## 2 The Proposed Method for Monitoring Abrasive Waterjet Cutting  
In this paper, the development of an in situ energy-based monitoring method for the Abrasive Waterjet Cutting (AWJC) of composite materials is described. The energy of the Abrasive Waterjet employed in the cutting process to erode the workpiece material is directly correlated with various process parameters such as the water pressure, feed rate, standoff distance, abrasive flow rate, and others.  
The proposed method relies on the theory that the AWJ energy is closely related to Acoustic Emission (AE) signals generated during the process. By analyzing these AE signals, the method can detect anomalous events through the identification of relative variations in energy-related signals.  
This monitoring technique takes into consideration both the direct jet energy involved in the erosion of the part and the jet energy lost due to friction with the cutting head. The _AE root mean square_ (\(AE_{RMS}\)) values are investigated for both cases. To monitor the direct jet energy involved in the cutting (erosion) of the part, an AE sensor is mounted on the workpiece outside the cutting counter. Additionally, to monitor the jet energy lost due to friction with the internal components of the cutting head (focusing tube), another AE sensor is mounted on the cutting head. Figure 2 illustrates the proposed monitoring method.  
Integrative energetic models of AWJC face challenges in establishing direct relationships between jet energies, process parameters, and process quality characteristics. The proposed method aims to empirically develop mathematical models for calculating the \(AE_{RMS}\) by considering key process parameters such as the water pressure, abrasive mass flow rate, feed rate, and material thickness. The models for \(AE_{RMS}\) offer a reference value (or the normal level) in AWJC process monitoring.  
The AE monitoring technique will present the following improvements:  
* Developing a smart monitoring/control system for detecting and predicting random machine malfunctions, which could damage the CM parts, also leads to a productivity and quality improvement, as well as a cost reduction.
* The variations in the AWJ energy and Acoustic Emission (AE) facilitate the verification of correct jet penetration. This ensures that the operator has selected the optimal combination of process parameters to achieve the required quality characteristics of the processed part.
* The implementation of state-of-the-art monitoring and control technologies boosts the competitiveness of companies using AWJ processing. The companies will be able to approach projects in high-end fields such as the automotive or aerospace industries, where the price of processed material is very high.  
Figure 2: The proposed method for monitoring Abrasive Waterjet Cutting process.  
* The integration of the proposed monitoring technique within the framework of digitalization and Industry 4.0/5.0 constitutes the basis of advanced technologies and methodologies, such as Sensor Integration, Data Analytics and AI, Digital Twin Technology, Cloud Computing and Edge Computing, Integration with MES and ERP Systems, Human-Machine Interface (HMI), and Cybersecurity.