Thread milling is an alternative to tapping in which tool wear is one of the main limitations. Infeed strategies significantly affect tool wear, which has not been studied in previous investigations. ...Hence, current research studies the effect of infeed strategies (radial, modified flank, and incremental) on flank wear during thread milling considering different cutting speeds. According to FEM simulations, the incremental method led to the minimum tool temperature and the highest cutting length (tool life). According to experimental results, incremental and modified flank infeed methods improved tool life up to 340 % and 80 %, respectively compared to the radial infeed method in cutting speed of 48 m/min. Also, the incremental infeed method was superior in higher cutting speeds.
•Study of the tool flank wear during the thread milling process using experimental procedure and numerical simulation.•Study the effect of infeed strategies (radial, modified flank, and incremental) on flank wear in different cutting speeds.•Study the wear mechanisms in different infeed strategies with special attention to the tool temperature.•FEM simulation of the tool temperature and wear; validation according to experimental results of flank wear.•Compare threads' surface quality according to three infeed strategies.
The chip formation for a Ti–6Al–4V alloy was studied at high cutting speeds combined with large uncut chip thicknesses (0.1–0.25mm). Orthogonal cutting tests were conducted by using uncoated carbide ...tools on a specific ballistic set-up with cutting speeds from 300m/min to 4400m/min (5–75m/s). A hypothesis on the mechanism of chip generation is proposed for this speed range validated by high-speed imaging system enabled direct observation of cutting process. A transition, from serrated more or less regular with localized shearing and possible presence of cracking, to discontinuous at very high speed is observed.
The inclination of the segment Φseg is shown as resulting from the primary shear angle Φ that can be modified by compression between the tool and the uncut part. A maximum value of 60° for Φseg is reached with increasing speed after which it decreases to 45° at very high speed.
The cutting speed appears as the most important factor when compared with the uncut chip thickness, in determining the formation of chips by affecting the frequency of segmentation, the shear angles and the crack length.
The significant reduction of cutting forces occurring with increases in cutting speed was firstly explained by the conflicting work hardening–thermal softening processes and then depended on whether the deformation phase of the chip segment is occurred.
► The Ti–6Al–4V alloy is machined with a cutting speed from 300m/min to 4400m/min. ► Orthogonal cutting conditions are realised on a specific ballistic device. ► The different chip morphologies are illustrated and studied. ► The high cutting speed effects on the morphology of the segmented chips are analyzed. ► Mechanisms of chip formation are proposed according to the high cutting speed.
Abstract As a new development direction of the domestic medium voltage distribution network, the flexible grounding method has a rapid expansion trend, and accordingly, the ground fault protection ...scheme needs to follow up quickly. This paper calculates and analyzes the distribution characteristics of transient electric quantities in the system under different fault conditions by establishing the transient equivalent model of shunt small resistor casting and cutting in the flexible grounding system. It is found that if transition resistance is small, the application of parallel small resistors will cause the transient zero sequence current amplitude of the faulty line to be maximum and have opposite polarity to the healthy line. When transition resistance is high, distribution characteristics of the transient zero sequence current projection component are also the same. Based on the above features, a flexible grounding system ground fault routing method is proposed, which can cope with a variety of ground fault situations in engineering practice with high reliability, and the correctness of the method is verified through simulation.
The research and application of high speed metal cutting (HSMC) is aimed at achieving higher productivity and improved surface quality. This paper reviews the advancements in HSMC with a focus on the ...material removal mechanism and machined surface integrity without considering the effect of cutting dynamics on the machining process. In addition, the variation of cutting force and cutting temperature as well as the tool wear behavior during HSMC are summarized. Through comparing with conventional machining (or called as normal speed machining), the advantages of HSMC are elaborated from the aspects of high material removal rate, good finished surface quality (except surface residual stress), low cutting force, and low cutting temperature. Meanwhile, the shortcomings of HSMC are presented from the aspects of high tool wear rate and tensile residual stress on finished surface. The variation of material dynamic properties at high cutting speeds is the underlying mechanism responsible for the transition of chip morphology and material removal mechanism. Less surface defects and lower surface roughness can be obtained at a specific range of high cutting speeds, which depends on the workpiece material and cutting conditions. The thorough review on pros and cons of HSMC can help to effectively utilize its advantages and circumvent its shortcomings. Furthermore, the challenges for advancing and future research directions of HSMC are highlighted. Particularly, to reveal the relationships among inherent attributes of workpiece materials, processing parameters during HSMC, and evolution of machined surface properties will be a potential breakthrough direction. Although the influence of cutting speed on the material removal mechanism and surface integrity has been studied extensively, it still requires more detailed investigations in the future with continuous increase in cutting speed and emergence of new engineering materials in industries.
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•Material removal mechanism of HSM is summarized considering material dynamic properties.•Machined surface integrity is discussed with emphasis on metallurgical alterations.•Cutting force/temperature and tool wear behavior in HSM are summarized.•The pros and cons of HSM are elaborated to guide its industrial application.•Challenges for further development of HSM and future directions are highlighted.
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High-power direct laser deposition (HP DLD) was utilized to fast generate AISI 316L stainless steel parts with large size and excellent mechanical properties. In order to efficiently ...manufacture the stainless steel parts with high surface quality and dimensional accuracy, a dry milling finish was applied. During the DLD process, heat retaining powder was employed to prevent buckling deformation. The effect of building direction on the microstructure, mechanical properties and machinability of the stainless steel was investigated. It was found that the microstructure was homogeneous, at the building direction of 0°, while a number of larger dendritic grains were present in the microstructure, at the building direction of 90°. The tensile properties and hardness values at the building direction of 0° were higher than those at the building direction of 90°. For both building directions, the decrement in surface roughness and the increment in cutting force and tool wear, were observed with the increase in cutting speed. The cutting force, tool wear and surface roughness of the additive manufactured stainless steel at the building direction of 0° were relatively higher, which implies that the anisotropy in the machinability could be utilized to increase efficiency and reduce production cost.
This paper investigates the brittle removal mechanism of ductile materials in ultra-high speed machining (UHSM). Firstly, a predictive model of critical cutting speed for UHSM is proposed with the ...theory of stress wave propagation. The predicted critical cutting speed for ductile-to-brittle transition of ductile materials is then validated by machining experiments of 7050-T7451 aluminum alloy at the cutting speeds ranging from 50m/min to 8000m/min. The experimental results show that fragmented chips are produced above the critical cutting speed of 5000m/min for 7050-T7451 aluminum alloy. The scanning electron microscopic (SEM) images of chips, chip roots and finished workpiece surfaces are observed and analyzed. Large amounts of brittle cracks and cleavage steps are observed on the fragmented chip surface obtained under the ultra-high cutting speed. Due to the remained brittle cracks, the finished surface quality obtained with UHSM is worse than that obtained with high speed machining. Secondly, the specific energy models for the chip formation are proposed and validated by experiments under ductile regime machining and brittle regime machining, respectively. The specific energies consumed for continuous and serrated chip formation mainly include plastic deformation energy located in the primary shear zone, the friction work between the tool–chip interface, and the chip kinetic energy. The plastic deformation energy accounts for the largest proportion among the total specific energy. Comparatively, the specific energy consumed during fragmented chip formation mainly includes the local kinetic energy of fragments and fracture surface energy. When the chip morphology evolves from serrated to fragmented one, the specific energy consumed reduces substantially, which demonstrates that the UHSM is beneficial for the energy saving. Lastly, taking both of the material removal efficiency and machined surface quality into consideration, the UHSM is recommended to be applied in rough machining or semi-finishing, while high speed machining is recommended to be applied in finishing process. This research firstly reveals the control mechanism for ductile-to-brittle transition of ductile materials under critical cutting speed (i.e. critical strain rate) considering solid mechanics and metal cutting principles as well as energy consumption simultaneously. This paper is enticing from both engineering and analytical perspectives aimed at revealing the mechanism of UHSM and instructing the optimization of machining parameters.
•A predictive model of critical cutting speed for UHSM is proposed and validated.•Micrographs of chips, chip roots and finished surfaces are observed and analyzed.•Specific energy model for the serrated chip formation is established.•Specific energy model for fragmented chip formation under UHSM is established.
•The variation of specific energy due to ductile-to-brittle transition is analyzed.
The surface integrity of single crystal (100)Ge machined by on-axis single point diamond turning was investigated. The specimen was machined with a -25◦ rake angle single crystal diamond tool, with a ...depth of cut of 10 μm and a feedrate of 4 μm/rev. Six circular bands were machined on the specimen at different cutting speeds, ranging from 0.2 m/s to 10 m/s, while keeping all other machining and geometrical parameters constant. The surface topography was measured by atomic force microscopy and the near surface lattice disorder was investigated by Raman spectroscopy. The cutting and thrust forces were measured during machining, and their frequency domain was analyzed. Machining resulted in four lobes with four-fold symmetry, with differing amounts of surface fracture at each cutting speed. It was found that increasing the cutting speed generates surfaces with less or no brittle fracture for all cutting directions, causing some lobes to be undistinguishable. As the speed increased, the cutting and thrust force decreased monotonically. The frequency content of the force changed accordingly with the appearance of the surface, with a shift from 8 oscillations per revolution to 4 oscillations per revolution.
Wire Electrical Discharge Machining (WEDM) represents a pivotal process in the fabrication of high-strength materials such as Ni-based alloys, which find extensive application in aerospace and ...nuclear industries. In this study, the machining parameters have been considered as Spark on time (T on ), wire-speed (WS), Servo Sensitivity (FR), and gap voltage (GV). The machining performance on Inconel 690 has been identified with the help of Cutting speed (CS) and average Surface roughness (SR) through WEDM using Molybdenum (Mo) wire. Taguchi’s philosophy has been considered in designing the experiments. The performance characteristics were analysed using a main effect plot and Analysis of Variance (ANOVA). The most significant parameter has been observed as T on . Furthermore, a hybrid optimization technique has been employed using ANN coupled with MOJAYA to obtain the optimum machining parameters. The confirmation tests have been conducted has maximum percentage of error has been found as 7.88%. The said hybrid techniques was provided optimisation results within 4.65 seconds and identified as suitable techniques for optimisation results for Inconel-690
Refractory high entropy alloys (RHEAs) have shown great promise for a multitude of advanced engineering applications due to their high mechanical stability from cryogenic temperatures to 1600 °C. ...However, the low ductility they exhibit at room temperature limits their machinability when traditional machining techniques are used. Studies on the nontraditional machining of RHEAs, on the other hand, are very limited. In the present work, MoNbTaTiZr RHEAs subjected to wire electrical discharge machining (WEDM) were examined using electron microscopy, contact profilometry, and nanoindentation. Voids, microcracks, and recast material were observed on the machined surfaces. A transition from roughing to finishing decreased the amount of recast material, but the density of observable voids and microcracks on the surface increased. Optimal results were obtained by finishing, where the surface quality was improved by the removal of recast material remaining from prior passes. The brass wire electrode provided a smoother surface while the copper-core electrode provided minor heat-affected zone in the MoNbTaTiZr samples. In the roughing cuts, a 7.00% improvement in surface roughness was achieved using the copper-core electrode compared to the brass electrode. In the semi-finishing and finishing cuts, the brass wire electrode provided improvements of 13.68% and 22.68%, respectively, compared to the copper-core electrode. On the other hand, the wear of the brass electrode was as much as 20.98% higher than that of the copper-core electrode.
Cutting mechanism of CFRP is different from that of a homogeneous metal. For metal, high speed cutting can improve machining quality and efficiency. However, there is no agreed conclusion on the ...effect of cutting speed on the cutting mechanism of CFRP. This paper studies the effect of cutting speed on cutting mechanism of CFRP and damage formation by using finite element and experiment methods. A three-dimensional finite element model of orthogonal cutting CFRP is established considering the strain-rate-dependent mechanical properties of resin and the anisotropy of fiber. By this model, cutting processes at micro level are simulated. Fracture evolution processes of fiber and resin are characterized. Furthermore, experimental data of cutting forces are obtained, and the machined surface microstructure are observed based on orthogonal cutting experiments. Subsurface morphology and degree of resin cracking extension in simulation and experiment are consistent with each other. Results show that with the increase of cutting speed, the fiber deformation and the affected area before fiber fracture obviously deceases. Accordingly, the resin cracking and extension degree caused by the excessive deformation of fiber also be greatly reduced. In addition, there is a trend that the specific energy gap for different chip formation modes becomes smaller and smaller.
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