Effect of cutting speed and cutting fluid on the BUE geometry of a SAE 12L14 free machining steel

A well known phenomenon, the "built-up edge - BUE", occurs at the chip/tool interface when multiphase materials are machined at low cutting speeds. Under high compressive stresses, seizure prevents the material from sliding over the tool's rake face. Although many reports have been published on the subject, studies of the BUE phenomenon have been marked by a lack of precision in determining its dimensions. This paper reports on a study of the BUE geometry of a SAE 12L14 steel machined at low speeds with and without a cutting fluid. Three quick-stop samples were prepared for each test condition (9 cutting speeds, with and without cutting fluid). The quick-stop samples were mounted perpendicularly in transparent acrylic resin to facilitate observation and the hardened resin sandpapered. The opposite face of the mounted sample was then ground to make the front and back faces parallel. After sandpapering and polishing, the samples were digitally photographed and their BUE geometries determined using an image analyzer. The measurements were done along the cutting width at five different points. It was found that the BUE dimensions varied considerably along the cutting width, and that the fluid reduced the BUE at the lowest cutting speed tested.