Formation mechanism of assembly stress induced by multi-source loading in a gantry-type machine tool

• A novel model was proposed to analyze the formation mechanism of multi-source load-induced assembly stress in the gantry frame of a CNC machine tool. • The testing system has been developed, and the calculation results of assembly stress fit well with the experimental data. • The influence of pre-tilt angle errors, threaded fasteners, and materials on assembly stress was systematically analyzed, and it was found that pre-tilt angle errors have the most significant impact on assembly stress. . The gantry frame, consisting of two vertical columns and a crossbeam, serves as the primary load-bearing structure in gantry-type machine tools. During assembly, the coupled effects of structural self-weight, bolt-preload-induced clamping, and inter-column backward-tilt mismatch lead to spatially non-uniform assembly stresses that cannot be adequately captured through linear superposition. This study develops a mechanics-based framework to quantify the conversion of tilt mismatch into additional interface resultants and its amplification into localized stresses. An assembly-level finite element model is established to incorporate gravity, preload non-uniformity, and frictional contact, in which bolt preload is introduced through an equivalent pretension pressure. The results indicate that the inter-column tilt mismatch plays a dominant role in assembly-stress formation and exhibits a nonlinear amplification trend with increasing Δθ. Under an identical total preload, a small-and-dense fastener layout results in a reduction of the peak interface stress by 10.14–19.05% compared with a large-and-sparse layout, whereas variations in frame material (HT250/HT300/QT600-2) exert only a minor influence. Strain-rosette measurements with digitally controlled tightening are used to validate the proposed model, with relative errors below 5% for most cases. The proposed methodology enables reliable prediction and control of gantry-level assembly stresses, thereby providing practical guidance for low-stress assembly and long-term geometric accuracy.