Tool-chip Interface Research Articles

An improved thermomechanical modeling for orthogonal cutting of AISI 1045 steel

In this paper, two Finite Elements (FE) models with different boundary conditions and mesh constraints were developed for orthogonal cutting of AISI 1045 steel by using an Arbitrary Lagrangian-Eulerian (ALE) approach, which allows the absence of the damage criterion and element distortion. We used a Johnson-Cook (J-C) rheological law for the behavior of the work material and a Coulomb's model for the friction at the tool-chip interface. The simulation results were confronted, on the one hand, with experimental data and, on the other hand, with those obtained by thermomechanical analytic modeling. For this last context, some corrections have been made to Oxley's theory by taking into account a non-uniform distribution of the stresses at the tool-chip interface. For this, the normal stress distribution is modeled with a power-law relationship, and tangential stress is weighted by a corrective coefficient. The models evaluation focused on the components of the machining force, the temperature at the tool-chip interface and chip thickness; close agreements with the experiments were observed.

Thermo-mechanical coupled flow behavior evolution of Zr-based bulk metallic glass

Machining is an essential process for manufacturing high-precision bulk metallic glass (BMG) components, but the flow behavior of thermodynamically metastable BMGs during machining with high temperature and high strain rate conditions is still unclear. In this study, the flow behavior of Zr-based BMG is investigated in an orthogonal cutting operation. The results show that the increase of the temperature at the initial stage of cutting enables the amorphous chips gradually change from a laminated structure to a viscous flow state, and attach to the cutting edge of the tool. The chip in the stable sticking area of the tool-chip interface is a composite material rich in various crystalline phases and quasi-crystals with obvious phase separation, while the chips far away from the interface still maintain the amorphous state with uniform composition. After the formation of stable adhesion, the cutting force and cutting temperature are relatively stable, and the viscous-fluid chips act as a protective layer for the tool, avoiding severe tool wear.

Determination of the Chip–Tool Contact Length in Orthogonal Cutting

Abstract This work presents an experimental–numerical approach aimed at determining the chip–tool contact length during orthogonal cutting of annealed AISI 4340 steel (223 HV) with TiN-coated tungsten carbide inserts. Initially, pin-on-disc tests were performed, followed by orthogonal cutting tests. The components of the cutting force were used to calculate the coefficient of friction in orthogonal cutting, and its value was compared with those obtained under sliding. Moreover, the cutting force components obtained experimentally were used to assess the reliability of the finite element model and estimate the temperature in the cutting zone. The contact length between chip and rake face was calculated based on the experimental feed force and shear strength of the work material and was compared with the results provided by an analytical model. The experimental–numerical approach can be considered more accurate due to the fact that it considers the effect of the tool–chip interface temperature on the shear strength of the work material. However, the analytical model is quite straightforward, since it only requires the values of chip thickness and undeformed chip thickness to estimate the tool–chip contact length.

Predictive model of chip segmentation in machining of high-strength metallic alloys

Chip segmentation is the dominant chip formation mechanism during the machining of high-strength metallic alloys which directly affects the machining productivity and the final product’s quality. This paper investigates the mechanism of shear band formation and its contact with the cutting tool for different titanium and nickel alloys. First, we reveal that the shear bands are in direct contact with the cutting tool due to rolling on its rake face, although the contact mechanism is different for titanium and nickel alloys. In addition, the effect of the stored energy at the tool-chip interface, which is believed to be the reason for chip segmentation in some studies, is investigated theoretically. We found that the stored energy at the tool-chip interface affects the strain rate temporarily and has minimal impact on the chip segmentation. Moreover, we provide a theoretical prediction of the workpiece material’s displacement, its distribution, and degree of segmentation for the first time without any post-mortem analysis of the produced shear bands. To this end, the rolling process must be taken into account for accurate prediction. We show that the segmented chip’s displacement can be accurately predicted without any fracture criterion since the shear band itself is a type of ductile material failure. It is shown that the shear bands can accommodate large strains (for example, around 45 when cutting Ti-6Al-4V at 60 m min−1 cutting speed) without fracture presumption.

Study on Chip Formation Mechanism of Single Crystal Copper Using Molecular Dynamics Simulations

Nano-cutting is an important development direction of the modern manufacturing technology. However, the research on the mechanism underlying nano-cutting lags far behind the practical application, which restricts the development of this advanced manufacturing technology. The chip formation process is the basic process of nano-cutting, and it is of key importance for the mechanism research of nano-cutting. In this paper, the nano-tensile behavior of single crystal copper was studied based on the molecular dynamics simulations. The toughness and brittleness characteristics of the copper at different temperatures were analyzed. Then, the molecular dynamics simulations of nano-cutting for single crystal copper with different toughness and brittleness were studied. The crystal structure, cutting force, stress–strain distribution and atomic motion characteristics were systematically investigated. The nano-chip formation mechanism of single crystal copper was revealed. The results show that the chip is formed through two ways, namely the shear and extrusion. The material near the free surface of the workpiece undergoes continuous shear slip and periodic long-distance slippage along the primary shear direction, forming the block chip in which the FCC and HCP structures are orderly distributed. The material near the tool-chip interface is extruded by the tool, block chip and stagnation zone to form the flowing chip with amorphous structure. As the temperature increases, the occurrence frequency of long-distance slippage in the block chip increases, while the slippage degree decreases. Besides, with the increase in temperature, the thickness of block chip formed by shear slip decreases, while the thickness of flowing chip formed by extrusion increases.

In-Process Cutting Temperature Monitoring Method Based on Impedance Model of Dielectric Coating Layer at Tool-Chip Interface

This paper introduces a novel approach to in-process monitoring of the cutting temperature at the tool-chip interface (TCI). Currently, there are no tools available in the commercial market for measuring and monitoring cutting processes at the TCI region. Therefore, most of the studies about evaluating cutting temperature rely on simulation results without knowing the true temperature at the actual TCI region. In addition, recent cutting temperature measurement techniques have measurement errors occurring resulting from difficulty in estimations at the TCI region. However, the proposed method enables the measuring of cutting temperature by directly probing the localized TCI using a cutting tool coated with dielectric material. The study was conducted by utilizing the impedance characteristics of the dielectric outer layer of the cutting tool. A chemical vapor deposition (CVD) diamond coated insert that is commercially available was considered for the study to avoid wear effect. Impedance response of the dielectric layer under varying temperature conditions is assessed by Nyquist diagram using an impedance analyzer. The result of the Nyquist diagram showed temperature-dependent impedance characteristics that showed good agreement with the results from the thermal experiment which was a comparison between impedance response and elevated temperature. The impedance at the TCI for monitoring cutting temperature is measured under a turning process on a lathe using a constant current source. The impedance responses showed a significant decrease in impedance under various machining conditions which indicates a rise in cutting temperature. Moreover, different machining conditions showed different temperature profiles. The impedance responses were further characterized for depth of contact, which found that a drop in impedance corresponded to an increase in depth of contact. Therefore, the study showed that in-process monitoring of the cutting temperature is possible using an impedance model of the dielectric coating layer at the local TCI. Furthermore, with its versatility, this method is expected to measure the vibration, chatters, cutting force, and so on, as the results showed that impedance is not only sensitive to temperature but also to contact area. The application and expectation of this study is to provide real-time machining data to help end users in manufacturing industry to improve product quality, productivity, and prolonged lifespan of cutting tools.

Effect of electroosmosis on lubricant penetration at the tool–chip interface

Conventional microcapillary lubrication theories explain lubricant penetration into capillaries at the tool–chip interface under the action of atmospheric pressure and capillary force without considering the electrokinetic effect caused by triboelectrification. In this study, the effect of electroosmosis on the penetration of water-based cutting fluid at the tool–chip interface of a turning process was investigated for the first time. An ionic adsorption model was proposed to adjust the zeta potential of different tool and workpiece materials in fluids, and a self-excited electric field at the tool–chip interface was obtained using an exoelectron emission test. The electroosmotic force related to the zeta potential and electric field intensity can regulate electrically driven fluid penetration. Cutting tests with a fixed self-excited electric field indicated that the cutting force obtained using a higher zeta potential fluid was lower than that obtained using deionized water and reversed zeta potential fluids (e.g. significant declines of 31.1 % and 44.3 % in AISI 304 turning). Moreover, scanning electron microscopy and energy dispersive X-ray spectroscopy analyses on the worn tool edges produced using the above fluids indicated a transfer from adhesive wear to micro breakage, which explains the positive correlation between penetration and zeta potential, owing to an elevated electroosmosis effect. The results presented in this paper are significant for understanding the influence of the electroosmosis effect on lubricant penetration to perfect the microcapillary lubrication theory and provide a reference for formulating metal working fluids.

Machinability analysis and multi-response optimization using NGSA-II algorithm for particle reinforced aluminum based metal matrix composites

In this study the effects of reinforcement particle size and cutting parameters on machining performance variables like cutting force, maximum tool-chip interface temperature and surface roughness of the machined surface have been investigated while machining Aluminum based metal matrix composites (MMCs). MMC bars with silicon carbide reinforcement having 10 % volume fraction and particle sizes of 5 μm, 10 μm and 15 μm are machined with polycrystalline diamond (PCD) inserts. Experiments are performed using central composite design (CCD) having four parameters with three levels. Response surfaces for each performance variables are generated using polynomial models. Single variable and interaction effects have been investigated using principal component analysis and 3D response charts. Multi-response optimization has been performed to minimize surface roughness and maximum tool-chip interface temperature using non-dominated sorting genetic algorithm II (NSGA-II). In addition, constraints have been applied to the optimization search to filter design points with high cutting forces and low material removal rate. Most of the optimal solutions are found to be with moderate cutting speeds, low feed rate and low depth of cuts.

Lubrication Mechanisms of a Nanocutting Fluid with Carbon Nanotubes and Sulfurized Isobutylene (CNTs@T321) Composites as Additives

Developing high-efficiency lubricant additives and high-performance green cutting fluids has universal significance for maximizing processing efficiency, lowering manufacturing cost, and more importantly reducing environmental concerns caused by the use of conventional mineral oil-based cutting fluids. In this study, a nanocomposite is synthesized by filling sulfurized isobutylene (T321) into acid-treated carbon nanotubes (CNTs) with a liquid-phase wet chemical method. The milling performance of a nanocutting fluid containing CNTs@T321 composites is assessed using a micro-lubrication technology in terms of cutting temperature, cutting force, tool wear, and surface roughness. The composite nanofluid performs better than an individual CNT nanofluid regarding milling performance, with 12%, 20%, and 15% reductions in the cutting force, machining temperature, and surface roughness, respectively. The addition of CNTs@T321 nanocomposites improves the thermal conductivity and wetting performance of the nanofluid, as well as produces a complex lubricating film by releasing T321 during machining. The synergistic effect improves the cutting state at the tool–chip interface, thereby resulting in improved machining performance.

Crater wear prediction in turning Ti6Al4V considering cutting temperature effect

Tool wear has great impacts on tool life and cutting parameter selection in the machining process. As ceramic inserts are widely employed in efficient machining, it is of great significance to predict accurately the wear of ceramic tools. Crater wear is one of the most significant tool wear modes when turning difficult-to-cut materials at high speeds. The purpose of this research is to demonstrate the forming and influence mechanisms of crater wear in Ti6Al4V turning with ceramic inserts while considering cutting temperature at the tool-chip interface. An effort is made to describe quantitatively the appearance of crater wear from the perspective of temperature distribution based on crater wear experiments under various cutting conditions. In order to obtain the cutting temperature distribution efficiently, an analytical temperature prediction model is used in this paper. Then, a prediction model for crater wear depth and width considering the influence of the maximum temperature is developed. The maximum crater wear depth and width models are validated by a series of cutting experiments, and the outcomes prove that the proposed models are practical. Additionally, the influence of various cutting parameters on crater wear is discussed. The cutting speed has the greatest impact on crater wear, followed by the feed rate. Furthermore, this research can be used to improve cutting parameters for controlling crater wear.

FEM and statistical-based assessment of AISI-4140 dry hard turning using micro-textured insert

AISI-4140 is a hardenable cold work tool steel widely used in metal cutting operations due to its superior strength and heat treatment capacity. During the dry hard turning of AISI-4140 steel, high cutting temperatures are generated in the tool-chip interface due to friction. Micro-textured tools are thought to improve cutting performances in dry hard turning. The motivation is that the more reducing the chip-tool interface area, the more decreasing the friction there. Therefore, the micro-textured tools can be helpful in all metal cutting applications. This study compared the effects of micro-grooved textures at different sections on either coated or uncoated inserts according to the cutting forces and interface temperatures using FEM and Grey Relation Analysis. Experimentally calibrated FEM simulations and a statistical approach have been built. Besides the general positive sense of the micro-textured tools' effects on machining performances, this study revealed a different unexpected nuance for dry hard turning of AISI-4140 with textured tools according to the design of simulations. Where textures grooved on rake face or flank face below nose radius textures, texture sections, or relationship with coatings was found to be independent for the dry hard turning of AISI-4140 in consideration of cutting temperature and resultant cutting force. It was found that the textured tools were not statistically significant contrary to expectation. The textured tools may not be the exact solution for all machining conditions.

Light emission of Zr-based bulk metallic glass during high-speed cutting: From generation mechanism to control strategies

Light emission is a unique machining feature during high-speed cutting of Zr-based bulk metallic glass (BMG), which significantly deteriorates the machining quality and efficiency. However, its generation mechanism is still unclear. In this study, the light emission of Zr-based BMG during high-speed cutting was quantified photometrically, and its correlation with cutting energy was investigated. The chemical composition change and the formation process of luminescent particles were analyzed. The generation mechanism of light emission was subsequently revealed. It was found that the light emission is due to the spontaneous ignition in air of Zr-based BMG particles with large specific surface area, produced by ductile tearing of the bottom of the chip. The friction energy of the tool-chip interface flowing into the chips is the dominant factor that triggers particle combustion. Therefore, from the perspective of controlling tool wear, machining strategies with controllable light emission were proposed. In order to suppress light emission, the primary method is to decrease the cutting speed and feed. The second is to improve the chip removal ability and the wear resistance of the tool. Cutting oil is only effective for suppressing light emission at low cutting speeds, while liquid nitrogen is not suitable for cutting Zr-based BMG due to increased tool wear. The findings of this work contribute to a deeper understanding of the generation mechanism of cutting features in glassy metals, and provide guidance for high-speed cutting process optimization of Zr-based BMG.

Studying the Effect of un Coated and Multilayer Coated Tools on Cutting Temperature in Turning Operation

The present work studies three variables (cutting velocity, feed rate, and cut depth) on hard turning cutting temperature of uncoated and multilayer-coated carbide (TiN, TiN/TiCN, TiN /Al2O3/ TiCN) inserts are used in AISI 1045 alloy steel. The tool's temperature was measured simultaneously, measuring the temperature of the tool-chip interface using infrared radiation (IR) pyrometer in this investigation. This study investigated the performance of four distinct coated and uncoated PVD and CVD tools during turning operations. Four cutting speeds (56, 88, 112, 141) m/min, four feed rates (0.065, 0.08, 0.16, 0.228) mm/rev., in the experiments, a constant cutting depth of (1) mm was used. The results also show that Coarse cutting tools have a lower tool temperature than uncoated ones. In comparison to uncoated and other coated tools, the three-layer (TiN/ Al2O3/ TiCN) coating is especially effective in a range of (32% to 39%) than uncoated inserts at various cutting velocity and constant feed rates, with varying feed rates and consistent cutting velocity and lower by approximately( 34% to 40%) than uncoated inserts.

Understandings the tribological mechanism of Inconel 718 alloy machined under different cooling/lubrication conditions

Machining of Ni-based superalloys is a challenging issue, and it may lead to tool deterioration, poor surface quality, and other structural defects. Therefore, the main theme of this study is to examine the effect of different sustainable cooling/lubrication conditions on the machining performance, surface integrity, and accompanying tribological aspects of Inconel 718 superalloy. In this context, the milling experiment variables were selected as two feed rates, two cutting speeds, and four cutting environments: dry, air, synthetic oil-based MQL, and LN2-assisted Cryo. Tool wear mechanisms, surface roughness/profile/topography, cutting performance (tool-chip interface temperature and energy consumption), chip shapes, microstructures, and micro-Vickers hardness of the machined surfaces were thoroughly analyzed to assess experimental observations. The Cryo medium reduces tool wear, surface roughness, cutting temperature, and cutting energy by 67 %, 61 %, 85 %, and 33 % in comparison with a dry environment, respectively. Abrasion, adhesion, and diffusion mechanisms were supposed to be the most dominant wear types following SEM observations. Besides, the Cryo environment concluded a reduction of grain size to ⁓ 4 µm in concomitant with an increase of micro-hardness ⁓ % 15. The whole observed outcomes agreed to a great extent with each other, asserting the effectiveness of the LN2 cooling protocol in improving machining characteristics of Inconel 718 superalloy.

Modeling for prediction of tool-chip interface temperature in internal cryogenic turning considering film boiling

The cutting temperature model is critical for studying surface quality and tool wear. Cutting temperature models have been widely studied. When liquid nitrogen is used as a cooling medium in machining, the liquid nitrogen will inevitably appear Leidenfrost effect and film boiling will occur. However, the effect of film boiling on the cutting temperature is rarely concerned in the former temperature model. In this research, a novel model for tool-chip interface temperature considering film boiling is proposed. The new proposed model fully considered the thickness of the gas layer caused by the Leidenfrost effect compared with current models including Kesriklioglu's model and Rozzi's model. Based on the model, the effects of different gas layer thickness on the gas layer temperature and the tool-chip interface temperature were analyzed. The results indicate that thickness of the gas layer has a significant effect on the heat transfer properties and the tool-chip interface temperature of liquid nitrogen during the cooling process. The effect of film boiling must be considered in the temperature modeling of liquid nitrogen cooling machining. The new proposed model was accurately validated with a maximum error of less than 20% compared to previous studies and cutting experiments. It is also demonstrated that the developed liquid nitrogen internal cooling turning tool can control the gas layer thickness to about 5μ. This study reveals the heat transfer mechanism of cryogenic cooling, which helps to improve the cooling efficiency and the reliability of cryogenic cooling processing in industrial applications.

Turning performance analysis and optimization of processing parameters using GRA-PSO approach in sustainable manufacturing

The main aim of this research work is to examine the impact of input process factors (cutting speed, feed rate, and depth of cut) on machining characteristics (arithmetic mean surface roughness, tool flank face wear and tool chip interface temperature) and further to optimize during turning of Incoloy alloy 800. The cutting tool used was PVD multilayer coated (TiAlN-TIN) carbide insert. The experiment was performed based on Taguchi L27 methodology with a focus on the sustainability of turning. Sustainable manufacturing is considered for accomplishing overall efficiency with regard to economic, environmental and social aspects. The ANOVA (Analysis of Variance) was employed to assess the contributions of input process variables on cutting variable outputs. Further, the main effect diagrams exemplified the influences of main parameters on response variables. ANOVA analysis results demonstrated that the feed rate was the most leading factor that affects average surface roughness. The relationship(s) among input process factors and the evaluated measured outputs are determined using a quadratic regression model. Taguchi grey relational analysis has been implemented to trial results so as to optimize responses. The results revealed that the grey relational grade is significantly improved (0.308) through the setting of optimal parametric combinations. This integrated Grey–Taguchi approach was established quite effectual for simultaneously optimization of multifaceted machining output responses of turning process. This study provides a novel strategy to develop the machining efficiency of Incoloy 800 steel toward the improvement of sustainable processes and provide suitable applications in aerospace industry.

A Methodology for Tribo-Mechanical Characterization of Metallic Alloys under Extreme Loading and Temperature Conditions Typical of Metal Cutting Processes

The present paper proposes a combined tribo-mechanical methodology for assessing friction under conditions representative of metal cutting, without resorting to machining process monitoring. The purpose is to withdraw the size effect’s contribution due to tool edge radius to the well-known overestimation of the friction coefficient. Comparative numerical analysis of several tribological tests led us to conclude that the ring compression test is one of the most suitable for reproducing the frictional conditions at the chip–tool interface. Two distinct metallic alloys were selected to demonstrate the application of the proposed methodology (UNS L51120 lead alloy and 18Ni300 maraging steel in conventional and additively manufactured conditions). The results help to better explain the influences of process parameters on the friction coefficient value under high temperature and high strain rate conditions. Results showed a typical increase in the coefficient of friction of up to 20% due to both temperature and strain rate parameters for 18Ni300. The results are of interest because they allow considering potential sources of error in the numerical simulation of metal cutting when the same friction coefficient value is considered for a wide range of cutting parameters.

A dynamic recrystallization based constitutive flow model for micro-machining of Ti-6Al-4V

The study proposes a coupled thermo-mechanical transient analysis to estimate the cutting performance during micro-machining of Titanium alloy. A constitutive flow model is used along with the effects of dynamic recrystallization which is how the strain-softening evolves at a high strain rate. The frictional stick-slip oscillations that arise from the process are introduced through a Fortran user-subroutine at the chip tool interface. Strain softening and dynamic recrystallization are observed, while the cutting strain exceeds the critical strain of 1.7, owing to strain localization. When the uncut chip thickness reduces from 3 μm to 1 μm which is lesser than the edge radius of the tool, the value of maximum residual stresses increases by a factor of 3.7 and a magnitude of chip reduction coefficient of 2.25 is observed due to a local negative rake angle. The level of residual stress, specific cutting energy and morphology of the chip are validated with literature. In addition, a user-defined material stiffening algorithm is proposed which revealed an increase of compressive residual stress at the surface by 20%.

Measurement and analysis of sustainable indicators in machining of Armox 500T armor steel

Armox 500T is a special type of armor steel possessing superior mechanical properties suitable for use in vehicles and buildings need for first priority protection. Since these products are large-scale, a welding groove needs to be created before joining which can be done by milling operations. This study aims to address this point by questioning the impact of clean environments, namely, dry, minimum quantity lubrication (MQL), and LN2-based cryogenic cooling on the machining performance measures during milling. The novelty of this paper is the investigation of the effects of different cutting environments on the milling performance of Armox 500T armor steel. The results from this study showed that cryogenic medium has an impressive impact on controlling the temperatures at tool-chip interface which directly reduces flank wear development. In addition, cryogenic and MQL-assisted machining is much better than dry environment in achieving improved surface properties, chip shape, and energy consumptions. Cryogenic cooling seems as the best option for hard milling pursued by MQL and dry environments, respectively, from the sustainability and machinability point of view.

Investigation of machinability of Ti–B-SiCp reinforced Cu hybrid composites in dry turning

MMCs (metal matrix composites) are widely used in many industrial applications thanks to their high specific strength. Nevertheless, this also poses a great challenge to their machinability due to rapid tool wear and poor surface finish caused by the added reinforcement particles. Improving the machinability of MMCs is of great importance as it will increase their performance and areas of applications. In this study, the machinability of Cu composites reinforced with Ti–B–SiC powder particles (0-2-4-6-8 wt.%) produced at different rates using powder metallurgy method was investigated. Cutting speed (Vc: 100–150 m/min) and feed rate (fn: 0.2–0.4 mm/rev) were used as cutting parameters. The effects of these parameters on surface roughness, flank wear, and cutting temperature were investigated. As a result of the turning experiments, it was observed that the surface roughness decreased with increasing reinforcement ratio, and thus the best surface roughness (Ra = 0.22 μm) was observed in the 8 wt.% reinforced sample. The cutting temperature and flank wear values increased as the reinforcement ratio increased. It was observed that cutting temperature at the chip–tool interface was the lowest (76 °C) in MMCs sample with 2 wt.% reinforcement. The lowest flank wear (0.93 mm) was also observed in the 2 wt.% reinforced sample. In addition, the chip morphologies of all samples produced at different ratios were investigated after the turning process.