A machine’s sensors take a beating during its lifetime. They can degrade over their lifetime of use due to force, corrosion, or the simple wear of everyday usage. It may be possible to significantly extend the lives of this important sensor equipment by housing them in solid metal. While it wouldn’t keep them operational forever, such a protective case could conceivably give them a much longer life cycle.
One of the problems with embedding sensors in protective metal casings, however, has been that some of them are damaged by exposure to the high temperatures necessary for the process. With the development of a new process, known as Ultrasonic Additive Manufacturing (UAM), sensors can be embedded in metal without the concurrent damage.
Ultrasonic additive manufacturing, a solid-state printing process, uses waves of sound to merge layers of metal foil. As a result, true, full density metallurgical bonds can be created for a variety of metals. When combined with other additive and subtractive processes, a number of highly complex geometries can be created and integrated. It would not be possible to create these complex forms with other conventional subtractive manufacturing processes when performed alone. UAM can create hollow, latticed, or honeycombed internal structures in addition. A number of different types of sensors have been successfully integrated into components using UAM processes, including thermocouples, strain sensors, accelerometers, and pressure transducers. One type of sensor, utilizing fiber optic Bragg gratings to give precise strain measurements, has been embedded in aluminum, increasing the amount of time between necessary maintenance operations.
Smart materials provide actuation and/or material property changes, but these materials do not act of their own free will. Instead, they must have an integrated mechanical and electronic structure. Most often, this is done through the attachment of smart actuators onto the structure. This type of actuator placement is seen with materials such as electrostrictive, magnetostrictive, shape memory alloy, piezoelectric, and electroactive polymers.
Limits in the manufacturing process previously prevented embedding the smart materials directly into the structures, despite the fact that this was a more sophisticated and highly desired approach. Traditional welding obviously brings with it significant problems related to the heat produced during the process. Similarly, fusion, bonded laminations, and sintering have been met with only small success. Given the solid-state nature of the UAM process, it can reliably integrate these materials without causing the damage resulting from the other previously available manufacturing processes. Aluminum blocks have been successfully embedded with wires, strips, and foils.
One practical application of this new method for manufacturing comes in addressing the problem of thermal expansion. When materials are heated they expand and when they are cooled, they contract. This shift can cause strain on materials leading to catastrophic failure over time. Within specific temperature ranges, however, shape memory alloys can act as a counter to the heating and expansion by being programmed to contract at those temperatures. The coefficient of thermal expansion (CTE), the measurement by which a materials contraction in reaction to heat is measured, has been shown to be reduced in the presence of these materials. In order for this to be the case, however, the shape memory alloy must be embedded into the metal itself and this is now possible given UAM technologies.
There are a number of other practical applications for UAM, from lamination of sensors into switch networks that expand potential frequency bandwidth, to impact detection in structural elements. As this technology comes to the attention of the advanced manufacturing community, we are sure to see a number of innovative applications spring up relatively quickly in the near future.
Let us know your opinion on this sophisticated technology, and what it may mean for manufacturers going forward, in the ultrasonic 3D printing forum thread on 3DPB.com.[Source: Fabrisonic.com]
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