Process Parameters Effects
Manufacturing constraints and build parameters, including process and printing parameters, affect the geometry, surface finish, microstructure, and mechanical properties of the printed components. This has been shown that component properties are significantly affected by parameters such as infill patterns (stacking sequence), air gap, printing orientation, road width, build layer thickness, extruder temperature, envelope temperature, and speed of deposition. Some of these parameters are shown in Fig. 1.
Fig. 1. Demonstration of the different involved printing and process parameters for FDM technology. Source: K.P. Dissertation
The fracture strength of extruded beads is affected by the initial wetting stage. Studies found that the initial wetting stage was significant at a slower cooling rate and resulted in strong bonding between layers to improve the component strength.
Components printed by FDM exhibit orthotropic material properties in terms of strength and stiffness, i.e., module of elasticity, yield, and ultimate stresses. These properties are subjected to different build parameters, including deposition strategy, orientations, void spaces between layers, and the bonding between the road in inter- and intra-layers. These parameters substantially alter the microstructures and govern the meso-structure of the printed components. For example, print orientation significantly alters the mechanical properties of the 3D printed components not only in polymeric base 3D printers but also in metal components. Surface finish is another critical factor affecting the performance, fatigue, and the endurance of AM components. Higher temperatures, lower layer thickness, and slower deposition speed are reported to improve the surface finish in FDM components.
In addition, raster orientation, part orientation, layer thickness, and air gap had a substantial effect on tensile strength, whereas other parameters such as raster width, contour width, extruder temperature, and color have little to no influences. Maximum mechanical properties have been reported when the applied force and the raster orientation occur in parallel.
Fig. 2. Schematic of deposition of the filament considering different W-to-D ratio and height(H): (a) As the bonding is developed between to contagious bead (road) while contact quality increases, the initial width (W) of the deposited bead reduces, and (b) front and side view of the filament deposited by extruder. Source: K.P. Dissertation
Also, it is becoming increasingly important to look into the effects of build parameters on microstructure, inter- and intra-layer bonding, and the presence of cavities, particularly for new high-performance and high-temperature polymeric materials such as PEEK, PEI, and composite polymers. The microstructure has significant influences on mechanical characteristics. Studies indicated that selection of the build parameters, such as raster orientation and air gap, required educated consideration to fulfill the uniform density inside the part, mainly made from new materials, which demand higher temperature for the extruder and actively controlled condition during printing. This extended consideration has to be addressed with further process optimization.
Residual stresses and distortion in 3D printed components by FDM have been exhibited on the bottom layer, and the increased number of layers imputed to the higher distortion and eventually greater stresses. Increasing the envelope temperature, decreasing the glass transition temperature, or CTE of materials also contributes to decreasing the distortion in 3D printed components. One hypothesis has suggested that high-temperature gradient and heat flux due to rapid cooling and heating cycles contributes to this phenomenon.
In summary, these studies suggest properties and characteristics of 3D printed components strongly depends on layer thickness, air gap, scan (extruder) speed, build orientation, raster angel, and envelope temperature; other parameters, such as raster width, contour width, number of contours, feed rate, and nozzle temperature, were observed to be less significant.