# Spare Parts Made by Additive Manufacturing to Improve Preventive Maintenance
## 1 Introduction  
Nowadays, AM applications can be found in many domains, for example, architecture and construction fields where 3D building models are printed on a reduced scale to have a future view of the real building before its construction and to study its characteristics before its creation [1]. In other fields such as the medical field [2, 3], real improvements have been made in prostheses that are used in almost every part of the human body, dental prostheses, transfemoral prostheses for the elbow and knee, etc. [4]. With 3D printing, engineers can develop and print very complex designs that allow them to make a wide variety of designs that can be modified at any time in CAD files. These modifications can be made when a variable needs to be changed, which makes the technology very flexible. This AM process works by melting the material and joining it to create layers which will form a volume or the 3D object. There is a wide variety of materials and manufacturing processes used in 3D printing. The material and technology used are connected depending on their type. The different AM concepts and methodologies used are standardised according to ASTM and ISO standards [5, 6]. This work aims to find out whether AM can play an important role in industrial maintenance, specifically in preventive maintenance. One of the main fields concerns the possible replacement of spare parts in the maintenance inventories of manufacturing companies, where the stock is very active for some parts but remains static for other parts. The real challenge is to know whether there are spare 3D printable parts in the inventory, to try to replace them with digital files. These digital files could be used to print the necessary parts on demand for preventive maintenance at any time without disturbing the production line and ensuring that they work like regular spare parts. [PERSON] et al. studied the modelling of scenarios of a spare parts supply chain in the aircraft industry. The spare parts supply chain of the F-18 Super Hornet fighter aircraft was selected as a case study because the air-cooling ducts of the environmental control system are manufactured using AM [7]. Researchers [PERSON] and [PERSON] examined how AM affects spare parts inventory management. The methodology was applied to a real-life study to highlight the impact of AM implementation on inventory strategies [8]. The use of AM technology allows for the on-demand printing of spare parts through 3D printing centres, eliminating the need for companies to maintain an inventory of spare parts. The cost of some spare parts in the additive manufacturing process is generally lower than in conventional manufacturing, the latter wasting a lot of material. AM makes it possible to produce very complex parts very quickly while saving material. It can be a very good potential tool for maintenance, especially when it comes to polymers. The reliability of spare parts has been studied by [PERSON] et al. in relation to parts manufactured by conventional methods. They have carried out material characterisation tests which have been compared with the original spare parts. They have also studied the comparative cost of both parts [9]. According to [PERSON] et al. [10] maintenance organisations should incorporate on-demand printing of spare parts into their maintenance processes with great cost savings. The fourth industrial revolution, also called Industry 4.0, integrates a set of emerging and converging technologies that add value to the whole product life cycle [11]. In this new industrial stage, all work activities in the value chain will be performed with intelligent approaches (Smart Working) based on information and communication technologies (ICTs). Industry 4.0 marks the beginning of a new industrial era in which different technologies are used to increase quality, productivity and efficiency in production systems. Industry 4.0 is bringing about a change in the design and operation of supply chains [12; 13].