Investigation of the influence of coating and the tapered entry in the internal forming tapping process

This work investigated the effect of forming speed, tap coating and the tapered region of the tap in the tapping forming process. Robust statistical analysis was employed to identify the influence of the main effects on the thrust force, torque and its correlation with the microhardness and the quality of the thread profiles. The experiments were carried out with two levels for each factor. The material used was the 7075-T6 aluminium alloy, which has a low density and good formability, which is used in moulds for injection of plastic, aeronautical and automotive components. The results showed that the factors forming speed, tap coating and the tapered region influenced the thrust force and torque. The forming speed of 50 m/min generated a reduction of 61.3% in thrust force, 8.2% of microhardness in the crest and an increase of 98.5% in torque, 5.8% of microhardness in the middle. Taps with TiN-T1 coated increased the thrust force in 12.3%, the torque in 15.2%, the microhardness in the crest of 10.3% and in the root 6.9%. The tapered region with profile type E increased the thrust force in 13.7% and microhardness in the crest of 15.0%. On the other hand, there occurred a reduction in the torque of 7.0%. The thread profile produced with the TiN-coated, taper tool type C, and forming speed of 10 m/min produced the best topography in the screw profile. The microhardness at the base was not influenced by the forming tapping process and showed the same value in all tests.