# Automatic Evaluation of the Robotic Production Process for an Aircraft Jet Engine Casing
## 3 Solution of the Problem
### Research Test Cell  
The tests were carried out in a production cell that processed TIG welding (Figure 2). It was designed as a dedicated cell for the processing of specific longitudinal welds of the intermediate case for the PW800 jet engine illustrated in Figure 3. The total length of the welds was seven m. The struts connected the inner part to the outer ring so this operation had a direct impact on the strength of the whole assembly and the accuracy of its fabrication.  
\begin{table}
\begin{tabular}{c c c c} \hline  & **2016** & **2019** & **2020** \\ \hline Reworked welds & (3.5\%) & (2\%) & (2\%) \\ Reworked parts & (36\%) & (27\%) & (28\%) \\ \hline \end{tabular}
\end{table}
Table 1: Year-by-year summary of weld seam and part rework data.  
The accuracy and repeatability of the process in the production cell, depended on many factors. With the large part (the diameter was approximately 1400 mm), which was composed of several dozen smaller components, it was difficult to achieve repeatability of the input parameters. It could be ensured to a limited degree during manual assembling procedure before the welding operation.  
The primary components of the production cell shown in Figure 2 included an ABB IRB 2600 ID six-axis industrial robot with an ABB IRBP B1000 five-axis positioner with a capacity of 1000 kg. An automated fixture, mounted on the positioner, featured pneumatic actuators, a number of sensors to verify the fixture status, and the position and orientation of the part in the fixture. The TIG welding process was carried out with a Fronius MagicWave 5000 automatic welder, which controlled the process settings with an internal program.  
The production cell also featured a Keyence CV-S200M video system, complete with a custom calibration system for the camera itself and the position of the TCP of tungsten electrode in the welding torch.  
The master control unit of the production cell was an ABB IRC5 industrial robot controller. Aside from operating the motion control program of the robot and the positioner, the unit also handled the communication with other devices installed in the production cell.  
The connection diagram of the production cell devices was based on EthernetIP and DeviceNet and is illustrated in Figure 4.  
Figure 3: Intermediate case of the PW800 jet engine.  
Figure 2: Robotic production cell at Pratt and Whitney Rzeszów S.A.  
The workstation also had a safety system managed by an ABB Pluto controller, which allowed the automatic operation at the cell only when all protections were secured. The operator could display the processing data and parameters outside the station, using an HMI panel and the visual compensation control provided by the video system.  
To adjust the robot motion path to the manufacturing tolerances of the part presented for processing, the production cell featured a vision system for trajectory correction. It read the locations of the workpiece edges (Figure 5) and output the relative values of its locations to the robot controller, which used the data to shift the pre-programmed path.  
The trajectory was corrected directly before the process, which ensured the correct location of the welding path relative to the edges being welded, according to the applied manufacturing process assumptions. The calibration of the welding torch combined with a camera was completed before processing the TIG welding and needed to be performed every time the tungsten electrode was replaced.  
Figure 4: Connection diagram of the test cell devices.  
Figure 5: Identification of the actual welding path position by the vision system.