Paul J. Wolcott

Optimizing Ultrasonic Additive Manufactured Al 3003 Properties With Statistical Modeling

Ultrasonic additive manufacturing (UAM) has proven useful in the solid-state, low tempe’rature fabrication of layered solid metal structures. It is necessary to optimize the various process variables that affect the quality of bonding between layers through investigation of the mechanical strength of various UAM builds. We investigate the effect of the process parameters tack force, weld force, oscillation amplitude, and weld rate on the ultimate shear strength (USS) and ultimate transverse tensile strength (UTTS) of 3003-H18 aluminum UAM built samples. A multifactorial experiment was designed and an analysis of variance was performed to obtain an optimal set of process parameters for maximizing mechanical strength for the tested factors. The statistical analyses indicate that a relatively high mechanical strength can be achieved with a process window bounded by a 350 N tack force, 1000 N weld force, 26 lm oscillation amplitude, and about 42 mm/s weld rate. Optical analyses of bond characterization did not show a consistent correlation linking linear weld density and bonded area of fractured surfaces to mechanical strength. Therefore, scanning electronmicroscopy (SEM) was conducted on fractured samples showing a good correlation between mechanical strength and area fraction that shows ductile failure. [DOI: 10.1115/1.4005269]

Characterisation of Al–Ti dissimilar material joints fabricated using ultrasonic additive manufacturing

Ultrasonic additive manufacturing (UAM) is a solid state manufacturing process for joining thin metal tapes using principles of ultrasonic metal welding. The process operates at low temperatures, enabling dissimilar material welds without generating harmful intermetallic compounds. In this study, a 9 kW UAM system was used to create joints of Al 1100 and commercially pure titanium. Viable process parameters were identified through pilot weld studies via controlled variation of weld force, amplitude and weld speed. Push-pin delamination tests and shear tests were performed, comparing as-built, heat treated and spark plasma sintering treated samples. Heat treated and spark plasma sintering treated samples yielded mechanical strengths over twice that of as-built samples. Electron backscatter diffraction measurements show that deformation and grain refinement only take place in the aluminium layers. Heat treated samples exhibit a thin intermetallic layer, which is hypothesised as constraining the interface, leading to the improved strength.

Effect of weld power and build compliance on ultrasonic consolidation

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.

Optimal welding parameters for very high power ultrasonic additive manufacturing of smart structures with aluminum 6061 matrix

Ultrasonic additive manufacturing (UAM) is a recent solid state manufacturing process that combines ad- ditive joining of thin metal tapes with subtractive milling operations to generate near net shape metallic parts. Due to the minimal heating during the process, UAM is a proven method of embedding Ni-Ti, Fe-Ga, and PVDF to create active metal matrix composites. Recently, advances in the UAM process utilizing 9 kW very high power (VHP) welding has improved bonding properties, enabling joining of high strength materials previously unweldable with 1 kW low power UAM. Consequently, a design of experiments study was conducted to optimize welding conditions for aluminum 6061 components. This understanding is critical in the design of UAM parts containing smart materials. Build parameters, including weld force, weld speed, amplitude, and temperature were varied based on a Taguchi experimental design matrix and tested for me- chanical strength. Optimal weld parameters were identi ed with statistical methods including a generalized linear model for analysis of variance (ANOVA), mean e ects plots, and interaction e ects plots.

Smart Switch Metamaterials for Multiband Radio Frequency Antennas

We investigate metal–matrix composite metamaterials with embedded electrical switches made of shape memory nickel–titanium (Ni–Ti) for use in broadband radio frequency (RF) antennas. Experiments show that a Ni–Ti ribbon can form an electrical contact that opens and closes depending on the Ni–Ti phase being austenite or martensite. Finite element modeling of thermal gradients illustrates the phase change within the ribbon. Ultrasonic additive manufacturing (UAM), a solid-state additive manufacturing process, was utilized for embedding a Ni–Ti switch in an aluminum matrix. The aluminum matrix must have structural-grade strength for use in load-carrying antennas; thus, mechanical testing was conducted to quantify the longitudinal tensile, transverse tensile, and shear strength of the UAM matrix. Reconfiguration using a Ni–Ti switch was proven using a shape memory switch on a monopole RF antenna producing an operating frequency shift from 270 to 185 MHz when the switch is connected. A planar microstrip line was used to demonstrate signal transmission and reflection efficiency in a smaller, second switch. Transmission tests yielded less than −10 dB signal reflection proving the feasibility of reconfigurable planar antenna arrays using smart switches.

Microstructure and mechanical property characterisation of aluminium–steel joints fabricated using ultrasonic additive manufacturing

ABSTRACT Driven by the interest to weld steel and aluminium in the solid state to prevent intermetallic formation, 9 kW ultrasonic additive manufacturing (UAM) has been used to fabricate Al 6061-4130 steel dissimilar metal builds. In addition, Al 6061-Al-6061 builds were fabricated using similar techniques to provide a baseline for mechanical property measurement. Mechanical testing performed using pushpin testing shows that steel–aluminium dissimilar metal welds fail across multiple layers while Al–Al welds delaminate from the substrate. Multi-scale characterisation indicates that the change in failure morphology is due to the formation of metallurgical bonds in the Al–steel builds. Texture analysis shows identical textures at the interface of Al–steel, Al–Al and Al–Ti joints; showing that the bond formation in all cases relies extensively on plastic deformation across multiple materials. In addition, no changes to the bonding mechanism occurred when the materials used as foils and substrate were swapped.

Radio frequency patch antenna reconfiguration with Ni–Ti shape memory alloy switches

Nickel–titanium shape memory alloys are employed to develop a multiband radio frequency antenna. Switches made from Ni–Ti electronically connect together a planar patch antenna arrangement, creating several electrical signal pathways that enable reconfiguration via resonance shifting. The changes in the antenna geometry, induced by the switches, create different working frequencies. The switches open and close due to an induced phase change from martensite to austenite via resistive heating from a separate electric circuit. A patch antenna was fabricated and then measured for S11 reflection coefficient, antenna gain, and radiation pattern at different configurations. The results show that the working frequency of the patch antenna arrangement is tunable from 2.25 to 2.43 GHz depending on the antenna geometry, while the antenna always maintains a high gain. The experimental results match well with simulations, indicating the potential for simulated design of future applications and geometries through shape memory actuators.

Seam Welding of Aluminum Sheet Using Ultrasonic Additive Manufacturing System

Ultrasonic welding was investigated as a method of joining 0.076 in. (1.93 mm) thick aluminum 6061 flat sheet material. Joints were produced with ultrasonic additive manufacturing (UAM) equipment in a modified application of the ultrasonic welding process. Through joint design development, successful welds were achieved with a scarf joint configuration. Using a design of experiments (DOE) approach, weld parameters including weld amplitude, scarf angle, and weld speed were optimized for mechanical strength. Lower angles and higher amplitudes were found to provide the highest strengths within the levels tested. Finite-element studies indicate that 5 deg and 10 deg angles produce an increased relative motion of the workpieces as compared to 15 deg, 20 deg, and 25 deg angles, likely leading to increased strength. Successful joints showed no indication of voids under optical microscopy. As-welded joints produce tensile strengths of 221 MPa, while heat treated joints produce tensile strengths of 310 MPa, comparable to heat treated bulk material. High-temperature tensile testing was conducted at 210 C, with samples exhibiting strengths of 184.1 MPa, similar to bulk material. Room temperature fatigue testing resulted in cyclic failures at approximately 190,000 cycles on average, approaching that of bulk material. [DOI: 10.1115/1.4034007]

Planar RF Antenna Reconfiguration With Ni-Ti Shape Memory Alloys

Nickel-titanium shape memory alloys (SMA) are utilized to achieve a multi-band RF (radio frequency) antenna through reconfiguration. Switches made from shape memory alloys electronically connect together a planar antenna arrangement, creating several electrical signal pathways and reconfiguration to be realized. The changes in geometry induced by the switching create different working frequencies of the antenna leading to multiple bands. The switches open and close due to an induced phase change from martensite to austenite via resistive heating from a separate electric circuit. Switch design is based on a previously successful switch geometry with the goal of miniaturizing the reconfigurable antenna system. Simulations were performed to determine an optimal geometry for reconfiguration with the switches to generate measurable changes in working frequency in a planar antenna. Based on these simulations, a planar antenna consisting of a dielectric material between conductive copper layers was designed and constructed for use with the SMA switches. The antenna design is based on a patch antenna that is reconfigured to new geometries as the SMA switches are activated. The working frequency of the planar antenna arrangement can be tuned to between 2.25 GHz and 2.43 GHz depending on geometry as measured with S11 signal reflection.Copyright