# Performance Investigation of Coated Carbide Tools in
## 3 Results
### Tool Performance Estimation Using FEA
#### 3.2.2 Stress Distribution During the Milling Process  
Considering the computation of the developed forces during the machining process, a numerical model was used applying explicit dynamics analysis based on [11]. In the FE model, the workpiece was treated as a plastic material, while the tool was considered rigid.  
Figure 8: (**a**) Numerical simulation of the perpendicular impact test; (**b**) Generation of Smith-like and Woehler diagrams based on FEA results.  
The mechanical properties of the coated insert were modeled via a bilinear anisotropic approach to account for elastic-plastic deformations, based on Figure 2. To ensure an accurate FEA simulation of the milling procedure, a flow stress model was incorporated to represent the material's constitutive behavior under large deformations and high-speed cutting conditions. In particular, the Johnson-Cook constitutive model was utilized, which describes the flow stress of the workpiece material as a function of strain, strain rate, and temperature. Moreover, the FE model incorporates the kinematics of face milling and the applied cutting conditions, including cutting speed, radial depth of cut, and feed rate. This approach accurately represents the motion of the cutting insert, its engagement with the workpiece material, and their subsequent interactions. The definition of the interactions between the cutting tool and the workpiece material was modeled using a frictional contact formulation. The stress fields generated during the process were concentrated near the contact area between the workpiece and the coated cutting insert, as depicted in Figure 9a. It is worth mentioning that the cutting forces \(\mathrm{F_{c}}\) and \(\mathrm{F_{kn}}\) are the result of the integration of the developed stress fields over the elements that remain in contact with the cutting tool and are calculated by the software. Next, these force distributions were approximated using a second-degree polynomial curve, where the pressure distributions (\(\mathrm{p_{c}}\), \(\mathrm{p_{kn}}\)) along the chip contact length (ccl) are presented in the right section of Figure 9a. As a result, the associated superficial normal '\(\mathrm{p_{n}}\)' and tangential '\(\mathrm{p_{t}}\)' pressures were applied to the respective elements within the ccl, as illustrated in the right section of Figure 9b. Taking into account the calculated cutting forces as well as the chip contact lengths and by applying a FE simulation model of the material removal process based on [19], the developed stresses at the cutting edge were also determined, as illustrated in the left part of Figure 9b. Finally, results of the maximum equivalent stresses on the test set are documented in Figure 9c.  
Figure 9: (**a**) Computation of the milling forces and the corresponding pressure distribution; (**b**) Determination of the stress fields in the cutting edge; (**c**) Maximum equivalent stresses at the test set.  
The outcomes of the milling FE simulation model coupled with the experimentally defined S-N diagram were considered in order to estimate the lifespan of the employed cutting tools on the test set. In particular, Figure 10 displays the forecasted number of cuts for each experiment of the test set, such as to achieve a flank wear equal to the predefined criterion. More specifically, the horizontal axis represents the number of cycles to failure (N) on a logarithmic scale, and the vertical axis shows the stress amplitude applied to the material during cyclic loading. Hence, the diagram indicates how many machining cycles the coated tool can endure before failure occurs. The main idea is that higher stress fields during the machining process (calculated via the FEM model in Figure 9c) would lead to a smaller number of cuts due to the determined Woehler diagram of Figure 8b [19].