# Intelligent Air Cutting Monitoring System for Milling Process
## 1 Introduction  
The evolution of manufacturing toward intelligent manufacturing, such as Industry 4.0, creates new challenges to high-quality and efficient manufacturing. Machining accuracy, machining efficiency, and tool life are the key factors for optimization in manufacturing. The machining parameters have a direct effect on the tool life, machining accuracy, and machining efficiency. Therefore, the design of cutting parameters and cutting paths are very important. Meanwhile, the NC (Numeric Control) machining process, as the main part of producing the product, requires a high-efficiency and intelligence level in NC machining process planning. Recently, the commercial CAM (Computer-Aided Manufacturing) software has come into wide use, but the process analysis and decision making still depend on the knowledge and experience of designers. Numerous problems, such as inefficient process planning and time-consuming preparation, occur as a consequence. Currently, reuse technology is utilized for the NC machining process, including group technology and machining process template. [PERSON] et al. [1] developed an automatic process planning method that integrates feature recognition and group technology. [PERSON] et al. [2] studied the NC process reuse method by using 3D CAD (Computer-Aided Design) model and CAM model data mining. This approach explores the NC process-parameter-driven characteristics of similar features through the analysis and mining of existing process data. However, it is difficult to make the micro process and macro process compatible, and requires many considerable adjustments due to the reusable NC process characteristics of multiple parts, manufacturing heterogeneity, machining parameter variability, and subpart level, therebycompromising the effectiveness of NC process reuse. The optimization approach of the NC machining process has been studied by [PERSON] et al. [3], where an annealing algorithm was proposed and simulated to obtain the shortest tool path. Similarly, [PERSON] et al. [4] optimized the cutting sequence in NC machining by developing a mathematical model for the shortest tool path. This method is limited for the machining of independent features and, therefore, limited in improving the efficiency of the overall machining. When the features in a subpart come together and feature recognition technology is used to create machining parameters, many air cutting paths may occur. The different technique for reducing the time of the NC program was investigated in previous studies [5; 6]. [PERSON] et al. [7] proposed a method to generate a tool path based on the 3D CAD model and eliminate the air cutting by modifying the tool path. As seen, the NC machining process created by CAM software is not optimal, many air cutting paths may be produced, and it is difficult to improve machining efficiency by modifying the cutting path due to the reliability considerations. Non-effective cutting will occur during the machining process. This is perhaps because the distance between tool position and workpiece is too far or due to groove occurrence during the machining processes. Besides, ballscrew error, backlash error or position error, etc., will also increase the non-effective cutting motion distance. The error caused by the machine itself leads to excess or insufficient moving distance, so creates an inconsistent product or non-standard size. If the product is overcut then it will be scrapped, resulting in not only a financial loss but also a waste of time. When the problem is discovered after mass production, it causes huge losses. Since the cutting fluid is often used in the machining process, it is impossible to observe overcutting or undercutting during processing. Meanwhile, if the air cutting of each section during the machining process can be known, it can help to know whether there is machining abnormality or air cutting, and also the abnormality can be modified and optimized. Therefore, the abnormality can be detected to reduce losses and improve the machining efficiency.