摘要

Hierarchical ribs can be used to keep balance between heat transfer enhancement and pressure drop reduction. The unique hierarchical structure which features a first-order asymmetric arc rib imposed by second-order microgrooves greatly reduces the pressure drop as well as enhances the heat transfer. However, it is hard for conventional machining techniques to generate such complicated configurations, especially freeform geometries in the micron range. Taking advantage of ultra-precision raster milling (UPRM), a novel one-step machining process, for advanced hierarchical ribs is proposed and demonstrated. In this paper, the principle of the cutting strategy for the second-order microstructures and cutting conditions that affect the basic features of the structures are discussed. In addition, three-level factorial design of cutting speeds, feed rates, and depth of cuts were set and used to machine hierarchical ribs on a copper workpiece. It was found that the cutting strategy was affecting the geometry of second-order microstructures of hierarchical ribs in UPRM. Moreover, the result revealed that at low levels of feed rate and cutting depth, a middle level of cutting speed provides a better quality of second-order microstructures than a middle level of feed rate, high level of cutting depth, and low level and high level of cutting speed. Maintaining a balance between machining efficiency and hierarchical structure generation quality is thoroughly assessed by machining second-order microgrooves on asymmetric arc primary surfaces.