Reduction of distortions in large aluminium parts by controlling machining-induced residual stresses

Large aluminium monolithic parts used in the aeronautic industry frequently show significant geometric distortions after the machining process. These distortions are the consequence of the initial residual stresses of the raw material as well as machining-induced residual stresses. Therefore, to minimise distortions, it is fundamental to understand the effect of the different parameters of the manufacturing process and define the optimum manufacturing strategy. This work studies the effect of initial residual stresses of aluminium plates and the residual stresses generated by the machining process on the final geometric distortions of the part. First, 7175-T7351 aluminium bars (40 mm wide × 38 mm thick × 400 mm long) were face milled at two different cutting conditions reducing the thickness to 6 mm. The distortions were measured in a coordinate measuring machine. The results revealed that the machining strategy significantly influenced the distortions, as a difference of 65% on distortions was found between the two cutting conditions. In addition, an FEM model to predict distortions was developed. This model considers initial residual stresses (measured by the contour method) and residual stresses induced by the machining process (measured by the hole drilling technique). Once the FEM model was validated, the study was extended to more complex geometries. These new studies revealed that final distortions are sensitive to machining-induced residual stresses. Furthermore, this finding indicates that it is possible to define machining conditions which generate desirable residual stress profiles to minimise part distortion

Mattin & Anthony Iles (ed.), Noise & Capitalism

Noise & Capitalism n’est pas un livre académique. Édité par Arteleku Audiolab , il ressemble plutôt à un projet artistique réunissant les contributions de différentes personnes . Le premier directeur de l’ouvrage, Mattin (http://mattin.org), est un artiste basque qui analyse les enjeux sociaux et économiques de la musique à partir d’un travail sur l’improvisation et le bruit. Le deuxième, Anthony Iles, est à la fois écrivain et éditeur londonien de projets comme la revue Mute (http://metamuge..

Iskiosural zaintiratu lesioen prebentzioa gizonezkoen futbolean

35 p. : il.-- Bibliogr.: p. 33-35Kirol munduan, orokorrean, lesio muskularrak ematea oso ohikoa izaten da, izan ere, kirolek, bere baitan, lehiaketa dute eta bertan azaltzen diren eskakizun fisikoak oso altuak izaten dira. Beraz, ildo beretik jarraituz, ez da harritzekoa, futbolean ere mota honetako lesioak azaltzea, jakina denez, batez ere partiduetan ematen diren eskakizunak, altuak izaten direlako (abiadura handiko korrikaldiak, esprintak, jauziak, noranzko aldaketak etab.). Hau esanda, futbolean agertzen den ohiko lesio muskular bat, iskiosural zaintiratu lesioa da, gehienetan, abiadura handiko korrikaldietan zehar gertatzen dena. Gai honekin lotuta, esan beharra dago, zorionez edo zoritxarrez, esperientzia maila nahiko altua daukadala, izan ere, azken denboraldietan asko jasan behar izan dut lesio mota hau. Azken hau da, hain juxtu, lan hau egiteko interes eta motibazio handiena, hainbestetan jasandako lesioaren arrazoia, jatorria edo zergatia zein den aurkitzeko jakinmin ikaragarria sortu didana. Hori dela eta, lan honen helburu nagusia, azken ikerketek iskiosural zaintiratu lesioaren inguruan errebisio bat egitea da, adierazten duten informazioa bilduz eta, horri esker, lesio honetan eragina duten faktore ezberdinak ezagutzeko eta aztertzeko. Behin hau eginda, bigarren helburu modura, lesio honen prebentzioan zentratutako indar entrenamendu baten proposamen teorikoa egitea izango da, aldez aurretik aipatutako faktoreak kontutan izanda

Función de la musculatura isquiosural durante la carrera a alta velocidad: revisión sistemática

49 p. -- Bibliogr.: p. 32-40Contexto: las lesiones musculares, y concretamente, la lesión por distensión isquiosural es la lesión por no-contacto más común en la mayoría de deportes en los que existe una gran demanda de carreras a alta velocidad. No obstante, a pesar de ser una lesión tan habitual entre estos deportistas, el mecanismo lesivo no está claramente definido. Objetivos: el objetivo principal de este estudio es examinar cuáles son las demandas específicas de los músculos isquiosurales durante la carrera a alta velocidad o sprint, para después analizar qué factores afectan a estas demandas, para tener una visión más completa de la lesión. Diseño: se llevó a cabo una revisión sistemática siguiendo la declaración PRISMA. Se realizó una búsqueda sistemática utilizando las bases de datos PubMed, Scopus y ScienceDirect, el martes, 18 de mayo de 2021. Después de una primera búsqueda general, se utilizaron las palabras clave junto con los operadores booleanos para seleccionar los estudios que cumplieran los criterios de elegibilidad basados en las preguntas PICOS. Los estudios incluidos cumplían los siguientes criterios de inclusión: (a) participantes mayores de 18 años, (b) análisis del mecanismo lesivo durante la carrera a alta velocidad o factores que influyen, (c) estudios descriptivos o de cohorte, (d) escritos en inglés, y (e) estudios publicados a partir del año 2000. Resultados: de 465 estudios iniciales se seleccionaron 14 para su inclusión en la revisión. Según los resultados, en cuanto al mecanismo lesivo, la gran mayoría de los estudios indican que el grupo isquiosural se encuentra bajo una gran demanda tanto en la fase final del swing como en la fase temprana de apoyo, en los dos casos mostrando picos de fuerza, para realizar una gran extensión de cadera y flexión de rodilla, aunque se cree que es más exigente el primero (swing), ya que se alcanzan longitudes músculo-tendinosas superiores y ejecutan trabajo negativo (contracción excéntrica). Sin embargo, a causa de diversos factores como el aumento de la velocidad, inclinación anterior del tronco, alteraciones lumbo-pélvicas, y las lesiones previas, estas mecánicas pueden verse modificadas e incrementar el riesgo de sufrir una lesión isquiosural. Conclusiones: los músculos isquiosurales se encuentran bajo una gran demanda mayormente durante dos momentos de la carrera a alta velocidad, que son la fase final del swing y la fase temprana de apoyo, siendo estos los puntos críticos en los que aumenta el riesgo de lesión. No obstante, es necesario considerar que una gran cantidad de factores influyen en la lesión isquiosural afectando directamente su función

A comparative study of residual stress profiles on Inconel 718 induced by dry face turning

Residual stress profiles induced by different dry face turning conditions are compared employing X-ray diffraction method, Hole-Drilling method and Finite Element Modelling. It is well known that the surface integrity condition has a great influence on the machined parts fatigue life, specially the residual stress profile. This issue is important when machining aeronautical critical parts, even more due to the difficulty of machining of nickel based superalloys, such as Inconel 718. This research work is focused on the identification of the residual stress profile uncertainty of experimental and numerical measurements. For this proposal, several measurements were carried out on a set of Inconel 718 samples machined with different conditions of cutting speed and feed rate under dry conditions. Although residual stress profiles are similar, differences are found between the three measurement techniques used in this study

Surface Integrity When Machining Inconel 718 Using Conventional Lubrication and Carbon Dioxide Coolant

Surface integrity induced by machining process affects strongly the performance of functional products, for instance, the fatigue life as well as the resistance to stress corrosion cracking. Consequently, it is relevant to evaluate the induced properties on and beneath the machined surface to ensure the good performance of the mechanical components while operating under either static or cyclic loads. Furthermore, this is even more important when designing critical components that withstand high loads at high temperatures. In this context, many studies have been carried out in order to characterize the surface integrity (residual stresses, surface roughness, micro-hardness of the affected layer) when machining Inconel 718. However, so far, the cryogenic effect on surface integrity of Inconel 718 is not well established although some preliminary works have already been developed. Therefore, this work aimed to point out the performance of cryogenic machining using the carbon dioxide CO2 as a cryogenic cutting fluid, considering as a reference the conventional lubrication. A comparative study has been carried out during turning operations of Inconel 718 using the same cutting parameters and the same tool geometry. Microhardness measurements showed that the CO2 condition induced higher strain hardening near the surface while conventional condition did not generate notable difference compared to the bulk material microhardness. With respect to residual stresses, results showed that conventional lubrication generated higher tensile residual stress near the surface along the cutting direction when using new tools. As for CO2 cryogenic condition, lower tensile residual stresses have been obtained near the surface. In addition, CO2 condition induced the largest compressive peak when using new and semi−worn tools in comparison with conventional lubrication

Unraveling the role of the thermal and laser impacts on the blackening of cinnabar in the mural paintings of Pompeii

The blackening of red cinnabar (α-HgS) pigment has traditionally been explained by its conversion into black metacinnabar (β-HgS). Scarce is however the scientific evidence that supports this hypothesis in polychrome artworks. As such transition occurs at around 345 °C, the thermal impact of the eruption of Mount Vesuvius in 79 AD could have induced this structural change of the pigment present in the mural paintings of Pompeii. This work aims to assess whether the mentioned volcanic eruption could be responsible of the cinnabar blackening through the formation of metacinnabar. The thermodiffractometry study of cinnabar-decorated fresco mock-ups stated that the formed β-HgS is not stable, observing its reversion into α-HgS. Moreover, sublimation of the cinnabar pictorial layer was registered, also when the cinnabar paint layer was protected by a coating of pyroclastic materials. In real blackened cinnabar Pompeian samples, it was not possible to identify metacinnabar by X-ray diffraction (XRD), but evidence of sublimation of mercury due to the thermal impact was observed. Hence, this blackening seems to be related mainly to the presence of calomel (Hg2Cl2) and a gypsum (CaSO4·2H2O) crust as degradation products of red cinnabar and the calcite mortar, respectively, and not to the formation of metacinnabar. Finally, laser-based techniques could also induce modifications in the HgS crystalline structure, resulting in an amorphous black product. Therefore, the elemental and molecular study of the species promoted by laser impact was carried out to avoid false positives in the metacinnabar detection or when the decorated surface has been subjected to laser cleaning.The research leading to these results has received funding from “la Caixa” Foundation (Silvia Pérez-Diez, ID 100010434, Fellowship code LCF/BQ/ES18/11670017). This work has been supported by the project IT1446-22 for Consolidated Research Groups, funded by the Basque Country Government. The authors acknowledge as well the funding provided by University of the Basque Country through the Institutionally Sponsored Open Access

Effect of innovative finishing operations on the tribological performance of steel 27MnCr5

Transmission shafts used in the automotive sector must have a good tribological performance, and therefore an enhanced surface integrity. This paper aims to study the effect of eco-friendly innovative finishing operations (belt finishing, cryogenic grinding and dry grinding) on the surface integrity and tribological performance of steel grade 27MnCr5, and compare to the behavior of components produced by conventional wet grinding process. For that purpose, a total of seven finishing conditions were analysed: wet grinding as reference, two dry grinding conditions, two cryogenic grinding conditions and two hard turning+belt finishing conditions. The surface integrity (roughness, residual stresses, hardness and microstructural defects) of samples was assessed. Finally, the step-loading test method was used to determine the scuffing resistance of the samples. Tested innovative finishing operations led to higher scuffing resistance than conventional wet grinding. Results demonstrate that higher surface hardness and roughness leads to higher scuffing resistance, while the effect of surface residual stresses is not significant

Influence of cryogenic grinding surface on fatigue performance of carburised 27MnCr5

Automotive transmission components are subjected to cyclic loads and, thus, must have a reliable fatigue performance. Since fatigue cracks nucleate at the surface, it is necessary to guarantee that its surface integrity accomplishes the required specifications. Typically, those components are finished by wet grinding after carburising heat treatment. However, there is an increasing demand to reduce pollutants and hazardous lubricants in the industry, and eco-friendly finishing operations have been highly encouraged. To this end, it is necessary to understand the effect of these novel finishing processes on surface integrity and, consequently, on fatigue behaviour. This study aims to assess the surface integrity and the fatigue performance of cryo-ground surfaces of 27MnCr5 steel, extensively used in fabricating shafts and gears for gearboxes. Fatigue specimens for pure torsion tests were initially case-hardened and afterwards finished using two different cryogenic grinding conditions applying liquid N2 and, as a reference, using the conventional wet grinding process. First, the surface integrity was analysed in terms of texture, residual stresses, microstructure, and microhardness. Second, the batches of specimens were tested under pure torsion fatigue. Surface residual stress relaxation was also measured during fatigue tests. Finally, fracture surfaces were observed to identify crack initiation sites and establish correlations with the surface integrity. Specimens produced by cryogenic and conventional wet grinding did not show microstructural defects or hardness reductions in the carburised layer. All conditions induced compressive residual stresses, and they barely relaxed during fatigue tests. Compressive residual stresses induced by cryogenic grinding were 10–20% lower than those generated by conventional wet grinding. This decrease resulted in a minor reduction of the fatigue resistance (4–6%) compared to the wet grinding. Importantly, this study demonstrates that with a slight geometrical radio correction in the design of the mechanical components (around 2.2%), cryogenic grinding generates pieces with the same fatigue strength as conventional grinding. Therefore, it confirms that cryogenic cooling could be a potential solution to replace pollutant coolant/lubricant fluid in grinding operations

Experimental evaluation and surface integrity analysis of cryogenic coolants approaches in the cylindrical plunge grinding

Replacement of pollutant fuids with eco-friendly strategies in machining operations signifcantly contributes to protecting the environment, diminishing global warming, and ensuring a healthier workplace for employees. This study compares cryogenic coolants with conventional coolants in cylindrical plunge grinding using a Cubic Boron Nitride (CBN) wheel. Samples of 27MnCr5 steel used in the manufacture of automotive transmission components were ground using (i) Liquid Nitrogen (LN2), (ii) a combination of LN2 +Minimum Quantity Lubrication (MQL), and (iii) a conventional coolant. The efects of the diferent cooling methods on the surface integrity of the ground surfaces were examined in terms of surface roughness, microstructural defects, microhardness profles, and residual stresses. In general, surface roughness was similar for the tested cooling systems, even after grinding three subsequent surfaces in which the process stability was analyzed. Interestingly, the use of eco-friendly cryogenic systems induced fewer microstructural defects than conventional systems, and particularly, LN2+MQL lead to more compressive surface residual stresses that would improve the in-service performance of components. These results show opportunities for replacing conventional pollutant systems with eco-friendly cryogenic strategies for refrigerating/lubricating grinding processes to reduce harmful efects on the environment and pose health risks to operators