High-Frequency Production

The additive process that grew out of ultrasonic welding provides an efficient way to produce complex work, including parts with embedded components and even parts made from dissimilar metals.

To gage how close additive manufacturing is to becoming a mainstream option for making metal parts, it is interesting to note this detail: Ultrasonic additive manufacturing machines from Fabrisonic of Columbus, Ohio, are programmed using a machining center’s CAM software. 

Specifically, the machines are programmed using PowerMill software from Delcam. With the software company’s help, Fabrisonic wrote a module (SonicCAM) that essentially turns the CAM algorithms inside-out. Instead of generating paths that remove material, the module generates paths that add material.
These same machines use conventional machining tool paths as well. A hybrid approach to part production combines additive and subtractive processing in one machine. The ultrasonic process builds metal workpieces by fusing and stacking 1-inch-wide strips. Then, where the design of the part calls for fine detail, a CNC milling spindle enters into the cycle. 
Using additive and subtractive processes together in this way overcomes multiple problems that potentially limit additive metal production. First, parts produced this way do not necessarily need subsequent operations. On this machine, the cycle can create a finished part. Second, putting down the material in 1-inch-wide strips enables the machine to achieve a build rate of 20 to 60 cubic inches per hour (depending on part complexity). This fast build rate means parts can be created quickly, starting with just a spool of material. To provide for such big parts, the largest Fabrisonic machine offers a work envelope of 6 by 6 by 3 feet.
Welding Process
But why “ultrasonic”? What is the meaning and the relevance of this term? A machining professional might not know, because ultrasonic additive manufacturing grew out of welding instead. Ultrasonic welding uses high-frequency vibration to join surfaces without melting. By welding layer upon layer upon layer in this way, the process can build solid parts. The Columbus-based Edison Welding Institute (EWI) has been developing this additive technology for years, and Fabrisonic is an entity newly formed by EWI to bring ultrasonic additive manufacturing to market.
There are few users yet. The company has targeted universities for its earliest sales because universities perform trials and generate data that will lead to a better understanding of the process’s capabilities. But company president Mark Norfolk says many of the potential applications are already clear.
One is complex metal parts, including mold and die tooling. Like other additive metal manufacturing methods, the ultrasonic process makes it possible to build mold components with intricate internal cooling channels that follow the mold’s geometry. (For video of a mold like this being created, see “Learn More” on the next page). In addition, because the process builds in layers, it can make very sharp features that would normally need EDM. For example, this machine could mill a 0.005-inch-radius corner, then build a 5-inch-high wall above it. The resulting feature would be difficult to achieve through machining alone.
Combining Metals
The more unusual potential applications draw on the distinctive advantages of the ultrasonic process. This metal-strip approach to layering can easily be paused to allow a user to add an element between layers, Mr. Norfolk says. Embedded sensors are one possibility. Ceramic mesh could also be applied this way, with the welded metal flowing around the mesh to create a metal-matrix composite. In fact, adding elements with thermal expansion characteristics very different from the host metal could provide control over the thermal response of the metal component.
Perhaps the most promising application area results from the fact that ultrasonic welding binds surfaces without melting. The solid-state weld provides a reliable way to join dissimilar metals. Two very different metals—titanium and aluminum, say—could be combined in shuffled layers to create a structure that mixes the properties of both. 
Alternatively, Mr. Norfolk says bonding a hard metal outer surface to a structure made from a lighter metal could provide a new means of manufacturing parts that require both durability and light weight, such as military armor. In applications needing tailored properties, one property could be obtained from one metal and the other property from another, without the metals having to liquefy and mix. 

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Video: Ultrasonic Additive Manufacturing

This video from Fabrisonic shows ultrasonic additive manufacturing being used to produce a mold with conformal cooling channels.