In Fused Filament Fabrication (FFF) the strength of the parts is weakened through the great amount of welding lines in contrast to for example injection moulding. The strength of the welding of the strands in vertical and horizontal directions depends strongly on the material and the processing parameters.
Due to the deposition behavior, temperature gradients and therefore thermal stresses will be generated during the printing. Hence, the parts tend to warp and as a result they can separate from the printing bed. Especially higher crystalline materials, such as polyolefins exhibit high warpage and are therefore prone to detaching from the bed and/or to delaminate between the layers.
In order to get a better understanding of the interaction between the strands and the printing bed, different measurements were performed.
In a first step, contact angle measurements between polymers, various printing bed surfaces and different solvents were conducted at room temperature, to obtain the polar and dispersive components. Out of them the interfacial tension between two solids was calculated.
To detect the influence on the bonding strength at different processing parameters, fracture mechanical tests for composite materials were performed. It is assumed that anisotropic material behavior dominates the structure of the parts and consequently the testing and description for composite materials can be applied.
Finally, an adhesion force device measuring the forces needed to remove a single polymer strand from the printer bed was developed. This test should give a better understanding of the adhesion forces between the bed and the material.
For high-quality parts and failure-free printing it is of great importance to investigate further into adhesive forces, as well as the bonding of the strands in 3D printing.