# Additive Manufacturing in Underwater Applications
## 5 Areas of Application
### Parts for Underwater Vehicles  
One of the most promising areas is in parts for underwater activities, including scientific research that requires some specific, individual solutions, such as housing [38] or grips. These elements are usually produced by traditional FDM technology in the air and used for different underwater applications. As a material for their production, the most popular types of polymers are used, including PLA and ABS [38]. It is also worth noting that this was one of the first applications of 3D printing for underwater purposes [23]. Other items produced using 3D printing technology and used as parts for underwater vehicles are [16; 96] propellers for high-drag vehicles, wings and tails for low-drag AUVs, legs and frames for multi-rotors, other motor transmission parts, robotic underwater gliders, robotic hands for underwater manipulation, components for a modular propulsion system, and other components. Other popular 3D-printed solutions that are useful for underwater vehicles are different types of grips and other sampling systems. Among them is a system for discrete water sample collection, constructed thanks to AM technology in a compact form, which is useful also in extreme underwater environments [97], as well as special grips for the collection of soft deep-sea organisms at depths above 2000 m [74]. This system makes some biological research possible thanks to the implementation of a new solution, which is necessary in a narrow area of specialization [98]. Another approach was applied in the case of the creation of an underwater super-limb [99]. In this prototype, 3D printing technology was also applied; however, the main purpose of this work was to create a wearable robot that provides divers with mobility assistance and gives the additional possibility of manipulating tools in the underwater environment [99]. As an element for more advanced application in the area of deep-sea exploration, 3D-printed syntactic foams were also investigated [43]. The main aim of this applicationwas to design better materials for improved buoyancy in underwater vehicles [43]. The results show that functionally graded foams based on the GMB/HDPE combination are a good material for this application [43]. Moreover, the usage of 3D printing technology for the manufacturing of pressure housings was investigated. These can be an element for underwater vehicles [50]. In this case, more durable materials have to be used, such as titanium alloys, which also require other technology. In this case, titanium hemispheres were created using LMD technology and tested for their resistance to external pressure [50]. The main advantage of using 3D printing technology for this purpose was the possibility of obtaining complex-shaped elements and enhancing the freedom of design--for example, the optimal geometry of penetration holes in the housing to support proper buoyancy in an underwater vehicle [50]. AM technology also provides an opportunity to obtain functionally graded materials (changing the composition and properties of the materials over the volume) [50]. These works demonstrate the feasibility of building pressure housings in AM [50]. Another less demanding housing system was manufactured using digital light synthesis (DLS) technology with EPX82 resin [45]. This type of housing is dedicated to complex coral reef monitoring and thus will be stacked with electronics. It can be used as a supporting system for vehicles or as a monitoring system placed on a reef for a certain period of time [45]. The 3D printing technology, in the context of creating underwater small vehicles such as drones, can be also used for modern fiber battery production [100]. The advantages of this solution are the light weight and structural power. The form of fiber allows also for the multi-functionality and multi-dimensionality of this solution, including the possibility of obtaining the battery in different shapes, such as fiber, fabric, and 3D object electronic systems [100].