Correlations of Geometry and Infill Degree of Extrusion Additively Manufactured 316L Stainless Steel Components

Indirect Induction Sintering of Metal Parts Produced through Material Extrusion Additive Manufacturing

Avoiding loose powders and resins, material extrusion additive manufacturing is a powerful technique to produce near-net shape parts, being a cheap and safe alternative for developing complex industrial-grade products. Filaments embedded with a high packing density of metallic or ceramic granules are being increasingly used, resulting in almost fully dense parts, whereby geometries are shaped, debinded and sintered sequentially until the completion of the part. Traditionally, "brown" debinded geometries are transported to conventional furnaces to densify the powder compacts, requiring careful tailoring of the heating profiles and sintering environment. This approach is decoupled and often involves time-consuming post-processing, whereby after the completion of the shaping and debinding steps, the parts need to be transported to a sintering furnace. Here, it is shown that sintering via indirect induction heating of a highly filled commercially available filament embedded with stainless steel 316L powder can be an effective route to densify Fused Filament Fabricated (FFF) parts. The results show that densities of 99.8% can be reached with very short soaking times, representing a significant improvement compared to prior methods. A hybrid machine is proposed, whereby a custom-built machine is integrated with an induction heater to combine FFF with local indirect induction sintering. Sintering in situ, without the need for part transportation, simplifies the processing of metal parts produced through material extrusion additive manufacturing.

Additively Manufactured 316L Stainless Steel Subjected to a Duplex Peening-PVD Coating Treatment

This research studies the individual and combined effects of mechanical shot peening and the deposition of TiAlCuN coating on additively manufactured 316L stainless steel. Shot peening has been found to induce a 40% increase in surface hardness, while the combined effect of shot peening and the coating produced an approximately three-fold increase in surface hardness when compared to the as-printed coupons. Shot peening reduced the surface roughness of printed metal coupons by 50%, showing that shot peening can also serve to improve the surface finish of as-printed 316L stainless steel components. The peening process was found to induce a compressive residual stress of 589 MPa, with a maximum affected depth of approximately 200 μm. Scratch testing of the printed and coated specimens showed complete delamination failure at a normal load of 14 N, when compared to hybrid treated samples which failed at 10 N. On the other hand, from the corrosion tests, it was found that the hybrid treated samples provided the optimal results as opposed to the other variables.

Mechanical Characterization of AISI 316L Samples Printed Using Material Extrusion

The main additive manufacturing (AM) methods to produce metal components are laser powder bed fusion and directed energy deposition, which are energy-intensive, time-consuming, and require high investment costs. An economical alternative is based on a new feedstock comprising a homogenous mixture of sinterable metal powders and a multi-component binder system. This feedstock enables the creation of metal components printed using the material extrusion (ME) technique. In this study, mechanical characterization of AISI 316L samples is conducted to identify the mechanical properties of parts printed using the metal ME process. The test results indicate an average maximum tensile stress of 426.6 ± 23.7 MPa and an elongation at break of 36%. Both the tensile and compressive yield stresses are approximately 150 MPa, demonstrating a symmetric response to the two opposite types of uniaxial loads. Rockwell B and Vickers hardness tests confirm the uniform behavior of the tested material. An X-ray diffraction analysis is conducted to assess the crystallographic structure of the ME 316L samples compared to that of the monolithic material. According to our study results, metal ME seems to be a promising technology to produce non-critical metallic parts that require good mechanical properties, good corrosion resistance, and complex shapes such as chemical tanks, heat exchangers, and medical instruments.