## 2 Materials and Methods  
### Data Acquisition  
This research focused on developing a system to monitor the wear and tear of tools in real time during manufacturing, eliminating the need for production stops. The system's success was measured by looking at the manufacturing signals gathered. The testing was conducted on a Busellato Jet 130 CNC machining center located in Thiene, Italy. This machine featured a 40 mm cutter head equipped with a single, replaceable carbide blade provided by Faba SA from Baboszewo, Poland. A chipboard sheet, sized 300 \(\times\) 150 mm, was used for the tests. It was firmly mounted on a measuring stand, where a groove of 6 mm was milled. The milling process was carried out at a spindle speed of 18,000 rpm and a feed rate of 0.15 mm per tooth, chosen based on an extensive literature review and practical know-how in processing chipboard. Tool condition was classified into three levels: green, yellow, and red. 'Green' indicated a new or well-kept tool; 'Yellow' pointed to moderate wear but still usable; 'Red' meant the tool was critically worn and needed immediate replacement. Tool wear was assessed using the maximum flank wear (\(VB_{max}\)) standard. Figure 1 shows a close-up look at how the tools wore out, with a focus on the \(VB_{max}\) value to check the tool's shape. To figure out if a tool was in 'Green', 'Yellow', or 'Red' condition, we used a Mitutoyo TM-505 microscope (Mitutoyo Corporation, Kanagawa, Japan). This microscope is known for its sharpness in measuring sizes and angles. Figure 1: Illustration of tool wear measurement using the \(VB_{max}\) parameter. We often stopped the milling to look at the tool's edge under the Mitutoyo TM-505 microscope (Mitutoyo Corporation, Kanagawa, Japan). This microscope can also have a special lens added to check more complex shapes, such as screws and gears. By doing these checks, we could tell how much the tool had worn out and categorize it into one of three wear levels. The specific numbers that defined each category were set as follows:  
1. The 'Green' category is for tools with wear and tear (VBmax) from 0 to 0.15 mm, broken down into four smaller wear stages;
2. Tools fall into the 'Yellow' category if their VBmax is between 0.151 mm and 0.299 mm, and this category is divided into two wear stages;
3. The 'Red' category is for tools with a VBmax over 0.299 mm, and this, too, has two stages of wear. Moreover, the setup for the experiment came with an array of sensors that could capture 11 different types of signals, such as the following:  
* Force value in the (1) \(X\) and (2) \(Y\)-axes (Kistler 9601A sensor; Impexron GmbH, Pfullingen, Germany);
* (3) Acoustic emission (Kistler 8152B sensor; Kistler Group, Winterthur, Switzerland);
* (4) Noise level (Bruel & Kjaer 4189 sensor; Bruel and Kjaer, Narum, Denmark);
* (5) Vibration level (Kistler 5127B sensor; Kistler Group, Winterthur, Switzerland);
* (6) Device-rated current (Finest HR 30 sensor; Micom Elektronika, Zagreb, Croatia);
* (7) Device-rated voltage (Testec TT-Si9001 sensor; Tsetec, Dreieich, Germany);
* (8) Head-rated current (Finest HR 30 sensor; Microm Elektronika, Zagreb, Croatia);
* (9) Head-rated voltage (Testec TT-Si9001 sensor; Tsetec, Dreieich, Germany);
* (10) Servo-rated current (Finest HR 30 sensor; Microm Elektronika, Zagreb, Croatia);
* (11) Servo-rated voltage (Testec TT-Si9001 sensor; Tsetec, Dreieich, Germany). Data acquisition was facilitated through the use of National Instruments PCI-6111 and PCI-6034E measurement cards (National Instruments Corporation, Austin, TX, USA), respectively, for acoustic emissions and other parameters. This setup ensured comprehensive monitoring, enabling detailed analysis and consistent sensor positioning relative to the workpiece and cutting zone throughout all measurements. The organization and  
Figure 2: Illustration of cutting edge geometry. specific characteristics of the collected data are summarized in the subsequent sections and illustrated with plots of raw signal samples for the selected parameters.