Research On Testing Temperature Cutter With NiCr/NiSi Thin-Film Thermocouple And Heat Transfer Mathematic Model

Cutting tool is essential as a core of precision machining processes. There are not exact and reliable mathematical models which can prediction the tool wear, tool breakage, cutting force and cutting temperature well during the cutting progress. So, the system of real-time monitor the cutting condition is highly required. The cutting temperature should be controlled, otherwise, the life span of tool and machining precision will be affected by the cutting temperature, which results in rejection rate raise and productivity drop. In this paper, a novel temperature sensing tool is developed, which can measure the transient cutting temperature accurately, moreover do research on static characteristic and dynamic characteristic of thin film thermocouple. The main content of this paper is as follows:Based on the diffuse thermoelectric power equation which is put forward by Mott and Jones, according to the fact that electrical conductivity can be replaced by the multiplication of electron mean free path λ and effective Fermi surface area A, thus the universal formula of thermoelectric power is given. By taking advantage of the expression of free electron mean path in gas model to describe λ, the relationship of thermoelectric power between thin film and bulk material can be deduced. Meanwhile, it suggests that the main influencing factors of Seebeck coefficient are film thermo junction thickness.In this paper, one-dimensional unsteady heat conduction model in composite medium is presented. Thereby, the integral mathematics model of heat conduction is founded, and from which the distribution function of temperature on thermocouple film layer is deduced. Meanwhile, Matlab7.0is used to solve the response time of distribution function of temperature, and the value of thin film thermocouple which deposition time is90min is0.2ms.In this paper, a novel temperature sensing tool is developed, and through the simulated cutting experiment show that the developed sensing tool can measure the cutting temperature accurately. In addition, the Seebeck coefficient is tested by LabVIEW temperature automatic calibration system. The dynamic response time of sensor indicates that has a significantly faster respose than conventional thermocouple. The static response is found to be linear with temperature up to600℃while Seebeck coefficient matched well with that of K-type thermocouple as the film thickness incremented. No significant differences in Seebeck coefficient and response time were observed, thinner film thickness results in a faster response but reduced Seebeck coefficient of thin film thermocouple.