Adhesive bonding of FDM-manufactured parts made of ULTEM 9085 considering surface treatment, surface structure, and joint design

Additive manufacturing has become increasingly popular over the past years. One of the most commonly used additive manufacturing process is the fused deposition modeling (FDM). In FDM, components are produced by depositing a molten plastic filament layer by layer on a build platform. The deposition takes place in a heated build chamber. Despite the many positive characteristics, the process principle leads to one main disadvantage. The maximum size of FDM-manufactured parts is limited by the size of the build chamber. Bigger parts can only be realized as an assembly group. Adhesive bonding is a commonly used joining method in the industry to produce resilient parts especially for lightweight applications and to join dissimilar materials. The aim of this study is to investigate the influence of the adhesive type, the surface character of FDM parts, and the design of the bond area on the bond strength. The parts to be investigated are made of ULTEM 9085. Six different adhesives (acrylate resin, polyurethane adhesive, and epoxy resins) and their compatibility with the ULTEM 9085 parts are investigated. Considering the surface character, the influence of different pretreatments (mechanical roughening, plasma activation) and different surface structures are tested. The surface is modified by adding a positive air gap and an interface structure, and by varying the raster angle of the top layer. Regarding the design of the bond area, six different designs (finger, scarf, butt, tongue-groove, t-peel, and overlap joint) are investigated. The results show that the maximum lap shear strength can be achieved by using two-component epoxy resins. The adhesion between the ULTEM 9085 and the polyurethane as well as for the acrylate resin is insufficient but can be increased by roughening the surface mechanically or by adding a positive air gap to the surface. The investigations also show a positive effect of the plasma treatment but only for the combination of ULTEM 9085 with the polyurethane adhesive. The best results for different bond designs are reached with the scarf and the finger joint.