This paper presents a systematic review on extrusion additive manufacturing (EAM), with focus on the technological development of screw-assisted systems that can be fed directly with granulated materials. Screw-assisted EAM has gained importance as an enabling technology to expand the range of 3D printing materials, reduce costs associated with feedstock fabrication, and increase the material deposition rate compared to traditional fused filament fabrication (FFF). Many experimental printheads and commercial systems that use some screw-processing mechanism can be found in the literature, but the design diversity and lack of standard terminology make it difficult to determine the most suitable solutions for a given material or application field. Besides, the few previous reviews have offered only a glimpse into the topic, without an in-depth analysis about the design of the extruders and associated capabilities. A systematic procedure was devised to identify the screw-assisted EAM systems that can print directly from granulated materials, resulting in 61 articles describing different pieces of equipment that were categorized as experimental printheads and commercial systems, for small- and large-scale applications. After describing their main characteristics, the most significant extruder modifications were discussed with reference to the materials processed and performance requirements. In the end, a general workflow for the development of 3D printers based on screw extrusion was proposed. This review intends to provide information about the state-of-the-art screw-assisted EAM and help the academy to identify further research opportunities in the field.

The purpose of this paper is to present a selection method based on analytic hierarchy process in the form of a case study, which benefits from quantitative data to assess the performance of low-cost 3D printers. The market of personal 3D printers has experienced a major boost in the last decade, with an apparently ever-increasing number of companies producing and selling machines. The huge variety of models available under $5000 has turned the selection of 3D printers into a complex task, often involving multiple questions. Many benchmarking parts have been proposed as a mean of comparing the performance of these machines in relation to geometric, mechanical and process aspects, with no consensus about the optimal model for every situation. Also, several decision-making methods mostly based on qualitative evaluation have been applied in order to rationalize the selection of such equipment. The evaluation metrics considered in the procedure were derived from a general goal, organized in a hierarchical structure and then compared according to the context of the research. A real application model, from an innovative project, was fabricated by three different machines and then evaluated regarding multiple criteria with distinct importance. The evaluation included surface roughness, dimensional and geometric accuracy, building time and material usage measurements. The case study shows a less subjective way to evaluate the performance of such machines, which can be easily implemented by the academic and 3D printing communities, considering different scenarios and even diverse technologies.

Dedico este trabalho aos meu pais, Antonio e Eliana, à minha noiva, Diana, aos meus irmãos Luciano e Paulo, e a meu amigo Guilherme Donatti pelo apoio, ajuda e dedicação durante todos os anos de trabalho e pesquisa. AgradecimentosAos meus pais pela atenção, dedicação, paciência e por estarem a todo tempo a meu lado durante toda a caminhada.À minha noiva, Diana, pelo amor incondicional, companheirismo, dedicação e entrega perante todas as dificuldades.Aos meus companheiros de laboratório Joaquim Manoel Justino e Henrique Takashi Idogava pelos anos de parceria, pesquisa e aprendizado.À minha orientadora Zilda de Castro Silveira pela atenção e oportunidade de desenvolvimento pessoal e profissional frente à linha de pesquisa.Ao meu grande amigo Guilherme Donatti pelo empenho no desenvolvimento da pesquisa conjunta, pela oportunidade de crescimento profissional e por acreditar em todo meu potencial.Aos amigos Henrique Garcia, Larissa Castelucci e Leonardo Simião pelo acolhimento e amizade em momento de grande necessidade.Às minhas amigas Sarah Mayrink e Bárbara Mayrink por todo apoio, auxílio e companheirismo.À Ana Paula Martins pelos conselhos e ajuda na reta final da pesquisa.