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This paper presents ultrasonic assisted friction stir welding (UaFSW), which is suggested to improve the weld quality and efficiency as a hybrid welding system. Ultrasonic-assisted processes have been coupled with tooling in various manufacturing processes to enhance the performance of conventional machining and bonding processes. For successful and effective implementation of the UaFSW, we must first consider how to integrate ultrasonics into the friction stir welding equipment. To solve this problem, we designed an ultrasonic horn to vibrate the FSW tool and transmit ultrasonic energy into the workpiece. Using a numerical modal and harmonic analysis, we fabricated and analyzed the ultrasonic horn under specific design considerations. Force was measured and compared during ultrasonic assisted and conventional friction stir welding. The mechanical properties of the workpieces were also investigated.

For the accurate analysis and design of microforming process, proper modeling of ma-terial behavior at the micro/mesoscale is necessary by considering the size effects. Two size effects are known to exist in metallic materials. One is the “grain size ” effect, and the other is the “feature/specimen size ” effect. This study investigated the feature/ specimen size effect and introduced a scaling model which combined both feature/ specimen and grain size effects. Predicted size effects were compared with three separate experiments obtained from previous research: a simple compression with a round speci-men, a simple tension with a round specimen, and a simple tension in sheet metal. The predicted results had a very good agreement with the experiments. Quantification of the miniaturization effect has been achieved by introducing two parameters, and , which can be determined by the scaling parameter n, to the Hall–Petch equation. The scaling model offers a simple way to model the size effect down to length scales of a couple of grains and to extend the use of continuum plasticity theories to micro/mesolength scales. DOI: 10.1115/1.271458

Increasing demands for miniature metallic parts have driven the application of microforming in various industries. Only a limited amount of research is, however, available on the forming of miniature features in high strength materials. This study investigated the forming of microfeatures in Type 304 stainless steel by using the coining process. Experimental work was performed to study the effects of workpiece thickness, preform shape, grain size, and feature size on the formation of features ranging from 320μmto800μm. It was found that certain preform shapes enhance feature formation by allowing a favorable flow of the bulk material. In addition, a flow stress model for Type 304 stainless steel that took into consideration the effects of the grain and feature sizes was developed to accurately model and better understand the coining process. Weakening of the material, as the grain size increased at the miniature scale, was explained by the Hall-Petch relationship and the feature size effect.

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