Abstract: How to accurately assess the remaining life of a used spindle is the key to its remanufacturability assessment. Based on this, it focuses on the current status of fatigue fracture failure of worn spindles, comprehensively considers the crack closure effect, and adds a crack expansion effective factor, and proposes a spindle remaining life evaluation model based on a nonlinear continuous fatigue damage model. In order to improve the fitting accuracy of the S-N curve of the main shaft, the fatigue test piece is made by cutting the shaft body of the original waste main shaft by wire cutting, and the six-level maximum stress obtained by the harmonic response analysis of the main shaft is used as the cyclic stress of the tensile and compression fatigue test, thereby obtaining S-N curve close to the actual spindle. For the problem of solving the parameters of the remaining life evaluation model of the spindle, the data and parameters obtained by the experiment are constructed by the least square method in nonlinear fitting to construct the S-N curve about stress and life. The Python method is used to solve the parameters in the model so that the evaluation model of the remaining life of the spindle is more accurate to ensure the accuracy of the prediction of the remaining life of the spindle. Taking the spindle of the CAK5085 CNC lathe of a machine tool group as an example, the remaining life evaluation is carried out. The comparison between the test data and the calculation results of the model verifies the accuracy and feasibility of the revised model.

Key words: remanufacturing, fracture mechanics, residual life evaluation, crack closure, S-N Curve