Processing rate and energy consumption analysis for additive manufacturing processes : material extrusion and powder bed fusion

Abstract

Additive technologies have given birth to an expanding industry now worth 5.1 billion dollars. It has been adopted widely in design and prototyping as well as manufacturing fields. Compared to conventional technologies, additive manufacturing technologies provides opportunity to print unique complex-shaped geometries. However, it also suffers from slow production rate and high energy consumption. Improving the rate and energy becomes an important issue to make additive manufacturing competitive with conventional technologies. Among all the different limiting factors including printing strategy, heat transfer and mechanical movement limitations, heat transfer is the fundamental limiting barrier preventing further improvement the production rate. This thesis looks at the heat transfer mechanisms in material extrusion and powder bed fusion processes. In all the models developed for these two processes, processing rate is bounded by an adiabatic rate limit at which all the input energy is perfectly utilized to heat up the material to its molten/flowable state. In material extrusion, fused deposition technology suffers low throughput due to poor conductive heat transfer, big area additive manufacturing technology achieves high throughput by introducing viscous heating at the cost of resolution. In powder bed fusion, due to the intensive laser heating, the process window is limited to ensure high density material while avoid excessive evaporation. Further study quantifies the inefficiency from heat transfer mechanisms which leads to lower processing rates than the adiabatic rate limit. Energy consumption for material extrusion and powder bed fusion machines are reviewed to evaluate significance of energy consumed to heat up the material. For fused deposition technology, most of the energy is consumed by environment heating; while for powder bed fusion technology, laser unit takes the most energy. Life cycle energy consumption for products made with powder bed fusion process is compared with same/similar parts made from conventional manufacturing processes to explore scenarios in which manufacturing with additive technologies is less energy intensive.