Application of ultrasonic vibrations in welding and metal processing: A status review

Piezoelectric composites are a class of functional materials consisting of piezoelectric active materials and non-piezoelectric passive polymers, mechanically attached together to form different connectivities. These composites have several advantages compared to conventional piezoelectric ceramics and polymers, including improved electromechanical properties, mechanical flexibility and the ability to tailor properties by using several different connectivity patterns. These advantages have led to the improvement of overall transducer performance, such as transducer sensitivity and bandwidth, resulting in rapid implementation of piezoelectric composites in medical imaging ultrasounds and other acoustic transducers. Recently, new piezoelectric composite transducers have been developed with optimized composite components that have improved thermal stability and mechanical quality factors, making them promising candidates for high temperature, high power transducer applications, such as therapeutic ultrasound, high power ultrasonic wirebonding, high temperature non-destructive testing, and downhole energy harvesting. This paper will present recent developments of piezoelectric composite technology for high temperature and high power applications. The concerns and limitations of using piezoelectric composites will also be discussed, and the expected future research directions will be outlined.

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High temperature, high power piezoelectric composite transducers

This study investigates combining longitudinal and torsional (L–T) vibration responses at the output face of a Langevin transducer. A mode degeneration method is adopted that converts the longitudinal response excited by the axially poled piezoceramic discs in the transducer into combined L–T vibration in the transducer front mass using geometric modifications of the wave path. The study uses three techniques; numerical, analytical, and experimental, in order to estimate and validate transducer electro-mechanical parameters for different geometric modifications, and also to evaluate transducer performance for different excitation levels in terms of the desired L–T response. A finite element (FE) analysis is used to optimise the mechanical structure of the transducer while the analytical model, which is based on an equivalent-circuit approach, is used to estimate the electrical impedance spectra and to confirm some of the FE calculations prior to fabrication. These models are then validated through an experimental characterization of the vibration response and impedance response and the results show that the operating frequency and torsionality can be tailored through modification of the transducer geometry.

A design approach for longitudinal–torsional ultrasonic transducers

Microstructure, welding mechanism, and failure of Al/Cu ultrasonic welds

The feasibility of ultrasonic bonding for hermetic microelectromechanical systems (MEMS) packaging has been demonstrated utilizing the solid phase vibration and welding process to bond two elements rapidly at low temperature. Two different approaches have been developed including lateral and vertical ultrasonic bonding setups with three sets of material bonding systems: In-to-Au, Al-to-Al, and plastics-to-plastics. The process utilizes purely mechanical vibration energy to enable low temperature bonding between similar or dissimilar materials without precleaning of the bonding surfaces. In these prototype demonstrations, the typical bonding process used tens of watts at room temperature environment and the bonds were accomplished within seconds for bonding cavities with areas of a few mm2 . Preliminary tests show that packaged MEMS cavities can survive gross leakage tests by immersing the bonded chip into liquids. As such, ultrasonic bonding could potentially be broadly applied for hermetic MEMS sealing and packaging especially where temperature limitation is a critical issue. Ultrasonic polymeric bonding could be applied for capping polymer-based microfluidic chips. This paper describes the ultrasonic bonding and hermetic sealing processes as well as the characterizations of bonding tools and equipment setups.

Ultrasonic Bonding for MEMS Sealing and Packaging

Complex vibration ultrasonic welding systems with large area welding tips.

High-frequency ultrasonic wire bonding systems

Complex vibration ultrasonic lap spot and seam welding systems of 27 kHz and 40 kHz are studied. Welding characteristics of 27 kHz and 40 kHz complex vibration lap spot welding systems with a longitudinal-torsional vibration converter were compared using aluminum plate specimens. And also, a lap seam welding system with a complex vibration disk welding tip was designed. Aluminum plates of various thickness were continuously joined at multiple positions uniformly using the complex vibration system.

Welding characteristics of 27 kHz and 40 kHz complex vibration ultrasonic metal welding systems

Complex vibration ultrasonic lap spot welding systems of 100 kHz are studied. The complex vibration welding tip vibrates in elliptical locus. Welding characteristics of 100 kHz, 60 kHz, 40 kHz and 27 kHz complex vibration systems with a longitudinal-torsional vibration converter were compared using aluminum plate specimens. Aluminum plates were welded independent to the directions between welding tip vibration direction and specimens. The vibration amplitudes of the welding systems required for obtaining sufficient weld strength become smaller, as the vibration frequencies become higher. The required vibration amplitude of aluminum plate specimens the 100 kHz system was smallest among them.

Ultrasonic complex vibration welding system using 100 kHz one-dimensional longitudinal-torsional vibration converter

Complex vibration ultrasonic lap spot welding systems of 100 kHz are studied. The complex vibration welding tip vibrates in elliptical locus. Welding character- istics of 100 kHz, 60 kHz, 40 kHz and 27 kHz complex vibration systems with a longitudinal-torsional vibration converter were compared using aluminum plate specimens. Aluminum plates were welded independent to the direc- tions between welding tip vibration direction and speci- mens. The vibration amplitudes of the welding systems required for obtaining sufficient weld strength become smaller, as the vibration frequencies become higher. The required vibration amplitude of aluminum plate specimens the 100 kHz system was smallest among them.

Tsutomu Sano

Papers

Complex vibration ultrasonic welding systems with large area welding tips.

High-frequency ultrasonic wire bonding systems

Welding characteristics of 27 kHz and 40 kHz complex vibration ultrasonic metal welding systems

Ultrasonic complex vibration welding system using 100 kHz one-dimensional longitudinal-torsional vibration converter

ULTRASONIC COMPLEX VIBRATION WELDING SYSTEM VIBRATION CONVERTER USING 100 kHi ONE-DIMENSIONAL LONGITUDINAL-TORSIONAL