# Novel Approach to Manufacture an AUV Propeller by Additive Manufacturing and Error Analysis
## 1 Introduction  
A conventional manufacturing technique such as investment casting is quite time-consuming and costly when it comes to the manufacturing of complex parts. Additionally, incorporating any change in design is extremely challenging for conventional manufacturing methods. In some designs, conventional manufacturing techniques are not applicable at all due to their limitations in dealing with complex geometries. Advances in the area of Additive Manufacturing (AM) (commonly known as 3D printing) methods have considerably increased the realization of intricate designs in physical 3D components, ready for direct applications, such as ceramics [1], biomedical parts [2; 3], textiles [3], food industry [4] and microfluidic devices [5]. There is a long list of AM methods, such as Fused Deposition Modelling (FDM) [6; 7; 8; 9], stereolithography [10; 11; 12] and selective laser sintering etc. [13; 14; 15]. In FDM, a thermo-plastic string in a semi-molten state is extruded through a nozzle that deposits a layer on the base plate. This process maintains on-going, layer-by-layer deposition, obtaining geometrical details of each layer through the Computer Aided Design (CAD) model [9]. For every layer to deposit, the base plate lowers down to the pre-defined value to allow the next layer. Effectively, any design that is modelled in software, either by implementing commercial CAD software or through mathematical equations, can be manufactured as a complete solid, hollow, or pre-defined inner and outer surface 3D printing. FDM allows parts to be manufactured in 3D easily and quickly. Despite the advantages of FDM, its restraining aspect is the process control on the geometry of the model to produce preciseand accurate dimensions, attributable to the lack of cohesion between adjacent filaments [16; 17; 18]. The cohesion problem leads micro-gaps to form in the physical model. It has been reported to reduce these air gaps by embedding thermally expandable microspheres that can be expanded in a post-heat treatment of the physical part [18]. Stereolithography is a 3D printing technique that works on the principle of using laser to harden liquid resin for the manufacture of 3D geometry. It involves a process whereby a photosensitive liquid is converted into a 3D solid with the help of a low-power laser, depositing material layer by layer. Stereolithography is used in many of these applications. However, there are two issues associated with this technique: the required process time and the mechanical properties of the printed component [19]. In addition to FDM and Stereolithography, there is another popular technique known as Selective Laser Sintering. This is a technique whereby a bed of powder, either in the form of resin, polymer, or even metal, is subjected to a high-power directional heating source, which allows it to be partially or fully melted and fused into a 3D component in a layer by layer manner. There are three different binding mechanisms in Selective Laser Sintering, namely liquid phase sintering, solid state sintering and full melting [20; 21]. The use of 3D printing for rapid tooling and manufacturing has promised to produce components with complex geometries according to computer designs. The range of applicability of 3D printing is increasing day by day with this technique being applied to intricate geometries. One such geometry that can be simplified from a manufacturing perspective is the propeller of an Autonomous Underwater Vehicle. The geometry of an AUV propeller is complex that requires a difficult process to manufacture through conventional methods. [PERSON] et al. [22] have optimized the size of the work piece to manufacture the AUV propeller blade, using a five-stage cold forging process, which was time consuming as well as costly in obtaining an end result. Researchers have made significant efforts to manufacture complex profiles, such as the aerofoils of AUV propellers, with different methods.