Enhancing Tensile Strength of FDM parts using Thermal Annealing and Uniaxial Pressure
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Additive manufacturing has been a revolutionary and disruptive technological development in the field of design and manufacturing with Fused deposition modelling (FDM) being at the forefront of this technology. But it is seen that parts printed using FDM suffer from an inherent deficiency of weak tensile strength in the out of plane direction (z-direction) thus limiting their application. This issue of weak z-direction strength is due to the weak Inter-bead bond strength of adjacent polymer interfaces. The purpose of this work is to increase this Inter-Bead bond strength thus increasing the overall tensile strength of the part. In this work, FDM was used to print tensile specimens made of Acrylonitrile Butadiene Styrene (ABS), which were subjected to varying values of isothermal heating and uniaxial pressure which was along the z-direction. Multiple values of temperature and pressure were chosen to investigate their effect of the deformation of the part and try to maintain geometric accuracy. The thermally annealed parts were then subjected to tensile loading to check the increase in strength. It was seen that when the parts were subjected to only thermal annealing there was a slight increase in the tensile strength of the part. But when the parts were subjected to a combination isothermal heating and pressure the increase in strength was considerably more as compared to only thermal annealing for the same time period. A cross sectional view of the layer to layer bonding was studied under the microscope which showed a change in the mesostructure of the part. From previous studies it had been seen that when two polymer interfaces have intimate contact while undergoing thermal annealing above the glass transition temperature Reptation occurred. This theory of Reptation was seen to be the reason for the considerable increase in strength and lead changes in the mesostructure of the part. The investigations done in this study provide ground work to increase the total structural strength of the parts with a special focus on the inter laminar bonding which affects the z-direction strength.