Session: MF-17-02 Advanced and Additive Manufacturing and Material Technologies (joint with D&A)-2

Paper Number: 153808

153808 - Determination of the Solid-State Resistance-Weldability of Additively Manufactured 304l Stainless Steel 

Abstract: 

Much research has been carried out in advanced and additive manufacturing in recent years. Little investigation has been conducted into the welding and joining of additively manufacture components. This paper is believed to be a first of its kind application of resistance spot welding to additively manufactured material components. Resistance spot welding is an often-preferred method of joining two dissimilar materials and it is not currently known if additively manufactured materials are dissimilar to their traditionally manufactured counterparts. Pinch welding is a subtype of resistance spot welding often used to close potentially hazardous, gas filled containers. Pinch welds at Savannah River National Laboratory were conducted on 304L stainless steel components to evaluate the validity of applying resistance spot welding to additively manufactured components. The components consisted of three different geometries; all of which were electrical discharge machined (EDM) from larger bulk components. Half hemispherical flat sheets were EDM and welded to include the as additively manufacture surface interface as the weld interface. Half tubes were also prepared using EDM for both the external and inner contours. Finally, short tube segments were fabricated by EDM cylinders and drilling. All weld conditions were duplicated on 304L SS tubing since the weld characteristics are well characterized in the literature. The samples were divided into two groups with different surface conditions. Group one was left in the as AM condition and group two was chemically pickled (Nitradd cleaned) before welding. A small subset of group one was used to validate the weld process window, which was selected based on historic SS tubing welds. Several characteristics have been identified as necessary for suitable welds. The thickness, width, extrusion ratio, wall thickness, and closure length of the welds were investigated by radiographic computed tomography (CT). The CT scans allowed for the examination of extrusions and expulsions within the tube. The welds were then prepared using standard metallographic techniques. Vickers hardness tests were performed on welded samples as well as the base materials. Weld symmetry was assumed, and hardness profiles were generated across one side of the weld indentation. These values are compared to that of the base tubing and AM materials. Weld closure length, thickness, and width are all traditional dimensions used in the qualification process. All three tubing types had parameters that fell outside of the requirements. This is not surprising, as the welding parameter window includes the edges of the known acceptable range. The AM tubing matched the traditional tubing, apart from falling within the upper range for weld closure length, which in actuality is a better result. AM Type 304L stainless steel welds performed in a manner very similar to conventionally formed stainless steel tubing. Common welding parameters produced similar bond lengths, thicknesses, and weld quality. The use of Nitradd cleaning improved the cleanliness of the bond line and fewer bond-line contaminants were observed. Extrusion ratios were up to 2.8 times larger in Nitradd cleaned tubes as compared to AR. An even greater difference was observed in the AM half-tubes, as no extrusions were present in the AR half-tubes; this result is likely due to differences in material constraint between tubes and hollowed out strips. The AM tubes all showed extrusions for the hot welds, but no difference in extrusion ratio was observed. This study produced too few samples to draw firm conclusions, therefore, a targeted study should be conducted in AM and traditional materials at high weld energies to verify the existence of this phenomenon and to quantify the effect.

Presenting Author: Jeremy Rogers Savannah River National Laboratory

Presenting Author Biography: Jeremy Rogers is a Staff Scientist in the Advanced Modeling and Simulation group at the Savannah River National Laboratory. Dr. Rogers received his Ph.D. in Mechanical Engineering, with a specialization in solid mechanics and materials science, from Texas Tech University. After completing his two year postdoctoral studies at Savannah River he was converted to Staff Scientist and now works to apply state-of-the-art science to provide practical, high-value, and cost-effective solutions to complex technical problems. He is the author of a dozen journal articles and technical reports. His current research interest are in the areas of heat transfer for additive manufacturing, weld, and braze modeling and the application of artificial intelligence/machine learning to identify, develop, and deploy innovative technologies to meet the needs of a variety of customers across the nation.

Authors:

Jeremy Rogers Savannah River National Laboratory
Colleen Hilla Savannah River National Laboratory
Paul Korinko Savannah River Nuclear Solutions