# Enhancing Vibration Analysis in Hydraulic Presses: A Case Study Evaluation
## 5 Signal Analysis and Discussion of the Results  
In the first step, an attempt was made to conduct a time analysis of the recorded signals. In this phase, the time course of the signal itself was analyzed. This was a basic analysis that allowed one to understand the basic characteristics of the vibrations, such as frequency, amplitude, and wave shape. Moreover, vibration measurements were also taken when the press was stationary to determine the background noise level, and the vibrations were monitored during impacts without parts. The sample results of these trials are presented in Figure 10.  
Figure 10: Time series of acceleration on the \(z\) axis for the (**a**) background noise level, (**b**) production cycle without parts, (**c**) normal production cycle, and (**d**) production cycle with increased press pressure. Figure 9: Time series of acceleration on the \(x\) axis for the (**a**) 1 m and (**b**) 3 m measurement points. From the conducted measurements, it was evident that the background noise level was uniform and averaged between 0.05 g to 0.08 g. The maximum vibration values of the press (over 6 g) were obtained during impacts without items. During the serial production of the tested part, the average vibration values of the press on each axis did not exceed 2 g. Based on the conducted tests, it can be concluded that the detail dampened the vibrations of the press body generated during the production process. For comparison, Figure 10d shows the time course of acceleration on the \(z\) axis for impact with the details of proper production, but with an increased press pressure (tonnage) of 10% (to the value of 850 t). Figure 10d shows that increasing the press pressure significantly affects the form of vibrations. Their amplitude decreased to 0.8 g. The reason for the observed phenomenon was the fact that when a given higher pressure was applied, the press moved down more slowly to reach the desired pressure, which directly translated into a lower value of structure vibrations. After the test research, actual measurements were initiated. A total of 1000 samples were recorded. Each recorded measurement was saved as a separate csv file, containing the following data:  
* Measurement time,
* Acceleration value on the \(x\) axis,
* Acceleration value on the \(y\) axis,
* Acceleration value on the \(z\) axis. Each file was then imported into a database using a prepared desktop application, thus enabling access to production data for selected plant services, technologists, and the maintenance department. In the next step, the measurements were subjected to analysis in the frequency domain. The recorded signals were analyzed in the range of up to 5000 Hz, which corresponded to half the transducer sampling rate. For this purpose, Fast Fourier Transform (FFT) was used. FFT allows one to transform signals from the time domain to the frequency domain. This allows one to identify the frequency components present in the signal, allowing one to better understand its characteristics. FFT allows the identification of harmonic vibrations, i.e., vibrations with frequencies that are multiples of the fundamental vibration frequency. This is important because some machine faults can lead to the generation of such harmonics. This analysis can reveal characteristic vibration frequencies that may indicate specific problems with the hydraulic press, such as loose bearings or misalignments. Figure 11 shows single-sided amplitude spectrums of the recorded signals. The frequency analysis revealed significant differences between the recorded operating moments of the hydraulic press. When analyzing the background (no production, Figure 12a), low frequencies up to 500 Hz dominated, with the main components occurring at 50, 225, and 450 Hz. In the case of operating without a part (Figure 11b), the frequencies around 3.2 kHz had the largest share in the signal spectrum, and there were boosts in the values for the low frequencies of 225 and 450 Hz.