Powder Bed Research Articles

A metal 3D-printed non-assembly mandrel for profile bending

Abstract In the overall regime of production technologies, bending processes allow production of complex parts and profiles in a precise, flexible, and economical way. It is important to manufacture tools which are universally applicable and easy to manufacture, since modern industries demand flexibility in terms of larger varieties or smaller batch sizes. In the past, it was difficult and time-consuming to manufacture bending tools, especially mandrels, due to their high geometric complexity and tight assembly of swivel joints. In this paper, we present a new design approach for the bending mandrel which is suitable for metal additive manufacturing that incorporates non-assembly mechanisms of joints. The hinges are systematically developed with particular focus on achieving a minimized gap and resultant clearance. As a test case, a mandrel is 3D printed by using the laser powder bed fusion technique and successfully tested in the rotary draw bending process parameterized for narrow bends in stainless steel tubes. In the light of these results, a solution is formulated for ease in manufacturing and faster rate of tool production, in this case bending mandrel. This methodology facilitates the production of small batch sizes and large product variants in bending processes. The research presented in this paper serves as a forward step towards economical production of complex parts in a highly flexible manner.

Deformation Behavior of Inconel 625 Alloy with TPMS Structure

Triply periodic minimal surfaces (TPMSs) are known for their smooth, fully interconnected, and naturally porous characteristics, offering a superior alternative to traditional porous structures. These structures often suffer from stress concentration and a lack of adjustability. Using laser powder bed fusion (LPBF), we have fabricated Inconel 625 sheet-based TPMS lattice structures with four distinct topologies: Primitive, IWP, Diamond, and Gyroid. The compressive responses and energy absorption capabilities of the four lattice designs were meticulously evaluated. The discrepancies between theoretical predictions and the fabricated specimens were precisely quantified using the Archimedes’ principle for volume displacement. Subsequently, the LPBF-manufactured samples underwent uniaxial compression tests, which were complemented by numerical simulation for validation. The experimental results demonstrate that the IWP lattice consistently outperformed the other three configurations in terms of yield strength. Furthermore, when comparing energy absorption efficiencies, the IWP structures were confirmed to be more effective and closer to the ideal performance. An analysis of the deformation mechanisms shows that the IWP structure characteristically failed in a layer-by-layer manner, distinct from the other structures that exhibited significant shear banding. This distinct behavior was responsible for the higher yield strength (113.16 MPa), elastic modulus (735.76 MPa), and energy absorption capacity (9009.39 MJ/m3) observed in the IWP configuration. To examine the influence of porosity on structural performance, specimens with two varying porosities (70% and 80%) were selected for each of the four designs. Ultimately, the mechanical performance of Inconel 625 under compression was assessed both pre- and post-deformation to elucidate its impact on the material’s integrity.

Real-time detection of powder bed defects in laser powder bed fusion using deep learning on 3D point clouds

ABSTRACT Powder bed defects are critical factors affecting the print quality and stability in Laser Powder Bed Fusion (LPBF). However, traditional 2D image-based powder bed defect monitoring methods are limited by sensitivity to lighting conditions and insufficient data capture. This study proposes a real-time defect monitoring system based on 3D point cloud data and deep learning approach. The system uses binocular vision to capture point cloud data in real time, enabling high-precision defect segmentation with advanced deep learning models. However, direct deep learning on point clouds can result in the loss of small defect features during downsampling. To address this, an indirect point cloud deep learning method based on 2D projection is introduced, which improves segmentation accuracy for small defects while reducing inference time. By deploying the trained model, this study establishes a closed-loop control system for powder bed defect detection and conducts real-world printing tests, demonstrating effective defect remediation capabilities. Although larger-scale industrial testing is still required, this research illustrates the significant potential of 3D point cloud-based deep learning in enhancing defect detection and quality control in additive manufacturing.

Oscillatory nature in melt-gas-powder interactions during laser powder bed fusion process revealed by CFD-DEM coupled modelling

ABSTRACT The laser powder bed fusion (LPBF) process encompasses interactions between different material states, including melt, gas, and powder. While observational techniques can capture specific states, they cannot be combined to produce a comprehensive monitoring how they are mutually interacted. Thus, an integrated modelling approach is a crucial solution for revealing their interactions. This study investigates melt-gas-powder dynamics under varying laser scan speeds through a coupled CFD-DEM multiphase model. Findings reveal that metal vapour consistently transitions from an initialisation phase to a processing phase, exhibiting consistent behaviour in the former but varied responses in the latter. A relationship is identified between scan speed and vapour flow angle (VFA), with higher speeds broadening the VFA. Significantly, three oscillatory behaviours are observed: first, the oscillation of locally intensified pressure (LIP) sites on keyhole walls, where vapour ejection modes shift and may become periodic at intermediate scan speeds; second, the oscillation of two induced argon vortex flows with opposite swirling directions; and third, a simultaneously induced varying drag force on powder spatter. These oscillations clarify various spatter mechanisms, offer insights for process optimisation, and suggest implications for process stability. The study also proposes future research directions to further elucidate these mechanisms.

Exploring the role of volume energy density in altering microstructure and corrosion behavior of nitinol alloys produced by laser powder bed fusion

In the realm of materials science and engineering, the pursuit of advanced materials with tailored properties has been a driving goal behind technological progress. Scientific interest in laser powder bed fusion (L-PBF) fabricated NiTi alloy has in recent times seen an upsurge of activity. In this study, we investigate the impact of varying volume energy density (VED) during L-PBF on the microstructure and corrosion behaviour of NiTi alloys in both scan (XY) and built (XZ) planes. The microstructural evolution in both planes was characterized by electron backscatter diffraction and phase change temperatures were characterized using differential scanning calorimeter measurements. Electrochemical experiments were carried out to compare the specimens produced at high laser energy density and low laser energy density. The results indicate that employing high laser energy density in the production of NiTi alloy induces discontinuous dynamic recrystallization, contributing to grain refinement. This in turn enhances the corrosion resistance of the specimen. X-ray photoelectron spectroscopy was employed to examine the type of oxide layer that developed on the samples. The increased resistance to corrosion in a high laser energy density sample can be associated with the formation of a stable and homogeneous passive layer with enriched TiO2 as opposed to Ti2O3. This exploration has unravelled the intricate relationship between VED, the microstructure, and the corrosion properties of L-PBF fabricated NiTi alloys, offering valuable insights into their performance for diverse applications.

Numerical Study to Analyze the Influence of Process Parameters on Temperature and Stress Field in Powder Bed Fusion of Ti-6Al-4V

This paper presents a comprehensive numerical investigation to simulate heat transfer and residual stress formation of Ti-6Al-4V alloy during the Laser Powder Bed Fusion process, using a finite element model (FEM). The FEM was developed with a focus on the effects of key process parameters, including laser scanning velocity, laser power, hatch space, and scanning pattern in single-layer scanning. The model was validated against experimental data, demonstrating good agreement in terms of temperature profiles and melt pool dimensions. The study elucidates the significant impact of process parameters on thermal gradients, melt pool characteristics, and residual stress distribution. An increase in laser velocity, from 600 mm/s to 1500 mm/s, resulted in a smaller melt pool area and faster cooling rate. Similarly, the magnitude of residual stress initially decreased and subsequently increased with increasing laser velocity. Higher laser power led to an increase in melt pool size, maximum temperature, and thermal residual stress. Hatch spacing also exhibited an inverse relationship with thermal gradient and residual stress, as maximum residual stress decreased by about 30% by increasing the hatch space from 25 µm to 75 µm. The laser scanning pattern also influenced the thermal gradient and residual stress distribution after the cooling stage.

Effects of Sc and Zr on the phase point defects of the three major intermetallic phases in Al-Zn-Mg-Cu alloys from first-principles calculations

Abstract In the Al-Zn-Mg-Cu alloys formed by Laser powder bed fusion( L-PBF ), the elements Sc and Zr are of great importance for the strengthening and toughening properties. The purpose of this study is to investigate the effect of the presence of Sc and Zr on the stability of the phase structure in an Al-Zn-Mg-Cu alloys. First-principles calculations have been used to analyse the influence of Sc and Zr on the mechanical properties of the primary strengthened precipitated phase in Al-Zn-Mg-Cu alloys. The elastic modulus and electronic structure of three main metallic phases containing two types of point defects (Scx, Zrx) have been calculated. Research has demonstrated that the plastic properties of some point defects are improved by the occupation of Sc and Zr elements. Among them, Al2CuMg and MgZn2 are strongly affected by Sc occupation, and Al2Cu are strongly affected by Zr occupation. Zrx-type point defects are more stable than Scx-type point defects in Al2Cu, MgZn2 and Al2CuMg. The charge density distribution near the point defect of Scx and Zrx is higher than the pure phase, and the charges near Scx and Zrx tend to aggregate in a particular direction. In summary, this study reveals the influence mechanism of the intrinsic modification of the main phase point defects of Sc and Zr on the mechanical properties is revealed by the first-principles calculation method, which provides a theoretical basis for the composition design and optimisation of Al-Zn-Mg-Cu alloys with Sc and Zr addition.

Static and dynamic response of SS316L thin-wall Origami and Auxetic structures fabricated through laser powder bed fusion

Static and dynamic response of SS316L thin-wall Origami and Auxetic structures fabricated through laser powder bed fusion

Process capability analysis of additive manufacturing process: a machine learning−based predictive model

Purpose Predicting dimensional and geometrical errors in 3D printing parts during the design stage can significantly enhance the product’s quality. This study aims to predict the form deviation and process capability in additive manufacturing (AM) specimens considering layer thickness, laser power and scan speed parameters in the laser powder bed fusion (LPBF) method. Various machine learning (ML) techniques are implemented to estimate the form deviation and process capability with the highest accuracy in 3D-printed cylindrical parts as a case study. Design/methodology/approach The workflow started by simulating the LPBF AM process using a finite element modeling approach. Then, different ML algorithms like artificial neural networks are used to predict the form deviation. The process capability value is forecasted using some classification ML models and process capability indices (PCIs) for cylindrical parts. Finally, concentricity tolerance classification is performed for cylindrical parts, which can ensure quality control issues in the production stage. Findings Results present an accuracy of about 93% for predicting form deviations and 95% accuracy for predicting PCI C_pm in PCI classification based on random forest model as an ML algorithm. Originality/value The noteworthy point of the research is accessing the form deviation due to AM and process capability evaluation in the AM process before the production stage, which has not been studied before based on the author’s knowledge. So that the product quality is evaluated based on the shape deviation and its tolerances in the AM process digital chain.

Interface characterization of additively manufactured Inconel 718 heterogeneous products: Microstructural and surface characteristics

Abstract The present work analyses the effect of laser powder bed fusion (LPBF) remanufacturing of wrought Inconel 718 on the metallurgical and surface characteristics of the part. The remanufactured part experienced geometrical mismatch due to computer-aided design (CAD) misalignment with the substrate. As a result, a ~200 μm shift in a material deposition is observed, leading to a material deposition without support from the substrate on one edge. The microstructural analysis of the remanufactured part showed an interface between the wrought substrate and LPBF processed layers. The substrate showed an equiaxed grain structure. However, a strongly textured columnar grain structure was observed in the remanufactured region. The remanufactured Inconel 718 showed lower micro-hardness, inhibiting the precipitation of strengthening precipitates during the LPBF process. The surface characterization showed a higher surface roughness and anisotropy in material distribution for overhanging edges due to layer deformation and lack of support from the substrate. It was observed that due to geometry mismatch, the overhanging side experienced layer deformation, thus leading to the formation of large undulations on the surface. A higher area fraction of fused powder particles on the overhanging side shows ineffective heat transfer due to the region's lack of efficient support.

A Review of Modeling, Simulation, and Process Qualification of Additively Manufactured Metal Components via the Laser Powder Bed Fusion Method

Metal additive manufacturing (AM) has grown in recent years to supplement or even replace traditional fabrication methods. Specifically, the laser powder bed fusion (LPBF) process has been used to manufacture components in support of sustainment issues, where obsolete components are hard to procure. While LPBF can be used to solve these issues, much work is still required to fully understand the metal AM technology to determine its usefulness as a reliable manufacturing process. Due to the complex physical mechanisms involved in the multiscale problem of LPBF, repeatability is often difficult to achieve and consequently makes meeting qualification requirements challenging. The purpose of this work is to provide a review of the physics of metal AM at the melt pool and part scales, thermomechanical simulation methods, as well as the available commercial software used for finite element analysis and computational fluid dynamics modeling. In addition, metal AM process qualification frameworks are briefly discussed in the context of the computational basis established in this work.

Investigating Fast Scanning Calorimetry and Differential Scanning Calorimetry as Screening Tools for Thermoset Polymer Material Compatibility with Laser-Based Powder Bed Fusion

Investigating Fast Scanning Calorimetry and Differential Scanning Calorimetry as Screening Tools for Thermoset Polymer Material Compatibility with Laser-Based Powder Bed Fusion

Multicavity structures with triply periodic minimal surface for broadband and perfect sound absorption manufactured by laser powder bed fusion

Multicavity structures with triply periodic minimal surface for broadband and perfect sound absorption manufactured by laser powder bed fusion

Review of the Microstructural Impact on Creep Mechanisms and Performance for Laser Powder Bed Fusion Inconel 718

Review of the Microstructural Impact on Creep Mechanisms and Performance for Laser Powder Bed Fusion Inconel 718

The effect of inter- and intra-layer delay time on TPU parts fabricated by laser powder bed fusion

The effect of inter- and intra-layer delay time on TPU parts fabricated by laser powder bed fusion

Optimising β-Ti21S Alloy Lattice Structures for Enhanced Femoral Implants: A Study on Mechanical and Biological Performance.

The metastable β-Ti21S alloy exhibits a lower elastic modulus than Ti-6Al-4V ELI while maintaining high mechanical strength and ductility. To address stress shielding, this study explores the integration of lattice structures within prosthetics, which is made possible through additive manufacturing. Continuous adhesion between the implant and bone is essential; therefore, auxetic bow-tie structures with a negative Poisson's ratio are proposed for regions under tensile stress, while Triply Periodic Minimal Surface (TPMS) structures with a positive Poisson's ratio are recommended for areas under compressive stress. This research examines the manufacturability and quasi-static mechanical behaviour of two auxetic bow-tie (AUX 2.5 and AUX 3.5) and two TPMS structures (TPMS 2.5 and TPMS 1.5) in β-Ti21S alloy produced via laser powder bed fusion. Micro-CT reveals printability issues in TPMS 1.5, affecting pore size and reducing fatigue resistance compared to TPMS 2.5. AUX 3.5's low stiffness matches cancellous bone but shows insufficient yield strength and fatigue resistance for femoral implants. Biological tests confirm non-toxicity and enhanced cell activity in β-Ti21S structures. The study concludes that the β-Ti21S alloy, especially with TPMS 2.5 structures, demonstrates promising mechanical and biological properties for femoral implants. However, challenges like poor printability in TPMS 1.5 are acknowledged and should be addressed in future research.

Comparative evaluation of powder spreading strategies to enhance powder bed quality in powder bed fusion additive manufacturing: A DEM simulation study

Comparative evaluation of powder spreading strategies to enhance powder bed quality in powder bed fusion additive manufacturing: A DEM simulation study

Avoiding cracks in multi-material printing by combining laser powder bed fusion with metallic foils: Application to Ti6Al4V-AlSi12 structures

Avoiding cracks in multi-material printing by combining laser powder bed fusion with metallic foils: Application to Ti6Al4V-AlSi12 structures

Advanced phenomenological models guided heat treating processes for LPBF Ti-6Al-4V alloy

Ti-6Al-4V (Ti64) alloy produced by laser powder bed fusion (LPBF) technique consists of an α′-martensite phase, which is usually brittle. Hence, heat treatments are required to promote the α՛→α+β and/or α→β transformations for microstructural optimization to achieve balances between strength and ductility. To guide the selection of heat treatment parameters for the design of LPBF Ti64 microstructures exhibiting optimized strength and ductility, this work explores the suitability of a Johnson-Mehl-Avrami-Kolmogorov (JMAK) and Lifshitz-Slyozov-Wagner (LSW) models. The work showed that the JMAK model can effectively model the heat treatment processes to predict volume fraction of constituent phases in LPBF Ti64. The transformation kinetics was predicted by an extended non-isothermal JMAK model based on differential scanning calorimetry (DSC) experimental data recorded during continuous heating. Moreover, hardness, as a mechanical property index, was measured for a set of specimens. The hardness initially decreased, then remained constant, and finally slightly increased with the increase in β phase fraction and underlying evolution of microstructure. When the β phase fraction was small < 3%, hardness decreased with the continuous coarsening of α lath during heat treatment process. The measured hardness and α lath width for the specimens followed the Hall-Petch relationship. Moreover, the α lath width and heat treatment time at a given temperature were found to undergo the LSW model. Hardness became independent on the β phase fraction of 3-8%, owing to the competition between α lath coarsening and solution strengthening. The hardness slightly increased when the β phase fraction was greater than 8%, because solid solution strengthening of the α phase played a dominant role over the coarsening of α lath width. The experimentally verified JMAK and LSW models are therefore discussed as effective tools to guide the selection of heat treatment parameters for designing the microstructure and hardness/strength of LPBF Ti64 alloy.

Flow stress modeling and microstructural evolution during hot compression of Al-4.8Mg-0.3Sc alloy produced by laser powder bed fusion

Flow stress modeling and microstructural evolution during hot compression of Al-4.8Mg-0.3Sc alloy produced by laser powder bed fusion