Efeitos do material de ferramenta e das técnicas de lubrirrefrigeração na vida da ferramenta e na superfície usinada por fresamento do ferro fundido branco alto cromo

Abstract

Mechanical components applied to ore crushing, drilling of oil wells and soil plowing need to be manufactured from materials with high resistance to wear, erosion and corrosion. The typical materials applied to the described conditions are cold work tool steels, high-speed steels and high-chromium white cast iron (HCWCI). The microstructures of these materials are a challenge for machining, particularly in the case of HCWCI. The HCWCI presents 28% of M7C3 carbides in a pearlite or martensitic matrix. Researches about machining of HCWCI are focused on the application of PCBN (Polycrystalline Cubic Boron Nitride) in hard turning due to high wear rates and temperatures on the cutting edges. However, in milling, conditions involve interrupted cutting and the cutting fluids may easily access the cutting region. In the latter case, the coated cemented carbides associated with lubricooling techniques may be an alternative to the process feasibility. The aim of this work is to evaluate the effects of the tool material and lubri-cooling techniques on tool lifetime and milled surface of the HCWCI. Therefore, two coated cemented carbide grades (PVD-TiAlN e PVD-TiAlN2) and PCBN grades associated with two lubri-cooling techniques (flood emulsion and liquid nitrogen - LN2) were applied to the milling tests. Three-dimensional wear parameters aided the evaluation of types of wear, aiming to understand the removed material from the cutting edges. The results showed the feasibility of the coated cemented carbide as tool material in milling of the HCWIC and that LN2 has increased twice the tool lifetime when compared to flood emulsion. Regarding the milled surface, higher values of compressive residual stresses are identified with the use of flood plus fresh cutting edges. However, the use of LN2 intensifies the shear mechanism during the cutting, preserving the mechanical characteristics similar to the original state.