Ultrasonic Additive Manufacturing

Ultrasonic additive manufacturing (UAM) is a solid freeform fabrication process also known as Ultrasonic Consolidation (UC).  It is a hybrid sheet lamination process that utilizes ultrasonic seam welding to merge metallic tapes [1,2,3] combined with computer numerically controlled (CNC) milling for dimension accuracy.

Schematic of UAM process [1]

2-step hybrid additive-subtractive process

UAM is a bond-then-form process that directly produces metallic components from a 3D model by successive use of low-temperature ultrasonic welding followed by CNC trimming of metal layers.

Parts are built up from bottom to top on a heated substrate, with temperatures ranging from room temperature to ~200C. Each layer is typically deposited as a combination of foils laid side by side rather than a single large sheet, as is typically practiced in sheet lamination processes. These layers are then trimmed using CNC milling to form the desired accuracy and geometry. This process works well with metals having low deformation resistance [4,5].

Step1: Ultrasonic seam welding

During UAM, a rotating sonotrode travels along the length of a thin metal foil (typically 100–150μm thick). The foil is held closely in contact with the base plate or previous layer by applying a normal force via the rotating sonotrode. The sonotrode oscillates transversely to the direction of motion, at a constant 20 kHz frequency and user-set oscillation amplitude. This procedure is repeated until a complete layer is placed. The next layer is bonded to the previously deposited layer using the same procedure.

Step2: CNC milling

Typically four layers of deposited metal foils are termed one level in UAM. After deposition of one level, the CNC milling head shapes the deposited foils/layers to their slice contour (the contour does not need to be vertical, but can be a curved or angled surface, based on the local part geometry).

Low surface roughness and high dimensional accuracy

CNC machining eliminates the stair-stepping effects found in other AM processes. The final products show low surface roughness and high dimensional accuracy that is independent of the foils layer thickness.

Not (yet) suited for components requiring supports

One drawback is the current lack of automated support formation in commercial systems. In other words, many components designed with complex overhanging geometries cannot be built using UAM.

As it stands, on-going research is focused on this aspect and may result in technique improvement in the future.

Take-away

UAM is a great environmentally friendly and cost-effective metal-forming technology. This process combines low-temperature ultrasonic bonding and additive-plus-subtractive processing to create complex, multifunctional 3D parts, including objects with complex internal features or embedded sensors, etc…

Get Inside Metal Additive Manufacturing

References

1. S. Shimizu, H.T. Fujii, Y.S. Sato, H. Kokawa, M.R. Sriraman, S.S. Babu, Mechanism of weld formation during very-high-power ultrasonic additive manufacturing of Al alloy 6061 , Acta Materialia 74 (2014) 234–243

2. Wimpenny DI, Bryden B, Pashby IR (2003) Rapid laminated tooling. J Mater Process Technol 138:214

3. I. Gibson, D. Rosen, B. Stucker, Additive manufacturing technologies, Springer, p228

4. www.solidimension.com

5. www.stratoconception.com