Ultrasonic Additive Manufacturing Process Research Articles

Multi-layer solid-state ultrasonic additive manufacturing of aluminum/copper: local properties and texture

Ultrasonic additive manufacturing (UAM) is an advanced joining technique that utilizes ultrasonic vibrations to bond layers of metal foil together. UAM offers several benefits over traditional manufacturing methods, including enhanced design flexibility and reduced material waste, and its potential applications in various industries such as aerospace, automotive, and biomedical engineering are being actively explored. The study employs a nanoindentation apparatus to investigate the effect of the UAM process on the local mechanical properties of the bonded interface, along with changes in microstructure, which were investigated using scanning electron microscopy and electron back-scattered diffraction. The results revealed a significant correlation between material hardness and local plasticity. EBSD has revealed that the grain size distribution of Al far from the interface contains 57% of the grains less than 3 µm in size, while at the interface this number rises to approximately 78%, indicating that the average grain size decreases as it approaches the interface. This result is consistent with nanoindentation results that demonstrated a gradual change in the hardness of Al foil far from the interface to close to the interface (the maximum penetration depth near the interface was 500 nm less than far from the interface). Both EBSD and nanoindentation disclose the effect of work hardening close to the interface, which is related to dislocation accumulation with a density of 8.6×10-10cm-2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$8.6\ imes {10}^{-10} {{\ ext{cm}}}^{-2}$$\\end{document} beneath the interface. The consistency of hardness and Young’s modulus with the pole figures and microscopic images demonstrated that plasticity flow and fine grain distribution would only occur in the vicinity of the interface in the softer metal region. Although the harder metal did not exhibit plasticity or recrystallization, the hardness, and Young’s modulus map indicated the formation of a layer of small grains close to the interface on the aluminum side owing to strain hardening and dynamic recrystallization.

Microstructure and mechanical properties of Ti/Al laminates fabricated by ultrasonic additive manufacturing assisted by Joule heat and post-welding heat treatment

In this study, a novel electrical-current assisted ultrasonic additive manufacturing (UAM) method was proposed and CP-Ti/Al3003 laminates were prepared by this process. The concept is that the Joule heat generated by the electrical current flowing through the CP-Ti foil is used to improve the material's plasticity, promote the interfacial bonding strength and continuous ultrasonic consolidation ability. Ti/Al laminates with excellent interfacial bonding strength and mechanical properties can be obtained by alternating the use of Ti foil and Al foil and subsequently applying post-welding heat treatment for interfacial strengthening. The current density distribution at the CP-Ti foil and Ti/Al interface was studied by finite element model. The interfacial microstructure of the laminates was characterized and analyzed by optical microscopy, scanning electron microscopy-energy dispersive spectroscopy, and X-ray diffraction, and the inhibition effect of current on the resonance cracking of Ti foil during the UAM process was verified. The effect of current on the interfacial bonding strength of the Ti/Al interface and the tensile strength of the laminates was investigated by peel test and tensile test. The growth kinetics of TiAl3 under the assisted current was also studied and CP-Ti/Al laminates with the tensile strength of 242.4 MPa in the rolling direction. The combined effect of Joule heating of current and subsequent post-weld heat treatment strengthened the reaction between Ti/Al and formed TiAl3 IMC layer and obtained CP-Ti/Al laminates without interface defects.

Review of recent trends in ultrasonic additive manufacturing: current challenges and future prospects

PurposeThis study aims to outline the current challenges in ultrasonic additive manufacturing (AM). AM has revolutionized manufacturing and offers possible solutions when conventional techniques reach technological boundaries. Ultrasonic additive manufacturing (UAM) uses mechanical vibrations to join similar or dissimilar metals in three-dimensional assemblies. This hybrid fabrication method got attention due to minimum scrap and near-net-shape products.Design/methodology/approachThis paper reviews significant UAM areas in process parameters such as pressure force, amplitude, weld speed and temperature. These process parameters used in different studies by researchers are compared and presented in tabular form. UAM process improvements and understanding of microstructures have been reported. This review paper also enlightens current challenges in the UAM process, process improvement methods such as heat treatment methods, foil-to-foil overlap and sonotrode surface roughness to increase the bond quality of welded parts.FindingsResults showed that UAM could solve various problems and produce net shape products. It is concluded that process parameters such as pressure, weld speed, amplitude and temperature greatly influence weld quality by UAM. Post-weld heat treatment methods have been recommended to optimize the mechanical strength of ultrasonically welded joints process parameters. It has been found that the tension force is vital for the deformation of the pre-machined structures and for the elongation of the foil during UAM bonding. It is recommended to critically investigate the mechanical properties of welded parts with standard test procedures.Originality/valueThis study compiles relevant research and findings in UAM. The recent progress in UAM is presented in terms of material type, process parameters and process improvement, along with key findings of the particular investigation. The original contribution of this paper is to identify the research gaps in the process parameters of ultrasonic consolidation.

Strengthening of pretreated aluminum during ultrasonic additive manufacturing

Strengthening effects in materials bonded by the high strain rate plastic deformation process, Ultrasonic Additive Manufacturing (UAM), were investigated. Aluminum (Al 6061) was pretreated by tempering and annealing prior to bonding through UAM. Following UAM, multiscale material characterization was performed. Tensile testing in the rolling (x) direction demonstrated the material became harder after the UAM process, and nanoindentation demonstrated the foil-foil interfaces became harder than the bulk foil material. The strengthening effects are a result of microstructure changes at the interfaces and in the bulk foil regions which were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy. These microstructure changes result from dynamic recrystallization, dynamic recovery, adiabatic heating, and precipitate dissolution. This study signifies the metallurgical features creating mechanical strength increases, rather than decreases, in UAM builds.

On the efficacy of post-build thermomechanical treatments to improve properties of Zirconium fabricated using ultrasonic additive manufacturing

Hot-isostatic pressing has been applied to Zirconium plate fabricated using the ultrasonic additive manufacturing (UAM) technique to enhance interfacial bond quality. Specimens heated to 800 C for 1 h at 100 MPa showed grain growth across many prior foil-to-foil interfaces, thereby increasing foil adhesion. In addition to the material softening induced by a loss of Hall-Petch strengthening, premature failure of specimens loaded parallel to the build direction was observed. Premature specimen failure was attributed to the local delamination at prior foil-to-foil boundaries where grain growth was pinned by Ti impurities introduced during the UAM process via the interaction between a Ti-alloy buffer foil and the welded Zr-foils underneath. In addition, the presence of Ti along select foil interfaces resulted in the nucleation and growth of secondary (Zr,Ti)(Fe,Cr) laves phases during higher-temperature thermomechanical processing. Using a combination of micro-scale X-ray computed tomography, fractography, and in-situ digital image correlation, the effect of defects along prior foil-to-foil boundaries was revealed as delamination-assisted plasticity accelerated specimen failure in preferred tensile orientations. These findings underscore the importance of impurity control when optimizing weld quality of higher-strength material systems using ultrasonic welding.

Interfacial texture and bonding strength of Cu/Al laminate metal composite fabricated by ultrasonic additive manufacturing

Interfacial texture and bonding strength of Cu/Al laminate metal composite fabricated by ultrasonic additive manufacturing (UAM) were investigated by electron backscattered diffraction, transmission electron microscopy and peeling tests. Results show that after the UAM process, Al foils have obvious shear texture or recrystallisation texture components in the region near the interface of Cu/Al, indicating that Al foils are prone to shear deformation during consolidation, which plays an essential role in the bonding formation of the two dissimilar metals. The rougher Cu foil surface produced by direct contact with sonotrode promotes more remarkable shear deformation of the mating Al foil near the interface during the subsequent consolidation pass, which obviously enhances the interfacial bonding strength.

Ultrasonic additive manufacturing of zirconium: Pilot results

Ultrasonic additive manufacturing (UAM) was successfully applied to the Zirconium material system to create a three-dimensional component prototype. The UAM process resulted in grain size refinement and significant localized deformation. Electron backscatter diffraction analysis revealed activated slip systems only applicable at high deformation temperatures, while texture analysis showed a decrease in measurable texture of the UAM build in comparison to the initial Zr-foil. Average tensile strengths in the X (sonotrode travel), Y (vibration), and Z (build) directions averaged 435 MPa, 458 MPa, and 359 MPa, respectively, demonstrating the viability of UAM for Zr-based materials. The delamination of some Z specimens along foil boundaries during loading suggests an interplay between interfacial Ti impurities introduced during welding and the spatial dependence of weld quality for this material system.

Investigation of shear failure load in ultrasonic additive manufacturing of 3D CFRP/Ti structures

Abstract Carbon fiber reinforced plastic (CFRP) is an extremely beneficial composite material in the aerospace and automobile industries owing to its high-strength-to-weight ratio, high stiffness, lightweight, and corrosion resistance. However, CFRP material alone is limited in its weight-bearing capabilities. A thin layer material such as Titanium (Ti) is often used along with CFRP laminates to address these issues. Traditional techniques used to join CFRP/Ti stacks include the use of adhesives, glues, or rivets, and bolts. These techniques have several limitations including weight addition, stress cracking, delamination, and limited operating temperatures. These limitations can be readily addressed by the use of solid-state welding techniques based on ultrasonic energy. One such technique is the Ultrasonic Additive Manufacturing (UAM) process, which is capable of fabricating 3D structures of CFRP/Ti laminar composites. Preliminary experimental studies proved the feasibility of using the UAM process to join CFRP/Ti stacks. Further development of this process needs a detailed investigation of the process parameters. This study aims to study the effect of critical process parameters including the ultrasonic energy and pre-surface roughness on the shear strength of the fabricated CFRP/Ti stacks using the UAM process. The study found that both ultrasonic energy and surface roughness have a positive impact on the resulting shear strengths of the UAM fabricated structures.

Power Ultrasonic Additive Manufacturing: Process Parameters, Microstructure, and Mechanical Properties

Additive manufacturing (AM) for fabricating 3D metallic parts has recently received considerable attention. Among the emerging AM technologies is ultrasonic additive manufacturing (UAM) or ultrasonic consolidation (UC), which uses ultrasonic vibrations to bond similar or dissimilar materials to produce 3D builds. This technology has several competitive advantages over other AM technologies, which includes fabrication of dissimilar materials and complex shapes, higher deposition rate, and fabrication at lower temperatures, which results in no material transformation during processing. Although UAM process optimization and microstructure have been reported in the literature, there is still lack of standardized and satisfactory understanding of the mechanical properties of UAM builds. This could be attributed to structural defects associated with UAM processing. This article discusses the effects of UAM process parameters on the resulting microstructure and mechanical properties. Special attention is given to hardness, shear strength, tensile strength, fatigue, and creep measurements. Also, pull‐out, push‐out, and push‐pin tests commonly employed to characterize bond quality and strength have been reviewed. Finally, current challenges and drawbacks of the process and potential applications have been addressed.

Detection of Crack Initiation and Growth Using Fiber Bragg Grating Sensors Embedded into Metal Structures through Ultrasonic Additive Manufacturing.

Structural health monitoring (SHM) is a rapidly growing field focused on detecting damage in complex systems before catastrophic failure occurs. Advanced sensor technologies are necessary to fully harness SHM in applications involving harsh or remote environments, life-critical systems, mass-production vehicles, robotic systems, and others. Fiber Bragg Grating (FBG) sensors are attractive for in-situ health monitoring due to their resistance to electromagnetic noise, ability to be multiplexed, and accurate real-time operation. Ultrasonic additive manufacturing (UAM) has been demonstrated for solid-state fabrication of 3D structures with embedded FBG sensors. In this paper, UAM-embedded FBG sensors are investigated with a focus on SHM applications. FBG sensors embedded in an aluminum matrix 3 mm from the initiation site are shown to resolve a minimum crack length of 0.286 ± 0.033 mm and track crack growth until near failure. Accurate crack detection is also demonstrated from FBGs placed 6 mm and 9 mm from the crack initiation site. Regular acrylate-coated FBG sensors are shown to repeatably work at temperatures up to 300 C once embedded with the UAM process.

Finite element analysis and simulation study of CFRP/Ti stacks using ultrasonic additive manufacturing

The hybrid laminar composite stack of carbon fiber reinforced polymer (CFRP) and titanium (Ti) are widely used in several critical engineering applications, including aerospace and automobile sectors. The joining of CFRP and Ti through conventional methods has several limitations such as weight additional, material damage, and lower fatigue life. Ultrasonic additive manufacturing (UAM) is a solid-state manufacturing process capable of joining layers of dissimilar materials. Experimental studies have successfully demonstrated the welding of CFRP and Ti through UAM process. However, there is a lack of understanding of the exact bonding process and influence of process parameter on weld quality during UAM. The present study investigates the bonding process and the effects of critical parameters in the UAM process of CFRP and Ti layers using finite element analysis and simulation technique. The simulation study reveals that the CFRP/titanium stacks encounter interfacial cyclic shear stresses and shear strains. The study found that the vibrational amplitude and surface roughness of the substrates play a critical role in achieving a proper weld. The simulation results are validated using experimentation. The finding of this study can help advance the commercialization of UAM process for welding dissimilar materials and composites.

Ultrasonic additive manufacturing using feedstock with build-in circuitry for 3D metal embedded electronics

Embedded electronics and sensors are becoming increasingly important for the development of Industry 4.0. For small components, space constraints lead to full 3D integration requirements that are only achievable through Additive Manufacturing. Manufacturing metal components usually require high temperatures incompatible with electronics but Ultrasonic Additive Manufacturing (UAM) can produce components with mechanical properties close to bulk, but with the integration of internal embedded electronics, sensors or optics. This paper describes a novel manufacturing route for embedding electronics with 3D via connectors in an aluminium matrix. Metal foils with printed conductors and insulators were prepared separately from the UAM process thereby separating the electronics preparation from the part consolidation. A dual material polymer layer exhibited the best electrically insulating properties, while providing mechanical protection of printed conductive tracks stable up to 100 °C. General design and UAM process recommendations are given for 3D embedded electronics in a metal matrix.

Ultrasonic Additive Manufacturing as a form-then-bond process for embedding electronic circuitry into a metal matrix

Ultrasonic Additive Manufacturing (UAM) is a hybrid manufacturing process that involves the layer-by-layer ultrasonic welding of metal foils in the solid state with periodic CNC machining to achieve the desired 3D shape. UAM enables the fabrication of metal smart structures, because it allows the embedding of various components into the metal matrix, due to the high degree of plastic metal flow and the relatively low temperatures encountered during the layer bonding process. To further the embedding capabilities of UAM, in this paper we examine the ultrasonic welding of aluminium foils with features machined prior to bonding. These pre-machined features can be stacked layer-by-layer to create pockets for the accommodation of fragile components, such as electronic circuitry, prior to encapsulation. This manufacturing approach transforms UAM into a “form-then-bond” process. By studying the deformation of aluminium foils during UAM, a statistical model was developed that allowed the prediction of the final location, dimensions and tolerances of pre-machined features for a set of UAM process parameters. The predictive power of the model was demonstrated by designing a cavity to accommodate an electronic component (i.e. a surface mount resistor) prior to its encapsulation within the metal matrix. We also further emphasised the importance of the tensioning force in the UAM process. The current work paves the way for the creation of a novel system for the fabrication of three-dimensional electronic circuits embedded into an additively manufactured complex metal composite.

Enabling internal electronic circuitry within additively manufactured metal structures – the effect and importance of inter-laminar topography

PurposeThis paper aims to explore the potential of ultrasonic additive manufacturing (UAM) to incorporate the direct printing of electrical materials and arrangements (conductors and insulators) at the interlaminar interface of parts during manufacture to allow the integration of functional and optimal electrical circuitries inside dense metallic objects without detrimental effect on the overall mechanical integrity. This holds promise to release transformative device functionality and applications of smart metallic devices and products.Design/methodology/approachTo ensure the proper electrical insulation between the printed conductors and metal matrices, an insulation layer with sufficient thickness is required to accommodate the rough interlaminar surface which is inherent to the UAM process. This in turn increases the total thickness of printed circuitries and thereby adversely affects the integrity of the UAM part. A specific solution is proposed to optimise the rough interlaminar surface through deforming the UAM substrates via sonotrode rolling or UAM processing.FindingsThe surface roughness (Sa) could be reduced from 4.5 to 4.1 µm by sonotrode rolling and from 4.5 to 0.8 µm by ultrasonic deformation. Peel testing demonstrated that sonotrode-rolled substrates could maintain their mechanical strength, while the performance of UAM-deformed substrates degraded under same welding conditions ( approximately 12 per cent reduction compared with undeformed substrates). This was attributed to the work hardening of deformation process which was identified via dual-beam focussed ion beam–scanning electron microscope investigation.Originality/valueThe sonotrode rolling was identified as a viable methodology in allowing printed electrical circuitries in UAM. It enabled a decrease in the thickness of printed electrical circuitries by ca. 25 per cent.

Effect of post weld heat treatment on the 6061 aluminum alloy produced by ultrasonic additive manufacturing

Ultrasonic additive manufacturing (UAM) is a solid-state additive manufacturing technique employing principles of ultrasonic welding coupled with mechanized tape layering to fabricate fully functional parts. However, parts fabricated using UAM often exhibit a reduction in strength levels when loaded normal to the welding interfaces (Z-direction). In this work, the effect of post-weld heat treatments (PWHT) on Al-6061 builds fabricated using the UAM process was explored aiming to improve the mechanical strength of the UAM builds. Tensile testing with digital image correlation (DIC) coupled with metallography along with multi-scale structure characterization (SEM-EBSD) was used to investigate and rationalize the mechanical performance of the UAM builds. It was established that PWHTs may improve the Z-strength level by the factor of ~3÷3.5 (from ~46 to 177MPa). The improvements in the strength level were primarily aided by material aging and grain growth across the bond interface.

Optimized welding parameters for Al 6061 ultrasonic additive manufactured structures

Abstract

On the stick-slip dynamics in ultrasonic additive manufacturing

Ultrasonic Additive Manufacturing (UAM) is a promising additive manufacturing process used to build complex structures by joining thin metal films. Layers of metal foil are joined by being compressed under moderate pressure using a rolling ultrasonic horn which vibrates at a high frequency in a direction transverse to the rolling motion. Foil–foil interfacial motion combined with moderate heating and pressure results in pure metal contact which causes atomic bonding. Unfortunately, large scale implementation of the UAM process is impeded by the presence of a range of build heights within which bonding between a new foil and the build feature cannot be initiated. This paper simplifies the UAM process into a lumped-parameter dry-friction oscillator and shows that complex stick-slip motions of the build feature near or above its resonance frequency are responsible for bond degradation. Specifically, as the height of the feature increases and its first modal frequency approaches the excitation frequency of the sonotrode, the relative motions between the tape and the feature become either pure stick or aperiodic. Pure stick responses, where the tape and the feature stick together, prevent interfacial motions necessary for bonding. Aperiodic motions, on the other hand, consist of slip trajectories interrupted by long stick intervals resulting in velocity bursts and nonuniform energy distribution at the interface. The adopted model and associated analysis also indicate that periodic uniform responses essential for bonding are always recovered once the critical build height is surpassed. These findings corroborate previous experimental results that demonstrate bonding is hard to initiate near or slightly below the problematic height but can be reinitiated above it.

Characterization of interfacial microstructures in 3003 aluminum alloy blocks fabricated by ultrasonic additive manufacturing

Ultrasonic additive manufacturing (UAM) is a solid-state processing technique that uses ultrasonic vibrations to bond metal tapes into near net-shaped components. The benefits of UAM include the production of complex geometries and the incorporation of smart materials to produce functional composites and join dissimilar metals. The majority of the current research focuses on processing parameter optimization to eliminate macroscopic void formation at the interface. The present study utilizes ion-channeling contrast imaging from a focused ion beam, electron backscattered diffraction and transmission electron microscopy to examine microstructural changes induced during the UAM process. The results indicate that there is a bonding mechanism due to localized plastic deformation of asperities that undergo recrystallization and grain growth across the interface. Evidence for localized solidification microstructures, generated due to frictional sliding between the sonotrode horn and the tape material, is also presented.

Micro-hardness of annealed and work-hardened copper polycrystals

Strengthening effects in materials bonded by the high strain rate plastic deformation process, Ultrasonic Additive Manufacturing (UAM), were investigated. Aluminum (Al 6061) was pretreated by tempering and annealing prior to bonding through UAM. Following UAM, multiscale material characterization was performed. Tensile testing in the rolling (x) direction demonstrated the material became harder after the UAM process, and nanoindentation demonstrated the foil-foil interfaces became harder than the bulk foil material. The strengthening effects are a result of microstructure changes at the interfaces and in the bulk foil regions which were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy. These microstructure changes result from dynamic recrystallization, dynamic recovery, adiabatic heating, and precipitate dissolution. This study signifies the metallurgical features creating mechanical strength increases, rather than decreases, in UAM builds.