Ensuring the Bending Stiffness of Pre-compressed Cantilever Boring Bars During Fine Boring

Abstract

The research discovers ensuring technological and dynamic capabilities of fine boring due to the use of cantilever boring bars with increased bending stiffness. Experimental design of the cantilever boring bar and a method for increasing its bending stiffness for fine boring of long holes of small diameter (d = 10–20 mm) with a ratio of l/d > 4 is proposed. Bending stiffness increases due to preliminary compression of the outer layers of the boring bar hollow housing with a unique lock pin-drawbar. The experiments were carried out first on pipes of different lengths, in which the effect of the drawbar increased bending stiffness significantly, and then the experiments were carried out on small diameter boring bars. The results of all experiments show a significant increase in bending stiffness and vibration resistance of unique small diameter boring bars for boring long holes. To study the bending vibrations, a testing bench was assembled based on a finishing boring machine. The measurements were carried out using strain-gauge transducers power on via the differential circuit. It has been established that the effect of boring bar drawbar leads to an increase in bending stiffness by about 1.3–1.4 times, and the vibration amplitudes during cutting decrease by about 2–3 times.