Chatter vibration induces a characteristic pattern on the milled surface, known as chatter marks, causing a poor surface quality. While several works deal with the prediction of the machined surface ...in stable condition, surface under chatter vibration has not been extensively studied: it is not clear how vibrations at high chatter frequency return highly spaced chatter marks on the surface. This paper investigates the chatter marks generation mechanisms focusing on this issue, i.e., on the surface spectral proprieties. The generation of the surface profile is regarded as a problem of sampling at the tooth pass frequency (in the time domain) and reconstruction (in the spatial domain) of the cutting tool displacements. Using this analogy, the paper highlights two main effects (aliasing and pseudo moiré), proposing specific formulations. The method is validated by a numerical investigation, based on a surface generation model coupled with a time-domain simulator of the milling process. Finally, an experimental validation is proposed. The formulations presented in this work provide an insight in the relation between chatter frequency and chatter marks pattern. Therefore, if the chatter frequency pattern over the spindle speed is known (e.g., identified via simulations or experiments), the proposed method could support the selection of cutting parameters which results in an acceptable surface, even in highly unstable cutting conditions.
•An insight of the surface generation mechanism in milling is proposed.•Surface profile is regarded as a problem of sampling at the ftp of the tool vibrations.•Two fundamental spatial frequencies are identified, composing chatter marks surface.•Formulations to predict spectral proprieties of chatter marks are provided.•Numerical and experimental tests prove the accuracy of the proposed approach.
•An integrated modeling method of ball screw feed system and milling process is proposed.•The forming mechanism of a new kind of quality defect shown as contour low frequency oscillation is ...explained.•An analytical model of motor torque with multi-frequency harmonics is presented.•The characteristics of contour oscillation under different milling condition are discussed.•An efficient experiment modal method considering rotational-DOF of ball screw feed system is given.
The present researches about feed drive system and milling process are almost independent with each other, and ignore the interaction between the two parts, especially the influence of nonideal motion of feed drive system on milling process. An integrated modeling method of ball screw feed system and milling process with multi-excitation effect is proposed in this paper. In the integrated model, firstly an analytical model of motor harmonic torque with consideration of asymmetrical drive circuit and asymmetrical permanent magnet is given. Then, the numerical simulation procedure of cutter/workpiece engagement during milling process with displacement fluctuation induced by harmonic torque is put forward, which is followed by the solving flow for the proposed integrated model. Based on the integrated model, a new kind of quality defect shown as contour low frequency oscillation on machined surface is studied by experiments and simulations. The results demonstrate that the forming mechanism of the contour oscillation can be ascribed to the multi-excitation effect with motor harmonic torque and milling force. Moreover, the influence of different milling conditions on the contour oscillation characteristics, particularly on surface roughness, are further discussed. The results indicate that it is necessary to explain the cause of the new kind of quality defect with a view of system integration.
All‐solid‐state mechanochemistry is experiencing an exciting period of renaissance, thanks in part to the recent discovery of its ability to realize chemical synthesis that is inaccessible to ...solution‐based methods. Among them, high‐energy ball‐milling is widely used in large‐scale preparation of metal oxide composites for lithium‐ion batteries (LIBs). However, ball‐milling‐induced high‐energy mechanical activation may destroy crystalline structure, and thus the electrochemical activity of many metastable oxides such as anatase titanium dioxide (TiO2). Herein, the mechanism that anatase TiO2 undergoes the crystalline‐amorphous phase transformation subject to ball‐milling is reported and a new pan‐milling mechanochemical technique for preparation of stable anatase TiO2/graphene (TiO2/GNS) composites is demonstrated. The pan‐milling technique not only preserves the original crystal structure of TiO2 but also realizes a good dispersion of TiO2 nanoparticles on graphene nanosheets through its unique 3D shear force. When used as anode for LIBs, the pan‐milled TiO2/GNS demonstrates high reversible specific capacity, excellent rate capability, and long cycle stability, in comparison to the ball‐milled TiO2/GNS that shows no capacity. By tapping into the huge potential of pan‐milling mechanochemistry, this work opens the door to large‐scale all‐solid‐state preparation of mechanical metastable oxides with desired electrochemical performance for energy storage.
An innovative all‐solid‐state mechanochemical technology, pan‐milling, is instituted for fabrication of mechanical metastable‐oxide nanocomposites. The pan‐milling method preserves the crystal structure of anatase TiO2 intact, which would otherwise be destroyed under a high‐energy ball‐milling process, resulting in excellent electrochemical performance when used as anode for lithium‐ion batteries. The discovery bears has profound significance in the context of extending the potential of mechanochemistry to metastable oxides for energy storage applications.
Mechanical milling and melting-strip casting-milling have been used to prepare FeCoNiSi0.4Al0.4 high entropy alloy (M-HEA and C-HEA respectively) powders. Both techniques have different solution and ...phase formation rules. The M-HEA powders have more FCC, and the opposite is true for C-HEA powders. In addition, the C-HEA powders have better elemental uniformity and a larger aspect ratio. Because of this, the C-HEA powders have a smaller Ms and a larger Hc; the Ms range from 93.6emu/g to 104.4emu/g, and the Hc vary from 81.5Oe to 159.6Oe. As the milling time increases, the variety of aspect ratios and uniformity give rise to the change of electromagnetic (EM) parameters for both HEA powders. Versus the EM parameters of M-HEA powders (ranging from 7.5 to 16 and from 0 to 1.4 for ε’ and ε”, respectively), these C-HEA powders have larger values (ranging from 11 to 26 and from 0 to 8 for ε’ and ε”, respectively). At the same time, the μ’ (varying from 1.78 to 1.90 at 2GHz) and the μ″ (up to 0.52) of C-HEA powders are larger than the M-HEA powders.
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•The mechanical milling method and melting-strip casting-milling method have been designed to prepare FeCoNiSi0.4Al0.4 HEA powders.•During this two kinds of technologies, the rules of dissolution and phase formation are different.•It has been proven that the C-HEA powders possess better uniformity and larger aspect radio than M-HEA powders.•The variety of aspect radio and uniformity lead to the change of electromagnetic parameters for both kinds of HEA powders.
The machining chatter is the major factor that results in low-dimensional accuracy, poor product quality, and even downtime when the industrial robots mill parts. Milling force is one of the highest ...responsive parameters that can depict whether machining chatter occurs and has widely been used for monitoring purposes. However, most of the milling force prediction methods focus on offline prediction, which cannot model and predict milling forces in real time for complex systems with varying dynamics and poses, making it difficult to reflect the machining process of industrial robotics in time. To address the above challenge, a time-series data-driven method is proposed for the milling force prediction of robotic machining, which explores two types of prediction modes based on particle swarm optimization and long short-term memory (PSO-LSTM) network. The first is a sequence-to-sequence mode, called time interval prediction (TIP) mode, which updates the network with actual values during deployment and can perform the next cycle prediction after one prediction step when milling starts. The second one is a point-to-sequence mode, named a single-step cycle prediction (SCP) mode, which updates the network with predicted values during deployment and only requires the offline optimized network model to predict milling forces at the beginning of milling. The PSO algorithm is utilized as the optimization component to determine the optimal hyperparameters for the TIP and SCP models, which is subsequently used for online prediction. Experimental validation was performed on a self-constructed robotic milling platform, and results indicate that the proposed approach performs well in predicting the milling force characteristics within the next 1 s of real-time milling.
Variable pitch and helix end mills disturb the regeneration mechanism that causes chatter vibrations, and as such, they enable stable, high-performance, and high material removal rate milling ...processes. The regeneration mechanism is altered by the non-uniform tool geometry that results in multiple or distributed delays between vibrations imprinted on the machined surface. The design procedure for these cutters needs characterization of the stability diagrams to decide the non-uniform geometry that improves the absolute minimum stable depth of cut as well as the changes in the size and location of stability pockets. This paper presents a unified method to rapidly analyze the stability of variable helix and pitch cutters with multiple or distributed delays using a non-iterative multi-frequency domain approach that uses the Nyquist criterion to check stability at every spindle speed and depth of cut tuple. Predictions are benchmarked with the established and widely used semi-discretization method and verified with previously published experimental data, which are further validated by our own experiments. The proposed method is as accurate as of the established one while offering computational savings of up to 94%. Since explorations of alternate and better designs were potentially precluded by the computational inefficiency of previous methods, and since the method proposed herein is fast and accurate, it can help to accelerate the design of improved variable helix and pitch end mills for their use in industrial settings.
•A task-dependent performance indexes is proposed to evaluate industrial robot stiffness.•Based on stiffness performance index, the posture and tool feed orientation are optimized during milling ...application.•Higher machining accuracy is achieved through proposed optimization models.•Properties of robot compliance in Cartesian space are analyzed.•Milling experiments validated the feasibility and effectiveness of the proposed optimization methods.
Industrial robots are promising and competitive alternatives for performing machining operations. A relatively low stiffness is the major constraint for the widespread use of industrial robots in machining applications. In this study, the stiffness properties of an industrial robot are analyzed to improve the machining accuracy of robotic milling, and optimization methods for the robot posture and tool feed orientation are established. First, based on the relationship between the external force and deformation of the robot end effector (EE), the normal stiffness performance index (NSPI) of the surface, which is derived from the comprehensive stiffness performance index (CSPI), is proposed to evaluate the robot stiffness performance for a given posture. The NSPI is proven to be independent of the magnitudes of the external forces and dependent on the directions of these forces. A distribution rule is then proposed for the NSPI with respect to any direction in the Cartesian space for a given posture, which clearly reveals the anisotropic property of the robot stiffness. By maximizing the NSPI, an optimization model is established to optimize the posture of a six degree-of-freedom (DOF) industrial robot in a milling application. Using the NSPI, the optimized tool feed orientation for robot planar milling is obtained. Finally, the results of the robot milling experiments are discussed to illustrate the feasibility and effectiveness of the proposed optimization methods.
This review aims to provide a description of the recent advances in the preparation of polymer nanocomposites via mechanical milling. An assessment of possible future scenarios that could be created ...by the utilization of improved experimental methodologies and a deeper understanding of structure-property relationship is also provided. It is then reported, in a logical sequence, crucial information on five subjects: (i) the motivation of fundamental and applied research in the field of thermoplastic and thermosetting polymer nanocomposites, (ii) the mechanochemical response of polymeric substances to mechanical activation, (iii) the broad spectrum of experimental behaviours exhibited by the most studied classes of polymers, (iv) the methodology for the mindful utilization of mechanical processing to mix polymers and disperse heterophases, and (v) the physico-chemical approach to describing the kinetics of mechanically activated transformations. In addition, critical questions regarding the advantages and disadvantages of mechanical processing compared to more conventional dispersion methods are highlighted. Finally, the general trends in the current research are discussed, and possible future perspectives in this field are briefly described.
In nanofluid minimum quantity lubrication (NMQL) milling of aviation aluminum alloy, it is the bottleneck problem to adjust the position parameters (target distance, incidence angle, and elevation ...angle) of the nozzle to improve the surface roughness of milling, which has large and uncontrollable errors. In this paper, the influence law of milling cutter speed, helical angle, and cavity shape on the flow field around the milling cutter was studied, and the optimal nozzle profile parameters were obtained. Using 7050 aluminum alloy as the workpiece material, the milling experiment of the NMQL cavity was conducted by utilizing cottonseed oil-based Al2O3 nanofluid. Results show that the high velocity of the surrounding air flow field and the strong gas barrier could be attributed to high rotating velocities of the milling cutter. The incidence angle of the nozzle was consistent with the helical angle of the milling cutter, the target distance was appropriate at 25–30 mm, and the elevation angle was suitable at 60°–65°. The range and variance analyses of the signal-to-noise ratio of milling force and roughness were performed, and the chip morphology was observed and analyzed. The results show that the optimal combination of nozzle position parameters was the target distance of 30 mm, the incidence angle of 35°, and the elevation angle of 60°. Among these parameters, target distance had the largest impact on cutting performance with a contribution rate of more than 55%, followed by incidence angle and elevation contribution rate. Analysis by orthogonal experiment revealed that the nozzle position parameters were appropriate, and Ra (0.087 μm) was reduced by 30.4% from the maximum value (0.125 μm). Moreover, Rsm (0.05 mm) was minimum, which was 36% lower than that of the seventh group (Rsm = 0.078 mm).
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