•Optimized variational mode decomposition is proposed to adaptively decompose a chatter signal.•The novel chatter monitoring method proposed is suitable for intermittent chatter detection.•A relative ...threshold, rather than an absolute threshold, is adopted due to the multi-working conditions in the cutting process.
In the milling process, chatter, which results in poor surface quality, dimensional errors, and reduced cutter and machine life, is one of the main limitations on performance. Consequently, a reliable, real-time detection method is desired to recognize chatter while it is developing. This study develops a novel method of online chatter identification for milling processes. In this method, optimized variational mode decomposition (OVMD) is used to decompose cutting force measurements, and the sub-components containing chatter information are extracted using a simulated annealing (SA) algorithm. The approximate entropy and the sample entropy are used to detect the onset of chatter. To evaluate the effectiveness of the proposed method, milling operations were performed and force measurements were collected for five types of operating conditions. The results show that the proposed method is suitable for detecting both continuous and intermittent chatter. Rather than establishing an absolute threshold for chatter detection, the onset of chatter is identified from relative changes in the entropy with time that occur under the various cutting conditions. The proposed method is shown to have greater sensitivity and stability than empirical mode decomposition (EMD).
This work focuses on the analysis of the edge forces generated in ball end milling of hardened alloy 55NiCrMoV6 steel. The investigated forces consider the effects of friction, rubbing and ploughing ...mechanisms between the work piece and tool flank face during machining process. The primary objective of the paper concentrates on the determination of edge forces in the range of variable surface inclination angles and increasing tool wear. The proposed approach involves the measurements of instant cutting forces in machine coordinates (Fz, Fy, Fz). Subsequently, the measured forces are converted to the forces in the tool coordinates (Ft_av, Fr_av, Fa_av). In the next step, the Ft_av, Fr_av, Fa_av forces are expressed in function of average uncut chip thickness. In order to obtain the edge forces values, the extrapolation of forces in the tool coordinates to the zero uncut chip thickness is made. The investigations reveal that edge forces are strongly affected by surface inclination angle and progressing tool wear. The growth of the tool wear induced the monotonic increase in edge forces values. Nevertheless, in case of surface inclination angles α≥15° the influence of this factor on edge forces was low. It was also shown that cutting force estimation with the consideration of the variable edge forces is characterized by a higher accuracy than one based on constant edge forces. Therefore, the proposed method can be employed in the reliable calibration of specific force coefficients contained in mechanistic cutting force models dedicated to the finish ball end milling of sculptured surfaces.
•Edge forces were determined based on measured extreme forces in machine coordinates;•Influence of surface inclination angle on edge forces’ values was presented;•Monotonic growth of edge forces together with progressing tool wear was observed;•Cutting force model including variable edge forces has high accuracy.
The dimensional tolerance of flexible, thin-walled aerospace parts can be violated by the excessive static deflections during milling. This paper proposes a method to predict the dimensional surface ...form errors caused by deflections of both flexible workpiece and slender end-mill in five-axis flank milling of thin-walled parts. The end-mill is modeled as a cantilevered beam. The stiffness of the thin-walled part varies as the metal is removed and the tool-part contact location changes. The time varying stiffness of the thin-walled part is predicted by an efficient structural stiffness modification method that only needs the FE model of the initial workpiece and avoids re-meshing the part at each cutter location. The cutting forces are distributed over both the cutting tool and the part in the engagement zone, and the effect of deflections on the immersion is calculated. The effect of radial runout of the tool is considered in chip thickness, hence in the cutting force prediction. Finally, the cutter and the workpiece deflections are considered to predict the surface errors left on the finished part. The proposed method has been proven in five-axis blade milling experiments.
•Dimensional form errors are predicted in five-axis flank milling of thin-walled parts.•Varying static stiffness of the flexible part is efficiently updated without re-meshing as the material is removed.•Effect of the combined tool and flexible part deflections on the cutter-workpiece engagement is considered.•The chip thickness is analytically calculated along the tool axis considering the five-axis process kinematics.•The proposed surface error prediction model is experimentally validated in five-axis flank milling of a sample blade.
Existing researches for studying the influences of mill's helix angle on peak cutting force were mainly carried out by using simulation or experimental means. Thus, the obtained conclusions were just ...empirical judgments or qualitative observations, which cannot be further used for optimally designing the helix angle of mills. This paper presents a theoretical method for the first time to reveal the working mechanism of peripheral milling tool's helix angle on peak cutting force through strict analytical formulation. To facilitate well understanding the effect of helix angle, variation tendency of peak cutting force versus helix angle is comprehensively studied by analyzing the formation principle of peak cutting force from the point view of both geometrical explanation and theoretical proof. Both infinitesimal element method and differential theory are used in the investigation procedure. It is proved that the peak value of cutting forces decreases with the increase of helix angle for a single engaged cutting edge. Combining this conclusion with the overlapping effect of multiple engaged cutting edges, optimal helix angle corresponding to the minimum of peak cutting forces is analytically derived to be the function of axial depth of cut, number of flutes and cutter diameter. Experimental verifications have been carried out to validate the proposed theory.
Accurate modeling and prediction of cutting forces are important for process planning and optimization in micro end-milling process. In order to exactly predict the cutting forces, an innovative ...uncut chip thickness algorithm is proposed by considering the combination of the exact trochoidal trajectory of the tool tip and the cutting trajectory of all previously passing teeth, tool run-out, minimum chip thickness and the material’s elastic recovery. The proposed uncut chip thickness algorithm also considers the variation of the entry and exit angles caused by tool run-out. To determine the cutting force coefficients, a finite element model (FEM) of orthogonal micro-cutting that considers strain hardening, strain rate sensitivity, thermal softening behavior, and temperature-dependent flow has been established. Based on the results from FEM analysis, the cutting force coefficients are identified and represented by a nonlinear equation of the uncut chip thickness, cutting edge radius and cutting velocity. The identified cutting force coefficients are integrated into a mechanistic cutting force model and used to simulate micro end-milling forces. The simulation results show a very satisfactory agreement with the experimental results.
Display omitted
•End milling of hybrid magnesium MMC (Mg + E-Waste CRT + BN).•Cutting forces, temperature and surface roughness were measured.•Effect of reinforcement, tool and machining factors in ...milling is explained.•Multi objective optimization through GRA and TOPSIS.•Amount of reinforcement and its size have noteworthy effect in MMC machining.
Present study investigates the effect of material and machining parameters on cutting force, surface roughness and temperature in end milling of Magnesium (Mg) Metal Matrix Composite (MMC) using carbide tool. Mg hybrid composite was fabricated by reinforcing Cathode Ray Tube (CRT) panel glass, an intensifying E-waste and Boron Nitride (BN) particles through powder metallurgy method. The milling experiments were conducted based on L27 orthogonal array designed by considering CRT glass particle size and weight percentage, tool diameter, speed, feed and depth of cut as input process parameters. Multi objective optimization was done through Grey Relational Analysis (GRA) and Techniques for Order Preferences by Similarity to Ideal Solution (TOPSIS). Both of the techniques provided a similar optimum parameter condition i.e. 10 µm particle size, 5% reinforcement, 8 mm diameter tool, 710 rpm speed, 20 mm/min feed and 0.5 mm depth of cut that outcomes in 139.48 N in-feed force, 63.92 N cross-feed force, 42.6 N thrust force, 68.96 °C temperature and 0.198 µm surface roughness. ANOVA is performed to identify significance and also the effect of each process variables on response parameters. Though all the parameters were found to be significant, reinforcement weight% and particle size affects the response parameters as that of machining parameters whereas speed turned to be the least significant factor.
•An exactly mechanics cutting force model is established in micro end-milling.•Tool trajectory, tool runout, the minimum chip thickness and the material's elastic recovery are considered in the ...determination of IUCT.•A new model to rectify the issue of tool runout effect on the cutting force.•Force coefficients as nonlinear function of the IUCT are extracted by FE simulation of micro orthogonal cutting.
Prediction of cutting force has great significance for controlling the micro-end-milling processes. In this study, a mechanics model for exactly prediction cutting force is comprehensively established by considering the variety of entry and exit angles for each engaged cutting edge and an accurate instantaneous uncut chip thickness (IUCT). The determination of IUCT has considered the combination of the minimum chip thickness, tool run-out, and the material's elastic recovery, which is embedded in the cutting force model. Further, cutting force coefficients as function of uncut chip thickness have been calculated by using finite element method (FEM). To verify the reliability of the presented cutting force model, a series of experiments for cutting force are conducted and experimental results are compared to cutting force predicted. The results demonstrate that the cutting force predicted is well in agreement with that of measured. The effects of elastic recovery and tool run-out on cutting force also are investigated. Some conclusion can be drawn that elastic recovery can more obviously affect the cutting force predicted with smaller the feed per tooth, the errors of experimental and predicted is getting smaller with increasing the cutting depth, the slight change of tool run-out will lead to a great variation in cutting force.
Display omitted
Accurate cutting-force measurements appear to be the key information in most of the machining related studies as they are fundamental in understanding the cutting processes, optimizing the cutting ...operations and evaluating the presence of instabilities that could affect the effectiveness of cutting processes. A variety of specifically designed transducers are commercially available nowadays and many different approaches in measuring cutting forces are presented in literature. The available transducers, though, express some limitations since they are conditioned by the vibration of the surrounding system and by the transducer׳s natural frequency. These parameters can drastically affect the measurement accuracy in some cases; hence an effective and accurate tool is required to compensate those dynamically induced errors in cutting force measurements. This work is aimed at developing and testing a compensation technique based on Kalman filter estimator. Two different approaches named “band-fitting” and “parallel elaboration” methods, have been developed to extend applications of this compensation technique, especially for milling purpose. The compensation filter has been designed upon the experimentally identified system׳s dynamic and its accuracy and effectiveness has been evaluated by numerical and experimental tests. Finally its specific application in cutting force measurements compensation is described.
•Cutting force measurements can be drastically affected by machine tool dynamics.•Dynamic compensation can extend the bandwidth of commercial dynamometers.•Two different approaches suitable for milling applications have been developed.•The effectiveness of the proposed approaches has been experimentally evaluated.•Examples in cutting force measurements compensation are shown.
The majority of cutting force models applied for the ball end milling process includes only the influence of cutting parameters (e.g. feedrate, depth of cut, cutting speed) and estimates forces on ...the basis of coefficients calibrated during slot milling. Furthermore, the radial run out phenomenon is predominantly not considered in these models. However this approach can induce excessive force estimation errors, especially during finishing ball end milling of sculptured surfaces. In addition, most of cutting force models is formulated for the ball end milling process with axial depths of cut exceeding 0.5mm and thus, they are not oriented directly to the finishing processes. Therefore, this paper proposes an accurate cutting force model applied for the finishing ball end milling, which includes also the influence of surface inclination and cutter's run out. As part of this work the new method of specific force coefficients calibration has been also developed. This approach is based on the calibration during ball end milling with various surface inclinations and the application of instantaneous force signals as an input data. Furthermore, the analysis of specific force coefficients in function of feed per tooth, cutting speed and surface inclination angle was also presented. In order to determine geometrical elements of cut precisely, the radial run out was considered in equations applied for the calculation of sectional area of cut and active length of cutting edge. Research revealed that cutter's run out and surface inclination angle have significant influence on the cutting forces, both in the quantitative and qualitative aspect. The formulated model enables cutting force estimation in the wide range of cutting parameters, assuring relative error's values below 16%. Furthermore, the consideration of cutter's radial run out phenomenon in the developed model enables the reduction of model's relative error by the 7% in relation to the model excluding radial run out.
•Cutting force model applied for the finishing ball end milling is proposed.•Run out is included also in expression of active length of cutting edge.•Surface inclination has quantitative and qualitative influence on cutting forces.•Small run out's value (3μm) can cause influential cutting force variations (~30%).•Proposed force model enables the obtainment of global estimation errors below 16%.
PDF