## 1 Introduction
[14] considered the time-varying of tool chip contact length in the end milling process and constructed a temperature distribution model of the rake face of indexable milling cutter through Green's function. When an integral carbide end mill is milling a plane, both its circumferential edge and bottom edge may be involved in the process of milling, thus generating milling heat. Consequently, [PERSON] et al. [15] established a new end milling heat model using a semi-analytical method, by considering the effects of the circumferential edge and bottom edge on cutting temperature. Heat intensity and heat distribution ratio are the two important physical parameters for establishing a cutting temperature field model. Therefore, heat intensity in the machining process may directly affect the amount of heat generated from cutting and affect the process precision owing to the thermo-elastic deformations. Processing technology, heat transfer mode and processing conditions are the main factors that affect heat intensity. Many studies have been carried out concerning these factors. First, through orthogonal continuous cutting, [PERSON] et al. [16] derived the heat intensity of the rake face based on numerical simulation and an inverse method algorithm. Furthermore, in the interrupted cutting of indexable milling cutters, [PERSON] et al. [17] calculated the heat intensity with time-varying characteristics by using an inverse heat conduction method. Similarly, based on the reverse heat conduction method, [PERSON] et al. [18] obtained heat intensity by thermocouple method embedded. Because of the unsteady milling process, [PERSON] et al. [19] calculated the unsteady heat intensity of indexable milling insert through the finite element simulation of the interrupted chip formation process. Considering the influence of processing conditions on heat intensity, [PERSON] et al. [20] established mathematical expressions on the heat intensity of end milling based on a polynomial method for feed per tooth, cutting speed, axial cutting depth, cutting width, edge radius, and rake angle. Taken together, during the process of studying the milling temperature of an integral flat end milling cutter, there is a lack of prior research on the time-varying and non-uniform characteristics of heat intensity in the RCZ as well as the non-uniform characteristics of heat intensity in the FWZ. Heat distribution ratio in the process of machining may directly affect tool temperature distribution. The main influential factors of the heat distribution ratio are processing technology; thermal number, which is a parameter defining how much accumulated heat in the primary shear zone is distributed by heat convection in comparison with thermal conduction; tool coating; and workpiece material. Numerous studies have been carried out on these factors. The thermal number of workpiece materials determines the amount of heat accumulated through heat convection in the shear zone. Therefore, some studies have investigated the relationship between thermal number and heat distribution ratio. Heat value parameters were applied to establish a calculation method for heat distribution ratio under continuous cutting conditions by [PERSON] et al. [21]. Moreover, [PERSON] et al. [22] extended the same parameters to the calculation of the heat distribution ratio in an interrupted cutting process. Tool coatings of different materials can have a significant impact on the generation and distribution of cutting heat within coated tools. Therefore, by using the characteristics and tool chip contact as well as the types of workpiece materials and tool matrix/coating materials, the heat distribution ratio of multi-coated tools can be accurately predicted, see [PERSON] et al. [23]. [PERSON] et al. [24] examined the heat distribution ratio of coated cutting tools based on the convective heat transfer principle. [PERSON] et al. [25] developed a two-dimensional finite element model under thermo-mechanical coupling to estimate the heat distribution ratio of tool chip.