Segmented Chip Formation Research Articles

Controlling segmentation in cutting of metals

We examine segmented chip formation and associated flow dynamics in cutting of metals of low-to-moderate workability using high-speed imaging. Segmentation is initiated by a surface instability – formation of a ductile crack in a prow – on workpiece surface ahead of the tool, this crack then propagates towards the tool tip. Prow-crack initiation occurs at a critical strain ˜0.75 that is independent of material and deformation geometry. This ductile failure is analyzed in terms of local hydrostatic stress state and stress triaxiality. Material-agnostic methods to suppress and enhance segmentation using constrained cutting and a mechanochemical effect are demonstrated.

Analysis of chip formation and cutting forces in end milling AISI D2 tool steel with different cutting tool geometries

The purpose of this study was to investigate and establish the correlations between milling tool geometry, cutting conditions, as input factors and the cutting forces variations and chips formation, as output factors when end milling of AISI D2 tool steel. The experiments were carried out using a Taguchi design array. The chip shape and microstructure and cutting force components were analyzed. The results of the study show that the cutting tool geometry has a great influence over segmented chip formation mechanism and cutting force levels.

Improved analytical prediction of chip formation in orthogonal cutting of titanium alloy Ti6Al4V

The aim of this paper is to propose an analytical model of chip formation for precise prediction of orthogonal cutting of Ti6Al4V. This alloy is used broadly in aerospace components; hence, prediction of thermomechanical parameters of its orthogonal cutting is crucial for various industrial applications. The suggested analytical model needs only cutting parameters and tool geometry as input; it can predict not only cutting forces but also main features of a primary shear zone and a tool-chip interface. A non-equidistant shear zone model is employed to calculate shear strains and a shear strain rate in the primary shear zone, and a simplified heat-transfer equation is used for temperature. A Calamaz-modified Johnson–Cook material model that accounting for flow softening at high strains and temperature-dependent flow softening is applied to assess shear stresses in the primary shear zone. In addition, a shear-angle solution is modified for Ti6Al4V. At the tool-chip interface, a contact length, equivalent strain and an average temperature rise are defined. Besides, the effect of sliding and apparent friction coefficients is investigated. For a sawtooth chip produced in the cutting process of Ti6Al4V, the segmented-chip formation is analysed. A chip-segmentation frequency and other parameters of the sawtooth chip are also obtained. The predicted results are compared with experimental data with the cutting forces, tool-chip contact length, shear angle and chip-segmentation frequency calculated with the developed analytical model showing a good agreement with the experiments. Thus, this analytical model can elucidate the mechanism of the orthogonal cutting process of Ti6Al4V including predictive capability of continuous and segmented chip formation.

Modeling of tool-chip contact length for orthogonal cutting of Ti-6Al-4V alloy considering segmented chip formation

In this work, the orthogonal cutting experiments on Ti-6Al-4V alloy were conducted at different cutting speeds(10—160 m/min)and feed rates(20—160 μm/rev). The tool-chip contact length was measured by the track of tool rake face; meanwhile, the chip morphology caused by the localized and overall chip deformation was characterized by the degree of segmentation and the chip compression ratio, respectively. These parameters were analyzed and calculated according to the segmented chip morphology. In addition, three modified models considering the overall chip deformation and the localized deformation of adiabatic shear band were proposed, and the constants of the models were calculated by the genetic algorithm optimization. Considering the overall and localized chip deformation, the value and variation trend of the tool-contact length predicted by these three models agreed well with the experimental results.

Cutting force sensor based on digital image correlation for segmented chip formation analysis

Conventional piezoelectric sensors cannot record the force fluctuations at high frequencies to monitor serrated chip formation. Recently, force measurements by using digital image correlation (DIC) have been reported thanks to imaging devices that become more and more efficient, thereby opening possibilities of high rate acquisition. This study proposes to apply DIC based on closed-form solutions in order to measure cutting forces at camera acquisition frequency. The considered displacement fields are obtained from the Flamant–Boussinesq solution. This method is first applied to picture pairs shot during the cut and then to a full sequence of pictures recorded upon orthogonal cutting of hardened AISI 52100 steel with a c-BN tool. To validate part of the corresponding mechanism, the change of cutting forces is finally investigated when chip segments are formed.

Effect of tool wear on chip formation during dry machining of Ti-6Al-4V alloy, part 1: Effect of gradual tool wear evolution

Geometric features of the segmented chip have been investigated along with the volume of material removed at a cutting speed at which tool wear is characterized by the gradual development of flank wear when cutting Ti-6Al-4V alloy. The chip geometric variables varied with an increase in the volume of material removed as the combined effect of change in tool’s geometry and increase in cutting temperature. Plastic deformation dimples were observed as periodical regions on the machined surface, a row on each undeformed surface and region on the top of the slipping surface of the segmented chip when cutting with new tool; these dimples on the undeformed surface and machined surface are elongated in the direction of chip flow. All these dimples became less with an increase in the volume of material removed and almost disappeared when the chip was removed with the worn tool at the end of its life. A model of segmented chip formation process has been proposed to satisfactorily explain the formation of the plastic deformation dimples on the undeformed surface and machined surface of the segmented chip produced with a new cutting tool and the transition of chip geometry with the evolution of tool wear.

Effects of alloying elements in UHC-steels and consequences for the machinability

Due to their high strength and reduced density aluminum-alloyed ultra-high-carbon steels (UHC-steels) show high potential for industrial applications. In an earlier study, segmented chip formation has been observed in turning alloyed UHC-steel. The formation of serrated chips imposes a limit on the productivity when machining this material. In order to enhance the machinability the chip formation mechanisms are investigated and recommendations for the tool design derived. Additionally, approaches for an optimized material processing (heat treatment) that improves the machinability are discussed. The recommendations are based on a detailed microstructure analysis by scanning electron microscopy (SEM), electron backscattering diffraction (EBSD), wavelength dispersive X-ray diffraction (WDX) and Auger electron spectroscopy (AES). Subsequent chip root experiments and micro indentation tests give further insight into the chip formation mechanisms. The observed chip formation mechanisms are connected to the obtained results on the microstructure of the aluminum-alloyed UHC-steel. It is shown that additional alloying components like chromium and manganese alter the microstructure and contribute to a serrated chip formation.

A physically based constitutive model for simulation of segmented chip formation in orthogonal cutting of commercially pure titanium

The accuracy of cutting simulations depends on the knowledge of micro-scale physics included in the constitutive and microstructure evolution models of the cutting process. This paper presents an enhanced physically based material model that accounts for microstructure evolution induced flow softening due to the inverse Hall–Petch effect below a critical grain size. The model's ability to simulate segmented chip formation and grain refinement in the shear bands produced in orthogonal cutting of commercially pure titanium is evaluated through finite element simulations and experiments. Results show good prediction accuracy for the cutting and thrust forces, chip morphology, and segmentation frequency.

Effects of machining parameters and tool geometry on serrated chip formation, specific forces and energies in orthogonal cutting of nickel-based super alloy Inconel 100

Nickel-based alloys are widely used in applications requiring high strength at elevated temperatures such as in aircraft jet engines. However, nickel-based alloys such as Inconel 100 are still considered difficult-to-machine metal alloys. In this study, specially designed orthogonal cutting tests on Inconel 100 nickel-based alloy have been conducted using WC/Co cutting tool with two varying rake angles, cutting edge radii and at wide ranges of cutting speed and feed. Effects of those parameters on specific forces have been investigated. Serrated and segmented chip formation is observed and the mechanics of segmented chip have been modeled and validated using the experimental test data. Chip microscopic images are utilized in measuring and calculating chip formation angles, shear strain, and shear strain rate in the main shear zone and within the shear bands. It was found that segmentation is highly influenced by machining conditions, and energy distributions calculated with regard to machining parameters reveal that friction dissipation and material separation are significant in machining of Inconel 100 nickel-based alloy.

Development of a Free-Machining (α + β) Titanium Alloy Based on Ti-6Al-2Sn-4Zr-6Mo

Titanium alloys are widely used in the aerospace and power generation industries due to their high specific strength and corrosion resistance. Titanium alloys like the modern (α +β) titanium alloy Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) are difficult to machine due to the formation of long chips which hinders automated manufacturing. In the present study, lanthanum has been added to Ti-6246 alloy to improve its machinability, i.e., to reduce the chips’ length. As lanthanum and Tin form La5Sn3 intermetallic phase, the 2% of Tin had to be replaced by 3% of zirconium. The matrix of Ti-6Al-7Zr-6Mo with lanthanum contains pure metallic lanthanum precipitates which have a relatively low melting point compared to titanium. Besides the standard alloy Ti-6246 two modified alloys, namely, Ti-6Al-7Zr-6Mo-0.9La and Ti-6Al-7Zr-6Mo-0.5La were investigated. During machining of these new free-machining alloys, short and strongly segmented chips are observed enabling automation of machining operations. This can be explained by softening of lanthanum particles during segmented chip formation. The microstructure, phase composition, and deformability of the new free-machining alloys were analyzed after different thermomechanical treatments. In addition, the mechanical properties of the modified alloys are investigated which are similar compared to the standard alloy.

Effect of Microstructure on Cutting Force and Chip Formation during Machining of Ti-6Al-4V Alloy

Dry machining was conducted on Ti-6Al-4V alloy with three different types of microstructure: globular, bi-modal and fully lamellar microstructures. The effects of cutting speed on the cutting force and chip formation were investigated. The differences in cutting force and chip morphology are found only at cutting speed lower than 100m/min. The main cutting force and chip thickness when machining Ti-6Al-4V alloy with globular microstructure are lower than these when cutting Ti-6Al-4V alloy with bi-modal and fully lamellar microstructures at cutting speed lower than 100m/min. The tendency of segmented chip formation is the highest for cutting Ti-6Al-4V alloy with fully lamellar microstructure and the lowest for machining Ti-6Al-4V alloy with bi-modal microstructure at cutting speed lower than 100m/min because of their differences in increase of shear strength with strain rate.

Modelling of segmentation-driven vibration in machining

Excessive vibration, such as chatter, is a common problem in machining processes. Meanwhile, numerous hard, brittle metals have been shown to form segmented chips, also known as sawtooth chips, during machining. In the literature, a cyclic cutting force has been demonstrated where segmented chips are formed, with the force cycle corresponding to the formation of segments. Segmented chip formation has been shown to be linked to high vibration levels in turning and milling processes. Additionally, it has been proposed that the amplitude of chatter vibrations can be limited by interference between the tool flank and wavy workpiece surface, a phenomenon known as tool-flank process damping. In this contribution, a model is proposed to predict the amplitude of forced vibration arising due to the formation of segmented chips during turning. The amplitude of vibration was calculated as a function of cutting parameters. It was demonstrated that the model can be extended to account for the effect of tool-flank process damping. For validation, titanium Ti6Al4V alloy was turned using a flexible toolholder, with surface speed ranging from 10 to 160 m/min, feed rate from 0.1 to 0.7 mm/rev and width of cut from 0.35 to 4 mm. In the experimental validation, 25 of 68 test cuts exhibited high-amplitude vibration. In 16 of these cases, the main cause was concluded to be chip segmentation, which can be predicted by the model. The model is thus considered of practical value to machinists.

Investigation on Chip Formation during Machining Using Finite Element Modeling

Titanium alloys are desirable materials for aerospace industry because of their excellent combination of high specific strength, lightweight, fracture resistant characteristics, and general corrosion resistance. Therefore, the chip morphology is very important in the study of machinability of metals as well as the study of cutting tool wear. The chips are generally classified into four groups: continuous chips, chips with built-up-edges (BUE), discontinuous chips and serrated chips. . The chip morphology and segmentation play a predominant role in determining machinability and tool wear during the machining process. The mechanics of segmented chip formation during orthogonal cutting of titanium alloy Ti–6Al–4V are studied in detail with the aid of high-speed imaging of the chip formation zone. The finite element model of chip formation of Ti–6Al–4V is suggested as a discontinuous type chip at lower cutting speeds developing into a continuous, but segmented, chip at higher cutting speeds. The prediction by using finite-element modeling method and simulation process in machining while create chips formation can contribute in reducing the cost of manufacturing in terms of prolongs the cutting tool life and machining time saving.

Strain Field Measurement in Orthogonal Machining of a Titanium Alloy

Improving the cutting processes by optimizing operating parameters necessarily involves understanding the thermo-mechanical mechanisms generated during chip formation. For this, numerical simulations are used to obtain the strain, stress and thermal fields near the tool tip. Nowadays, the validation of numerical simulation models of cutting is based on macroscopic results such as chip geometry and cutting forces generated by the machining process. However, it is not appropriate to validate local fields by macroscopic results. So, it is important to validate numerical cutting simulations on the bases of measured local strain fields. This article aims to study the feasibility of strain field measurement in orthogonal machining of the titanium alloy Ti64. A high-speed camera was used to provide data for segmented chip formation analysis. A microscope was related to the camera to observe an area of about 0.7x0.7mm² around the tool tip. An optimum adjustment of camera settings, lighting, workpiece surface preparation and cutting conditions allowed to obtain an acceptable image quality for analyzing with Correli [1] software. At low cutting speed, Correli qualitatively identify the position of the primary shear band and its evolution over the time.

Finite Element Investigation of the Influence of Thermophysical Parameters on Segmented Chip Formation during High Speed Cutting

A 2D fully thermal mechanical coupled finite element model is applied to study the influence of material parameters on serrate chip formation during high speed cutting process. The serrated chip formation during high speed machining was predicted. Of interests are the effects of thermal conductivity, specific heat and density. Results showed significant influence of these thermophysical parameters on the serrated chip phenomena, especially in the case of the density. Increasing thermal conductivity specific heat and density lead to a decreasing degree of segmentation. The influence of the thermal conductivity on the cutting force and the specific heat on maximum temperatures in the shear band is also discussed.

A Finite Element Study of Chip Formation Process in Orthogonal Machining

This paper examines the plane strain 2D Finite Element (FE) modeling of segmented, as well as continuous chip formation while machining AISI 4340 with a negative rake carbide tool. The main objective is to simulate both the continuous and segmented chips from the same FE model based on FE code ABAQUS/Explicit. Both the adiabatic and coupled temperature displacement analysis has been performed to simulate the right kind of chip formation. It is observed that adiabatic hypothesis plays a critical role in the simulation of segmented chip formation based on adiabatic shearing. The numerical results dealing with distribution of stress, strain and temperature for segmented and continuous chip formations were compared and found to vary considerably from each other. The simulation results were also compared with other published results; thus validating the developed model.

Development of Advanced and Free-Machining Titanium Alloys by Micrometer-Size Particle Distribution

The chip formation process of four different titanium alloys has been studied in several cutting experiments. Alloys containing more than 50% of a-phase at room temperature and aged metastable b-alloys form segmented chips independent of the cutting conditions. Solution treated metastable b-alloys show a cutting parameter dependent change from continuous to segmented chip formation. Lanthanum has been added to all four alloys. The microstructure of these alloys consists of a titanium matrix and micrometer-size particles. The presence of grain boundary particles leads to enhanced grain stability at elevated temperatures. In addition, short chips are observed during metal cutting only in case pure metallic rare-earth metal particles are present.

Evidence of thermoplastic instability about segmented chip formation process for Ti–6Al–4V alloy based on the finite-element method

A ductile failure law and an energy-based failure criterion have been implemented in a 2D finite-element (FE) model to simulate the segmented chip formation process in titanium alloy (Ti–6Al–4V) machining. The variations of stress and strain are taken into account in defining the material failure criterion. The cutting forces and chip morphology calculated by FE model are compared with experimental results in good agreement, validating the FE model. Stresses, strains, cutting temperatures, and stiffness degradation along adiabatic shear bands (ASBs) are analysed during the segment formation process to investigate the segment formation mechanism. It is found that the variation trend of strains is the same as that of temperatures, in addition, the variation of strains and their changing-rate lag slightly behind those of temperatures. These observations provide a new evidence of thermoplastic instability along ASB and increase the understanding of segmented chip formation mechanism. Furthermore, simulation results show that ASB morphology and its forming mechanism are mainly caused by thermoplastic instability in primary deformation zone and friction characteristic in the second deformation zone.

FEM Prediction of Chip Morphology during the Machining of Particulates Reinforced Al Matrix Composites

Chip morphology and segmentation play a predominant role in determining the machinability and tool wear during the machining of SiC particulates reinforced Al matrix composites. In this paper, a 2D coupled thermo-mechanical finite element model was used for simulating the segmented chip formation at different cutting conditions. The generation of segmentation is achieved by element erase and the shear failure, as well as the continuous adaptive remeshing technical. The results show that the chip is often discontinuous at lower cutting speeds, and with the increasing of the cutting speed, the chip becomes serrated. Fundamental observations from the simulations are concluded and a guideline for further research is proposed.

Numerical Simulation of Cutting Force and Temperature Field in High Speed Machining of Titanium Alloys

Improvements in manufacturing technologies require better modeling and simulation of metal cutting processes. A fully thermal-mechanical coupled finite element analysis (FEA) was applied to model and simulate the high speed machining of TiAl6V4. The development of serrated chip formation during high speed machining was simulated. The effects of rake angle on chip morphology, cutting force and the evolution of the maximum temperature at the tool rake were analyzed with the finite element model. The simulation results show that the segmented chip formation results in cutting force fluctuation. Although the segmentation frequency of the chip increases with the increase of the rake angle, the degree of segmentation becomes weaker and the cutting force fluctuation amplitude decreases. The predicted temperature distribution during the cutting process is consistent with the experimental results given in a literature.