Geometrical and microstructural size effects in progressive forming using wires

With the increasing trend toward product miniaturization, progressive forming has been widely used in fabricating meso‑/micro-scaled parts using sheet metals. However, there are difficulties for such processes and sheet metals to be employed to manufacture the parts and components with local rotating features, and their rotating axis is not in the extruding/forming direction. In this work, a progressive forming process directly using metal wires was first developed. The constitutive model using the brass CuZn35 wires of different diameters (0.4–1.2 mm) as a case study material with different grain sizes (30.9–159.2 μm) was developed. By using the multi-scaled fork-shaped parts with flat tines and cylindrical heads as case micro-parts to be micro-formed, the dimensional errors induced by springback increased with the grain size while decreasing as the specimen size increased. The surface quality deteriorates with the increase in grain size, and the micro-cracks form more easily on the side surface of micro-parts with larger grains. The undesired geometry issue of the fabricated parts was overcome by optimizing the tool design. This work further expands the promising application of the progressive forming process in the high-efficiency fabrication of meso‑/micro-scaled parts with irregular features.