Desenvolvimento e avaliação de estratégias trocoidais para o fresamento do aço AISI 4340 temperado e revenido

Abstract

Trochoidal trajectory shows to be efficient for rough machining of grooves in materials with low machinability index, since it decreases the engagement angle and reduces the cutting load on the cutting edges. The trochoidal trajectories have variations of their path which mainly influences the machining time. Information on the influence of this tool path variations are scarce in the literature. This research presents the influence of trochoidal strategy and the tool helix angle on the milling of AISI 4340 steel (40 HRC) using coated carbide tools, considering the machining time, the cutting force and wear mechanism. A methodology for the creation of trochoidal strategies (circular and ellipsoidal), based on parametric equation, was developed and applied to the experiments. Variations of the trochoidal trajectory suggesting the machining time reduction were created with this methodology. The results showed that the ellipsoidal trajectory promoted a reduction of 23% in the theoretical machining time, as compared to the circular trajectory. Higher cutting force was obtained using of the ellipsoidal trajectory and the increase of the helix angle tends to reduce it, regardless of the type of trajectory. The mathematical definition of the trajectories of the cutting edges in the trochoidal paths, circular and ellipsoidal, allowed to determine the thickness of the undeformed chip as a function of time. It was possible to modify the cutting force model, developed by Altintas, which presented similarity between the experimental and simulation data. By comparing the experimental and simulated data, 𝐾𝑡𝑒=110 N/mm, 𝐾𝑟𝑒 = 200 N/mm e 𝐾𝑓𝑒 = 23 N/mm values were obtained for the material adopted in this research. Tool life is a complex variable to estimate for the machining conditions adopted in this study due to the wear type and mechanisms on the cutting edges: mechanical and thermal cracks, notch wear and chipping.