MnBi low-temperature phase (LTP) has excellent magnetic intrinsic properties and attractive characteristics as a permanent magnet material. It is necessary to synthesize fine particles of MnBi-LTP ...with a size close to that of its single magnetic domain (<inline-formula> <tex-math notation="LaTeX">\approx 500 </tex-math></inline-formula> nm) to improve the magnetic anisotropic characteristics. Although the room-temperature ball milling process has been reported as a common method to reduce MnBi particle size, it has an inevitable limitation in reducing the powder size due to the low milling energy, as well as the powder agglomeration by the cold welding phenomenon. In this study, we synthesized fine particles of MnBi-LTP by the cryo-milling process at a temperature of 77 K. Phase analysis and magnetic properties were examined as a function of the amount of stearic acid for the cryo-milled powders. As a result, it was found that stearic acid as a surfactant plays an important role in suppressing the decomposition of the magnetic phase that occurs during the cryo-milling process. Consequently, high-purity fine MnBi-LTP particles, with ( BH )max of 9.25 MGOe, were obtained through this method. Thus, this indicates that the cryo-milling process has the potential to synthesize fine MnBi-LTP particles with superior magnetic properties.
Macro electromechanical milling has recently attracted increasing attention because numerous large thin-walled structures composed of difficult-to-cut materials are employed in the aerospace field. ...This paper reviews recent developments in state-of-the-art macro electromechanical milling. The fundamental aspects of material removal mechanisms, such as the generation and breakdown behaviors of passive oxide films of typical difficult-to-cut materials, were discussed. Rapid methods for breaking down passive films are summarized, and simulation methods for the machining process coupling multiple physical fields are introduced. Specific electrochemical milling methods, including fly mode electrochemical milling and sink electrochemical milling, are classified. Efforts made to improve process performance, such as the material removal rate, surface quality, and machining accuracy, are discussed. In addition, the main hybrid electrochemical milling methods, including electrochemical discharge milling, mechano-electrochemical milling, and electrochemical mill grinding, are also presented.
Numerous efforts have been made to fabricate Li2TiO3 tritium breeding ceramics with satisfactory density and mechanical strength while maintaining a fine grain structure. In this study, high‐energy ...ball milling was performed to promote grain refinement and amorphization of TiO2 and Li2CO3 powders, thereby preparing Li2TiO3 ceramic at a reduced sintering temperature. In the presence of high‐energy ball milling, powder mixtures with particle sizes of 24–29 nm were obtained, and the formation of β‐Li2TiO3 occurred at 400°C. The relative density and crushing load of Li2TiO3 ceramic pebbles improved as the ball‐to‐powder ratio and milling time increased. The Li2TiO3 ceramic pebbles sintered at 900°C exhibited a tiny grain size, satisfactory relative density (89%), and excellent crushing load (121 ± 13 N). The results also demonstrated that Li2TiO3 ceramic possessed the maximum thermal conductivity and ionic conductivity under the conditions of a 20:1 ball‐to‐powder ratio and 20 h milling time, that is, 5.028 W/m·K and 1.87×10−2 S/m at room temperature. Overall, the high‐energy ball milling process has shown advantages in the fabrication of tritium breeding ceramics with fine‐grained structure and excellent comprehensive performance.
This paper investigates the effect of vibration applied in feed direction on the burr generation mechanism in vibration-assisted micro milling. Kinematic analysis and finite element simulation are ...conducted for micro slot milling. Due to the vibration assistance in the feed direction, up milling and down milling takes place periodically on both of the cutting-in and cutting-out sides. This results in a reduction of burr formation. The results from both simulation and experiment confirm that the size of the top burrs in the down milling side of the slot are reduced significantly due to vibration assistance compared with conventional micro milling.
•Established a generic tool flank wear model with adjustable coefficients;•Identified the relationship of the critical times to the adjustable coefficients in the model;•Defined a method to predicate ...tool life with the wear model;•Proposed an intelligent approach for online tool life prognosis.
Tool wear condition is a key factor in milling which directly affects machining precision and part quality. It is essential to seek a convenient method to model and predict tool states. A generic wear model with adjustable coefficients is proposed and validated in this study. Considering the inner mechanisms of different wear stages, the entire tool life is split into three mainly wear zones by critical time, which correspond to three main types of wear: running-in wear, adhesive wear, and three-body abrasive wear. The wear model is validated based on the experimental data, compared with other celebrated wear models, and then further improved to enhance the adaptability and generalization. It is shown that the generalized wear model can discriminate tool wear ranges accurately. The determination coefficient of the wear model is more than 98% with the experimental data. Based on the proposed model, an approach for tool life prognosing and tool wear condition evaluating is proposed. The predictive real-time monitoring data of tool life and wear can be obtained timely with a genetic algorithm.
In order to solve the drawbacks of carboxylated cellulose nanocrystals (CNCs) prepared by critic acid (CA) hydrolysis method, such as low yield and low esterification degree, herein, ball milling ...assisted CA hydrolysis method was applied to obtain carboxylated CNCs and cellulose nanofibers (CNFs) with fine and uniform size, high yield and carboxyl content, good crystallinity, and good thermal stability. It was discovered that the diameter of CNCs and CNFs were decreased and the size uniformity was improved. The yield of CNCs was obviously improved to 39.8 % due to the promoted esterification reaction, which was 3.3 times of that without ball milling. Moreover, the carboxyl group content of CNCs and CNFs were improved to a maximum of 0.52 and 0.48 mmol/g, respectively. As ball milling progressing, more amorphous regions were destroyed and cellulose bundles were dissociated, resulting in CNCs and CNFs with high crystallinity. The thermal decomposition temperature of CNCs and CNFs were ranged from 317 to 331℃, which was higher than that had reported. This work provided an effective route for carboxylated CNCs with good yield, esterification degree and other performance, which was beneficial for the subsequent applications in the field of biomaterials.
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•Ball milling assisted citric acid hydrolysis was applied to prepare carboxylated CNCs and CNFs with good performance.•The yield of CNCs was obviously improved to 39.8 %, which was 3.3 times of that without ball milling.•The carboxyl group content of CNCs and CNFs could be up to 0.52 and 0.48 mmol/g, respectively.
The milling force has an important influence on tool wear and workpiece deformation, which is an important reference factor for selecting milling parameters. In this paper, based on the friction ...angle of the primary shear zone obtained from the orthogonal cutting simulation experiment, a three-dimensional instantaneous milling force prediction model is established, with an iterative model of ploughing force coefficient developed. By introducing the friction angle and establishing a new model of the tool-workpiece engagement area, the applicability of the prediction model of milling force is greatly improved, that is, based on a set of orthogonal cutting experiments, this model can predict the three-dimensional instantaneous milling forces under arbitrary geometric parameters of tool and cutting parameters. The accuracy of the milling force prediction model is verified by the milling experiment of aluminum alloy 2A14, and the prediction error of the milling force model is less than 30%. The results show that the relative error of average milling force decreases with the increase of cutting speed, so the prediction model of milling force has high accuracy under high cutting speed conditions.
Nowadays, the prototypes of microfluidic systems are generally produced via micromilling of thermoplastic polymethyl methacrylate (PMMA). The main limitations are the design of micro tools with ...diameters
D
≤ 50 μm adapted for each application, and the understanding of the machining process itself. The objective of this research work is to contribute to mastering the process of PMMA micromilling with tool diameters
D
≤ 50 μm on a 3-axes precision milling machine. For this purpose, the process design must include the complete process chain—from the CAD/CAM data up to the final structure geometry. The main requirements are the manufacture of microfluidic structures with R
a
< 60 nm on the groove bottom and a top burr overhang h
0
< 3 μm. Based on the experimental results, milling parameters were established and the influence of the tool geometry on the burr formation was determined. Finally, CAD/CAM machining strategies were recommended.
The milling of thin parts is a high added value operation where the machinist has to face the chatter problem. The study of the stability of these operations is a complex task due to the changing ...modal parameters as the part loses mass during the machining and the complex shape of the tools that are used. The present work proposes a methodology for chatter avoidance in the milling of flexible thin floors with a bull-nose end mill. First, a stability model for the milling of compliant systems in the tool axis direction with bull-nose end mills is presented. The contribution is the averaging method used to be able to use a linear model to predict the stability of the operation. Then, the procedure for the calculation of stability diagrams for the milling of thin floors is presented. The method is based on the estimation of the modal parameters of the part and the corresponding stability lobes during the machining. As in thin floor milling the depth of cut is already defined by the floor thickness previous to milling, the use of stability diagrams that relate the tool position along the tool-path with the spindle speed is proposed. Hence, the sequence of spindle speeds that the tool must have during the milling can be selected. Finally, this methodology has been validated by means of experimental tests.
A GdIII‐based porous metal–organic framework (MOF), Gd‐pDBI, has been synthesized using fluorescent linker pDBI (pDBI=(1,4‐bis(5‐carboxy‐1H‐benzimidazole‐2‐yl)benzene)), resulting in a ...three‐dimensional interpenetrated structure with a one‐dimensional open channel (1.9×1.2 nm) filled with hydrogen‐bonded water assemblies. Gd‐pDBI exhibits high thermal stability, porosity, excellent water stability, along with organic‐solvent and mild acid and base stability with retention of crystallinity. Gd‐pDBI was transformed to the nanoscale regime (ca. 140 nm) by mechanical grinding to yield MG‐Gd‐pDBI with excellent water dispersibility (>90 min), maintaining its porosity and crystallinity. In vitro and in vivo studies on MG‐Gd‐pDBI revealed its low blood toxicity and highest drug loading (12 wt %) of anticancer drug doxorubicin in MOFs reported to date with pH‐responsive cancer‐cell‐specific drug release.
MOF nanocarrier: A new GdIII‐based porous metal–organic framework, Gd‐pDBI, with an elongated rotatable linker (DBI=(1,4‐bis(5‐carboxy‐1H‐benzimidazole‐2‐yl)benzene) was synthesized. Gd‐pDBI is biocompatible, water‐stable, and acid/base‐tolerant. Mechanical grinding yielded nanocrystals with excellent water dispersibility, and they feature the highest loading of the anticancer drug doxorubicin (DOX) and cancer‐cell‐specific drug release.
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