Milling Mode Research Articles

Evaluation of the intaglio surface trueness and fit of zirconia crowns fabricated using different machining strategies with a chairside CAD/CAM system.

The present study aimed to evaluate the intaglio surface trueness and fit of zirconia crowns depending on the different machining strategies used with the Cerec system. Thirty duplicate tooth models for a single zirconia crown were randomly assigned to three groups (n = 10) according to the machining mode used for fabrication: grinding, wet milling, and dry milling. The scan data of the final crowns were compared with their design data to evaluate the intaglio surface trueness. The marginal and internal fit were evaluated using a cross-sectional method. The time required for the machining and sintering processes was measured for each group. The wet-milling group showed better trueness (root mean square: 13.8 ± 1.0 μm) than the grinding and dry-milling groups (P < 0.001). The marginal gap was greater in the grinding group (58.6 ± 28.9 μm) than that in the wet- and dry-milling groups (P < 0.001). The dry-milling group required the shortest time for the manufacturing process. All machining modes fabricated crowns with a clinically acceptable trueness and fit. However, the dry-milling mode was advantageous for the chairside CAD/CAM system with respect to time efficiency.

Methodology of design and research of vibration stability of cylindrical milling cutters with non-uniform tooth inclination angle

The сalculation and construction of a structural scheme of a cylindrical milling cutter with different pitch and non-uniform angle of inclination of teeth, with increased vibration resistance, are considered. The dependence of the forced oscillation frequency of the milling cutter on the milling modes, pitch and inclination angle of the teeth is obtained, which makes it possible to study the vibration resistance of the milling cutter in comparison with a non-uniform pitch milling cutter with a constant inclination angle of the teeth. The "resistance" of the studied cutter to resonances arising during milling is shown. Keywords:cylindrical milling cutter, tooth inclination angle, resonance, milling mode Yakov_Liberman@List.ru, ovsiannikovavaleriya@mail.ru, Lubov202055@yandex.ru

Исследование гранулометрического состава измельченного продукта, полученого при измельчении доломита в центробежной мельнице вертикального типа

Introduction. Modern medium (10–200 microns) and fine (0.1–10.0 microns) powders have a high cost, which limits the scale of their production and use. This assumes the implementation the latest achievements in the field of creating new equipment that is not inferior in its technical characteristics to the best foreign models into industry. The use centrifugal mills of vertical type for grinding various raw materials has shown their high efficiency in obtaining materials in the range – 0.2–0.01 mm. Studies of these mills operation under various operating conditions made it possible to create a large data set on the dependence of the crushed material granulo-metric composition on the design features of the mills and technological parameters of the grinding process. The results of a previously study of the granulo-metric composition a finely dispersed crushed product integral distribution according to particle size classes less than 80 microns were presented. They were obtained in a Brookhaven BI-XDC X-ray analytical centrifuge by measuring particle sizes in natural sedimentation mode, when the centrifuge disk was stationary during the experiment. The studies of the particle size differential distribution of a finely dispersed crushed product according to particle size classes less than 80 microns, which have not been carried out to date are of particular interest. Purpose of the study. The differential distribution study of the finely dispersed granulo-metric product composition obtained by grinding lump dolomite in a centrifugal mills of vertical type under different operating modes. Materials and methods. To solve this problem, samples of crushed material were taken from grinding dolomite from the Bosninsky deposit (RNO-Alania) in a centrifugal mill of the vertical type MV-0.3 with a 300 mm rotor diameter with following technological modes of the grinding process: mill rotor speed n = 310; 360 min–1, height of the material column above the rotating rotor H = 180; 270 mm, test time – 6 hours. Selected samples with a size class of –0.08 mm were analyzed in an X-ray analytical centrifuge Brookhaven BI-XDC, designed to determine the particle size distribution in the range from 0.01 to 100 microns. The measurements were performed on a suspension prepared from a mixture of 0.5 g of the selected sample with a 20% solution of sucrose and distilled water. Samples with a size class of 0.08 mm were weighed on laboratory scales LV SP.005.048 RE. The resulting suspension was dispersed in an ultrasonic bath for 3–5 minutes. After dispersion, the suspension was poured into the analyzer disk. While stirring, the lower absorption baseline line of a homogeneous particle suspension was measured. The obtained data from the analysis of the fine fractions size of were processed by the centrifuge computer software and graphs of the differential distribution of particles were constructed for various technological modes of grinding dolomite in a centrifugal mill. During the processing of the experiments, minor bursts in the concentration of the crushed product were not taken into account. The results and discussion. For the first time, a differential analysis of the granulo-metric composition of finely dispersed material with a particle size of –0.08 mm, obtained by grinding lump dolomite in a centrifugal mill of the vertical type under different mill operating modes, was carried out. Under all investigated operating modes of the centrifugal mill, the main part of the fine fraction in the mill outlet was in the range from 1.197 to 4.643 μm, and in steady-state operation it varied from 1.310 to 4.601 μm. The range of fine particle sizes has maximum values when the height of the column of crushed material above the rotating mill rotor and the rotation speed of the mill rotor decrease, and minimum values are observed when the height of the column of crushed material above the rotating mill rotor increases and the rotation speed of the mill rotor increases. Resume. 1. The article presents the results of the granulo-metric composition differential distribution study of a finely dispersed product obtained by grinding lump dolomite in a centrifugal mill of the vertical type. 2. The conducted studies have shown that, despite the positive results in obtaining fine particles with a size of 0.001 microns (nanoparticles) by mechanical means, the industrial production of nano-materials when grinding lump mineral raw materials in a vertical centrifugal mill is not economically profitable due to the low specific productivity and high energy intensity of the grinding process. 3. The obtained research results can be useful in the design of centrifugal mills.

Generation of Mechanical Characteristics in Workpiece Subsurface Layers through Milling.

The generation of mechanical characteristics in workpiece subsurface layers as a result of the cutting process has a predominant influence on the performance properties of machined parts. The effect of the end milling process on the mechanical characteristics of the machined subsurface layers was evaluated using nondestructive methods: instrumented nanoindentation and sclerometry (scratching). In this paper, the influence of one of the common processes of materials processing by cutting-the process of end tool milling-on the generation of mechanical characteristics of workpiece machined subsurface layers is studied. The effect of the end milling process on the character of mechanical property formation was evaluated through the coincidence of the cutting process energy characteristics with the mechanical characteristics of the machined subsurface layers. The total cutting power and cutting work in the tertiary cutting zone area were used as energy characteristics of the end milling process. The modes of the end milling process are considered as the main parameters affecting these energy characteristics. The mechanical characteristics of the workpiece machined subsurface layers were the microhardness of the subsurface layers and the total work of indenter penetration, determined by instrumental nanoindentation, and the maximum depth of indenter penetration, determined by sclerometry. Titanium alloy Ti10V2Fe3Al (Ti-1023) was used as the machining material. Based on the evaluation of the coincidence of the cutting process energy characteristics with the specified mechanical characteristics of the machined subsurface layers, the milling mode effect of the studied titanium alloy, in particular the cutter feed and cutting speed, on the generated mechanical characteristics was established.

Особенности расчета температуры резания при высокоскоростном фрезеровании алюминиевых сплавов без применения СОЖ

Introduction. The calculation of temperature during high-speed milling of aluminum alloys is of interest, since temperature can act as one of the main limiting factors in choosing rational milling modes. This is especially important when milling thin-walled products used in aircraft construction, since its high values can lead to local warping of the structure. It is not possible to control the temperature factor in production conditions, which makes it necessary to develop a mathematical model for calculating temperature. The purpose of the work is to develop a methodology for predicting the cutting temperature during high-speed milling of aluminum alloy workpieces for cutting conditions, in which it is not possible to use cutting fluid. Methods. This paper presents experimental studies of the cutting temperature during high-speed milling of aluminum alloy workpieces without the use of cutting fluid using non-contact temperature measurement methods. The results obtained were used to determine the coefficients substituted into formulas for calculating temperatures on the front and back surfaces of the cutting blade. Results and discussions. Based on the results of experimental tests and theoretical modeling, a temperature graph is drawn up. A comparison of experimental studies of milling of aluminum alloy D16T, with changing cutting conditions (the cutting speed changed) with theoretical data, gave a satisfactory result. The average relative error when comparing experimental data with theoretical one is 6.05 %. Based on experimental data, it can be concluded that the comparison of experimental data for measuring cutting temperatures is in satisfactory agreement with the proposed method of theoretical calculation of temperatures. The advantage of this technique is that it allows, without time-consuming and costly experimental studies, theoretically calculate (forecast) the temperatures on the front and back surfaces of the cutting blade, as well as the cutting temperature, for those narrow milling conditions, where effective heat removal from the cutting zone is impossible. It can also be used for milling aluminum alloys, the mechanical and thermophysical properties of which differ.

Исследование влияния элементов режима и шага зубьев фрезы на технологические параметры и температурное поле процесса обработки заготовок тонкостенных деталей

When machining workpieces of thin-walled parts, the temperature field differs from the field, which is formed during massive workpieces treatment. The reason for this is that machining of a thin-walled billet is interfered with its surface, being opposite to the one under machining. It has a significant effect on the temperature field, since the intensity of heat removal from this surface into the environment is significantly less than heat removal into the underlying layers of a massive material blank. In this regard, the problem of finding a rational mode of the machining process of thin-walled workpieces is relevant. The aim of the study is to determine the effects of the elements of the milling mode of thin-walled workpieces and milling cutter teeth space on the technological parameters of the milling process of titanium alloy workpieces and to develop recommendations for choosing this milling mode. For this purpose, a numerical modeling of the technological parameters of the milling process of blanks of massive workpieces and thin-walled parts made of titanium alloy, was performed experiencing various combinations of feed to the milling cutter tooth, cutting speed and milling cutter teeth space. When machining a thin-walled workpiece, due to less intense heat removal from the cutting zone into the workpiece, the temperatures in the areas of chip contact with the front surface of the tooth, the back surface of the tooth with the workpiece and the temperature of the workpiece itself are higher than when in a massive workpiece treatment. The patterns of changes in the parameters of the milling process of thin-walled workpieces depending on the feed, cutting speed and the milling cutter teeth space are established. With a larger tool stepover, the average and maximum temperatures in the areas of chip contact with the front surface of the tooth and the back surface of the tooth with the workpiece are lower in most of the combinations of mode elements used. Equations that establish the effect of feed on the milling cutter tooth, cutting speed and spacing of teeth on the parameters of the machining are obtained. The results of the study will allow choosing a rational milling mode and spacing of teeth in the work on workpieces of thin-walled parts made of titanium alloy.

Phase field study on phase stability at high temperatures in nanograined Fe–Ni alloy prepared by plastic deformation

The phase stability at high temperatures in nanograined Fe–Ni alloy prepared by surface mechanical attrition treatment (SMAT) and ball milling (BM) modes are drastically different. For example, the onset temperature (As) of reverse martensitic transformation (RMT) of nanocrystal prepared by SMAT is higher than that of coarse crystal, while BM exhibits the opposite result. The elastoplastic phase field model for RMT was first proposed to investigate the correlation between RMT and its forward martensitic transformation (FMT), in turn, the above experimental phenomena were revealed in this paper. The prepared nanocrystals with the same diameter (15 nm) by SMAT and BM mode were taken as representative examples. The simulation results indicated that the strain energy is relaxed by the applied strain during FMT in nanocrystalline prepared by smaller plastic deformation mode (e.g. SMAT), but it is enhanced by larger plastic deformation mode (e.g. BM). The stored strain energy in BM mode is much larger than that in SMAT mode, and hence the driving force provided for subsequent RMT is also larger in BM mode. Therefore, the phase stability of the martensitic nanocrystals prepared by BM mode at high temperatures is much lower than the counterpart by SMAT mode, which agrees well with the experimental measurements.

Calculation of force parameters of workpiece machining process with end mill cutters

The aim is to develop and validate an operational methodology for calculating the force parameters and characteristics of the tool and the process of milling structural materials with end milling cutters. The structural schemes of machining and force models of oblique cutting processes in the modes of axial tool feed and continuous plastic deformation of the processed material were used when developing the method of preliminary calculation of the total axial force working on the cutting edge of end milling cutters. The rotating tool tests were conducted on a Hermle UWF 1202 H 3-axis machining center supplemented with a Kistler piezoelectric dynamometer (model 9272). Authors suggested, developed and tested the preliminary calculation method applied to the force characteristics of the machining process of workpieces by end milling cutters, considering how the energy power of ductile fracture of the machined material affects the process. Contact friction arising on the front and rear surfaces of the cutting tool does not reach the limiting value being subject to the Coulomb – Amonton law, that is, it is estimated by the dependence directly proportional to the normal pressure. After calculations, we defined the materials of the workpiece for milling, that is 45 steel (AISI 1045), and the end two-tooth cutter, uncoated T14K8 alloy, which was used to produce samples. The following milling modes were established: 4 mm boring depth; 50, 100 and 150 m/min cutting speeds; 0.05 and 0.1 mm/rev cutting tool feed. Deviation of the measured values of axial cutting force from the calculated values in the range of changing values of tool feed rate was found to be no more than 11%, and in the range of changing values of cutting speed no more than 15%. The developed calculation and analytical methodology for estimating force parameters of the machining process by end milling cutters provides an increase in the efficiency and reliability of the preliminary prognostic calculation of operating parameters and characteristics of cutting elements of end milling cutters.

ЭФФЕКТИВНОСТЬ ПРИМЕНЕНИЯ КРИВОШИПНО-ПОЛЗУННОГО ПРИВОДА ДЛЯ ФРЕЗЕРОВАНИЯ ВАФЕЛЬНОГО ФОНА

The paper presents the design of an experimental cutting tool feed drive based on a slider-crank mechanism. A feature of the technology of milling a regular waffle background pattern is the need for regular repetition of cells, usually rectangular shape. This requires the development of a tool feed mechanism that provides а high processing speed and a significant reduction in cutting forces to prevent deformation of the cell shape. The drive design presented in the work provides feed rate up to 43 m/min with cutting speed up to 942 m/min. This eliminates the exit of the mechanism out of the cell dimensions, as well as provides a significant reduction of cutting forces up to 10 N and removes the problem of using coolant (dry machining). This is a feature of the high-speed milling mode, when the feed rate and cutting speed are significantly higher than traditional ones, and the cutting depth does not exceed 1 mm. The productivity of this milling process is much higher than traditional milling modes and, in addition, it causes less heating of the part, as almost all the heat escapes with the chips. The practical significance of the development is the increase of productivity of the equipment for waffle background milling in fuel tanks from aluminium alloys due to the application of the high-speed drive based on the slider-crank mechanism. The authors offered to mount it instead of the standard spindle on large-sized milling gantry-type machines. This makes it possible to use the high-speed milling modes at cutting forces of several newtons for reducing the weight of the power and moving parts of the drive and increasing the feed rate.

Effect of Milling Strategy on the Surface Quality of AISI P20 Mold Steel

This paper explores the impact of various milling strategies, including up-milling, down-milling, and hybrid approaches, on the surface roughness of AISI P20 mold steel. The study is methodically divided into three stages to comprehensively understand the effects of these strategies. The first stage involves milling single slots with varying cutting parameters to establish baseline effects. The second stage examines the effects of consistent milling strategies (up-up and down-down) on surface quality. The third stage probes into hybrid strategies (up-down and down-up) to assess their effectiveness. Central to this investigation is not only the type of milling strategy but also how cutting speed and feed rate influence the resultant surface roughness. Our findings indicate that up-milling generally leads to a 22% increase in surface roughness compared to down-milling. This trend is visually verified by surface texture analyses. When comparing consistent strategies, up-up milling tends to produce rougher surfaces than down-down milling by approximately 25%, characterized by distinctive scratches and feed mark overlays. Remarkably, while the hybrid milling strategies do not exhibit significant differences in surface roughness, variations in cutting speed and feed rate play a crucial role. Specifically, at lower speeds, hybrid milling achieves smoother surfaces than the identical double milling mode, while at a cutting speed of 100 m/min, the double mode demonstrates a notable decrease in roughness. Additionally, this study introduces a color mapping simulation for machined pockets, validated by experimental results, to predict surface roughness based on the strategic history of milling, thereby offering valuable insights for optimizing milling processes.

Investigation of milling performance and removal process mechanism of 3D SiCf/C-SiC composites using brazed diamond tools

The present paper evaluates the machinability of brazed diamond tools for milling 3D SiCf/C-SiC composites. Defined three milling modes of fiber orientation, transverse, longitudinal, and perpendicular, and surfaces, SA (transverse and longitudinal), SB (transverse and perpendicular), and SC (longitudinal and perpendicular), are chosen to reveal factors influencing milling force and surface integrity. Besides, the removal process mechanism is analyzed through high-speed cameras. The results show that combining fiber orientations influences milling force waveform, whereas surface quality is related to fiber orientation and damage types. The lower cutting speeds obtain better surface quality on SA surfaces, while superior surface quality on SB and SC surfaces is attained with higher cutting speeds. Dominant damage modes include direct fiber breakage and matrix fragmentation. Moreover, the removal process is sequentially matrix cracking and fiber/matrix debonding, fiber breakage, and ultimate failure. Toughening mechanisms of composites containing fiber bridging and fiber pullout are observed during milling.

Material removal mechanisms affected by milling modes for defective KDP surfaces

Surface defects which are caused by diamond fly-cutting can degrade the optical characteristics of KDP crystals by inducing the laser damage and resultantly shortening the service life when working in the condition of extremely high-power laser irradiations. The ball-end milling repair can totally remove the defects and correspondingly enhance the ability of the KDP crystals to resist laser damage. However, because of the existence of pull-milling, push-milling, down-milling, and up-milling in the complex machining trajectory, it is of great challenge for soft-brittle KDP crystals to achieve full plastic domain milling of repair points for obtaining ultra-smooth repaired surface. In this study, theoretical models of the maximum uncut chip thickness (UCT) considering the defect are constructed in the various milling modes. The cutting force and surface morphology affected by milling modes on the defective surface are simulated using a three-dimensional (3D) finite element model. Combined with the simulations, micro-milling tests are employed to confirm the influence of milling modes on the material removal mechanisms for defective KDP crystals by cutting force, surface morphology, surface roughness and specific cutting energy (SCE). It is found that defects could reduce the maximum UCT to distinct degrees in the various milling modes. Defects have a greater influence on the maximum UCT in the push-milling mode than that in the pull-milling mode, while the influence is the same in the up-milling and down-milling modes. Interestingly, the ductile removal mode occurs on the both defect-free and defective surfaces in the pull-milling mode when the feed per tooth (fz) is 0.5 µm/z. In contrast, the brittle-ductile transition caused by surface defects occurs in the other three milling modes. Furthermore, defects would lead to severer size effect in the all milling modes. When the fz is 0.1 µm/z, for the defective surface, the SCE is larger and the ploughing effect is more significant in the push-milling mode compared to the pull-milling mode. More importantly, as a result of the difficulty of chip discharge, the SCE is greater in the up-milling mode than in the down-milling mode on the defective surface. This work reveals the influence mechanism of milling modes on the material removal process for defective KDP crystals and offers a theoretical foundation and technical value for improving the repaired surface quality of functional KDP crystals served as the optical devices.

ELECTRODYNAMICS OF HIGH-PRECISION ITERATIVE FEED ELECTRIC DRIVE OF MACHINING CENTER WITH INERTIAL LOAD

The kinematical diagram and refined mathematical model of steady motion in machining mode of high-precision itera-tive multichannel differential-geared electric feed drive of machining center with substantially inertial working tool are presented. The structural-algorithmic diagram of a three-channel control system of an electric drive, represented by various options for implementing an iterative algorithm for the interaction of control channels is given. Concretization of computer model is completed to simulation of movements of iterative two- and three-channel electric drive with sub-ordinated adjustment of control channels, destined for displacement of working tool feed mechanism in face milling mode. Comparative assessment in time and frequency areas of quality indicators to improve the feed accuracy using the proposed multichannel electromechanical system is completed. Comparison is made with similar on purpose, but dif-ferent on speed of operation, modern single-channel gearless feed electric drives, which traditionally used on heavy metal cutting machines and machining centers. It is shown that in compensated two- and three-channel electric drive compared to even broadband single-channel asynchronous feed electric drive with frequency-current vector control a significant increase not only in speed of operation, but also in the dynamic accuracy of feed control practically in the entire range of working tool movements can be achieved. It is determined that iterative three-channel electric drive potentially provides a level of quality control of the working tool, unattainable not only in the corresponding traditional single-channel electric feed drives of various types, but in a similar construction two-channel differential-reducer feed electric drive. References 10, figures 5, table 1.

Моделирование технологических параметров процесса фрезерования заготовок деталей из поликарбоната при различных режимах обработки

Computer simulation of technological parameters in the milling process of polycarbonate workpieces under various processing modes is realized. The parameters are recorded at various points in the contact time of the milling cutter tooth with the workpiece. The regularities of changes in the parameters of the milling process, including forces and temperatures in the contact zones of the facing with the cutter tooth or in case of tooth contact with the workpiece, depending on the elements of the milling mode, are found. It’s also found that the temperatures in the contact zone of the tooth with the workpiece are higher than in the contact zone of the tooth with the facing. The pattern of temperature distribution in the surface layer of the workpiece is distilled. Mathematical dependences describing the relationship of temperatures with the elements of the milling mode, are obtained

Prediction of GTE vanes deflection by analytical models of technical and geometric initial data in cross line milling on multi-axis CNC machines

In the process of milling the profile of the vanes of a gas turbine engine on multi-operational machines, a technological scheme of transverse line shaping is used. According to this scheme, the vane rotates around its own axis, it is machined with a mill with a spherical working surface, which performs rotation and interpolated axial movement. The required parameters of the surface quality of the vane airfoil profile (profile accuracy and surface roughness parameter) are provided by assigning a combination of controlled processing parameters. However, today there are no recommendations on the calculation and assignment of combinations of controlled parameters for the milling of complex-profile surfaces, which is the profile of the flow path of the GTE compressor vanes. For each line and angle of rotation of the vane, the accuracy of the vane profile will be determined depending on the amount of vane deformation, which should not exceed the tolerance for its manufacture. In the course of the analysis of geometric relationships in the contact zone of the curved profile of the flow part of the vane and the mill with a spherical working surface, dependences were obtained to determine the magnitude of the force component during milling and its projection on the Y axis, as well as the effective diameter of the mill, which are necessary to calculate the magnitude of the total deformation of the vane. A methodology is proposed and analytical models are obtained for determining and assigning a combination of controlled parameters of the milling mode that provide a given accuracy of the vane airfoil profile when developing a control program for the vane milling process on a CNC machine.

Удосконалення конструкції системи базування поздовжньо-фрезувальних верстатів

Based on the analysis of the designs of peripheral-milling machines, it was found that, according to the principle of operation, all the machines have a movable locating system, which is the dominant factor influencing the accuracy of machining and introduces an error of up to 60% of the total error of machining on these types of machine. As a result of theoretical studies on the influence of the structures of the locating systems, it was found that on a jointing machine, the greatest error is caused by the height of the rear plate placement, while on a thicknessing machine - the presence of rollers in the table plate. To improve the accuracy of machining on peripheral-milling machines, it is proposed to replace the movable locating system with the positional locating of workpieces on the feeding carriage. The design of a four-side peripheral-milling machine S20PK has been developed based on the principle of operation of a cyclo-through type with positional locating of blanks on a feeding carriage, which ensures the accuracy of machining a profiled bar measuring 4,000 x 200 x 200 mm within ±0.07–0.34, as well as the possibility of machine operation with the participation of one operator. As a result of experimental studies, a regression model of the dependence of machining accuracy on the S20PK machine on the feed rate and the thickness of the removed layer was obtained, which makes it possible to set rational milling modes to ensure machining accuracy in accordance with the requirements of current standards (± 0.1 mm).

Preparation of Nitrogen-doped Holey Multilayer Graphene Using High-Energy Ball Milling of Graphite in Presence of Melamine.

Holey graphene, consisting of graphene sheets with in-plane nanopores, has recently attracted more attention as it expands graphene applications to other fields inaccessible by the pristine graphene. To ensure an effective implementation of holey graphene in the market, it is crucial to explore new preparation methods that are simple, cost effective, eco-friendly, versatile, and scalable. While ball milling of graphite in presence of exfoliating agents was found very effective in the preparation of graphene (doped and undoped) and graphene-composites, this technique remains unexplored for the preparation of holey graphene. In the present work, Nitrogen-doped multilayer holey graphene sheets were prepared by an all-solid, one-step procedure based on high-energy ball milling of graphite as the starting material in presence of melamine in a shaker-type mill for 1 hour under ambient conditions. Melamine acted simultaneously as an exfoliating agent to enhance the exfoliation of graphene layers and a diluent to protect graphite against the continuous fragmentation into amorphous carbon during the high-energy "shock" mode of ball milling. The high-energy "shock" mode of ball milling of graphite in presence of melamine induced the formation of multilayer defective graphene as an intermediate product before being converted into N-doped multilayer holey graphene after the removal of the in-plane defects during the milling process. The characterization of the final product confirmed the formation of N-doped multilayer holey graphene with a content in nitrogen as high as 12.96 at.%, making it promising for energy storage and energy conversion applications.

Microstructure, Wear and Corrosion Behaviors of Electrodeposited Ni-Diamond Micro-Composite Coatings

For the micro-milling of hard and brittle materials, to avoid crack formation, a tool with ductile milling mode is required. Composite electrodeposition technology was used to prepare a Ni–diamond coating on the surface of brass. The surface microstructure, composition and surface roughness of the coating were studied with a scanning electron microscope, X-ray diffractometer and roughness tester. The adhesion strength was studied by scratch test, the wear resistance was analyzed by wear test, and the corrosion resistance was investigated by Tafel curves and electrochemical impedance spectra (EIS). It was found that the distribution of diamond particles of the Ni–diamond coating was relatively uniform, and the content was relatively high. The internal stress of the coating prepared by the composite electrodeposition technology was very low. With the incorporation of the diamond particles, the surface roughness of the coating tended to decrease. The wear experiment showed that the wear scar diameter of the corresponding glass ball for the Ni coating was 1.775 mm and the roughness was 13.88 ± 2.811 µm, while that for the Ni–diamond coating was 2.680 mm and 8.35 ± 0.743 µm, respectively, indicating that the tool coating with uniform diamond particles had a strong ability to process workpieces with significantly improved surface quality. The particle press-in mechanism not only improved the wear resistance of the coating, but helped to prolong the service life of the tool. The results of the EIS test and Tafel curves showed that the Ni–diamond coating had a lower corrosion current, and the corrosion resistance of the coating surface was improved. The experimental results showed that the micro-diamond coating prepared by the composite electrodeposition technology had good bonding strength, low internal stress, and significantly improved wear resistance and corrosion resistance.

Evaluation of the effect of milling mode and margin definition on adaptation of chairside digitally designed and fabricated ceramic veneers.

The present study aimed to evaluate the effect of the milling mode and margin defining method on the marginal and internal adaptation of digitally designed and fabricated ceramic veneers. Forty extracted central incisors were prepared for ceramic veneers. The veneers were categorized into four groups (n = 10) based on the milling mode (fine or extra-fine) and design (automatic or manual defining of cervical and incisal margins). The veneers were cemented to the teeth using resin cement and then polished. After cementation, the teeth were embedded in clear polyester resin, then cut into three sections. Absolute marginal gap at the cervical margins (AMGC), marginal gap at the incisal (MGI) and cervical (MGC) margins, and internal gap (IG) at the axial wall were evaluated using a scanning electron microscope. Two-way analysis of variance (ANOVA) and t tests were used (α = 0.05) for the statistical analysis. The margin defining method affected the adaptation of the internal and incisal margin; the automatic (software) margin defining method resulted in a smaller MGI (P = 0.038) and IG (P = 0.009) than the manual defining method. The type of milling mode did not affect the marginal gap. The margin defining method affected the marginal gap at the incisal margin and the internal gaps. (Int J Comput Dent 2022;25(3):277-285; doi: 10.3290/j.ijcd.b2588153).

Simulation of the process of milling and grinding cylindrical surfaces by an oriented tool in one setup

Purpose. Improvement of schemes for processing the cylindrical surfaces of the shafts of gearboxes and transmissions of large-sized equipment. Development of modular spatial models of the processes of milling and grinding of the cylindrical surfaces of the shafts of gearboxes and transmissions of military and civil vehicles. Development of a model for dressing a grinding wheel with a diamond tool. Methodology. Creation of general and particular modular mathematical models of the processes of removal of allowance and shaping during rough and finish milling and finishing grinding of non-rigid cylindrical surfaces was carried out using a matrix apparatus for transforming coordinate systems. This made it possible to describe the treatment process using standard matrices. The calculations were carried out in the mathematical package Mathcad. To obtain a graphic display of the mathematical model of the instrumental and machined surfaces, the standard functions of the software package and the developed logical blocks were used. Findings. A technique for processing cylindrical surfaces of revolution with an oriented tool is proposed. Roughing, finishing and polishing are carried out in one setup. Roughing and finishing are carried out with an oriented cutter with replaceable multifaceted carbide inserts. The angle of orientation of the cutter is selected from the condition of maximum loading of the end section. Thus, the roughing stock is removed by the end face and by the finishing periphery, while the maximum component of the cutting force is directed along the axis of the part and does not cause deformations in the radial direction. Final finishing is carried out with a wide grinding wheel. The angle of orientation of the grinding wheel is selected from the condition of uniform distribution of the allowance along the periphery. A scheme for dressing the working surface of a grinding wheel with a diamond pencil with a constant feed is proposed. Originality. Modular spatial models of the processes of milling and grinding of the cylindrical surfaces of the shafts of gearboxes and transmissions of military and civil vehicles were developed. A model for dressing a grinding wheel is proposed. The use of the proposed models makes it possible to conduct a more detailed analysis of the processes of stock removal and shaping. Practical value. Dependencies are proposed for choosing the optimal angles of orientation of the cutter for roughing and finishing milling and the grinding wheel for finishing. The accuracy of parts is increased due to the elimination of the resetting error. The cost of manufacturing is reduced due to the maximum full use of cutting carbide inserts, by turning them and operating the worn finishing edge in the rough milling mode, as well as by increasing the resource of the grinding wheel.