Additive manufacturing processes, like the Fused Deposition Modeling (FDM) process, do not need product-specific tools and create parts directly from the CAD data. In the FDM process, the semi-finished product, a wire of a thermoplastic polymer, is melted and forced through a nozzle. The continuous positioning of this nozzle allows the polymer to weld together strand by strand and layer by layer to produce a component. Because no mold is used in the FDM process, no holding pressure can be generated as in injection molding processes, in which the holding pressure is used to minimize the shrinkage and warpage of the part.
In the FDM process, the part is generated in an ambient pressure environment. Each strand cools down and shrinks separately. This causes residual stresses in the part that can lead to major warpage and a complete stoppage of the process. This is the main reason why the material selection in the FDM process is restricted in comparison to conventional polymer processing technologies.
In this paper, the warpage of different polymers is quantified as a criterion for evaluating the processability of polymers in the FDM process. Due to the process principle, the part properties in the FDM process are mainly influenced by the machine quality and the data processing, so that it is difficult to test a material for FDM independently of the machine and the data processing. Considering these influences, a custom-built specimen is created to test and quantify the warpage of different types of blended and reinforced polyamide 6. Considering the experimentally investigated warpage, the materials can be evaluated and the warpage can be related to the shrinkage investigated in pvT measurements.
This procedure allows the machine- and process-independent rating of the processability in terms of warpage for different materials. Alongside other criteria, this is a necessary step to develop new materials with good processability in the FDM process.