# An Overview of Material Extrusion Troubleshooting
## 1 Introduction  
Material extrusion (ME) is the second most popular form of additive manufacturing (AM) process with 844,800 and 499,500 searches on Google as well as Google Scholar, respectively, after Powder Bed Fusion that has been searched 578,000 and 26,820,000 times, respectively. The term 'ME' was commonly searched together with 'Fused Deposition Modelling' and 'Fused Filament Fabrication'. These three terms refer to the same AM process of additively building up material by selectively dispensing through a nozzle or orifice [1]. The technology involves the material from a spool of filament that is loaded into the printer, melted above its glass transition temperature (T\({}_{g}\)) for amorphous polymers and above its melt temperature (T\({}_{m}\)) for semi crystalline polymers to be selectively dispensed through the heated extrusion nozzle and deposited onto the build platform at a predetermined location (Figure 1) [2]. As the use of desktop ME machines has gained widespread adoption, this paper discusses several key design strategies and considerations to produce high quality ME parts and focuses on the current issues concerning the desktop ME process which is not machine specific. The purpose of this paper is to serve as a troubleshooting guide to determine and remedy common causes of problems and symptoms. This review summarizes the findings of many development engineers, researchers at equipment manufacturers, scientists, ME users and our personal experience available in the open literature. These findings were derived from working with desktop Cartesian printers that use a system of X-Y-Z coordinates to determine the location of the extrusion nozzle, but similar issues could also be encountered in Delta ME machines, Polar ME machines or extruders fitted to robotic arms. Advantages and Disadvantages of ME  
ME processes allow a wide variety of materials with diverse characteristics and properties to be used, ranging from commodities, engineering, to high-performance thermoplastics, composites, and functional materials (Table 1). Examples of commercially available commodity thermoplastics used in ME include polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), high impact polystyrene (HIPS), styrene acrylonitrile (SAN), and polypropylene (PP). Examples of engineering polymers commercially available for ME include acrylonitrile styrene acrylate (ASA), polymethyl methacrylate (PMMA) polyamide 6 (PA6), polyamide 66 (PA66), polyamide 12 (PA12), polycarbonate (PC), thermoplastic polyurethane (TPU), polyethylene terephthalate with glycol (PETG), recycled PET (rPET), thermoplastic elastomer (TPE), polyoxymethylene copolymer (POM-C), thermoplastic copolyester elastomer (TPC), polyvinyl alcohol (PVA), polyhydroxyalkanoate (PHA), butenediol vinyl alcohol (BVOH), blended with PLA and other blends of polymers (Table 3) [3]. Examples of high-performance polymers available as filaments for ME include polyphenylsulfone (PPSF, PPS or PPSU), polyetherimide (PEI), polyamide imide (PAI), polyaryletherketone (PAEK), polyether ether ketone (PEEK), polyvinylidene floride (PVDF) [3]. Examples of composite filaments include Carbonyte (PA with carbon fibers), and other engineered polymers such as those with wood fibers, glass-filled fibers or particles, carbon fibers and magnetic particles like ferrites, as well as special polymer blends with ceramic, cement and metal for sintering applications [3; 4]. Figure 1: The material extrusion (ME) process. ME processes offer end-users desktop equipment at a lower price range as compared to other AM technologies in the market as well as at a professional and industrial level for higher precision and performance components fabrication (Table 2). An open-source ME printer offers end-users the freedom to utilize third party filaments that fit the machine parameters, while a closed system limits the use to only materials offered by the printer manufacturer [18].