INDUSTRY 4.0 Figure 6. LMD process monitoring by coaxial pyrometer: left) Temperature measurement during the additive process of a blade reconstruction. Right) Temperature measurement and results on a test probe. There are some industrial applications of real-time control of machi- ning operations. For example, electric power monitoring is used by Scania to optimize the camshaft grinding process in the automotive sector. In addition, by means of a simpli ed thermal model, the grin- ding parameters are controlled in order to avoid thermal damage due to grinding wheel wear and a variable cutting length caused by the lobular geometry of the cams. There are many examples in other processes. In gure 6, the tem- perature monitoring of the LMD process is shown. The temperature measured by a pyrometer can be used as a control signal for defect detections. Other applications of pyrometers can be seen in laser har- dening operations for laser power control [7,8]. Another example, is the complete model developed by the UPV/EHU applied to aeronautical structural parts [9] to predict cutting forces and chatter-type vibra- tions in the 5 axis milling of blisk or impeller type parts. The model is based on cutting force values, measured with piezoelectric sensor. The machining parameters can be modi ed during the operation to avoid the appearance of vibrations while thin walls are machined. Since bla- des are thin walls structures, they present very low rigidity and it is very probable that the combination of vibrations and de ection of the blades lead on severe damage of the part. The introduction of process monitoring makes the machining process more robust and reliable. Hybrid manufacturing – additive manufacturing and machining combination During the last years, Additive Manufacturing processes (AM) are growing rapidly. Besides the well-known boom of low-cost 3D printers (used for polymer part manufacturing), it is necessary to highlight the increase of AM systems capable of manufacturing metallic parts. These systems combine the advantages of the AM processes with full operational and functional parts. The additive manufacturing techni- ques can produce high complex and customized parts by means of a layer-by-layer manufacturing strategy. This ability is currently invol- ving deep changes in mechanical design paradigms and some parts or even assemblies are being fully re-designed in a much more complex way, since AM is able to produce this parts. Thus, some example in aeronautics presents a single part instead a 4-5 part assembly, with a more than 40% weight reduction. On the other hand, AM processes present still limitations in the accuracy of critical dimensions and surface nishing of the components. Thus, metal part AM is usually combined with a nal machining step. Both processes complement each other by creating a synergy that opens the door to greater adap- tability in product creation. Additive Manufacturing processes in the Industry Currently, there are different metal AM technologies that are in cons- tant development. An initial classi cation can be made in two large groups of metal AM processes. Selective Laser Melting (SLM): Represent the “metal 3d printers” and it is becoming popular in some sectors. SLM produces full functional parts with high repeatability and precision (in the order of 0.1mm). The layer-by-layer process is based on a preplaced powder bed layer. These layers can range between 30 to 100 m and powder size is below 65 m in diameter. Once the powder bed is placed, a laser is guided by a scanner selectively melting the areas where it is desired to add mate- rial. The process is carried out in an inert chamber with a controlled atmosphere of inert gas (Argon). Laser Metal Deposition (LMD): LMD process is based on the combina- tion of a laser source and a metal powder injection. The laser creates a melt-pool on a substrate and the metal powder is injected into the melt-pool. The result is the addition of a certain amount of material in the processed area. The powder is injected by a speci c nozzle and the powder is dragged by an inert gas stream (usually Argon). The result is a high quality and low dilution material addition. If the pro- cess is repeated in a layer-by-layer strategy, complex structures can be obtained. Thus, while SLM create full metal parts from zero, the LMD deposit material on pre-existing parts. The main advantage of the SLM process are the high quality, the accuracy and the resolution of the parts, while the most remarkable drawback is the part size. On the other hand, LMD process can be used for complex part repair, coating applica- tions and it can be implemented on a conventional machine-tool and be applied on large parts. Moreover, LMD can be implemented as an additional process into a machining centre, introducing the hybrid concept machines. Hybrid machines There are different examples of process combination into the same machine, such as multitask machines that combine turning and milling operations. Thus, different manufacturers have created hybrid machi- nes that combines additive manufacturing and machining operations. These machines not only serve to manufacture high complexity parts, but also can be used for the repair and coating of existing parts. In some cases, high added value parts are damaged during service con- ditions. In this cases, the LMD process can be applied to add material and machining operations can give the nal tolerance to the part. The main bene t is that parts can return to its original functionality instead becoming a useless scratch. Figure 7 shows the AM of an industrial part by LMD. One of the main drawbacks of the AM is still the relatively low knowledge about the processes. Therefore, some parameters as the material compatibility, laser power, resulting temperature gradients, residual stresses, local thermal distortions... are some of the factors that keep the LMD as a technology still in development. However, there are already machines that combine LMD with machining process to meet the requirements of the new generation designs. In the eld of research, these hybrid machines are usually the result of retro tting or modi cation of machining centres where a LMD head is usually insta- lled in parallel to the machining spindle. 54<<