Evaluation of EDM inclusion into the conventional polishing of printed Co-Cr alloy by selective laser melting / Avaliação da inclusão de EDM no polimento convencional da liga de Co-Cr impressa por fusão seletiva a laser

Objective: The selective laser melting (SLM) technique used in manufacturing results in a rougher surface that requires more satisfying processing than conventional hand-finishing operations. The electro discharge machine (EDM) has various possibilities in the adjustment of surfaces. The present study assesses whether the participation of the EDM technique with the conventional finishing and polishing methods enables surface improvement for the Cobalt-Chromium alloy fabricated by SLM. Material and Methods: Twenty discs of cobalt chromium alloy were fabricated by SLM, divided equally into two groups: (TF) control group for finishing and polishing in the conventional method in accordance with the manufacturer's recommendations; and (EF) group for conducting polishing incorporating the EDM method. Results: The EF group recorded the lowest mean value of surface roughness and the highest mean value of micro hardness compared to the TF group. Furthermore, statistically significant differences (P < 0.05) were found for surface roughness as well as micro hardness. Conclusion: Reliance of the electric discharge machine proactively within finishing and polishing procedures promotes competence in the conventional polishing method and improves the surface properties of cobalt chromium alloy printed by SLM technology (AU)

Objetivo: A técnica de fusão a laser seletiva (SLM) usada na fabricação resulta em uma superfície mais rugosa a qual requer um processamento mais satisfatório do que o acabamento manual. A máquina de eletro descarga (EDM) possui várias possibilidades no ajuste de superfícies. O presente estudo avalia se a participação da técnica EDM associada aos métodos convencionais de acabamento e polimento possibilita a melhora da superfície da liga Cobalto-Cromo fabricada através da SLM. Material e Métodos: Vinte discos de liga de cromo-cobalto foram confeccionados por SLM, e divididos igualmente em dois grupos: (TF) grupo controle, realizado acabamento e polimento pelo método convencional de acordo com as recomendações do fabricante; e (EF) grupo do polimento associado ao método EDM. Resultados: O grupo EF registrou o menor valor médio de rugosidade superficial e o maior valor médio de microdureza em relação ao grupo TF. Além disso, diferenças estatisticamente significativas (P < 0,05) foram encontradas para rugosidade superficial, assim como para a microdureza. Conclusão: A confiança na máquina de descarga elétrica proativamente nos procedimentos de acabamento e polimento promove a competência no método de polimento convencional e melhora as propriedades de superfície da liga de cromo-cobalto impressa pela tecnologia SLM(AU)

Corrosion Resistance Measurement of 316L Stainless Steel Manufactured by Selective Laser Melting.

Selective laser melting (SLM) technology is ushering in a new era of advanced industrial production of metal components. It is of great importance to understand the relationship between the surface features and electrochemical properties of manufactured parts. This work studied the influence of surface orientation on the corrosion resistance of 316L stainless-steel (SS) components manufactured with SLM. The corrosion resistance of the samples was measured using linear polarization resistance (LPR) and electromechanical noise (EN) techniques under three different environments, H2O, 3.5 wt.% NaCl, and 20% H2SO4, analyzing the horizontal (XY) and vertical (XZ) planes. The microstructure and morphology of the samples were obtained by optical (OM) and scanning electron microscopy (SEM). The obtained microstructure showed the grains growing up from the fusion line to the melt pool center and, via SEM-EDS, the presence of irregular and spherical pores was observed. The highest corrosion rate was identified in the H2SO4 solution in the XZ plane with 2.4 × 10-2 mm/year and the XY plane with 1.31 × 10-3 mm/year. The EN technique along with the skewness factor were used to determine the type of corrosion that the material developed. Localized corrosion was observed in the NaCl electrolyte, for the XY and XZ planes (-1.65 and -0.012 skewness factors, respectively), attacking mainly the subgrains of the microstructure and, in some cases, the pores, caused by Cl ions. H2O and H2SO4 solutions presented a uniform corrosion mechanism for the two observed orientations. The morphology identified by SEM was correlated with the results obtained from the electrochemical techniques.

Enhanced Mathematical Model for Producing Highly Dense Metallic Components through Selective Laser Melting.

In this work, a previously developed mathematical model to predict bulk density of SLMed (produced via Selective Laser Melting) component is enhanced by taking laser power, scanning speed, hatch spacing, powder's thermal conductivity and specific heat capacity as independent variables. Experimental data and manufacturing conditions for the selective laser melting (SLM) of metallic materials (which include aluminum, steel, titanium, copper, tungsten and nickel alloys) are adapted from the literature and used to evaluate the validity of the proposed enhanced model. A strong relation between dependent and independent dimensionless products is observed throughout the studied materials. The proposed enhanced mathematical model shows to be highly accurate since the computed root-mean-square-error values (RMSE) does not exceed 5 × 10-7. Furthermore, an analytical expression for the prediction of bulk density of SLMed components was developed. From this, an expression for determining the needed scanning speed, with respect to laser power, to achieve highly dense components produced via SLM, is derived.

A Mathematical Dimensional Model for Predicting Bulk Density of Inconel 718 Parts Produced by Selective Laser Melting.

In this work, dimensional analysis is used to develop a general mathematical model to predict bulk density of SLMed components taking volumetric energy density, scanning speed, powder's thermal conductivity, specific heat capacity, and average grain diameter as independent variables. Strong relation between dependent and independent dimensionless products is observed. Inconel 718 samples were additively manufactured and a particular expression, in the form of a power-law polynomial, for its bulk density, in the working domain of the independent dimensionless product, was obtained. It is found that with longer laser exposure time, and lower scanning speed, better densification is attained. Likewise, volumetric energy density has a positive influence on bulk density. The negative effect of laser power in bulk density is attributed to improper process conditions leading to powder particle sublimation and ejection. A maximum error percentage between experimental and predicted bulk density of 3.7119% is achieved, which corroborates the accuracy of our proposed model. A general expression for determining the scanning speed, with respect to laser power, needed to achieve highly dense components, was derived. The model's applicability was further validated considering SLMed samples produced by AlSi10Mg and Ti6Al4V alloys. This article elucidates how to tune relevant manufacturing parameters to produce highly dense SLM parts using mathematical expressions derived from Buckingham's π- theorem.

Laser-Assisted Synthesis of Cu-Al-Ni Shape Memory Alloys: Effect of Inert Gas Pressure and Ni Content.

The paper explores the applicability of laser-assisted synthesis for producing high density Cu-Al-Ni alloys with shape memory characteristics, that could be further developed towards a method of additive manufacturing of large size Cu-based shape memory alloys (SMA). The manufacturing approach consists in laser melting of elemental powder mixture in a controlled atmosphere of varying relative pressure of protective argon gas, producing alloys of 14.2 wt.% Al and Ni content varying between 2 and 4 wt.%. All the fabricated alloys are found to have attained martensitic microstructures capable of SMA specific phase transformations in the temperature range from 85 to 192 °C. Both gas pressure and content of Ni are found to affect the specific transformation temperatures, transformation enthalpies, and mechanical properties. In particular, increasing gas pressure suppresses the austenite to martensite transformation reducing microhardness. In conclusion, the selective laser melting (SLM) employed in this work is shown capable of producing high density Cu-Al-Ni SMA (porosity ≈ 2%).

Anatomical reproducibility through 3D printing in cranio-maxillo-facial defects / Reproducibilidad anatómica a través de impresión 3d en defectos cranio-maxilo-faciales

The planning and 3D reconstruction in craniofacial defects based on anatomical principles of symmetry and passive adaptation has evolved radically the past few years. This article recounts the possibility to develop personalized and extensive craniofacial implants. We present a case of a patient with a 10-year trauma sequel evolution; the patient lost the right frontal bone, supraorbital wall and part of the temporal fossa. From the computerized tomography, and by using Materialise software (3-Matic and Mimics). Subsequently, the printing was performed using the virtual planning with a laser printer in titanium where the piece was elaborated with the determined specifications in the planning; surgery was performed without complications in which the implant was placed via a coronal approach, which did not require any type of adaptation. After a two-year follow-up we observed a correct position, symmetry, absence of infection or any other alteration. It is concluded that the planning and 3D printing are suitable to perform craniofacial reconstructions with a low morbidity, shorter surgical time, and with an adequate facial symmetry and aesthetic return.

La planificación y reconstrucción 3D en defectos craneofaciales se basa en principios anatómicos de simetría y pasividad en la adaptación, evolucionando rápidamente en los últimos años. El presente articulo presenta la posibilidad de rehabilitación de un paciente con trauma importante gracias a un implante craneofacial extenso. Se presenta el caso de un sujeto con evolución de 10 años de una secuela de trauma, donde perdió el hueso frontal, pared supraorbitaria y parte de la fosa temporal. A partir de una tomografía computadorizada, utilizando un software de planificación Materialise (3-Matic and Mimics) se construyó un modelo virtual a través de un implante de pieza única para cubrir íntegramente el defecto; se planificó la posición junto a la cantidad y longitud de tornillos a utilizar. A continuación se realizó la impresión de la pieza mediante una impresora laser de titanio donde la pieza fue construida según las especificaciones de la planificación; la cirugía fue realizada sin complicaciones en el cual el implante fue instalado a través de un acceso coronal sin necesidad de ningún tipo de adaptación. Después de dos años de seguimiento se observa una posición correcta, simétrica y en ausencia de infecciones u otro tipo de alteración. Se concluye que la planificación e impresión 3D es viable de realizar en reconstrucción craneofacial con baja morbilidad, disminución del tiempo quirúrgico, obteniendo una adecuada simetría y estética facial.