Developing an Ultrasonic Consolidation “Process Map”

Ultrasonic consolidation process is a solid-state fabrication process that combines computer control contour milling and ultrasonic welding of metal foils to produce a solid freeform part. There has been much work performed to understand the underlying physics of this process, in particular bonding mechanism. The occurrence of recrystallization was observed in ion beam images, indicating temperature elevation and plastic deformation strain near the bonding interface the key control parameters of bonding formation. Based on this diffusion bonding hypothesis, a comprehensive computational model was developed which is capable of describing thermal mechanical coupling with multi component geometry system. This model has been applied to investigate the evolution of the temperature and plastic strain in the metal foils subjected to ultrasonic vibration under various UC process conditions. A thermal-mechanical analysis of the bonding process of Al-Cu alloy material pair was performed to obtain the temperature elevation and plastic strain at the joint interface. Specially, the process conditions were correlated to the highest temperature and plastic strain at the contact interface so as to form a “process map”. This map reveals that the temperature and plastic strain obtained at the joint interface fall into a band in the strain-temperature coordinate system for the process conditions under which bonding can form. To accomplish bonding requires a good match between temperature and plastic deformation. This limits the process to a narrow region in the strain-temperature coordinate system. With both high temperature elevation and plastic strain, material structure tends to be destroyed, while no bonding can be formed with low temperature elevation and plastic strain. Simulation results as such process map has been evidently supported by the experimental results.