Additive manufacturing using Fused Filament Fabrication: evolution and trends

This paper discusses Fused Filament Fabrication (FFF) technology to know their evolution and trends, analyzing the materials, workforce, machinery, methods, and management been used. A literature review is done regarding FFF usage between 2010–2020. Data is analyzed for identify the countries that are applying this technology, the industrial sector, academic resources available and a curve is tted to data for forecasting a trend until 2025. Projections indicate a growth of 300% for workforce in FFF usage for 2025, 280% for machinery, 312% for materials, 275% for the creation and modication of methods and, 320% growth for management activities.


Introduction
The development of manufacturing industry along with the development of new technologies, represents an area of interest concerning the impact that new technologies and the insertion of the Industry 4.0 has in a productive sector. Considering that situation, this research is focused on presenting the advances that the Additive Manufacturing (MA) has had, especially, the Fused Filament Manufacturing (FFF) technology, also known as Fused Deposition Modeling (FDM) due that this technology is the most used in the world [1][2][3][4]. This technology has a high acceptance due to low cost in equipment, materials diversity, easy processing, and exibility in operations [5][6][7][8]. FFF has had high impact as a manufacturing process, therefore, this article reports the growth, as well as a synthesis of the AM and FFF technology. Thus, the objective of this article is to present the evolution of the FFF technology under ve aspects: materials, manpower, machinery, methods, and management.

The development of the manufacturing industry and its growth
The manufacturing industry growth along with the incorporation of new technologies represents a challenge for business groups towards 2025, and in such situation, the critical question for manufacturers and investors who must establish priorities regarding the use of resources is: What is the projection of the manufacturing industry growth? [9]. These priorities start from the premise associated with customer satisfaction (focused on service, quality, and unit cost), as well as manufacturer satisfaction (focused on decreasing costs and increasing pro ts) [10].
Since the growth of the industry has triggered the development of several analyzes that are focused on comparative indexes between the market growth and the development of countries that are immersed in manufacturing activities. According to Organization [11], manufacturing growth by 2025 is projected at 2.7%; reaching up to $18 trillion in a total value and an employment rate growth of up to 590 million.
In order to synthesize the information regarding the market projections made by Economics [12], Table 1 presents the countries with the highest growth in the manufacturing industry according to the market size in millions of dollars. The second column presents the market size in millions of dollars, the third column presents the projected growth in millions by 2025, and the fourth column shows the corresponding growth percentage.
Similarly, in countries with the highest growth, it is necessary to identify the countries that will have the lowest growth projected by 2025. Table 2 presents the information regarding this classi cation, where the second column shows the market size in millions of dollars, the third column presents the projected growth in millions for the 2025 years, and the fourth column shows the corresponding growth percentage.  Due to the growth prospects, the manufacturing industry faces new challenges as a result of the products and services diversi cation, which, due to their constant evolution and innovation are led by the automotive industry. Table 3 presents the comparison of the most developed productive sectors within the manufacturing industry, according to the impact on developments and the number of emerging places participating in the sector [13][14][15][16][17][18][19]. Note that the dominance of the automotive industry is shown in terms of new products development per year, as well as the number of emerging manufacturing centers participating in these developments. Regardless of the type of manufacturing employed, either a Subtractive Manufacturing (SM) or an Additive Manufacturing (AM), the growth of the manufacturing industry continues to represent a challenge for those involved [20-22, 10, 12].

Additive manufacturing industry
Because of the appearance of Stereolithography (SLA), which is the rst additive manufacturing technology in 1980, the classic process of material subtraction paradigm was broken, enabling the rise of freedom in the design of components and the reduction of classic process stages [23,22].
Furthermore, the AM is known as a rapid prototyping or 3D prototyping manufacturing that has been characterized as a manufacturing process in which the adhesion of materials layer by layer manages to reproduce or materialize a digital design [24][25][26]. In o cial terms and in according to F2792 [27], AM is the "process of joining materials to build objects from a 3D data model, usually layer by layer". The AM implements seven technologies: Sterol lithography (SLA), Fused Filament Fabrication (FFF), Laminate Object Manufacture (LOM), 3D printing (3DP), Selective Laser Sintering (SLS), Laser Engineered Net Shaping (LENSTM), and Electron Beam Melting (EBM), which are selected for their operation depending on the type of material and nish that the user requires [28,29,24].
Also, the AM has created high expectations regarding its feasibility dealing with the future of manufacturing processes, which is due to the ease of manufacturing complex components, reducing material waste, and ease of operation. Therefore, growth expectations project a 16% growth in the industrial and professional printers sector by 2020 and a 40% growth in desktop and personal computers for the same year [20]. On the one hand, considering that the growth of the automotive industry rebounds manufacturing, it is necessary to show that AM in the automotive industry currently represents a manufacturing segment with growth expectations in several areas. Figure 1 presents the analysis performed by SmartTech [30] with the subcategories of products generated by the AM for the automotive industry.
Regarding the development of AM considering the regions where it has had the most development [31], can be said that North America have been focused on manufacturing products for advanced aerospace technologies, as well as for the defense sector, in addition to manufacturing metal components and 3D printing for the automotive industry [2,32]. On the other hand, the direct competition of USA is China, because it has been focused on the development and mass 3D printing for the manufacture of aerospace components [33,34]. For its part, Europe has been focused on the implementation of AM in naval applications and industrial components [30,22,31,23].
As a result, it is important to present the projections of the AM that have a positive trend, for example, it will grow approximately by 15% between 2020 and 2025. The participation of the AM in the automotive industry will be 36% more for 2020-2025, 51% in participation for the aerospace and medical industry, and 23% for the printing of different types of devices [35,11,2,3,22]. Growth projections by region in trillions of dollars are presented graphically in Fig. 2.

Additive Manufacturing and Fused Filament Fabrication technology
The Fused Filament Fabrication (FFF) also called Fused Deposition Modeling (FDM) is an additive manufacturing process that uses lament as a row material [36]. This technology works extruding liquid thermoplastic. The thermoplastic liquid is rst over heated in an extruder, then is deposited in a "hot" at bed. The term "hot" is between quotation marks because not all the materials used by this technology requires the at bed to be in a high temperature to print a component.
In FFF, the user rst creates a design using a special design software. After the design is complete, it is saved as an .STL le to be loaded in an interfacing software of the FFF equipment. The interface uses a software to converts the le and slices the model into sections, as well as determines a group of instructions to establish how the layers will be printed. After the instructions are sent to the printer, the build material is extruded through a heated nozzle by layer until the part is completed [37].
Due to the facility to operate FFF equipment and the low cost that it represents for users, FFF technology has become a AM technology with one of the most economic gains implementing the printing hardware that has the highest growth projection in the eld with a pro t of $550 billion dollars for printers and hardware by 2025 [20,21]. In order to expose the impact of the FFF technology, Fig. 3 presents the growth graphically corresponding to the comparison between 2020 and 2021.
Moreover, due to the growth projections of the AM, it is important to identify the needs that manufacturers will have to solve in the demands of quali ed personnel [4,38,39], more e cient printing equipment [40,41], materials with innovative characteristics [42][43][44], as well as the actions by e cient management of the FFF process [23,45,46]. Therefore, this article analyzes the growth and development of this technology, which, based on the information obtained, makes a projection about the growth of some aspects: manpower, materials, machinery, methods, and management, as well as the recommendations to solve these types of needs.

Methodology
The methodology is implemented to identify the evolution of the FFF, which is the proposed by Gómez-Luna et al. [47]. Figure 4 presents the diagram of the three phases that are used in the methodology.
Since the interest in the evolution and trends of the FFF is focused on ve factors (manpower, machinery, materials, methods, and management), two syntaxis are considered. Speci cally, the two syntaxis are integrated by the combination of the ve aspects that were previously mentioned, as well as the name of the technology that is implemented (FFF or FDM). In addition, for the search, review, and analysis of the information databases, internet publications, internet sites, and news were considered.
1. Phase 1 Information search. This phase is focused on the process of information collection. The sources considering were the following data bases: Springer, Science Direct, Emeraldinsight, and EBSCO. The internet sites considered were: www.additivemanufacturign.com/category/news, www.materialstoday.com/additive-manufacturing/news/, www.tctmagazine.com/3d-printingservices-bureaux-news, and www.additivemanufacturingtoday.com. The research syntax was integrated in rst term by the words "Fused Filament Fabrication" and "Fused Deposition Modeling" in combination with the words "machine develop", "materials develop", "methods develop", "manpower develop/in uence" and, "management develop". The period of research is restricted from 2010 to 2020. 2. Phase 2 Information organization. Because the AM technology interest is FFF or FDM, the classi cation considers ve categories: manpower, machinery, methods, materials, and management. In order to consider a resource that must be integrated in the manpower category, the information describes skills, knowledge, and experience. For the machinery category, the documents considered describes the modi cation of at least one component in the printer. In the case of materials, the information contains the description lament and components. Finally, management category is associated to the supply chain, facilities, and the resources that are indirectly related with the FFF process. 3. Phase 3 Analysis of the information. The last phase is focused on analyze the information, the record of the results generated by this search are deployed considering the manpower, machinery, materials, methods, and management categories. The structure used in each category is integrated by a table with the results of the bibliography and websites research, a graph with the tendency of the results mentioned, and nally a synthesized discussion about the results.

Manpower
Users of the FFF equipment generally are familiar with design or engineering knowledge, because the use of printing equipment requires a basic knowledge for generating a printed element in FFF. Speci cally, FFF equipment users can be divided into designers or engineers for the stage related to the component design. 3D printer designers, engineers, or technicians in operation are required for the component printing stage and the inspection process, and technicians are needed for the component nishing stage. Table 4 presents the results of the bibliographic and database search subjected to the "Fused Filament Fabrication and Manpower" and "Fused Deposition Modeling and Manpower" syntax. Considering the results obtained by searching the databases and the most in uential and dominating sites on the subject of Fused Filament Fabrication associated with workforce, it is possible to identify that the combination of the two key terms present a growing trend (See Fig. 5), that is, during the last ten years, the issue associated with trained personnel and the handling of printing equipment through FFF technology has received special interest among researchers from social, humanity, and engineering elds that have been focused on the skills and knowledge that the management and operation of FFF equipment demands.
Considering the t of the proposed model with a determination coe cient of 93.92%, it is expected that the development of publications based on the use of the Fused Deposition Modeling, Fused Filament Fabrication and Manpower syntax are focused on the skills required for the industry grow according to Table 5. Demand for basic cognitive skills, it refers to attention, memory, self-awareness, reasoning, motivation, association capacity, cognitive exibility, and problem solving, which with the development of new technologies their demand decrease in more than 15% by 2030.
Demand for manual and physical skills, known also as endurance, strength, speed, exibility, agility, and power, which tend to decrease in 14% due to the design of the tasks, consequently, they tend to reduce elements that generate fatigue and stress.
On the one hand, the nature of the man-machine relationship that in the case of this research is a printer-operator relationship, the required skills are focused on manual skills that are required for the process of preparing and adjusting the printing equipment, a demand for cognitive abilities associated with homework attention and reasoning for problem solving. On the other hand, a specialized knowledge development that is focused on technological skills is required, since the operation of the equipment interface represents the ability to manage computer equipment, data management, and use of the network, which in contrast to the demand for social skills practically does not exist, because the user interaction with others is reduced to the exchange of only speci c information.

Machinery
The development of new printing equipment has grown rapidly in recent years. The FFF equipment manufacturers have focused their efforts on improving equipment characteristics along with reducing costs. [51,21,22,31]. Aiming to improve the quality of printed components, the new equipment features: high-quality and low-cost of components [23,52,36]. Table 6 presents the results obtained by searching for data associated with the combination syntax between "Fused Filament Fabrication and machinery" and "Fused Deposition Modeling and machinery". The growth of the FFF technology has led to the development of new research as well as reports on research journals and specialized web sites. To evidence the growth, Fig. 6 presents the records on the growth in terms of the FFF teams' development. Also, it is possible to project with a coe cient determination of 98.59% a signi cant growth in terms of the number of developments registered in research sources. Table 7 shows the projection of publications expected for the next six years. The operation of an FFF printer is led by a simple method that is based on three main elements: a at bed or printing plate in which the material is deposited to form the impression, a roll of raw material known as lament, and nally an assembly called extruder, which is made up of a nozzle, a motor, temperature generation elements, and temperature control elements.
Moreover, the evolution of the FFF printing equipment can be described as one of the most important achievements throughout its short history according to Savini, Savini [53].
1980 rst development of the Cast Filament Printing equipment by Scott Crump. 1990, Fused Deposition Modeling or Fused Filament Fabrication 3D printers begin with the "Printing equipment at everyone's reach" marketing stage.
2005, the Rap Rap movement begins, which consists of opening operating codes of printing equipment to the community, this opening of codes and resources involves pre-manufacture printer components, component designs on web platforms to be replicated, operation and preparation of codes that are used in the pre-process stages.
2009, the patent registration of the rst FDM print expires, thereby, achieving the opening and development of new companies in charge of replicating the printing technology for molten lament. Currently, brands diversify, as a result, the sale prices of printing equipment and expanding the offer of these equipment decrease.
Since the commercialization of printing equipment, developers have entered the competition to attract a larger market. Concerning this growth and development, the best printing equipment and its characteristics are advertised annually. The results obtained from the evaluation of the FFF printing equipment by Hanson [54] are presented in Table 8.
As it is mentioned, the development of printing equipment allows FFF printing technology to be more accessible to the market, managing to provide manufacturing equipment at low cost (from 200 US), Table 8 The best FFF printer from January 2020 [54].

Materials
Printing materials are other of the most interesting elements involved in the development of FFF technology. Since its inception, the use of lament or thread has become the main characteristic of printing equipment, because the shape of the material is the only one that has undergone two changes, as well as having the presence of only two dimensions of material in the market: 1.75 mm and 2.85 mm.
In the search for information associated with this factor in the FFF industry, it is possible to identify that along with the development of printing equipment, materials are the most developed factor in the eld of research. Table 9 presents the results of the search based on the syntax between "Fused Filament Fabrication and materials" and "Fused Deposition Modeling and materials." Because of the materials development, it is possible to discard that the applications of greater focus are those that are used by the medical industry. In these applications the main focus is identifying publications concerning with the density of the polymer, the transition value associated with the temperature transition, resistance characteristics (Young's modulus), the tensile strength, the elongation point up to the break, the limit temperature de ned for the decomposition point, and the ideal operating temperature.
In addition, it is evident that the materials development presents an ideal alternative for the growth of the printing industry using FFF technology. Figure 7 presents the evidence of this growth, where an exponential growth associated with the generation of results is observed, subjected to the search syntax "Fused Deposition Modeling and materials" and "Fused Filament Fabrication and materials." Based on the proposed model, the projection of the formally identi ed research resources for the next six years can be made. Table 10 shows the corresponding projection with a coe cient determination of 97.33%. The rapid development of the materials that are implemented in the FFF has different needs of users. Speci cally, the use of polymers, such as PLA (Polylactic acid) and ABS (acrylonitrile butadiene styrene) are related to the attribute of hardness, in this sense, ABS is more rigid, therefore, the selection of this material depends on the model print that is subjected to high stresses.
On the other hand, the implementation of PLA is de ned by the characteristics of the process, in which it is not necessary to isolate the process during the printing stage, since the material does not present changes when it is in contact with the environment during the printing process, while for the implementation of ABS, it is required to be isolated from the environment and with a controlled temperature during the printing process. In addition, under these circumstances, the development of materials has achieved a signi cant growth depending on the function the prototype is subjected and to the printing process. In order to synthesize the development of materials, their applications, and characteristics, Table 11 presents the materials implemented in the existing FFF processes and available for users by 2020 according to Technologies [55].
As it is previously mentioned, the development of materials implemented by the FFF technology is the area where the most developments have been registered, thereby, it provides the possibility of producing prototypes with different characteristics, mainly physical and mechanical.

Methods
Unlike the rapid growth and development in the eld of FFF materials and technology, research development has been focused on the methods implemented, but it has not evolved much in the past ten years. Table 12 presents the results of the matches obtained using the "Fused Deposition Modeling and methods" and "Fused Filament Fabrications and methods" syntax. The results obtained from the databases and the internet sites identify variations in the methods, mainly based on the use of software for designing and pre-processing, optimization strategies of the component related to variations in the lling, orientation, and printing of the component, as well as to the follow-up activities of the printing process and post process.
In fact, with the results obtained from the bibliographic search and from the database, the graph in Fig. 8 is developed, which shows a clear trend towards the development of new methods applied to the FFF technology. It is worth mentioning that the modi cations and records found are focused on small modi cations and the use of instruments to adjust the principal equipment for the printing process.
According to the proposed model, it is possible to make a projection of the possible publications for the next six years. Table 13 was developed with a coe cient determination of 98.59%. The third stage is associated with manufacturing, in this stage the strength attributes associated with the type of material that is used and the quality of nish must be de ned. Once the component is manufactured, the user decides to give the nal nish, this is the fourth stage, therefore, the component is subjected to some processes for extracting excess material, applying layers or paint, among others.
Finally, in case of a batch small production with a different approach for prototyping, the manufacturer can perform quality inspection tests in the shipment for the nal user, and in case that they are prototyping elements, the components are sent to the laboratories or to the research and development centers for their use. Figure 9 presents schematically the method that is used in the manufacture of components through the FFF technology, with the steps previously described.

Management
Regarding the management concept used as one of the ve factors of the FFF technology development, the term of management has been directed, according to the results obtained, towards the impact that the use of technology will have on the supply chain. It has recently been identi ed that companies that implements this technology have started to create and manufacture a wide range of articles with new shapes, in which the versatility of the material, the quality of the printed component, the response times, as well as the component design exibility is beyond the traditional production system. The management factor compared to the other four factors is the one that has the least evidence of publications associated with database and technological platforms. Table 14 shows the results that has been published during the last decade. Despite the limited evidence about administration, the fth factor from the FFF technology development tends to continue evolving. To proof this, the results of the publications are presented in Fig. 10.
The projections are optimistic regarding the modi cation of the supply chain due to the use of MA technologies, as well as the development of 3D printing within the new age of manufacturing. However, it must be established that manufacturing through FFF or any of the other AM technologies will immediately replace traditional manufacturing processes along with all the strategies established to achieve the administration of classic manufacturing systems.
In addition, the use of the FFF requires a management system that is not really different from the one that is used in the subtractive industry, in this case, the AM literature review and websites research, especially related to the FFF, demonstrate that the independence of the equipment makes the system manufacturing more agile, which is due to the amount of human resources that must be managed to achieve the printing of a component, the process of acquiring materials for printing, after-sales activities that are required in case the organization of printing through FFF needs them, as well as the minimum activities required for the FFF technology to operate properly from an individual manufacturing point of view to a small-scale manufacturing perspective.
According to the proposed model, it is possible to make a prediction about what is expected for the next six years, the results obtained are presented in Table 15, which have been estimated with the constructed model with a coe cient determination of 98.55%. Finally, the administration activities of a single printing equipment are reduced to the administration of a single human resource, who has the capacity to perform all the required tasks to achieve the operation of the FFF equipment for a customized printing or low scale. This inherently projects the growth of the skills required by 2030 for FFF users, as well as a manufacturing system with a less complex and cheaper management structure.

Conclusions
The development of this section is exposed based on the ve elements that were analysed during the development of this research: manpower, machinery, materials, methods, and management.
Regarding the workforce, the development of FFF tends to demand people with basic digital skills, the exchange of information, and the management of network information, since the operation of the FFF equipment is carried out through internal networks. Specially, it requires personnel with the ability to solve problems that are generated by the operation of the equipment and process failures, which do not require a high physical effort, but intermediate manual skills are needed.
Moreover, the development of printing equipment was diversi ed from the commercial opening with the expiration of the rst patent. The opening has led to the equipment that is currently available to a larger market, at a low cost, with basic operating characteristics, as well as with characteristics of average layer quality between 50 and 400 microns. These attributes allow users to make higher quality developments, and in some cases, smaller production of batches.
The development of materials for the FFF technology has been favored with a signi cant growth because of the appearance of this type of technology, which initially had two substrates: PLA and ABS. Currently, the development of materials is an area of opportunity in which there are more than 10,000 different types of materials, which is why it is updated on the needs concerning the prototyping of new components.
In addition, unlike materials, the method is one of the items that has not evolved much regarding the FFF technology. However, the records show that both researchers and users have made a constant effort to improve the way in which they obtain their components. It is worth mentioning that the literature review found as evidence of improvements in the method, which is basically scarce compared to the information available on digital platforms and social networks, consequently, there is the possibility of making a formal record on the improvements despite that the improvements that are developed have a short life cycle caused by the rapid development of technology.
Finally, the factor associated with the administration of projects applying FFF tends to develop a simpler and cheaper management model of the productive systems, because of the team's autonomy and the skills that the users must have for the operation of a sustainable system. Also, the present analysis is a study that considers the current state of the FFF technology, therefore, the development and growth of this type of technology is available for the development of technological factors, as well as for the impact that FFF has on new manufacturing systems.

Declarations
Funding: this research did not receive any nancial support.
Con icts of interest/Competing interests: The authors declare no con ict of interest regarding this paper.
Availability of data and material: This research reports a literature review and analyzes trends. The analyzed data can be requested to the corresponding author.