Improving the quality of hole processing in welded products made of dissimilar materials with a new boring tool

Nowadays, structures welded from dissimilar steels have found a wide application in mechanical engineering. One workpiece that belongs to this class is a shut-off solenoid valve. As evidenced in practice, a single-pass boring cycle of a dissimilar welded structure with a 0.5-m tool overhang is accompanied by an autowave process (AWP), which evolves into unstable operation mode. Dynamically, unstable state of the closed-loop system results from the fact that the tool is unable to cope with the damping of divergent oscillations, as it passes the boundary between Steel 45 and 12Cr18N10T sections. This leads to degradation of macro-geometric parameters, especially surface roughness. In order to solve this problem, authors propose a new design of the boring tool with an expanding cone integrated into its body, so that it creates a stress-strain state around the boring bar. Enhancement of the state allows to manage dynamic parameters of the developed tool in a wide range. Preliminary dynamic tests and computer modeling specify that the developed tool possesses a damping coefficient, enhanced by a factor of 1.3, and a Q-factor, decreased by a factor of 1.8, as compared to the equivalent. Research results demonstrate that compared to the equivalent tool, deflection of the modular damped boring bar decreased by 30 % when boring Steel 45 and 12Cr18N10T sections. Dynamic field trials also allowed to detect a positive trend in decreasing AWP amplitude and improving surface roughness by 44%. It allows to draw a conclusion that the developed modular damped boring bar is a more efficient tool to cope with damping of oscillation amplitude at the boundary of two dissimilar steels. As a result, the required parameters of surface roughness and form accuracy are achieved.