Additive Manufacturing Methods for Soft Magnetic Composites (SMCs)

Abstract

Currently, electromagnetic core designs are limited by silicon steel laminations, which are used to reduce eddy current losses. Steel laminations are difficult to shape into complex designs and create significant waste during processing. They are expensive to manufacture in complex shapes for novel motors which is why powder metals, more specifically soft magnetic composites (SMCs), are a promising alternative to laminations [1]. These composites are made from ferromagnetic powder particles, such as iron powder, and a thin insulating coating that separates each particle. The selection of iron-based powder, such as pure iron or an iron-nickel alloy, is based on whether AC or DC magnets are involved in the final assembly [1-2]. The coating on the SMC can be either an organic, or inorganic coating. SMC cores made from organic (polymer) bonded iron particles should have a low polymer content, which ultimately reduce the physical strength of the core [1]. Additive manufacturing is the creation of a three-dimensional object from a computer-aided design (CAD) model by adding material layer by layer. AM systems for metallic particles can be classified into three main areas: powder bed systems, powder feed systems, and wire feed systems [3]. Powder bed fusion consists of selective laser melting (SLM) and direct metal-laser sintering (DMLS). These methods use a laser beam to scan over an evenly spread out powder bed, selectively melting portions of the powder. Once the laser sinters the beads, another layer will be spread on top. After the printing is complete, the resulting product is retrieved from the powder bed [4]. Binder jet printing works by applying an adhesive binder, either silicate or an aqueous-based, onto a layer of powder and then briefly heating it to partially cure. Once the previous layer of beads is together, another layer will be spread on top by raking powder across the work area. This process is completed until it forms into the desired shape. The final shape is then cured in a furnace at a fixed temperature for a varying amount of time to obtain the desired density. The longer the SMC is cured, the higher the density will be [1-3]. Powder bed fusion, on the other hand, is the main method of additive manufacturing in industrial settings for metallic materials. Samples of iron powder coated with phosphorus were printed using the binder-jet printing process and the direct metal laser sintering process. The binder-jet samples were cured for one hour at 1500°F to burn off the binder, and then held at 2300°F for one hour to allow for densification. The DMLS printed samples were printed on a rotating bed printer which alters the