## 3 Results  
### The Workpiece and Milling Process Setup for the Experimental Research  
The workpiece selected for experimental research had external dimensions of \(2092\times 1116\times 540\) mm and was made of STW22 03M steel (Figure 4). The mechanical properties of this type of steel are [34]: yield strength \(R_{p0,2}=170\)-\(360\) MPa, tensile strength \(R_{m}=440\) MPa, and elongation \(A=22\)-\(28\%\). Its chemical composition is up to \(0.12\%\) of C, up to \(0.6\%\) of Mn, up to \(0.045\%\) of P, and up to \(0.045\%\) of S. The workpiece was clamped on a table of the MIKROMAT 20V (VEB Mikromat, Dresden, Germany) portal machining center. Despite very similar geometry and physical properties, the tested workpiece was different from the one described in [28; 30]. Moreover, the supporting structure's scheme (number of secondary supports and their positions) has been different as well. In Figure 4, only the adjustable screws are indicated. The remaining 10 supports of the workpiece were not marked to maintain the clarity of the figure. The tightening torques of those secondary supports were not changed during experiments. Although the tested workpiece is not a typical thin-walled element, its dominant forms of natural vibrations with frequencies in the 100-500 Hz band are observed in the vicinity of the surface to be processed in the face milling process. Moreover, the method of mounting it on the machine table using mounting screws that cause different values of the tightening torques of these screws results in a change in the parameters of the modal model of the workpiece, in various, but repeatable, mounting variants. The above, combined with  
Figure 4: Tested workpiece shown: (**a**) clamped on the machine tool table and (**b**) as a simplified scheme with accelerometers (A1–A5) and adjustable fastening screw (I–IV) locations indicated. the unchanged model of cutting process dynamics, has a significant impact on the level of tool-workpiece vibrations in the face milling process. For the milled surface (length 2092 mm, width 58 mm), full face milling was performed from left to right (i.e., from the side of accelerometer A1 to A5). The milling tool was Sandvik R390-044C4-11M060 (Sandvik AB, Stockholm, Sweden) having a diameter of \(\phi\)44 mm, with four indexable inserts, R390-11 T3 08M-PM 1130 having a corner radius of 0.8 mm, a helix angle of the main cutting edge of 12\({}^{\circ}\), and a cutting edge angle of \(\kappa_{r}=90^{\circ}\). For all of the passes, spindle speed was set to \(n=1300\) rpm and feed speed was \(v_{f}=600\) mm/min. The nominal cutting depth was \(a_{p}=1\) mm. Such a significant value of the tool's rotational speed actually justifies the advisability of taking into account the influence of the spinning effect on the dynamic properties of the structural subsystem. The measurement points were distributed along the milled surface on the inner side of the workpiece. Five IEPE DJB A/120/V 75g (DJB Instruments, Suffolk, UK) accelerometers were used. For impact modal tests, the PCB 086C03 (PCB Piezotronics Inc., Depew, NY, USA) modal hammer was used. The sampling frequency for all signals was 10 kHz. Signals were acquired using a real-time NI (National Instruments, Austin, TX, USA) PXI 8861 controller with PXI 4496 dynamic signal acquisition card running proprietary developed measurement and analysis software in NI LabView RT environment. At first, the fastening screws were screwed with a torque of 90 Nm. This setting, which was a standard according to the normal manufacturing scheme of the production company for this workpiece, was later treated as a reference for selecting simulation parameters and, later, for the evaluation of the simulations and milling experiments. For this setting, modal tests for each sensor location were carried out, and later, the milling process was performed. Then, after each modal test for a different screw setting, milling operations were performed in order to compare its results with simulations to evaluate the method.