Cutting Force Variation Research Articles

Modeling dynamic stability in high-speed micromilling of Ti–6Al–4V via velocity and chip load dependent cutting coefficients

An increase in the demand for miniaturized components has resulted in the development of mechanical micromachining processes, such as micromilling. However, scaling down the process for micromilling operations require micro-tools, whose stiffness values are orders of magnitude lower than the conventional tools. The limited stiffness of the micro-end mills is a big impediment in machining difficult-to-cut materials, such as hardened steels and Ti-alloys. To address this issue, the cutting forces and hence the chip loads need to be reduced by using very high spindle rotational speeds. However, at lower chip loads ploughing may occur instead of cutting resulting in cutting force variation and high spindle speeds can excite higher order modes. Consequently, high spindle speeds and low chip loads in a tool with limited stiffness can lead to chatter induced dynamic instability which deteriorates the part quality, surface finish and tool life. Hence, identification of stable cutting parameters is necessary to avoid the chatter in high speed micromilling. Since the dynamic stability depends on the speed and the chip load (feed/flute), mechanistic force model with a constant cutting coefficient will yield inaccurate results. In this paper, the mechanistic force model based on velocity and chip load dependent cutting coefficient has been incorporated into the analytical stability model to predict the cutting forces and the stability lobe diagrams for high-speed micromilling of Ti6Al4V. The force predictions from the mechanistic model using velocity and chip load dependent cutting coefficient are in better agreement with experimentally measured forces as compared to constant cutting coefficients. Up to a spindle speed of 70,000rpm, the maximum prediction errors in stability boundary for a 500µm diameter end-mill using constant and velocity–chip load dependent cutting coefficients are ~33% and ~11%, respectively.

Three-dimensional dynamic cutting forces prediction model during micro-milling nickel-based superalloy

Nowadays, there are urgent demands of micro structure/parts which have high strength in high-temperature environment in the fields such as aerospace, energy, power, biomedical, etc. Nickel-based superalloy with high strength and high hardness under high temperature is the suitable material for manufacturing this kind of micro parts. Aimed at the problem of the complicated cutting force variation rule when micro-end milling nickel-based superalloy, the cutting forces model during micro-end milling of nickel-based superalloy processing is studied. Firstly, micro-end milling hole experiments are carried out to establish the radical run-out prediction model of cutting edge, which lays the foundation for establishing the cutting thickness calculation model during micro-end milling. Then, based on the minimum cutting thickness value, micro-end milling of nickel-based superalloy process is divided into two different cutting processes: shear-dominant regime cutting process and ploughing-dominant regime cutting process. Moreover, cutting forces prediction model during shear-dominant regime cutting process is developed based on the cutting forces in proportion to cutting layer area, which takes the effect of ploughing into account. Meanwhile, cutting forces prediction model during ploughing-dominant regime cutting process is developed based on the cutting force in proportion to interference volume between the flank surface of cutting tool and the workpiece. The experiment results verify that the cutting forces prediction results and experiment results are well matched.

Study on Simulation of Machining Deformation and Experiments for Thin-walled Parts of Titanium Alloy

Deformation problems are main factors affecting the precision of machining the thin-walled parts. This paper focuses on the thin-walled parts of titanium alloy that is the difficult-to-machine material, based on the analysis of deformation characteristics and force, the milling force mathematical model of the ball-end milling cutter was established. On the basis of the 3D milling model of thin-walled parts of titanium alloy, the deformation regularity and cutting force variations were analyzed with the finite element simulation method. Through the experiments of machining thin-walled parts, the cutting force model was verified. The experiments results and simulations results match well. The work provides an effective basis for further study on the control of machining deformation of thin-wall parts of titanium alloy.

Online condition monitoring in micro-milling: A force waveform shape analysis approach

The cutting force variations have long been studied for machining condition monitoring, due to their sensitivity to the tool conditions. These variations could be the statistics of the amplitude, features extracted from frequency components, wavelet coefficients, etc. Different from most current approaches, this paper introduces a novel online approach that directly correlates tool conditions with the force waveform variations and estimates the tool condition based on their corresponding singularity degree density functions. The singularities of waveforms are measured with Holder exponents (HEs), which are extracted from their wavelet transform modulus maxima. Experimental studies have shown that the HEs reflect the changes of tool conditions. The HE features are found robust to working condition variations, and their probability density functions are discriminate for tool state estimation in micromilling.

Cutting force, tool life and surface integrity in milling of titanium alloy Ti-6Al-4V with coated carbide tools

Titanium alloys are widely used in aeronautics that demands a good combination of high strength, good corrosion resistance and low mass. The mechanical properties lead to challenges in machining operations, such as high process temperature as well as rapidly increasing tool wear. In this work, three carbide end mills have been used in machining of titanium alloy Ti-6Al-4V. The first tool is coated with TiAl; the second and the third are coated with multi-layers or with a single layer of TiAlN. The cutting force and the tool life have been experimentally investigated and put into relationship with the process parameters under dry cutting condition. The quality of the machined surfaces has been evaluated by measuring the roughness of the machined surfaces. Finally, the correlation among cutting force variation, tool wear propagation and surface roughness has been analyzed and discussed. These three tools demonstrate to be able to maintain their hardness and other mechanical properties at the high cutting temperatures that they encountered.

Finite Element Simulation Research on a Large Cutting Depth and Quasi-High Speeds 3-D Milling of Titanium Alloys

In this paper, based on finite element software DEFORM, the model of a large cutting depth and quasi-high speeds milling of titanium alloys is built to study the cutting temperature and cutting force variation along with the change of cutting parameters. The simulation results show that: the location of the maximum cutting temperature appears in the cutting edges of the tool nose circular profile. Meanwhile, due to workpiece material rebound in the cutting process, the interface between workpiece and tool flank face occurs serious extrusion, which results in relatively high cutting temperature on the workpiece machined surface. In addition, cutting speed and feed rate per tooth play a key role in influencing the cutting temperature. However, the influence of cutting depth on the cutting temperature is less clear. With the increase in the feed rate and depth of cut, cutting force increased significantly. In particular, within the scope of the cutting speeds under the given conditions, the cutting force has a tendency to decrease with the cutting speed increasing over 120m/min.

Investigation of tool geometry effect and penetration strategies on cutting forces during thread milling

The application of thread milling is increasing in industry because of its inherent advantages over other thread cutting techniques. The objective of this study is to investigate the effect of milling cutter tool geometry on cutting forces during thread milling. The proposed method can compare the performance of milling cutters in spite of the different number of tooth. The best thread milling cutter among the studied tools was determined from the cutting forces point of view. Furthermore, this study also pinpoints the best penetration strategy that provides minimum cutting forces. Lower cutting force variations will lead to fewer vibrations of the tool which in turn will produce accurate part.

The Effects of TiAlN and TiN Coating during End Milling of INCONEL 718

Inconel 718 is a registered trademark of Special Metals Corporation that refers to a family of austenitic nickel-chromium-based super alloys. This material usually being used or operate in high temperature and extreme condition like aerospace industry, turbocharger rotors and seals. This research presents an experimental study of the cutting force variation, surface roughness, tool life and tool wear in end milling Inconel 718. The experimental results showed that flank wear was the predominant failure mode affecting tool life for TiAlN and TiN coated carbide tool. TiAlN is the better coated tool than TiN because it produce better surface finish and resultant force. Feed rate is one of the parameter that effecting results in this experiment. The higher feed rate will shorten the life of the tool. Although for the cutting condition, the situation is quite different where the proper cutting speed will maintain the tool life and tool wear for cutting tool. The overall study shows that TiAlN coated carbide tool with cutting speed 100 m/min, depth of cut 0.5 mm and feed rate 0.1 mm/tooth is the optimum parameter in this experiment.

Surface texture generation during cylindrical milling in the aspect of cutting force variations

The work presented here concentrates on surface texture analysis, after cylindrical milling of hardened steel. Cutting force variations occurring in the machining process have direct influence on the cutter displacements and thus on the generated surface texture. Therefore, in these experiments, the influence of active number of teeth (zc) on the cutting force variations was investigated. Cutting forces and cutter displacements were measured during machining process (online) using, namely piezoelectric force dynamometer and 3D laser vibrometer. Surface roughness parameters were measured using stylus surface profiler. The surface roughness model including cutting parameters (fz, D) and cutting force variations was also developed. The research revealed that in cylindrical milling process, cutting force variations have immediate influence on surface texture generation.

Mesoplasticity approach to studies of the cutting mechanism in ultra-precision machining

There have been various theoretical attempts by researchers worldwide to link up different scales of plasticity studies from the nano-, micro- and macro-scale of observation, based on molecular dynamics, crystal plasticity and continuum mechanics. Very few attempts, however, have been reported in ultra-precision machining studies. A mesoplasticity approach advocated by Lee and Yang is adopted by the authors and is successfully applied to studies of the micro-cutting mechanisms in ultra-precision machining. Traditionally, the shear angle in metal cutting, as well as the cutting force variation, can only be determined from cutting tests. In the pioneering work of the authors, the use of mesoplasticity theory enables prediction of the fluctuation of the shear angle and micro-cutting force, shear band formation, chip morphology in diamond turning and size effect in nano-indentation. These findings are verified by experiments. The mesoplasticity formulation opens up a new direction of studies to enable how the plastic behaviour of materials and their constitutive representations in deformation processing, such as machining can be predicted, assessed and deduced from the basic properties of the materials measurable at the microscale.

Effect of Rotation Speed and Eccentricity on Dynamic Movement Characteristics of BTA Deep-Hole Boring Bar

Since the actual boring bar physical system is characteristic of strong nonlinear, it is difficult to apply analytic method to solve. For studying the effect of dynamic characteristics induced by speed changing and eccentricity, simulations are completed for bifurcation of displacement with the variable rotation speed, no matter whether there exists cutting force. It is shown that with the speed increasing, the system's dynamic characteristic become complicated, namely, the dynamic periodic motion varieties from single, multiple to quasi periodic in turn. Analogously, eccentricity leads to the increase of the complexity of systems dynamic characteristics. The periodic motion also transforms from single, quasi, triple to quasi periodic in sequence. The cutting force variation plays an importance role on the movement stability of the system.

Cutting force variation with respect to tilt angle of trajectory in elliptical vibration V-grooving

2-dimensional vibration assisted cutting also referred to as elliptical vibration cutting(EVC) is recognized as one of the promising strategies to ensure precision micro machining because of its characteristics such as reduction of cutting resistance and enhancement of machining quality. Previous studies found that effectiveness of EVC increases with the excitation frequency and the amplitude of vibration as well. To further optimize the EVC process the effect of the tilt angle of an elliptical tool trajectory on the machining quality was investigated. The tilt angle was modified by modulating relative magnitude and phase of voltages supplied to two piezoelectric materials constituting an elliptical vibration cutting mechanism. From successive V-grooving experiments involving duralumin and brass materials with cutting depth down to 5 μm from 30 μm, it was found that there exists an apparent correlation between the tilt angle and machining quality. At a tilt angle between 20 ∼ 30°, the cutting resistance was a minimum, leading to enhancement of machining quality. The increase in reverse frictional force between the chip and rake face of cutting tool appears to cause the cutting resistance to decrease.

Framework for evaluation of the relative contribution of the process on porosity–cutting force dependence in micromilling of titanium foams

Porous titanium, characterized by interconnected and large open-cell structures, constitutes one of the most promising bone substitutes that are currently available for surgical orthopedic and dental implantation procedures. Since little is known about the behavior of this highly porous material during material removal operations, the main objective of this study was to develop a framework capable of evaluating the effect of cutting speed, cutting depth, and feed rate on the interplay between porosity and cutting force signatures, as experienced during microslot cutting experiments. The comparisons performed between optically determined porosity and cutting force profiles by means of standard random data analysis metrics (correlation coefficient, power spectral density, and coherence) revealed that the presence of a material discontinuity has a prevalent effect on cutting force variation in the case of micromilling processes characterized by (1) less intensive machining regimes and (2) larger cutter/workpiece engagement zones. The proposed methodology is useful in selection of the investigative approach to be taken in assessment of the micromachining-related behavior of highly porous foams subjected to micromilling operations.

Finite element modelling of shear angle and cutting force variation induced by material anisotropy in ultra-precision diamond turning

This paper addresses a key theoretical problem in the mechanics of ultra-precision machining – shear angle prediction and cutting force variation induced by crystallographic anisotropy. The constitutive equation of crystal plasticity is implemented in the finite element modelling of the chip formation at micro-scale to take into account the effect of crystallographic orientations of the work piece to be cut. The theoretical prediction of shear angle and cutting force variation reveals two distinguished phases of pre-compression and steady-state cutting in ultra-precision diamond turning. The predicted patterns of cutting force variation are in good agreement with published experimental results.

Study on the Cutting Prediction of Supercritical Material

The technology of the artificial neural network (ANN) was applied in the research of supercritical material cutting. Two-dimensional Gaussian surfaces of the three cutting elements and workpiece surface hardness had been established fitting through JMP software. Base on the orthogonal milling experiments, the rules of cutting forces variation were forecasted, as well as the effect to the hardness on workpiece surface. The cutting parameters selected according to the process were built, providing an important basis for the optimization of machining conditions. The prediction results were in good agreement with the experimental results. DOI: http://dx.doi.org/10.11591/telkomnika.v11i9.3265

Experimental Investigation of Hard Turning Mechanisms by PCBN Tooling Embedded Micro Thin Film Thermocouples

Temperature-distribution measurements in cutting tools during the machining process are extremely difficult and remain an unresolved problem. In this paper, cutting temperature distributions were measured by thin film thermocouples (TFTCs) embedded into polycrystalline cubic boron nitride (PCBN) cutting inserts in the immediate vicinity of the tool-chip interface. The embedded TFTC array provides temperature measurements with a degree of spatial resolution (100 μm) and dynamic response (150 ns) that is not possible with currently employed methods due to the micro-scale junction size of the TFTCs. Using these measurements during hard turning, steady-state, dynamic, as well as chip morphology and formation process analyses were performed based on the cutting temperature and cutting force variations in the cutting zone. It has been shown that the temperature changes in the cutting zone depend on the shearing band location in the chip and the thermal transfer rate from the heat generation zone to the cutting tool. Furthermore, it became evident that the material flow stress and the shearing bands greatly affect not only the chip formation morphology but also the cutting temperature field distributions in the cutting zone of the cutting insert.

Characterization of Cutting Force Induced Surface Shape Variation in Face Milling Using High-Definition Metrology1

High-definition metrology (HDM) systems with fine lateral resolution are capable of capturing the surface shape on a machined part that is beyond the capability of measurement systems employed in manufacturing plants today. Such surface shapes can precisely reflect the impact of cutting processes on surface quality. Understanding the cutting processes and the resultant surface shape is vital to high-precision machining process monitoring and control. This paper presents modeling and experiments of a face milling process to extract surface patterns from measured HDM data and correlate these patterns with cutting force variation. A relationship is established between the instantaneous cutting forces and the observed dominant surface patterns along the feed and circumferential directions for face milling. Potential applications of this relationship in process monitoring, diagnosis, and control are also discussed for face milling. Finally a systematic methodology for characterizing cutting force induced surface variations for a generic machining process is presented by integrating cutting force modeling and HDM measurements.

Assessment of cutting forces in high-speed milling of Inconel 718 considering the dynamic effects

Aerospace material Inconel 718 is well known for its poor machinability. This article presents an experimental study of the cutting forces in high-speed dry milling of Inconel 718 using a milling cutter with coated carbide inserts. An assessment of the cutting force variations is conducted using statistical approaches and wavelet decomposition taking into consideration the dynamic effects. The averaged peak force values, the peak force variation range and distribution, and the skewness are evaluated. It shows that cutting speed does not have a significant influence on the averaged peak cutting force for the range tested. The tool–workpiece vibrations at the cutter entry stage and exit stage are generally more significant. Moreover, wavelet packet decomposition at level 3 with the DB4 wavelet and Shannon entropy is found to be an effective approach to identify the chatter onset.

Finite element simulation of effect of residual stresses during orthogonal machining using ALE approach

In this paper, a finite element model has been developed to predict the effect of residual stress induced in the work material during multiple pass turning of AISI 4340 steel. Chip morphology and force variation during machining are also quantified using the FE model. Finite element model was developed using arbitrary Lagrangian-Eulerian formulation along with Johnson-Cook material model and Johnson-Cook damage model. The finite element model developed in this study was validated experimentally by studying the chip morphologogy and cutting force variation during the machining. Results indicate that there is good correlation existing between numerical results and experimental results.

New mathematical method for the determination of cutter runout parameters in flat-end milling

The cutting force prediction is essential to optimize the process parameters of machining such as feed rate optimization, etc. Due to the significant influences of the runout effect on cutting force variation in milling process, it is necessary to incorporate the cutter runout parameters into the prediction model of cutting forces. However, the determination of cutter runout parameters is still a challenge task until now. In this paper, cutting process geometry models, such as uncut chip thickness and pitch angle, are established based on the true trajectory of the cutting edge considering the cutter runout effect. A new algorithm is then presented to compute the cutter runout parameters for flat-end mill utilizing the sampled data of cutting forces and derived process geometry parameters. Further, three-axis and five-axis milling experiments were conducted on a machining centre, and resulting cutting forces were sampled by a three-component dynamometer. After computing the corresponding cutter runout parameters, cutter forces are simulated embracing the cutter runout parameters obtained from the proposed algorithm. The predicted cutting forces show good agreements with the sampled data both in magnitude and shape, which validates the feasibility and effectivity of the proposed new algorithm of determining cutter runout parameters and the new way to accurately predict cutting forces. The proposed method for computing the cutter runout parameters provides the significant references for the cutting force prediction in the cutting process.