corrosive environmental applications, such as steam turbine blade. Amongst metallic materials, SS304L has been reported to have superior corrosion resistance in such environments. Therefore, 3D printing of complex-shaped parts using SS304 maybe a promising strategy to introduce 3D printing techniques for nuclear industry application. To obtain robust and stable products that can withstand extreme environments, optimization of the SS304 manufacturing process conditions is required. This study investigated the effects of process parameters including laser power, scan speed, coaxial gas flow, and feeder rate using the DED method with a 4 way nozzle. It was found that laser power has an effect on grain growth behaviors. If the other variables are fixed and the scan speed is above a certain value, then the scan speed does not affect surface oxidation. The feeder rate is related to height. As the feeder rate increases, the height increases. Coaxial gas works to prevent oxidation and damage to the optic components and is not a critical factor in determining the size of the deposited material. These results can be utilized in future studies to accelerate the process design time of other 3D printed materials and future applications using SS304L

Study on microstructures and mechanical performance of laser transmission welding of poly-ether-ether-ketone (PEEK) and carbon fiber reinforced PEEK (CFR-PEEK)

The reliable assembly of poly-ether-ether-ketone (PEEK) and carbon fiber-reinforced PEEK (CFR-PEEK) is crucial to effective load transfer within lightweight and high-stiffness structures, which are commonly demanded in aeronautical, automobile, and medical industries. In this work, laser transmission welding of PEEK and CFR-PEEK has been performed by using a 1070 nm Nd:YAG fiber laser. The effects of process parameters including laser power, laser scanning speed, and clamping pressure on joining quality have been investigated via mechanical, morphological, and thermal characterization. Results show that strong bonds have been formed by entanglements of polymer chains at the joining interface and the mechanical embedment between carbon fibers and PEEK. The formation mechanisms of bubble defects have been classified into three types. One of them was eliminated by scanning the joints twice, which significantly improved joints' mechanical performance and hermeticity with the maximum joining strength reaching 11.6 MPa. Also, a comparative study between PEEK/PEEK and PEEK/CFR-PEEK joints shows that the existence of carbon fibers within the CFR-PEEK significantly increased joints' decomposition threshold, joining region, and strength due to their great thermal conductivity. Besides, the influence of the welding process on the crystallinity of PEEK was analyzed, which was then improved from 11.7% to 34.1% through annealing.

The Study on Resolution Factors of LPBF Technology for Manufacturing Superelastic NiTi Endodontic Files.

Laser Powder Bed Fusion (LPBF) technology is a new trend in manufacturing complex geometric structures from metals. This technology allows producing topologically optimized parts for aerospace, medical and industrial sectors where a high performance-to-weight ratio is required. Commonly the feature size for such applications is higher than 300–400 microns. However, for several possible applications of LPBF technology, for example, microfluidic devices, stents for coronary vessels, porous filters, dentistry, etc., a significant increase in the resolution is required. This work is aimed to study the resolution factors of LPBF technology for the manufacturing of superelastic instruments for endodontic treatment, namely Self-Adjusting Files (SAF). Samples of thin walls with different incline angles and SAF samples were manufactured from Nickel-Titanium pre-alloyed powder with a 15–45 μm fraction. The printing procedure was done using an LPBF set-up equipped with a conventional ytterbium fiber laser with a nominal laser spot diameter of 55 microns. The results reveal physical, apparatus, and software factors limiting the resolution of the LPBF technology. Additionally, XRD and DSC tests were done to study the effect of single track based scanning mode manufacturing on the phase composition and phase transformation temperatures. Found combination of optimal process parameters including laser power of 100 W, scanning speed of 850 mm/s, and layer thickness of 20 μm was suitable for manufacturing SAF files with the required resolution. The results will be helpful for the production of NiTi micro objects based on periodic structures both by the LPBF and μLPBF methods.

Combining the Finite Element Analysis and Kriging Model for Study on Laser Surface Hardening Parameters of Pitch Bearing Raceway.

Laser surface hardening is used to improve the fatigue performance of the large diameter pitch bearing. Determination of the process parameters by a trial and error method, depending on the experience of the technician, by changing the parameters repeatedly for each laser surface hardening process is time-consuming and costly. In this paper, a method of analyzing the maximum temperature and depth of a hardened layer during the laser surface hardening process for a pitch bearing raceway of a wind turbine is proposed, which combines finite element simulation and the Kriging model. A three-dimensional finite element model of a pitch bearing ring was established using ABAQUS. The temperature field analysis was performed. The effects of process parameters including laser power, scanning speed, and laser spot radius on the depth of the hardening layer were investigated. Then, taking into account the interactional effects of different process parameters, Kriging models were constructed to reflect the relationship between input process parameters and output responses. The results show that the Kriging approximation model has a small relative error compared with the simulated results and can be used to predict the hardened layer depth.

Predictions of in-situ melt pool geometric signatures via machine learning techniques for laser metal deposition

ABSTRACT Laser metal deposition (LMD) can produce near-net-shape components at high build-up rates for many applications, e.g. turbine blades, aerospace engine parts, and patient-specific implants. However, builds suffer from distortion and defects associated with ineffective process control. For example, melt pool features including height, depth, and dilution are transient, while process parameters including laser power, scanning speed, and powder feed rate remain constant in an open-loop LMD system. Improving product quality requires estimating these transient features to enable process control. This paper presents a semi-dynamic, data-driven framework to address this challenge. The framework correlates combined process parameters (laser power, scanning speed, powder feed rate, line energy density, specific energy density) and features from melt pool thermal images (melt pool width, area, mean temperature, maximum temperature) with hard-to-monitor, melt-pool-related features (height, depth, dilution). Sixty single-track experiments were conducted to acquire sensing data and dimensions of the track cross-sections. Significant input features for training machine learning (ML) models were selected based on Spearman’s rank correlation coefficient. Results show that the correlation between hard-to-monitor melt-pool-wise features, combined process parameters, and limited in-situ sensing data are described well by the models presented here. Critically, an artificial neural network (ANN) showed the best performance.

Modelling the complex evaporated gas flow and its impact on particle spattering during laser powder bed fusion

The additive manufacturing (AM) of metals is becoming an increasingly important production process with the potential to replace traditional techniques such as casting. Laser Powder Bed Fusion (LPBF) is used in many applications to print metal parts from powder. The metal powder is heated locally with sufficient laser radiation that the liquid melt easily reaches its boiling temperature, which leads to a metallic vapour jet that can entrain both powder bed particles and molten droplets. The small size of laser-matter interaction site makes a detailed experimental analysis of the process challenging. Synchrotron X-ray imaging experiments are one of the few methods which can capture the dynamic melting and solidification processes. Comparing such experiments with computer simulations of the process is an important approach in order to better understand the manufacturing process and to analyse the influence of process parameters on the evaporated gas jet and the subsequent impact on particle ejection, leading to potentially reduced AM component quality. The melting and solidification of the metal powder is simulated using an Eulerian multiphase approach based on a control volume discretization of powder bed and substrate and a volume of liquid separation from melt and gas phase. The gas phase modelled as an ideal gas reaches velocities up to 100 m/s. Lagrangian particle tracking in the simulation demonstrates that the velocity fields calculated by the Eulerian multi-phase approach in combination with a standard drag-force model lead to particle accelerations in good agreement with those measured experimentally. In order to avoid numerical laborious Lagrangian calculations, a direct method to compare an Eulerian multiphase simulation with synchrotron X-ray experiments was introduced and validated . This approach is used to analyse the influence of process parameters including laser power and laser speed on the maximal acceleration of particles from the melt pool area. While the particle acceleration increases linearly with line energy in the conduction mode, a linear decrease of the acceleration with increasing line energy can be found in the transition mode before the acceleration increases again with line energy in the keyhole mode.

Machining-induced surface integrity of Inconel 718 alloy fabricated by powder bed fusion additive manufacturing under various laser processing parameters

Parameters used in laser powder bed fusion (LPBF) process are key factors that influence the surface integrity and thus mechanical properties of Inconel 718 components fabricated by additive manufacturing (AM) technique. For this reason, various parameters with different settings through trial and error approach have used by AM community to fabricate Inconel 718 components. These AM fabricated components generally required post treatment or processing including finish machining, to enhance their surface properties. This study presents a systematic investigation on the effect of volumetric energy density, and various LPBF processing parameters including laser power, layer thickness, and scanning speed on the as-printed specimens and the surface integrity aspects, namely surface quality, porosity, and microhardness. Furthermore, using machining operations specifically finish milling on these specimens under constant machining parameters, the effect of as-printed conditions on the machinability responses including burr formation, cutting forces are evaluated accordingly. Moreover, the interrelationship between LPBF processing parameters-machining-surface and subsurface aspects are also examined. This study reveals that LPBF additive manufacturing parameters have remarkable influence on the printed Inconel 718 specimens. Results also showed that parameters including laser power, scanning speed and layer thickness also have an effect on both the machinability and final surface and subsurface properties of the AM fabricated Inconel 718 specimens. It should be also noted that there is a notable relationship between volumetric energy density and the machinability of the AM printed Inconel 718.

An investigation on cutting of the MWCNTs doped composite plates by CO2 laser beam

PurposeThe purpose of this study is to obtain strong materials with multiwall carbon nanotubes (MWCNTs) doped and investigate laser cut of MWCNTs also find the effect of the laser cutting parameters on composite materials.Design/methodology/approachThe laminated composite plates were manufactured by using a vacuum infusion process. The mechanical properties of the composite materials produced were determined according to American Society for Testing and Materials (ASTM) D3039M, ASTM D3171, ASTM D 792 and ASTM D2583. A 130 Watts carbondioxide (CO2) laser cutting machine was used for drilling the two different composite plates with a thickness of 1.6–1.5 mm. Three variables were considered as process parameters including laser power (in three levels of 84.50, 104.00 and 127.40 W), cutting speed (in three levels of 4, 6, 8 mm/s) and 14 mm fixed focal position.FindingsThe fibers could not be cut due to insufficient melting in the experiments performed using 84.50 and 104.00 W laser power but the cutting was successfully completed when the laser power was 127.40 W. However, as the cutting speed increased, the contact time of the laser beam with the material decreased, so the kerf decreased, but the increased laser power created a thermal effect, causing an increase in hardness around the cutting surface. This increase was lower in MWCNTs doped composites compared to pure composites. It has been found that the addition of nanoparticles to layered glass fiber composite materials played an effective role in the strength of the material and affected the CO2 laser cutting quality.Originality/valueThis study is a unique study in which the CO2 laser cutting method of MWCNT-doped composite materials was investigated and the machinability without cutting errors, such as delamination, splitting, distortion and burring using the most suitable laser cutting parameters was revealed.

A simple and convenient approach to fabricate gas permeable mould steel by selective laser melting

ABSTRACT Gas permeable steel can extract gases from the mould cavity during the injection moulding process. This study proposed a simple and convenient approach to fabricate gas permeable steel by selective laser melting (SLM). By regulating SLM processing parameters including laser power, scanning velocity and hatch spacing, we tried to seek appropriate parameters for fabricating gas permeable steel. Firstly, the effects of each processing parameter on porosity, pore size and distribution were studied separately. Then, by simultaneously regulating these parameters, the synergistic effects of laser power, scanning velocity and hatch spacing were evaluated. By simultaneously lowering laser power and increasing scanning velocity, samples with the porosity of 20% ~ 30% and gas permeability of 3.54×10-13 m2 was obtained and these values are comparable to commercial gas permeable steel. However, the mechanical properties were relatively poor due to the low specific energy and insufficient melting.

Influence of processing parameters on the quality of titanium-coated glass welded by nanosecond pulse laser

Glass welding has important application value. In order to efficiently obtain strong and transparent glass welded joints, a 30nmTi coating was added as an absorption layer between the two glasses, and a nanosecond pulse laser with a Galvo scanning system was employed. The effects of processing parameters including laser power (3–10 W), scanning speed (20–400 mm/s), and repetition frequency (20–80 kHz) on the transmittance and tensile strength of joints were discussed systematically. The effect of laser power is the most significant. The transmittance and tensile strength first increases as the laser power increases, followed by a decrease. The optimum laser power, scanning speed, and repetition frequency was 8 W, 100 mm/s, 20 kHz, respectively. The average transmittance was 83.6% and the tensile strength reached 38.07 MPa. The Micrographs of the welding interface and the fracture surface obtained by a confocal laser scanning microscope (CLSM) were used to discuss the welding mechanism with different gap sizes and different processing parameters. When the gap and processing parameters are appropriate, the irradiated titanium film and nearby glass will melt and form a continuous molten pool, through which the glass is stably connected together. The welded joint is uniform and tight, and its fracture surface extends into the glass substrates of several hundred microns.

Process maps and optimal processing windows based on three-dimensional morphological characteristics in laser directed energy deposition of Ni-based alloy

Constructing processing window to fabricate defect-free components with high forming quality and desired performance has been crucial in directed energy deposition. Due to its complexity as a mass and energy time-dependent system, it is still a key problem to be solved for laser powder-fed additive manufacturing to choose opportune processing parameters. In this paper, single scan track experiments were conducted under various combinations of processing parameters including laser power, scanning speed and powder feeding rate. Scan tracks had been thoroughly investigated through three-dimensional information including surface, longitudinal section and transverse section, which were correlated to each other in showing track morphological characteristics in directed energy deposition. Surface ripples, resembling fish scale in welding and chevron in selective laser melting, were found in directed energy deposition under low powder feeding rate and high linear energy density. Furthermore, several quantitative indexes, which were dimensionless mean roughness and ripples’ interval in surface, dimensional roughness in longitudinal section and dilution rate in transverse section, were used to evaluate the forming quality. These quantitative indexes were found to be closely related to the defects in additive manufacturing, and forming quality and accuracy of additive-manufactured components. Relationship between proposed indexes and processing parameters was studied and the mechanism behind it was also discussed. Five states which were no fusion, lack of fusion, optimum, rough surface and undesired dilution rate were distinguished based on the proposed quantitative indexes. Finally, a processing window based on these indexes was proposed for the laser powder-fed additive manufacturing for Inconel alloys. It is found that powder feeding rate affects the distribution of the five states and laser power, scanning speed affect the range of the five states.

Influence of process parameters on the joint characteristics during laser joining of aluminium alloy and CFRTP

Fiber laser joining of 6061 aluminium alloy and carbon fiber reinforced thermoplastic composite (CFRTP) was performed in this work. The effect of three process parameters including laser power, traveling speed and defocus distance on the bonding interface and joint properties was investigated. Shear tests were performed to evaluate the joint strength in different variables. X-ray photoelectron spectroscopy (XPS) was adopted to confirm the chemical states of elements at the interface. The results indicated that the shear strength of joints first increased and then decreased with the increase of heat input. Insufficient flow of CFRTP could not fill the grooves of aluminium alloy surface at low heat input. The resin was decomposed at excessisvely high heat input, causing pores remained at the interface. The fracture mode was determined as the interface failure. XPS result revealed that no new chemical bond was found at the interface, and the mechanical interlocking between aluminium alloy and CFRTP was main bonding mechanism. The maximum shear strength was 23.8 MPa, which was obtained as laser power, traveling speed and defocus distance was 1100 W, 5 mm/s and +10 mm, respectively.

Retracted] Optimizing the Characteristics of the Laser Hardfacing Process Parameters to Maximize the Wear Resistance of Ni‐Based Hard‐Faced Deposits Using the RSM Technique

The nickel‐based Colmonoy‐5 hardfacing alloy is used to hard‐face 316LN austenitic stainless steel components in fast reactors. The nominal composition (in wt%) was listed as follows: 0.01 C, 0.49 Si, 0.87 Mn, 17.09 Cr, 14.04 Ni, 2.56 Mo, 0.14 N, and balance Fe. Hardfacing is a technique of applying hard and wear‐resistant materials to substrates that need abrasion resistance. The thickness of hardfacing deposit varies between 0.8 mm and 2 mm based on parameter combinations. In this study, laser hardfacing process parameters including laser power, powder feed rate, travel speed, and defocusing distance were optimized to reduce weight loss of laser hard‐faced Ni‐based deposit. The tribological characteristics of reactor‐grade NiCr‐B hard‐faced deposits were investigated. The RSM technique was used to identify the most important control variables resulting in the least weight loss of the nickel‐based alloy placed on AISI 316LN austenitic stainless steel. Statistical techniques like DoE and ANOVA are utilized. Changing the laser settings may efficiently track the weight loss of laser hard‐faced nickel alloy surfaces. These are created using the response surface technique. The deposit produced with a laser power of 1314 W, powder feed rate of 9 g/min, travel speed of 366 mm/min, and defocusing distance of 32 mm had the lowest weight loss of 16.4 mg. Based on the F value, the powder feed rate is the major influencing factor to predict the hardness followed by power, travel speed, and defocusing distance.