For small batches, prototypes, and customized mass production, additive manufacturing is a prominent technology in the production of complex thermoplastic parts. A frequently used process is Fused Deposition Modeling (FDM). For more and more applications, additive manufactured components have to be joined in order to form larger functional assemblies. Laser transmission welding (LTW) of thermoplastics is an industrial established technique, e.g. for joining injection molded parts in the automotive sector. Compared to injection molding, the FDM process itself results in an inhomogeneous structure with a significant amount of air inside a component. Because the part is built up layer by layer, it supports the formation of cavities inside the weld seam and thus a reduction in the weld seam strength. To optimize the weld seam quality, new strategies for the design of FDM parts for LTW are being investigated. Welded parts are being analyzed with tensile testing and cross sections.