Estudo da usinabilidade de ferros fundidos vermiculares de alta resistência nos processos de furação e fresamento

Abstract

The constant search for greater energy efficiency led to the search for materials that allow the construction of lighter and more resistant internal combustion engines. Vermicular cast iron stands out among these new materials due to its superior mechanical properties; however, these properties also drastically reduce its machinability compared to gray cast iron. In this work, the machinability of three types of vermicular cast iron was investigated, one of class 450 and two other of class 500. The higher resistance of the vermicular cast iron of class 500 was obtained through the graphite refining, and in one of the materials also molybdenum was added, resulting in higher hardness. The analysis of the tribosystem through face milling tests in ramp allowed to estimate the friction coefficient at the cutting interface, as well as the reciprocating test in the three materials contributed to simulate the machining tribosystem. The cutting temperatures in the milling process were measured using a thermocamera, observing a high correlation between them and the mechanical properties of the three materials investigated. In the drilling process, the correlation of several output variables from the machining process, mechanical and metallurgical properties, as well as the monitoring of acoustic emission signals and consumed electrical power, were investigated. It was observed that the combination of the nodularity of the material and the electric current signal of the machine presents the best cost-benefit for the prediction and monitoring of tool wear. The wear predictive capacity of the electric current signal was further investigated in the face milling process in workpieces with different surface conditions (solid and pre-drilled). These analyses indicated that the mean quadratic deviation (RMS) of the electric current signal has the best capacity for monitoring the process. Finally, the machinability of the three materials was investigated in the face milling process of solid plates of the three materials for different machining parameters, lubricating and cooling atmospheres (dry and minimal quantity of lubrication - MQL), geometries and coatings of the cutting tools. These analyses allowed to conclude that the graphite refining reduces the machinability of the material and that thermal cracks are the most frequent wear mechanism when milling these materials.