Experimental Study on Milling Hardened SKD Steel Using Micro CBN Ball-End Mills

Abstract

Micro ball-end milling process features the ability of machining complex surfaces, precision machining accuracy, and excellent machined surface roughness. However, because the diameter of a micro milling tool is very small, a rapid progress of tool wear or even tool breakage usually happens when machining a high-strength hardened mold steel using improper machining parameters. As a result, the machining cost would rise due to the quality defect in machined workpiece. In this study, to investigate how the machining parameters affect the cutting behaviors, a series of experiments using micro CBN ball-end mills with a diameter of 0.5 mm were performed to cut the SKD11 mold steel with hardness of HRC 61. The machining parameters are selected as the feeding speed (f) being 840, 960 and 1,080 mm/min, depth of cut (ap) being 30, 45, 60 μm, and spindle speed (vs) being fixed as 30,000 rpm. According to the experimental results, the measured three-axis cutting forces, flank wears, and surface roughness of machined workpiece are highly related to the cutting length. It is expected that the measured results can be used to construct a performance function of a micro ball-end tool. With referring to the performance function, the tool life can be well expected, and thus a progress in machining efficiency without tool failure can be achieved.

Effect of Tool Tilting Angle on Tool Wear and Surface Roughness in Micro Ball End Milling

“…Although Liu et al [1] had reported the machining characteristics in the micro ball end milling without the inclination of the spindle, it is hard to say that the cutting performances by the micro ball end mill are sufficiently investigated. In order to obtain a fine finished surface of mold with an inclined plane and a free form surface, it is necessary to understand the characteristics of the micro ball end milling so that the tool wear reduces and the machining accuracy improves.…”