Heat Partition Coefficient Research Articles

Physics based modelling of interface temperatures in machining with multilayer coated tools at moderate cutting speeds

A new thermal model is presented for turning with tools with multilayer coatings. In the previous paper [Int. J. Mach. Tools Manuf. 43 (2003) 1311] devoted to the thermal problems in dry turning of steels with tools treated with multilayer coatings with an intermediate Al2O3 layer new analytical models for estimating the heat partition to the chip and the average interface temperature were derived and the predictions were compared with experimental results. In this paper, a physics based modelling concept has been applied to both the individual layer and the composite layer approach to develop an estimate of the average and the maximum steady-state chip-tool interface temperatures in orthogonal turning. Different approaches for determining the heat partition coefficient for sliding bodies of defined thermal properties were tested. Experiments using the work and the tool as the thermocouple pair have verified that the proposed models accurately predict the temperatures for uncoated and coated tools for a range of cutting speeds. As a result a new computational algorithm, for predicting with reasonable accuracy the average and peak values of the temperatures at the chip-coating/substrate interface at cutting speeds up to 200 m/min, has been recommended.

SIMULTANEOUS ESTIMATION OF FRICTIONAL HEAT FLUX AND TWO THERMAL CONTACT PARAMETERS FOR SLIDING CONTACTS

In the dry friction between two solids in imperfect contact, the determination of temperature distribution within solids needs the knowledge of: (1) heat flux generated by friction, (2) thermal contact conductance, and (3) intrinsic heat partition coefficient. In this article, numerical study is conducted in order to estimate the values of these parameters from simulated temperatures. Numerical investigations and a sensitivity analysis are performed in order to show the feasibility and the needed conditions for an accurate estimation. In order to take into account the measurements noise, statistical investigations using a stochastic approach and Monte Carlo method are also performed.

A computational approach to evaluate temperature and heat partition in machining with multilayer coated tools

In this paper, analytical models for estimating the interface temperature and heat partition to the chip in continuous dry machining of steels with flat-faced tools treated with multilayer coatings are presented. The database for modeling includes changes in the thermal properties of both workpiece and substrate/coating materials and the Peclet and Fourier numbers occurring at actual interface temperatures. Process outputs involve the average tool–chip interface temperature, the tool–chip contact length, the friction energy and the heat balance between the moving chip and stationary tool. It was found that the heat partition coefficient varies significantly from 0.65 to 0.8 when using multilayer coated tools, and changes from 0.5 to 0.6 for uncoated carbide tools. This implies that the use of multilayer coated tools causes about 30% more heat generated due to friction to be transferred into the moving chip. In general, both power and linear models can be used to estimate the interface temperature.

Abstract

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.

Dyestuff diffusion from gas phase into HPET film

In order to obtain basic data for heat transfer printing processes, partition coefficients and concentration profiles of three dyes (1-aminoanthraquinone; 1,4-diaminoanthraquinone, 1,4,5,8-tetraaminoanthraquinone) in PET films were measured at different but constant temperatures (130–180°C) and at different but constant total pressures (5–35 mmHg). Considering the filter paper and the laminated PET film as substrates 1 and 2, respectively, of a composite system, the diffusion coefficients D 1 and D 2 of the dyes in substrate 1 (air gap = filter paper) and 2 (PET film), were evaluated from the measured concentration profiles by curve fitting applying an appropriate diffusion relationship for the corresponding system. The extracted diffusion coefficients D 1 were of the order of 0.1 to 10 cm 2/min whereas D 2 ranged from 10 −8 to 10 −7 cm 2/min. Compared with common diffusion coefficients of the corresponding dyes in air, the values of D 1 are extremely small. The measured partition coefficients ranged from 10 4 to 10 6. In addition, it was verified that D 1 and D 2 are independent of the total pressure.

Estimation of rake temperatures in free oblique cutting

A model for analysing temperatures in free oblique cutting with sharp cutting tools is developed by utilising a recent solution for temperature distributions on a rectangular heat source moving obliquely on a semi-infinite conducting medium. The source obliquities introduced at the shear and rake planes by the tool obliquity are identified and a procedure is developed to compute the temperature distributions and heat partition coefficients at the shear and rake planes. For mild steel cut by a H.S.S. tool, the mean tool-chip interface temperature estimated by the new model is in close agreement with that measured by the tool-work thermocouple method. It is noted that the introduction of tool obliquity results in temperature and heat partition coefficient distributions which are essentially similar to those obtained in orthogonal cutting. The mean tool-chip interface temperature is found to decrease with increasing tool obliquity.