Investigations on burr formation mechanisms and surface quality when micro-milling duplex stainless steel (UNS S32205)

Abstract

Micromilling is a high-precision machining process that has been widely used to produce components or provide micro-characteristics on macro-sized parts. It is imperative that surfaces generated by micro-machining have high specifications and quality, translated as low surface roughness and a minimum number of burrs. Deburring processes are difficult to control, and the need to assure process quality motivated a study of this work focused on burr formation and surface quality when micromilling duplex stainless steel (UNS S32205). For this purpose, slots were machined using a 4-axis computer numerically controlled (CNC) micromachining center equipped with TiN-coated carbide microtools (381 µm diameter (0.015 inch)). Optimization experiments were performed in order to choose the most suitable cutting conditions. The measurements of burr height and surface roughness were made using a profilometer. In addition, milled slots were analyzed using a scanning electron microscope (SEM). The results showed that top burrs were dominant, and the main types presented on the up-milling side were feather burrs and primary burrs. On the down-milling side, burrs presented a rather irregular shape. The width of the root of the burr presented values very close to the size of the metallurgical phases of the material, and burrs formed at distances that are comparable to the spacing between both phases, such as, α-ferrite and γ-austenite. Surface roughness is higher when using increased cutting speeds, implying that lower speeds produce a measure of surface roughness in line with component specifications that appears to be dependent on the type of burr formed during milling and associated tool wear.