Simulation study of deep hole tapping in TC4 rivet body threads

The rivet body is the main load-bearing part of the aerospace titanium alloy flat-section large base foot threaded blind rivets. Controlling the internal thread forming process during development is a critical challenge. For the deep hole tapping and forming process of TC4 rivet body, the force characteristics of the rivet body and tap in the tapping process are studied by finite element simulation, the relationship model between the torque and stroke of the tap is established, and the influence of key process parameters on the tapping force is studied by combining with parametric simulation. The results show that after the tap cutting edge is rotated out, the maximum effective stress in the rivet body is about 10.12% of the cutting stage. The distribution area of the effective strain field gradually increases with the tapping process, and the average effective strain of the formed thread section is greater than that of the thread section being formed. The torque prediction of the tap in the cutting stage and the calculated value of each simulation test group have an error of less than 10%. As the base hole diameter increased from 2.78 to 2.90 mm, the average torque of the tapping process decreased from 372.762 8 to 292.224 2 N∙mm. As the shear friction coefficient increased from 0.2 to 1.0, the average torque of the tapping process increased from 313.099 3 to 427.203 9 N∙mm. As the work-in speed decreased from 1.75 to 1.05 mm/s, the average tapping torque decreased from 373.072 2 to 334.333 7 N∙mm.