A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 3 2 0 Ultrasonic additive manufacturing (UAM) originated from ultra- sonic metal welding, first developed in the 1950s. Through innovation, partnerships, and foresight, UAM has evolved into a high-volume manufacturing process. Modern applications include welding of battery tabs, thin foil packaging, and electronic wire production. The UAM process comprises three force vectors acting on a metal foil feedstock applied to an existing metal surface. Those three forces include a downward force compressing the two surfaces, ultrasonic vibration scrubbing both surfaces, and rolling to advance the process forward. The tool used to deliver these forces is a highly engineered component called a “horn” designed to resonate at a specific frequency (20-50 kHz). The process begins by pressing a thin metal foil onto another metal object. This object can be another metal foil, ametallic baseplate, a previously applied metal, an existing device or component made of metal, or an existing device or component with a metallic surface. While under a constant downward force, lateral ultrasonic energy (vibration) is applied, scrubbing the mating faces. This shearing motion disperses surface oxides through friction to allow direct contact of pure metal on pure metal, producing minimal heat and creating a solid state atomic bond. The heat and plastic deformation promote diffusion and recrystallization, resulting in a true metallurgical bond between the two metallic objects. Ultrasonic welding can be accomplished at very low temperatures without requiring a special environment (Fig. 1). ULTRASONIC CONSOLIDATION Headquartered inAnnArbor, Mich., Solidica Inc. was founded in 1999 by Dr. Dawn White to commercialize a new rapid prototyping technique called ultrasonic consolidation (UC). UC combined room-temperature welding using ultrasonic energy with CNC milling to create 3D metal parts. Computer- aided manufacturing software was adapted to create industry-standard G-code for operations similar to CNC mills. As such, UC was the first “hybrid” metal 3D printing process using additive and subtractive technologies to make the final product. Early success was found in the rapid development of aluminum parts for injection molds and tooling. The combination of CNC milling with a fast metal deposition process allowed the Formation brand of machines to quickly create parts with sharp, deep features and complex internal passages while maintaining CNC accuracy and surface finish. The low-temperature nature of the ultrasonic bond TECHNICAL SPOTLIGHT ULTRASONICADDITIVE MANUFACTURING: DEVELOPMENT AND COMMERCIALIZATION A unique method of additive manufacturing using ultrasonic energy excels at mixed metal applications, earning it the 2022 ASM Engineering Materials Achievement Award. Fig. 1 — Stages of ultrasonic metal bond formation.