## 5 Discussion  
The aim of this research was to propose a methodology intended for the design of a portal machine centre that would appropriately combine the application of the previously mentioned methods and would be generally applicable to the development of other machine tools. The outputs from the various analyses thus were used as inputs to subsequent analyses with the aim of progressively optimising the portal machine. Although no publications were found dealing with the methodology of the application of a suitable combination of CAx tools for machine tool development, it was possible to use the findings from research on the various methods. The individual analyses performed in this research were solved in accordance with previously published data, especially in the creation of the digital twin of the machine. First of all, it was necessary to select representative workpieces and technological operations. TO was used for the model with the proposed rough dimensions of the machine. During the development of the model for TO, the available resources were used for the design of the mesh, the selection of boundary conditions, and the definition of objective functions. At the same time, a CAM program and postprocessor were performed to obtain the input data for the simulations of the digital twin. The input to the TO was a model with rough dimensions with full volume. This model did not contain ribs and technological details to minimise computational time. For the purpose of the subsequent stiffness and stress calculations, the resulting model had to be modified to respect the manufacturing technology of the casting. Therefore, wall thicknesses, chamfers, and ribs were oriented specifically with respect to the results from the TO and manufacturing technology. Stiffness, stress, and modal analyses were performed on the modified model. The mesh creation and selection of boundary conditions again corresponded with the available articles. The limit value of 50 kN/mm was verified for the stiffness analysis. This value was empirically chosen based on experience at the company SMT a.s. and also corresponded with the available references [28]. The results of all of these simulations were very important to determine the final dimensions of the machine. CAD models were modified based on the results and were used as input to subsequent MCD and machining simulations. A digital twin of the machine (one of the key elements of Industry 5.0) was used to perform the machining simulations and to verify the functionality of the developed machine. The results obtained from the numerical analyses were verified using MCD simulations and simulations of the digital twin of the machine. The machining simulations were also used to verify that the representative workpieces could be safely machined on a machine with the proposed dimensions, with specific tools and specific accessories. The proposed methodology allows for optimisation of the dimensions of any proposed machine and subsequent verification of these dimensions through machining simulations of specific parts. The computational time for stiffness and stress analysis was in the order of tens of hours and even in the order of days for modal analysis and TO. The computational difficulty was determined by the complexity of the individual parts of the model, the fineness of the mesh, and the utilisation of contact elements. The possibility of algorithising the whole methodology seems to be a suitable area for further research. This process would include exporting and importing CAD models between analyses and automatically processing the results. A number of articles have been found dealing with the utilisation of CAx tools [24; 25] in machine tool development. In most cases, these tools have been used separately, namely, CAD tools for model creation, CAE tools for advanced simulations [8; 11; 26; 28; 29; 55; 56], CAM tools (CAM for machining simulations [27]), or tools using digital twin [13; 42] (MCD for mechatronic concepts [41]).