Torneamento de aço endurecido ABNT - D6 com ferramenta de PCBN refrigerada através de galerias internas

Abstract

Machining is one of the most used manufacturing processes in the world and is based on the removal of material from the part. Of all the mechanical energy generated by the engine of the machine tool, more than 95% is converted into heat during the cut. Due to these conditions, the temperature in the cutting tool can reach values of 1200 °C, as when machining of hardened steels, which results in a shorter tool life. Cutting fluids are the most used means for cooling the machining region in industries, but they are not sustainable due to their cost, difficult disposal, and risks to operators, in addition to not being recommended on some occasions. This work aims to design and test an internal cooling system in Polycrystalline Cubic Boron Nitride (PCBN) tools, which circulates a closed-circuit mixture of water and ethylene glycol, which is used in the turning operation of hardened steel ABNT D6 and comparison with dry machining. A factorial design was used with two levels and three variables: cooling method (dry machining and internally cooled tool - ICT), feed rate and cutting speed, with depth of cut constant in all the tests. Tool life, cutting temperature, cutting force and workpiece surface roughness was the output variables considered. The ICT system provided a significant reduction in the temperature of the tool rake surface, measured using a thermographic camera, despite being the least significant variable in the maximum temperature. In the tool life tests, the FRI system increased the tool life in all situations analyzed compared to dry machining, despite the cutting speed being more significant. The most influential variables in the cutting force were feed rate, due to increased area of cutting; and cooling, in which the FRI system showed higher values, due to a decrease in temperature. The only significant factor for roughness was the condition of the edge geometry, in which the worn tool provided a better surface finish. Both flank and crater wears were observed, with the latter higher for dry machining because of higher cutting temperatures. Abrasion and diffusion were the prevailing wear mechanisms.