In a previous blog post we introduced ultrasonic additive manufacturing (UAM). Let’s see what unique opportunities for manufacture this technology can provide.
Compared with more conventional manufacturing techniques, UAM offers a few advantages. These are the main ones:
(i) Small thermal distortions : the tapes temperature during ultrasonic vibrations joining/welding (ie plastic distortion welding) only reaches up to 30%/50% of the actual metal melting point;
(ii) Less stringent requirements and reduction of manufacturing costs as it is not necessary to carry out machining under controlled atmosphere;
(iii) Reduction of environmental constraints and their management: using of detergent for tape surface degreasing before machining is unnecessary;
(iv) High productivity given the high deposit-and-trim rate.
Specific applications suited for UAM include
UAM can generate complex internal features within metallic materials. These include honeycomb structures, internal pipes or channels, and enclosed cavities. Internal geometrical features are trimmed via CNC milling before the next layer is deposited.
Yet, not all internal feature types are possible.
Without support materials, internal features must be designed and oriented in such a way that the sonotrode is always supported by an existing, rigid feature while depositing a subsequent layer. As a result, for instance, internal cooling channels are limited in size and cannot be perpendicular to the sonotrode traveling direction.
Besides, all of the top downward-facing surfaces of these internal features will have a stair-step geometry as the CNC can only mill the upward-facing surfaces.
In theory, any metal which can be ultrasonically welded is a candidate material for the UAM process.
Materials which have been successfully bonded using UAM include various aluminium alloys, nickel alloys, brass, and steels, etc.. In addition to metal foils, other materials have been used: for instance, alumina fiber-reinforced Al matrix composite tapes and prewoven stainless steel AISI 304 wire meshes have been bonded to aluminium substrates using UAM.
By depositing various metal foils at different desired layers or locations during UAM, multimaterial structures or functionally gradient materials can be produced. This option can be used to control composition variation and the property changes for various applications. For instance, by changing materials it is possible to optimize thermal conductivity, wear resistance, strength, ductility, and other properties at specific locations within a part.
Fibre embedment and smart stuctures
Since UAM operates at relatively low processing temperatures, many types of optical fibers can be deposited without damage. The most commonly embedded fibres are silicon carbide structural fibres optical fibres within aluminium matrices. Fibers can also be placed and embedded between dissimilar materials. Data and energy can be optically transported through the metal structure.
Smart structures are structures which can sense, transmit, control, and/or react to data, such as environmental conditions. In a smart structure, sensors, actuators, processors, thermal management devices, and more can be integrated to achieve a desired functionality.
Fabrication of smart structures is difficult for conventional manufacturing processes, as they do not enable full three-dimensional control over geometry, composition and/or placement of components.
UAM offers several advantages for this application: 1) UAM is a process whereby metal structures can be formed at low temperatures, 2) larger internal cavities can designed to enable placement of electronics, actuators, heat pipes, or other features at optimum location within a structure . Sensors for recording temperature, acceleration, stress, strain, magnetism, and other environmental factors have been fully encapsulated and have remained functional after UAM embedment.
 Stratoconception. www.stratoconception.com
 Ryan Hahnlen, Marcelo J. Dapino, Matt Short, Karl Graff, Aluminum-Matrix Composites with Embedded Ni-Ti Wires by Ultrasonic Consolidation, Proc. of SPIE Vol. 7290 729009-2
 J.O. Obielodan A. Ceylan L.E. Murr B.E. Stucker, (2010),"Multi-material bonding in ultrasonic consolidation", Rapid Prototyping Journal, Vol. 16 Iss 3 pp. 180 – 188 - http://dx.doi.org/10.1108/13552541011034843
 Y. Yang et al. / Journal of Materials Processing Technology 209 (2009) 4915–4924
 Robinson C, Stucker B, Coperich-Branch K, Palmer J, Strassner B, Navarrete M, Lopes A, MacDonald E, Medina F, Wicker R (2007) Fabrication of a mini-SAR antenna array using ultrasonic consolidation and direct-write. Second international conference on rapid manufacturing. Loughborough, England
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