Investigation of the Pull-Out Behaviour of Metal Threaded Inserts in Thermoplastic Fused-Layer Modelling (FLM) Components

Abstract

To provide detachable, secure and long-term stable joints in fused-layer modelling (FLM) components or assemblies, metal threaded inserts are widely used as extrinsic interfaces. However, the load-bearing capacity of such inserts is influenced by the inhomogeneous, anisotropic material structure of the FLM components. This work evaluates the influence of the joining zone design and the printing process parameters on the achievable joint properties. Therefore, we printed thermoplastic FLM test specimens with varying parameters for infill density, wall thickness, layer height and nozzle temperature. Subsequently, metal threaded inserts were warm-embedded into the test specimens and investigated in quasi-static pull-out tests. The results show that the infill density in the joining zone has the largest impact on the joint strength and should be 70% or higher. Furthermore, an analysis of different wall thicknesses around the pre hole shows that a minimum value of 2.4 mm is required for the selected insert geometry to achieve a high pull-out force. Increasing the wall thickness beyond this value does not significantly affect the joint strength. The results provide an improved base for detailed understanding and interface design in FLM components for the integration of metal threaded inserts as well as for further investigations regarding different printing materials and load types.

Keywords

• additive manufacturing
• fused-layer modelling
• joining
• metal threaded insert
• pull-out test