How does varying the layer height in FDM printing primarily affect part strength in the Z-axis?

Varying the layer height in FDM (Fused Deposition Modeling) printing primarily affects part strength in the Z-axis by influencing the interlayer bonding. Layer height refers to the thickness of each individual layer deposited during the printing process. A smaller layer height generally leads to increased Z-axis strength because it increases the contact area between adjacent layers. This increased contact area provides more opportunity for the molten filament to fuse together, creating stronger bonds. This is because the thinner layers cool more quickly allowing for better fusion and minimizing cooling stresses within each layer. Conversely, a larger layer height reduces the contact area between layers, potentially weakening the bonds in the Z-axis. While larger layer heights can speed up printing, they may compromise the structural integrity of the part, especially when stress is applied perpendicular to the layers. For example, a part printed with a 0.1mm layer height will generally exhibit greater tensile strength in the Z-axis compared to an identical part printed with a 0.3mm layer height, assuming all other printing parameters are held constant.