Simulation and Experimental Study of Combined Helical Milling for Countersunk Holes

6061-T6 aluminum alloy is widely used in aerospace equipment and is typically positioned and joined with other components through riveting or bolted connections. In many cases, these joints require countersunk holes, making the quality of the countersunk holes a critical factor that directly affects connection quality and structural reliability. This paper focuses on the combined helical milling of countersunk holes in 6061-T6 aluminum alloy. First, the cutting mechanism of countersunk hole helical milling is analyzed, and models for the undeformed chip geometry and cutting forces in countersunk hole helical milling are established. A novel combined helical milling process for countersunk holes is then proposed. Subsequently, a finite element simulation is conducted to analyze the cutting mechanism and validate the proposed method. Finally, experimental studies are performed to investigate cutting force variations and material removal behavior during the milling process, further verifying the feasibility of the combined helical milling strategy. The results demonstrate that this novel method can be effectively applied to achieve high-precision countersunk hole machining.