Chip Interface Research Articles

Tool life and wear mechanism of coated and uncoated Al2O3/TiCN mixed ceramic tools in turning hardened alloy steel

The focus of this paper is the continuous turning of hardened AISI 52100 (∼63HRc) using coated and uncoated ceramic Al2O3–TiCN mixed inserts, which are cheaper than cubic boron nitride (CBN) or polycrystalline cubic boron nitride (PCBN). The machinability of hardened steel was evaluated by measurements of tool wear, tool life, and surface finish of the workpiece. Wear mechanisms and patterns of ceramic inserts in hard turning of hardened AISI 52100 are discussed. According to the results obtained, fracture and chipping type damages occur more frequently in uncoated tools, whereas crater wear is the more common type of damage in TiN coated tools. Most important result obtained from the study is that TiN coating and crater wear affect chip flow direction. In uncoated ceramic tool, the crater formation results in decrease of chip up-curl radius. Besides, uncoated cutting tool results in an increase in the temperature at the tool chip interface. This causes a thermal bi-metallic effect between the upper and lower sides of the chip that forces the chip to curl a smaller radius. Chips accumulate in front of the tool and stick to the workpiece depending on the length of the cutting time. This causes the surface quality to deteriorate. TiN coating not only ensures that the cutting tool is tougher, but also ensures that the surface quality is maintained during cutting processes.

Machinability of a near beta titanium alloy

In this paper, the machinability of a near beta Ti25Nb3Mo3Zr2Sn titanium alloy with different heat treatment histories has been investigated in terms of cutting force, chip temperature and chip formation. A solution treatment was performed followed by ageing at different temperatures for the near beta alloy. It has been shown that the same alloy behaves differently during machining at various cutting speeds after different heat treatments. The observations have been explained in terms of friction effects and the hardness of the materials. It has been concluded that the ductility of a workpiece plays a significant role in determining its machinability. High friction at the tool–chip interface in a ductile workpiece resulted in a higher degree of chip segmentation and a larger undeformed surface length in each chip.

Design of a Speech Decoding System Based on Cortex

In consideration of the importance of phonetic system, the oral broadcasting systems have appeared in more and more places such as subways, bus stations and supermarkets and so on. The aim of this paper is to introduce a high performance speech decoding system based on Cortex. On the basis of introduction to each part, the function of main chip has been described in detailed. The interface of main chips has been defined. The software structure is also discussed. The system adopting Cortex as microprocessor, 5605 as the MP3 decoder chip, can decode MP3 and WMA files stored in SD card. Equipped with a character LCD display module, the system performance has greatly improved by using Cortex processor.

Experimental investigations on cryogenic cooling by liquid nitrogen in the end milling of hardened steel

Milling of hardened steel generates excessive heat during the chip formation process, which increases the temperature of cutting tool and accelerates tool wear. Application of conventional cutting fluid in milling process may not effectively control the heat generation also it has inherent health and environmental problems. To minimize health hazard and environmental problems caused by using conventional cutting fluid, a cryogenic cooling set up is developed to cool tool–chip interface using liquid nitrogen (LN 2). This paper presents results on the effect of LN 2 as a coolant on machinability of hardened AISI H13 tool steel for varying cutting speed in the range of 75–125 m/min during end milling with PVD TiAlN coated carbide inserts at a constant feed rate. The results show that machining with LN 2 lowers cutting temperature, tool flank wear, surface roughness and cutting forces as compared with dry and wet machining. With LN 2 cooling, it has been found that the cutting temperature was reduced by 57–60% and 37–42%; the tool flank wear was reduced by 29–34% and 10–12%; the surface roughness was decreased by 33–40% and 25–29% compared to dry and wet machining. The cutting forces also decreased moderately compared to dry and wet machining. This can be attributed to the fact that LN 2 machining provides better cooling and lubrication through substantial reduction in the cutting zone temperature.

Analysis of a new Segmentation Intensity Ratio “SIR” to characterize the chip segmentation process in machining ductile metals

In machining, chip morphology has an important effect on several cutting parameters such as tool wear, chip flow, vibration, etc. This research work aims to analyse the chip segmentation phenomenon for ductile metals. The aeronautical aluminium alloy A2024–T351 has been selected for the study. Using Finite Element modelling, segmentation process has been analysed and quantified with a new physical parameter called “Segmentation Intensity Ratio”. The SIR parameter which leads to a better analysis of the chip morphology is defined as a ratio between the equivalent plastic strain inside and outside shear bands within the chip. Using this parameter the effect of cutting conditions and tool geometry on the chip segmentation can be clearly shown. Also the fluctuation of the contact length, the tool–chip interface temperature as well as the cutting force oscillations with respect to cutting speed are carefully discussed when segmentation occurs. A correlation between chip formation process and cutting force oscillation is established as well as a correlation between average cutting force reduction and segmentation intensity when cutting speed increases. Finally, a parametric analysis was conducted to highlight the effect of the friction on the chip segmentation intensity.

Optimization of Multipass Turning Parameters by Genetic Algorithm

Optimization of cutting parameters is one of the key obstacles for CAD/CAM integration. In this work optimum cutting parameters, the best sequence, number, and type of passes of turning operation are determined by Genetic Algorithm (GA). Proposed optimization strategy ensures that no constraint will be violated at the optimum condition and determines the optimum number and type of passes such as rough, finish and semi-finish passes to complete a multipass turning operation. Here objective function is the unit production cost and constraints are limits of cutting force, power, tool life, stability condition, tool chip interface temperature, surface finish, feed rate to depth of cut ratio and the available rotational speed of spindle of machine tool.

Enhancing material removal processes using modulation-assisted machining

The controlled application of low-frequency modulation to machining – Modulation Assisted Machining (MAM) – is shown to effect discrete chip formation and disrupt the severe contact condition at the tool–chip interface. This enables chips of different morphologies, including discrete-particle like chips, to be created, and prescription of the machined surface texture. A model for MAM is used to describe chip formation regimes and textures. Benefits include improved chip management; enhanced lubrication; reduction of tool wear; and enhanced material removal rates. Prototype implementation of MAM in processes such as drilling and turning is described in case studies.

Hybrid modelling of sliding–sticking zones at the tool–chip interface under dry machining and tool wear analysis

Tool wear in machining processes strongly depends on the tool–chip interface. The sliding–sticking zones at this interface depend on the evolution of the local conditions of stress, velocity and temperature. Several authors have shown that because of the complexity of the tool–chip contact, the tribological conditions are not fully understood and accurate predictive models have yet to be developed. To propose a realistic model of chip formation, a hybrid analytical–numerical approach is presented in this work for the orthogonal cutting process. This simplified approach can be very useful for analysing the interaction between the chip formation process and the tribological conditions at the tool–chip interface. An analytical model is used to analyse the thermomechanical material flow in the primary shear zone, the tool–chip contact length, the local friction coefficient and the sliding–sticking zones. In addition, the temperature distribution in the chip is studied by numerical means. The effects of cutting conditions and material behaviour are evaluated. In the case of machining of Ti6Al4V titanium alloy, a quantitative comparison between model and experimental results is also provided to analyse the wear process.

Chip formation in orthogonal cutting considering interface limiting shear stress and damage evolution based on fracture energy approach

Modeling of metal cutting has proved to be particularly complex, especially for tool–chip interface. The present work is mainly aimed to investigate the limiting shear stress at this interface in the case of Titanium alloy (Ti–6Al–4V) dry cutting based on a FE-model. It was first shown that the surface limiting shear stress is linked to the contact pressure and the coefficient of friction (CoF). A relationship between CoF and the limiting shear stress was given, and the effect of the temperature on the limiting shear stress was also considered. After that, an orthogonal cutting model was developed with an improved friction model through the user subroutine VFRIC in Abaqus/Explicit software. The numerical results obtained were compared with experimental data gathered from literature and a satisfied agreement was found. Finally, the effects of cutting speed, CoF and tool-rake angle on chip morphologies were analyzed.

Application of regression and artificial neural network analysis in modelling of tool–chip interface temperature in machining

In this paper, the regression analysis (RA) and artificial neural network (ANN) are presented for the prediction of tool–chip interface temperature depends on cutting parameters in machining. The RA and ANN model for prediction tool–chip interface temperature are developed and mathematical equations derived for tool–chip interface temperature prediction are obtained. The tool–chip interface temperature results obtained from mathematical equations with RA and ANN model and the experimental results available in the literature obtained by using AISI 1117 steel work piece with embedded K type thermocouple into the uncoated cutting tool ( Korkut, Boy, Karacan, & Şeker, 2007) are compared. The coefficient of determination ( R 2) both training and testing data for temperature prediction in the ANN model are determined as 0.999791289 and 0.997889303 whereas; R 2 for both training and testing data in the RA model are computed as 0.999063 and 0.999427, respectively. The correlation obtained by the training ANN model are better than the one obtained by training RA model. The training ANN model with the Levenberg–Marquardt (LM) algorithm provides more accurate prediction and is quite useful in the calculation of tool–chip interface temperature when compared with the trained RA method in machining. On the other hand, prediction values obtained the testing RA model is slightly better performance than the testing ANN model. The results show that the tool–chip interface temperature equation derived from RA and ANN model can be used for prediction.

Friction and wear behaviors of the carbide tools embedded with solid lubricants in sliding wear tests and in dry cutting processes

Abstract Micro-holes were made on the surface of WC/TiC/Co carbide, MoS2 solid lubricants were filled into these micro-holes. Reciprocating sliding tests and dry cutting tests were carried out with this carbide tools. Results showed that the friction coefficient of conventional carbide is much higher than that of the carbide embedded with solid lubricants in sliding tests. The cutting forces, temperature, and friction coefficient at the tool–chip interface of the tool embedded with solid lubricants were reduced compared with that of the conventional tool. Two mechanisms responsible were found, the first one is explained as the formation of self-lubricating film at the tool–chip interface, which was released from the micro-hole and smeared on the rake, and served as lubricating additive; the other one was explained by the reduced contact length at the tool–chip interface, which contributes to the decrease of direct contact area between the chip and rake face.

Chip morphology of normalized steel when machining in different atmospheres with ceramic composite tool

Dry cutting tests in air and nitrogen atmospheres with a ceramic cutting tool were carried out on normalized AISI 1045 steel. SEM and EDX techniques are employed to observe the chip morphology and tribological mechanisms are simultaneously discussed. The finite element model of chip formation was created to determine the effective stress and strain distributions in the chip and workpiece. Compared in nitrogen, the friction coefficient in air was reduced when the cutting speed is at 160 m/min and the feed rate is 0.1 mm/r. Experimental data and observation revealed the formation of a lubricating film at the tool–chip interface, which related to the difference chip morphology in air and nitrogen.

A new friction law for sticking and sliding contacts in machining

In this paper, a thermomechanical modelling of the material flow is developed, and the tool–chip contact length and the sliding–sticking zones are characterised analytically. Furthermore, the finite element method is used to solve the non-linear thermal problem in the chip. The effect of cutting conditions and material behaviour on the sliding–sticking zones and on the temperature distribution and local friction along the tool–chip interface is evaluated. It has been found that the sliding–sticking zones strongly control the local conditions of stress, velocity and temperature. A qualitative comparison between the proposed model and experimental results is provided.

A calibrated dual-wavelength infrared thermometry approach with non-greybody compensation for machining temperature measurements

We report the development of a new approach for determining temperatures using the dual-wavelength infrared thermometry technique, which does not presume greybody behaviour and compensates for the spectral dependence of emissivity. This approach is based on Planck's radiation equation and explicitly accounts for the wavelength-dependent response of the IR detector and the losses occurring due to each of the elements of the IR imaging system that affect the total radiant energy sensed in different spectral bands. A thorough calibration procedure is utilized to determine a compensation factor for the spectral dependence of emissivity, which is referred to as the non-greybody compensation factor (NGCF). Calibration and validation experiments are carried out on Aluminum 6061-T6 targets with two different surface roughnesses. Results show that this alloy does not exhibit greybody behaviour, even though the two spectral bands used were relatively close to each other, and that the spectral dependence of emissivity is influenced by the surface finish. It is found that non-greybody behaviour of low emissivity surfaces can lead to significant systematic error in dual-wavelength IR thermometry. The inclusion of the NGCF eliminates the systematic error caused by the invalidity of greybody assumption and thus improves the accuracy of the measurements. Non-greybody-compensated dual-wavelength thermography is used to measure the chip temperature along the tool–chip interface during orthogonal cutting of Al 6061-T6 and sample results at three different cutting speeds are presented.

Improvement of Anti-Adhesive Properties of Cutting Tool by Nano/Micro Textures and Its Mechanism

In cutting of aluminum alloys, one of the most serious problems is chip adhesion to cutting tool surface, leading to tool breakage. To solve this problem, we used a surface engineering approach, namely, a highly functionalization of tool surfaces by textures to determine the role of textured surfaces in: (i) retaining cutting fluid and (ii) reducing actual contact area between the tool and chips. In this study, a DLC-coated cutting tool with nano/micro-textured surface using femto-second laser technology was developed. A series of aluminum alloy face-milling experiments showed that the nano/micro-textured surface significantly improved anti-adhesiveness at the tool chip interface. Moreover, through wet and dry cutting experiments, the mechanism of the improvement of anti-adhesive properties was also discussed.

Documentation of tool wear progress in the machining of nodular ductile iron with silicon nitride-based ceramic tools

Nowadays, the HPM of cast irons is based on silicon nitride ceramic and CBN cutting tools. This paper characterizes and correlates several outputs of the cutting process of nodular cast iron using uncoated and Al 2O 3/TiN coated Si 3N 4 ceramic tools resulting from wear progress and destruction of tool faces. Investigations include tool wear curves, tribological behaviour of the tool–chip interface and tool wear mechanisms occurring on contact surfaces. The image-based characterization of worn surfaces employs such techniques as SEM, BSE and EDX analysis. The occurrence of various wear mechanisms, such as abrasive, adhesive and chemical wear was revealed.

Influence of a High-Pressure Lubricoolant Supply on Thermo-Mechanical Tool Load and Tool Wear Behaviour in the Turning of Aerospace Materials

In the field of machining difficult-to-cut materials like titanium or nickel-based alloys, the use of a high-pressure lubricoolant supply may result in a significant increase of productivity and process stability. Due to enhanced cooling and lubrication of the cutting zone and thus reduced thermal tool load, tool wear can be decreased which allows higher applicable cutting speeds. Furthermore, the process stability can be increased as a result of effective chip breaking and chip evacuation. The present paper investigates the effect of high-pressure lubricoolant jets, directed into the tool—chip interface, in a longitudinal turning process with cemented carbide tools. For this type of lubricoolant supply the reduction of the contact length between tool and chip is an important detail. In turning of Inconel 718 and Ti6Al4V, the cutting tool temperature, tool wear, and resulting chip forms as well as the ratio of cutting forces and tool—chip contact area were analysed as a function of the lubricoolant supply pressure and flowrate (up to 300 bar, 55 l/min). To study the effect of the high-pressure lubricoolant supply, reference tests were carried out using conventional flood cooling. The results suggest that the tool temperature can be decreased by almost 25 per cent by the use of a high-pressure lubricoolant supply for both machined workpiece materials. However, due to the different tool wear mechanisms of the presented materials and the change in the specific load on the cutting edge during machining, the resulting tool wear was influenced differently. In the best case, tool wear could be reduced in an order of magnitude of 50 per cent, while in other cases tool wear even increased significantly due to the use of a high-pressure lubricoolant supply.

Numerical and analytical modeling of orthogonal cutting: The link between local variables and global contact characteristics

The response of the tool–chip interface is characterized in the orthogonal cutting process by numerical and analytical means and compared to experimental results. We study the link between local parameters (chip temperature, sliding friction coefficient, tool geometry) and overall friction characteristics depicting the global response of the tool–chip interface. Sticking and sliding contact regimes are described. The overall friction characteristics of the tool are represented by two quantities: (i) the mean friction coefficient qualifies the global response of the tool rake face (tool edge excluded) and (ii) the apparent friction coefficient reflects the overall response of the entire tool face, the effect of the edge radius being included. When sticking contact is dominant the mean friction coefficient is shown to be essentially the ratio of the average shear flow stress along the sticking zone by the average normal stress along the contact zone. The dependence of overall friction characteristics is analyzed with respect to tool geometry and cutting conditions. The differences between mean friction and apparent friction are quantified. It is demonstrated that the evolutions of the apparent and of the mean friction coefficients are essentially controlled by thermal effects. Constitutive relationships are proposed which depict the overall friction characteristics as functions of the maximum chip temperature along the rake face. This approach offers a simple way for describing the effect of cutting conditions on the tool–chip interface response. Finally, the contact length and contact forces are analyzed. Throughout the paper, the consistency between numerical, analytical and experimental results is systematically checked.

Finite element modelling of the thermo-mechanical behavior of coatings under extreme contact loading in dry machining

During metal cutting processes, intensive friction and high temperature generated at the tool chip interface affect the cutting zone of the tool, by inducing damage and wear. To improve the cutting tool's life, thin hard coatings, synthesized by physical or chemical vapor deposition (PVD or CVD) techniques, are often used as protective layers. In this work, numerical/theoretical analysis of dry machining has been performed to study the impact of different coating layers on the machining process. Four cases are considered: an uncoated tool made of tungsten carbide (WC–Co) and coated tungsten carbides in three different configurations. The first one is made of one layer namely TiN, the second one (hypothetical carbide insert) is composed of two layers (Al2O3 and TiN), and the last one has three layers (TiCN, Al2O3 and TiN). The workpiece material is an AISI 316L stainless steel. All cutting conditions are fixed in order to highlight the effect of coatings independently from others influencing parameters. The analysis has shown the impact of the different configurations of coatings on the temperature level inside the tool and on its surface, on the pressure and also on the cutting and feed forces.

Finite Element Analysis of the Effects of Tool-Chip Friction on Cutting Temperature Field

The heat generation caused by tool-chip friction and chip deformation strongly influences the tool wear and tool life in metal cutting processes. The focus of this paper is on the effect of tool-chip on cutting temperature field. A series of ¬finite element simulations have been performed, in which a modifi¬ed Coulomb friction law is used to model the friction along tool–chip interface. A tool rake angle ranging from 10° to 45°, a inclination angle ranging from 0° to 20°, and a friction coefficient ranging from 0.1 to 0.6 have been considered in simulations. The results of these simulations show that the maximum cutting temperature increases with the increasing of tool-chip friction coefficient at different rake angle and inclination angle. The form of tool wear mainly appears as crater wear when the friction coefficient is less than 0.5, and the cutting edge tends to split when the friction coefficient is larger than 0.6.