Milling Conditions Research Articles

On the scope of mechanochemical activation: The case of Cu/ZnO catalytic systems

ZnO was submitted to different conditions of high-energy ball milling to thoroughly study the outcome of mechanochemical activation. Structural modifications led to a decrease in crystallite size and an increase in micro-strain and specific surface area (SBET) with milling time. Different copper amounts were added on pristine (reference) and activated support by incipient wetness impregnation. Cu deposited over activated support showed an enhanced metal-support interaction since part of Cu2+ could be introduced into milled ZnO lattice, replacing Zn2+ ions and/or locating in lattice interstitials. Moreover, further analyses suggested an electron transfer from activated support to metal, generating a mixture of Cu2O–CuO species, particularly at the interface between metal and support. N2O chemisorption studies gave Cu particle sizes of 1.3, 1.9 and 3.5 nm (for 0.2, 0.5 and 1 wt% Cu, respectively) and thus a good metal dispersion over ZnO was achieved. Hence, support's activation by milling process showed to be an excellent approach to improve both metal-support interaction and metal dispersion of supported catalysts.

Mechanical performance of high-entropy (AlCrNbSiTi)N films fabricated by high-power impulse magnetron sputtering over a wide compositional window

We designed nine distinct compositions of AlCrNbSiTi high-entropy alloy targets by adjusting the Al, Cr, Nb, and Ti contents, while maintaining the Si content at 7.7 at.%. We fabricated (AlCrNbSiTi)N films using the high-power impulse magnetron sputtering (HiPIMS) technique. By analyzing the microstructure and properties of the films, we have identified an expanded compositional window. This expansion enables (AlCrNbSiTi)N films with varying composition ratios to consistently demonstrate excellent mechanical properties. This consistency proves advantageous in terms of both sputtering target preparation and coating applications. In this study, all films had a single face-centered cubic (NaCl-type) structure with a crystallite size of ∼6 nm and lattice constant of ∼4.22 Å. The hardness of the films varied between 25.9 and 27.6 GPa. The thickness of the oxide layer formed when the films were annealed at 800 °C for 2 h under atmospheric conditions was approximately 30 nm, regardless of the composition. We also examined the cutting properties of (AlCrNbSiTi)N coatings on carbide cutting tools. Under dry milling conditions and extended cutting distances, the (AlCrNbSiTi)N coatings exhibited a remarkable reduction in flank wear length, with reductions of 78%, 64%, and 68% when compared to the commercial coatings TiN, TiAlN, and AlTiN, respectively. Furthermore, these coatings remained intact without peeling during milling on a 304 stainless steel workpiece. This research demonstrates that the combination of HiPIMS and high-entropy (AlCrNbSiTi)N could provide hard coatings with excellent performance during cutting. The characteristics of the coatings are attributable to the fineness and high density of the films deposited by HiPIMS and the synergistic lattice distortion and cocktail effects, which are similar in the compositional window of the designed alloy system.

Prediction of milling force based on identified milling force coefficients and tool runout parameters in time-frequency domain

Milling force is the key variable related to machining performance. Mechanistic models are commonly used to predict milling forces. However, the identification process of milling force coefficients and tool runout parameters in this model is prone to local optimal solutions. This paper develops a time–frequency domain identification method, and then the prediction of milling force is implemented on this basis. First, a milling force model considering the influence of tool runout is established, where the milling force coefficients and tool runout parameters are identified based on the time–frequency domain identification method. The simulation and experimental data are used to compare the time–frequency domain identification method with the time-domain and frequency-domain identification methods, respectively. Then, the variation of milling force coefficients and tool runout parameters with milling conditions is studied, based on which the linear interpolation method of coefficients and parameters is used to predict the milling force. Finally, the effectiveness of the milling force prediction is verified by experiments.

Prediction Model for the Evolution of Residual Stresses and Machining Deformation of Uneven Milling Plate Blanks.

During aerospace thin-walled component processing, the prediction and control of machining deformation have gained increasing attention. The initial residual stress in the blank is a major factor leading to the occurrence of machining deformation. This paper proposes the concept of uneven milling during the workpiece machining process, which is caused by the variation in local cutting depth resulting in uneven material removal thickness. Based on the elasticity theory, an analytical model is established to predict the evolution of overall residual stress and machining deformation in beam-like aluminum alloy components under uneven milling conditions. The effectiveness of the model is verified through finite element simulations and experiments. The results are as follows: (1) Under uneven milling conditions, the analytical model can accurately predict the distribution of residual stress and the machining deformation within the ZX section of the workpiece. (2) The uneven distribution of bending stress arises from the different curvature radii of various positions after workpiece deformation, leading to a 1 MPa to 3 MPa difference in stress between the middle and both ends of the workpiece. (3) During the layer-by-layer milling process, the magnitude of workpiece deformation is related to the stress state of the material removed, and there is a deformation superposition effect on the lower surface of the workpiece, further exacerbating the overall machining deformation.

Effect of compaction pressure on cold compaction of AA2024 swarf generated during milling operation

The solid-state recycling of aluminium swarf is a promising alternative to the conventional practice of remelting, which can lead to the loss of aluminium. The compaction process is an important step in the solid-state recycling of aluminium swarf. This study investigated the effect of cold compaction pressure on the material behaviour, density, and microstructure of compacted AA2024 machining swarf. The milling swarf was initially cleaned and chemical composition analysis was carried out. Morphology of swarf particle exhibited a wavy and straight regions attributable to milling conditions. The swarf then compacted at room temperature for 3 different pressure level viz. 1000, 1500, and 2000 kgf/cm2. The results showed that the density of the compacts increased with the increase in compaction pressure, reaching a value of 85% of the density of AA2024 at a pressure of 2000 kgf/cm2. Microstructure was analysed using scanning electron microscope to understand the bonding at the the swarf-swarf particle boundary. Vickers hardness results indicated that the hardness values of the compacted specimens also increased slightly with increasing compaction pressure. The overall combination of factors viz. plastic deformation, reorientation, rupturing of oxide layers, and mechanical interlocking contributes to the strength and compaction of swarf particles when subjected to higher compaction pressure used in this study. Further studies are in progress to improve the densification of the compacted specimens and to evaluate their suitability for extrusion applications.

Mechanochemical Synthesis of Corannulene: Scalable and Efficient Preparation of A Curved Polycyclic Aromatic Hydrocarbon under Ball Milling Conditions.

Corannulene, a curved polycyclic aromatic hydrocarbon, is prepared in a multigram scale through mechanochemical synthesis. Initially, a mixer mill approach is examined and found to be suitable for a gram scale synthesis. For larger scales, planetary mills are used. For instance, 15 g of corannulene could be obtained in a single milling cycle with an isolated yield of 90 %. The yields are lower when the jar rotation rate is lower or higher than 400 revolutions per minute (rpm). Cumulatively, 98 g of corannulene is produced through the ball milling-based grinding techniques. These results indicate the future potential of mechanochemistry in the rational chemical synthesis of highly curved nanocarbons such as fullerenes and carbon nanotubes.

Mechanochemical Assisted Chemoselective and Stereoselective Hydrogen‐Bonding Catalyzed Addition of Dithiomalonates to Enones

AbstractDithiomalonates proved to be active nucleophiles in the stereoselective additions to chalcones, dienones, and en‐ynones affording the desired Michael adducts with moderate to good yield and enantioselectivities up to 98%. In contrast, the analogous dibenzyl malonate remained inactive. Bifunctional Cinchona squaramides secured the effective chirality transfer and the selectivity towards Michael adducts of various bisthiomalonates following the soft enolization approach. The thioester's nature impacted the reactivity and stability of the reactants or products. The reactions performed in solution led to the product, but it required prolonged time along with byproducts formation such as sulfa‐Michael adducts, thus limiting the applicability of more reactive dithioesters. On the contrary, the reactions performed under solvent‐free, ball milling conditions furnished adducts in substantially less time, with negligible or no byproduct generation. Therefore, the mechanochemical approach revealed to be an effective tool for supporting the hardly effective reactions under standard solution conditions. The conducted comprehensive KS‐DFT studies are in line with the experimental observations shedding more light on the intricate active nucleophile formation at a molecular level and different chemical reaction pathways, as well as indicating the crucial transitions state governing the observed stereoselectivities.

Optimization of electrical and mechanical properties of a single-walled carbon nanotube composite using a three-roll milling method

In this study, the electrical and mechanical properties of carbon nanotube (CNT)/polydimethylsiloxane (PDMS) composites were optimized using a three-roll milling dispersion method. Depending on the number of CNT walls, such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), the three-roll milling conditions required to optimize the electrical conductivity of CNT/PDMS composites are quite different. In addition, the mechanical properties of the CNT/PDMS composites depend on the dispersion time. These properties were improved under an appropriate three-roll milling time but gradually deteriorated after excessive processing time. To demonstrate and optimize this phenomenon, various mechanical, electrical, and thermal properties of the CNT/PDMS composites were measured with respect to the type of CNT, milling time, and filler weight fraction. Morphological and structural analyses were also conducted on the CNT fillers and composites after milling.

Mechanochemical Synthesis of Aryl Fluorides by Using Ball Milling and a Piezoelectric Material as the Redox Catalyst

AbstractAryl fluorides are important structural motifs in many pharmaceuticals. Although the Balz–Schiemann reaction provides an entry to aryl fluorides from aryldiazonium tetrafluoroborates, it suffers from drawbacks such as long reaction time, high temperature, toxic solvent, toxic gas release, and low functional group tolerance. Here, we describe a general method for the synthesis of aryl fluorides from aryldiazonium tetrafluoroborates using a piezoelectric material as redox catalyst under ball milling conditions in the presence of Selectfluor. This approach effectively addresses the aforementioned limitations. Furthermore, the piezoelectric material can be recycled multiple times. Mechanistic investigations indicate that this fluorination reaction may proceed via a radical pathway, and Selectfluor plays a dual role as both a source of fluorine and a terminal reductant.

Mechanochemical Synthesis of Aryl Fluorides by Using Ball Milling and a Piezoelectric Material as the Redox Catalyst.

Aryl fluorides are important structural motifs in many pharmaceuticals. Although the Balz-Schiemann reaction provides an entry to aryl fluorides from aryldiazonium tetrafluoroborates, it suffers from drawbacks such as long reaction time, high temperature, toxic solvent, toxic gas release, and low functional group tolerance. Here, we describe a general method for the synthesis of aryl fluorides from aryldiazonium tetrafluoroborates using a piezoelectric material as redox catalyst under ball milling conditions in the presence of Selectfluor. This approach effectively addresses the aforementioned limitations. Furthermore, the piezoelectric material can be recycled multiple times. Mechanistic investigations indicate that this fluorination reaction may proceed via a radical pathway, and Selectfluor plays a dual role as both a source of fluorine and a terminal reductant.

Effect of milling parameters on machinability of SA508-3 steel in high-speed milling with uncoated and coated carbide tools

SA508-3 steel is popularly used to produce core unit of nuclear power reactors due to its outstanding ability of anti-neutron irradiation and good fracture toughness. Additive forging is a new technology for manufacturing SA508-3 steel forgings. However, the production efficiency and interface bonding quality of heavy forgings are respectively limited by the processing efficiency and surface quality of substrates in the additive forging process. High-speed milling technology is an effective method for improving machining efficiency and quality. Unfortunately, only a few studies on the milling of SA508-3 steel have been reported. In this study, we studied high-speed milling of SA508-3 steel and compared the cutting performances of uncoated, titanium aluminum nitride (TiAlN)-coated, and Al2O3-coated carbide tools. The tool life and cutting force were evaluated using various milling parameters under dry milling conditions. The wear modes and mechanisms were also investigated. The results show that adhesive wear occurs more frequently in the uncoated carbide tool, whereas coating flaking is predominant in the Al2O3- and TiAlN-coated carbide tools. Furthermore, the Al2O3-coated carbide tool showed better cutting performance than the TiAlN-coated and uncoated carbide tools considering the tool life and surface quality. The tool life of the Al2O3-coated carbide tool reached 200 min and the removed workpiece material was 182 × 103 mm3 under the blunt tool criteria. The study of tool life and wear behavior based on the practical cutting experiments contribute to the improvement of the milling quality and provides a theoretical basis for tool material selection and process optimization in milling SA508-3 steel.

A Hybrid Approach for Predicting Critical Machining Conditions in Titanium Alloy Slot Milling Using Feature Selection and Binary Whale Optimization Algorithm

Monitoring the machining process is crucial for providing cost-effective, high-quality production and preventing unwanted accidents. This study aims to predict critical machining conditions related to surface roughness and tool breakage in titanium alloy slot milling. The Siemens SINUMERIK EDGE (SE) Box system collects signals from the spindle and axes of a CNC machine tool. In this study, features were extracted from signals in time, frequency, and time–frequency domains. The t-test and the binary whale optimization algorithm (BWOA) were applied to choose the best features and train the support vector machine (SVM) model with validation and training data. The SVM hyperparameters were optimized simultaneously with feature selection, and the model was tested with test data. The proposed model accurately predicted critical machining conditions for unbalanced datasets. The classification model indicates an average recall, precision, and accuracy of 80%, 86%, and 95%, respectively, when predicting workpiece quality and tool breakage.

A Cyclic Calibration Method of Milling Force Coefficients Considering Elastic Tool Deformation

In metal-cutting technology, milling plays an important role in the product development cycle. The accurate modeling and prediction of milling forces have always been research hotspots in this field. The mechanical model based on unit-cutting force coefficients has a high prediction accuracy of cutting forces, and it is therefore widely used in the modeling of milling forces. The calibration of the cutting force coefficients can be realized by linear regression analysis of the measured average milling forces, but it needs to carry out multiple groups of variable feed slot milling experiments with full radial depth of cut, and it cannot well represent the interaction condition in peripheral milling with a non-full radial depth of cut. In peripheral milling, the tool will inevitably deform under the influence of cutting force in the direction perpendicular to the machining surface. If the force-induced deformation is ignored, the calibration of the cutting force coefficients will be out of alignment. For this non-slot milling condition where one side of the tool is mainly stressed, a cyclic calibration method for milling force coefficients considering elastic deformation along the axial contact range is proposed. Firstly, the cutting force coefficients are preliminarily calibrated by the experimental data, and, secondly, tool deformation is calculated through a preliminarily calibrated cutting force model cycle until convergence, before cutting boundaries are updated. The cutting force coefficient is then calibrated again, and it is brought back to the cantilever beam model in order to calculate the tool deformation again. The above process is repeated until the cutting force coefficient is convergent. Finally, the cutting force coefficients are obtained in order to predict and model the milling forces.

On-line tool wear monitoring under variable milling conditions based on a condition-adaptive hidden semi-Markov model (CAHSMM)

Since tool wear during machining process imposes a significant limitation on production quality as well as efficiency, on-line tool wear monitoring (TWM) is one of considerably crucial issues for intelligent manufacturing system. However, there is still a lack of universal on-line TWM techniques appropriate for the practical production process with variable machining parameters. Therefore, this study proposes a highly condition-adaptive method for tool wear state monitoring and remaining useful life (RUL) estimation under time-varying operation conditions. Multi-domain features are first extracted from vibration, acoustic emission and sound signals, and subsequently fused by the kernel principal component analysis (KPCA) to highlight discriminative information correlated to tool wear. A condition-adaptive hidden semi-Markov model (CAHSMM) is established to describe the evolution of tool wear, in which the accelerated failure time model (AFTM) embedded with Taylor tool life equation is utilized to determine the state transition probabilities that are strongly dependent on cutting parameters and duration time. Moreover, to extrapolate the Gaussian mixture models (GMMs) used to represent the observation probability beyond the range where they were trained, a Moment matching based on-line unsupervised transfer learning (OUTL) method is developed. After obtaining the state transition and observation probabilities, a modified forward algorithm is eventually implemented so as to assess tool wear online. Both the dataset from milling experiments of Ti6Al4V and PHM 2010 are employed for verifying the effectiveness of the proposed method. The results show that the presented method enables to reliably evaluate wear state and RUL of the cutter even under time-switching operation parameters, which demonstrates its promising potential for industrial applications.

Confirmation of n‐Hexane as an Inert Co‐Solvent in the Production of Functionalized Silicon Nanoparticles from Reactive High‐Energy Ball Milling

AbstractAlkanes such as n‐hexane have been used as co‐solvents in the production of functionalized semiconductor nanoparticles from alkenes and alkynes using Reactive High Energy Ball Milling (RHEBM) under the assumption that they are non‐reactive under typical milling conditions. In this paper, a comparative study with two hydrocarbon solvents of comparable chain length, 1‐hexyne, and n‐hexane, and their milling products using three different commercially available silicon precursors, namely single crystal silicon wafers and polycrystalline particles having a nominal size of 4 µm and 1 mm, is reported. It is found that nanoparticle formation and surface functionalization in all the three silicon systems occurs only with 1‐hexyne; n‐hexane is non‐reactive and does not lead to appreciable functionalized nanoparticle formation under the conditions studied. Nanoparticles (where formed) and microparticle byproducts of appropriate samples are characterized by Transmission electronic microscope (TEM), Fourier transform infrared (FTIR), Photoluminiscence spectroscopy (PL), Nuclear magnetic resonance 1H/13C NMR, and thermogravimetry TGA to separately confirm nanoparticle formation and surface functionalization.

Locating cellular contents during cryoFIB milling using cellular secondary-electron imaging

Cryo-electron tomography (cryoET) is a powerful technology that allows in-situ observation of the molecular structure of tissues and cells. Cryo-focused ion beam (cryoFIB) milling plays an important role in the preparation of high-quality thin lamellar samples for cryoET studies, thus, promoting the rapid development of cryoET in recent years. However, locating the regions of interest in a large cell or tissue during cryoFIB milling remains a major challenge limiting cryoET applications on arbitrary biological samples. Here, we report an on-the-fly localization method based on cellular secondary electron imaging (CSEI), which is derived from a basic imaging function of the cryoFIB instruments and enables high-contrast imaging of the cellular contents of frozen-hydrated biological samples. Moreover, CSEI does not require fluorescent labels and additional devices. The present study discusses the imaging principles and settings for optimizing CSEI. Tests on several commercially available cryoFIB instruments demonstrated that CSEI was feasible on mainstream instruments to observe all types of cellular contents and reliable under different milling conditions. We established a simple milling-localization workflow and tested it using the basal body of Chlamydomonas reinhardtii.

On-line surface roughness classification for multiple CNC milling conditions based on transfer learning and neural network

On-line surface roughness classification for multiple CNC milling conditions based on transfer learning and neural network

Peroxymonosulfate assisted mechanochemical remediation of high concentration DDTs contaminated soil

DDTs (DDT and its metabolites) contaminated sites urgently need to be treated efficiently and greenly. In this study, a horizontal planetary mechanochemical method with co-milling additives was developed aiming at efficiently degrading high-concentration DDTs in historical contaminated soil (∼7500 mg/kg). Peroxymonosulfate (PMS) was firstly used to the mechanochemical degradation of DDTs in historical contaminated soil, with a degradation efficiency of over 95% after 1 h of milling under the optimal milling conditions (CR = 30:1, r = 500 rpm, R = 1:4). Mechanism study indicated that DDTs in soil were partially dechlorinated and mineralized. The main products formed might be chlorinated aliphatic hydrocarbons, which need further treatment by ball milling or other methods. Under the action of mechanical energy, PMS could oxidize DDTs in soil through non-radical way rather than common radical way. Then, a comprehensive assessment of this remediation method was conducted by analyzing the changes in soil properties and acute biotoxicity after ball milling. Although PMS had a great performance on the degradation of DDTs, especially p, p’-DDE, it would cause the acidification and salinization of soil. Therefore, further pH adjustment and desalination treatment were suggested to reduce the negative impacts. This work successfully presents a practical approach to mechanochemical remediation of DDTs contaminated sites.

The experiment and simulation of enhanced mechanical performance for polyethylene terephthalate/high‐density polyethylene composites via domain size control

AbstractSolid‐state shear milling (S3M) equipment is proficient for achieving room‐temperature ultrafine grinding of multicomponent polymers, demonstrating significant potential in polymer blending and waste plastic recycling. However, a systematic investigation of S3M's ability to control the domain size of multicomponent polymer is currently lacking, which was of great potential for the high‐value recycling of waste plastics that are difficult to separate and thermodynamically incompatible. As the raw material of beverage bottle, polyethylene terephthalate/high‐density polyethylene (PET/HDPE) system with tremendous production was hard to be recycled together. Therefore, in this study, we chose PET/HDPE for the study of domain size control efficiency of S3M on mechanical properties of polymer blend. We also measured the processing parameters during the fabrication of PET/HDPE blended powder to determine the optimal manufacturing parameters for the polymer composite with outstanding mechanical property. After 30 milling cycles, the powder size of PET/HDPE gradually decreased from 849.8 μm (2 cycles) to 43.2 μm, which related to PET domain size of 71.9 and 5.2 μm, respectively. Meanwhile, at 24 milling cycles, the PET/HDPE composites reached the highest tensile strength of 27.6 MPa, meeting the most proper milling condition for PET/HDPE system. Finite element computer simulation was introduced to further investigate the domain size influence on mechanical property of PET/HDPE composites, which acquired similar results with the experimental value before excessive milling cycles. Based on both the experimental results and simulation support, a theoretical basis for the domain‐size‐control analysis of S3M in multicomponent waste polymer recycling was established.

Experimental study on the effect of the milling condition of an aluminum alloy on subsurface residual stress

Aluminum alloys used in monolithic parts for aerospace applications are subjected to distortion and residual stress (RS) generated by milling, affecting the product fatigue life. Particularly, the change in RS with depth (z) has a characteristic distribution with a maximum compressive RS at a z several tens of micrometers from the surface; however, the RS value depends on the measurement method used. In this study, the RS distribution with z from the surface after milling was measured for the AA7050-T7451 aluminum alloy by two-dimensional X-ray diffraction (2D method). The results were compared with those of four prior measurement methods, and the validity of 2D method was verified. The changes in subsurface RS with z showed similar distributions under all measurement conditions except when cos(α)-XRD was employed. The 2D method provides high repeatability. The in-plane RS distribution was also measured using 2D method to investigate the effect of milling conditions on this distribution. The RS values varied markedly depending on the measurement position, particularly at a small collimator diameter of 0.146 mm, allowing detection of localized extreme RS values. The maximum RS at z = 0 mm was − 85.6 MPa at a cutting speed of vc = 200 m/s and feed per tooth of fz = 0.05 mm, while it was − 16 MPa for vc = 450 m/s and 6.8 MPa for fz = 0.2 mm, revealing that the compressive RS changes to tensile RS as vc and fz increase.