# Enhancing Vibration Analysis in Hydraulic Presses: A Case Study Evaluation
## 5 Signal Analysis and Discussion of the Results
During a normal production cycle (Figure 12c), the dominant frequencies of the spectrum are 170, 510, and 850 Hz. For the last case considered, i.e., production with increased press pressure (Figure 11d), there was no visible boost in the 3.2 kHz range. There were also low frequency components of 225 and 450 Hz. Based on the conducted frequency analysis, it can be clearly stated that it is suitable for analyzing the recorded signals, and thanks to it, the four cases discussed could be characterized in a clearer way. This fact may be useful, for example, to control the set press pressure. In the next step of the analysis, two-dimensional spectrograms were separately calculated for each of the tested cases and selected measurement points. They presented time-frequency images of the recorded signal. The presented spectrograms were described using a scale in the form of a color palette bar. Figure 12 shows examples of the two-dimensional spectrograms. Figure 11: Single-sided amplitude spectrum for the (**a**) background noise level, (**b**) production cycle without parts, (**c**) normal production cycle, and (**d**) production cycle with increased press pressure. Figure 12: Examples of two-dimensional spectrograms for the (**a**) background noise level, (**b**) production cycle without parts, (**c**) normal production cycle, and (**d**) production cycle with increased press pressure. By analyzing the determined spectrograms, it can be concluded that there were characteristic bands showing increased amplitude shares for the low frequency band (up to approximately 10 Hz). Analyzing Figure 12b-d, one can notice the moment of impact visible in color changes around 3-3.5 kHz, appearing for 2.5 s of the measurement. In the case of production without parts, the change occurring around 3 kHz was the narrowest one. For a better representation of results, a waterfall plot was created. A waterfall plot is a graphical representation commonly used in signal processing and analysis to visualize the frequency content and changes in amplitude of a signal over time or frequency. It is particularly useful for displaying the spectral characteristics of time-varying signals, such as those encountered in vibration analysis, audio processing, and radar. Figure 13 presents the created waterfall plots. The results presented in Figure 13 confirm all previous findings, further highlighting the nature of the changes in the spectrograms described above. In each of the presented cases, there were components with low frequencies (below 100 Hz), while for the pressing torque itself, there were components with frequencies of approximately 3000-3500 Hz (Figure 13b-d). The analysis performed in this study shows that the vibration level depended on some production parameters (number of parts simultaneously produced, press pressure, etc.). These data are part of a recipe containing a set of parameters and press settings for a specific part. Therefore, vibration measurements can be used as an element of controlling the settings of production parameters. Additionally, real-time vibration monitoring can be used to diagnose the technical condition of a hydraulic press and help develop a predictive  
Figure 13: Spectrograms of the measured signals: (**a**) background noise level, (**b**) production cycle without parts, (**c**) normal production cycle, and (**d**) production cycle with increased press pressure. motion maintenance system. An increase in vibration values or a change in their frequency may indicate an approaching emergency condition. It is worth noting that the proposed measuring system was tested during serial production at a production plant located in the southern part of Poland. The possibility of changing the operating parameters of the press was therefore limited, so only the press pressure and number of parts simultaneously produced were taken into account in the analysis. In order to determine in detail the impact of press pressure on the form of vibrations, a number of tests should be carried out with variable input parameters.