Microstructural evolution of Ti6Al4V in ultrasonically assisted cutting: numerical modelling and experimental analysis

This paper aims to elucidate the effect of ultrasonically assisted cutting (UAC) on microstructure in a machined surface and a chip of Ti6Al4V alloy. To investigate microstructural evolution, a FE-based cutting model with an enhanced material formulation and temperature dependent material properties was developed. A Johnson-Mehl-Avrami-Kolmogorov (JMAK) model for the Ti6Al4V alloy was employed to simulate dynamic recrystallization and predict a resultant grain size. Due to a specific thermomechanical load in UAC, the distributions of strains, strain rates and temperatures in a workpiece in the machining process were investigated. In this study, five points under the machined surface and ten points under the unmachined one were tracked to compare the evolution of a grain size and its average magnitude in the alloy subjected to conventional cutting (CC) and UAC. Besides of numerical modelling and experimental studies for the resultant grain size were compared and additional validation using microhardness measurements were conducted. The results showed that the average grain size of the machined surface and the chip in case of UAC was larger and more uniform than that in case of CC. The study also presents discussions about the effect of a vibration amplitude, a feed rate and a cutting speed on the average grain size in machining of Ti6Al4V. The comparison between CC and UAC indicates that the change in average grain size in UAC was smaller than that in CC, thus demonstrating a lower level of damage in UAC

Improved analytical prediction of chip formation in orthogonal cutting of titanium alloy Ti6Al4V

The aim of this paper is to propose an analytical model of chip formation for precise prediction of orthogonal cutting of Ti6Al4V. This alloy is used broadly in aerospace components; hence, prediction of thermomechanical parameters of its orthogonal cutting is crucial for various industrial applications. The suggested analytical model needs only cutting parameters and tool geometry as input; it can predict not only cutting forces but also main features of a primary shear zone and a tool-chip interface. A non-equidistant shear zone model is employed to calculate shear strains and a shear strain rate in the primary shear zone, and a simplified heat-transfer equation is used for temperature. A Calamaz-modified Johnson-Cook material model that accounting for flow softening at high strains and temperature-dependent flow softening is applied to assess shear stresses in the primary shear zone. In addition, a shear-angle solution is modified for Ti6Al4V. At the tool-chip interface, a contact length, equivalent strain and an average temperature rise are defined. Besides, the effect of sliding and apparent friction coefficients is investigated. For a sawtooth chip produced in the cutting process of Ti6Al4V, the segmented-chip formation is analysed. A chip-segmentation frequency and other parameters of the sawtooth chip are also obtained. The predicted results are compared with experimental data with the cutting forces, tool-chip contact length, shear angle and chip-segmentation frequency calculated with the developed analytical model showing a good agreement with the experiments. Thus, this analytical model can elucidate the mechanism of the orthogonal cutting process of Ti6Al4V including predictive capability of continuous and segmented chip formation

Enhanced machinability of SiC-reinforced metal-matrix composite with hybrid turning

Particle-reinforced metal-matrix composites are promising engineering materials thanks to their superior mechanical and thermal properties. However, their poor machinability is a deterrent for use in wider applications, due to the presence of hard ceramic particles, which results in rapid tool wear during machining. Ultrasonically assisted turning (UAT) is a hybrid machining technique, in which the cutting tool is made to vibrate at high frequencies and low amplitudes. In this study, the machinability and tool wear of machining SiCp/Al metal matrix-composite was compared for dry UAT and conventional turning with the use of a cemented carbide (WC) and a polycrystalline diamond (PCD) tool. With the use of ultrasonic assistance, a significant reduction in cutting forces was achieved with a slight increase in cutting temperature. Continuous and semi-continuous chips were obtained in UAT, with better surface topography. A chip-formation mechanism in UAT show increased ductility of the workpiece material when subjected to a repeated high-frequency microchipping process. Abrasive and adhesive wear occurred on the WC tool in both conventional turning and UAT. However, the machined surface obtained in UAT with a WC tool was comparable and sometimes even better than that achieved with the PCD too

Improvements of machinability of aerospace-grade Inconel alloys with ultrasonically assisted hybrid machining

Aerospace-grade Ni-based alloys such as Inconel 718 and 625 are widely used in the airspace industry thanks to their excellent mechanical properties at high temperatures. However, these materials are classified as ‘difficult-to-machine’ because of their high shear strength, low thermal conductivity, tendency to work-harden and presence of carbide particles in their microstructure, which lead to rapid tool wear. Machining-induced residual stresses in a machined part is an important parameter which is assessed since it can be used to evaluate overall structural resilience of the component and its propensity to fatigue failure in-service. Ultrasonically assisted turning (UAT) is a hybrid machining technique, in which tool-workpiece contact conditions are altered by imposing ultrasonic vibration (typical frequency ~ 20 kHz) on a tool’s movement in a cutting process. Several studies demonstrated successfully the resulting improvements in cutting forces and surface topography. However, a thorough study of UAT-induced residual stresses is missing. In this study, experimental results are presented for machining Inconel 718 and 625 using both conventional turning (CT) and UAT with different machining parameters to investigate the effect on cutting forces, surface roughness and residual stresses in the machined parts. The study indicates that UAT leads to significant cutting force reductions and improved surface roughness in comparison to CT for cutting speeds below a critical level. The residual stresses in machined workpiece show that UAT generates more compressive stresses when compared to those in CT. Thus, UAT demonstrates an overall improvement in machinability of Inconel alloys

Enhanced machinability of SiC-reinforced metal-matrix composite with hybrid turning

Particle-reinforced metal-matrix composites are promising engineering materials thanks to their superior mechanical and thermal properties. However, their poor machinability is a deterrent for use in wider applications, due to the presence of hard ceramic particles, which results in rapid tool wear during machining. Ultrasonically assisted turning (UAT) is a hybrid machining technique, in which the cutting tool is made to vibrate at high frequencies and low amplitudes. In this study, the machinability and tool wear of machining SiCp/Al metal matrix-composite was compared for dry UAT and conventional turning with the use of a cemented carbide (WC) and a polycrystalline diamond (PCD) tool. With the use of ultrasonic assistance, a significant reduction in cutting forces was achieved with a slight increase in cutting temperature. Continuous and semi-continuous chips were obtained in UAT, with better surface topography. A chip-formation mechanism in UAT show increased ductility of the workpiece material when subjected to a repeated high-frequency microchipping process. Abrasive and adhesive wear occurred on the WC tool in both conventional turning and UAT. However, the machined surface obtained in UAT with a WC tool was comparable and sometimes even better than that achieved with the PCD too

Macromolecular Amplification of Binding Response in Superaptamer Hydrogels

It is becoming more important to detect ultralow concentrations of analytes for biomedical, environmental, and national security applications. Equally important is that new methods should be easy to use, inexpensive, portable, and if possible allow detection by the naked eye. By and large, detection of low concentrations of analytes cannot be achieved directly but requires signal amplification by catalysts, macromolecules, metal surfaces, or supramolecular aggregates. The rapidly progressing field of macromolecular signal amplification has been advanced using conjugated polymers, chirality in polymers, solvating polymers, and polymerization/depolymerization strategies. A new type of aptamer-based hydrogel with specific response to target proteins presented in this report demonstrates an additional category of macromolecular signal amplification. This superaptamer assembly provides the first example of using protein-specific aptamers to create volume-changing hydrogels with amplified response to the target protein. A remarkable aspect of these superaptamer hydrogels is that volume shrinking is visible to the naked eye down to femtomolar concentrations of protein. This extraordinary macromolecular amplification is attributed to a complex interplay between protein–aptamer supramolecular cross-links and the consequential reduction of excluded volume in the hydrogel. Specific recognition is even maintained in biological matrices such as urine and tears. Furthermore, the gels can be dried for long-term storage and regenerated for use without loss of activity. In practice, the ease of this biomarker detection method offers an alternative to traditional analytical techniques that require sophisticated instrumentation and highly trained personnel

Polymeric Micelles Formed by Splitting of Micellar Cluster

Polystyrene-b-poly(acrylic acid) (PS-b-PAA) diblock copolymer chains form aggregates with bimodal distribution in toluene. The introduction of polystyrene-b-poly(ethylene oxide) (PS-b-PEO) chains leads to the formation of mixed micellar cluster due to the hydrogen-bonding complexation between PAA and PEO. By using laser light scattering and transmission electron microscopy, we have investigated the structural evolution of the mixed micellar cluster. As the standing time increases, the cluster split into regular complex micelles composed of PS-b-PAA and PS-b-PEO chains. Our results reveal that the hydrogen-bonding complexation between PAA and PEO in the core and the repulsion between PS chains in the corona as a function of the molar ratio (r) of PEO to PAA manipulate the evolution

Improved analytical prediction of chip formation in orthogonal cutting of titanium alloy Ti6Al4V

The aim of this paper is to propose an analytical model of chip formation for precise prediction of orthogonal cutting of Ti6Al4V. This alloy is used broadly in aerospace components; hence, prediction of thermomechanical parameters of its orthogonal cutting is crucial for various industrial applications. The suggested analytical model needs only cutting parameters and tool geometry as input; it can predict not only cutting forces but also main features of a primary shear zone and a tool-chip interface. A non-equidistant shear zone model is employed to calculate shear strains and a shear strain rate in the primary shear zone, and a simplified heat-transfer equation is used for temperature. A Calamaz-modified Johnson-Cook material model that accounting for flow softening at high strains and temperature-dependent flow softening is applied to assess shear stresses in the primary shear zone. In addition, a shear-angle solution is modified for Ti6Al4V. At the tool-chip interface, a contact length, equivalent strain and an average temperature rise are defined. Besides, the effect of sliding and apparent friction coefficients is investigated. For a sawtooth chip produced in the cutting process of Ti6Al4V, the segmented-chip formation is analysed. A chip-segmentation frequency and other parameters of the sawtooth chip are also obtained. The predicted results are compared with experimental data with the cutting forces, tool-chip contact length, shear angle and chip-segmentation frequency calculated with the developed analytical model showing a good agreement with the experiments. Thus, this analytical model can elucidate the mechanism of the orthogonal cutting process of Ti6Al4V including predictive capability of continuous and segmented chip formation

Microstructural evolution of Ti6Al4V in ultrasonically assisted cutting: numerical modelling and experimental analysis

This paper aims to elucidate the effect of ultrasonically assisted cutting (UAC) on microstructure in a machined surface and a chip of Ti6Al4V alloy. To investigate microstructural evolution, a FE-based cutting model with an enhanced material formulation and temperature dependent material properties was developed. A Johnson-Mehl-Avrami-Kolmogorov (JMAK) model for the Ti6Al4V alloy was employed to simulate dynamic recrystallization and predict a resultant grain size. Due to a specific thermomechanical load in UAC, the distributions of strains, strain rates and temperatures in a workpiece in the machining process were investigated. In this study, five points under the machined surface and ten points under the unmachined one were tracked to compare the evolution of a grain size and its average magnitude in the alloy subjected to conventional cutting (CC) and UAC. Besides of numerical modelling and experimental studies for the resultant grain size were compared and additional validation using microhardness measurements were conducted. The results showed that the average grain size of the machined surface and the chip in case of UAC was larger and more uniform than that in case of CC. The study also presents discussions about the effect of a vibration amplitude, a feed rate and a cutting speed on the average grain size in machining of Ti6Al4V. The comparison between CC and UAC indicates that the change in average grain size in UAC was smaller than that in CC, thus demonstrating a lower level of damage in UAC

Additional file 1 of Randomized quantile residuals for diagnosing zero-inflated generalized linear mixed models with applications to microbiome count data

Additional file 1. Additional Simulation Results and RQR Functions for R package ‘glmmTMB’