Dynamic Response Near Critical Build Heights in Ultrasonic Additive Manufacturing

Previous ultrasonic additive manufacturing (UAM) models ignore higher-order modes or do not simulate the entire weld cycle when studying the dynamics near critical height-to-width ratios. A multi-modal model was developed to study the dynamics near critical build heights. The cause for the critical height-to-width ratio is dynamic interaction between the substrate and sonotrode. As the build height approaches the critical height-width-ratio, the current model predicts a local maxima in the transverse velocity response directly under the moving load (simulated sonotrode excitation). This is validated by experimental observations from previous studies. However, the current model predicts that as the height is further increased, a maximum in the transverse velocity response occurs at a height-to-width ratio of 1.2 due to resonance of higher-order modes. This result indicates that a single mode-approximation is insufficient to describe the dynamics near critical build heights. In studying the time response for an entire weld cycle (1.5 s), the amplitude of the velocity response in the transverse direction varies greatly. This indicates that assuming a quasi-static or analyzing a short time period in a model excludes potential dynamics during an entire weld cycle (on the order of 1 s).

Mechanical and Microstructural Characterization of Percussive Arc Welded Hyper-Pins for Titanium to Composite Metal Joining

The manufacture of Ti- composite hyper-joints for aerospace applications requires arrays of pins to be attached to a metal component’s surface. Here, the feasibility of using percussive arc micro-welding for this purpose has been explored, applied to dissimilar Ti alloys, to allow advantage to be taken of tailored pin properties. To simulate the process, Timetal21s wire pins were welded to a Ti-6Al-4V baseplate under optimized parameters. Analysis of the welds indicated the presence of martensitic microstructures and chemical inhomogeneity in the melt pool, as a result of the rapid weld cycle (5 ms). The performance of the welded pins was assessed by a micro-tensile and a pin shear/bend test, assisted by FE modeling.

Cascaded Control of Power Input and Welding Temperature During Sealing of Spent Nuclear Fuel Canisters

The friction stir welding procedure to seal copper canisters requires variable power input throughout the 45 minute long weld cycle to keep the welding temperature within the process window. This is due to variable thermal boundary conditions throughout the weld cycle which, together with fast disturbances in the spindle torque, requires control of both the power input and the welding temperature to achieve a stable and robust process. By using a cascaded loop that determines the power input requirement, the regulator will not be dependent on repeatability in the necessary power input between weld cycles. As a result, a more accurate and reliable closed-loop control of the welding temperature is acquired.