Improving inner structure and properties of additive manufactured amorphous plastic parts: The effects of extrusion nozzle diameter and layer height

Abstract

Material extrusion is an efficient additive manufacturing process for thermoplastic materials in the field of rapid prototyping, rapid tooling, rapid manufacturing and rapid repair. Parts to be additive manufactured of acrylonitrile butadiene styrene (ABS Terluran GP 35) with mechanical properties close to the data sheet specification of injection molded parts are in the focus of this study. An in-house process chain from the plastic pellets to the finished additive manufactured product is developed to monitor and to define the process parameters for each individual processing step using the terpolymer. By varying the parameters extrusion nozzle diameter and layer height, the production-related internal part structure and the surface topography of the additive manufactured tensile test specimens are improved in such a way that the mechanical property yield strength rises from 55% to 75% of the data sheet specification for injection molded ABS parts. The elongation at break increases from 42% up to 70% of the specified data. The smallest extrusion nozzle diameter in connection with the smallest layer height provide the densest internal part structure, the lowest surface roughness and the best mechanical properties. Especially the ductility was controlled by the manufacturing parameters since the number of pores introduced in the internal part structure determine the number of crazes. Apart from ductility, even with low layer height but larger extrusion nozzle diameter, the resistance to failure of the material extrusion manufactured parts improves significantly and saves manufacturing time by a factor of 10.