Effect of weld power and build compliance on ultrasonic consolidation

Abstract

Purpose Ultrasonic additive manufacturing (UAM) is a fabrication technology based on ultrasonic metal welding. As a solid-state process, temperatures during UAM fabrication reach a fraction of the melting temperatures of the participating metals. UAM parts can become mechanically compliant during fabrication, which negatively influences the ability of the welder to produce consistent welds. This study aims to evaluate the effect of weld power on weld quality throughout a UAM build, and develop a new power-compensation approach to achieve homogeneous weld quality. Design/methodology/approach The study utilizes mechanical push-pin testing as a metric of delamination resistance, as well as focused ion beam and scanning electron microscopy to analyze the interface microstructure of UAM parts. Findings Weld power was found to negatively affect mechanical properties and microstructure. By keeping weld power constant, the delamination energy of UAM coupons was increased 22 per cent along with a consistent grain structure. As a result, to ensure constant properties throughout UAM component construction, maintaining weld power is preferable over the conventional strategy based on amplitude control. Research limitations/implications Further characterization could be conducted to evaluate the power control strategy on other material combinations, though this study strongly suggests that the proposed approach should work regardless of the metals being welded. Practical implications The proposed power control strategy can be implemented by monitoring and controlling the electrical power supplied to the welder. As such, no additional hardware is required, making the approach both useful and straightforward to implement. Originality/value This research paper is the first to recognize and address the negative effect of build compliance on weld power input in UAM. This is also the first paper to correlate measured weld power with the microstructure and mechanical properties of UAM parts.

Dynamics of ultrasonic additive manufacturing

“…These weld speed levels have little to no influence on welder performance or efficiency. This observation corroborates other 9 kW UAM experimentation [22] and energy transfer models [28] because slower weld speeds (V t ) were found to linearly improve bond quality. In other words, the imparted energy to the weld interface (E welder ), and ultimately bond quality, is linear with speed because imparted mechanical power (P mech ) is not a function of welder speed within the investigated speed range,…”

“…In UAM, many joints are made and the build geometry changes throughout component construction. Consequently, unwanted resonances can occur [25,26] and the amount of deformation at the weld interface decreases as the build becomes more compliant with added layers [27,28]. Due to less deformation occurring at the weld interface and because deformation is a leading mechanism for bonding, the bond quality degrades with additional layers.…”

Ultrasonic nondestructive evaluation of metal additive manufacturing.

“…UAM stack quality is dependent on geometry as substrate stiffness affects the ultrasonic energy input. The effect of build compliance on power drawn during UAM has been reported by Hehr et al [103]. Optimum vibration amplitude is dependent on component geometry.…”

“…3. A decreasing trend was observed in the ultrasonic velocity after the initial recovery in the builds made at higher vibration amplitudes, which could be attributed to the increasing compliance of the UAM stack leading to lower transfer of power during welding [103]. It was also observed that the difference between components can be broadly distinguished through ultrasonic velocity.…”

“…Several studies focus on developing optimal process parameters for UAM and then eliminating defects through post-weld treatments [11,23,27,94,103,113,114,115,116]. To form a good bond, there must be enough power input into the ultrasonic weld while at the same time ensuring that already bonded interfaces are not pulled apart due to excessive vibration or power input [103]. Defects in UAM are labeled as Type-1 for inter-layer defects and Type-2 for intertrack defects [4,115].…”