Additive manufacturing (AM) is poised to bring about a revolution in the way products are designed, manufactured, and distributed to end users. This technology has gained significant academic as well as industry interest due to its ability to create complex geometries with customizable material properties. AM has also inspired the development of the maker movement by democratizing design and manufacturing. Due to the rapid proliferation of a wide variety of technologies associated with AM, there is a lack of a comprehensive set of design principles, manufacturing guidelines, and standardization of best practices. These challenges are compounded by the fact that advancements in multiple technologies (for example materials processing, topology optimization) generate a "positive feedback loop" effect in advancing AM. In order to advance research interest and investment in AM technologies, some fundamental questions and trends about the dependencies existing in these avenues need highlighting. The goal of our review paper is to organize this body of knowledge surrounding AM, and present current barriers, findings, and future trends significantly to the researchers. We also discuss fundamental attributes of AM processes, evolution of the AM industry, and the affordances enabled by the emergence of AM in a variety of areas such as geometry processing, material design, and education. We conclude our paper by pointing out future directions such as the "print-it-all" paradigm, that have the potential to re-imagine current research and spawn completely new avenues for exploration. The fundamental attributes and challenges/barriers of Additive Manufacturing (AM).The evolution of research on AM with a focus on engineering capabilities.The affordances enabled by AM such as geometry, material and tools design.The developments in industry, intellectual property, and education-related aspects.The important future trends of AM technologies.

The status, challenges, and future of additive manufacturing in engineering

Additive manufacturing (AM), widely known as 3D printing, is a method of manufacturing that forms parts from powder, wire or sheets in a process that proceeds layer by layer. Many techniques (using many different names) have been developed to accomplish this via melting or solid-state joining. In this review, these techniques for producing metal parts are explored, with a focus on the science of metal AM: processing defects, heat transfer, solidification, solid-state precipitation, mechanical properties and post-processing metallurgy. The various metal AM techniques are compared, with analysis of the strengths and limitations of each. Only a few alloys have been developed for commercial production, but recent efforts are presented as a path for the ongoing development of new materials for AM processes.

The metallurgy and processing science of metal additive manufacturing

A pseudo composite material, may include, inter alia, a first phase and a second phase, wherein each phase may include, inter alia, an organic compound, wherein each phase comprising a multiplicity of construction layers, wherein the layers were deposited by ink-jet printing, wherein the pseudo composite material exhibits non-homogeneous three-dimensional structure. A method is disclosed for the preparation of a pseudo composite material. An apparatus is disclosed for printing a pseudo composite material. Furthermore, there is disclosed a method for printing a three-dimensional object using various suitable materials.

Compositions and methods for use in three dimensional model printing

Friction stir based welding and processing technologies - processes, parameters, microstructures and applications: A review

There is provided a method capable of decreasing a friction force in friction stir welding, in which a welding tool is used. In a method of friction stir welding workpieces together by rotating and pressingly plugging a welding tool, formed from a harder material than the workpieces, into a weld zone of the workpieces and moving the welding tool relatively in a welding direction, a power supply device allows a current to flow between the welding tool 1 and the workpieces to cause resistance heating of the welding tool. Combined use of resistance heating makes it possible to decrease a friction force. Preferably, a conductive ceramic is coated on surfaces of the welding tool to cause resistance heating.

Friction stir welding method

A system and a method of fabricating a three-dimensional object on a substrate includes adding material layers incrementally and consolidating the layers by using ultrasonic vibrations and pressure. The layers are placed in position to shape the object by a material feeding unit, and they come in various forms, including flat sheets, segments of tape, strands of filament or single dots of material. The material may be plastic or metallic, and composition may vary discontinuously or gradually from one layer to the next, creating a region of functionally gradient material. The invention permits the construction and repair of dense objects, including fiber-reinforced composites and aerospace structures. Excess material may be removed one or more layers are bonded, including following end of the process after the final object is fabricated. The layers are fed sequentially and additively according to a layer-by-layer computer-model description of the object, which is generated by a computer-aided design/manufacturing (CAD/CAM) system. Ultrasonic welding equipment applicable to the invention preferably includes an ultrasonic generator, a transducer, a booster and a head unit or sonotrode.

Ultrasonic object consolidation

A system and a method of fabricating a three-dimensional object consolidates material increments in accordance with a description of the object using a process that produces an atomically clean faying surface between the increments without melting the material in bulk. The CAD system (60) interfaces with a numerical controller (70), which controls an actuation system. The actuation system brings the support feed unit (62), the support ultrasonic welding unit (66), the object feed unit (64) and the object ultrasonic welding unit (68) into proper position in the work area (75), so that the ultrasonic consolidation of the layers takes place according to the CAD description of the object. In alternative embodiments, electrical resistance, and frictional methodologies are used for object consolidation. The invention further facilitates the construction and repair of dense objects, including fiber-reinforced composites and aerospace structures.

Object consolidation through sequential material deposition

Friction heating and bonding are used to consolidate sequentially applied metals, plastics or composites to previously deposited material so as to form a bulk deposit in a desired shape. Monolithic or composite sheets, tapes and filaments can be consolidated using the approach. A system according to the invention includes a source of friction; a mechanism for applying a forging load between a feedstock power supply and a work surface; a work-head, which may have various configurations depending on the geometry of the feedstock to be used; a material feeding system; and a computer-controlled actuation system which controls the placement of material increments added to an object being built. A computer model of the object to be built is used to generate commands to produce the object additively and automatically. The approach provides a solid, freeform fabrication technique that requires no tooling, operates in the solid state, and creates a bond directly at the faying surfaces (i.e., acts only at the location where bonding/consolidation of the material increments is desired).

Object consolidation employing friction joining

Machine tools combine material addition via ultrasonic object consolidation and subtractive techniques for imparting high-dimensional accuracy to a finished object. A material supply and feeder, ultrasonic horn, and feedstock cutting device are integrated with a material removal subsystem preferably including a cutting tool and an excess material removal system. Any metal, plastic or composite material suitable for ultrasonic joining may be employed as a feedstock, and these material may assume the form of tapes, sheets, wires, filaments, dots or droplets, with the feeding and material cutting components being designed for the specific feedstock employed. The cutting tool for excess material removal, may be a knife, drill/mill, grinding tool, or other tool capable of accurately cutting the external contour of a cross section of the part being built, and for removing excess feedstock remaining following the application process. The material removal could consist of a vacuum or blower system, chip auger, or other suitable apparatus. A machine disclosed as part of the preferred embodiment is able to deposit material in one step, and optionally and selectively remove it in another. Through the expeditious combination of deposition and removal, the fabrication of objects of arbitrary shape may be realized.

Ultrasonic object consolidation system and method

An efficient method of iden- tifying power supply pulsing parameters for pulsed gas metal arc welding based on statistical experimental design is pre- sented. Fractional factorial screening ex- periments are combined with D-optimal experimental designs to allow the user to develop an accurate wire feed rate model for varying pulsing conditions and to characterize the desirable one droplet per pulse (ODPP) operating region for a given wire type and diameter. Equations defining the wire feed rates and time at a given peak current required for ODPP transfer are presented. Compared to con- ventional techniques, a very small num- ber of experiments is required. A power- supply-dependent approach and a more generic method employing measured rather than nominal current values are presented. Joints produced using this ap- proach are evaluated and found to meet applicable bead geometry standards.

Dawn White

Papers

Ultrasonic object consolidation

Object consolidation through sequential material deposition

Object consolidation employing friction joining

Ultrasonic object consolidation system and method

Experimental approach to selection of pulsing parameters in pulsed GMAW