Numerical analysis on the drilling force of pneumatic impactors under different working conditions and structural parameters

This study presents a numerical analysis of impact forces in down-hole hammer (DTH) using finite element method (FEM) and impact drilling dynamics theory. A Type 80 pneumatic drill model was constructed based on the Holmquist-Johnson-Cook (HJC) constitutive criterion, integrating three-dimensional mechanical design via INVENTOR and nonlinear dynamic simulations through ANSYS LS-DYNA with APDL parametric programming. The stress distribution during rock fracturing was systematically investigated, and impact forces under varying drill bit configurations, operational parameters, and initial rock surface geometries were quantitatively analyzed. Numerical results were fitted to derive empirical solutions, with maximum relative errors ranging from - 9.40% to 8.23%. Key findings indicate that optimizing the distribution angle (α) of drill bit inserts from an initial 25° to 0° reduced the peak impact force to a minimum value of 200.65 kN, yielding a peak-to-minimum force ratio of 1.291. Additionally, the transition angle (γ) of pre-drilled rock boreholes significantly influenced force distribution patterns. These results provide critical theoretical insights for optimizing the mechanical design and operational parameters of DTH hammer systems in hard rock drilling applications.