Study on micro helical milling of small holes with flat end mills

Helical milling as an eco-friendly hole-making process has various advantages comparing to conventional drilling process and has been widely studied. But micro helical milling for small holes was not investigated. This paper focuses on preliminary studies on micro helical milling of small holes with flat micro end mills. The cutting phenomena of the radial and axial cutting edges are considered and discussed separately. Based on the size effect existing in microcutting processes, the minimum undeformed chip thicknesses (h (min)) for both radial and axial cutting edges are identified for work material copper C26000 by finite element method and micro helical milling experiments. Since burrs are noticed during experimental studies, burrs at the hole entrance are analyzed elementarily and it shows that the burr size has a relation with the critical conditions in micro helical milling. The study turns out that the ratio of h (min) to cutting edge radius in micro helical milling is from 0.6 to 0.68 and is larger than that of conventional microcutting processes for various materials, which is usually in the range from 0.14 to 0.43. It is a good sign for micro helical milling of small holes with higher productivities since the ratio of h (min) to tool cutting edge radius is larger than that of conventional microcutting processes.