Development of Functionally Gradient Materials Using Ultrasonic Additive Manufacturing

Recently, high-performance lightweight materials with outstanding mechanical properties have opened up their way to some sophisticated industrial applications. As one of these systems, aluminum matrix composites/nanocomposites (AMCs) offer an outstanding combination of relative density, hardness, wear resistance, and mechanical strength. Until now, several additive manufacturing methods have been developed for fabrication of 3D metallic components among them, selective laser melting (SLM), electron beam melting (EBM), laser metal deposition (LMD), Wire+Arc additive manufacturing (WAAM), and ultrasonic additive manufacturing (UAM) are of prime significance. Unlike other methods, in ultrasonic additive manufacturing, the ultrasonic waves are used instead of applying the sintering process. This technique is well-known for its ability to produce 3D components by repeating the alternative welding and machining procedures at low temperatures. This is why it can overcome the technological issues arisen from the high-temperature sintering. The present review strives to provide an inclusive introduction to the principles of ultrasonic additive manufacturing method and recent advances in ultrasonic additive manufacturing of aluminum matrix composites/nanocomposites. Also, the challenges of this new emerging technique, i.e. its dependence to the applied weld power, is addressed in the paper. The authors attempt to give some perspectives to the researchers for further investigations in this new-emerging field.

Carbon fiber reinforced plastic (CFRP) are advanced engineering materials which are recognized as the most sought-after composite for several industrial applications including aerospace and automotive sectors. CFRP have superior physical and mechanical properties such as lightweight, high resilience, high-durability and high strength-to-weight ratio. CFRP composites stacked up with titanium to form multi-layered material stacks to enhance its load bearing capability. Traditional methods of stacking up CFRP and titanium involves using either high strength adhesives or rivets and bolts. The laminate structures joined by these methods often tend to fail during high load-bearing applications. Conventional metal welding technologies use high heat causing high thermal stresses and microstructural damages. Ultrasonic welding is a solid-state joining process, which has the capability of welding dissimilar materials at relatively low temperatures using ultrasonic vibration. Ultrasonic additive manufacturing (UAM) process is an ideal method to weld CFRP and Titanium. During the ultrasonic welding process, two dissimilar materials under a continuous static load are subjected to transverse ultrasonic vibrations, which results in high stress and friction between the two surfaces. This research focuses on the study of ultrasonically welding CFRP and Titanium stacks using UAM process. The study involves experimentation performed on an in-house built UAM setup. Finite element analysis is performed to understand the distribution stresses and strains during the UAM process. In this study, CFRP and Titanium layers are successfully welded using UAM process without causing any melting or significant heating. The finite element analysis study revealed that during UAM process, CFRP/Titanium stacks are subject to repeated cyclic shear stress reversals resulting in a strong weld joint. The stress-strain diagram during the process showed a considerable increase in plastic strain during the UAM process. The outcomes of this study can be used to further the industrial applications of the ultrasonic additive process as well as other ultrasonic welding based processes involving dissimilar materials.

Metal Additive Manufacturing (AM) is increasingly being used to make functional components. One of the barriers for AM components to become mainstream is the difficulty to certify them. AM components can have widely different properties based on process parameters. Improving an AM processes requires an understanding of process-structure-property correlations, which can be gathered in-situ and post-process through nondestructive and destructive methods. In this study, two metal AM processes were studied, the first is Ultrasonic Additive Manufacturing (UAM) and the second is Laser Powder Bed Fusion (L-PBF). The typical problems with UAM components are inter-layer and inter-track defects. To improve the UAM process, an in-situ quality evaluation technique was desired. Several NDE techniques were tested in a lab environment before ultrasonic NDE was chosen as a practical, robust, and cost-effective NDE tool. An in-situ monitoring setup was designed and built on an UAM system. NDE results showed interesting features that were simulated through analytic and finite element wave-propagation models. AM layers with defects were characterized as an intact layer and a finite interfacial stiffness spring. The spring stiffness coefficient is a quality parameter that was used to characterize AM layers through a model-based inversion method. In-situ and post-process NDE provided an understanding of defect generation and propagation in UAM. A novel solid-state repair mechanism based on Friction Stir Processing (FSP) was proposed and demonstrated. The quality of L-PBF components depends on several factors including laser power, scan speed, hatch spacing, layer thickness, particle shape/size distribution and other build conditions. Developing process parameters for a new material is an expensive and complex optimization problem. Post-process ultrasonic NDE tests revealed that the model-based in-situ quality monitoring developed for UAM is also applicable to L-PBF Additive Manufacturing. A similar NDE set-up was designed and installed on an open-architecture L-PBF system. A layer-by-layer bond quality evaluation demonstrates the ability to detect good-quality bonds hidden behind poor-quality regions for Inconel 625 alloy. A cost-effective, process parameter development methodology has been proposed and demonstrated.

Functionally Gradient Materials (FGM) smoothly transition from one material to another within a single object, allowing engineers to customize the physical response of different regions of the object by modifying the material composition at each region. New FGM research makes design, manufacturing, and use of FGM objects a promising alternative to homogeneous objects or composites with one direction of gradation. Heterogeneous anisotropic artifacts can be manufactured with specific 3D printing processes and potentially bring significant increases in functionalities. However, many challenges exist while designing and manufacturing these objects. This paper explores these challenges and suggests needed research. In particular the ability to model FGM objects, setup and run optimization algorithms, create manufacturing process plans, and control the manufacturing process all need more research and better software tools. In addition, researchers must rigorously test optimally designed FGM objects in order to validate the FGM object properties and the FGM design process before adoption of FGM objects by industry is likely to occur.

The advent of additive manufacturing has opened up new frontiers in developing metal structures that can have complex geometries, composite structures made of dissimilar metals, and metal structures with embedded sensing and actuation capabilities. These types of structures are possible with ultrasonic additive manufacturing (UAM); a novel manufacturing technology that combines additive manufacturing through the ultrasonic welding of thin metal foils with computer numerical control (CNC) milling. However, the process suffers from a critical limitation, i.e., a range of build heights within which bonding between a foil and the substrate cannot be originated. This work has two research objectives, the first is a fundamental understanding of the complex dynamic interaction between the substrate and ultrasonic horn, or sonotrode. Specifically, it focuses on the effects that specific modes of vibration have on the dynamic response of the substrate. The second objective is to utilize the UAM process to create metal structures with an embedded sensor that can detect contact or impact. In addressing the first objective, a semi-analytical model was developed to determine the response to three forcing descriptions that approximate the interfacial friction between the foil and substrate induced by sonotrode compression and excitation. Several observations can be seen in the results: as the height increases the dominant modes of vibration change, the modes of vibration excited also change during a single weld cycle as the sonotrode travels across the length of the substrate, and finally the three forcing models do not have a significant impact on the substrate response trends with height and during the weld cycle. In addressing the second objective, three prototypes were created by embedding a triboelectric nanogenerator (TENG) sensor within an AL3003 metal-matrix. TENGs utilize contact electrification between surfaces of dissimilar materials, typically polymers, combined with electrostatic induction to generate electrical energy from a mechanical excitation. The sensors demonstrate a discernible response over a 1-5 Hz frequency range. In addition, the sensors have a linear relationship between output voltage and a mechanically applied load, and have the ability to sense contact through both touch and due to an impacting object.

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.

Ultrasonic consolidation has been shown to be a viable metal-matrix-based smart composite additive layer manufacturing process. Yet, high quantity fibre integration has presented the requirement for a method of accurate positioning and fibre protection to maintain the fibre layout during ultrasonic consolidation. This study presents a novel approach for fibre integration during ultrasonic consolidation: channels are manufactured by laser processing on an ultrasonically consolidated sample. At the same time, controlled melt ejection is applied to aid accurate fibre placement and simultaneously reducing fibre damage occurrences. Microscopic, scanning electron microscopic and energy dispersive X-ray spectroscopic analyses are used for samples containing up to 10.5% fibres, one of the highest volumes in an ultrasonically consolidated composite so far. Up to 98% of the fibres remain in the channels after consolidation and fibre damage is reduced to less than 2% per sample. This study furthers the knowledge of high volume fibre embedment via ultrasonic consolidation for future smart material manufacturing.

Advancements in understanding the microstructure and properties of additive manufacturing Ti-6Al-4V alloy: A comprehensive review

During the forging process, hot forging dies can easily sustain damage, including thermal softening, crack extension, wear and so on. The existing homogeneous hot forging die steel cannot meet the service performance requirements. However, the strengthening technology based on functionally gradient material (FGM) technology and surface cladding together can relieve the thermal stress. Based on the zoning of the temperature field distribution during continuous working, the structural design method and preparation process for the long life hot forging die are proposed in this paper; meanwhile, multilayer metal coating based on FGM was carried out and the temperature field, the stress field distribution for the homogeneous materials and the multilayer metal material hot forging die were analysed and compared. The results prove that using long service life hot forging die technology combined with FGM and surface cladding can relieve the overall stress value.

Worldwide trends in functional gradient materials research and development

Fused Deposition Modeling (FDM) is a popular style of additive manufacturing (AM) where a 3D object is fabricated by a molten material deposited into successive 2D layers. Multi-material 3D printing is particularly challenging due to poor adhesion between dissimilar plastics. The majority of currently available multi-material printers use separate nozzles for each material. Therefore, they are incapable of producing devices made of functionally gradient materials (FGM). FGM is a special class of engineering material exhibiting spatially inhomogeneous content, which tailors the material for specific functional and performance requirements. In this work, we present the design and characterization of a bi-material co-extruder system. This specialized extruder is capable of printing two thermoplastic materials through a single nozzle and is also capable of altering the composition of the deposited material while printing. It is also exceptional in that the internal structure of the hot end can be easily accessed and is a more adaptable design than previously reported co-extruders. The extruder was installed on a Geeetech PI3 Pro C printer. Then, some simple structures were printed using pairs of materials including polylactic acid (PLA), acrylonitrile butadiene styrene (ABS) and high impact polystyrene (HIPS). Without any internal mixing features, the composition of the output (for instance, different colored PLA) was determined from microscopic images of cross-section of the extrudates.

The capabilities of additive manufacturing technologies to fabricate multi-material structures have been investigated in many studies. However, only a few of the technologies have been used to fabricate products for direct application. The full development of the capability will enable the fabrication of innovative engineering structures consisting of function-specific material members that cannot be realized using conventional methods. In this work, a methodology for fabricating dual-material engineering structures using ultrasonic additive manufacturing (UAM) was developed. An example structure consisting of members designed to carry tension and compression loads were fabricated using composite materials and Al 3003 matrix material respectively. MetPreg®/Al 3003 and Ti/Al 3003 composite materials were respectively used as tension members in two different structure samples. Single-material copies of the dual-material structures were fabricated using Al 3003 for load-carrying capability comparison. The results of the load tests carried out shows that the dual-material structures could withstand much higher loads than similar structures entirely made of the matrix Al 3003 material. This is an indication that UAM can be effectively used to fabricate multi-material engineering structures.

Metal Sheet Lamination – Ultrasonic

This article is a detailed account of additive manufacturing (AM) processes for copper and copper alloys such as copper-chromium alloys, GRCop, oxide-dispersion-strengthened copper, copper-nickel alloys, copper-tin alloys, copper-zinc alloys, and copper-base shape memory alloys. The AM processes include binder jetting, ultrasonic additive manufacturing, directed-energy deposition, laser powder-bed fusion, and electron beam powder-bed fusion. The article presents a review of the literature and state of the art for copper alloy AM and features data on AM processes and industrial practices, copper alloys used, selected applications, material properties, and where applicable, compares these data and properties to traditionally processed materials. The data presented and the surrounding discussion focus on bulk metallurgical processing of copper components. The discussion covers the composition and performance criteria for copper alloys that have been reported for AM and discusses key differences in process-structure-property relationships compared to conventionally processed material. The article also provides information on feedstock considerations for copper powder handling.

Ultrasonic Additive Manufacturing (UAM) is an innovative process technology that uses sound to combine layers of metal produced from foil stocks. The variation seen in UAM from other AM techniques is that metals are not melted but joined by ultrasonic welding instead. This technique uses high-frequency vibration to bond the surfaces of metal foils while the metal remains firm. The addition of foils by stacking one on the other by this welding technique leads to the creation of solid parts. This method creates high-density metallurgical bonds without melting the metals. This proves to be advantageous, as it avoids changes in grain size, phases, and precipitation reactions. It also aids in bonding dissimilar metals without creating any brittle intermetallic bonding. UAM provides a major application of embedding electronics in solid metal parts to fabricate microelectronics systems like micro-processors, telemetry, and sensors.