Sintering simulation and validation for the sinter-based fused filament fabrication process route

Abstract

Fused Filament Fabrication (FFF) process is one of the widespread additive manufacturing processes and is also used for printing numerous metal feedstocks besides polymers. Metal Fused Filament Fabrication (MFFF) offers a huge potential for complex metallic parts. When manufacturing metal components using sinter-based additive manufacturing, the sintering process poses the greatest challenges. Additively manufactured green parts shrink by up to 30% during sintering depending on factors, such as material composition, process variables during printing and sintering as well as the geometry of the green part. To predict shrinkage and support the development of new components a simulation is helpful to reduce defect production, improve dimensional accuracy, systematize the process and detect undesirable deformations. As a plus, the simulation improves the understanding of the process chain. Sintering simulation has been used recently for different manufacturing technologies apart from MFFF printed components. As part of this paper, the commercial and established software Simufact Additive from Hexagon AG is applied to MFFF components made of the material SS316L, using a module which was intentionally developed for Metal Binder Jetting-based process routes. The effects of MFFF proprietary process parameters and two sintering cycles with different parameters (sintering temperature, holding time, and heating rate) on the properties of the metallic components were examined. The investigations show that the results of commercially available software for binder jetting can be applied in principle. However, a systematic deviation occurs showing a gap between shrinkage rates of simulation and experiment. One reason for the deviation is not calibrating the material model for constants, such as Coulomb friction, grain growth and sinter stress. Their effect in combination with the characteristics of the MFFF process with its creation of voids leads to an offset in the evaluation of the shrinkage. It was demonstrated that typical characteristics of the MFFF process, such as printing-induced voids, can be effectively mapped and considered within the simulation framework. However, incorporating these features alone did not fully resolve the deviations between simulated and experimental results. A key source of this discrepancy is the use of suboptimal sintering temperatures (1137 °C and 1270 °C), which fall below the ideal densification range for SS316L. These conditions not only limited final density but also contributed to significant deformation, especially in geometrically complex parts. Nevertheless, the study showed that Simufact Additive, although originally developed for binder jetting, is applicable to the MFFF process to a certain degree. For a simple cuboid geometry, the simulation achieved an absolute shrinkage and final density deviation of approximately 3%, corresponding to a 25% relative standard deviation. This work serves as a practical example and initial guide for simulation-assisted design and sintering process optimization in industrial MFFF applications.