Assessment of Crystallinity Development during Fused Filament Fabrication through Fast Scanning Chip Calorimetry

Abstract

Although semi-crystalline polymers are associated with considerably better mechanical properties and thermal stability compared to their amorphous counterparts, using them as feedstock for Fused Filament Fabrication still poses some major challenges. Hence, the development of printed part crystallinity during printing should be fully understood in order to control the developed weld strength, as well as part shrinkage and warpage. Infrared thermography was utilized to record the thermal history of deposited layers while printing a single-layer wall geometry, employing two PA 6/66 copolymers with distinct molecular weights as feedstock. Print settings were varied to establish which settings are essential to effectively monitor final part crystallinity. The resulting temperature profiles were simulated in a Fast Scanning Chip Calorimetry device that allows for the rapid heating and cooling rates experienced by the printed polymer. Both liquefier temperature and print speed were found to have very little influence on the total attained crystallinity. It became apparent that the build plate, set at a temperature above the polymer’s glass transition temperature, imposes a considerable annealing effect on the printed part. A reduced molecular weight was observed to enhance crystallinity even more strongly. The presented methodology proves that Fast Scanning Chip Calorimetry is an effective tool to assess the impact of both print parameters and feedstock characteristics on the crystallization behavior of semi-crystalline polymers over the course of printing.

The effect of build orientation on both flexural quasi-static and fatigue behaviours of filament deposited PA6 polymer

“…Another challenge to print PA6 is that they prone to warping. One of the reasons for warping is the semi-crystallinity of the PA6 polymers [26] , [27] , [28] , [29] . Another reason is the temperature differences through the thickness.…”

“…A key reason for their limited use is attributed to their severe shrinkage and warpage that occurs during part cooling and crystallization. Polymers with high crystallinity distort and warp more during FFF process, in comparison with amorphous plastics, due to the considerable volume reduction associated with the formation of ordered, more densely packed regions during crystallization [26] , [27] , [28] . This causes parts that are fabricated with polyamide to warp more and detach from the build platform, compared to those with ABS [29] .…”

The Study of Physico-Mechanical Properties of Polylactide Composites with Different Level of Infill Produced by the FDM Method

“…The aim of this study was to evaluate changes in physical-mechanical properties of the samples manufactured by 3D printing technology using PLA that is subsequently subjected to crystallization. Such studies have, of course, already been discussed by other researchers who indicated the positive effect of PLA crystallization on mechanical properties [5,6,[32][33][34]. Feng also discusses the impact of water absorption by the samples produced by the 3D method on their mechanical properties (which are known to be sensitive to water ageing).…”

Additive Manufacturing for Self-Healing Soft Robots

“…Owing to the low viscosity and the self-healing character, the typical layer and line marks of the 3D-printing process (FFF) are not visible after printing, as is clearly shown in Figure 7b. Owing to the continued elevated temperature after deposition, due to both the heated bed and the deposition of layers on top, 41 the successive layers become covalently bonded to each other without the need of post-treatments. This allows to print airtight components, an important feature in soft pneumatic robotic systems.…”