Root structure design for hybrid manufacturing of multi-material structures

This research proposes a joining method between a metallic substrate and an additively manufactured (AM) polymer part without the use of adhesives or fasteners. Ideally, a polymer could be extruded onto a metallic substrate with sufficient bond strength; however, due to the characteristics unique to each material, adhesion does not occur. This research investigated an alternative joining method using a root structure of polymer imbedded into the metallic substrate. As the use of hybrid manufacturing methods continues to increase, the proposed method presents an ability to create in-envelope multi-material structures without the need to re-fixture parts. The objective of this work is to identify a relationship between the design characteristics of the root structure geometry and the strength of the connection. In this work, two different experiment groups were designed to investigate this relationship. The first group utilizes physical experimentation and is broken down into three experiments. First, a baseline of strength was established by creating and testing ASTM 638 samples of material printed via the PE-1 extruder from Hybrid Manufacturing Technologies at three different printing temperatures. Second, five different root structures were created via conventional tools and tensile tested to determine the strength of each root structure. Third, samples were created using one root structure at three different temperatures for both printing and substrate pre-heating to evaluate the effect on shear strength. The second experiment group consists of an FEA investigation to study the effect of root structure geometry and parameter settings on strength. The impact of this work is in providing a new method for joining dissimilar materials in a hybrid manufacturing system and lays the groundwork for a mathematical model to aid in the design of root structure geometries depending on the application of the multi-material system