Heat Partition Ratio Research Articles

Heat partition in dry orthogonal cutting of unidirectional CFRP composite laminates

Carbon fiber reinforced polymer (CFRP) components can be generally prepared near-net-shape, however, they still need machining after manufacturing to meet the geometrical accuracy with excellent surface quality required for assembly. Due to the cutting temperature is prone to exceed the glass-transition temperature of the resin, the irreversible chemical and mechanical degradation are therefore difficult to avoid. It becomes a crucial challenge to eliminate the particular thermal effect on the composite machining process. In comparison with the temperature measurement, the analytical model not only can reveal the physical essence of thermal effect, but also can predict the temperature field distribution to provide the reasonable cutting parameters. In particular, a key parameter for calculating the cutting temperatures is the heat partition ratio. However, the research work on this issue was rarely found. In this paper, a fiber orientation-based analytical model was developed to predict the heat partition ratio based on the classical Hertz contact theory. The finite element model was also built with the validation of the experimental measurement from the thermal imaging tests. The results suggest the heat partition ratio is mainly determined by the cutting parameters. Moreover, the fiber orientations have a remarkable impact on this ratio. Due to the heat partition ratio is considerably larger in a CFRP workpiece than the cutting tool, more heat energy was transferred to the CFRP during machining. Therefore, a small depth of cut leads to a reduced tendency for thermal effect on the CFRP composites.

Two-dimensional finite element analysis investigation of the heat partition ratio of a friction brake

A two-dimensional coupled temperature–displacement finite element model is developed for a pad-disc brake system based on a restricted rotational pad boundary condition. The evolution of pressure, heat flux, and temperature along the contact interface during braking applications is analysed with the finite element model. Results indicate that different rotational pad boundary conditions significantly impact the interface pressure distribution, which in turn affects interface temperature and heat flux distributions, and suggest that a particular pad rotation condition is most appropriate for accurately modelling friction braking processes. The importance of the thermal contact conductance in the analysis of heat transfer in friction braking is established, and it is confirmed that the heat partition ratio is not uniformly distributed along the interface under normal and high interface thermal conductance conditions.

Numerical and Experimental Investigation of Thermal Damage in Drilling of CFRP Composites

Carbon fiber reinforced polymer (CFRP) composites are extensively used in aerospace applications due to their light weight and special strength. Drilling of holes is the most frequently used machining operation for CFRP composites. In the drilling process, heat conduction with the anisotropic thermal properties of CFRPs is a complex process that requires special considerations. In this study, a 3D finite element (FE) model is developed to predict the temperature fields in drilling of laminated composites, considering the unique features of CFRPs, i.e., the multi-ply structures and anisotropic thermal properties. The thermal energy is determined from the cutting forces and the cutting parameters. A novel methodology is proposed to determine the heat partition ratio between the CFRP and the drilling tool. It considers the tool speed and geometry, the material properties, as well as the tool coating. The predicted temperature and thermal damage are validated experimentally, which are in good agreement with the measurements.

Experimental and numerical analysis of thermal phenomena in the wear of single point diamond dressing tools

Grinding technologies represent a critical step in the production of high added-value and high precision parts for strategic industrial sectors such as aerospace, automotive, biomedical, and wind generation. Whilst a number of factors related to the grinding wheel are important for optimizing the grinding process, there is no doubt that the wheel surface topography is the most influential factor. Surface topography is induced not only by the nature of the wheel itself, but also, more importantly, by the dressing process. Dressing is periodically carried out in order to recover the abrasive capacity of the wheel once excessive wear of abrasive grits has occurred. The high temperatures and contact forces present in dressing lead to wear of the diamond dressing tool, which in turn damages the topography of the wheel surface. Although the scientific literature has paid attention to the phenomena involved in dressing tool wear, some issues are still in need of explanation. Thus, the aim of the present study was to address the unresolved issue concerning the relationship between dressing temperatures and dressing tool wear. Using a combined empirical and modeling approach, the work reported here shows that temperatures on the surface of the dressing tool can be reduced by as much as 35% when using high conductivity materials in the tool holder. In addition, a methodology has been devised in order to estimate accurate values of the heat partition ratio towards the diamond dressing tool. The results show that the heat partition depends primarily on the dressing mechanism involved. Its values range from 0.97 (when friction between the dressing tool and the grinding wheel prevails) to 0.54 when grain breakage and pull-out occur at higher dressing depths. It has been analyzed and measured the wear suffered by the diamond under interesting designed tests. It has been demonstrated that the effective reduction of temperatures during process led us to take a lower wear rate of the diamond.

Temperature in the railway disc brake at a repetitive short-term mode of braking

The finite element (FE) model to determine the transient temperature field in the ventilated disc brake of the traction diesel multiple unit (DMU) has been proposed. The advantage of the developed numerical model is the representation of mutual motion of the stationary pad and the rotating disc, by a heat source of arbitrary shape moving over the stationary disc. Computations were carried out for the pad and the disc separately introducing the heat partition ratio. Both the single and the multiple modes of braking were examined. The calculated distributions in contact temperature were compared with the corresponding results obtained from analytical solutions of the boundary-value thermal problem of friction, and with experimental data determined by the method of thermocouples. It was demonstrated that the calculated mean temperature on the friction surfaces of the brake components and the bulk temperature of the disc during multiple brake application agree well with the corresponding results, obtained by methods mentioned above.

Experimental Investigation of Heat Partition Ratio for the Cutting Tool at a Cutting Speed Ranging from 38 to 6500 m/min

This paper investigated the variation in a heat partition ratio of the cutting tool with the cutting speed ranging from 38 m/min to 6500 m/min. The orthogonal high-speed cutting experiment was performed utilizing an impact cutting tester developed. The cutting length in this study was 60 mm. The temperatures at the tool-chip interface were measured directly with three pairs of Cu/Ni micro thermocouples fabricated on the rake face. The temperature rises rapidly from the beginning of cutting, and then levels off when a cutting distance exceeds about 10 to 20 times the depth of cut. The distance depends on the cutting speed. Using the temperatures measured, a variation in the heat partition ratio with cutting time was estimated with the aid of a FEA. The heat partition ratio at the end of cutting estimated decreases approximately from 7 % to 1 % as the cutting speed increases from 38 m/min to 6500 m/min. The heat partition ratio estimated is quite higher than that calculated by employing an analysis assuming the steady state, particularly under the high speed cutting conditions.

From the microscopic interaction mechanism to the grinding temperature field: An integrated modelling on the grinding process

The microscopic interaction mechanism between grains and workpiece material in grinding contact zone is extremely complicated which will take many interrelated and coupled factors into consideration, such as grinding wheel topographies, grain distributions, physical and mechanical properties of material, the emergence of grinding forces and heat energies, the partitioning and transfer of grinding heat, etc. However, the current theories and models are unable to integrate all of the above factors into an organic-whole model. Former researchers usually focused on several of above aspects and made assumptions to simplify those theories. However, these assumptions will weaken the mathematical relationship between grinding conditions and ground surface qualities and will increase the difficulties of understanding on the nature of grinding process. The work of this paper is an attempt on this purpose. It is based on the author's previous work of a microscopic interaction mechanism model between grains and workpiece material in grinding contact zone which will describe the interaction situation of a grain with any size, protrusion height and location, then the distributions of each type of grains were obtained. Single plowing and cutting grain force models were developed based on R.L. Hecker's single grain force model and M.E. Merchant's metal cutting theory, then led into grinding force distribution. The heat partition ratio model of W.B. Rowe was applied on the discrete grinding contact zone, a new developed heat flux profile transferred into workpiece surface was obtained, which was usually assumed to be rectangular, triangular and parabolic in shape in former researches. In order to confirm the rationality of this new heat flux profile, a comparison on temperature fields and grinding forces has been made between results from FE-models and experiments, under both wet and dry grinding conditions. Comparison results showed that this new developed integrated grinding process model has more precise prediction ability on grinding forces and grinding temperatures.

Heat transfer at the grinding interface between glass plate and sintered diamond wheel

Heat transfer analysis is of great importance for temperature prediction during grinding. Indeed the grinding parameters have to be adjusted to accelerate the manufacturing process while minimizing thermal damage to the workpiece. The temperature survey is especially critical for the grinding of glass material because of its low thermal conductivity inducing high temperature rise. In our study, temperatures at different locations in the sintered diamond composites of the grinding wheel are measured using thermocouples and a radio transmission technique. The glass temperature is measured using thermocouple strips on both side of glass plate, the grinding wheel providing the electrical connection between them. Results during grinding with a 6500 rpm rotation velocity shows temperature lower than 80 °C inside the grinding wheel while temperature up to 900 °C is found on glass. An inverse approach is used to compute the wall heat flux and temperature at the wall of the grinding wheel using a 2D axisymmetric heat transfer model. A 1D non linear heat transfer model including conduction and radiation is used to obtain the wall heat flux of the glass material. Knowing temperatures and heat fluxes on both side of the interface, one deduces information on thermal contact resistance, generated heat flux and partition ratio. So, the heat generated by the grinding is estimated between 223 and 399 W depending on the grinding process conditions and is localized on the glass side of the interface. The thermal contact resistance at the glass/sintered diamond composites figures out to be very high with a value greater than 3.8 10−3 m2K W−1.

Cutting temperature analysis considering the improved Oxley’s predictive machining theory

This article deals with the identification of the temperature distributions in the chip, tool and workpiece based on orthogonal cutting data estimated analytically from the improved version of the Oxley’s machining theory, including the strain-hardening constant (n eq) and the Johnson–Cook (JC) flow stress equation. The improved Oxley’s machining theory and thermal model were separately considered to compute temperature distributions. The initial parameters (δ, C 0, ϕ) and temperature factors (η, ψ) of Oxley’s model were optimized to improve the computation efficiency and estimation accuracy. The thermal model considers the effects of the primary and secondary heat sources. The primary heat source was depicted as a uniformly acting oblique band. The secondary heat source was modeled by applying non-uniform distribution of the heat partition ratio. The estimated results were compared with the published results of an experimental investigation in machining of AISI 1045 steel. It was found that the results of the improved Oxley’s model were closer to the experimental values than the outcomes of its extended version. A detailed set of the temperature distributions was introduced and the estimated temperature values were in good agreement with the experimental results.

Experimental Investigation of Thermal Boundary Conditions During Metal Cutting

Thermal boundary conditions in metal cutting are of major significance for the credibility of thermal models. Relevant boundary conditions need to be defined at the characteristic regions of metal cutting: the shear zone, the contact zone of chip and tool, the clearance face and the work piece surface. In this contribution, the experimental investigation of the thermal boundary conditions at these characteristic regions is presented. The boundary conditions were investigated by detailed analysis of infrared thermal images. Different materials and cutting parameters were investigated. From the investigation heat source strengths and heat partition ratios were yielded.

Experimental and analytical combined thermal approach for local tribological understanding in metal cutting

Metal cutting is a highly complex thermo-mechanical process. The knowledge of temperature in the chip forming zone is essential to understand it. Conventional experimental methods such as thermocouples only provide global information which is incompatible with the high stress and temperature gradients met in the chip forming zone. Field measurements are essential to understand the localized thermo-mechanical problem. An experimental protocol has been developed using advanced infrared imaging in order to measure temperature distribution in both the tool and the chip during an orthogonal or oblique cutting operation. It also provides several information on the chip formation process such as some geometrical characteristics (tool-chip contact length, chip thickness, primary shear angle) and thermo-mechanical information (heat flux dissipated in deformation zone, local interface heat partition ratio). A study is carried out on the effects of cutting conditions i.e. cutting speed, feed and depth of cut on the temperature distribution along the contact zone for an elementary operation. An analytical thermal model has been developed to process experimental data and access more information i.e. local stress or heat flux distribution.

A modified model for estimating the contact length in surface grinding

The real contact length during the grinding process is considered as an important subject for researchers, mainly because it reflects the intensity of the responses such as grinding forces and temperature generation. In order to measure and assess the real contact length, many experimental techniques and prediction models are available in the literature. Among all these models, the model developed by Rowe and Qi is being used widely by researchers because of its ability to make close predictions with real values. Rowe and Qi coined the term called roughness factor in their model. This factor varies with grinding environments and wheel–work material combinations. To decide it for a new environment, one has to do the laborious experimental work. In this article, the roughness factor has been analysed from the grinding temperature and the heat partition ratio point of view and expressed so that without experimental work prediction of the roughness factor can be done. For this, a new factor called as the thermal factor has been proposed based on the roughness factor modifications. Its good correlation with dimensionless temperature and heat partition ratio under different grinding environments have been presented and discussed in the current communication. It seems that the thermal factor can be helped in an easy and accurate prediction of the contact length during grinding operations.

Friction heat conduction and entransy of friction lining

PurposeThis paper aims to analyze the friction heat conduction and entransy of two friction linings in the high‐speed slide accident of a mine friction hoist.Design/methodology/approachFirstly, the dynamic thermophysical properties were analyzed and their fitting equations were also obtained. Additionally, the dynamic heat partition ratio was obtained according to the dynamic thermophysical properties. Then, a simple method was developed to solve the temperature rise of friction lining. Finally, based on the theoretical model of temperature rise, the entransy of friction lining with respect to T and t were gained.FindingsThe error of temperature rise between simulation result and experiment result is less than 7 per cent, which proves that the theoretical model is correct. The entransy decreases with the temperature below 40°C and it increases after 40°C. The entransy of lining K is a little higher than that of lining G within 19 s, but the entransy of lining G is much higher than lining K after 19 s and the entransy difference gets great gradually. It is indicated that the lining K has good heat‐resistant property which is of great benefit to the tribological property of friction lining.Practical implicationsThe authors' study provides a fundamental basis for developing a new friction lining with good heat‐resistant property, and it also brings forward a new quantitative method to evaluate the heat‐transfer capability of friction materials.Originality/valueA simple method was introduced to calculate the temperature rise of friction lining with the consideration of dynamic thermophysical properties and dynamic heat partition ratio. And the entransy of friction lining was obtained to evaluate the heat‐transfer capability of friction linings quantitatively.

An Application for Analysis of Temperature during Cold Rolling

The problem of software creation for the analysis of transient temperature field in cold rolling of metals is under consideration. Firstly, the mathematical model of the process of heating the strip and rolls at cold rolling it is proposed. This model assumes that the generation of heat during the rolling takes place due to friction on the contact surface of the rolls and the strip as well as plastic deformation of the strip material. Next, some fragments of created application for the purpose of an overall numerical analysis of heat partition ratio between the rolls and a strip as well as the temperature in any point of these elements are presented.

Thermal simulation of a pin on a rotating cylinder jacket system

In this paper specimen level measurements and finite element simulations are introduced in order to study the thermal behaviour of a pin and wheel sliding contact configuration. The pin-like specimen is processed from cast iron and models the local contact of a railway brake block and wheel tire. The sliding contact is treated in the framework of a 3 dimensional problem in order to achieve reliable results. The paper also treats with the heat partition problem by distributed heat source and moving heat source models. The results are compared to measured datas and show that the classical heat partition approach is not valid for the friction pair examined i.e. the contact. However authors determine the exact heat partition ratio by an iterative approach and give explanations on the experienced temperature differences.

Finite Element Analysis of Heat Partition in a Pad/Disc Brake System

The heat partition ratio is an important input parameter in simulation carried out by the finite element method (FEM) of the transient temperature fields in such elements as brakes, a pad, and a disc. Therefore, the aim of this article is to study the influence of nine various (experimental and theoretical) formulas for heat partition ratio on temperature in a pad/disc tribosystem. The real dimensions, operating conditions, and thermophysical properties of materials of two different disc brake systems were adopted for the finite element analysis. The evolutions of the temperature on the contact surface of the pad, obtained for different heat partition ratios, are compared with corresponding experimental data. The results revealed a significant influence of heat partition ratio on the evolution of pad maximal temperature, whereas the disc contact temperature was reasonably stable and coincided with most cases under consideration.

Research on the Heat Partition Ratios in Grinding Area

Grinding temperature is the main factor to limit the improvement of grinding efficiency. The main reason of grinding temperature rise is amount of heat transfer into the workpiece in grinding process. How to determine the proportion ratio, which heat transfers into the workpiece, is the main research issue to the precise machining scholars. In this paper, the heat resistance model is used to analyze the proportional coefficient about how much heat transfer into the grinding wheel, and the factors which to influence this coefficient are discussed. The moving heat source method is used to calculate the temperature field caused by single grain heat source, and the heat integral method is used to calculate the heat contains by the grinding chip, and then the heat proportional coefficients transferring into the chip and workpiece are determined respectively.

Predictive Analytical and Thermal Modeling of Orthogonal Cutting Process—Part I: Predictions of Tool Forces, Stresses, and Temperature Distributions

In this paper, a predictive thermal and analytical modeling approach for orthogonal cutting process is introduced to conveniently calculate forces, stress, and temperature distributions. The modeling approach is based on the work material constitutive model, which depends on strain, strain rate, and temperature. In thermal modeling, oblique moving band heat source theory is utilized and analytically combined with modified Oxley’s parallel shear zone theory. Normal stress distribution on the tool rake face is modeled as nonuniform with a power-law relationship. Hence, nonuniform heat intensity at the tool-chip interface is obtained from the predicted stress distributions utilizing slip line field analysis of the modified secondary shear zone. Heat sources from shearing in the primary zone and friction at the tool-chip interface are combined, heat partition ratios are determined for temperature equilibrium to obtain temperature distributions depending on cutting conditions. Model validation is performed by comparing some experimental results with the predictions for machining of AISI 1045 steel, AL 6082-T6, and AL 6061-T6 aluminum. Close agreements with the experiments are observed. A set of detailed, analytically computed stress and temperature distributions is presented.

Predictive Analytical and Thermal Modeling of Orthogonal Cutting Process—Part II: Effect of Tool Flank Wear on Tool Forces, Stresses, and Temperature Distributions

In this paper, predictive modeling of cutting and ploughing forces, stress distributions on tool faces, and temperature distributions in the presence of tool flank wear are presented. The analytical and thermal modeling of orthogonal cutting that is introduced in Part I of the paper is extended for worn tool case in order to study the effect of flank wear on the predictions. Work material constitutive model based formulations of tool forces and stress distributions at tool rake and worn flank faces are utilized in calculating nonuniform heat intensities and heat partition ratios induced by shearing, tool-chip interface friction, and tool flank face-workpiece interface contacts. In order to model forces and stress distributions under the flank wear zone, a force model from Waldorf (1996) (“Shearing Ploughing, and Wear in Orthogonal Machining,” Ph.D. thesis, University of Illinois at Urbana-Champaign, IL) is adapted. Model is tested and validated for temperature and force predictions in machining of AISI 1045 steel and AL 6061-T6 aluminum.

CUTTING TEMPERATURE MODELING BASED ON NON-UNIFORM HEAT INTENSITY AND PARTITION RATIO

ABSTRACT The understanding of temperature distribution along the tool-chip interface is important for machining process planning and tool design. Among many temperature modeling studies, uniform heat partition ratio and/or uniform heat intensity along the interface are frequently assumed. This assumption is not true in actual machining and can lead to ill-estimated results at the presence of sticking and sliding. This paper presents a new analytical cutting temperature modeling approach that considers the combined effect of the primary and the secondary heat sources and solves the temperature rise along the tool-chip interface based on the non-uniform heat partition ratio and non-uniform heat intensity along the interface. For the chip side, the effect of the primary shear zone is modeled as a uniform moving oblique band heat source, while that of the secondary shear zone is modeled as a non-uniform moving band heat source within a semi-infinite medium. For the tool side, the effect of the secondary heat source is modeled as a non-uniform static rectangular heat source within a semi-infinite medium; and the primary heat source affects the temperature distribution on the tool side indirectly by affecting the heat partition ratio along the interface. Imaginary heat sources are considered as a result of the adiabatic boundary condition involved along the tool-chip interface and of the insulated boundary conditions along both the chip back side and the tool flank face. The temperature matching condition along the tool-chip interface leads to the solution of distributed heat partition ratio by solving a set of linear equations. The proposed model is verified based on the published experimental data of the conventional turning process and it shows both satisfactory accuracy and improved match.