# Tribological Analysis of PETG Fire-Retardant Samples Manufactured by FFF
## 1 Introduction  
Additive Manufacturing (AM) is not just a new way of producing, it is a new way of thinking about manufacturing. For the first time, we are no longer constrained by molds, tools, or standards imposed by mass production. It is possible to design parts that not only fit a specific shape but also respond precisely to the demands of their final application. Geometry, internal structure, and functional properties are integrated from the design stage, allowing for optimized and customized solutions like never before [1]. This approach does not replace traditional manufacturing; rather, it complements, expands, and challenges it to evolve. Additive manufacturing is, in essence, an invitation to reimagine what we manufacture, how we do it, and above all, why [2]. The increasing accessibility of additive manufacturing and computer-aided design (CAD) software has led to the widespread adoption of AM in today's industry, especially in biomedical, automotive, and aerospace applications. These sectors benefit from the so-called \"complexity for free\" paradigm, which suggests that geometric complexity can be increased without significantly raising the cost of the final product [3]. However, recentstudies have questioned this notion, showing that design complexity can negatively affect manufacturing time and material consumption [4]. Nevertheless, when managed properly, complex designs can serve as performance indicators in AM, optimizing dimensional accuracy and process sustainability [5]. This, combined with the inherent sustainability of additive processes, has accelerated their adoption across various industrial sectors [6; 7; 8]. Still, the most sought-after feature is not complexity per se, but the ability to create parts with optimized properties--either by modifying the design or by incorporating new or multi-material combinations. As a result, new materials are continuously being developed to meet the specific performance needs of parts, beyond just their mechanical properties. For example, functionally graded materials can tailor properties such as thermal or mechanical resistance within a single part, which is particularly valuable in the aerospace sector [9]. In this industry, flame resistance is also essential, and specific developments of flame-retardant polymers such as ULTEM or PAEK have already been adapted for additive processes like selective laser sintering [10]. Research on polymer powders such as PPSF has also shown promising results as new fire-resistant materials for 3D printing in critical applications [11]. Thermal stability has always been a limiting factor in the service behavior of polymers. According to [PERSON] et al. [12], improving fire resistance or thermal stability typically requires either chemical modification or the addition of other materials in the form of additives. These additives have enabled the development of thermoplastic filaments suitable for additive manufacturing, specifically for material extrusion processes. According to ISO/ASTM 52900:2021 [13], Material Extrusion (MEX) is a family of processes where material is extruded through a nozzle, changing its state in order to be deposited layer by layer, ultimately building a three-dimensional shape [14; 15]. Within this family of processes, Fused Filament Fabrication (FFF) is the most commonly used technique, typically involving thermoplastic materials [7; 14], such as Acrylonitrile Butadiene Styrene (ABS), Polylactic Acid (PLA), Polycarbonate (PC), and Polyethylene Terephthalate Glycol (PETG). This places FFF within the broader category of polymer additive manufacturing. In addition to these, new trends focus on the use of other materials, particularly reinforced organic matrix composites [7; 14]. The incorporation of additives into these polymers has enabled the development of flame-resistant materials. Flame-retardant grades of ABS [16], PLA [17], PC [18; 19], and PETG [20] are now available.