Experimental investigation and statistical optimisation of the selective laser melting process of a maraging steel

Selective Laser Melting (SLM) is an Additive Manufacturing process (AM) that built parts from powder using a layer-by-layer deposition technique. The control of the parameters that influence the melting and the amount of energy density involved in the process is paramount in order to get valuable parts. The objective of this paper is to perform an experimental investigation and a successive statistical optimization of the parameters of the selective laser melting process of the 18Ni300 maraging steel. The experimental investigation involved the study of the microstructure, the mechanical and surface properties of the laser maraging powder. The outcomes of experimental study demonstrated that the hardness, the mechanical strength and the surface roughness correlated positively to the part density. Parts with relative density higher than 99% had a very low porosity that presented closed and regular shaped pores. The statistical optimization determined that the best part properties were produced with the laser power bigger than 90 W and the velocity smaller than 220 mm/s

Análise do impacto do processo organosolv para pré-tratamento de biomassa lenhocelulósica na redução das emissões de gases com efeito de estufa (GEE)

CIES2020 - XVII Congresso Ibérico e XIII Congresso Ibero-americano de Energia SolarRESUMO: No âmbito do projeto H2020 AMBITION, foram desenvolvidos processos de pré-tratamento inovadores e energeticamente eficientes, a fim de serem integrados num conceito de melhoria do processamento da biomassa para a produção de correntes líquidas de açúcares e derivados de lenhina para aplicações em bioenergia e produtos de valor acrescentado. O objetivo deste trabalho consiste em analisar os impactos ambientais do pré-tratamento organosolv de biomassa (palha de trigo e resíduos de eucalipto) utilizando misturas etanol/água, a fim de avaliar a sua integração num processo multiproduto de modo a originar elevados rendimentos de açúcares e recuperar lenhina de alta qualidade num conceito de biorrefinaria. O processo foi simulado em SuperPro Designer (Intelligen Inc.) para determinar os balanços de massa e energia, bem como para desenvolver o Inventário de Ciclo de Vida (LCI). A Avaliação do Ciclo de Vida (ACV) foi realizada utilizando o software SimaPro 9.0 (PRé Consultants BV) com a base de dados Ecoinvent 3.5, sendo comparada com os processos clássicos de pré-tratamento à escala industrial (e.g. explosão com vapor). O processo organosolv com etanol e para uma razão líquido-sólido (RLS) padrão de 10, apresenta resultados em termos de emissões de GEE (numa abordagem gate-to-gate) ligeiramente superiores aos obtidos para a explosão com vapor, concluindo-se posteriormente que na tecnologia organosolv, só a redução da RLS pode conduzir a melhorias significativas em termos ambientais.ABSTRACT: Within the H2020 AMBITION project, innovative and energy efficient pre-treatment processes were developed in order to be integrated in a biomass processing improvement concept that would produce liquid streams of sugars and lignin derivatives for applications in bioenergy and added-value products. The objective of this work is to analyse the environmental impacts of organosolv pre-treatment of biomass (wheat straw and eucalyptus residues) using ethanol/water mixtures in order to assess its integration in a multi-product process to produce high sugar yields and recover high quality lignin in a biorefinery concept. The process was modelled in SuperPro Designer (Intelligen Inc.) to determine mass and energy balances as well as to develop the Life Cycle Inventory (LCI). The Life Cycle Assessment (LCA) was performed using SimaPro 9.0 software (PRé Consultants BV) with the Ecoinvent 3.5 database and compared with classical industrial scale pre-treatment processes (e.g. steam explosion). The organosolv process with ethanol with a standard liquid-to-solid ratio (LSR) of 10, presents, in terms of GHG emissions (in a gate-to-gate approach), slightly higher GHG emissions than those obtained for the steam explosion, leading to the conclusion that a reduction in the solid-liquid ratio in organosolv technology causes significant environmental improvements.info:eu-repo/semantics/publishedVersio

Innovative non-destructive thermographic evaluation of mechanical properties in dissimilar aluminium probeless friction stir spot welded (P-FSSW) joints

This study introduces a novel non-destructive methodology based on step-heating laser thermography technique to evaluate the mechanical strength of dissimilar aluminium joints produced through probeless friction stir spot welding (P-FSSW). The proposed approach enables the quantitative analysis of the thermo-mechanically stirred region, distinguishing two different morphologies (ductile and mixed) correlated with the joint’s ultimate mechanical strength. Eleven welded joints were analysed by using two of them used for calibration through thermographic tests, Chisel and scanning electron microscopy (SEM) analyses. At the same time, nine underwent tensile-shear tests were carried out to correlate thermographic parameters (A1, A2) with maximum force (Fmax). Statistical analysis revealed that the ductile area (A2) is the most significant parameter, exhibiting a robust correlation with Fmax (r = 0.81). A simplified regression model based on A2 demonstrated high reliability (adjusted R2 = 0.60). This methodology provides a significant advancement in non-destructive quality control for P-FSSW joints, paving the way for its integration into industrial applications. The developed procedure offers a reliable, contactless, and scalable solution for real-time industrial inspection of P-FSSW joints, representing a significant alternative to conventional destructive testing methods

A pragmatic continuum level model for the prediction of the onset of keyholing in laser powder bed fusion

Laser powder bed fusion (L-PBF) is a complex process involving a range of multi-scale and multi-physical phenomena. There has been much research involved in creating numerical models of this process using both high and low fidelity modelling approaches where various approximations are made. Generally, to model single lines within the process to predict melt pool geometry and mode, high fidelity computationally intensive models are used which, for industrial purposes, may not be suitable. The model proposed in this work uses a pragmatic continuum level methodology with an ablation limiting approach at the mesoscale coupled with measured thermophysical properties. This model is compared with single line experiments over a range of input parameters using a modulated yttrium fibre laser with varying power and line speeds for a fixed powder layer thickness. A good trend is found between the predicted and measured width and depth of the tracks for 316L stainless steel where the transition into keyhole mode welds was predicted within 13% of experiments. The work presented highlights that pragmatic reduced physics-based modelling can accurately capture weld geometry which could be applied to more practical based uses in the L-PBF process

Statistical modelling and optimization of nanosecond Nd:YAG Q-switched laser scarfing of carbon fiber reinforced polymer

This paper explores the effects of laser scarfing on a CFRP tape consisting of unidirectional carbon fiber with a layup of [(45/0/-45/90)4] sym with a total laminate dimension of 5.952 mm. The laser system used in the experimental investigations consisted of a nanosecond Nd: YAG laser source with an average maximum power of 20 W in a pulsed mode. The material was a with a total laminate of 5.952 mm. The laser process aims to investigate the surface modification by laser ablation. In more details, the effects of scanning speed (550 - 650 mm/s) and frequency (23 - 27 kHz) for three different scanning strategies on the scarfing depth, specimen dimensions (in x and y direction) and surface conditions were studied by full factorial experimental plan. By scarfing, the fibers were either oxidized, partially stripped, stripped and excessively stripped. After the statistical analysis, the best results in terms of surface conditions were achieved with the x-parallel laser scanning strategy, where the presence of excessively stripped fibers was not noticed. The mixed-hatching (MH) mode was the strategy that produced the worst results for the scarfing depth, which can negatively affect the ablation rate, even if it turns out to be the most stable strategy. The best results in terms of scarfing depth and x-y dimensions were achieved with MH mode, and with a scanning speed of 600 mm/s and a frequency of 27 kHz

A methodology for multi-object optimization of laser/MIG hybrid welding process

In this article a methodology for multi-object optimization of laser/MIG hybrid welding of Al-Mg alloy is proposed. For modeling and analyzing the experimental responses, the response surface methodology (RSM) and the multiple response prediction (MRP) approaches were coupled. The laser power and the process speed were the input parameters, while heat affected zone, the porosity and the lack of penetration sizes the experimental outputs. Then, the optimized solution was implemented in a validated FEM model, for quicker numerical experiments. Finally, the methodology was tested with an experiment. The presented methodology can be applied to optimize weld quality in various welding processes

Multi-objective optimization of laser milling of 5754 aluminum alloy

Laser milling is a new, very flexible process for micro-fabrication, suitable for machining difficult-to-machine materials, like ceramics, dielectrics, carbide and hardened steel with good productivity and surface. Optimal selection of process parameters is highly critical for successful material removal and achieving high surface quality. It is crucial for Laser Milling to enhance the productivity of the process in terms of maximization of the material removal rate (MRR), calculated as the ratio between the volume of removed material and the process time, saving at the same time a good surface quality, and to correlate this index to the ablation depth and to surface roughness. In contrast, laser ablation suffers from the usual incompatibility of high ablation depths and good surface quality. The objective of this paper was to demonstrate that the careful laser choice and process optimization can result in a satisfactory compromise for both. This goal was achieved with a simultaneous statistical analysis of ablation depth, material removal rate and surface roughness. Moreover, a multi-objective statistical optimization was performed for improving machining productivity and surface quality. The dependence of the ablation depth, MRR and surface roughness on the laser fluence was also analyzed. All experimental tests were conducted on the 5754 aluminum alloy using a nanosecond Nd:YAG laser with a wavelength of 1064 nm

Numerical and experimental investigation of probeless friction stir spot welding of a multilayer aluminium alloy compound

This paper presents the experimental and numerical results of the influence of dwell time (30, 60, 90 s), down force (2450, 4900, 7350 N), and rotational speed (1000, 1500, 2000 RPM) on microstructure, microhardness, and material flow during solid-state welding. Probeless friction stir spot welding (P-FSSW) with a flat tool shoulder was assisted to form a metal compound of AA2024, AA6082, and AA5754 aluminium plates with different thicknesses in lap configuration. The analysis of the experimental data and numerical results showed that down force had a significant influence on the material flow and the quality of the welds. High friction energy, and subsequent intensive material flow, promoted the vortexes formation, which improve metals mixing and grain refinements

3D Finite Element Analysis in the selective laser melting process

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