Stick-Slip Dynamics in Ultrasonic Consolidation

Ultrasonic consolidation (UC) is a solid state rapid manufacturing process derived from ultrasonic welding of thin metal foils coupled with contour milling to achieve functional accurate components. Solidica Inc developed the process. The bonding of metal is accomplished by the local application of high frequency vibration energy under pressure producing a metallurgical bond without melting the base material. Its unique nature allows the design and fabrication of structural panels for satellites, production of injection molding tools, functionally graded structures, metal-matrix composites, embedded sensors, armor, and fiber embedded adaptive structures. It is commonly theorized that interfacial motion and friction at the bonding interface play a prominent role in the bonding process by removing surface contaminants, allowing direct metal to metal contact, and producing sufficient stress to induce plastic flow. The substrate’s geometry is also crucial in the bonding process. Researchers have experimentally observed that as the height of build specimen approaches its width, the bonding process degrades, and no further foils may be welded. Numerical simulations indicate that for features built at the nominal width (approximately 0.94 inches) the welding process excites several of the feature’s natural frequencies near the operating frequency of the ultrasonic welder, causing a resonance. This paper presents two modeling approaches to explain the behavior of the substrate as its dimensions approach the critical geometry: a finite element analysis and a lumped parameter model. We compare both models and present preliminary experimental results to verify their respective accuracies.