# A Review on Recent Trends and Applications of IoT in Additive Manufacturing
## 2 IOT-Enabled 3D Printing Applications
### Digital Twin  
A digital twin (DT) is a virtual version of a physical item or process that is able to collect data from the real world in order to accurately depict, validate, and mimic the behavior of its physical twin in the present and the future. The ability to make decisions based on data, monitor complicated systems, validate and simulate products, and manage object lifecycles are all made significantly easier by its presence [32]. NASA was the first association to forge the definition of DT; it has been described as \"an integrated multi-physics, multi-scale, probabilistic simulation of a vehicle or a system that uses the best available physical models, sensor updates, fleet history, etc., to mirror the life of its flying twin\" [33; 34]. Even though digital twin technology is considered to be a recent innovation in Industry 4.0, the concept behind it has been around for quite some time. The concept of digital twin technology was first discussed publicly in 1991, but it was not until 2002 that [PERSON] of the University of Michigan developed the idea in connection to product life cycle management (PLM) [35; 33]. The model that was presented is known as the \"Mirrored Spaces Model,\" and it is comprised of three components: actual space, virtual space, and a connecting mechanism for the flow of data and information between the two [33; 36]. A similar idea developed by [PERSON] in 1991 has since become popular; in the so-named \"Mirror Worlds,\" software models imitate reality based on information that is input from the actual world, [37]. The conceptual model that was suggested by [PERSON] in 2006 was originally referred to as the \"Mirrored Spaces Model,\" but in 2006, it was renamed the \"Information Mirroring Model\" [33; 35; 38]. However, at the time, there were no practical implementations of digital twin due to a lack of technological developments in simulation software, data management, and storage systems, limited or no connection of devices with the Internet, immature machine algorithms, and other issues. In the end, [PERSON] of NASA came up with a brand new phrase, which was \"digital twin,\" in the year 2010. In the NASA roadmap, it was also referred to as the \"Virtual Digital Fleet Leader.\" Figure 4 outlines the timeline and development of digital twin throughout the course of human history. Figure 3: Recent advancements in IoT. Digital twins (DTs) are formed by employing technology that merges the IoT, software analytics, AI, and specific network visuals to imitate real assets or processes. DTs are used to model and simulate complex systems (physical twins). In DT technology, we embed connectivity between physical assets and their digital counterparts and enhance their connectivity with their digital representations using six primary features, such as sensors, actuators, data, integration, analytics, and the digital twin, as shown in Figure 5. In addition, we embed connectivity between physical assets and their digital counterparts in DT technology. As the Internet of Things implementations provide access to massive data and enormous digital ecosystems, it is also becoming simpler to construct and maintain digital twins with a high level of realism. In the years to come, digital twin technology is going to establish itself as one of the most important software tools for changing product creation. According to [PERSON] et al. and [PERSON] et al., the DT has the potential to considerably enhance the AM process by optimizing the various process parameters and providing a framework for the design of the component and support structure [39; 40]. It can also, monitor possible process failures with simulations and real-time data from sensors, and store and process data obtained from a variety of sensors [40]. The elimination of printing errors is the single most important task that can be assigned to a DT by an AM since this will result in more efficient use of resources, which in turn will raise a company's profit and lower its expenses [39].