This paper aims to analyze the fatigue response of PLA parts manufactured through fused filament fabrication (FFF). The influence of four factors (layer height, fill density, nozzle diameter and velocity) on the fatigue performance of cylindrical specimens is studied through an L27 Taguchi experimental design. This design is run for two different infills: linear and honeycomb. Specimens have been tested on a rotating fatigue bending machine. The optimal set of parameters and levels resulting in the highest number of cycles to failure have been determined, and implemented to manufacture a second set of specimens, which have been tested at different stress levels to represent the Wöhler curve. Fill density proves to be the most influential parameter on fatigue life, followed by layer height. The tests undertaken to represent the Wöhler curve revealed that 35.8 MPa can be considered as a lower threshold of the endurance limit for this kind of specimens. This value can be useful to use these devices to manufacture human implants, as PLA is a biocompatible material. The main novelty of this paper is that no previous fatigue life assessment of PLA parts manufactured through FFF has been developed.Peer ReviewedPostprint (author's final draft

This paper aims to analyse the mechanical properties response of polylactic acid (PLA) parts manufactured through fused filament fabrication. The influence of six manufacturing factors (layer height, filament width, fill density, layer orientation, printing velocity, and infill pattern) on the flexural resistance of PLA specimens is studied through an L27 Taguchi experimental array. Different geometries were tested on a four-point bending machine and on a rotating bending machine. From the first experimental phase, an optimal set of parameters deriving in the highest flexural resistance was determined. The results show that layer orientation is the most influential parameter, followed by layer height, filament width, and printing velocity, whereas the fill density and infill pattern show no significant influence. Finally, the fatigue fracture behaviour is evaluated and compared with that of previous studies’ results, in order to present a comprehensive study of the mechanical properties of the material under different kind of solicitations.

The aim of this paper is to analyze the performance of a RepRap 3D printer liquefier by studying its thermal behavior, focusing on the convective heat dissipation developed along the liquefier body during the 3D printing process of a workpiece. More specifically, this work tackles with the influence of the airflow generated by a fan coupled to the extruder, on the heat transfer mechanisms during the printing process. The airflow is thus taken as the variable of study. The temperature at the top of the liquefier body, where a low temperature is desirable for the correct preservation of the 3D printer components, is analyzed to assess the results for the different printing conditions. For the development of this study, a finite elements model was used to determine the theoretical temperature profile of the liquefier in a steady state working regime. This mathematical model was then validated with experimental data registered with four thermocouples fixed on the tested extruder. The data was taken for different airflows, finding a relation between printing parameters and resulting tem- perature profile. The liquefier used for experimental data acquisition was the BCNozzle model, designed by the BCN3D Technologies of the Polytechnic University of Catalonia. Determining the correct working parameters is necessary to optimize the fused filament fabrication process on which 3D printing is based, ensuring a suitable temperature distribution along the liquefier body. This would allow a correct position of the melting front along the liquefier channel, and at the same time, a non-excessive temperature at its top, next to the feeding mechanism. This is the relevance of this study, through which a model is obtained to analyze the heat transfer mechanisms, applicable for other working regimes and other extruders based on the same working principles.Postprint (author's final draft

This paper explores the effects on the surface roughness, hardness and residual stress of G10380 steel specimens milled and treated with a ball-burnishing process assisted by vibrations. These vibrations are incorporated through the attachment of an induced coil module to a conventional burnishing tool, with forces transmitted through a pre-loaded spring. A positive effect of vibrations on the improvement and efficiency of the burnishing treatment is demonstrated, empirically proving that the vibrations introduce additional energy into the system that aids with displacements along the surface of the material to reallocate the crystalline structure. Significant results are found in terms of final surface roughness, which is highly improved in comparison to conventional burnishing treatments, even with fewer passes and a significant time reduction. Less robust results are observed in terms of specimen hardness and residual stress, but future improvements could be derived with a thorough development of the vibration system.

Ball-burnishing induces compressive residual stresses on treated materials by the effect of plastic deformation. The result is an increase in the fatigue life of the treated part, retarding the initiation of cracks on the surface. Compressive residual stresses have been previously measured by X-ray diffraction near the surface, revealing considerably high values at the maximum analyzed depth, in relation to other finishing processes such as shot peening. However, the maximum analyzed depth is very limited by using this technique. In this paper, the incremental hole drilling (IHD) technique is tested to measure residual stresses, being able to reach a 2-mm measuring depth. To that objective, a commercial strain gage is used and calibrated using finite element model simulations. A second Finite Element Model based on material removal rate is developed to obtain the equations to calculate the strain release through IHD. Finally, residual stresses are measured experimentally with that technique on two different materials, confirming that ball-burnishing increases the compressive residual stresses in layers up to 0.5¿mm deep for the testing conditions, which is a good response to industrial needs. The method proves to be suitable, simple and inexpensive way to measure the value of these tensions.Preprin