Avaliação da rugosidade e da microdureza do Poliuretano Termoplástico (TPU) após a retificação plana tangencial

Abstract

Due to its high impact strenght, low specific weight and great corrosion and abrasion resistance, the Thermoplastic Polyurethane (TPU) has been increasingly used as a structural material in many engineering applications, some of which require a superior finish and homogeneous surfaces. Grinding is an abrasive machinining process that enables to achieve narrow dimensional and geometric tolerances, specially low roughness values. Thus, the use of grinding process is an interesting alternative to provide superior finishing and low geometric and dimensional deviations in components made from Thermoplastic Polyurethane. However, due to the peculiarities of the grinding process with conventional grinding wheel, most of the heat generated in the process is directed to the workpiece, what can lead to thermal damages such as hardness loss, cracks, grinding burn, among others, that can reduce the component’s performance and lead to losses. Therefore, it is important the proper selection of the cutting parameters to conciliate productivity with maintenance of workpiece’s integrity. Epecifically for the Polyurethane, which belongs to the polymer class, the literature is still scarse in terms of the grindability of the material, even in relation to the most suitable grindind wheel. In this context, this study was proposed to evaluate the influence of cutting parameters typically of grinding of steels, such as radial depth of cut and workspeed, in the roughness parameters (R_a, R_t e R_z) and in the microhardness of TPU after peripheral surface grinding, also analyzing the rectified surfaces using na optical microscope. A White Aluminum Oxide grinding wheel and a semi-synthetic fluid were employed. The results showed that increasing the depth of cut from 15 µm to 25 µm with the lowest workspeed (Vw) of 2.7 m/min, there was no variation in roughness. However, when grinding with the highest workspeed of 7.5 m/min, the same increment in depth of cut generated an increase in the values of R_a, R_t e R_z of 8%, 63% e 30%, respectively. With regard to microhardness results, it was observed a hardening in regions 20 µm below the ground surface when using Vw equal to 2.7 m/min, with microhardness results between 11 HV and 11.5 HV. Furthermore, it was verified by the images obtained by optical microscope presence of intense side flow material on the surfaces machined with depth of cut of 25 µm.