Study of the ultrasonic stress relief method for assembly of flex lead in inertial devices

The micro inertial device is widely used in the aerospace field when high measuring precision is required. The reaction torque from the residual stress of flex lead, which is generated in the assembly process, is a significant source of error. To address this problem, a stress relief method based on ultrasonic aging is designed and studied in this paper. An experimental platform is established using a high frequency, low amplitude ultrasonic system to improve the uniformity of the plastic stress distribution. The deformation of flex lead is measured by a visioning system. Experiments are carried out for two kinds of flex lead with Phi 150 and Phi 30 mu m in profile diameter. Ultrasonic loading time and amplitude are studied, and results indicate that the released stress increased gradually with ultrasonic loading time in the initial stage. Up to a specific value, it remains constant with the subsequent ultrasonic loading. The ultrasonic loading times required for the flex leads in different sizes to achieve constant balance are different, and longer times are needed for the thicker sizes. The stress relief degree is about 20%, and it can be enhanced by increasing ultrasonic amplitude. But damage will be caused by the enhanced impact from ultrasonic vibration in larger amplitude.