A study on extruded ﬁlament bonding in fused ﬁlament fabrication Ana Elisa Costa IPC/i3N – Institute for Polymers and Composites, Department of Polymer Engineering, University of Minho, Guimarães, Portugal Alexandre Ferreira da Silva CMEMS-UMinho – Center of Electro Mechanical Systems, University of Minho, Guimarães, Portugal, and Olga Sousa Carneiro IPC/i3N – Institute for Polymers and Composites, Department of Polymer Engineering, University of Minho, Guimarães, Portugal Abstract Purpose – The performance of parts produced by fused ﬁlament fabrication is directly related to the printing conditions and to the rheological phenomena inherent to the process, speciﬁcally the bonding between adjacent extruded paths/raster. This paper aims to study the inﬂuence of a set of printing conditions and parameters, namely, envelope temperature, extrusion temperature, forced cooling and extrusion rate, on the parts performance. Design/methodology/approach – The inﬂuence of these parameters is evaluated by printing a set of test specimens that are morphologically characterized and mechanically tested. At the morphological level, the external dimensions and the voids content of the printed specimens are evaluated. The bonding quality between adjacent extruded paths is assessed through the mechanical performance of test specimens, subjected to tensile loads. These specimens are printed with all raster oriented at 908 relative to the tensile axis. Findings – The best performance, resulting from a compromise between surface quality, dimensional accuracy and mechanical performance, is achieved with a heated printing environment and with no use of forced cooling. In addition, for all the conditions tested, the highest dimensional accuracy is achieved in dimensions deﬁned in the printing plane. Originality/value – This work provides a relevant result as the majority of the current printers comes without enclosure or misses the heating and envelope temperature control systems, which proved to be one of the most inﬂuential process parameter. Keywords Mechanical properties, Fused ﬁlament fabrication, Dimensional accuracy, Bonding, Mesostructure Paper type Research paper 1. Introduction Fused ﬁlament fabrication (FFF) 3D printing process is possibly the most popular rapid prototyping manufacturing technique because of the low equipment prices, commercial availability of a large range of non-conventional ﬁlament materials (electrically conductive, reinforced, ﬂexible, magnetic, thermochromic, among many others) and huge variety of equipment, including multi-material capability and large printing volumes. The fast and recent developments led to a greater ambition: the use of this technique for the production of functional prototypes and small series of ﬁnal parts or products. This new paradigm requires demanding features, such as adequate mechanical performance and dimensional accuracy. However, and because of its intrinsic nature, the FFF process is not capable to take total advantage of the mechanical properties of the raw materials it uses, as the extruded paths (raster), deposited in successive rows and layers, are bonded with no extra pressure, or with a short duration compression during the deposition stage. In addition, the temperature of the previously deposited paths decreases during the printing stage and, hence, the thermal conditions for molecular diffusion between them are not the most favorable. In what concerns to the printed parts ﬁnal dimensions, there is some lack of control, since the extruded material shrinks upon cooling, experiencing different thermo-mechanical conditions. In fact, the temperature of the neighboring zones and the weigh supported by each extruded path vary in space and time along the printing stage. Furthermore, shrinkage cannot be constrained, contrarily to what happens in the majority of the conventional polymer processing technologies. The polymers used in this technique should present enough melt viscosity to preserve the deposited path shape and printed geometry until solidiﬁcation. On the other hand, to get a homogeneous part, adhesion and molecular diffusion between neighboring extruded paths is required. These two objectives, dimensional accuracy and mechanical performance, are, therefore, conﬂicting. Because of the relevance of the topic, the The current issue and full text archive of this journal is available on Emerald Insight at: www.emeraldinsight.com/1355-2546.htm Rapid Prototyping Journal 25/3 (2019) 555–565 © Emerald Publishing Limited [ISSN 1355-2546] [DOI 10.1108/RPJ-03-2018-0062] The authors acknowledge the funding by FCT with the reference projects UID/EEA/04436/2013 and UID/CTM/50025/2013, by FEDER funds through the COMPETE 2020 – Programa Operacional Competitividade e Internacionalização (POCI) with the reference project POCI-01-0145- FEDER-006941. Received 13 March 2018 Revised 11 August 2018 Accepted 11 August 2018 555 Downloaded by UNIVERSIDADE DO MINHO At 13:50 16 April 2019 (PT)