Effects of process parameters on force reduction and temperature variation during ultrasonic assisted incremental sheet forming process

The incremental sheet forming (ISF) is an innovative dieless forming process featured with high formability and short lead time which is suitable for rapid prototyping and small volume production. The integration of ultrasonic (US) vibration into the ISF process can significantly reduce the forming force and bring other benefits. In this work, the impacts of process parameters including the sheet material, US power, feeding speed, and tool diameter, on force reduction and temperature increment were studied. The force reduction contains two components—the stress superposition-induced force reduction and acoustic softening-induced force reduction. The stress superposition-induced force reduction was analyzed by finite element simulation while the total force reduction was detected by experiments since currently, the unknown mechanism of the acoustic softening cannot be modeled. The temperature increment was measured by a high-speed infrared camera. The results show that the force reduction can go up to 56.58% and the temperature increment can be as high as 24.55 °C. In general, the material with a higher yield stress results in a higher force reduction and a higher temperature increment. A higher US power or a lower feeding speed can significantly enhance the force reduction and the interface temperature increment. The tool with a smaller diameter has a comparable effect as a larger tool, but a larger vibration amplitude is required.