Increasing of Strength of FDM (FFF) 3D Printed Parts by Influencing on Temperature-Related Parameters of the Process

Abstract

Current work investigates how user-controlled parameters of 3D printing process define temperature conditions on the boundary between layers of the part being fabricated and how these conditions influence structure and strength of the part. The process studied is fused filament fabrication with a desktop 3D printer and the material utilized is PLA (polylactic acid). As a characteristic of the part strength the fracture load in the case of a three-point bend and calculated related stress were used. During the printing process parts were oriented the long side along the Z axis, thus, in the bend tests, the maximum stress occurred orthogonally to the layers. During the fabrication process temperature distribution on the samples surface was monitored with thermal imager. Sample mesostructure was analyzed using SEM. The influence of the extrusion temperature, the intensity of part cooling, the printing speed and the time between printing individual layers were considered. The influence of all the parameters can be expressed through two generalizing factors: the temperature of the previous layer and the flow efficiency, determining the ratio of the amount of extruded plastic to the calculated. A regression model was proposed that describes the effect of the two factors on the printed part strength. Along with interlayer bonding strength, these two factors determine the formation of the part mesostructure (the geometry of the boundaries between individual threads). It is shown that the optimization of the process parameters responsible for temperature conditions makes it possible to approximate the strength of the interlayer cohesion to the bulk material strength.

Optimization of the 3D Printing Parameters for Tensile Properties of Specimens Produced by Fused Filament Fabrication of 17-4PH Stainless Steel

“…While presenting individual parameter, the other two are maintained at mean values. The results of the tensile strength dependence on the extrusion temperature are also in agreement with the results obtained for PLA [49,[62][63][64], in which an increase in extrusion temperature led to higher tensile strengths. The increase in tensile properties can be explained by the improved fluidity (decreasing viscosity) of the material, which decreases flow resistance as it passes through the nozzle.…”

Hardware Factors Influencing Interlayer Bonding Strength of Parts Obtained by Fused Filament Fabrication<strong></strong>

“…It is worth mentioning that the sample design (shape and dimensions) was originally verified for use with UM2 3D printer. No issues with samples stability while printing with UM2 were observed neither in current nor in earlier studies [25,30]. However, all other machines in the study incurred Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 9 May 2019 doi:10.20944/preprints201905.0108.v1…”

“…Recent studies [25,30] have introduced and verified a relatively simple and informative technique for evaluating the interlayer bonding strength of a part obtained with FFF. The technique is based on three-point bending procedure with loading a sample printed with a long-side oriented along the Z axis ( Figure 1).…”

“…The thickness of the tube wall was defined by the "shell thickness" parameter and was set to 2.4 mm. The choice of this exact shape and sample size was determined by the desire to obtain data compatible with previous studies [25,30]. It is worth mentioning that the sample design (shape and dimensions) was originally verified for use with UM2 3D printer.…”

“…Modern slicers allow to set any values (including those beyond physical capabilities of a particular 3D printer) to any parameters, including but not limited to layer thickness, hotend and bed temperatures, linear motion speed, acceleration, cooling fan speed. There are many recent studies on different parameters influencing printed parts strength, including extrusion temperature [21][22][23][24][25], layer thickness [26][27][28][29][30][31], printing speed [25,29,32], part orientation [27,29,31,33,34] and constitution [27,35,39,40]. However, the findings often do not fit together, or even can come to direct contradiction.…”