| dc.description.abstract | Micro electrical discharge machining (Micro-EDM) is a critical technology to fabricate high aspect ratio 3D micro-components. However, the surfaces of micro- components manufactured by micro-EDM will exhibit micro-cracks that will produce notch effects, and lead to stress concentration and reduction of fatigue strength. This paper performs micro-tensile and micro-bending tests to investigate the influence of various roughness and sizes on the fracture strength of micro WC-shafts manufactured by micro-EDM, and determines the origin of the fracture in the specimen. Moreover, the further study on improvement of fracture strength of WC EDMed specimen through micro chromium electroplating is conducted. Besides, we also examine the influence of roughness and sizes on the surface topography of chromium coating.
The experimental results indicate that the discharge current, axial surface area, volume, and length of the specimen will affect its tensile and bending fracture strength. For specimens with the same size, the mean tensile and bending fracture strength decrease as discharge current increases, and the fracture probability of the specimens also increase. For specimens with the same diameter and discharge capacity, increasing the length, volume or axial surface area reduces the mean fracture strength, and increase the fracture probability. For specimens with the same discharge capacity, reducing the length or axial surface area will increase the mean bending fracture strength, and reduce the bending fracture probability. Besides, the experimental results of micro chromium electroplating indicate that, under the same electroplating parameters, the specimen with rougher discharge surface will exhibit a higher roughness on the chromium coating. Furthermore, the surface integrity effect of coating and the surface integrity within different roughness coatings will also improve with the increase of the electroplating time. Moreover, under the same electroplating current, the EDMed specimen with a smaller diameter can produce a chromium coating with compact build, but will also generate larger crystalline solids that lead to a rough surface. On the tiny scale, an EDMed specimen coated with electroplating will reduce scattered distribution of tensile fracture strength and the tensile fracture probability, and enhance tensile strength. | en_US |