Modeling of Drag Finishing: Influence of Abrasive Media Shape

Drag finishing is a widely used superfinishing technique in the industry to polish parts under the action of abrasive media combined with an active surrounding liquid. However, the understanding of this process is not complete. It is known that pyramidal abrasive media are more prone to rapidly improving the surface roughness compared to spherical ones. Thus, this paper aims to model how the shape of abrasive media (spherical vs. pyramidal) influences the material removal mechanisms at the interface. An Arbitrary Lagrangian–Eulerian model of drag finishing is proposed with the purpose of estimating the mechanical loadings (normal stress, shear stress) induced by both abrasive media at the interface. The rheological behavior of both abrasive slurries (media and liquid) has been characterized by means of a Casagrande direct shear test. In parallel, experimental drag finishing tests were carried out with both media to quantify the drag forces. The correlation between the numerical and experimental drag forces highlights that the abrasive media with a pyramidal shape exhibits a higher shear resistance, and this is responsible for inducing higher mechanical loadings on the surfaces and, through this, for a faster decrease of the surface roughness

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

Determination of emissivity and temperature of tool rake face when cutting AISI 4140

A method for measuring tool temperature in the tool/chip contact zone of the rake face of a tool during dry orthogonal cutting using thermography is presented. This method used a new calibration method that combined with a standard camera calibration allows to estimate surface emissivity. The effect of material deposition and tool oxidation on the emissivity is analyzed. These techniques effectively showed thermal field on the rake face when machining AISI 4140

In-SEM micro-machining reveals the origins of the size effect in the cutting energy

High-precision metal cutting is increasingly relevant in advanced applications. Such precision normally requires a cutting feed in the micron or even sub-micron dimension scale, which raises questions about applicability of concepts developed in industrial scale machining. To address this challenge, we have developed a device to perform linear cutting with force measurement in the vacuum chamber of an electron microscope, which has been utilised to study the cutting process down to 200 nm of the feed and the tool tip radius. The machining experiments carried out in-operando in SEM have shown that the main classical deformation zones of metal cutting: primary, secondary and tertiary shear zones—were preserved even at sub-micron feeds. In-operando observations and subsequent structural analysis in FIB/SEM revealed a number of microstructural peculiarities, such as: a substantial cutting force related to the development of the primary shear zone; dependence of the ternary shear zone thickness on the underlaying grain crystal orientation. Measurement of the cutting forces at deep submicron feeds and cutting tool apex radii has been exploited to discriminate different sources for the size effect on the cutting energy (dependence of the energy on the feed and tool radius). It was observed that typical industrial values of feed and tool radius imposes a size effect determined primarily by geometrical factors, while in a sub-micrometre feed range the contribution of the strain hardening in the primary share zone becomes relevant

A Coupled Eulerian Lagrangian Model to Predict Fundamental Process Variables and Wear Rate on Ferrite-pearlite Steels

A coupled Eulerian-Lagrangian Finite Element model of the orthogonal cutting process was developed to predict the influence that ferritepearlite steel variants have on fundamental process variables and tool wear. As a case study, this paper is focused on two different ferritepearlite inclusion free alloys, where mainly the influence of ferrite-pearlite ratio was tested. Flow stress behavior based on dynamic compression tests and thermal properties function of temperature were characterized for model input parameters. The numerical model is compared with orthogonal cutting tests where the cutting and feed forces, tool temperature, chip morphology and tool wear related variables were measured. Globally, predicted tendencies match with experiments in forces and temperatures. Widest differences on predictions were found for chip thickness and tool-chip contact length. Predicted wear rates are in accordance to experimentally measured values

Innovative Method dedicated to the development of a ferrite-pearlite grade regarding its MAChinability (IMMAC): final report

Ferrite-pearlite (FP) steels are the most common material for engineering and automotive industries (gear box parts, crankshaft, connecting rods, injection parts…). Without any extensive research, considering the different morphology of ferrite-perlite possible to achieve, it may be assumed that the machining performances are highly dependent on the FP parameters. Nevertheless, even now, we observe larger tolerances on requirements specification on FP steels which cause variability on microstructure morphology not always perceptible with standard metallurgical characterizations. In some case, the technical specification causes complex customer complaints between steelmakers and their customers: the microstructure seems as expected but unacceptable variability in machinability is observed. IMMAC project aims to develop a numerical method to predict the machining performances of designed FP steels depending on their microstructural parameters; and to use this method as a flexible steel development strategy to better design the machinability-improved grades tailored according to the part and its machining range. Three cutting technologies were studied: turning, drilling and broaching. The figure below shows a scheme of the research approach with proposed work packages (WP) interrelation. D0, D1 and D2 are main deliverables of the project

Effect of Post-Processing Treatment on Fatigue Performance of Ti6Al4V Alloy Manufactured by Laser Powder Bed Fusion

Fatigue properties of parts are of particular concern for safety-critical structures. It is well-known that discontinuities in shape or non-uniformities in materials are frequently a potential nucleus of fatigue failure. This is especially crucial for the Ti6Al4V alloy, which presents high susceptibility to the notch effect. This study investigates how post-processing treatments affect the mechanical performance of Ti6Al4V samples manufactured by laser powder bed fusion technology. All the fatigue samples were subjected to a HIP cycle and post-processed by machining and using combinations of alternative mechanical and electrochemical surface treatments. The relationship between surface properties such as roughness, topography and residual stresses with fatigue performance was assessed. Compressive residual stresses were introduced in all surface-treated samples, and after tribofinishing, roughness was reduced to 0.31 ± 0.10 µm, which was found to be the most critical factor. Fractures occurred on the surface as HIP removed critical internal defects. The irregularities found in the form of cavities or pits were stress concentrators that initiated cracks. It was concluded that machined surfaces presented a fatigue behavior comparable to wrought material, offering a fatigue limit superior to 450 MPa. Additionally, alternative surface treatments showed a fatigue behavior equivalent to the casting material.This research was funded by the Departamento de Desarrollo Económico, Sostenibilidad y Medio Ambiente of the Basque Government (ELKARTEK 2022 KK-2022/00070), by the Departamento de Desarrollo Económico y Competitividad of the Basque Government (ELKARTEK 2019 KK-2019/00077) and by the European Union (project TIFAN, JTI-CS-2013-1-ECO-01-066)

Corrigendum to “Mechanical characterization and modelling of Inconel 718 material behavior for machining process assessment” [Mater. Sci. Eng. A 682 (2017) 441–453]

Corrigendum to “Mechanical characterization and modelling of Inconel 718 material behavior for machining process assessment” [Mater. Sci. Eng. A 682 (2017) 441–453

Measurement of plastic strain and plastic strain rate during orthogonal cutting for Ti-6Al-4V

Finite Element Modelling used to predict machining outcomes needs to be supplied with the appropriate material thermomechanical properties which are obtained by specific testing devices and methodologies. However, these tests are usually not representative of the extreme conditions achieved in machining processes and the obtained material law may not be suitable enough. Inverse identification could address this problem by obtaining material thermomechanical properties directly from machining outcomes such as cutting forces, temperatures, strain or strain rates. Nevertheless, this technique needs to be supplied with accurate machining outcomes. However, some of them such as strain or strain rate are difficult to be properly measured. The aim of this paper is to present a methodology to measure plastic strain and strain rate during orthogonal machining under plane strain conditions. The main idea is to create a physical microgrid in a workpiece and to analyze the distortion suffered by this grid. The novelty of the method consists on its capability of measuring strain and strain rate fields in a very localized area (primary shear zone) using a single image. The methodology was applied in orthogonal cutting of Ti-6Al-4V under cutting conditions that are representative of the broaching process. Experimental results were compared with DIC measurements, analytical results based on unequal division shear zone model, literature results and with numerical fields obtained from an AdvantEdge-2D model

Mechanical and electrical properties of additively manufactured copper

Additive Manufacturing (AM) has become the new paradigm of design and production strategies. While structural and functional materials are the most implemented ones, it is also possible to manufacture parts using precious metals, being copper one of the most interesting. Among AM technologies, the novel Atomic Diffusion Additive Manufacturing (ADAM) hasrecently included this material between available ones. ADAM is free from thermal and energetic issues caused by high reflectivity and conductivity of copper which other AM encounter. Therefore, it could be a great alternative to manufacture pure copper. In this work ADAM was used to fabricate pure copper specimens in order to measure electrical and mechanical properties. The influence of a machining post processes in strength and ductility is also discussed. Results are compared with wrought C1 1000 copper and published results of other AM technologies. Despite the newness of ADAM, significant improvement in surface roughness and comparable results in other properties was observed. However, further research shall be done to optimize the manufacturing parameters in order to increase the relative density value, as it was found to be significantly lower than in other AM technologies