Development of a calculation routine that determines the local interlayer strength of plasticizing additively manufactured components
The advantages of additive manufacturing processes are always offset by the disadvantages of the anisotropic mechanical component characteristics caused by the process. One particular challenge is the significantly lower interlayer strength in the build-up direction compared to the strength within the respective individual layer level. In the “Interlayer strength of plasticizing AM” project, a calculation routine was therefore developed that determines the local interlayer strength of plasticizing additively manufactured components as efficiently as possible before production.
The interlayer strengths were determined on the basis of the geometric information and production parameters stored in the machine code. The calculation routine consists of two sub-routines that build on each other. The first sub-routine is used to calculate the local temperature curves in the interlayer area and is based on the manufacturing parameters and geometric component information stored in the machine code. The second routine is used to calculate the local interlayer strength and uses the simulated temperature curve as the basis for the calculation. To validate the calculated temperature curves, an option for process-integrated recording of the process temperature was implemented for both fused filament fabrication (FFF) and the screw extrusion process (SEP).
The FEA program package Abaqus including the “AM Modeler” plugin was used to simulate the additive manufacturing process and the associated determination of interlayer temperature and strength. The plugin was used to model the time-dependent incremental strand and layer-by-layer manufacturing principle of the SEP and FFF process for any given part. Part volume elements were successively activated and a temperature was transferred. The part geometry was defined by importing an STL file into the simulation environment. The component geometry was then overlaid with an “event series” containing the production path information.
© IKVA comparison of the experimentally determined interlayer temperatures with the simulated interlayer temperatures during strand deposition shows good agreement. The results clearly show that the process simulation robustly predicts the interlayer temperatures. The calculation of the interlayer strength is based on the de Gennes reptation model. A routine developed at IKV for predicting the weld line strength of amorphous thermoplastics was used as the basis for calculating the healing (Hopmann, Ch.; Onken, J.; Untersuchung der prozess- und geometrieabhängigen Zug- und Schubfestigkeit von Bindenähten in Polystryol, Kunststofftechnik 15 (2019) 2, pp. 148-168). The prediction of the routine provides an indication of the extent to which the theoretical strength is achieved in the calculated healing process. The calculated stress in the simulation reaches a similar order of magnitude as the real tensile test used for validation. As no other mesostructural influences are taken into account in the calculation of the tensile strength, a higher tensile strength is possible in the simulation compared to the real tensile test.
Details and funding
Project title: Development of a method for improved prediction of local mechanical component properties for plasticising additive manufacturing processes
Short title: Inter layer strength plasticising AM
Project duration: 03/2022 – 03/2024
Contact at IKV: Tibor Fritsch, M.Sc. RWTH
Funding by: Bundesministerium für Wirtschaft und Klimaschutz, IGF-Vorhaben 22191 N
