UAM creates metallic components from a 3D model using a bond-then-form process based upon successive low-temperature ultrasonic welds followed by CNC trimming of the layers of metal that have been built up. This trimming of the foils allows the fabricator to create the desired geometry and accuracy of the finished parts.
The layers are typically deposited as foils placed side-by-side rather than using a single large sheet, with the 3D parts being built from the bottom up on a heated substrate. Since the metals are not melted, the temperatures used can range from as low as room temperature to around 200°C.
Once a layer has been placed, the CNC machine is used to trim the deposited foils/layers into the desired shape, before the process either starts again with a new layer, or the final part is complete.
Here are the stages of UAM, with some more detail on how the process works:
Stage One - CAD Modelling:
As with most additive manufacturing processes, a CAD model needs to be created of the required object. This model is sliced into layers as an .STL file which the UAM machine reads to build the finished part.
Stage Two – Ultrasonic Seam Welding:
A base plate is fixed onto the machine anvil, onto which a layer of metal foil is placed. This thin layer of metal foil is typically 100–150μm thick.
A rotating sonotrode travels along the length of the foil, simultaneously holding the foil in place through normal force and the ultrasonic oscillations it produces. The sonotrode oscilates transversely to the direction of motion at a constant 20 kHz frequency and with an amplitude that can be set by the user.
This process is repeated with another length of metal foil until a complete layer is placed over the base plate. Subsequent layers can then be built upon the first layer of foil. Typically, four layers of metal foil are termed as being one level in UAM. Once this first level is deposited, a CNC mill can be used to shape the deposited foils…
Stage Three – CNC Milling:
A CNC mill is used to trim any excess foil from the component to achieve a geometry that matches the CAD design. A CNC mill is usually used until a height of 3-6mm are reached, at which point a smaller finishing mill can be used to create required tolerances and surface finishes. The mill can be used to slice the foils at a variety of angles to create vertical cuts, curves or angles in the final part.
Stages two and three are repeated, with more layers being deposited, trimmed and finished until the final part is produced. This final object is then removed from the anvil and separated from the base plate.
UAM offers a number of advantages over other manufacturing processes:
- High Dimensional Accuracy and Low Surface Roughness: The high levels of dimensional accuracy and the low surface roughness are produced independent of the thickness of the metal foil layers.
- Produce Parts With Internal Channels: It can be difficult to produce parts with complex internal channels using some additive manufacturing processes. UAM allows channels to be produced, combining additive and subtractive methods to form channels that can be used for applications including cooling.
- Bonding Multiple Metals: UAM doesn’t use high heats that can change the microstructure of metals. Because of this, it can be used to bond dissimilar metals without creating mismatches or brittle structures, allowing for different metals to be used in a structure.
- Embedding Sensors and Circuitry: UAM parts can be printed with in-built sensors and circuitry. The low strains and temperatures involved in the process mean that sensitive components are not damaged as the structure is built up around them.
- Low Material Wastage: UAM also has a reduced material wastage compared to techniques that use more hollowing out of parts, such as selective laser sintering
However, there are still areas for development with UAM, as a lack of automated support formation means that it can be difficult to create components with complex overhanging geometries.
The effectiveness of UAM is reliant on the quality and accuracy of the CAD 3D modelling, which can require powerful software to produce. In addition, UAM machines can be expensive to buy.
Due to the ability to bond a range of different metals, UAM is ideal for a range of aerospace and automotive applications, where lightweight components are important for fuel economy and the associated environmental impact.
The ability to produce cooling channels is another boon for these industries, as well as for wider industrial manufacturing, medical device production and for manufacturing high tech equipment.
Being able to create parts with built-in sensors and circuitry means that UAM is also used for high-tech devices and Internet of Things products. With an increasing number of industries embedding sensors and tracking devices into products, UAM is the perfect solution for such components.
Ultrasonic additive manufacturing is a cost-effective metal forming process that offers a range of benefits above other additive manufacturing processes.
Being a low temperature, ultrasonic bonding technique, UAM allows for the creation of complex, multifunctional 3D components, including those made from dissimilar metals and with complex internal features, channels, sensors or circuitry.