# Automatic Evaluation of the Robotic Production Process for an Aircraft Jet Engine Casing
## 3 Solution of the Problem
### Identification of Essential Process Parameters  
In the first step of the research, the manufacturing process and devices of the production cell were studied to identify which data affected the process, meaning the input data and the data that were the direct contributors to the process results. Each manufacturing process had many variables and parameters, the identification of which required in-depth understanding of the structure and operating principles of the devices involved. Figure 6 provides a schematic summary of the identified parameters in three subgroups: calibration parameters, motion parameters, and welding process parameters. To provide a proper correlation of the measurements from the vision system and the robot positioning system, a dedicated calibration routine was developed. Collected and written data described the actual position of the welding torch electrode (torch TCP: Px, Py, Pz) and the camera point of focus (camera TCP: Rx, Ky, Kz) in the coordinate system referenced to the industrial robot's tool mount flange (Figure 7). Figure 6: Simplified diagram of the TIG welding process with the identified parameters. Figure 7: Diagram of the torch and vision coordinate systems. The vision system was responsible for finding the welding path and calculating the corrections for robot. The welding trajectory was analyzed directly before welding and the analysis results were stored in the robot controller to be used in the welding process. Each welding path was defined by three points and compensation was specified for each of the trajectory point as C1, C2, C3 (Figure 5). Parameters for the TIG welding process were the values which define the process flow. The primary variables were welding current (I) and welding voltage (U) provided by the welder machine, which was a constant current source in this case. The flow parameters of shielding gas distribution to the weld face and to the weld root were also considered (A1, A2, A3, see Table 2 line 5). They were executed by the gas flow controllers, with the specific values being stored in the robot's program and set and verified in every step of the process. It was critical for the robot to maintain a uniform welding speed (v) with a low motion acceleration (a) to limit vibration, which was detrimental to the welding process. Given the large dimensions of the part and the tolerances acceptable in the manufacturing process discussed here, the WeldGuide system was used to maintain a fixed welding arc length by correcting the electrode distance from the workpiece surface. Main parameters of the WeldGuide system were correction value per measurement step (W, see Table 2 line 8) and the total incremental correction value (S, see Table 2 line 8). For each of these parameters, their signal sources were defined, as well as the properties, which included the value type, the value range and units, and the measurement frequency. The defined parameters are listed in Table 2.  
Direct communication between the IRC5 controller and the devices at the production cell allowed the read and save defined in-process parameters as the designed structure, in order for them to be used in further data analysis. After improvements were made for the programs already operating on the controller, a data recording frequency of over 40 times per second was achieved. Considering that a single weld seam was made in approximately 1 min, approximately five MB of data were produced from a single part in the robotic TIG welding operation.