Machining Stability Research Articles

Effect of interpulse voltage on recast layer machined by HSWEDM

ABSTRACT To improve the cutting speed and reduce burned layer caused by the accumulation of discharge products during high energy high-speed wire electrical discharge machining (HSWEDM), it is necessary to further study the discharge characteristics. Based on not changing the original high-frequency pulse power supply and servo feed system, an interpulse voltage power supply module is designed to improve the electrolysis effect. Comparative results show that under the same experimental conditions, the interpulse voltage can improve machining stability and cutting speed during high-energy rough cutting. The thickness of the recast layer can be reduced by 37.1%. The recast layer can be greatly reduced by the rough cutting and trimming process. The interpulse voltage has a major influence on the finishing process. The thickness of the recast layer can be further reduced from 16.65 μm to 6.23 μm by optimizing the order of interpulse voltage applied to the process.

Experimental Study on Entropy Features in Machining Vibrations of A Thin-walled Tubular Workpiece

In machining processes, chatter vibrations are always regarded as one of the major limitations for production quality and efficiency. Accurate and timely monitoring of chatter is helpful to maintain stable machining operations. At present, most chatter monitoring methods are based on the energy level at specified chatter frequencies or frequency bands. However, the spectral features of chatter could change during machining operations due to complexity and time-varying dynamics of the physical machining process. The purpose of this paper is to investigate the time-varying chatter features in turning of thin-walled tubular workpieces from the perspective of entropy. The airborne acoustics was selected as the source of information for machining condition monitoring. First, corresponding to the distinguishing surface topographies relevant to machining conditions, the features of the sound signal emitted during turning of the thin-walled cylindrical workpieces were extracted using the spectral analysis and wavelet packet transform, respectively. It was shown that the dominant vibration frequency as well as the energy distribution could shift with the transition of the machining status. After that, two relative entropy indicators based on the spectrum and the wavelet packet energy were constructed to identify chattering events in turning of the thin-walled tubes. The experimental results demonstrate that the proposed indicators could accurately reflect the transition of machining conditions with high sensitivity and robustness in comparison with the traditional FFT-based methods. The achievement of this study lays the foundations of the online chatter monitoring and control technique for turning of the thin-walled tubular workpieces.

Prediction and Experimental Study of Tire Slip Rate Based on Chassis Sinkage Amount

In view of the problems that the fuselage inclines and the driving straightness is difficult to guarantee due to the sinking and sliding of the wheels when the high-clearance plant protection machine is working in the paddy field, this paper takes high-clearance wheels as the research object, based on the paddy field driving environment, establishes a prediction model of the wheel subsidence through derivation, and explores the influence of different wheel parameters on the subsidence characteristics through experiments, so as to improve the chassis trafficability. At the same time, using the test data under different wheel parameters, the prediction model of the settlement of the working chassis with high clearance is correspondingly modified. Finally, the paddy field trafficability of the working chassis is compared and analyzed based on different tire parameters. The results show that when the wheel slip rate is 0.5, the traction force of the solid tire is 37% higher than that of the pneumatic tire; when the height of the wheel spike increases, the traction force increases, and the settlement decreases obviously; proper increase of the wheel diameter can improve the passing performance of the chassis; with the increase of the tire width, the angle of soil penetration decreases while the tire is driving, and the angle of the slope climbing increases; and when the load changes, the driving coefficient is proportional to the traction coefficient, and the tire resistance coefficient is inversely proportional to the traction coefficient. Through the research on the settlement mechanism of the high-clearance operation chassis and the analysis of the paddy field trafficability, the stability of the high-clearance plant protection machine in the paddy field has been improved, providing a platform and guarantee for subsequent precision operation.

Experimental Research on the Dynamic Stability of Internal Turning Tools for Long Overhangs

The roughness origin of machined surfaces is caused by the following physical causes: the copying of the shape and the roughness of the cutting part of the tool into the workpiece, the existence of vibration of the tool, and the existence of the build-up edge (BUE) on the cutting edge. The current work aims to analyze the vibration amplitude of tools. The roughness of the machined surfaces was observed on hardened steel workpieces. Internal turning technology was used, and we used several different boring bars (steel; carbide; tuned mass damper—TMD; impact damper—ID) and an internal turning operation using CBN inserts. We revealed the tool’s slenderness coefficient (TSC) values for stable cutting operations. For the steel holder, the value is TSC ≤ 4.25; for the carbide holder, the value is TSC ≤ 5.5; for the TMD holder, the value is 4.5 ≤ TSC ≤ 7.75; and for the ID holder, the value is TSC ≤ 8. The surface’s roughness was practically unchanged within the limits of stable machining. However, if the tools exceed the presented stable limits, vibration and roughness parameters deteriorate significantly; an example parameter (Ra) deteriorated from 0.350 μm to 1.832 μm.

Stability analysis of pocket machining with the spiral tool path using the discontinuous Galerkin method

Pocket machining is widely used in the aerospace and automotive industries. The spiral tool path ensures smooth and consistent pocket machining. However, high-efficiency pocket machining places great demand for the stability of the milling processes. In this paper, the mechanics and dynamics of pocket machining along the spiral tool path are modeled, and a time-domain method is proposed to predict the stability of pocket machining in the framework of the discontinuous Galerkin method (DGM). The mechanics of pocket machining is modeled on the basis of computing the varying cutter-workpiece engagement. The cutting forces are predicted and experimentally verified. Further, the dynamic model of pocket machining is established and the stability of the pocket machining process is predicted with the stability lobes of representative feed directions along the spiral tool path. The DGM based time-domain method is proposed to improve the computational accuracy and efficiency of the stability analysis. The predicted stability of pocket machining along the spiral tool path is validated by the experimental results.

Crack formation of camshaft castings: Hot tearing susceptibility and root causes

As a widely used cyclical motion component, the camshaft plays a key role in the accuracy and stability of the whole machine. Micro hot cracks in the camshaft casting process are an important cause of failure in subsequent machining and operation. In this paper, the hot tearing susceptibility of the camshaft in the casting process was studied using the alloy composition (carbon equivalent and Mn/S ratio) and mold preheating temperature. The formation mechanism of the hot tear source was analyzed through the microscopic morphology of the fracture-sensitive cross-section. Using the improved Clyne-Davies model and the newly proposed hot tearing susceptibility (HTS) model, the results show that as the carbon equivalent and Mn/S ratio increase, the hot tearing susceptibility of the camshaft first decreases and then increases. The hot tearing tendency of the casting can be reduced by appropriately increasing the mold preheating temperature. The microscopic morphology indicates that the initiation and propagation of the crack source are caused by the excessively serious non-equilibrium solidification of the camshaft metal fluid. Finally, potential countermeasures are proposed to decrease micro hot cracks in camshaft castings, including the adjustment of alloy composition, optimization of casting process parameters, and improvement of system solidification conditions.

Hybrid forecasting system considering the influence of seasonal factors under energy sustainable development goals

As environmental concerns and the energy crisis intensify, advancing the use of new energy sources such as wind and photovoltaic is an important means to achieve sustainable energy development. However, the random fluctuation characteristics and seasonality of wind and light make them difficult to predict, which brings many operational risks to grid security and power dispatch. Therefore, this paper uses the Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) as the decomposition algorithm, which can effectively avoid the problems of modal confusion and noise residuals and better identify the trend, seasonality and nonlinear characteristics of the series. The Particle Swarm Optimization (PSO) algorithm is also utilized to improve the prediction accuracy and stability of the Extreme Learning Machine (ELM). Combining CEEMDAN and PSO-ELM models, a high-precision hybrid forecasting system that can effectively reduce the effects of stochastic fluctuations is proposed. In this paper, wind speed data from four different seasons at Changma wind farm in China are selected to verify the effectiveness and generalization ability of this hybrid prediction system. The results show that the improvement of ELM by PSO and CEEMDAN significantly improves the prediction accuracy of the model, and the hybrid prediction system can be applied to time series with different data characteristics and variation patterns in each season, and its prediction accuracy and model performance are significantly better than other comparative models.

Learning machining stability diagrams from data using neural networks

Machining instabilities are detrimental. model predicted stability charts help identify cutting parameters for stability. Since models disregard speed-varying cutting force characteristics and dynamics, charts fail to guide stable cutting in industrial praxis. This study shows how supervised neural networks can learn stability charts from data. The learning capacity of this machine learning model depends on the size of the training dataset, its train-test split, the learning rate, the activation function, the number of hidden layers, and the number of neurons in each layer. This is the first study to examine how hyperparameters influence learning machining stability diagrams. Learnings from a linear stability dataset are transferrable to nonlinear datasets, demonstrating the prediction model is physics-agnostic. Predictions accuracies of up to 97.2% were obtained. Since the data used to train the model includes all the vagaries and uncertainties of the cutting process, the results can inform self-optimizing and autonomous machining systems.

Learning machining stability using a bayesian model

Instabilities in machining can be detrimental. Usually, analytical model-predicted stability charts guide selection of cutting parameters to ensure stable processes. However, since inputs to the model seldom account for the speed-dependent behaviour of the cutting process or the dynamics, models often fail to guide stable cutting parameter selection in real industrial settings. To address this issue, this paper discusses how real experimentally classified stable and unstable cutting data with all its vagaries and uncertainties can instead be used to learn the stability behaviour using a supervised Bayes' learning approach. We expand previously published work to systematically characterize how probability distributions, training data size, and thresholding influence the learning capacity of the Bayesian approach. Prediction accuracies of up to 95% are shown to be possible. We also show how the approach nicely extends itself to a continuous learning process. Results can hence inform further development towards self-optimizing and autonomous machining systems.

Tool vibration isolation in hard turning process with magnetorheological fluid damper

Tool vibration in metal cutting significantly influences the surface finish and machining stability. Suppressing the tool vibration to enhance the finished product quality is the need of the hour. The current study proposes the augmentation of a Magnetorheological (MR) fluid damper to suppress tool vibration in hard tuning with easy installation without structural modification. The MR fluid damper changes its damping coefficient with the magnetic field to regulate variable cutting conditions. An optimal composition of MR fluid has been prepared in-house to be used in the damper. The in-house MR fluid is compared with commercial MR fluid. The comparison shows that in-house prepared MR fluid performs equally well compared to commercial fluid. The MR damper effectively damps high-amplitude vibration at aggressive cutting conditions. The L9 Taguchi design of the experiment opted to arrive at minimal machining parameters to evaluate the damper's performance in machining two workpiece materials, namely oil-hardened nickel steel (OHNS) and high carbon high chromium (HCHCR D2) die steel. The surface roughness and tool vibration are reduced with the damper. It is noted that in-house MR fluid performed equally well as commercial MR fluid. The tool wear study is also carried out to monitor the influence of external damping over tool life. The stability lobe diagram is obtained analytically with experimental validation to mark the stability limit of the machining condition. The stability boundary increases with the damper enabling aggressive cutting conditions.

Machinability analysis of micro-milling thin-walled Ti-6Al-4V micro parts under dry, lubrication, and chatter mitigation conditions

Micro-milling technology is an efficient method for machining titanium alloy thin-walled micro parts. However, the machinability of thin-walled microstructures can be greatly affected by chatters due to their weak stiffness, especially in difficult-to-machine materials like titanium alloys. In order to obtain high-quality thin-walled micro parts, a chatter mitigation strategy is presented and its mechanism is analyzed in this paper. The titanium alloy workpiece is submerged into a kind of high-viscosity fluid, which can improve machining stability by increasing the damping of the micro-milling process. The stability lobe diagrams (SLD) are established, and the machinability is analyzed and compared under different machining conditions. The cutting force, surface roughness, micro-tool wear, and dimension accuracy of thin-walled micro parts are selected as the evaluation criteria for the machinability assessment. Well-designed micro-milling experiments are carried out under dry, lubrication, and chatter mitigation conditions using the same cutting process parameters. The results show that the use of cutting fluid can effectively improve machinability under stable cutting processes, but the effect of cutting fluid is weakened under chatter machining. The proposed chatter mitigation strategy can suppress regenerative chatter throughout the micro-milling process for thin-walled micro parts and improve their machinability comprehensively.

Investigation on a sustainable composite method of glass microstructures fabrication—Electrochemical discharge milling and grinding (ECDM-G)

Glass structures with microchannel morphology play an important role in the fields of biology, medicine and MEMS. The non-traditional machining methods currently used to machining glass have problems such as excessive energy consumption, poor sustainability, and harmful to operators and the environment. To achieve precision, efficient, green, sustainable production and save resources, a novel composite machining method of electrochemical discharge milling and grinding (ECDM-G) was proposed in this paper. Compared with tranditional electrochemical discharge machining, lower discharge energy is applied, and KH2PO4 solution is used as electrolyte instead of alkaline solution, thus realizing energy-saving and green machining. Compared with mechanical grinding, tool wear is reduced and the sustainability of machining is improved. In the theoretical part, the heat conduction process of electrochemical discharge was simulated and the softening effect of workpiece material was analyzed. Furthermore, the matching mathematical model between electrochemical discharge energy and material removal by grinding was established. So as to accurately control the energy and avoid waste. In the experiment part, the key parameters were determined through the Plackett-Burman experiment, and then the Box-Behnken experiment was conducted on the key parameters and the Response Surface Methodology (RSM) was used to obtain the optimal combination of machining parameters. Compared with mechanical grinding, the problems of edge collapse and breakage are solved. The overcut is reduced by 35.1%, the edge damage is reduced by 42.2%, the surface morphology is improved and the surface roughness value is reduced by 47.7%. Compared with ECDM, the problems of heat affected zone and thermal defects are solved. The overcut is reduced by 49.1%, the edge damage is reduced by 56.6%, the surface feather morphology is removed and the surface roughness value is reduced by 74.9%. The machining stability and consistency of ECDM-G method are analyzed by machining array microchannels. Finally, with the optimized machining parameters, the microfluidic chip with typical microchannel structure was fabricated by ECDM-G, and the tool electrode has no severe wear after machining the long path complex structure, which proves that ECDM-G can be an energy-saving, sustainable and effective method for machining precision glass microstructures with high quality, and further shows that ECDM-G has industrial application prospects in the manufacturing of key biological and medical components.

Machining stability improvement in LPBF printed components through stiffening by crystallographic texture control

The quality requirements of functional parts manufactured by the laser powder bed fusion imply post-processing machining operations. These components include thin walls, hollow and complex shapes that can lead to machining instability. This paper presents a strategy to exploit the inherent crystallographic effect as a tool for stiffening and improving machining stability by considering the orientation of machining bending loads and the crystalline orientation distribution. Three samples were manufactured under the same LPBF parameters but different crystallographic orientations. The results show that the optimal crystalline direction increases static and dynamic stiffness and stability, reducing machining chatter risks.

Compensation method of wire electrode wear for reciprocating micro wire electrical discharge machining

Reciprocating micro wire electrical discharge machining (Micro-WEDM) has the advantage of high thickness cutting because it mainly relies on the high wire speed to remove discharge production. The wire electrode wear (WEW) not only affects the machining stability and quality, but also greatly increases the risk of wire breakage in long cycle machining. Aiming at the WEW of the micro wire electrode used in reciprocating, a method of introducing compensation voltage between pulse interval (Toff) is proposed in this paper. This method can enhance the existing electrochemical effect in WEDM and compensate the WEW by means of metal ion reduction deposition effect. The verification experiment of no-load pulse indirectly shows the feasibility of the compensation method. Too large compensation voltage will affect the Toff deionization and machining stability. Its value should be less than the maintenance voltage of normal discharge. The average thickness of recast layer decreases first and then increases with the increase of compensation voltage. The minimum thickness of recast layer is about 4.7 μm at 15 V, which is 62.4 % lower than that without compensation voltage. The high conductivity dielectric can reduce the WEW, while the compensation voltage can greatly enhance this effect. Compared with the initial cutting stage，the micro wire electrode has no wear basically until the cutting area exceeded 50,000 mm2, and the cutting speed maintains above 45 mm2/min. The distribution of elements on the surface of wire electrode indicates that the strength of electrolysis is improved by the method of WEW compensation.

ОЦЕНКА ВЛИЯНИЯ БАЛАНСА МОЩНОСТЕЙ НА РЕЗУЛЬТИРУЮЩУЮ УСТОЙЧИВОСТЬ ГЕНЕРАТОРОВ С УЧЕТОМ РЕКОНСТРУКЦИИ В АВАРИЙНЫХ И ПОСЛЕАВАРИЙНЫХ РЕЖИМАХ ПРИМЕНИТЕЛЬНО К ЭНЕРГЕТИЧЕСКОМУ УЗЛУ ПРЕДПРИЯТИЯ ЧЕРНОЙ МЕТАЛЛУРГИИ

Relevance For stable operation of electrical equipment of power supply systems of industrial enterprises, it is necessary to evaluate and present measures that will solve the set tasks in an integrated manner. Thus, there is a need to assess the resulting stability when introducing new generating capacities in emergency and post-emergency modes, taking into account unbalanced capacities. The object of the study is a power hub characterized by a complex configuration with a voltage class from 0.4 to 500 kV and contains its own generation sources. The main consumer of which is the largest producer of ferrous metallurgy. Aim of research The aim of the work is to determine the influence of the power balance on the resulting stability of generators in emergency and post-emergency modes. Research methods To achieve this goal, an algorithm has been developed, which is the basis of the KATRAN program complex. Results This algorithm makes it possible to study the short-circuit elimination mode with separation from the power system as a result of relay protection and automation action with determination of the power unbalance share. According to the results of the work, power areas with violation of the resulting stability of synchronous machines and the resulting power unbalance, allocated as a result of the short circuit, were identified, which allowed to issue additional recommendations on connecting loads in the network or their disconnection in emergency mode. The obtained recommendations will allow to increase the reliability of power supply of the enterprise in order to increase the volume and quality of manufactured products.

Modeling of logging machine stability operating with a vertically held tree

The article presents the results of mathematical modeling of the stability of a logging machine with a vertically held tree when it is removed from the canopy of the forest. The calculation schemes for two positions of a vertically held tree are described. The substantiation of the idealization for the calculation schemes of a vertically held tree is given. The dynamic stability equations of a logging machine with a vertically held tree are constructed on the basis of second kind Lagrange equations system. Due to analyze the interrelationships between dynamic parameters and processes of a logging machine with a vertically held tree, motion differential equations were integrated taking into account external influences and initial conditions. Using the MATLAB program, the integration operations of second kind Lagrange equations system were carried out for two cases: 1) The vertical tree is rigidly fixed and repeats the deviations of the logging machine; 2) The tree is perfectly held vertically with any deviations of the logging machine. The input parameters for the calculation were the rigidity of the connections, the parameters of the logging machine, the gripping cutting device (GCD) and the tree. The parameters of the slope of the logging machine were set using the implementation of a Gaussian random process with a given correlation and variance. The dynamic stability study of a logging machine with a vertical tree showed that the ideal tree alignment in a vertical position leads to a decrease in the inertia moment of the system and to a significant decrease in the frequency of angular and linear oscillations compared with a rigidly fixed tree.

丘陵山地玉米联合收获机车架结构设计与有限元分析

In view of high center of gravity and poor stability of traditional corn harvesters, a corn combine harvester frame is designed for hill and mountain operations based on TRIZ theory. The frame supports engine mode of middle engine rear drive, consisting of a front frame and a rear frame. The tail of the front frame is welded under the head of the rear frame. The front frame has reduced height and increased width to allow lower center of gravity and better stability of the whole machine. The left and right longitudinal beams of the front frame have different heights to allow better trafficability of the whole machine. A 3D model is established using Solidworks software and incorporated with ANSYS software to perform finite element analysis and modal analysis on the frame. It turns out that under full-load bending and full-load torsion conditions, the frame strength and stiffness meet the mechanical performance requirements, and the frame displays fine dynamic characteristics. According to the analysis results, the frame is optimized under the goal of light weight. While the frame strength and stiffness requirements are met, the frame mass is lowered by changing the frame component thickness. After optimization, the entire frame volume is reduced by 14.27%, with mass reduced by 14.3%, and the strength and stiffness conform to the requirements, thus achieving lightweight optimization of the frame.Moreover, The stability analysis of the corn combine harvester shows the overturning angle of uphill is 45.3°, the overturning angle of downhill is 45.7°, and the overturning angle of slopel is 40.2°.

A time-frequency approach to ensuring stability of machining by turning

This paper reports a new approach to ensuring the stability of the turning process, which is based on the frequency-time characteristics of the technological machining system (TMS). The approach uses a mathematical model of the turning process as a single-mass system with one degree of freedom, taking into account negative feedback on the normal coordinate and positive feedback with a delay in cutting depth. A new criterion for the stability of the cutting process as a system with a delay in positive feedback is proposed, based on the analysis of frequency characteristics in the form of a Nyquist diagram. It is proved that such a system will be stable when the chart of its Nyquist diagram does not cover a point with coordinates [+1, 0] on the complex plane. The validity of the new criterion has been confirmed by comparing the simulation results in the time range with the location of the Nyquist diagram on the complex plane. Based on the new criterion of stability, an algorithm for automatic construction of a Stability Lobes Diagram (SLD) has been developed. The necessary a priori parameters of TMS, the ranges of frequency change, and the calculation step for constructing such a characteristic in the coordinates "cutting depth – spindle rotational speed" have been determined. The adequacy of the obtained results is confirmed by a full-scale experiment to assess the roughness of machined parts under cutting modes that fall into the area of stability and instability on the SLD chart. The full-scale experiment proved the possibility of a significant reduction in roughness according to the Rz parameter, from 43 µm to 18 µm, while increasing productivity by 1.28 times. The use of a stability lobes diagram is especially effective when programming CNC lathes where it is possible to select the spindle speed in a wide range.

Machinability of B4C-reinforced Al2014 metal matrix composites in electric discharge machining

This study was conducted to clarify the effect of various variables such as the type of electric discharge machining, discharge current and reinforcement content of B4C-reinforced Al alloy metal matrix composite on workpiece removal rate, electrode wear rate and material removed per discharge pulse, which are not extensively explored in the literature. B4C-reinforced Al2014 matrix composite samples containing 5 and 10 vol.-% B4C particles, produced by vacuum infiltration method, were machined with electric discharge machining and powder mixed electric discharge machining at various discharge current settings. In both types of machining processes, the workpiece removal rate and electrode wear rates decreased and increased, respectively, when the reinforcement contents of the composites increased. However, powder-mixed electric discharge machining enhanced the machining stability, and a comparatively higher workpiece removal rate was observed with a decreased electrode wear rate. On the other hand, by increasing the discharge current, which was also verified as the most effective machining parameter in variance analysis, both workpiece removal rate and electrode wear rate values increased in both machining techniques. The experimentally calculated volumetric workpiece material removed by a discharge pulse was compared to that of a model in the literature, and they were also found to be consistent with each other.

Model of force interaction for stability prediction in turning of thin-walled cylindrical workpiece

Turning of the thin-walled cylindrical workpiece is technologically highly demanding process due to the high flexibility of the workpiece. In this paper, a mathematical treatment of integral-based model of the cutting force which takes into account feed, cutting speed, depth of cut and tool nose radius leading to a model of tool-workpiece interaction is presented. The force interaction together with the compliant workpiece dynamics leads to a machining stability formulation. The effect of the aforementioned parameters on characteristic exponents is calculated and validated by comparison with experimentally identified exponents. One of the outputs with immediate practical value is identification of the process damping, which is in the studied case shown to be significantly higher than structural damping of the workpiece itself. This means that without loss of reliability in stability prediction the experimental modal analysis of a given workpiece may be omitted and workpiece’s dynamics may be described only by mass and stiffness matrices which can be easily and reliably obtained by a finite element analysis.