Ultrasonic Additive Manufacturing Of Steel PDF Download

Ultrasonic additive manufacturing (UAM) is a solid-state manufacturing technology that produces near-net shape metallic parts. UAM has been demonstrated to make robust structures with a variety of material combinations such as Al-Al, Al-Ti, Cu-Cu, and Al-Cu. However, UAM welding of high strength steels has proven challenging. The focus of this work is to develop a fundamental understanding of the structure-property-process relationship of UAM steel welding through experiments and modeling. Process and post-processing methods to improve UAM steel weld quality were investigated. A custom shear test was first developed and optimized to test the mechanical strength of UAM builds. The second study demonstrated the UAM fabrication of stainless steel 410 builds which possess, after post-processing, mechanical properties comparable with bulk 410 material. Fracture surface analyses confirm the weld quality improvement caused by increasing the baseplate temperature and the application of hot isostatic pressing (HIP) post weld. In the third study, a higher weld power is demonstrated by using a cobalt-based sonotrode coating, achieving shear strengths comparable to bulk 4130 material without post treatment. Weld parameters for making UAM 4130 builds were optimized via a design of experiments study. Baseplate temperature of 400 ̊F (204.4 ̊C), amplitude of 31.5 μm, welding speed of 40 in/min (16.93 mm/s), and normal force of 6000 N were identified as optimal within the selected process window. Analysis of variance and main effect plots show that normal force, amplitude, and welding speed are significant for interfacial temperature. Similar analyses show that normal force and amplitude have a statistically significant effect on shear strength. Residual stress in UAM 4130 samples was measured for the first time using neutron diffraction. The maximum tensile residual stress for UAM 4130 is found to be relatively low at 176.5 MPa, which suggests a potentially better fatigue performance of UAM builds compared to fusion-based additive manufactured parts. FE models that describe the stress distribution and predict the fatigue performance of UAM steel builds were developed. The models predict that the fatigue cracking of the interface between the baseplate and the first layer of foil (0th interface) occurs while welding the 10th layer of 4130 steel foil, which agrees with the experimental observation. Further computational analyses indicate that a taller crack-free UAM steel build can be produced if a higher shear strength can be achieved at the 0th interface using a relatively higher welding speed and lower ultrasonic power input. A UAM thermal model predicting the temperature rise due to heat generation from frictional sliding and plastic deformation during the UAM welding process was developed. Computational case studies indicate that a decrease in welding speed, an increase in vibration amplitude, a decrease in normal force, or an increase in baseplate temperature would lead to an increase in the peak temperature. Overall, 26 out of 32 measured peak temperatures fall into the range predicted by the UAM thermal model. The agreement between model predictions and experimental results validates the UAM thermal model.