High Efficiency Machining Research Articles

Surface integrity of holes machined by electrochemical discharge drilling method

Micro-hole structures are widely used in aircraft engines, but they are difficult to fabricate because of stringent machining quality requirements. Electrochemical discharge drilling (ECDD) is a hybrid machining method for fabricating small holes in nickel-based superalloys that uses low-conductivity salt solution as the working fluid. Electrical discharge and electrochemical dissolution occur simultaneously in the ECDD process. ECDD is expected to achieve micro-holes with high machining efficiency and without any recast layer, but little research has been carried out on the surface integrity. In this study, the surface morphology, element composition, residual stress, microhardness, and recast layer properties of the ECDD machined holes were analysed. The results show that the surface integrity of the holes improves by the ECDD method, and there is no recast layer, no melted debris, and no tensile residual stress. Moreover, with an increase of the working fluid conductivity from 0.005 to 3.6 mS/cm, the residual stress of the ECDD machined hole becomes compressive, the microhardness of the wall no longer decreases significantly, and the surface roughness of the wall decreases to Ra = 1.69 μm. Furthermore, the average diameter and the taper angle of ECDD machined hole increase with the increase of machining time. In addition, the entrance of the ECDD machined hole has a round corner without a sharp edge, and its radius-of-curvature is approximately 150 μm.

High-quality and high-efficiency machining of stone-plastic composite with diamond helical cutters

Abstract Stone-plastic composite is a relatively new engineering material that is widely used in the decoration industry. Determination of the optimal machining conditions for this composite is important for the manufacturing industry. This work investigates the cutting quality of stone-plastic composite during helical milling with diamond cutters, focusing on the damage mechanism and surface roughness of the machined surface. Response surface methodology was used to model and establish the relationship between surface roughness and cutting conditions. Analysis of variance was adopted to study the significant contributions of each factor and two-factor interactions on surface roughness. An inclined U-shaped waviness was found on the machined surface, with damage patterns of cracking and pitting mainly located in the peaks of the cutting waves. The optimal combination for cutting was found to be a helical angle of 70°, cutting speed of 51.2 m/s, feed per tooth of 0.26 mm, and cutting depth of 0.72 mm; hence, these parameters are proposed for use in industrial stone-plastic composite machining for optimal cutting quality and machining efficiency.

Prediction of chatter stability for enhanced productivity in parallel orthogonal turn-milling

To increase productivity and the material removal rate, an increasing number of factories have been employing multiple tools for simultaneous cutting. Among these tools is parallel orthogonal turn-milling, which is an important parallel-processing method. However, a dynamic interaction occurs during the cutting processes due to the waviness induced on the shared cutting surface and the dynamic coupling through the machine structure, creating machining vibrations, or chatter, which affect the quality of the machined surface. Therefore, to reduce or avoid the vibration problem during the cutting process, chatter stability of parallel orthogonal turn-milling was examined in this study. Initially, a chatter mechanism model of parallel orthogonal turn-milling was designed, and the limit-critical axial depth of the cut formula was obtained. Next, the model parameters of the machine tool were obtained based on the hammer test method. A parallel orthogonal turn-milling stability lobe diagram (SLD) with tool tip runout was constructed. Finally, the experimental results were verified on a high-efficiency turn-milling machine tool. The results showed that chatter can be predicted for parallel orthogonal turn-milling and an SLD can provide a reference for the selection of machining parameters. In addition, the SLD can also guide the formulation of processing technology specifications. Our results are extremely significant for ongoing research in the field of machining methods.

Investigation of the trajectory uniformity in water dissolution ultraprecision continuous polishing of large-sized KDP crystal

Large-sized potassium dihydrogen phosphate (KDP) crystals are an irreplaceable nonlinear optical component in an inertial confinement fusion project. Restricted by the size, previous studies have been aimed mainly at the removal principle and surface roughness of small-sized KDP crystals, with less research on flatness. Due to its low surface damage and high machining efficiency, water dissolution ultraprecision continuous polishing (WDUCP) has become a good technique for processing large-sized KDP crystals. In this technique, the trajectory uniformity of water droplets can directly affect the surface quality, such as flatness and roughness. Specifically, uneven trajectory distribution of water droplets on the surface of KDP crystals derived from the mode of motion obviously affects the surface quality. In this study, the material removal mechanism of WDUCP was introduced. A simulation of the trajectory of water droplets on KDP crystals under different eccentricity modes of motion was then performed. Meanwhile, the coefficient of variation (CV) was utilized to evaluate the trajectory uniformity. Furthermore, to verify the reliability of the simulation, some experimental tests were also conducted by employing a large continuous polisher. The results showed that the CV varied from 0.67 to 2.02 under the certain eccentricity mode of motion and varied from 0.48 to 0.65 under the uncertain eccentricity mode of motion. The CV of uncertain eccentricity is always smaller than that of certain eccentricity. Hence, the uniformity of trajectory was better under uncertain eccentricity. Under the mode of motion of uncertain eccentricity, the initial surface texture of the 100 mm × 100 mm × 10 mm KDP crystal did achieve uniform planarization. The surface root mean square roughness was reduced to 2.182 nm, and the flatness was reduced to 22.013 μm. Therefore, the feasibility and validity of WDUCP for large-sized KDP crystal were verified.

Research on flying cutting technology with micro pyramid array structure

The fabrication of optical elements with microstructural arrays has attracted more and more attention. Single-point diamond flying cutting technology has been gradually applied to the fabrication of microstructures with the advantages of high efficiency, low cost and high machining accuracy. This paper mainly studies the influence of repeated positioning errors of machine tools and errors introduced by cyclic machining on micro-structure turning effect when flying cutter turning micro-pyramid structure, analyses the conditions of secondary groove generation in V-groove turning, studies the methods of restraining secondary groove generation, and finally verifies through experiments that the generation of secondary groove can be restrained by controlling the turning depth greater than the minimum turning depth.

A hybrid approach for cutting force prediction in flank milling based on analytical and 3D finite element method

Flank milling is one of the most widely used milling processes characterized by high machining efficiency. However, due to the low thermal conductivity and high-temperature strength of nickel-based superalloy Inconel 718, flank milling of Inconel 718 is still an extremely difficult and challenging task in which the milling cutter suffers large cutting force and excessive tool wear. Therefore, prediction of cutting force in milling process has caused due attention and became a major concern in manufacturing process. The present work is thus aimed at developing a new cutting force model for flank milling, which might try to eliminate the drawbacks of pure analytical force model, data-based reasoning method (DBRM), and full three dimensional (3D) finite elements (FE) model. The hybrid cutting force model is conducted by discretizing cutting edge into fragments based on infinitesimal method and regarding each fragment as a 3D oblique cutting FEM model. With the integration of 3D predicted cutting force along the axis considering the run-in and run-out effect of each cutting edge, the predicted cutting force can be obtained. Finally, the predicted results showed a good agreement with that of experimental.

FEM-based optimization approach to machining strategy for thin-walled parts made of hard and brittle materials

Thin-walled parts are widely used in the aerospace, automotive, and medical industries. High machining efficiency is desired as much of the material needs to be removed. The aggressive machining strategies are often applied but tend to cause poor surface finish, inadequate machining tolerance, and even fracture of workpiece. Thus, it is of vital importance to adopt reasonable machining strategy and choose accurate machining parameters considering of both the machining efficiency and quality. In this paper, an optimization approach to enhance machining efficiency for thin-walled parts made of hard and brittle material without compromising machining quality was proposed. The core idea of the proposed approach is to minimize the maximum stress of the thin-walled part during machining by optimizing the workpiece shape based on finite element method (FEM). The stiffness of the thin-walled parts during machining retains high while the machining induced deformation is small. The optimization approach was experimentally validated on K9 glass, and the maximum deformation of the thin-walled part for the optimal machining strategy decreases significantly compared with that of traditional machining strategy and the total machining time is reduced by 44%.

Dynamic Hysteresis Modeling for Magnetic Circuit Analysis by Incorporating Play Model and Cauer’s Equivalent Circuit Theory

Quantitative analysis of iron loss taking magnetic hysteresis behavior into account is essential to development of high-efficiency electric machines. In a previous article, a novel magnetic circuit model incorporating a play model was proposed. It was clear that the proposed model can calculate the hysteresis loop of the magnetic reactor with high accuracy and high speed. However, there is a possibility for further improvement in the calculation accuracy of the minor loop generated from carrier harmonics under PWM excitation because the influence of the skin effect cannot be considered. Therefore, this article describes that the Cauer's equivalent circuit theory, which can represent dynamic hysteresis characteristics considering the influence of the skin effect, is applied to the magnetic circuit model, and indicates the validity of the proposed method experimentally.

Look-ahead-window-based interval adaptive feedrate scheduling for long five-axis spline toolpaths under axial drive constraints

Scheduling of the five-axis spline toolpath feedrate is of great significance for high-quality and high-efficiency machining using five-axis machine tools. Due to the fact that there exists nonlinear relationship between the Cartesian space of the cutting tool and the joint space of the five feed axes, it is a challenging task to schedule the five-axis feedrate under axial drive constraints. Most existing methods are researched for routine short spline toolpaths, however, the five-axis feedrate scheduling method expressed for long spline toolpaths is limited. This article proposes an interval adaptive feedrate scheduling method based on a dynamic moving look-ahead window, so as to generate smooth feedrate for long five-axis toolpath in a piecewise manner without using the integral toolpath geometry. First, the length of the look-ahead window which equals to that of the toolpath interval is determined in case of abrupt braking at the end of the toolpath. Then, the interval permissible tangential feed parameters in terms of the velocity, acceleration, and jerk are determined according to the axial drive constraints at each toolpath interval. At the same time, the end velocity of the current interval is obtained through looking ahead the next interval. Using the start and end velocities and the permissible feed parameters of each interval, the five-axis motion feedrate is scheduled via an interval adaptive manner. Thus, the feedrate scheduling task for long five-axis toolpath is partitioned into a series of extremely short toolpaths, which realizes the efficient scheduling of long spline toolpath feedrate. Experimental results on two representative five-axis spline toolpaths demonstrate the feasibility of the proposed approach, especially for long toolpaths.

Sustainable and high-efficiency green electrical discharge machining milling method

Conventional electrical discharge machining (EDM) milling methods have some disadvantages when used to machine difficult-to-cut materials, including low machining efficiency, high energy consumption, severe electrode wear, and poor processing environments. In this paper, a sustainable and high-efficiency EDM milling method is proposed for solving the above problems. A high-efficiency green pulse power supply with high energy is designed and different environmentally friendly working fluids are used for machining experiments. The energy utilization rate, environmental performance, and machining performance under different conditions of this new method are studied. The results show that the proposed method presents high machining efficiency, low energy consumption, mild electrode wear, and environmentally friendly features. The material removal rate can reach 900.66 mm3/min and the relative electrode wear rate is 1.20% when machining the 17-4 PH stainless steel workpiece. It is found that the new pulse power supply increases the energy utilization rate by more than 200%. Compared with the conventional EDM milling methods, the proposed method can meet the requirements of energy-saving and sustainable production.

Modeling and detection of the prepared tool edge radius.

High-speed and high-efficient machining is the inevitable development direction of machining technology. The tool edge preparation can improve the life, cutting performance, and surface quality of a tool and help to achieve high-speed and efficient machining. Therefore, precise modeling and detection of the micron-level contour of a tool edge are crucial for edge preparation. The aim of this study is to provide the model and detect method of the prepared tool edge radius. The mathematical model of the milling tool trajectory is established through the Matlab. The material removal model by single abrasive particle is established based on the energy conservation principle and energy absorption theory. The material removal model by multiple abrasive grains on the cutting tool edge is constructed using the statistical methods. The mathematical model of the edge radius is established through the geometrical relationship. The milling edge preparation contour detection system is setup based on the machine vision principle through LabVIEW software. Finally, the edge radius at different process parameters is determined by the mathematical model and detection system, and the results are compared with the results of the scanning electron microscopic measurement (SEM). Through the Comparison and analysis of the edge radius measured by the SEM and calculated by the proposed model. The maximum error between the analytical results and SEM measurements is 11.18 μm, while the minimum error is 0.07 μm. Through the comparison and analysis of the edge radius measured by the SEM and the edge detection system. The maximum difference between the two methods is 2.71 μm, and the minimum difference is 0.31 μm. The maximum difference in percentage is 9.2%, and the minimum difference in percentage is 1.2%. The edge preparation mechanisms of a single particle and multiple particles on the tool edge are explained. A mathematical model of the edge radius is established, which provides a basis for a deeper understanding of the edge preparation effect. Based on the machine vision principle, the prepared tool micron-level edge detection method is proposed. The histogram specification method, median filtering, multi-threshold segmentation method, and Canny edge detection operator are adopted to obtain the edge contour. The comparison result shows that the mathematical model of the edge radius is accurate, and the proposed tool edge detection method is feasible, which lays the foundation for edge preparation and realization of high-speed and high-efficient machining.

Fundamentals of Machine-Tool Leasing in the Russian High-Tech Industry

The constraints on the supply of high-efficiency machine tools to Russia’s high-tech industry are identified. The corresponding supply systems are categorized. Within that framework, the role of equipment leasing is discussed. A systems approach to the leasing market permits the use of intelligent support systems for leasing decisions. The main obstacles to management innovation are considered.

A modeling and prediction method for plunge cutting force considering the small displacement of cutting layer

In the process of plunge milling, the main cutting force is along the axial direction, and usually, the machining system has good axial rigidity, so it can withstand large cutting loads. This characteristic makes plunge milling particularly suitable for high-efficiency rough machining and semi-finishing of difficult-to-cut materials. The cutting force in the plunge milling process is usually large, and when the process parameters are not selected properly, the plunge milling is prone to the back-off phenomenon. In view of the characteristics of large cutting force and high cutting temperature in Inconel 718 plunge milling process, considering the small displacement of the actual tool tip caused by cutting force and cutting vibration, this article establishes a plunge milling force model based on the combination of analytical method and three-dimensional finite element method. The micro-displacement caused by vibration is obtained through dynamic modeling and modal test methods. Combined with the macro-displacement of cuter back-off under the action of the cutting force during the single-tooth run-in and run-out process, the modified cutting layer parameters are obtained, and optimized cutting force of plunge milling is obtained.

Microfiber release from real soiled consumer laundry and the impact of fabric care products and washing conditions.

Fiber release during domestic textile washing is a cause of marine microplastic pollution, but better understanding of the magnitude of the issue and role of fabric care products, appliances and washing cycles is needed. Soiled consumer wash loads from U.K. households were found to release a mean of 114 ± 66.8 ppm (mg microfiber per kg fabric) (n = 79) fibers during typical washing conditions and these were mainly composed of natural fibers. Microfiber release decreased with increasing wash load size and hence decreasing water to fabric ratio, with mean microfiber release from wash loads in the mass range 1.0-3.5 kg (n = 57) found to be 132.4 ± 68.6 ppm, significantly (p = 3.3 x 10-8) higher than the 66.3 ± 27.0 ppm of those in the 3.5-6.0 kg range (n = 22). In further tests with similar soiled consumer wash loads, moving to colder and quicker washing cycles (i.e. 15°C for 30 mins, as opposed to 40°C for 85 mins) significantly reduced microfiber generation by 30% (p = 0.036) and reduced whiteness loss by 42% (p = 0.000) through reduced dye transfer and soil re-deposition, compared to conventional 40°C cycles. In multicycle technical testing, detergent pods were selected for investigation and found to have no impact on microfiber release compared to washing in water alone. Fabric softeners were also found to have no direct impact on microfiber release in testing under both European and North American washing conditions. Extended testing of polyester fleece garments up to a 48-wash cycle history under European conditions found that microfiber release significantly reduced to a consistent low level of 28.7 ± 10.9 ppm from eight through 64 washes. Emerging North American High-Efficiency top-loading washing machines generated significantly lower microfiber release than traditional top-loading machines, likely due to their lower water fill volumes and hence lower water to fabric ratio, with a 69.7% reduction observed for polyester fleece (n = 32, p = 7.9 x 10-6) and 37.4% reduction for polyester T-shirt (n = 32, p = 0.0032). These results conclude that consumers can directly reduce the levels of microfibers generated per wash during domestic textile washing by using colder and quicker wash cycles, washing complete (but not overfilled) loads, and (in North America) converting to High-Efficiency washing machines. Moving to colder and quicker cycles will also indirectly reduce microfiber release by extending the lifetime of clothing, leading to fewer new garments being purchased and hence lower incidence of the high microfiber release occurring during the first few washes of a new item.

Fabrication of micro rotary structures by wire electrochemical grinding

Micro rotary structures have attracted increasing attention in many industrial applications. However, the fabrication of complex micro rotary structures with high strength, high hardness, and low rigidity, poses a significant challenge to traditional machining methods. To solve this difficult problem, this study proposes a novel method of fabricating complex micro rotary structures by using wire electrochemical grinding (WECG), which is an anodic dissolution process and has no machining force. WECG, a type of ECM, has some major advantages over wire electrical discharge grinding (WEDG): no electrode wear, absence of residual stress, good surface quality, low machining cost, and high machining efficiency. Firstly, this study investigated the influences of the process parameters on the dimensional accuracy of the micro grooves produced, then optimized these process parameters. A qualitative simulation of WECG was conducted to reveal the reason for the trumpet-like micro grooves fabricated by WECG. Finally, based on the optimal process parameters, several different kinds of rotary structures were successfully produced by WECG. The experimental results demonstrate that WECG is a promising method for fabricating complex rotary structures of difficult-to-cut materials at low cost and with high efficiency.

Investigation on ultrasonic elliptical vibration boring of deep holes with large depth–diameter ratio for high-strength steel 18Cr2Ni4WA

An ultrasonic elliptical vibration boring device for deep hole parts was designed, and the modal analysis, harmonic analysis, and transient analysis of this device were analyzed using finite element method. The results of harmonic analysis proved the feasibility of the design scheme, and transient analysis results indicated that the design scheme could realize elliptical vibration of the tool tip. The structure parameters of this device were optimized based on finite element analysis. Impedance measurement results of the device indicated that the ultrasonic elliptical vibration boring device was reliable. Ultrasonic elliptical vibration boring experiments of deep hole parts for high-strength steel 18Cr2Ni4WA were performed on a high-precision machine tool. The experimental results indicated that increasing the excitation voltage could effectively reduce the cutting force and surface roughness, and improve the stability of the boring process. Decreasing the rotation speed, feed speed, and cutting depth could effectively reduce the cutting force and surface roughness, and improve the stability of the boring process. Compared with traditional boring, ultrasonic elliptical vibration boring can significantly reduce the boring force, surface roughness, cutting chip length, and vibration of the boring bar. This work is of great significance for achieving high-efficiency and precision machining of deep hole parts.

Analytical methods for the radial electromagnetic vibration of stator in permanent magnet motors with an amorphous alloy core

The urgent demand for high efficiency of electrical machines leads to the preliminary application of amorphous alloy, however the accompanying vibration problem becomes more complex. The radial electromagnetic vibration of the amorphous stator core in a permanent magnet motor is analytically investigated in this paper. The magnetic field distribution approach considering the slotted effects and eccentricity is proposed and the air-gap magnetic flux density is validated by the finite element method. The magnetization and magnetostriction characteristics of the amorphous alloy are obtained. The dynamic models for the stator core including yoke sections and the tooth-yoke sections are respectively established. The Maxwell stress and magnetostriction stress are integrated in the magneto-mechanical coupling model. Dynamic responses in the stator core for different radii, position angles and times are analyzed. Vibrations of conventional core with silicon steel and amorphous core are compared. The spatial and temporal characteristics of the dynamic responses in the stator core are explored. The origins and corresponding weights in the electromagnetic vibration at different rotating speeds are revealed. Experiments of a modified permanent magnet motor equipped with the amorphous core are conducted. The theoretical results are validated well by experiments. Results demonstrate that the vibration level of the amorphous core is larger than the silicon steel core when other conditions are the same. Radial vibrations of the stator core are caused by the Maxwell stress, magnetostriction stress and their interaction effects. The weight of magnetostriction effects is improved with the increasing rotating speed. These findings provide an insight into the mechanism of electromagnetic vibration in amorphous stator core and can be helpful for the design of high-efficiency electrical machines.

High-efficiency smooth-surface high-chatter-stability machining of thin plates with novel face-milling cutter geometry

This paper presents a new technology to realize high-efficiency, smooth-surface, and high-chatter-stability machining of flexible thin plates with the proposed face-milling cutter geometry. Radius end mills are widely utilized for high-efficiency and smooth-surface machining, but they generally have low machining stability, i.e. chatter vibrations often occur. It is well known that the chatter stability depends on the structural flexibility and the cutting conditions, whereas it is less known that it strongly depends on the cutter geometry. In this study, a novel face-milling cutter geometry is proposed to improve chatter stability, especially for regenerative chatter, without sacrificing the high efficiency and the surface smoothness in radius end milling. The validity of the milling technology utilizing the proposed cutter geometry is verified analytically and experimentally.

Electrochemical milling of narrow grooves with high aspect ratio using a tube electrode

Abstract Metallic narrow grooves with high aspect ratio, referred to here as deep narrow grooves (DNGs), are used widely in precision instruments, medical devices and other industries. However, because DNGs are usually less than 4 mm in width with depth-width ratio (aspect ratio) more than 2, it remains extremely challenging to machine them with high precision and efficiency, especially for blind (i.e., closed-end) cases. Therefore, this paper proposes a novel method of electrochemical milling using a tube electrode to fabricate a DNG by single-pass milling. A multi-physics coupling model, including a gas-liquid two-phase flow field and an electric field, was built to investigate the flow field distribution in the inter-electrode gap as well as the current density distribution at the DNG edge with different electrolyte pressures. Related experiments were also conducted. The simulation and experimental results indicated that a higher pressure was associated with a high electrolyte velocity, and had a significant influence on the machining process. First, the high electrolyte velocity in the inter-electrode gap could enhance the mass transfer and improve the sectional profile of the DNG. Second, when the electrolyte flowed out, the high electrolyte velocity could overcome self-gravity and reduce the accumulation at the edge of the DNG, which decreased the electrolyte volume fraction in the two-phase flow field at the DNG edge. Thus, the current density distribution at the outlet edge was decreased, and the corner radius at the edges of the DNGs was reduced. Then, systematic experiments were performed with different machining parameters (including electrolyte pressure, pulse parameters and feeding speed) to investigate their influence on the DNG dimensions; with the optimized parameters of an electrolyte pressure of 0.9 MPa, applied voltage of 12 V, pulse frequency of 9 kHz, pulse duty cycle of 40 % and feeding speed of 0.36 mm/min, a complex narrow groove of width 1.32 ± 0.02 mm (mean ± standard deviation) and depth 8.05 ± 0.01 mm was well fabricated with single-pass milling, and the aspect ratio reached 6.1, showing a high precision and efficiency machining method.

Effect of cutting parameters and tool rake angle on the chip formation and adiabatic shear characteristics in machining Ti-6Al-4V titanium alloy

Ti-6Al-4V titanium alloy is widely used in aeronautical parts and the high-efficiency machining and manufacturing process is surely a challenging work. The cutting parameters’ proper selection and tool geometric angles’ adoption will affect the material removal process in terms of chip formation and machined surface formation processes. In this paper, Abaqus finite element software was utilized to model and simulate the Ti-6Al-4V titanium alloy cutting process. The setting and selection of the constitutive model, material failure criterion, friction attribute, and heat transfer model make sure that the simulation is more in line with the actual cutting process. The correctness of the simulation model is verified by comparing the cutting forces and chip morphological characteristics obtained by the simulation with the experiments. Then, the effect of cutting parameters and tool rake angle on the chip formation and analyses of the adiabatic shear banding process was investigated, by using the machining simulation tests with different tool rake angles and cutting speeds. Results illustrate that the chip segmentation degree increases with the increase of cutting speed and feed rate, while it decreases with the increase in rake angle. The adiabatic shear-banding chip formation mechanisms were revealed by analyzing the relationship between shear strain, shear stress, chip segmentation degree, and high-temperature shear zone in undeformed plot contours. The serrated chip formation process when machining titanium alloy accompanies with the dramatic changes of shear strain and stress in adiabatic shear banding.