Search Results (1,509)

Net-shaped casting processes in the automotive industry have proved to be difficult to simulate due to the complexities of the interactions amongst thermal, fluid, and solute transport regimes in the solidifying domain, along with the interface. The existing casting simulation software lacks the necessary real-time estimation of thermophysical properties (thermal diffusivity and thermal conductivity) and the interfacial heat-transfer coefficient (IHTC) to evaluate the thermal resistances in a casting process and solve the temperature in the solidifying domain. To address these shortcomings, an axial directional solidification experiment setup was developed to map the thermal data as the melt solidifies unidirectionally from the chill surface under unsteady-state conditions. A Dilute Eutectic Cast Aluminum (DECA) alloy, Al-5Zn-1Mg-1.2Fe-0.07Ti, Eutectic Cast Aluminum (ECA) alloys (A365 and A383), and pure Al (P0303) were used to demonstrate the validity of the experiments to evaluate the thermal diffusivity (α) of both the solid and liquid phases of the solidifying metal using an inverse heat-transfer analysis (IHTA). The thermal diffusivity varied from 0.2 to 1.9 cm²/s while the IHTC changed from 9500 to 200 W/m²K for different alloys in the solid and liquid phases. The heat flux was estimated from the chill side with transient temperature distributions estimated from IHTA for either side of the mold–metal interface as an input to compute the interfacial heat-transfer coefficient (IHTC). The results demonstrate the reliability of the axial solidification experiment apparatus in accurately providing input to the casting simulation software and aid in reproducing casting numerical simulation models efficiently. Full article

In selective laser melting (SLM), real-time visual inspection of powder spreading quality is essential for maintaining dimensional accuracy and mechanical performance. However, reflections from metallic chamber walls introduce non-uniform illumination and reduce local contrast, hindering reliable defect detection. To overcome this problem, a chamber-reflection-aware image enhancement method is proposed, integrating a physical reflection model with a dual-channel deep network. A Gaussian-based curved-surface reflection model is first developed to describe the spatial distribution of reflective interference. The enhancement network then processes the input through two complementary channels: a Retinex-based branch to extract illumination-invariant reflectance components and a principal components analysis (PCA)-based branch to preserve structural information. Furthermore, a noise-aware loss function is designed to suppress the mixed Gaussian–Poisson noise that is inherent in SLM imaging. Experiments conducted on real SLM monitoring data demonstrate that the proposed method significantly improves contrast and defect visibility, outperforming existing enhancement algorithms in peak signal-to-noise ratio (PSNR), structural similarity index (SSIM), and natural image quality evaluator (NIQE). The approach provides a physically interpretable and robust preprocessing framework for online SLM quality monitoring. Full article

This study introduces a composite method that integrates a diamond-coated tubular grinding electrode with short electric arc machining (SEAM) for GH4099. Mechanical micro-grinding and arc erosion act concurrently within the inter-electrode gap, enabling an in situ “erode–dress” coupling in which the grinding action levels nascent craters and promotes debris evacuation while SEAM supplies localized thermal–electrical energy for removal. A design-of-experiment scheme probes discharge and grinding factors, and performance is evaluated by material removal behavior, electrode wear, and surface integrity. Within a robust window (12–24 V; 500–2000 r/min), the composite process sustains stable discharges without catastrophic melting at 24 V and yields dense, uniform textures. Representative surfaces show controllable areal roughness (Sa ≈ 14–27 µm across 80#–600#), reflecting a practical finishing–efficiency trade-off. Multi-scale characterization (3D topography, cross-sectional metallography, SEM) evidences suppression of recast steps, macro-protrusions, and irregular pits, with more evenly distributed, shallower grinding traces compared to those with single-mode SEAM. The comparative analyses clarify discharge stabilization and recast-layer mitigation mechanisms, establishing a feasible pathway to high-quality, high-efficiency composite SEAM of GH4099 without resorting to overly aggressive electrical conditions. Full article

This study addresses the issue of adapting the thermal drilling process for joining dissimilar thin-walled materials—sheets made of non-ferrous metal alloys and polymer composites with a thermoplastic matrix reinforced with glass and carbon fibers—without the use of connecting elements and without disrupting the continuity of the reinforcing fibers. An extensive metallographic study was conducted on bushings formed in thin metal sheets made of EN AW 6082 T6 aluminum alloy and AZ91 magnesium alloy obtained during separate drilling procedures. Experiments were also performed where the metal sheet and composite material overlapped, using both direct and sequential drilling above the melting point of the polymer matrix, applying various process parameters. The dimensions of the resulting bushings and the suitability of their profile for joining with composites were evaluated. The results suggest the possibility of joining metals and fiber composites through thermal drilling, and suitable joining process parameters and conditions are specified. To limit composite delamination, it is advisable to make a hem flange on the reverse side of the joints. CT scans confirmed the deflection of fibers around the hole in the composite without compromising their integrity. The load-bearing capacity of the joints and the possibility of creating hybrid mechanical–adhesive joints between these materials are the subject of Part Two of this study. Full article

Selective Laser Melting (SLM) of 316L stainless steel was studied with a focus on the combined influence of laser power and scan speed on tensile behavior. A full factorial design generated 27 experiments, and mechanical properties (yield stress, ultimate tensile strength, elongation, and Young’s modulus) were analyzed using analysis of variance (ANOVA) and quadratic regression models. Artificial Neural Networks (ANNs) were trained on selected datasets to capture nonlinear dependencies, achieving excellent predictive accuracy (R² > 0.998). Fractographic observations validated the trends, confirming ductile fracture at low scan speeds and brittle behavior at high scan speeds. Full article

In this study, an analytical model was developed to evaluate the influence of laser powder bed fusion (LPBF) process parameters on process-induced porosity during the 3D printing of stainless steel 316L. First, the temperature distribution, governed by a moving point heat source model of the laser, was used to predict the melt pool geometry during the melting stage. This prediction was then refined to account for the formation of the solidified cap. By analyzing the interaction between melt pool size and other process parameters, such as hatch spacing and layer thickness, criteria were established to distinguish between porosity caused by lack of fusion, porosity due to keyhole formation, and defect-free samples. A series of experiments were conducted, and porosity was measured using micro-CT analysis. The results showed that the porosity predicted by the model remained within an acceptable error range compared with the experimental measurements, with errors ranging from 10.5% to 24.78% and a mean error of 16.48%, demonstrating the accuracy of the developed model. Full article

In this article, models for prediction of surface hardness for SLM specimens are presented. In experiments, EOS Maraging Steel MS1 was processed using EOS M 290 3D printer via selective laser melting (SLM). To predict hardness of SLM specimens, several machine learning methods were applied, including genetic programming, neural network, multiple regression, k-nearest neighbors, support vector machine, logistic regression, and random forest. In the research, fractal geometry was used to characterize the complexity of SLM-shaped microstructures. It was found that fractal geometry combined with machine learning techniques together greatly improved our comprehension of the intricacies of surface analysis and provided highly efficient predictions. All the applied algorithms exhibited predictability above 90%, with the best average result of 98.7% for genetic programming. Full article

Powder addition onto a molten-lead surface followed by stirring is widely used for desilvering during lead bullion refining operations. We model submerged zinc particle injection by coupling (i) a transient particle–metal reaction following Ohguchi with a time-dependent reaction efficiency E, (ii) a Stefan-type estimate of the zinc melting time Tf, and (iii) hydrodynamic descriptors of residence (τ_res) and mixing (τ_mix) times. The model is validated against experiments under a benchmark condition (gas velocity U = 3.32 m/s, 70% submergence), achieving a mean absolute percentage error of 1.13% for the experimental desilvering curve. A parametric study over lance submergence (30–90% of bath depth), injection velocity (3.32–9.79 m/s), and geometric scalings of lance and kettle identifies conditions where the hydrodynamic residence time τres approaches the Stefan melting time, maximizing liquid-Zn contact with molten Pb. Specifically, the proposed optimum balances the competing effects of plume buoyancy at high velocities—which tends to reduce residence time—against the deeper injection depth, ensuring that particles remain submerged long enough to fully melt and react. Within 16 simulated scenarios, the pair “90% submergence + U = 9.79 m/s” provides the best multi-criteria performance (desilvering fraction, E, and residence time) under realistic constraints. A parametric sensitivity analysis ranks injection velocity and submergence as the dominant levers, with geometry playing a secondary role over the tested ranges. The coupled hydrodynamic–kinetic framework provides quantitative guidance for optimizing industrial desilvering by particle injection and is extensible to other powder-injection refining operations. Full article

The article presents a method of measurement and a test stand for determining the specific electrical resistivity of granular carburizing materials most commonly used in foundry practice. The research was conducted for synthetic graphites (GS) and petroleum cokes (KN) using a test stand proposed by the authors of the study and protected by a patent. It was shown that this measurement method allows for a clear distinction between the tested materials. For synthetic graphites, specific resistivities in the range of 35.9–144.5 μΩ·m were obtained, while for petroleum cokes the range was 172.1–1390 μΩ·m. The main aim of the study was to determine whether there is a correlation between the measured electrical resistivity of the tested materials and the carburization efficiency obtained in melting experiments. Therefore, the article also presents the course and results of studies on the process of cast iron melting in laboratory induction furnaces, where the carburizing material was introduced into the induction furnace with a fixed charge. Carburization efficiencies obtained for synthetic graphite ranged from 86.6% to 94.4%, and from 65.5% to 85.31% for petroleum coke. Based on the measurement results, a statistical analysis was carried out, yielding a relationship with a coefficient of determination R² = 0.92. The research confirmed the possibility of a quick assessment of carburizers in terms of their assimilation degree by molten metal. This is valuable information both for scientific research and industrial applications. The presented results form part of ongoing studies aimed at explaining the differences occurring within a given group of materials (petroleum cokes and synthetic graphites). Full article

As coal mining operations extend deeper underground, the importance of refuge chambers as temporary shelters for miners grows given the heightened risk of accidents. The severe geothermal conditions in deep mines present significant challenges to temperature regulation within these chambers, potentially subjecting miners to hazardous heat exposure. The utilization of phase change plates (PCPs) presents a promising approach to improving temperature regulation performance. To systematically investigate the enhancement effects of nano-graphite particles (NGPs) and fin structures on the thermal performance of phase change materials (PCMs), this study conducted thermophysical property tests and temperature-controlled melting experiments to analyze the influence of varying NGP concentrations on the thermal characteristics of PCMs, while observing their melting behavior. Four PCP models were designed: base PCM, PCM with NGPs, plate fin, and pin fin. Based on the enthalpy-porosity method, numerical simulations were performed to systematically evaluate the melting kinetics and temperature regulation performance of each design under extended operation conditions. The findings indicate that while NGP doping markedly increases the thermal conductivity and peak melting temperature of the PCM, it also results in a reduction in latent heat capacity. The NGP-enhanced No. 25 paraffin wax (RT25) PCP reduced the surface temperature by 1.02 °C compared to the base material. During extended operation, the NGP-based model outperformed others, maintaining effective temperature regulation for 149.8 h, 13 h longer than the base PCM and exceeding the standard requirement by 53.8 h. This underscores its notable advantages in thermal management. These advancements offer a valuable reference for the utilization of PCP in refuge chambers, thereby augmenting their temperature regulation capabilities. Full article

An optimized extrusion process is desired for both an environmentally friendly and economically sustainable recycling process. The aim of this study is to simulate the melt conveying zone of a single-screw extruder when using contaminated polymers instead of commonly used pure materials, to optimize a mechanical recycling process, and to reduce the number of measurements needed for rheological input data by using mixing rules. Polypropylene (PP) is blended with a polyamide 12 (PA 12) grade and another PP grade to introduce polymer impurities into the material. The blends are subjected to extrusion experiments in a lab-scale single-screw extruder with pressure and temperature sensors along the barrel. An isothermal analytical simulation model is proposed using representative shear rate values and rheological mixing rules to calculate the pressure distribution along the screw channel throughout the melt conveying zone. The rheological input data for the simulation is taken from high-pressure capillary rheometric measurements, but also substituted with values derived from mixing rules. The results show that the application of the shear viscosity through mixing models yields simulated pressure values similar to those measured in the experiments. With the introduction of representative viscosity into the model, relative deviations of around 5% at certain screw speeds can be achieved. Full article

BJ3DP has unique advantages compared to other energy-beam-based additive manufacturing technologies, such as lower residual stress, arising from the lack of heat during the printing process and the uniformity of the sintering process. However, attaining both high density and dimensional precision in metallic materials remains a challenge in BJ3DP. This study presents a systematic investigation into the fabrication of high-melting-point pure chromium (Cr) via binder jetting 3D printing (BJ3DP), with a focus on optimizing the printing parameters and sintering conditions. An orthogonal experiment identified the optimal printing parameters as a layer thickness of 75 μm and a binder saturation of 60%, which resulted in green parts with a relative density of 57.1%—a representative value for BJ3DP processes that demonstrates effective parameter optimization. Subsequently, the green parts were sintered at 1800 °C for 9 h, resulting in a maximum density of 97.35%. The hardness of the as-sintered BJ3DP Cr parts was superior to that of samples produced by conventional levitation melting (184.20 HV vs. 171.20 HV). This work demonstrates that the no-heat printing strategy of BJ3DP effectively mitigates issues related to residual stress and cracking, providing a viable method for producing high-melting-point metallic materials. Full article

Liquid γ-TiAl alloy was prepared by vacuum induction melting within graphite crucibles, then cast using a centrifugal technique. In this process, the degree of superheat (ΔT)—defined as the temperature above the melting point—was carefully controlled, with experiments conducted at ΔT of 200 K (i.e., 200 Kelvin above the melting temperature). It was observed that carbon content in the alloy increased nonlinearly as the melt was held longer in the graphite crucible; for example, carbon concentration rose from an initial value of approximately 0.21 at% to 0.98 at% after 100 s of holding and to 2.11 at% at 650 s of holding. When the melt was held for over 100 s at ΔT = 200 K, titanium carbide (TiC) and titanium aluminum carbide (Ti₂AlC) particles formed along the crucible wall. This resulted in changes to the phase fractions and a corresponding increase in aluminum concentration in the melt. Two types of Ti₂AlC phases were observed: one consisted of coarse Ti₂AlC particles, which were crystallized through peritectic reaction from the TiC carbide and liquid phase. The other consisted of fine Ti₂AlC particles, which were decomposed from the α₂ (Ti₃Al) phase within the interlamellar regions. After 20 s of holding at ΔT = 200 K, carbon rapidly dissolved into a solid solution. Prolonged holding led to significant grain refinement: the microstructure evolved from columnar to equiaxed grains, primarily due to TiC crystallization. This transition is significant because finer, equiaxed grains can enhance mechanical properties such as strength and toughness. The findings provide valuable insight into the interaction between graphite crucibles and γ-TiAl melts, demonstrating how controlled superheat and holding time influence carbon uptake, carbide formation, and microstructural evolution—factors critical for optimizing the performance and manufacturability of γ-TiAl components. Full article

To meet the surface polishing requirements of aluminum nitride (AlN) ceramics, this study developed a multi-objective optimization experimental model based on response surface methodology (RSM), with surface roughness as the key optimization target. A systematic series of femtosecond laser polishing experiments were conducted. Polishing effectiveness and the evolution of material properties under different process parameters were comprehensively evaluated through surface morphology characterization, microhardness testing, friction and wear experiments, and energy-dispersive X-ray spectroscopy (EDS) analysis. The experimental results indicated that the optimal combination of process parameters, as determined by RSM optimization, was identified as a laser power of 17.43 W, pulse frequency of 292.29 kHz, and scanning speed of 1004.82 mm/s. Under these parameters, femtosecond laser polishing significantly reduced the surface roughness of the AlN ceramic, with the initial Ra value decreasing from 2.513 μm to 0.538 μm, a reduction of 78.57%. Compared to CO₂ laser polishing (R_a = 0.817 μm), femtosecond laser polishing demonstrated superior performance in enhancing surface quality. Analysis of the microstructural mechanisms revealed that the femtosecond laser, due to its ultra-short pulse characteristics, effectively suppressed the expansion of the heat-affected zone. It passivated surface microcracks through a photothermal ablation effect and reduced the thickness of the subsurface damage layer. Furthermore, the friction coefficient and wear rate of the polished samples decreased, indicating a significant improvement in wear resistance. On the numerical simulation front, a multi-physics model describing the interaction between the femtosecond laser and AlN ceramic was established based on the non-equilibrium two-temperature model (NTTM) coupled with solid mechanics. The key innovation of our model is the full coupling of heat transfer and solid mechanics, which allows for an accurate revelation of the material morphology evolution mechanism during femtosecond laser ablation. The model’s accuracy is confirmed by the excellent agreement with experimental results, showing relative errors of only 3.23% and 12.5% for the melt pool width and depth, respectively. Full article

Microwave fracturing and assisted mechanical breakage offer efficient and cost-effective rock excavation potential. However, these methods have not been well studied or understood for the deployment of in situ recovery (ISR) in mining, which could benefit from microwave-induced cracking to accelerate in situ leaching. This paper reports on investigations into the effects of microwaves on rock transport properties, specifically for in situ recovery applications. The research focused on microwave fragmentation of a synthetic ore with composition and particle size similar to many wet ore-bearing deposits, as well as hard lithium-bearing rock (spodumene) as a natural analogue, to assess changes in porosity and permeability after microwave treatment. The experiments involved exposing samples with varying water content to heating with different microwave energy levels, followed by examining the impact on the induced crack characteristics. All the samples were characterized by a suite of measurements before and after microwave treatment, including scanning electron microscopy (SEM), Nuclear Magnetic Resonance (NMR), nitrogen gas permeameter-porosimeter, and P-wave velocity measurements. The results showed a strong dependence of rock properties after microwave treatment on water content. At high water content (100%), NMR results showed a substantial increase in porosity, by nearly 17% and a dramatic 47-fold rise in permeability, from 0.65 mD to 311 mD. However, the treatment also caused partial melting of the sample, rendering it unsuitable for further testing, including permeability and P-wave velocity. At moderate water content (20%), permeability substantially increased (233–3404%), which was consistent with the observation of multiple cracks in SEM images. These changes led to low P-wave velocity values. This research provides crucial insights into microwave fracturing as a method for in situ recovery in mining. Full article