A new method for metal 3D printing that avoids melting and sharply reduces power consumption has been demonstrated by Reverb Industrial, a California-based developer of advanced manufacturing technologies, in collaboration with Arizona State University. The research, published in MDPI, shows that Resonance-Assisted Deposition (RAD) can fabricate dense aluminum alloy components at machine power levels of just 100 to 300 watts. By comparison, laser powder bed fusion systems typically operate at 10 to 20 kilowatts, consuming 300–500 megajoules per kilogram of aluminum alloys processed, equivalent to about 1 megajoule per cubic centimeter.
RAD is based on the phenomenon that high-frequency oscillatory strain lowers the apparent yield stress of metals and enhances diffusion across interfaces. In practice, the system applied vibrations at 40 kilohertz with amplitudes below several tens of micrometers during deposition. Each cycle shaped a segment of wire feedstock into a flattened voxel while simultaneously promoting atomic diffusion with neighboring material. These combined effects allowed shaping and joining to occur without heating, enabling the team to print net-shape aluminum 6061 structures. Components included thin-walled samples with high aspect ratios that are typically challenging for fusion-based techniques. Earlier studies had shown that oscillatory strain can be roughly 30 times more efficient than heating for reducing yield stress, and the effect is magnified in real systems where heat transfer losses further reduce efficiency.
The researchers constructed a three-axis motion platform in which the build plate moved in the X–Y plane and the print head moved in the Z direction. Aluminum 6061-O wire feedstock with a diameter of 0.35 millimeters, supplied by California Fine Wire Company, was passed through a hollow shear-strain transfer tool attached to a piezoelectric transducer. The feedstock had a tensile strength of 140 megapascals and elongation of 17.1 percent. In each compression cycle, the wire was shaped into a voxel at the deposition site, with oscillatory strain reducing yield stress and promoting bonding. The tool lifted, moved laterally by a step size of 1 millimeter, and repeated the process. Track overlap was tested at 0.6 and 0.7 millimeters to compare complete filling versus incomplete overlap. Toolpathing used two outer walls with ±45° infill patterns, with overlap conditions determining whether voids remained or space filling was complete.
Microscopy revealed how the joining mechanism worked. When pure aluminum voxels were deposited on nickel, bright-field images showed high defect densities in regions near the interface, including stacking faults. These defects enhanced diffusion, producing interfacial zones 80 to 140 nanometers wide. Calculations indicated that diffusion of this scale would require temperatures of 320 to 420 °C if caused by heating alone. Thermal measurements during deposition showed increases of only 5 to 10 °C, demonstrating that enhanced diffusion came from oscillatory strain rather than melting. Energy-Dispersive Spectroscopy (EDS) line scans across the Al–Ni interface confirmed concentration gradients created by this defect-driven mechanism. The setup used a 200 kilovolt accelerating voltage and a step size of 5 nanometers, allowing quantitative measurement of elemental diffusion. Native oxide layers broken during initial contact were sometimes trapped at the boundary, influencing later fracture behavior.
Mechanical performance reflected these interfacial characteristics. Micro-computed tomography scans of printed parts showed that with sufficient overlap, density reached 99.95 percent of the feedstock material. Samples with 0.7 millimeter inter-track spacing displayed voids, while those with 0.6 millimeters achieved near-complete consolidation. Tensile testing of coupons printed horizontally and vertically, conducted at 150 millimeters per minute, revealed ultimate strength at about 75 percent of the annealed feedstock wire. The study found low anisotropy in strength but higher anisotropy in elongation. Vertical coupons exhibited brittle fracture along interfaces where oxides were trapped, while horizontal samples showed more ductile behavior. Fracture surface images displayed extensive plastic deformation in interlayer regions but brittle separation at oxide-rich zones. Surface roughness tests indicated top-layer values of 10–20 micrometers Ra, while sidewalls measured 15–25 micrometers Ra. The scalloped profile along vertical surfaces resembled patterns common in polymer extrusion printing.
Energy consumption data emphasized the contrast with conventional approaches. At the voxel level, RAD required 3.79 × 10⁻⁴ joules per cubic millimeter for shaping and joining. Laser powder bed fusion typically consumes about 100 joules per cubic millimeter, representing a difference of five orders of magnitude. At the machine scale, the RAD platform drew 100 to 300 watts depending on operating conditions, even when build plate heating was used for in-process annealing. By contrast, laser and electron-beam systems consume tens of kilowatts. Conventional fusion-based processes lose efficiency at several stages, including electrical-to-optical conversion, absorption of laser energy, and heat transfer to surrounding material. Parasitic heating further increases consumption because extra power must be dissipated to maintain laser performance. In RAD, mechanical strain energy is directly coupled into the crystalline lattice, avoiding these inefficiencies and reducing system-level demand by factors of ten to one hundred.
Reverb Industrial and Arizona State University present RAD as a distinct route for additive manufacturing. By shaping and joining metal wire without melting, the method sidesteps common issues such as absorptivity variation, melt-pool instability, and high thermal gradients. While elongation along the build direction remains limited due to oxide entrapment at interlayer boundaries, the process demonstrates high density, substantial strength, and exceptional energy efficiency.
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Featured image shows the tool pathing strategy used for printing the components. Image via MDPI.
