Enhancing heating uniformity of radio frequency additive manufacturing via functional grading

Abstract

Radio Frequency Additive Manufacturing (RFAM) is an additive manufacturing process that utilizes Radio Frequency (RF) radiation as the sole heat source to heat and sinter an entire object simultaneously. Parts are fabricated selectively from powders, similarly to powder bed fusion but with RF radiation replacing laser or electron beams as the energy source. Typical polymer powders, such as nylon 11 or 12, are relatively transparent to RF energy sources, but polymer powders that are doped with conductive additives selectively absorb RF energy. By depositing electrically conductive dopants into selective regions of an insulating polymer powder bed, those regions of the powder bed can be sintered quickly and volumetrically via RF radiation into engineered parts. Previous work demonstrated that heating uniformity is a challenge related to the dopant density and the geometry of the part, but simulations suggested that it can be addressed by functionally (spatially) grading the dopant density. In this work, those simulation-based, functionally graded designs are fabricated for the first time via a combination of binder jetting additive manufacturing and sintering in an RF heating apparatus. The heating uniformity and geometric accuracy of the functionally graded samples are evaluated and compared to that of uniformly doped samples. The results show that functionally graded samples exhibit enhanced heating uniformity and improved geometric accuracy.