Influence of drilling incidence angle on the drilling force distribution of pneumatic impactor

Pneumatic impactor is widely used in the drilling process of various medium and high hard rocks with poor drill ability. Currently, there is relatively little analysis on the impact of the inclination of the rock surface during the drilling process on the drilling efficiency and excavation capability of pneumatic impactors. Based on the dynamic theory of impact drilling and finite element method (FEM), the constitutive model of HJC criterion and INVENTOR 3D mechanical structure design software, a 3D numerical analysis system of piston-bit head-rock during pneumatic impactor drilling is established by ANSYS LS-DYNA, a nonlinear dynamic analysis software. The numerical results of drilling force at different incidence angles are analyzed in detail. For the rock without initial hole, the ratio of maximum to minimum drilling force under the conditions of considering incidence angle δ, only considering incidence angle β and considering both β and δ is 3.114, 3.161 and 3.873, respectively. For the rocks with initial holes, the ratio of maximum to minimum drilling force under the same and different incidence angles is 1.810 and 2.090, respectively. Through nonlinear fitting for numerical results, the corresponding fitting solution is obtained, and the relative error between fitting solution and numerical solution is analyzed to be between 11.72%~15.58%, which can meet the requirements of engineering application. The analysis results provide references for the mechanical structural optimization design and use of pneumatic impactor.