Chip Contact Length Research Articles

Performance profiling of solid lubricant for eco-friendly sustainable manufacturing

Abstract The intense heat generation during machining is critical to the workpiece quality. Coolant and lubrication therefore play decisive roles in machining. The conventional cutting fluids employed in machining have certain limitations with regards to their use for ecological and economic reasons. However the need for sustainable manufacturing and better surface quality urged to explore the merits of the lubricants that are eco-friendly such as solid lubricants that are proved to be a feasible alternative to the conventional cutting fluids. Solid lubricants, if employed properly, could control the machining zone temperature effectively by intensive removal of heat from the machining zone. If friction at the tool and workpiece interaction can be minimized by providing the effective lubrication, the heat generated can be reduced to some extent. It will also help reduce wear, thus improving the tool life and the surface finish. These are also used to reduce the force and the energy consumption. So the performance of the solid lubricant needs to be evaluated from tribological point of view. For this, an open tribometer has been envisaged to get the friction coefficient between the coated carbide tool and the austenitic stainless steel AISI 304 workpiece at machining - type situations. Hence this study investigate the effects of the machining parameters and the different machining environments on the machinablity aspects namely surface roughness, tool wear, tool - chip contact length, net cutting specific energy, chip morphology and the chip thickness ratio while machining austenitic stainless steel AISI 304 by TiAlN coated tungsten carbide inserts of the different tool geometry. To show the effectiveness of the solid lubricant, a comparative performance analysis, under the different environments was conducted. Results indicate that there is considerable reduction in the average flank wear (35%–60%), net cutting specific energy (40%–49%); tool-chip contact length (40%–60 %), chip thickness ratio (32%–65%) and the surface roughness (10%–39%) with the solid lubricant assisted machining compared to that of wet and dry machining. This study established that the solid lubricant assisted machining is an eco-friendly sustainable manufacturing process for the industry.

Cutting performance investigation based on the variable friction model by considering sliding velocity and limiting stress

Fast and accurate cutting force prediction is still one of the most complex problems and challenges in the machining research community. In this study, a modified finite element model is presented to predict cutting force and cutting length in turning operations of AISI 1018. Unlike the existing research, in which the mean friction coefficient μ was taken, a variable friction coefficient μ involving the sliding velocity between chip and tool is presented in this article. The sticking–sliding friction model is adopted, and the maximum limiting stress in sticking region is calculated by considering the thermal softening and normal stress distribution. Experiments have been performed for machining AISI 1018 using tungsten carbide tool, and simulation results have been compared to experiments. The simulation results of the modified finite element model have shown better outputs in predicting cutting force, tangential force, and tool–chip contact length on the rake face. The results of this article not only are meaningful to optimize tool design and cutting parameters but also can provide a clear understanding of contact behavior between tool rake face and chip.

Investigation of machining characteristics of hard-to-machine Ti-6Al-4V-ELI alloy for biomedical applications

Dry machining of Ti-6Al-4V alloy was investigated using SNMA120408 grade inserts. The material studied is designed for orthopedic applications. The effects of main cutting speed (VC), at constant feed rate (F) and depth of cut (DC) on machining characteristics (Feed force (Ff), radial force (Rf), Tangential Force (Tf)) and surface integrity (i.e., tool-chip contact length, chip segmentation, surface roughness, and tool wear) were examined. Experimental data indicate the cutting speed as the major parameter with direct impact on the machining characteristics. Increasing of the cutting speed promotes higher tangential forces that allow a decrease of the chip contact length; a smaller contact length results in a lower surface roughness and flank wear rate, respectively. To gain further insight from the simulated turning process an advanced Finite Element (FE) model was developed. The numerical model was built on the DEFORM-3D commercial software by incorporating the experimental cutting parameters. The numerical simulations results agree very well with experimental outputs in terms of cutting forces (FCS), tool-chip (T-C) contact length. Therefore, it was possible to estimate with accuracy the effective stress (σE) and the cutting temperature (TC). Further, due to its high robustness, the numerical model developed can be implemented in solving the industrial challenge (i.e., biomedical field) for predicting formations of serrated chip segment, chip thickness, potential types of chips, types of fracture mechanism and tool wear mechanism/rate generated during machining process.

Experimental study on the chip morphology, tool–chip contact length, workpiece vibration, and surface roughness during high-speed face milling of A6061 aluminum alloy

In this study, experiments of high-speed face milling of A6061 aluminum alloy with a carbide insert milling cutter under dry cutting conditions were conducted. The contact length between tool and chip, the workpiece vibration amplitude, and the arithmetic average surface roughness were measured under varying cutting conditions (cutting speed, feed rate, and depth of cut). The characteristics of chip morphology were observed using scanning electron microscope. Experimental results showed that the increasing cutting speed reduced the tool–chip contact length, the workpiece vibration, and the surface roughness. The tool–chip contact length, the workpiece vibration, and the surface roughness were all increased with increasing cutting depth and feed rate. The results of chip morphology showed that the chips with serrated form were generated under high-speed cutting conditions. Moreover, scratch lines, plastic deformation cavities, and local molten chip material were observed on the slide chip surface.

Characterization and prediction of chip formation dynamics in machining austenitic stainless steel through supply of a high-pressure coolant

Use of a high-pressure coolant supply (HPC) can lead to a considerable improvement in machining performance and process stability during the cutting of difficult materials such as stainless steels. Due to the high pressure of the coolant jet, a hydraulic wedge was formed at the tool–chip interface and thus reduced tool–chip contact length and friction behavior. Moreover, the cutting stability can be enhanced as a result of efficient chip breakability. The goal of this work is to evaluate how chip morphology is influenced by three thin jets of pressurized coolant directed into the tool–chip interface during machining of AISI 304 austenitic stainless steel and compare the resulting performance of the tool with dry and conventional coolant conditions. Furthermore, this research evaluates the influence of tool wear on the chip forming mechanism during the turning process. An analysis of the chip generated under machining emphasizes the hypothesis that variations in the cutting tool wear directly affect the chip shape and type of chip segmentation. Finally, a theoretical model was developed to predict the chip upcurl radius under HPC machining. This model is based on shear plane and structural mechanical theories which evaluate plastic strain and the bending moments along the length of the curled chip. The chip upcurl radius values from the developed theoretical model were found to be in good agreement with those measured in the machining tests.

Characterisation of friction at the tool–chip interface for orthogonal cutting of Ti-6Al-4V alloy

ABSTRACTThe main objective of this work is to characterise the frictional phenomena at the tool–chip interface and evaluate the contact pressure in the secondary deformation zone of machining. Due to the tool–chip–workpiece trio contact complexity in machining, there is a lack of fundamental understanding related to tribological parameters. During cutting, the coefficient of friction (CoF) and contact pressure along the rake face depend upon stresses, interface temperature, the velocity of the chip and tool–chip contact length. Under critical conditions, stresses and temperature are very high at the cutting edge which results in tool wear and sometimes premature failure of the tool. Existing pin-on-disc technique fails to reproduce the extreme contact conditions observed on the rake face while cutting. Accurate predictive models, considering separate sticking and sliding zones for the secondary deformation zone are yet to be developed. A new tribometer was designed to correlate the coefficient of friction and pressure distribution with variable chip velocities. Based on this tribometer design, pin-on-workpiece experiments were performed on Ti-6Al-4V with tungsten carbide spherical pins. It was observed that sliding velocity is one of the most influential parameters affecting the coefficient of friction. However, the variation in pressure distribution along the rake face was observed to be very less.

A slip-line model for serrated chip formation in machining of stainless steel and validation

Machining of difficult-to-cut materials producing serrated chip formation has generated a significant interest among academic researchers and industry groups because of the need for understanding the fundamental mechanisms to model the process. Therefore, various analytical and numerical models have been developed in the recent past to investigate such machining operations. The slip-line theory is one of the established modeling methods, but slip-line modeling of serrated chip formation has not been investigated adequately. In this study, a new slip-line model for serrated chip formation in machining with rounded cutting edge tool is presented along with its associated hodograph. In addition, Oxley’s theory was integrated to the proposed slip-line model for stainless steel material, and the model was validated by experimental results. A good agreement between the experimental and analytically predicted results was obtained. The proposed slip-line model offers predictions of cutting and thrust forces, ploughing force, maximum and minimum chip thickness values, tool–chip contact length, chip up-curl radius, thickness of the primary shear zone, angular position of the stagnation point, shear strain, shear strain rate at the shear plane, and the prevalent flow stress.

3D finite element investigations on textured tools with different geometrical shapes for dry machining of titanium alloys

Effect of texture shapes and texture area density for machining applications is a potential topic of investigation. However, it is difficult to fabricate perfect dimensions by using available micromachining techniques. Finite element simulations can be an effective way to understand the effect of texture density, texture depth and different geometric shapes on machining performances. The present study deals with the 3D finite element investigations of different texture shapes to predict cutting forces during machining of titanium alloy under dry condition. Available Johnson–Cook material model parameters have been investigated to select suitable parameters for 3D finite element studies in titanium machining. Different geometrical shapes (circular, square, triangular and elliptical shape) with the constant area are modeled at the rake face of cutting tools to incorporate textures. The effects of texture shape are studied for variation in cutting forces with different texture area density and depth. The effect of texture shape is found to be less influential for dry cutting however area density is found to have the most dominant effect on cutting forces. Further, the linear regression model for tool–chip contact length has been developed for the textured and untextured tools under different machining parameters. The developed model has incorporated the chip serration effect (serration peak and valley heights) in the contact length model. The contact length model for the textured tool has been developed for the first time, and the contact length variation has been compared with the plain tools. The results reveal that textured tools have limited applicability for dry cutting of titanium alloys. Further, the associated mechanism of contact area reduction for textured tools has been found to be not applicable at increased feed and cutting speeds due to chip embedment into textured space.

Influence of oxygen on the tool wear in machining

High temperatures generated in machining are known to facilitate oxidation wear. A controlled atmosphere chamber was developed to investigate the effects of oxygen on tool wear and high speed machining tests were conducted on air and in argon. Cemented carbide, cermet and cubic boron nitride tooling was used on alloyed steel, hardened tool steel and superalloy Alloy 718. Machining in argon resulted in higher flank wear, higher cutting forces, and larger tool–chip contact length on the rake face. However, in hard machining, argon atmosphere reduced rake cratering. Transmission electron microscopy of tools worn on air showed formation of nanocrystalline Al2O3 film on the rake when machining aluminium containing Alloy 718, while no oxide films was detectable in the other cases.

FE simulation of linear and elliptical ultrasonic vibrations in turning of Inconel 718

Utilization of ultrasonic vibrations in turning operation is an advanced method to improve processing of materials. The aim of the present study was to develop a finite element model in order to investigate the effect of ultrasonic vibrations on machinability factors in turning of Inconel 718. Conventional turning in addition to linear and elliptical ultrasonic-assisted turning were simulated and the effect of these processes on cutting forces, shear angle, chip thickness, sticky zone, and temperature distributed on tool rake face was analyzed. Besides, the experimental tests were conducted and the cutting forces have been measured to validate the simulation outputs. As a result, analysis of chip formation shows that the values higher than 45° for shear angle is achieved when elliptical vibration is added to the cutting process. Furthermore, increase of shear angle coupled with decrease of temperature on tool rake face causes the sticky zone in tool–chip contact length to be reduced compared to the conventional turning. Moreover, the influence of cutting speed on tool–chip engagement time in ultrasonic-assisted turning is simulated.

Evaluation of modified jatropha-based oil with hexagonal boron nitride particle as a biolubricant in orthogonal cutting process

Crude jatropha oil (CJO) has been acknowledged as an environmentally benign metalworking fluid (MWF) in the machining industry. However, one drawback found in CJO is that it has poor thermal-oxidative stability that leads to poor lubrication behavior. Henceforth, the objective of this study was to evaluate the machining performances of the newly developed modified jatropha oil (MJO) as a lubricant-based oil. The CJO was improvised through transesterification process at various molar ratios of jatropha methyl ester (JME) to trimethylolpropane (TMP) (MJO1, MJO3, and MJO5) and through the addition of various concentrations of hexagonal boron nitride (hBN) particles, ranging between 0.05 and 0.5 wt.%. The newly developed MJO were compared to CJO and synthetic ester (SE) by considering both viscous and tribological behaviors. In addition, the orthogonal cutting process was carried out on AISI 1045 through minimum quantity lubrication (MQL) methods to evaluate the machining performances (i.e., cutting force, cutting temperature, chip thickness, tool chip contact length, and specific energy). Interestingly, kinematic viscosity and viscosity index were improved with the increase in JME/TMP molar ratio and concentration of hBN particles. MJO5 added with 0.05 wt.% of hBN particles (MJO5a) exhibited the best tribological behavior correlated with excellent machining performances by reducing the cutting force, cutting temperature, chip thickness, tool chip contact length, and specific energy. MJO5a exemplified its potential on the lubricant market place with regard to the environmental concern and energy saving.

Interaction between the local tribological conditions at the tool–chip interface and the thermomechanical process in the primary shear zone when dry machining the aluminum alloy AA2024–T351

In this work, a predictive machining theory, based on a finite element model, were applied to dry orthogonal cutting of aluminum alloy AA2024–T351. In order to analyze the effects of chip formation process and local friction coefficient on the thermomechanical load along the tool rake face and the round cutting edge, an Arbitrary Lagrangian Eulerian (ALE) model was developed. To validate the present model, the FE results have been compared to the experimental data for a wide range of cutting speed. This shows a good agreement in both trends and values for cutting forces and tool–chip contact length. The ALE approach appears as an appropriate formulation to reproduce: (i) the tribological conditions corresponding to large values of friction coefficient such as in dry machining of aluminum alloys, and (ii) the material flow process around the round cutting edge. It was observed that a transition from a sliding contact to a sticking–sliding contact occurs when the local friction coefficient and the thermal softening are large enough. Predicted results show also that the decrease of the cutting forces as the cutting speed increases is mainly due to the variation of the tool–chip contact length in terms of cutting velocity. The effect of material flow around the round cutting edge on the distributions of frictional stress and pressure has also been analyzed.

Thermomechanical approach for the modeling of oblique machining with a single cutting edge

ABSTRACTThis article aims to predict performances of oblique machining with a single cutting edge. A thermomechanical approach for the modeling of oblique cutting with a single cutting edge is proposed. A good agreement was found between predicted and experimental data. New rules were established to determine experimentally the average friction coefficient and chip flow angle at the rake face. The computation algorithm permits to predict all thermomechanical parameters such as cutting forces, cutting temperatures, and chip geometry. Besides, all predicted oblique machining parameters are mainly controlled by the Po-criterion, which is defined as the ratio of tool–chip contact length to uncut chip thickness.

Environment Friendly Machining of Ni–Cr–Co Based Super Alloy using Different Sustainable Techniques

In order to eradicate the use of mineral based cutting fluid, the machining of Ni–Cr–Co based Nimonic 90 alloy was conducted using environment friendly sustainable techniques. In this work, uncoated tungsten carbide inserts were employed for the machining under dry (untreated and cryogenically treated), MQL, and cryogenic cutting modes. The influence of all these techniques was examined by considering tool wear, surface finish, chip contact length, chip thickness, and chip morphology. It was found that the cryogenically treated tools outperformed the untreated tools at 40 m/min. At cutting speed of 80 m/min, MQL and direct cooling with liquid nitrogen brought down the flank wear by 50% in comparison to dry machining. Similarly at higher cutting speed, MQL and cryogenic cooling techniques provided the significant improvement in terms of nose wear, crater wear area, and chip thickness value. However, both dry and MQL modes outperformed the cryogenic cooling machining in terms of surface roughness value at all the cutting speeds. Overall cryotreated tools was able to provide satisfactory results at lower speed (40 m/min). Whereas both MQL and cryogenic cooling methods provided the significantly improved results at higher cutting speeds (60 and 80 m/min) over dry machining.

Performance of flank face structured cutting tools in machining of AISI/SAE 4140 over a range of cutting speeds

It is well documented that surface structuring can improve the tribological performance of mechanical parts. For tooling, recent studies have focussed on structures applied to the rake face, the face in contact with the chip. This study investigates the impact of structures created on the flank face of the tool, which has not been widely explored. The flank face is an important area of focus because flank wear is a common end-of-life criterion for cutting tools. This article reports on the application of femto-second lasers to generate surface structures on the clearance face of the tool and their effect on tool–chip contact phenomenon and tool wear. A comparative study was conducted between machining with unstructured and structured cutting tools. Orthogonal cutting tests were performed over a range of cutting velocities, and flank wear, cutting power, compression ratio and tool–chip contact length were measured. The impact of a sticking and sliding contact was evaluated. Results showed a significant decrease in feed and cutting forces for a tool with flank-faced structures. The approach was a promising surface engineering innovation to improve the performance of cutting tools.

Investigation on the effect of an auxiliary pulsing jet of water at the top side of chip during hard turning of AISI 4340 steel with minimal fluid application

Machining with minimal fluid application is a new technique for reducing the usage of cutting fluid that ensures green manufacturing on shop floor. During minimal fluid application, a high velocity minimal pulsing jet of proprietary cutting fluid was applied at the tool work interface. In the present work an auxiliary high velocity minimal pulsing jet of water was applied at the top side of the chip in addition to the pulsing jet of cutting fluid at the tool work interface during turning of hardened AISI 4340 steel. The effect of auxiliary pulsing jet of water on the top side on cutting performance is investigated in comparison with conventional turning with minimal fluid application. From the experimental results, it was observed that the presence of an auxiliary jet of water on the top side of the chip promoted chip curl by Rebinder effect. Increase in chip curl resulted in less tool chip contact length thereby reduces the friction, cutting force and cutting temperature.

Effects of cutting parameters on chip morphology and tool wear in high-speed face milling of hardened steel

High-speed face milling of hardened steel was conducted to investigate the effects of cutting parameters on chip morphology and tool wear. It was found that the tool–chip contact length decreased substantially as the cutting speed increased over 2000 m/min. The adiabatic shear theory is more suitable for describing the formation of individual saw-tooth obtained in the present study. When the cutting speed was relatively low, relatively long tool life can be obtained at large radial depth of cut. On the contrary, when the cutting speed was relatively high, smaller radial depth of cut was beneficial for the acquisition of longer tool life. When the cutting speed was relatively low, due to relatively high mechanical load at relatively small radial depth of cut, large flaked region arose on the tool rake face and the main wear mechanisms of the tool flank face was fracture. However, when the radial depth of cut was relatively large, because of the relatively low mechanical load, there was no flaking on the tool rake face. There existed thermal crack perpendicular to the cutting edge due to the relatively high cutting temperature. When the cutting speed was relatively high, due to the drastically reduced tool–chip contact length, there was very small area of coating delamination near the cutting edge (at relatively small radial depth of cut) or no wear near the cutting edge (at relatively large radial depth of cut).

Continuous and ultra-fine grained chip production with large strain machining

In this study, orthogonal cutting technique as a severe plastic deformation (SPD) method for producing chips with an ultra-fine grained microstructure and fair mechanical properties is investigated; further, it has been suggested that by controlling the cutting velocity and contact length between tool and material, it is possible to produce a severely deformed and continuous chip with unrestored microstructure even at high cutting velocities. Solution treated Al-6061 samples in plane strain condition were severely deformed through applying various cutting velocities (from 50 to 2230mm/s) for three different rake angles (−5°, −10° and −20°) in fixed cutting parameters. Chip thickness, contact length, shear strain, and Vickers microhardness variations were examined for different samples and chip formation mechanism was discussed for different processing conditions. In addition, the microstructure of especial produced chips was studied using transmission electron microscopy (TEM). The results showed that during the dominance of seizure mechanism at the contact surface, microhardness and shear strain (as well as contact length) have inverse dependency upon the variation of the cutting velocity. The results are discussed by considering the heat-time effect contribution in the final microstructure and mechanical properties.

Extended infrared thermography applied to orthogonal cutting: Mechanical and thermal aspects

The temperature knowledge is essential to understand and model the phenomena involved in metal cutting. A global measured value can only provide a clue of the heat generation during the process; however the deep understanding of the thermal aspects of cutting requires temperature field measurement. This paper focuses on infrared thermography applied to orthogonal cutting and enlightens an original experimental setup. A lot of information were directly measured or post-processed. These were mainly focused on the geometrical or thermo mechanical aspects of chip formation, i.e. tool–chip contact length, chip thickness, primary shear angle, heat flux generated in the shear or friction zones, and tool–chip interface temperature distribution. This paper proposes an experimental setup and post-processing techniques enabling to provide numerous, fundamental and original information about the metal cutting process. Some comparisons between collected data and previous experimental or theoretical results were made.

An enhanced constitutive material model for machining of Ti–6Al–4V alloy

Material failure due to adiabatic shear banding is a characteristic feature of chip formation in machining of Ti–6Al–4V material. In this paper, an enhanced Zerilli–Armstrong (Z-A) based material flow stress model is developed by accounting for the effects of material failure mechanisms such as voids and micro-cracks on the material flow strength during shear band formation. These effects are captured via a multiplicative failure function in the constitutive material flow stress model. The strain and strain rate dependence of the material failure mechanism are explicitly modeled via the failure function. The five unknown constants of the failure function are calibrated using cutting force data and the entire model is verified using separate force, chip segmentation frequency and tool–chip contact length data from orthogonal cutting experiments reported by Cotterell and Byrne (2008a,b). Model predictions of these quantities based on the enhanced material model are shown to be in good agreement with experiments over a wide range of cutting conditions.