Regarding the issue of the assembly torque of the aluminum alloy bushing of the subframe and the connecting bolts to the body of a certain model exceeding the upper limit of the monitoring window and triggering an alarm, through the analysis of the bolt assembly curve, it is found that the reason for alarm is that when the assembly torque reaches the upper limit of the monitoring window, the bolt tightening has not reached the process angle yet (this position is assembled by using the torque angle method). The comparison results between the bolt states of normal assembly and alarm show that the anti-slip teeth under the bolt head of assembly alarm is embedded in the gasket, while the anti-slip teeth of the gasket of the normal assembly bolt is embedded in the aluminum alloy bushing. The anti-slip teeth embedded in the gasket under the bolt head of the assembly alarm will drive the gasket to rotate, resulting in an increase in the friction diameter, friction coefficient of the bolt head, and assembly torque, thereby causing the assembly curve alarm. The embedding of anti-slip teeth under the bolt head into the gasket is due to insufficient heat treatment of the gasket, resulting in a softer hardness that is lower than the design required value.

Assembly curve alarm  /  Low gasket hardness  /  Aluminum alloy bushing