Abstract
The reliable determination of modal mass, damping and stiffness coefficient (modal parameters) for the particular machine-toolholder-tool system is essential for the accurate estimation of vibrations, stability and thus the machined surface finish formed during the milling process. Therefore, this paper focuses on the analysis of ball end mill's dynamical properties. The tools investigated during this study are monolithic ball end mills with different slenderness values, made of coated cemented carbide. These kinds of tools are very often applied during the precise milling of curvilinear surfaces. The research program included the impulse test carried out for the investigated tools clamped in the hydraulic toolholder. The obtained modal parameters were further applied in the developed tool's instantaneous deflection model, in order to estimate the tool's working part vibrations during precise milling. The application of the proposed dynamics model involved also the determination of instantaneous cutting forces on the basis of the mechanistic approach. The research revealed that ball end mill's slenderness can be considered as an important milling dynamics and machined surface quality indicator.
Highlights
Ball end milling is usually applied in the production of dies, molds and turbine blades
The c, k, fo = f(λ) dependencies are described by the power functions, which means that in a range of higher tool slenderness values (λ ≥ 70.2 mm-1), the differences in modal parameters’ values are decreasing and stabilizing
That the decline in c, k, fo values can be undesirable because it can lead to the growth of tool deflections during milling, reduction of process dynamical stability, as well as the higher risk of resonance phenomenon
Summary
Ball end milling is usually applied in the production of dies, molds and turbine blades These processes are very often carried out in finish conditions, the high quality of the machined surface is required. According to Jun et al [11] and Wojciechowski et al [12], tool’s working part instantaneous displacements during precise milling are significantly affected by the tool deflections induced by cutting forces and machinetoolholder-tool system’s geometrical errors (e.g. tool run out). Research carried out by Lopez de Lacalle et al [13] revealed that during finish curvilinear ball end milling of hardened steel, the cutting forces significantly affect the values of surface location errors (SLE). The obtained results can be further applied to the optimal selection of tool’s overhang allowing the minimization of vibrations and improvement in surface finish
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