Prediction of Cutting Temperature Distribution in Transient Heat Conduction of Monolayer Coated Tools Based on Non-Fourier Heat Conduction during Machining of H13 Hard Steel
Abstract
A predictive model for transient heat conduction during the machining of hard steel based on non-Fourier heat conduction was developed. A mono layer cutting tool coated with TiN coating of carbide substrate was used with 2μm thickness. The work piece material used was a cylindrical bar of H13 hard steel, 300mm length and 70mm external diameter. The cutting speed range was 35.9-244.4m/min, feed rate of 0.2m/rev and depth of cut of 0.2mm. A developed wireless temperature measurement was employed with the thermocouple sensor embedded in the turning tool. The developed model is simplified and contains hypothetical conditions. An infinitesimal convective heat conduction coefficient makes the boundary to be an adiabatic or thermostatic boundary. During machining, the coated tool and workpiece material's heat dissipation are neglected. Prediction was done and compared between the Fourier heat conduction model and the non-Fourier heat conduction to reveal the non-Fourier model effect on transient heat conduction. Predictions by the two models are considerably dissimilar with 77.10C difference at 0.1s cutting time. The predicted temperature difference between the two models when the cutting duration is 10 s is 4.90C. The temperature tends to stabilize when the cutting time is sufficient and heat conduction reaches its steady state. From the results, it can be concluded that the transient heat conduction model is more suitable for the intensity transientstate in the process of cutting heat conduction. The prediction error is less than 12%, which is acceptable for industrial applications and proves the efficiency of the developed model.
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Introduction
In recent years, more and more coated tools have been used in metal cutting operations, particularly when machining materials that are challenging to machine. The hardness and wear resistance of the tool are both increased by the application of a tool coating [1,2]. The thin film coating on the cutting tool surface contributes significantly to the process of heat conduction into the cutting tool body and can increase tool strength and reduce friction between tools and workpieces. For the investigation of the thermal effect on tool life and workpiece quality, the analysis of the temperature distribution within the tool's body is crucial. During the cutting process, coated tools generate and conduct heat considerably different from uncoated tools due to the presence of the tool coating film. The tool coating’s low coefficients of friction can minimize the cutting force and temperature. The tool coating can also be used as a heat-resistant material for cutting tools to stop excessive temperature from escaping into the tool matrix. Because of this, coated tools are frequently used in machining [3], and the coating clearly increases a tool's lifespan.
Three states of heat conduction can be distinguished during the cutting process: the intensity transient state, the transient state, and the steady state. The cutting temperature in steady-state heat conduction was extensively studied using Fourier heat conduction. To explain the change in coated tool temperature during dry milling of nickel-based super alloys for a turbine blade, Sijie Yan et al. [4] proposed a thermal model. The model was developed using steady-state heat conduction differential equations. To estimate the tool temperature distribution at various tool states, the proposed model calculates both the heat fluxes into the tool from the rake face and due to flank wear. The affect of flank wear is viewed according to the rapid tool wear mechanism.
Conclusion
The cutting temperature of a monolayer coated tool in both steady-state and unsteady-state conditions was examined in this research. The cutting temperatures of TiN-coated tools under various heat conduction conditions were computed based on the analytical models. The following conclusions were drawn:
1. When the cutting duration was sufficiently small, the temperatures underwent a fluctuating change process, which progressively vanished as the transient degree weakened. The cutting temperature rose and eventually stabilized as the cutting time increased, shifting from a transient-state to a steady-state in terms of heat conduction. The lower the tool body temperature is, the closer it is to the coated surface while the cutting time is constant.
2. It is discovered that the cutting heat transient conduction of coated tool machining exhibits the non-Fourier heat conduction effect. The non-Fourier heat conduction model may effectively capture the thermal disturbance and thermal delay brought on by thermal shock when the heat conduction is transient heat conduction.
3. The prediction error is less than 12%, which is acceptable for industrial applications and proves the efficiency of the developed model.