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This paper aims to comprehensively review ultrasonic additive manufacturing (UAM) process history, technology advancements, application areas and research areas. UAM, a hybrid 3D metal printing technology, uses ultrasonic energy to produce metallurgical bonds between layers of metal foils near room temperature. No melting occurs in the process – it is a solid-state 3D metal printing technology.

The paper is formatted chronologically to help readers better distinguish advancements and changes in the UAM process through the years. Contributions and advancements are summarized by academic or research institution following this chronological format.

This paper summarizes key physics of the process, characterization methods, mechanical properties, past and active research areas, process limitations and application areas.

This paper reviews the UAM process for the first time.

The 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).

Various 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.

Results show evidence of good bonding between many combinations of materials, thus illustrating increasing potential for multi‐material fabrication using UC.

Multi‐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.

This paper presents an offset‐based tool path generation method for STL format three‐dimensional (3D) models. The created tool‐paths can be effectively used to near‐net‐shaped parts, in particular those created using rapid prototyping.

The STL model is first offset by the distance of the selected cutter radius using a unique 3D offset method. The intersections between the top facing triangles of the offset model and tool‐path drive planes are calculated. The intersection line segments are sorted, trimmed and linked to generate continuous top envelope curves, which represent interference‐free tool paths.

The developed offset‐based algorithm can rapidly and successfully generate interference‐free tool paths as continuous lines, instead of a collection of discrete tool location points. The strategy of using adaptive step‐over distances based on local geometrical information can significantly increase machining efficiency.

The current tool path generation method only works for ball‐end mills. The entire surface of the STL model is treated as a single composite surface to be machined using raster milling. To improve machining efficiency, an automatic surface splitting algorithm could be developed to divide the model into several regions based on the characteristics of a group of triangular facets, and then machine these identified regions using different strategies and cutters.

The offset‐based tool‐path generation algorithm from STL models is a unique and novel development, which is useful in the rapid prototyping and computer‐aided machining areas.

Recently, 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.

In 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 (E_t), to evaluate to the magnitude of transmitted energy into the workpiece during UC.

It is found that linear weld density, E₀ and E_t are affected by process parameters in similar manners.

The current model is developed based on several simplifying assumptions, and energy dissipation and bond degradation during UC are not considered in the model.

The current model gives a useful understanding of the effects of process parameter on the bond formation in UC from an energy point of view.

This paper presents a unique method to recognize circular holes from 3D models in the STL format. The topological information generated by this method enables identification of holes and tool path generation for holes which should be drilled rather than milled.

A method based on a set of developed algorithms is used to identify closed loops from a STL model, identify which closed loops correspond to cylindrical holes, find hole orientations, locations and diameters, and calculate the depth for the recognized holes. The developed procedure and algorithms have been implemented in Visual C++ to illustrate the efficacy of the method.

The implementation results showed that the developed algorithms can successfully recognize circular holes of differing sizes on both simple and complex surfaces, and in any orientation. Tool paths can thus be generated from STL models to more efficiently and accurately machine circular holes.

The developed method requires that at least one simple closed loop exist for each potential hole.

A new and unique hole recognition method for use with STL models was developed. This method is useful for accurately and efficiently machining parts with circular holes from STL models as well as finish machining near‐net shape parts with circular holes created using rapid prototyping.

Ultrasonic consolidation (UC) is a novel additive manufacturing process developed for fabrication of metallic parts from foils. While the process has been well demonstrated for part fabrication in Al alloy 3003, some of the potential strengths of the process have not been fully explored. One of them is its suitability for fabrication of parts in multi‐materials. This work aims to examine this aspect.

Multi‐material UC experiments were conducted using Al alloy 3003 foils as the bulk part material together with a number of engineering materials (foils of Al‐Cu alloy 2024, Ni‐base alloy Inconel 600^® AISI 347 stainless steel, and others). Deposit microstructures were studied to evaluate bonding between various materials.

It was found that most of the materials investigated can be successfully bonded to alloy Al 3003 and vice versa. SiC fibers and stainless wire meshes were successfully embedded in an Al 3003 matrix. The results suggest that the UC process is quite suitable for fabrication of multi‐material structures, including fiber‐reinforced metal matrix composites.

This work systematically examines the multi‐material capability of the UC process. The findings of this work lay a strong foundation for a wider and more efficient commercial utilization of the process.

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.

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.

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.

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.

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.

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.

This paper investigates wetting and infiltration of zirconium diboride by copper and copper/boron alloys in order to more effectively create electrodes for electrical discharge machining.

A high temperature furnace outfitted with a video recording system was utilized to observe wetting angles between molten copper alloys and zirconium diboride at various temperatures. A parallel, investigation of the thermodynamics involved with oxidation in the system was also undertaken.

This study showed that zirconium diboride can be wet by pure copper under carefully controlled conditions where oxygen contamination is minimized, and that the wetting angle increases with increasing temperature. Thermodynamic calculations reinforce the contention that oxygen contamination is the key barrier to wetting and infiltration. The addition of boron to copper significantly improves the wetting characteristics, and enables wetting and infiltration under higher oxygen contamination conditions.

This study illustrated that boron must be added to copper to achieve infiltration when surface oxides are present.

Infiltration of porous 3D green shapes of ceramics and metals is a common method for producing metal and ceramic components using rapid prototyping. Good wetting of the porous material by the infiltrant material is necessary for successful infiltration using capillary forces. This paper illustrates the alloys and conditions under which it is possible to produce electrodes of zirconium diboride/copper using rapid prototyping.

The purpose of this paper is to investigate the effectiveness of locking or staking of fasteners with epoxy material systems to prevent loss of preload in aerospace environments.

A quantitative experimental method is adopted to evaluate epoxy material systems for staking of fastener assemblies subjected to varying dynamic and thermal loads. A statistical design of experiments is employed to probe specific design parameters.

Results show that epoxy application can provide satisfactory fastener locking under a variety of service conditions. It is found that: Epon 828 epoxy provides superior fastener locking compared to 3M Scotch‐Weld Epoxy 2216; epoxy application around screw threads is more effective than application around screw head; and abrading the plate surfaces with 180 grit SiC paper is not an effective or useful surface preparation technique.

The paper is limited to two commercial epoxy material systems and does not consider important qualitative considerations for industrial use such as cure time and viscosity.

This and future paper may form the basis of new standards for epoxy staking in the global aerospace industry.

This paper is believed to be one of the very few original experimental studies of fastener staking available in the open literature.

The purpose of this paper is to present a new method for automated post machining process planning for a hybrid manufacturing process. The manufacturing process is expected to generate complex functional parts by taking advantage of free form surface creation from additive manufacturing and high-quality surface finishing from CNC milling.

The hybrid process starts with additive manufacturing to generate a near net shape part with pre-defined machining allowances on surfaces requiring high quality surface or tight tolerances, along with integrated fixture geometry. The next step is to conduct automated machining process planning to determine critical parameters such as setup angle, tool selection, depth, tool containment, and consequently, the NC code to machine the part.

This method is shown to be a feasible solution for rapidly creating functional parts. The tests have been conducted to validate the method developed in this paper.

This paper introduces a new automated post machining process planning method for integrating additive manufacturing with a rapid milling process.