Ultrasonic Consolidation Research Articles

Role of friction on the thermal development in ultrasonically consolidated aluminum foils and composites

Ultrasonic consolidation is a solid-state bonding process capable of producing metal and metal matrix composite parts. In this work a friction-based heat generation model is proposed to characterize the thermal development of ultrasonically consolidated aluminum foils and continuous fiber alumina reinforced aluminum metal matrix composite tape as a function of process control parameters. The friction coefficient between mating surfaces is determined experimentally, and the credibility of using both a constant friction coefficient and a process dependent friction coefficient is assessed. In most cases a constant friction coefficient is capable of producing results that are within 15% error; while a process dependent friction coefficient achieves an average error of 7%.

Ultrasonic Consolidation and Ignition Characteristics of Thermite Composites

The fabrication and characterization of metal‐based energetic composite materials are currently being examined for a range of new applications. A newly developed ultrasonic consolidation process is used for the synthesis of Al/Fe2O3 and Al/Cu2O compacts over a wide range of powder ratios at room temperature. Powder consolidation was achieved by a multistep procedure involving simultaneous application of pressure and ultrasonic vibrations. The observed reaction characteristics of the composites are similar to those of previously reported thermite compacts prepared by a traditional powder metallurgy method.

Thermal transients during processing of materials by very high power ultrasonic additive manufacturing

Dynamic recrystallisation at interfaces has been suggested as the bonding mechanism in the joining of metallic tapes, during very high power ultrasonic additive manufacturing. To understand the reasons for such occurrence of dynamic recrystallization, thermal transients from the interface regions were recorded during processing of aluminum alloy (3003 and 6061 series) and 11 000 copper tapes under similar conditions. Measurements in 3003 Al were also carried out for different processing parameters. Measured peak temperatures were seen to increase with increase in shear strength of the material and ultrasonic vibration amplitude. The observations have been rationalized based on interfacial heating at asperities due to adiabatic plastic deformation.

Dislocation Density-Based Finite Element Method Modeling of Ultrasonic Consolidation

A dislocation density based constitutive model has been developed and implemented into a crystal plasticity quasi‐static finite element framework. This approach captures the statistical evolution of dislocation structures and grain fragmentation at the bonding interface when sufficient boundary conditions pertaining to the Ultrasonic Consolidation process are prescribed. Hardening is incorporated using statistically stored and geometrically necessary dislocation densities (SSDs and GNDs), which are dislocation analogs of isotropic and kinematic hardening respectively. The GND considers strain‐gradient and thus renders the model size‐dependent. The model is calibrated using experimental data from published refereed literature and then validated for the Aluminum 3003 alloy. Introduction As a direct result of ongoing research efforts in ultrasonic consolidation (UC) worldwide [1], it has become apparent that a new approach to modeling of UC bonding is needed. A model which provides a better understanding of the effects of process parameter changes on grain refinement, plastic deformation and bonding during UC will better enable researchers to predict which materials will bond, how the mechanical properties of UC-produced parts can be improved, and how to better design the next generation of UC equipment. The continuum properties of parts made using UC are strongly dependent upon the micromechanics of the bonded interface [1]. Interfacial-scale microstructures can be studied fundamentally using electron microscopy [1] and can be used to correlate atomic and mesoscopic mechanisms of deformation to their continuum counterparts. A dislocation density-based crystal plasticity Finite Element Model (FEM) can capture the statistical distribution of dislocations, partials and various deformation mechanisms at the bonding interface as inputs to predict macroscopic deformation profiles as a function of energy input characteristics. These input characteristics are a function of the process parameters used in a UC machine, namely vibration amplitude, normal force, ultrasonic frequency, welding speed, sonotrode geometry and temperature. Problem Formulation It has been shown that material sheets subjected to UC undergo inhomogeneous plastic deformation through their thickness [1]. Classical continuum plasticity theories do not fully explain this phenomenon [2]. Therefore, a study of strain localization and grain refinement at the material interfaces during UC bonding is required. The following steps lead to the calculation of these localized strains and their effects. Large Deformation Quasi-Static Crystal Plasticity Description The deformation map in space and time is described by the total deformation gradient tensor F (Figure 1). Applying the Kroner-Lee assumption, F is decomposed into elastic Fe and plastic gradient Fp tensors using multiplicative operator theory

Role of substrate stiffness in ultrasonic consolidation

In ultrasonic consolidation (UC), if the substrate is not stiff enough, no friction can occur between the foil being deposited and the substrate, which is essential for achieving bonding. The requirement that the substrate be stiff enough to resist deflection can impose certain geometrical restrictions on the process. Further, build orientation can have a strong influence on the process. In the current work, the role of substrate stiffness in UC was investigated. Freestanding rectangular ribs of three different widths in aluminium alloy AA 3003 were built in three different orientations such that the long axis of the rib is parallel, perpendicular and at 45° to the direction of sonotrode vibration. Studies show that freestanding ribs can only be built to a modest height-to-width ratio of around 1. Build failures occur not only because the substrate stiffness reduces with build height, but also due to a number of machining-related problems that accumulate as more and more layers are added. The results show that building freestanding rectangular ribs is best done by orienting the long axis of the rib at 45° to the direction of sonotrode vibration.

CubeSat Fabrication through Additive Manufacturing and Micro-Dispensing

Fabricating entire systems with both electrical and mechanical content through on-demand 3D printing is the future for high value manufacturing. In this new paradigm, conformal and complex shapes with a diversity of materials in spatial gradients can be built layer-by-layer using hybrid Additive Manufacturing (AM). A design can be conceived in Computer Aided Design (CAD) and printed on-demand. This new integrated approach enables the fabrication of sophisticated electronics in mechanical structures by avoiding the restrictions of traditional fabrication techniques, which result in stiff, two dimensional printed circuit boards (PCB) fabricated using many disparate and wasteful processes. The integration of Additive Manufacturing (AM) combined with Direct Print (DP) micro-dispensing and robotic pick-and-place for component placement can 1) provide the capability to print-on-demand fabrication, 2) enable the use of micron-resolution cavities for press fitting electronic components and 3) integrate conductive traces for electrical interconnect between components. The fabrication freedom introduced by AM techniques such as stereolithography (SL), ultrasonic consolidation (UC), and fused deposition modeling (FDM) have only recently been explored in the context of electronics integration and 3D packaging. This paper describes a process that provides a novel approach for the fabrication of stiff conformal structures with integrated electronics and describes a prototype demonstration: a volumetrically-efficient sensor and microcontroller subsystem scheduled to launch in a CubeSat designed with the CubeFlow methodology.

Finite element analysis of ultrasonic insertion of SiC fibre in aluminium alloy 6061

In this work, a computational framework has been proposed to successfully simulate the fibre embedding using ultrasonic consolidation process. The main components of the proposed computational approach are a developed constitutive model and a friction model which are especially suitable for the condition of ultrasonic process. The effect of different process parameters, such as velocity of sonotrode, displacement amplitude of ultrasonic vibration and applied loads are studied. The presented work especially focuses on the quality of the developed weld and the fibre coverage due to the plastic flow around the fibre. The areas of maximum plastic flow predicted by the simulation are confirmed by the EBSD microstructural studies.

Fibre embedding in aluminium alloy 3003 using ultrasonic consolidation process—thermo-mechanical analyses

This work presents a computational framework based on finite element methods to simulate the fibre-embedding process using ultrasonic consolidation process. The computational approach comprises of a material model which takes into account thermal and acoustic softening effects and a friction model which indicates the realistic friction behaviour at the interfaces. The derived material model and developed friction model have been incorporated in finite element model. Using the implemented material and friction model, thermo-mechanical analyses of embedding of fibre in aluminium alloy 3003 has been performed. Effect of different process parameters, such as velocity of sonotrode, displacement amplitude of ultrasonic vibration and applied loads, is studied and compared with the experimental results. The presented work has specially focused on the quality of the developed weld which could be evaluated by the friction work and the coverage of the fibre which is estimated by the plastic flow around the fibre. The computed friction work obtained from the thermomechanial analyses performed in this study show a similar trend as that of the experimentally found fracture energies.

Statistical Characterization of Ultrasonic Additive Manufacturing Ti/Al Composites

Ultrasonic additive manufacturing (UAM) is an emerging solid-state fabrication process that can be used for layered creation of solid metal structures. In UAM, ultrasonic energy is used to induce plastic deformation and nascent surface formation at the interface between layers of metal foil, thus creating bonding between the layers. UAM is an inherently stochastic process with a number of unknown facets that can affect the bond quality. In order to take advantage of the unique benefits of UAM, it is necessary to understand the relationship between manufacturing parameters (machine settings) and bond quality by quantifying the mechanical strength of UAM builds. This research identifies the optimum combination of processing parameters, including normal force, oscillation amplitude, weld speed, and number of bilayers for the manufacture of commercially pure, grade 1 titanium+1100-O aluminum composites. A multifactorial experiment was designed to study the effect of the above factors on the outcome measures ultimate shear strength and ultimate transverse tensile strength. Generalized linear models were used to study the statistical significance of each factor. For a given factor, the operating levels were selected to cover the full range of machine capabilities. Transverse shear and transverse tensile experiments were conducted to quantify the bond strength of the builds. Optimum levels of each parameter were established based on statistical contrast trend analyses. The results from these analyses indicate that high mechanical strength can be achieved with a process window bounded by a 1500 N normal force, 30 μm oscillation amplitude, about 42 mm/s weld speed, and two bilayers. The effects of each process parameter on bond strength are discussed and explained.

Mechanical Properties and Microstructures of SiC Fiber-reinforced Metal Matrix Composites Made Using Ultrasonic Consolidation

Ultrasonic consolidation was used for making SiC fiber-reinforced Al 3003 matrix composites. Peel tests, tensile tests, and bend tests were carried out on the composite specimens as well as on ultrasonically consolidated Al 3003 specimens containing no SiC fibers. The objective of this study was to examine whether the ultrasonically embedded SiC fibers serve as effective reinforcements or not. Incorporation of SiC fibers resulted in a considerable improvement in peel strength and tensile strength of ultrasonically consolidated parts. However, bend tests revealed some deterioration in the shear strength of the parts due to the presence of fibers. The results of mechanical testing are discussed based on microstructural and fractographic studies.

Platform Embedded Slot Antenna Backed by Shielded Parallel Plate Resonator

A new cavity architecture for applications in design of resonator-backed slot antennas with a height less than <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\lambda/15$</tex> </formula> profile is presented. This architecture renders cavity heights as low as <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\lambda/130$</tex> </formula> and small lateral dimensions. Miniaturization of the supporting cavity resonator is achieved by meandering the passage from the bottom of the cavity resonator to the slot aperture. Unlike conventional cavity resonators, the proposed design operates in a TEM mode which allows for wider bandwidth operation and miniaturization of lateral dimensions. Ultrasonic consolidation technique is employed to fabricate the complicated cavity structure monolithically. Measurements verify the proposed antenna exhibits excellent gain and front-to-back ratio (FTBR). Wide-band mode of the antenna is achieved by using a carefully designed microstrip feed across the slot aperture which facilitates a fictitious short along the slot aperture. The antenna is then flush-mounted onto an arbitrarily built metallic platform and is shown to feature consistent impedance matching. The FTBR is found to improve when the antenna is embedded into the platform. The same antenna architecture is redesigned for VHF band operation using standard multi-layer PCB technology and consistent functionality is verified.

Effect of height to width ratio on the dynamics of ultrasonic consolidation

PurposeThe purpose of this paper is to focus on the changing dynamics of the ultrasonic consolidation (UC) process due to changes in substrate geometry. Past research points to a limiting height to width ranging from 0.7 to 1.2 on build features.Design/methodology/approachResonances of a build feature due to a change in geometry are examined and then a simple non‐linear dynamic model of the UC process is constructed that examines how the geometry change may influence the overall dynamics of the process. This simple model is used to provide estimates of how substrate geometry affects the differential motion at the bonding interface and the amount of energy emitted by friction change due to build height. The trends of changes in natural frequency, differential motion, and frictional energy are compared to experimental limits on build height.FindingsThe paper shows that, at the nominal build, dimensions of the feature the excitation caused by the UC approach two resonances in the feature. In addition trends in regions of changes of differential motion, force of friction, and frictional energy follow the experimental limit on build height.Originality/valueThis paper explores several aspects of the UC process not currently found in the current literature: examining the modal properties of build features, and a lumped parameter dynamic model to account for the changes in of the substrate geometry.

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.

Effect of substrate dimensions on dynamics of ultrasonic consolidation

An FEM model is developed for a fundamental study of the time-dependent mechanical behavior of the substrate and its dimensions on ultrasonic consolidation. The simulation shows that for a given vibration condition, the amplitude of contact friction stress and displacement stabilizes to a saturated state after certain number of ultrasonic cycles. With the increased substrate height, the amplitude of contact frictional stress decreases, while that of contact interface displacement increases. The reason for the decrease in the frictional stress at the contact interface for certain substrate heights is the complicated wave interference occurring in the substrate. An analytical wave model has been built to validate the FEM model. A specific substrate geometry ( height: width = 1.0) generates a minimum frictional strain state at the interface as a result of wave superposition. Such minimum strain state is believed to have produced the “lack of bonding” defect for the geometry. The energy density and transfer coefficient at the contact interface with different substrate heights is used as an indicator to correlate with the bond formation in ultrasonic bonding.

Reaction Assisted Ultrasonic Consolidated TiNi

This investigation has examined the feasibility of fabricating near-net shape components containing TiNi shape memory constituents by combining the attributes of ultrasonic consolidation and reaction heat treatment. An optimization design of experiment was conducted to determine the ultrasonic consolidation control parameters, e.g., sonotrode rotational velocity, amplitude and normal force, which would result in the maximum weld quality as defined by the linear weld density. Subsequent thermal treatment of the consolidated compact resulted in the formation of a graded Ti-TiNi-Ni microstructure.

Multi‐material bonding in ultrasonic consolidation

PurposeThe increasing interest in engineering structures made from multiple materials has led to corresponding interest in technologies, which can fabricate multi‐material parts. The purpose of this paper is to further explore of the multi‐material fabrication capabilities of ultrasonic consolidation (UC).Design/methodology/approachVarious combinations of materials including titanium, silver, tantalum, aluminum, molybdenum, stainless steel, nickel, copper, and MetPreg® were ultrasonically consolidated. Some of the materials were found to be effective as an intermediate layer between difficult to join materials. Elemental boron particles were added in situ between selected materials to modify the bonding characteristics. Microstructures of deposits were studied to evaluate bond quality.FindingsResults show evidence of good bonding between many combinations of materials, thus illustrating increasing potential for multi‐material fabrication using UC.Originality/valueMulti‐material fabrication capabilities using UC and other additive manufacturing processes is a critical step towards the realization of engineering designs which make use of functional material combinations and optimization.

The effect of interface topography for Ultrasonic Consolidation of aluminium

Ultrasonic Consolidation (UC) is an additive manufacturing technology which is based on the sequential solid-state ultrasonic welding of metal foils. UC presents a rapid and adaptive alternative process, to other metal-matrix embedding technologies, for ‘smart’ metal composite material production. A challenge that exists however relates to optimising, for bond density and plastic flow, the interlaminar textures themselves that serve as the contact surfaces between the foils. UC employs a sonotrode connected to a transducer to exude ultrasonic energy into the metal foil being sequentially deposited. This sonotrode to metal contact imparts a noteworthy topology to the processed metals surface that in turn becomes the crucial substrate topology of the subsequent layers deposition. This work investigated UC processed Al 3003 samples to ascertain the effect of this imparted topology on subsequent layer deposition. Surface and interlaminar topology profiles were characterised using interferometry, electron and light microscopy. The physical effect of the topology profiles was quantified via the use of peel testing. The imparted topology profile was found to be of fundamental significance to the mechanical performance and bond density achieved within the bulk laminate during UC. The UC process parameters and sonotrode topology performed a key role in modifying this topology profile. The concept of using a specifically textured sonotrode to attain desired future smart material performance via UC is proposed by the authors.

Microstructure evolution of 6061 O Al alloy during ultrasonic consolidation: An insight from electron backscatter diffraction

6061 O Al alloy foils were welded to form monolithic and SiC fibre-embedded samples using the ultrasonic consolidation (UC) process. Contact pressures of 135, 155 and 175 MPa were investigated at 20 kHz frequency, 50% of the oscillation amplitude, 34.5 mm s −1 sonotrode velocity and 20 °C. Deformed microstructures were analysed using electron backscatter diffraction (EBSD). At all contact pressures deformation occurs by non-steady state dislocation glide. Dynamic recovery is active in the upper and lower foils. Friction at the welding interface, instantaneous internal temperatures (0.5–0.8 of the melting temperature, T m), contact pressure and fast strain rates result in transient microstructures and grain size reduction by continuous dynamic recrystallization (CDRX) within the bonding zone. Bonding occurs by local grain boundary migration, which allows diffusion and atom interlocking across the contact between two clean surfaces. Textures weaken with increasing contact pressure due to increased strain hardening and different grain rotation rates. High contact pressures enhance dynamic recovery and CDRX. Deformation around the fibre is intense within 50 μm and extends to 450 μm from it.

An analytical energy model for metal foil deposition in ultrasonic consolidation

PurposeRecently, a number of research projects have been focused on an emerging additive manufacturing process, termed ultrasonic consolidation (UC). The purpose of this paper is to present an analytical energy model aimed at investigating the effects of process parameters on bond formation in UC.Design/methodology/approachIn the model, two factors are defined, energy input to the workpiece within a single cycle of ultrasonic vibration (E0) and total energy input to the workpiece (Et), to evaluate to the magnitude of transmitted energy into the workpiece during UC.FindingsIt is found that linear weld density, E0 and Et are affected by process parameters in similar manners.Research limitations/implicationsThe current model is developed based on several simplifying assumptions, and energy dissipation and bond degradation during UC are not considered in the model.Originality/valueThe current model gives a useful understanding of the effects of process parameter on the bond formation in UC from an energy point of view.

Surface damage during ultrasonic consolidation of 3003‐H18 aluminum

PurposeThe purpose of this paper is to examine the formation of surface damage associated with the ultrasonic consolidation (UC) of single ply 150 μm thick 3003‐H18 foil to a 3003‐18 build plate and the relationship between the development of this damage state with the linear weld density (LWD) achieved during consolidation.Design/methodology/approachThe influence of the consolidation control variables on the area fraction of the sonotrode induced top foil surface damage is established through application of a full factorial three‐level design‐of‐experiment methodology, the control variables limits being fixed by the capability of the UC system.FindingsDetailed analysis of the foil top surface structure after consolidation reveals the presence of two characteristic, damaged and undamaged, regions. The former corresponded to plastically deformed areas, these being formed as a result of interaction of the foil top surface with the sonotrode, while the latter corresponded to the original foil surface. Sonotrode normal load, vibrational amplitude and its rotational velocity are found to have an interdependent affect on the development of the sonotrode‐induced top surface damage. Top surface damage initiates upon impression of the sonotrode into the foil surface followed by the commencement of oscillatory and forward rotational motion of the sonotrode. Finally, evidence is presented that the degree of sonotrode induced top surface damage bears a direct relationship with the linear ultrasonic weld density developed at the foil‐build plate interface, increasing top surface damage being associated with increased LWD.Originality/valueA linear relationship between the degree of bonding at the foil‐build plate interface and the plastically deformed area on the foil top surface is established, this correlation demonstrating that bond formation between foils during UC depends on effective frictional conditions at the sonotrode‐foil interface.