Effects Of Runout Research Articles

Time-varying dynamic modeling of micro-milling considering tool wear and the process parameter identification

Micro-milling technology is widely used in the manufacturing of micro three-dimensional complex parts in aerospace, mechanical equipment, biomedical devices, electronic components, and other fields due to its advantages of high machining accuracy, small size, and complex surface. Consequently, understanding its machining process is essential. This study proposes a time-varying dynamic micro-milling process model with the effects of tool runout, tool wear, and cutting status and explores the stable cutting domain of real-time machining. Considering the time-varying characteristics of the cutting process, combined with measured data and particle filtering method, the cutting force coefficients and tool wear parameters in the dynamic model at different times are identified. The dynamic equation of micro-milling is derived using a discrete method, and the stability of the cutting process is evaluated. Multiple cutting experiments are conducted on the Al6061, and the test data are compared with simulated values. The comparison results show that the accuracy of the proposed model in predicting the cutting state can reach 100%, and the average error of cutting force prediction is 7.72%. The research results can provide theoretical guidance for the safety evaluation of micro-milling and the selection of machining conditions.

Dynamic Modeling for Chatter Analysis in Micro-Milling by Integrating Effects of Centrifugal Force, Gyroscopic Moment, and Tool Runout.

During micro-milling, regenerative chatter will decrease the machining accuracy, destabilize the micro-milling process, shorten the life of the micro-mill, and increase machining failures. Establishing a mathematical model of chatter vibration is essential to suppressing the adverse impact of chatter. The mathematical model must include the dynamic motions of the cutting system with the spindle-holder-tool assembly and tool runout. In this study, an integrated model was developed by considering the centrifugal force induced by rotational speeds, the gyroscopic effect introduced by high speeds, and the tool runout caused by uncertain factors. The tool-tip frequency-response functions (FRFs) obtained by theoretical calculations and the results predicted by simulation experiments were compared to verify the developed model. And stability lobe diagrams (SLDs) and time-domain responses are depicted and analyzed. Furthermore, experiments on tool-tip FRFs and micro-milling were conducted. The results validate the effectiveness of the integrated model, which can calculate the tool-tip FRFs, SLDs, and time responses to analyze chatter stability by considering the centrifugal force, gyroscopic effect, and tool runout.

Investigation of the Effects of CNC Tool Runout on Machining of 1.2379 Steel and Tool Life

Investigation of the Effects of CNC Tool Runout on Machining of 1.2379 Steel and Tool Life

Analysis and modeling of cutting force considering the tool runout effect in longitudinal-torsional ultrasonic vibration-assisted 5 axis ball end milling

The longitudinal-torsional ultrasonic vibration-assisted milling (LTUVAM) can improve the machining quality compared with conventional milling (CM), and the machining quality is closely related to cutting force which is affected by the tool runout effect. In this study, a mechanistic force model for longitudinal-torsional ultrasonic vibration-assisted 5 axis ball end milling considering the tool runout effect is proposed. First, the cutting edge motion model considering the effects of tool runout and ultrasonic vibration is established. Then, based on the analysis of the cutting edge motion relative to the workpiece, the uncut chip thickness (UCT) is computed by means of the geometrical calculation method, and the engaged cutting edge elements are determined according to the Z-map method, the ultrasonic milling force model is established after determining the cutting force coefficients and tool runout parameters through calibration tests. Moreover, the impact of different parameters on dynamic separating characteristics of LTUVAM is studied by the tool-workpiece contact rate. Finally, the verification tests are carried out, and the experimental results show the effectiveness of the ultrasonic milling force model.

Force model of two-flute continuous milling based on tool deflection

Accurate modeling of the instantaneous uncut chip thickness is one of the key issues in milling mechanics. Although most current cutting force models take into account the effects of tool deflection and tool run-out, they only consider single-edge continuous milling processes and do not consider processes where multiple edges are simultaneously engaged in milling. Considering the tool runout and tool deflection that affect the end milling process, a novel uncut chip thickness algorithm based on two-flute continuous milling is proposed in this paper, and an analytical force model for actual milling is established. There is no need to use iterative methods, and the predictive power can be obtained by solving a linear system of equations, so the computational cost is greatly reduced. At the same time, stainless steel 316 was processed, and the experimental results showed that the predicted force was in good agreement with the measured force.

Modeling of variable-pitch/helix milling system considering axially varying dynamics with cutter runout offset and tilt effects

In order to meet the growing industrial demand of high quality and high efficiency machining, long cutters with larger axial depth of cut are extensively implemented in peripheral milling of deep pockets, grooves, and thin-wall parts. However, due to their high flexibilities, chatter easily occurs during the machining process. It has been demonstrated that milling cutters with variable pitch and/or variable helix angles can mitigate the chatter, which are gaining increasingly important applications. Although this kind of cutters have been studied in some detail in previous research, few studies have focused on the interaction dynamics complicated by actual cutter runout in long tool-part contact zone.This paper systematically studies the dynamics and stability of variable-pitch/helix milling system with long end cutters. The cutters are divided into a series of axial disks, and each axial disk includes several cutting elements which are equal to the number of teeth. Variations of pitch and helix angles, cutter run-outs including radial offset and axial tilt, and mode shapes with the cross terms in the orthogonal direction, are assigned to these cutting elements. The system, involving multiple regenerative delays as well as the axially varying dynamics, is formulated as a matrix form of time-periodic delay differential equation with multi-modal dynamic parameters. An updated cross-axis and cross-point modal testing method is then proposed to obtain the dynamic parameters, which can effectively avoid multiple hits when impacting the cutter with hammer. The stability lobes are predicted in state space by developing an improved semi-discretization method, by which the pitch variations and actual runout effects on stability are investigated. It is shown that the stability lobes differ significantly when the combined effects of cross-axis and cross-point FRFs and actual cutter runout are considered. A series of cutting experiments is conducted to demonstrate the proposed model and method. Results show that these lobes well agree with the experimental results.

Stability analysis for a milling system considering multi-point-contact cross-axis mode coupling and cutter run-out effects

Stability analysis is essential for milling operations to enable high machining productivities without sacrificing surface quality and introducing significant surface errors. Its exact implementation depends on the dynamics modeling with reliable requirement of system’s dynamic parameters. However, existing modal testing strategies neglect the cross-axis mode coupling effect along the multi-point-contact zone between the tool and workpiece. This leads to some losses of accuracy for the dynamic parameters and further makes the dynamic model fail to reflect the real tool-workpiece interaction mechanism. Aiming at improving the model accuracy, a novel modal testing strategy is proposed, which takes both the cross-axis and cross-point mode coupling effects into account in identifying the dynamic parameters. Meanwhile, new parameter identification technique is theoretically given when processing measured direct, cross-axis and cross-point frequency response functions. And matrix assembly technique is also presented for matching the identified dynamic parameters to the system dynamic equation. On the other hand, instead of single-point-contact dynamics assumed at the tool tip, a dynamic model with multi-point-contact dynamics is developed for a common multi-delay milling system, where run-out effect is included for calculating multiple regenerative dynamic cutting forces. The resulting multi-delay system dynamic equation is then solved by an improved semi-discretization method. To validate the developed model with the dynamic parameters obtained by the proposed modal testing strategy, down and up milling experiments are carried out, and two cutters with different diameter are employed in the experiments. The results show that the proposed approach significantly improves the stability prediction accuracy of a milling system especially involving a big axial depth of cut.

A cutting force model based on compensated chip thickness in five-axis flank milling

In the five-axis flank milling process, the instantaneous undeformed chip thickness (IUCT) and the entry/exit angles vary continuously because of the complex tool path and workpiece geometry. The changes result in time-varying cutting forces in consecutive cutting operations, which are difficult to predict. This paper comprehensively considers the effects of cutter runout on the IUCT and the influence of the curved tool path on the entry/exit angles in the calculation of cutting force. A simplified IUCT model is presented based on compensated chip thickness in five-axis flank milling. Compared with the existing IUCT model, it can achieve high precision and greatly improves the calculation efficiency. Subsequently, the entry angles of surface with varied curvature are verified. Five-axis flank milling experiment for a non-developable ruled surface was conducted to verify the proposed theory. The results show that the proposed cutting force model has the ability to predict the cutter forces with a high precision and can be used in simulations and optimizations of five-axis flank milling.

A new method for determining the instantaneous uncut chip thickness in micro-milling

The calculation accuracy of instantaneous uncut chip thickness (IUCT) plays a very important role in the modeling of milling processes. Tool runout is an obstacle to the accurate calculation of IUCT in micro-milling. This paper focuses on the calculation of IUCT and proposes a new method for determining the IUCT in micro-milling. Firstly, the effects of tool runout and single-edge cutting on nominal uncut chip thickness were analyzed. Then, the calculation methods of nominal uncut chip thickness and actual uncut chip thickness in micro-milling were proposed respectively, which took into account the impact of tool runout, single-edge cutting, intermittent chip formation, and the minimum chip thickness. The pseudo-single-edge cutting which may occur in single-edge cutting was discussed. Finally, nominal uncut chip thickness and actual uncut chip thickness in micro-milling were analyzed respectively. The calculated results showed higher accuracy compared to conventional method.

FEM simulation of micromilling of CuZn37 brass considering tool run-out

Micro-milling process of CuZn37 brass is considered important due to applications in tool production for micro replication technology. Variation in material properties, work material adhesion to tool surfaces, burr formation, and tool wear result in loss of productivity. Chip shapes together with localized temperature, plastic strain, and cutting forces during micro milling process can be predicted using Finite Element (FE) modelling and simulation. However, tool-workpiece engagement suffers from tool run-out affecting process performance in surface generation. This work provides experimental investigations on effects of tool run-out as well as process insight obtained from 3D FE simulations with and without considering tool run-out. Scanning electron microscope (SEM) observation of the 3D chip shapes demonstrates ductile deformed surfaces together with localized serration behavior. FE simulations are utilized to investigate the effects of cutting speed on cutting forces. Cutting force and chip morphology results from simulations are compared with force measurements, and actual chip morphology acquired by SEM revealing reasonable agreements.

Stability modeling with dynamic run-out in high speed micromilling of Ti6Al4V

The low flexural rigidity of the micro-tool makes it susceptible to failure under high cutting forces and/or unstable process conditions. One way to counter the effect of low flexural rigidity is to use high rotational speed which reduces the chip load and, therefore, the cutting forces acting at the tip of the micro-end mill. However, high rotational speeds can amplify the effects of run-out and misalignment. This speed-dependent tool eccentricity, known as dynamic run-out, can be much larger than the quasi-static (speed independent) run-out. The dynamic run-out is more pronounced at high rotational speeds (∼100,000 RPM) due to the increased centrifugal force. The chip thickness is modified due to the dynamic run-out which affects the cutting forces and the stability. It is necessary to incorporate the dynamic run-out in the chip thickness model for an accurate prediction of the forces and the stability limits in high speed micromilling. Consequently, this paper is focused on characterizing the dynamic run-out and incorporating its effect on the undeformed chip thickness, cutting forces and stability limits. The predicted cutting forces with the modified chip thickness due to dynamic run-out shows a better agreement with the experimentally measured cutting forces as compared to the quasi-static run-out and ideal cycloidal chip thickness based force models. The predicted cutting force with dynamic run-out in the feed-direction gives an error of 11.54% as opposed to a relatively large error of 73.1% with a quasi-static run-out based model at 100,000 rpm. The Nyquist stability criterion has been used to predict the stability for 2-DOF chatter model of micromilling process. At a chip load of 3 µm/flute, the predicted stable depth of cut is higher if the dynamic run-out is included at high rotational speeds (> 51,500 rpm). This increase is attributed to a high dynamic run-out which results in cutting via only one flute. However, if the dynamic run-out is relatively low (between 29,500 rpm and 51,500 rpm), both the flutes are engaged in machining and the predicted limit is lower than that of the quasi-static run-out. The predicted values are in reasonably good agreement with the experimentally determined chatter onset points for most cases.

Finite element simulation of high speed micro milling in the presence of tool run-out with experimental validations

Micro milling process of CuZn37 brass is considered important due to applications in tool production for micro moulding and micro replication technology. The variations in material properties, work material adhesion to tool surfaces, burr formation, and tool wear result in loss of productivity. The deformed chip shapes together with localized temperature, plastic strain, and cutting forces during micro milling process can be predicted using finite element (FE) modeling and simulation. However, tool-workpiece engagement suffers from tool run-out affecting process performance in surface generation. This work provides experimental investigations on effects of tool run-out as well as process insight obtained from simulation of chip flow, with and without considering tool run-out. Scanning electron microscope (SEM) observation of the 3D chip shapes demonstrates ductile deformed surfaces together with localized serration behavior. FE simulations are utilized to investigate the effects of micro milling operation, cutting speed, and feed rate on forces, chip flow, and shapes. Predicted cutting forces and chip flow results from simulations are compared with force measurements, tool run-out, and chip morphology revealing reasonable agreements.

Investigation on the subsynchronous pseudo-vibration of rotating machinery

Subsynchronous pseudo-vibration (SPV) of rotating machinery is one of the primary reasons for fault misdiagnosis. SPV has similar signal signatures to those of a real fault, which usually leads to excessive maintenance or even unscheduled shutdown. For this reason, it is essential to investigate the root causes of SPV so as to reduce unnecessary downtime and maintenance cost. Aiming at this issue, a novel signal model for rotor non-contact vibration is built to describe the generating mechanism of one kind of SPV by considering the combined effects of rotor axial motion and detection surface runout on vibration signal. To obtain more discriminative fault features from the vibration signals, the two-dimension holospectrum (2DH) is employed to integrate the phase information from two perpendicularly installed sensors. The characteristics of precession orbit used to describe the lateral motion of a rotor could be fully extracted by 2DH. It is shown that the precession orbit at the fault feature frequency will degenerate into a straight line when SPV occurs, and thus the eccentricity of precession orbit could be considered as a key feature for discriminating SPV from real subsynchronous vibration (RSV). The effectiveness of proposed method was validated on a rotor test rig. By using this method, the SPV problem of a real gearbox in a blast furnace blower set in a steel mill was successfully diagnosed.

Evaluation Indicators of the Runout Effects on Milling Forces and Regenerative Stability

Runout is an unavoidable phenomenon accompanying milling processes, which may significantly affect the cutting forces and the regenerative stability. Since the influences of runout are closely related to cutting conditions such as tool structure, feed per tooth, depth of cut, etc., it is improper to evaluate the influences merely by the runout parameters themselves. In this paper, the runout values and the process parameters are jointly analyzed to study their effects on cutting forces and regenerative stability of milling processes with variable pitch and variable helix tools. Afterwards, two simple indicators, i.e., the process indicator and the signal indicator are presented to estimate the runout effects under various cutting conditions. Numerical simulations and cutting experiments verify that the proposed indicators are feasible, though not perfect, ways to evaluate the runout effects.

A multi-order method for predicting stability of a multi-delay milling system considering helix angle and run-out effects

In this paper, a multi-delay milling system considering helix angle and run-out effects is firstly established. An exponential cutting force model is used to model the interaction between a work-piece and a cutting tool, and a new approach is presented for accurately calibrating exponential cutting force coefficients and cutter run-out parameters. Furthermore, based on an implicit multi-step Adams formula and an improved precise time-integration algorithm, a novel stability prediction method is proposed to predict the stability of the system. The involved time delay term and periodic coefficient term are integrated asa comprehensive state term in the integral response which is approximated by the Adams formula. Then, a Floquet transition matrix with an arbitrary-order form is constructed by using a series of matrix multiplication, and the stability of the system is determined by the Floquet theory. Compared to classical semi-discretization methods and full-discretization methods, the developed method shows a good performance in convergence, efficiency, accuracy, and multi-order complexity. A series of cutting tests is further carried out to validate the practicability and effectiveness of the proposed method. The results show that the calibration process needs a time of less than 5min, and the stability prediction method is effective.

Improved tooth trajectory model for prediction of milled surface geometry

ABSTRACTThe prediction on surface roughness and surface geometry in peripheral milling operation is a crucial but tedious task. The current researches concerned are almost based on circular tooth trajectory assumption to simplify analysis and modeling, and some models derived from true tooth trajectory are not concise enough or have certain limitation when put into practice. A novel idea on account of the principle of curvature circle approximation to true tooth path curve in cutting contact point nearby is presented, and the relevant mathematical theory is established. Then by means of specific curvature circles, mathematical models and analysis methods of surface roughness are discussed systematically, which cover two situations—cutting with and without runout effect. The validity and superiority of the models are demonstrated by experimental studies and numerical simulations. Finally, based on the suggested models and analytical methods, the effects of runout, feed rate, and cutter geometry on surface roughness and geometry are studied in depth, and several significant mathematical formulas and quantitative conclusions are reached, which would contribute to the theory of milled surface studies.

Application of linear and nonlinear vibration absorbers in micro-milling process in order to suppress regenerative chatter

In this paper, linear and nonlinear vibration absorbers are designed to suppress regenerative chatter in micro-milling process. Suppressing regenerative chatter leads to improve surface finish. Micro-milling process is considered as a two degree of freedom system, and the run-out effects of cutting tool are also taken into account. Linear and nonlinear absorbers in two directions are composed of mass, spring and dashpot elements. The optimum values of the absorber parameters are determined by means of an optimization algorithm in order to minimize the cutting tool vibration. The effectiveness of different types of the absorbers in micro-milling process is illustrated. The optimum parameters for each type of absorbers are presented.

Numerical simulation of milling forces with barrel-shaped tools considering runout and tool inclination angles

• A numerical model to predict cutting forces in milling with barrel-shaped mills is proposed. • It can handle the influence of tilt-lead angles and variable runout along tool axis. • Validation tests were performed in a 5-axis milling centre. • Results from the model were consistent with real instantaneous cutting forces. The main market studies depict a future in which all one-aisle aeroplanes will mount engines composed of elements with complex surfaces. Among the new generation of tools, the barrel-shaped tools were released to the market for the machining of such types of surfaces. However, there are no evidences reported in the literature about how do these tools work. This work presents for the first time a mathematical model based on the numerical discretization of barrel cutters to predict the cutting forces. The effects of helix angle, runout and lead and tilt angles were included and the model was validated for a range of conditions in a 5-axis machine. In this line, this paper enables future mathematical developments including more details and aiming at other complex problems.

A runout measuring method using modeling and simulation cutting force in micro end-milling

In the process of micro end-milling, the micro tool axis is not the same line of the spindle axis due to the eccentricity of the tool-holder-spindle assembly, which is called tool runout. Tool runout has significant effects on cutting force variation, which can lead to higher peak forces and uneven tool wear of the cutter. Hence, a runout model must be included in a cutting force modeling to simulate accurate cutting force during micro-milling process. In this paper, the method for modeling and simulation to measure a runout of tool-holder-spindle in micro end-mill was developed. The simulated cutting force with regard to runout was compared with the measured cutting force. It is noted that they had similar variation pattern and closely matched amplitude levels. The result indicated that the effects of tool runout were predominant for the 0.9 mm diameter and at low feed per tooth.

3D surface topography analysis in 5-axis ball-end milling

This article presents a new analytical model to predict the topography and roughness of the machined surface in 5-axis ball-end milling operation for the first time. The model is able to predict the surface topography and profile roughness parameters such as 3D average roughness (Sa) and 3D root mean square roughness (Sq) by considering the process parameters such as the feedrate, number of flutes, step-over and depth of cut as well as the effects of eccentricity and tool runout in 5-axis ball-end milling. This model allows to simulate the effects of the lead and tilt angles on the machined surface quality in the virtual environment prior to the costly 5-axis machining operations. The effectiveness of the introduced surface topography prediction model is validated experimentally by conducting 5-axis ball-end milling tests in various cutting conditions.