Pretightening sequence planning of anchor bolts based on structure uniform deformation for large CNC machine tools

As the key base component of large computer numerical control (CNC) machine tools, the machine bed is required to be firmly fixed to the foundation by anchor bolts, which will supply the reliable accuracy datum for the whole machine tools. However, its pretightening state (e.g. structural deformation) significantly depends on the pretightening sequence of anchor bolts. In this article, the influence of pretightening sequence of anchor bolts on the pretightening state is analyzed considering the elastic interaction effect. To predict the structural deformation of machine bed in different pretightening sequences, an analytical deformation model is established using the discrete strain values as the boundary condition. Moreover, the undetermined correlation parameters are calculated using the particle swarm optimization (PSO) method. To verify the validity of the proposed method, two typical pretightening sequences of anchor bolts were employed for the large CNC rolling lathe (CK14825) bed installation. From results comparison, it showed that the pretightening sequence from middle to sides could guarantee the uniform deformation of machine bed.