Study on ultrasonic micro-forging with ball-head on microstructure and mechanical properties of 316 L stainless steel...

Additive manufacturing technology is widely applied in mechatronics, aerospace, biomedicine and transportation fields due to its advantages of flexible design, high material utilization rate, ease of producing complex components. However, due to the rapid heating and cooling rates, metal components are prone to defects such as pores, cracks, and incomplete fusion, resulting in insufficient comprehensive mechanical properties compared with traditional manufacturing. In this paper, a set of ball-type ultrasonic micro-forging device with high degree of movement freedom and easy concentration of ultrasonic vibration energy was independently designed and successfully integrated into the directional energy deposition (DED) equipment, achieving synchronous assistance of ultrasonic and micro-forging during the DED printing process. The effects of ultrasonic vibration and micro-forging process parameters on the microstructure and performance of 316 L stainless steel components by DED were revealed. The cavitation effect and acoustic flow effect of ultrasonic vibration can interfere with the melt, destroy columnar grains, and promote the formation of equiaxed grains. It also promotes the growth, vibration and rupture of the tiny bubbles in the melt, thereby reducing the occurrence of defects such as holes, and refining the grain size. An appropriate micro-forging pressure (10%∼20% compression degree) can effectively reduce the fluctuation and spatter of the molten pool, and inhibit the formation of surface defects such as pores and unfused regions during the forming process. At the same time, it leads to dendrite breakage and promotes grain refinement, thereby enhancing the surface quality, density, and comprehensive mechanical properties of the components. This research has great guiding significance for the development of metal additive manufacturing technology.