Factors affecting interface bonding in multi-material additive manufacturing

Abstract

Additive Manufacturing (AM), also known as 3D printing, is the fabrication of products through the addition of materials layer-by-layer. Multi-material additive manufacturing (MMAM) techniques produce parts of two or more materials, where assembly operations can be avoided. Therefore, FFF MMAM is a technique that allows the use of multiple materials in fused filament fabrication (FFF) to create a single printed product. The aim of this dissertation was to study the factors affecting MMAM. The objectives to reach that aim included reviewing existing works based on MMAM, mainly polymer FFF, where the material combinations, the printing parameters and types of testing were understood and examined. Other objectives included the design of part(s) relevant to this case study, conducting design of experiments (DOE) based on design, materials, and processing parameters, and carrying out parts’ performance test, and analysing the results. With regard to equipment used, the E3D Multi-Material Filament 3D Printer was utilised throughout this study. This study comprehensively started with a material selection based on several criteria such as, the weldability of two polymers, whether the material combination had been already studied, the availability of the materials in filament form, whether the polymers are from dissimilar monomers, within the E3D processing temperature and ensuring that the chosen polymers have different characteristics in terms of toughness and brittleness. The chosen polymer combination was PC and PMMA. Assembly and machine calibration of the E3D printed were also accomplished. Additionally, two designs of experiments were conducted for the order of printing the two materials. This included a 1/2 2-Level Fractional Factorial Design where the main processing parameters which affect the interface bonding of polymeric materials were examined such as the layer thickness and the raster width. Moreover, the design and testing of the multi-material parts was limited to lap-shear testing adopted from lap-shear standards for adhesives to understand and evaluate the impact of the DOE factors on lap-shear strength. From the obtained results, it was concluded that the interface bonding of the PMMA/PC specimens was stronger than for the PC/PMMA specimens. Furthermore, additional designs of the PMMA/PC specimens were completed to determine whether the different contact areas influence the interface bonding. However, this was not the case as strong interface bonding was still obtained.