# The Key Role of Laser Ultrasonics in the Context of Sustainable Production in an I 4.0 Value Chain
## 4 The Key Role of LUS in a Smart Manufacturing Production Site
### [PERSON] in a Smart Production Lab  
As already indicated, the LUS method is implemented to support the holistic construction of a SPL with regard to the creation of a DM/DS/DT, and to support it along the depicted value chain as a holistic auxiliary and quality inspection tool. The MUL 4.0 project progressing at the Montanuniversitat Leoben, in the form of a comprehensive SPL, encompasses parts of the holistic value chain. This value chain covers multiple technically different and geographically separated production sites, which are connected via a production network in order to transparently gather, store, and share data for analysis purposes. The starting point of the value chain, as depicted in Figure 2, is the Chair of Nonferrous Metallury (NFM), which specifically deals with aluminum alloys and has a miniature continuous casting facility. It enables the casting of a wide variety of common and newly developed alloys, as well as recycled material. This provides the feedstock for the Chair of Metal Forming (MF), where it is delivered. From here it can be further processed in a variety of methods both cold, or annealed to a specific temperature in a digitized industrial furnace. One possibility would be rolling in a miniature rolling mill that has been transformed into a CPPS. A black box machine learning approach allows rolling from a certain thickness to the desired final thickness in multiple passes, specifying the optimal pass schedule [32]. Another option would be forging in a hydraulic press capable of forces up to 1 MN. This press is being transformed into a fully integrated CPPS and is capable of recording data such as forces and temperature during upsetting, and automatically transferring them to a Supervisory Control and Data Acquisition (SCADA) system. The data is pre-processed and transmitted to a higher-level tracking system. Based on the raw material, this system can assign the process data to the respective product and provide information about the respective location. This data is additionally used throughout the value chain for input parameters for the FEA, in order to virtually represent the effects of the process conditions on the final product, and thus serve as a QC tool. Finally, the generated product can be heat treated to adjust the optimal material properties and then be machined to the final product. The value chain introduced here is illustrated in Figure 2.  
The application of the LUS in the SPL is intended to provide a fundamental contribution to the creation of a DT. This consists of a FEA for the respectively considered heating or forming process of the specimen with microstructural information prevailing in the material. As already mentioned, the description of the microstructural behavior requires a large number of material parameters in order to be able to calculate various material responses as a function of strain, strain rate, and temperature, by means of a microstructure model. Therefore, the coupling of a LUS system with a TMTS, which records these characteristic values of the deformation as well as the corresponding time, is inevitable. This coupling enables the acquisition of data of the forming process via the TMTS Gleeble 3800, as well as in-situ data of the microstructural processes by a trigger signal from the same time and its correlation. Although the LUS system only provides information on the velocity and attenuation of the ultrasonic waves, these can be automatically transferred to various microstructural changes using programmed evaluation routines, as exemplified in Section 4. This makes it possible to obtain information about grain size, recrystallization behavior, or phase transformations during the experiment. Based on the corresponding recording of the flow curve and the flow behavior, a microstructural change from the LUS data can be assigned to the corresponding flow curve parameters.