Heat Partition Coefficient Research Articles

Friction and heat partition coefficients in incremental sheet forming process

To understand the thermo-mechanical behaviour in incremental sheet forming (ISF), it is important to precisely determine the interfacial and thermal-relevant parameters including coefficient of friction (COF) and heat partition coefficient (HPC), and to characterise the effect of thermo-mechanically induced heat generation under ISF processing conditions. In the present study, a new tool path-defined straight groove test combined with mechanical and thermal detection is proposed to determine the COF and HPC of Aluminium alloy (AA1050) and commercially pure titanium Grade 1 (CP Ti Grade 1) sheets. The experimental and numerical results show that the determined COF and HPC values are sufficiently accurate. The interaction between friction force and thermal response is observed by this testing method. A novel theoretical thermal model is developed to correlate the relationship between friction-induced heat generation and the thermal effect. The results indicate that the new theoretical model can capture the temperature distribution and variation under different processing conditions, and the results show a good agreement with the finite element (FE) simulation. The presented testing method and theoretical model provide an insight into the determination of the thermal-relevant parameters (COF and HPC), and the quantification of the effect of friction-induced heat generation on the thermal response of the materials.

A quantitative method of calculating transient nonlinear heat partition coefficient between clutch friction discs with deep learning

In the current clutch temperature field study, the generally used constant heat partition coefficient tends to overestimate the separator disc temperature and underestimate the friction disc temperature. Although some researchers have found the characteristics of the time-varying heat partition coefficient, a suitable method is still needed to apply it to temperature calculations. This study provides a quantitative method for the application of the transient nonlinear heat partition coefficient to temperature calculations. The finite difference method is adopted to figure out the time-varying curve of the heat partition coefficient by coupling the contact temperature of the friction components. The numerical results show that the heat partition coefficient is independent of rotation speed with three stages: initial value, rapid time-varying, and steady-state. Different from the analytical method, we apply a deep learning method to train the quantisation function to characterise these three stages, avoiding complex formula derivation. As a result, the quantitative function can characterise the time-varying heat partition coefficient accurately, with an average error of 0.19%, 3.05% and 0.62% for the inert, time-varying, and steady-state stages, respectively. In addition, the accuracy of applying the quantisation function in temperature simulation is verified by friction experiments, and the error is less than 8%. This is superior to the results of solving the temperature field by a constant heat partition coefficient.

Adaptation of rectangular and trapezoidal time functions to simulate the rotational motion of the brake disc

Numerical modeling of the rotational motion of the brake disc during frictional heating requires the use of specialized software. In this paper, an alternative approach was proposed consisting in the simulation of the displacement of the heating region contained within the boundaries of the friction surface of the brake pad relative to the stationary disc. The moving heat source effect was obtained using rectangular time functions generated based on the operating parameters and dimensions of the brake components. The first part of the article discusses the mathematical basis for the construction of time curves in relation to the solid brake disc combined with a pad in the shape of the angular section of a ring. Braking simulations were carried out using the finite element method (FEM) based software for 3D, 2D axisymmetric and 1D models of the disc. The calculated temperature filed changes were confronted with the results obtained using the 3D model developed based on standard methods. The temperature on the contact surface of the disc in the position of the mean radius at the end of braking, determined using the 2D axisymmetric and the 3D model with adaptation of rectangular time functions as well as the 3D reference model agreed well and were equal to 157.83 °C, 157.87 °C, and 157.90 °C, respectively. In the second part of the study, the 3D model of periodic heating was extended to the disc brake of a railway vehicle. The results of the calculations for the ventilated disc and segmented brake pad were compared with the experimental data obtained during testing on a full-scale dynamometer test stand. The maximum temperature values obtained on the basis of the 3D-pulse, 3D numerical models and measured on the test stand were equal to 73.3 °C, 74.4 °C and 75.6 °C, respectively. The insignificant temperature difference, i.e. below 3 %, obtained using the 3D-pulse heating model and measured using a thermocouple, confirms the correctness of the developed algorithm for simulating the rotational motion of the disc as well as the calculation methodology incorporating the heat partition coefficient (HPC).

An improved thermal model for the orthogonal cutting considering non-uniform heat partition of shear heat source

Temperature distribution and heat partition have a significant impact on tool life and machined surface integrity in metal cutting process. In this work, the concept of non-uniform heat partition of the shear heat source on the shear plane was proposed, and an improved cutting thermal model was proposed based on this concept. The improved thermal model had a continuous temperature field at the shear plane compared with the previous thermal model. Comparing the thermal model before and after improvement with the finite element model (FEM), it was found that the temperature distribution of the improved thermal model was closer to the FEM. In addition, a calculation method for the heat partition coefficient of the shear heat source considering mass transfer and the ratio of the heat flow entering workpiece, chip and tool to the total heat generated during the cutting process were proposed based on the improved thermal model. The results were compared with the regression models proposed before, and showed that the shear angle is an indispensable factor for analyzing the heat flow in the cutting process when the thermophysical properties of workpiece remain unchanged.

Finite element investigation of cutting performance of Cr/W-DLC/DLC composite coated cutting tool

DLC has been applied as coating material in the machining of difficult-to-cut materials, and shows a good cutting performance. In this study, Cr/W-DLC/DLC-coated tools were compared with other three kinds of coated tools (TiC-, TiAlN-, Al2O3-) to investigate the cutting performance in the machining of Al–Si alloy. The influence of Cr/W-DLC/DLC-coated tools on the cutting performance under different cutting speeds was studied. Cutting force, cutting temperature, heat partition coefficient, cutting deformation rate, plastic deformation of machined surface, the interface temperature, and stress were investigated numerically with the aid of finite element method (FEM). Actual cutting experiments were carried out to verify the FEM models by means of the cutting force and cutting temperature measurement. The investigation results show that Cr/W-DLC/DLC-coated tool had the best cutting performance among these four kinds of coated tools. With the increasing of cutting speeds, cutting force and cutting temperature showed an increase trend, while the plastic deformation depth of machined surface and heat partition into cutting tool all showed a decrease trend during the machining with Cr/W-DLC/DLC-coated tool. This investigation can provide the theory basis or technical guidance for the cutting practice with Cr/W-DLC/DLC-coated tools.

Computational Method for Heat Partition at the Rail-Armature Interface Based on Least Squares Regression

The sliding electrical contact interface will generate a huge total heat source including Joule heat and frictional heat when an armature slides along a pair of rails driven by Lorentz forces. The total heat is partitioned at the contact interface flowing into armature and rail respectively. The heat partition at the rail-armature interface and the resulting temperature rise have important effects on the melt wear characteristics of the contact material. A computational method was proposed for determining heat partition at the rail-armature interface based on least squares regression. Temperatures equations of rail and armature were developed in terms of an unknown heat partition function. Solution equations of heat partition function were derived by matching the average temperature of rail and armature at the contact surfaces. The heat partition function was assumed to be a polynomial form and an estimate for the heat partition function was obtained by minimizing the error term in the least squares sense. Then, effects of polynomial order on the heat partition function are analyzed. Furthermore, the heat partition solution from the least squares regression and previous analytical method are compared. Variation characteristics of heat partition coefficient were also analyzed. In the end, the variation mechanism and influencing factors of heat partition coefficient were discussed.

МОДЕЛИРОВАНИЕ ТЕПЛОВОГО СОСТОЯНИЯ СОПРИКАСАЮЩИХСЯ ТВЕРДЫХ ТЕЛ С УЧЕТОМ ЭНЕРГОВЫДЕЛЕНИЯ В ЗОНЕ КОНТАКТА

The paper describes a numerical model simulating thermal conditions of contacting solids considering heat release in the contact region. The finite-volume model is implemented in the Logos Heat digital product within the Logos software package. Logos Heat serves for numerical simulations of heat transfer processes in solids and in air gaps without convective heat transfer. Its methods and algorithms enable thermal simulations of three-dimensional and two-dimensional (including axisymmetric) structures under steady and unsteady conditions using nonconformal mesh models considering contact energy release. We selected and considered the most common ways to determine the heat partition coefficient for the energy released by two solids being at rest or in sliding contact. The methods and algorithms incorporated in the numerical scheme of the Logos Heat product to consider the contact energy release were assessed using a case with a known exact solution and numerical data reported in. The analysis of the calculated data shows that the maximum error does not exceed 0.1% for the resting model and 8% for the sliding-contact model, which indicates that the methods and algorithms are appropriate for such simulations. However, it should be noted that, within the Logos Heat numerical scheme, the solution calculated by Charron's formula introduces an error, which is one order higher than the error associated with the temperature conduction method, and creates a temperature discontinuity at the contact.

Temperature and Heat Partition Testing in the Cutting Zone for Turning AISI 321 Steel

This article shows selected results of experimental tests and the results of analytical and numerical modelling of the thermal characteristics of the cutting process. The tests were conducted for the case of the dry turning of austenitic steel AISI 321 with cutting tools with a flat rake face. The research aimed to determine the actual division of thermal fluxes in the zone of contact between the chip and the rake face. As a result of such work, a formula for a new heat partition coefficient and a formula for calculating the average contact temperature were developed. The results showed that the formulas developed can be a useful tool to estimate heat distribution in the cutting zone quickly.

PVD AlTiN coating effects on tool-chip heat partition coefficient and cutting temperature rise in orthogonal cutting Inconel 718

Significant cutting temperature rise is induced in dry machining Inconel 718 with high cutting speed due to its low thermal conductivity and high hot hardness. PVD AlTiN coating can avoid direct contact between tool substrate and moving chip, which will affect tool-chip interface heat partition and temperature rise. However, few studies were relevant with the effect of AlTiN coating on tool-chip interface heat partition and temperature rise in dry cutting Inconel 718. In this study, the tool-chip interface temperature rises due to heat generations in primary and secondary deformation zones (PDZ and SDZ) are predicted with various heat partition coefficients, respectively. The cutting temperatures measured by two-color thermometer are utilized to determine the heat partition coefficient, and to verify the proposed interface temperature predictive model for dry orthogonal cutting Inconel 718 at cutting speed 40, 80 and 120 m/min with uncoated and PVD AlTiN coated tools. It is found that AlTiN coating decreases crater wear, and tool-chip contact length compared with that using uncoated tool. AlTiN coating decreases the maximum tool-chip interface temperature 39.00 °C and 5.47% compared with that using uncoated tool at 120 m/min. Heat partition model RG-W and RR was suitable for temperature prediction with least summary relative errors in cutting Inconel 718 with uncoated and AlTiN coated tools. The results illustrate that the PVD AlTiN coated tool could be beneficial in high-speed dry cutting Inconel 718 due to its less tool-chip interface temperature rises and tool crater wear.

The heat partition into cutting tool at tool-chip contact interface during cutting process: a review

Thermal load on cutting tool has a noteworthy influence on tool wear, tool life and machined surface quality. The heat partition coefficient into cutting tool characterizes the proportion of cutting heat flowing into it. This article provides an overview of the determining methods and influencing factors on the heat partition. Analytical modelling and hybrid FEM-experimental method are principal methods for identifying heat partition. The analytical models include uniform distribution and non-uniform distribution heat partition models. By reviewing influencing factors on the heat partition, it is found that thermal conductivities of workpiece and cutting tool, cutting speed and machining processes have greater influence on the heat partition compared with other influencing factors. The current researches on the determination of heat partition into cutting tool regard the tool-chip contact interfaces as perfect contact but not reveal true nature of the contact interface. The true contact only at the asperities at the tool-chip interface is observed through microscopic inspection. Oxide layer is generated on TiAlN coated tool rake face. Therefore, further research for the heat partition should consider the thermal contact resistance due to the non-perfect contact at tool-chip interface and the oxide layer generated on tool rake face.

Numerical simulation of friction stir-assisted incremental forming with synchronous bonding of heterogeneous sheet metals

Friction stir-assisted incremental sheet forming with synchronous bonding is developed as a novel variant of incremental sheet forming, by which the two sheet metals form incrementally and get bonded simultaneously. Numerical simulation of this process is crucial in revealing the forming mechanism and optimizing the process compared with expensive physical tryouts. A coupled thermo-mechanical finite element model was established to take the contact and heat transformation in every interface into consideration, and VUINTER contact subroutine which can express the heat partition coefficient and coefficient of friction was complied, validated and revised by groove tests. The effectiveness of the numerical simulation was verified by experiments. Furthermore, a comparative study based on numerical simulation is conducted to analyze the effects of process variables including feed rate, spindle speed, wall angle and vertical step size on temperature, thickness, and central bulge.

Modelling for prediction of time-varying heat partition coefficient at coated tool-chip interface in continuous turning and interrupted milling

Knowing heat partition coefficient at tool-chip interface is important for accurate estimating the distribution of heat flux and temperature field in metal cutting process. The heat partition coefficient in steady metal cutting has been widely analyzed. However, the time-varying effect of heat partition coefficient is rarely investigated in metal cutting with coated tool. In this research, a novel model for prediction of the transient heat partition coefficient at coated tool-chip interface was proposed. The time-varying heat partition coefficient was quantitatively calculated. The new proposed model fully considered the coating thickness and material thermal properties compared with current models including Shaw's model, Kato-Fujii's model and Reznikov's model. The time-varying heat partition coefficients in continuous turning and interrupted milling process were comparatively analyzed. Results showed that the time needed for attaining quasi-steady-state of heat partition was about tens of milliseconds. The heat partition coefficient was mainly dependent on tool coating and workpiece thermal properties rather than tool substrate thermal properties. The heat partition coefficient was decreased with the increase of interrupted cutting speed. The new proposed model was verified accurate compared with former research and cutting experiment. The proposed methodology can guide for design and selection of coated tool in metal cutting production.

Analytical model and material equivalent methods for steady state heat partition coefficient between two contact discs in multi-disc clutch

The heat partition coefficient between two finite thickness contact discs during long-time sliding is studied with a coupled finite element method. Results show that the heat partition coefficient varies from its initial value to another steady state value rapidly instead of being a constant all the time. An analytical solution of the temperature field under invariant heat flux input is deduced, which tells that there exists a unique critical thickness ratio between the contact discs that keeps the heat partition coefficient a constant. An equivalent method for single-material contact bodies is proposed that is capable of calculating the steady state heat partition coefficient for any thickness ratio. It reveals that the steady state heat partition coefficient only has relationship with the mass density and the heat capacity of the materials and the thickness ratio. Based on this method, a two-step material equivalent method is further proposed for the contact discs that have friction linings on them. The solution shows that the steady state heat partition coefficient in this situation is also only determined by the material properties and the layer thicknesses. A test bench of multi-disc clutch is set up and a series of sliding experiments are conducted to validate the proposed equivalent methods and solutions of steady state heat partition coefficient. The measured experimental temperature variations show that the temperature level of the separator disc in the clutch is overestimated with the constant heat partition coefficient of semi-infinite model, while it is close to those calculated results with steady state heat partition coefficient. Therefore, the temperature fields of the contact discs during long-time sliding with constant speed can be figured out efficiently using the steady state heat partition coefficient with only small error, and these equivalent methods benefit the multi-disc clutch design and temperature estimation in practical applications.

Multiscale thermomechanical modeling of frictional contact problems considering wear – Application to a pin-on-disc system

This paper presents a multi-scale strategy for thermomechanical simulation of frictional systems, as brakes, taking into account the scale of the contact interface phenomena which is much lower than the macro scale of the system. At macro scale, a finite element model is considered to model the system components. At micro scale, the thermal and mechanical contact problems are solved considering surface roughness and wear. At this scale, semi analytic methods, accelerated with the Fast Fourier Transform, and optimization techniques are used. As regards wear, Archard's law is used with a wear rate coefficient depending on temperature. From these models, contact parameters such as stiffness and heat partition coefficient are integrated into the macroscale model, and this for each surface element. Moreover, the solving scheme is transient allowing to update the surface topography under thermomechanical and wear effects. As an example, this multi-scale strategy is used to study the thermomechanical behavior of a pin-on-disc system. Moreover, implications of the interface on friction induced vibrations are also investigated. With this model, the influence of the interface behavior and wear on the system response, are clearly shown. Conversely this strategy gives results locally, close to the physical mechanisms involved in the contact. A comparison is performed with a classical model considering a perfect flat contact.

Quasi-Static Thermal Modeling of Multiscale Sliding Contact for Unlubricated Brush Seal Materials

Prediction of contact temperature between two materials in high-speed rubbing contact is essential to model wear during unlubricated contact. Conventionally, assumptions of either a steady or an annular heat source are used for slow and high speed rotation, respectively. In this paper, a rotating heating source is solved using an in-house finite element method code. This captures the full geometry and rotating speed of the rubbing bodies. Transient heat transfer is modeled quasi-statically, eliminating the need for a transient 3D simulation. This model is shown to be suitable for contact temperature prediction over a wide range of rotating speeds, anisotropic thermal conductivity, and nonuniform thermal boundary conditions. The model calculates heat partition accurately for a thin rotating disk and short pin combination, which cannot be predicted using the existing analytical solutions. The method is validated against ansys mechanical and experimental infrared thermography. Results demonstrate that the annular source assumption significantly underpredicts contact temperature, especially at the rubbing interface. Explicit modeling of a thin disk results in higher heat partition coefficients compared with the commonplace semi-infinite length assumption on both static and rotating components. The thermal anisotropy of tuft-on-disk configurations is evaluated and compared to a uniform pin-on-disk configuration. Despite the effective thermal conductivity (ETC) in the bristle tuft being approximately 1 order of magnitude lower than along the bristle length (treating the bristle pack as a porous medium), its impact on heat partition and contact temperature is shown to be limited.

Analytical solution of thermal conduction in a two-layer cylinder modeling oscillator roller in an offset machine

The aim of this work is to propose a mathematical formula describing the temperature distribution in the inking unit of the offset printing machine caused by the phenomenon of friction between the cylinders that remain in contact, namely between pairs of inking rollers. Those rollers are made of different materials, one is made of steel and the other is covered with rubber. Moreover, beside the circular motion, the steel roller moves in a reciprocating way along the cylinder pivot. This paper describes a model of cooling of a thermostatted roller in the offset printing machine. The described analytical solution of thermal conduction for a two-layer cylinder has been achieved with the Laplace transform. Additionally, the paper contains an analysis of heat partition coefficient for the cylindrical layers.

Heat partition and rake face temperature in the machining of H13 steel with coated cutting tools

Lots of heat generated in the cutting deformation zone can cause the temperature rising of cutting tool and workpiece during the cutting process. Tool temperature is mainly depended on the heat energy entering into tool in the secondary deformation zone. Higher working temperature can weaken the cutting tool strength and then deteriorate the tool wear. Advanced coating layer deposited on the tool substrate can change the tool-chip friction and affect the heat partition in the tool-chip interface. In order to reveal the mechanism of heat conduction in the secondary deformation zone, the model of heat partition into cutting tool was built. With the aid of finite element method (FEM), the relative parameters which were necessary for the solving of heat partition model were quantified. Actual cutting experiments were carried out to the verification of the FEM models by means of the cutting force and temperature measurement. Influences of coatings (i.e., coating materials, coating thickness) and cutting speeds on the heat partition were analyzed. And then, rake face temperatures obtained at four kinds of coated tools were compared. The investigation results showed that TiC coating appears as the maximum value and Al2O3 coating appears as the minimum value of heat partition coefficient into cutting tool among these four kinds of coatings (i.e., TiC, TiN, TiAlN, Al2O3). With the increasing of coating thickness and cutting speeds, heat partition into cutting tool all showed a decrease trend. Al2O3-coated tool had the maximum rake face temperature among these four kinds of coated tools; however, the location of peak temperature on the rake face of Al2O3-coated tool was the shortest distance from the tool tip.

RETRACTED: Characterization of friction properties at the work material/cutting tool interface during the machining of randomly structured carbon fibers reinforced polymer with Poly Crystalline Diamond tool under dry conditions

Carbon fiber reinforced polymers (CFRP) are increasingly employed within the aerospace industry. Therefore, a lot of Finite Element models have been developed in order to understand their material removal mechanisms. Among the scientific issues faced by these works, the identification of friction coefficients remains a strategic field of research. This paper aims at characterizing the friction properties between composite and cutting tool materials. The specific tribological conditions during machining of such heterogeneous materials are discussed in the paper, especially the configuration of the tribosystem. This paper presents the development of an original tribometer designed to simulate conditions corresponding to machining of randomly structured CFRP materials. It provides quantitative values of friction coefficient and heat partition coefficient depending on sliding velocities.

Thermomechanical modelling of the tool–workmaterial interface in machining and its implementation using the ABAQUS VUINTER subroutine

In this paper the complex thermomechanical behaviour at the tool – workmaterial interface in machining has been analysed. The contact behaviour is formulated in the frame of a Lagrangian Finite Element approach. The thermomechanical laws governing the tool – workmaterial interface in machining have been implemented via the VUINTER subroutine of ABAQUS/Explicit FE code. Using this interface, velocity dependent heat partition coefficient of the frictional heat has been implemented. Numerical results (calculated heat flux transmitted into the tool and cutting force) have been compared to experimental ones for different cutting conditions, which are in good agreement. It is shown that different couples of the heat partition and heat transfer coefficients can give the same heat flux transmitted in the tool. In addition, with the new developed VUINTER subroutine, it is possible to implement any mathematical model governing the friction and heat exchange for simulations of complex contact behaviours. • Metal cutting has been modelled and analysed focussing on the heat exchange at the tool–workmaterial interface. • The contact problem has been formulated in the frame of the finite element method. • Thermomechanical laws governing the tool–workmaterial have been implemented in a finite element code. • Rate-depend heat partition coefficient law has been implemented through the Abaqus VUINTER subroutine. • Comparisons between experimental and numerical heat fluxes and cutting forces have been performed.

Identification of friction and heat partition model at the tool-chip-workpiece interfaces in dry cutting of an inconel 718 alloy with cbn and coated carbide tools

Abstract This paper aims at characterizing the frictional behaviour at the cutting tool-workmaterial interface during the dry machining of a Inconel 718 in its aged state with various coated carbide tools and c-BN tools. A specially designed open tribometer has been used to characterize friction coefficient, heat partition coefficient under extreme conditions corresponding to the ones occurring in cutting. The tribometer provides the evolution of the apparent friction coefficient and of the heat partition coefficient for a large range of sliding velocity and contact pressure. It has been shown that friction coefficient as well as heat partition coefficient decrease with sliding velocity or contact pressure. A threshold effect of the contact pressure has been highlighted. On the contrary, any sensitivity to coatings deposited on carbide has been observed, whereas c-BN leads to very low friction coefficients.