A novel design for double-bending elliptical vibration boring device and its performance evaluation.

Steel precision matching parts are widely used in aerospace and automobiles. In order to ensure the stability of the system, the matching parts' mating surfaces, such as inner holes and outer shafts, are required to achieve nano-surface roughness and submicron-shape accuracy. Diamond-cutting technology is generally used for ultra-precision machining processes. However, it is not suitable for machining steel due to the active chemical reactions. Ultrasonic elliptical vibration cutting technology can significantly reduce the cutting heat to suppress the chemical wear of diamond tools. Consequently, this study proposes a novel simple theory-simulation design method for an ultrasonic elliptical vibration boring (UEVB) device. The device works in two six-order bending vibration modes, generating an elliptical tool motion in the plane determined by the nominal cutting direction and the cutting depth direction. Through the impedance test, frequency sweep test, and amplitude test, the test results of the device match well with the simulation results. The experimental results of cutting S136 steel show that the UEVB technology suppresses system chatter by 10 % and reduces surface roughness Ra by 72 % compared with common boring. Additionally, the tool has much light wear and the machined surface roughness is Ra 11.3 nm, which realizes the ultra-precision cutting of steel by diamond tools. Furthermore, the roundness of the processed hole, with a diameter of 30 mm, reaches 0.473 μm, which is significantly better than the highest standard grade G1 (0.5 μm). These results verify the feasibility of the proposed method.