Stability Of Machining Process Research Articles

CHATTER MITIGATION IN REAMING: EXPLORING EFFECTIVE TOOL HOLDER DESIGN

Reaming is a crucial technology in finishing operations, demanding high stability in the machining process for optimal results. The clamping system significantly influences the dynamic properties of the system tool – clamping - machine and is key in mitigating chatter. The introduction of new designs in clamping exchangeable reaming heads presents several challenges, particularly in terms of vibration suppression. This study explores various constructions of clamping bars, examining their dynamic properties in both static conditions and during machining. Through these evaluations, the research aims to understand how different designs impact the stability and effectiveness of reaming operations. The measured data from these experiments reveal how the construction of the holder influences machining process stability, providing insights into optimizing clamping system designs for improved reaming performance. the outcomes of this study contribute to the development of more effective and efficient clamping systems for finishing operations.

Acceleration and deceleration control algorithm of CNC system based on deep neural network reinforcement learning and MCU

Acceleration and deceleration control, as one of the key technologies in high-speed CNC system, directly affects the machining efficiency, the stability of machining process and the error of machining follow. Therefore, it is necessary to study and explore new acceleration and deceleration control methods in high-speed CNC system to ensure the smooth feed and improve the machining accuracy. Therefore, the acceleration and deceleration control algorithm of NC system based on deep reinforcement learning and single chip microcomputer is studied. The theoretical basis of deep reinforcement learning is analyzed, and the acceleration of acceleration and deceleration is calculated based on the linear acceleration and deceleration control. The whole integer operation of single chip microcomputer is used to estimate the value range of each step. The variation characteristics of trajectory motion are predicted so that acceleration and deceleration can be processed across program segments. The velocity of transfer point is calculated by the rate of change of feed velocity vector, and the speed of multi-program is smoothed by adjusting the allowable contour error. Based on the proximal strategy optimization algorithm in deep reinforcement learning, the acceleration and deceleration control model of CNC system is established to realize the acceleration and deceleration control. The experimental results show that the proposed algorithm has better control effect, shorter time and smaller interpolation error, which can ensure the NC system to feed smoothly at high speed.

Chatter Stability Prediction for Deep-Cavity Turning of a Bent-Blade Cutter.

The bent-blade cutter is widely used in machining typical deep-cavity parts such as turbine discs and disc shafts, but few scholars have studied the dynamics of the turning process. The existing mechanism of regenerative chatter in the metal-cutting process does not consider the influence of bending and torsional vibration, the change of tool profile and the complex machining geometry, so it cannot be directly used to reveal the underlying cause of the chatter phenomena in the deep inner cavity part turning process. This paper attempts to investigate the dynamic problem of the bent-blade cutter turning process. The dynamic model of a bent-blade cutter is proposed by considering the regenerative chatter effect. Based on the extended Timoshenko beam element (E-TBM) theory and finite element method (FEM), the coupling between the bending vibrations and the torsional vibrations, as well as the dynamic cutting forces, are modeled along the turning path. The vibration characteristics of the bending-torsion combination of cutter board and cutter bar, together with the dynamical governing equation, were analyzed theoretically. The chatter stability of a bent-blade cutter with a bending and torsion combination effect is predicted in the turning process. A series of turning experiments are carried out to verify the accuracy and efficiency of the presented model. Furthermore, the influence of cutting parameters on the cutting process is analyzed, and the results can be used to optimize the cutting parameters for suppressing machining vibration and improving machining process stability.

Study on the dynamic influence of the distribution of cutting depth on the ground surface quality in a precision grinding process

Focusing on the excitation mechanisms of self-excited vibration and forced vibration, a time-delay differential model of the radial cutting depth of a single active abrasive grit is presented. Based on the principle of the layered superposition characteristics of each component of radial cutting depth, a full discrete simulation technology is used to analyze the dynamic mechanisms of different vibration excitations on the grinding characteristics. The reliability of the dynamic mechanisms is verified by the corresponding grinding experiments. The verification results demonstrate that static and dynamic components in the grinding dynamics, including radial cutting depth, grinding force, surface roughness and surface morphology of workpiece are greatly influenced by total material removal rate, followed by speed ratio and grinding directions. With the increase of cutting depth, the variation amplitude of grinding process influenced by forced-vibration mechanism are nearly twice larger than those influenced by self-excited vibration mechanism. When speed ratio reduces to a half, surface roughness of workpiece improves by nearly 33 %. The stability of machining process and finish surface of workpiece during up-grinding are better than those during down-grinding, where force reduction by up to 10 % and surface finish improvement by 37 %.

Cutting Performance and Wear Mechanism of Multilayer Diamond‐Coated Tools

Monolayer and multilayer diamond films are deposited on WC‐Co cemented carbide by hot‐filament chemical vapor deposition. The growth characteristics of diamond coatings are analyzed. Cutting performance characteristics such as tool life and the stability of machining process in the machining of presintered ZrO2 are compared based on the variation of cutting speed and resultant cutting force, and workpiece surface roughness. For the monolayer diamond coatings, as the concentration of CH4 increases from 1% to 5%, the diamond crystal is transformed from micron columnar crystal to nanocluster crystal. The multilayer diamond coatings combine the advantages of micron‐ and nanocrystalline structures. The multilayer diamond‐coated tool exhibits longer service life and better machining quality. Because of the appearance of the brittle–plastic conversion mechanism, the surface integrity of ZrO2 processed by multilayer diamond‐coated tool is relatively high. As for the uncoated tool, the workpiece is mainly machined by brittle spalling. The interfacial stratified fracture system between the interlayers is proposed to be the toughening mechanism of the multilayer structure.

Towards energy efficient milling of variable curved geometries

Development of energy efficient machining is the present focus to industries for reduction of energy consumption and making the manufacturing system more sustainable. The continuous fluctuation in force profile during machining of variable curved components creates a barrier in stable machining and in cutting power consumption. The fluctuation in force profile happens due to alteration in chip load in the presence of workpiece curvature. The current research work intends to develop an energy efficient machining strategy for milling of variable curved components where more uniform cutting force and power profiles are accomplished due to constant chip load along the peripheral length of curved geometry. The proposed strategy is compared with conventional cutting in order to confirm the acceptability of the present algorithm. The proposed algorithm involves mechanics of milling, cutting forces and cutting power consumption. It is formulated based on constant chip load by regulating entry angle of milling cutter according to workpiece curvature along the peripheral length. Thus, the cutting power fluctuation occurred due to variation of workpiece curvature is reduced by regulating tool-workpiece engagement. The energy consumption during machining is reduced almost 22 % using the proposed approach. It results into developing an energy efficient machining strategy for milling of variable curved geometry. It also provides stable machining process and increased tool life by reducing tool wear due to reduction of force fluctuation during metal removal process.

An analytical formulation of ZOA-based machining stability for complex tool geometries: application to 5-axis ball-end milling

The paper describes a computationally convenient analytical formulation of the stability of the cutting process with respect to self-excited vibrations in the case of five-axis milling based on the commonly used zero-order approximation. In the case of five-axis milling with general milling cutters, it is difficult to calculate stable machining process conditions for two main reasons. The first reason is the difficulty of calculating the mean value of the cutting force Jacobian with respect to the regenerative displacement (closely related to a milling directional matrix) for a generally inclined tool, and the second reason is the nonlinearity of this Jacobian with respect to the process parameters, which means that the problem cannot be reduced to a linear eigenvalue problem as is usual for linear cases (e.g. cylindrical milling with respect to the axial depth of cut). In the first part, this paper presents a modification of the calculation of the machining stability limits for a nonlinearly dependent cutting force Jacobian. A new formulation of this Jacobian for a general tool based on the surface integral over the tool and workpiece engagement region is presented which leads directly to the mean value of the Jacobian of the cutting force (direction matrix) without the need to calculate it as a function of time and then calculate the mean value over one revolution. The advantage is that if we can analytically describe the engagement area, we also obtain an analytical relation for the cutting force Jacobian. This is presented with the practical example of a generally inclined ball-end mill. This analytical formulation of the force Jacobian allows the calculation of its derivatives with respect to the technological parameters (depth of cut, step over, tilt and lead angles), which is useful both for the calculation of stability diagrams and for solving optimization problems related to machining stability.

Experimental Investigation of the Effect of EDM Debris Particles Mixed into the Dielectric Fluid on Tool Feed Rate in Drilling-EDM

In this paper the potential of the recirculation of the EDM debris particles of the workpiece material into the dielectric fluid to increase the tool feed rate vf in drilling Electrical Discharge Machining (drilling-EDM) is experimentally investigated. Two-Channel electrodes made of copper (Cu) and brass (CuZn) in the range from 1.0 mm to 2.5 mm were used. The effect of the EDM debris particles in the dielectric fluid was investigated at a discharge current ie of 25 A, a discharge duration te of 50 μs and a duty cycle of 80 % by comparing the EDM pulse characteristics and the feed rate vf of the EDM process with and without debris particles added to the dielectric fluid (particle concentrations C1 = 2.5 g/l and C0 = 0 g/l, respectively). By the recirculation of EDM debris particles the feed rate could be increased up to 36 % depending on the machining conditions. Furthermore, it was observed that the increase in the feed rate is due to the increase of the percentage of discharge pulses and the decrease of short-circuit pulses as well as a more stable machining process.

Modeling and Predicting the Machined Surface Roughness and Milling Power in Scot’s Pine Helical Milling Process

Helical milling with the advantages of stable machining process, a well-machined surface quality, etc., is an interest of researchers and producers. Machined surface roughness (arithmetic mean deviation (Ra) and maximum height of the assessed profile (Rz)) and milling power consumption as two main machining characteristic parameters were studied and chosen as response factors to evaluate the machinability of Scots pine helical milling. Input variables included helical angle of milling cutter, rotation speed of main shaft, and depth of milling. Response surface methodology was applied for the design of experiments, data processing and analysis, and optimization of the processing parameters. The results showed that Ra and Rz decreased with an increase in helical angle and rotation speed of main shaft, though increased with an increase in depth of milling. Milling power increased when the helical angle and depth of milling increased and showed a slight downward trend as the rotational speed increased. The quadratic models were applied to predict the values of Ra, Rz, and milling power due to the high values of R2 of 0.9895, 0.9905, and 0.9885, respectively. The plot of predicted and actual values also indicated that the created models had good predictability. The optimized combination of helical angle, rotation speed, and depth of milling are 64°, 7500 r/min, and 0.5 mm, respectively. The effects of input variables and the quantitative relation between input variables and response variables were revealed clearly. These achievements will be useful for guiding the selection of helical milling parameters to achieve the purposes of improving processed surface quality and saving the processing power consumption.

The effect of roller-bearing stiffness on the machining process stability

The industry uses machining process monitoring to predict the tool’s life and workpiece quality. Its accuracy and prediction are crucial for producing higher quality parts and keeping productivity. Process monitoring systems measure the machining process in real time through several strategically placed sensors on the machine tool. The difference between a “fingerprint signature” and the actual data determines the quality of a good production cycle. The alarms appear when a deviation from the standard exceeds the pre-set tolerance limit. The “fingerprint signature” is the result of previous measurements and from dynamic models. These models only consider the excitation frequencies and neglect some of the nonlinearities related to the machine. Additionally, high-speed machining requires higher sample rates, and as a consequence, the signal has less resolution and fewer frequencies. In most cases, the machine is considered a linear system. This work presents a dynamic model that considers the bearings’ excitation forces and their effect on chattering. The model produces numerical results, and these results are compared with experimental data. The results presented in this work show that the bearing excitation frequencies modify the chatter response.

Chatter identification of thin-walled parts for intelligent manufacturing based on multi-signal processing

Machine chatter is still an unresolved and challenging issue in the milling process, and developing an online chatter identification and process monitoring system towards smart manufacturing is an urgent requirement. In this paper, two indicators of chatter detection are investigated. One is the real-time variance of milling force signals in the time domain, and the other one is the wavelet energy ratio of acceleration signals based on wavelet packet decomposition in the frequency domain. Then, a novel classification concept for vibration condition, called slight chatter, is proposed and integrated successfully into the designed multi-classification support vector machine (SVM) model. Finally, a mapping model between image and chatter indicators is established via a distance threshold on the image. The multi-SVM model is trained by the results of three signals as an input. Experiment data and detection accuracy of the SVM model are verified in actual machining. The identification accuracy of 96.66% has proved that the proposed solution is feasible and effective. The presented method can be used to select optimized milling parameters to improve machining process stability and strengthen manufacturing system monitoring.

A novel micro-EDM method to improve microhole machining performances using ultrasonic circular vibration (UCV) electrode

The difficulties in circulating working fluid and expelling discharge debris are major challenges for microhole machining by micro electrical discharge machining (micro-EDM). To solve this issue, a novel micro-EDM method that adopts ultrasonic circular vibration (UCV) electrode was proposed in this study, aiming at effectively improving the microhole machining performances. A piezoelectric device for UCV electrode with 32.85 kHz frequency and 3 μm trajectory radius was developed and its basic principle was analyzed. To better understand the effect of UCV electrode on microhole machining process, the solid-liquid two-phase flow simulation was conducted, and the flow field distribution and discharge debris movement in machining gap were studied. Machining experiments of deep microhole (aspect ratio = 9.4) showed that the UCV electrode can effectively lower the electrode retreat frequency and prevent the debris adhesion at the inner wall. 10 × 10 microhole array machining experiments were also carried out in this study. Results showed that the inlet and outlet of microhole array have better morphologies when using UCV electrode, and the diameter consistency of inlet and outlet were improved by 22% and 2.8% compared with rotating electrode. The advantages of UCV electrode in improve microhle machining performances can be mainly attributed to the significantly enlarged flow velocity of working fluid and enhanced capacity of working fluid to expel debris particles in terms of number and efficiency. Meanwhile, the increased relative velocity between electrode and workpiece is also effective to discontinue the abnormal discharges and achieve stable machining process.

Analytical and experimental stability analysis of AU4G1 thin-walled tubular workpieces in turning process

The development of the manufacturing-based industries is principally due to the improvement of various machining operations. Experimental studies are important in researches, and their results are also considered useful by the manufacturing industries with their aim to increase quality and productivity. Turning is one of the principal machining processes, and it has been studied since the 20th century in order to prevent machining problems. Chatter or self-excited vibrations represent an important problem and generate the most negative effects on the machined workpiece. To study this cutting process problem, various models were developed to predict stable and unstable cutting conditions. Stability analysis using lobes diagrams became useful to classify stable and unstable conditions. The purpose of this study is to analyze a turning process stability using an analytical model, with three degrees of freedoms, supported and validated with experimental tests results during roughing operations conducted on AU4G1 thin-walled tubular workpieces. The effects of the tubular workpiece thickness, the feed rate and the tool rake angle on the machining process stability will be presented. In addition, the effect of an additional structural damping, mounted inside the tubular workpiece, on the machining process stability will be also studied. It is found that the machining stability process is affected by the tubular workpiece thickness, the feed rate and the tool rake angle. The additional structural damping increases the stability of the machining process and reduces considerably the workpiece vibrations amplitudes. The experimental results highlight that the dynamic behavior of turning process is governed by large radial deformations of the thin-walled workpieces. The influence of this behavior on the stability of the machining process is assumed to be preponderant.

Stability analysis of regenerative vibration in turning operation using I-kaz3DTM signal processing approach

This paper presents a stability analysis to predict regenerative vibration during turning process. Although the stability of machining process has been widely studied in metal cutting it still presents a challenge as surface roughness, tool wear and productivity have to be considered. If the tool is vibrating as it removes material, these vibrations are imprinted on the workpiece surface as a wavy profile. However, the relative phasing between the surface waviness from one pass to the next determines the level of force variation and whether the operation is stable or unstable. Then we investigate the unstable and stable phenomena during the machining process by discussing the number of time-domain simulation to determine the force and surface roughness values these stability thresholds. A signal processing was carried out using I-Kaz3D technique to identify the effect between the unstable and stable phenomena. The results show that the relationship between I-kaz3D coefficients and surface roughness values can be considered very highly correlated.

Research on the Effects of Machining Parameters on the Surface Location Error for a Milling Process

The surface location error is an inevitable phenomenon which is caused by the forced vibration under a stable machining process. The surface location error (SLE) is dependent on the machining parameters. Therefore, this paper proposes a method to study the effect of each machining parameter on the surface location error. An algorithm based on the cutting force dynamic model is proposed to predict the SLE in frequency domain. And then a case study is performed on the milling process of a real vertical machining center. The variation ranges of the spindle speed, axial cutting depth, radial cutting depth and feed rate per tooth are first determined. Eight specific values of each machining parameter is selected, and an orthogonal experiment table is established to arrange the schemes to predict the corresponding SLEs. Then the range analysis is used to analyse the values of the machining parameters and the obtained SLEs. Results show that the spindle speed is the most dominant factor affecting the SLE and an optimal machining parameters combination related to a minimum SLE is determined based on the optimal level of each machining parameter.

Analysis of the flow field in counter-rotating electrochemical machining

In electrochemical machining (ECM), the electrolyte flow field has marked influence on the processing stability, efficiency and surface quality. This paper presented a new electrolyte flow mode to improve the flow field distribution in counter-rotating electrochemical machining (CRECM), in which the electrolyte flows into the processing zone from both sides and top of the fixture, and flows out from the bottom of the fixture. The flow field distributions were analyzed and simulated via computational fluid dynamics (CFD) software. The simulation results showed that the low-velocity area in CRECM was eliminated and the velocity distribution was more uniform by using the optimized flow mode. Experiments were also conducted using a specific fixture. The experimental results indicated that a stable machining process with a small inter-electrode gap could be achieved, and the ECM accuracy was remarkably improved. The sidewall taper angles and rounded corners of the machined convex structure were reduced to be only about -0.8° and 0.6 mm.

The Effect of the Low Frequency Mode of the Machine Tool Structure on the Milled Surface Generation

The prediction of machining process stability and surface generation is primarily based on the dynamics of the tool and work piece. However, the vibrations caused by the low frequency of machine tool structure also affect the stability of machining process and the surface integrity in the condition of low speed and heavy load. Therefore, this paper presents a milling time domain simulation model based on the low frequency mode of machine tool structure to study the effect of the low frequency mode of the machine tool structure on the surface generation. Based on this model, the correlation between the multimode natural frequencies of machine tool structure and the surface waviness is studied and the effect of the inertia force caused by the change of cutting speed on the surface shape is studied. Finally, a set of cutting tests is performed to verify the surface generation prediction.

Precision Control of Kerf in Metal Cutting Using Dry Micro WEDM: Issues and Challenges

Micro dry wire EDM is a process where gas is used as the dielectric fluid instead of a liquid. In this process certain modifications of a wire EDM are needed during the machining operation to achieve stable machining. Optimizing kerf to get high dimensional accuracy is one of the critical issues in micro dry wire EDM. The fundamental modelling for optimum kerf using micro dry wire EDM has not been formulated yet. Due to the complex phenomenon, the prediction of optimum kerf in a micro dry wire EDM process is rather difficult. Hence, the main objectives of this research are to improve the micro dry wire EDM process and to develop mathematical models for optimum kerf using micro dry wire EDM. During the process improvement of micro dry wire EDM, various machining setup will be involve in order to achieve the most stable process. The most stable machining process will be used to prove the developed mathematical models. A mathematical relationship between kerf and process parameters is anticipated. The mathematical models in conjunction with experimental data will eventually produce the desired theory. The developed process and mathematical model of kerf is a breakthrough in fabricating products such as micro tools, molds etc. with optimum kerf and high dimensional accuracy. The successful completion of this research will contribute to the environmental friendly micromachining process.

Study on Gap Flow Field Simulation in Small Hole Machining of Ultrasonic Assisted EDM

When machining a small hole with high aspect ratio in EDM, it is hard for the flushing liquid entering the bottom gap and the debris could hardly be removed, which results in the accumulation of debris and affects the machining efficiency and machining accuracy. The assisted ultrasonic vibration can improve the removal of debris in the gap. Based on dynamics simulation software Fluent, a 3D model of debris movement in the gap flow field of EDM small hole machining assisted with side flushing and ultrasonic vibration is established in this paper. When depth to ratio is 3, the laws of different amplitudes and frequencies on debris distribution and removal are quantitatively analysed. The research results show that periodic ultrasonic vibration can promote the movement of debris, which is beneficial to the removal of debris in the machining gap. Compared to traditional small hole machining in EDM, the debris in the machining gap is greatly reduced, which ensures the stability of machining process and improves the machining efficiency.

Predictive model of milling force for complex profile milling

Cutting force, temperature, and stress on a cutting tool reflect the working condition of the cutting tool. Among these, the cutting force is relatively easier to be monitored and more reflective of the machining process stability. In this study, a new model of the milling force applied for a complex profile milling cutter has been developed based on the infinitesimal method. A dynamic contact model has been implemented through analyzing the working status of each section on the complex milling cutter. An underlying database is established in the form of response surfaces from simulation. The model of milling force for a complex profile milling cutter has been validated to be accurate by the comparison between the calculated and measured milling forces.