Wear mechanisms of TiN coated tools during high-speed tapping of GGG50 nodular cast iron

Ductile irons are among the most used materials in the automotive industry. One of the critical problems during manufacturing of powertrain components is the fast wear of cutting tools because it can lead to defects in the part. This work investigates the wear mechanisms of TiN coated high-speed steel (HSS) taps when machining GGG50 cast iron under high-speed conditions. SEM images and EDS analysis at the chamfered and cylinder teeth demonstrate that adhesion of iron to the cutting tool is the dominating wear mechanism. Fatigue-fracture and coating removal were also observed in many zones of the tap surface. Furthermore, wear progression is reflected on the evolution on the tapping torque with hole number. An on-line monitoring of this variable could be useful to detect an excessive wear of the tap and prevent the loss of tolerances in the threads.