# Automatic Evaluation of the Robotic Production Process for an Aircraft Jet Engine Casing
## 2 Problem Definition  
In modern jet engines, such as PW800 engine (Figure 1), complex structural assemblies, such as welded thin-wall assemblies, are implemented to reduce manufacturing costs and overall weight. This approach demands the application of advanced material joining processes, the development of the manufacturing technology, and the method of process control. Thin-wall components, such as jet engine casings, are flight safety critical components. Each manufactured part passes iterative quality control operations: visual inspection, CMM, and NDT, including FPI (fluorescent penetrant inspection). This topic is of considerable economic importance. Time-consuming processing and the use of special and expensive materials increases the value of these components up to several hundred thousand U.S. dollars. To minimize the expensive manual processing operations, aerospace manufacturers strive to automate and robotize their production processes [26; 27]. This approach is harmonized with the concepts of Industry 4.0. The impulse for industrial robot implementations is the opportunity of securing high stability and repeatability of process parameters such as welding or deburring [28]. Moreover, it is reasonable to eliminate the human factor and the harmful conditions present in manufacturing processes, such as plasma spray coating or the application of paint coatings with the addition of hexavalent chromium, which has been qualified as a carcinogen. Automation and robotization in the aerospace industry has a characteristic feature: it is critical that the developed and implemented automation and robotization solutions meet their project specifications in the long term. This is determined by the operating lifetime of aerospace engines, which require that their components shall be manufactured for 20 to as  
Figure 1: Pratt and Whitney PW800 jet engine. much as 30 years. Production lines and stations in aerospace manufacturing are required to ensure long-term operating reliability throughout the whole production cycle, by design. The requirements specified for these facilities, such as welding process conformity inspection, working conditions improvement, and improvement of business financial results, inspired the investigation into the automation of quality control processes for the welding of jet engine casings. Currently, following the welding operation, the casing is removed from the production cell fixtures and undergoes an inspection process, which may qualify the part to be in compliance, qualify it for rework, or qualify it as scrap. A rework operation requires fixing the part back in the robotic production cell. The process of installation and calibration of a large workpiece such as this increases the hour demand of the work and decreases the capacity of the production line. In a discussed operation there are nearly four meters of welded seams for a single casing part. The collected production data revealed that only a small number of welds were reworked. This was evidence that the welding process was highly stable. In fact, even one non-conformity in a part made it necessary to transport it back to the workstation; in 2016, this was 36% of all parts manufactured in the year. The ratio improved in subsequent years. However, in 2019 and 2020, still over 25% of the parts were required to be handed back to the production cell for welding rework. The data are summarized in Table 1.  
Given the applied materials and the complex production process, the value of manufactured components is very high. This implies the necessity of error elimination in key manufacturing processes, which include operations performed in robotic cells. Action was taken to reduce the costs of rework. The research discussed in this paper was aimed at developing the assumptions for the inspection system to detect in-process anomalies that result in defected parts.