INDUSTRY 4.0 Figure 3. Integral CAD/CAM solution for the production process of a blade by a combination of LMD and machining processes [UPV / EHU]. Other alternative is to project virtual images on real objects using SAR (Spatial Augmented Reality) devices. The main difference in this case is the use of the environmental objects to project the virtual ima- ges, without using any screen. This alternative is becoming the most important in industry. For example, Volkswagen Group is working on the Marta Project to implement this type of devices in its production lines. Airbus is also working on projects that introduce digital image projection in production lines, in order to show relevant information during the assembly. In addition to the device types, there are also different alternatives from the user interaction point of view. In gene- ral, there are 4 types of user interface. The tangible, collaborative, hybrid interfaces or emerging multimodal interfaces, the latest to be created, allow the user to choose the mode of interaction depending on the needs. On the other hand, the way in which the user enters the input signals to the device can be very different. The most common devices are gloves, wireless bracelets or smartphones. Augmented Reality is becoming popular in some sectors. Probably, the most outstanding examples are the use on smartphone games, but there are other applications such as tour guides, navigation or online education platforms that are becoming very relevant. Regarding to the industrial sector, and despite its great potential impact, the integration of AR is relatively slow. The main stoppers of these implementations are the high reliability requirements of the industry for this type of applications, combined with the need of easy portable solutions, which are dif cult to design for many applications. Nevertheless, augmented reality can be a key technology not only in the most automated or robo- tized work cells, but also in maintenance and repair tasks required in any production process. For example, all the early maintenance tasks can be stored in smartphones or the alarms of a production line can be highlighted and positioned in real time without having to read them on a panel. It could also display real-time data such as pressure, ow or other variable levels simply by scanning the installation to be checked. There can be many different examples and there are still many applica- tions of AR that have not been developed yet, but many indicators show that AR will be implemented over the next few years and will become typical in the factories of the future. Simulation and virtual manufacturing tools Virtualization of manufacturing processes is one of the main goals for the optimization of production lines. The main advantage is to predict and estimate different parameters by virtual tests, which is much cheaper and faster than setting up the process by trial and error techniques. In this line, the current context where manufacturing of low-added value parts have been moved to low-cost countries make necessary to manufacture complex parts. These parts use to combine low-machinability materials and complex designs, involving complex machining operations in 5 axis milling machines or combining simulta- neous turning and milling operations in a multi-task machine. Therefore, it is very dif cult to deal with the programming and setting-up of the process in a reliable way if virtual manufacturing tools are not used. In order to meet these new industrial challenges, the Industry 4.0 model involves virtualization tools to produce a complete virtual replica of the machining process, going through all its phases and without having to test the process in the real machinery. In this way, the vir- tual manufacturing tools that have been developing since the 90s have undergone a remarkable advance during the last 5 years. On the other hand, the number of users of these tools is also growing rapidly. On the other hand, the number of multi-axis machines is continuously growing. These machine-tools include 4 and 5 axis milling and multi- task machines for simultaneous turn-milling operations. One of the consequences of the proliferation of these machine-tools is the need for complex multiaxis programming, including CAD/CAM software as a mandatory tool. CAD/CAM systems allow the control and optimi- zation of machining strategies and it is possible to de ne the tools to be used. On the other hand, current CAD/CAM tools simulate the machining operations in order to check the consistency of the path and a collision-free programming. In the same way, main tool and clamping device suppliers have introduced the option of downloading virtual models from the catalogues to be directly imported into CAD/ CAM environments. In this way, the trend goes towards the construc- tion of more complex and detailed virtual models, very similar to the real environments. For example, the virtual machining simulation some years ago include the CAM trajectories (usually in APT format), the blank and may include also the xturing. This scheme allows a rapid simulation of the machining paths, detecting potential collisions and defects on the strategy, but there is no information about the machine tool behaviour or other parameter related with the process. Nowadays, the virtual machining software use to start with the real ISO-code pro- gram and may also include machine tool kinematics and mechatronics. The result of this simulation can detect real machine tool behaviour or even tolerance deviation at corners. Despite the great potential impact of AR, its integration in the industrial sector is relatively slow 50<<