Surface Integrity in Rotary Broaching of Ti6Al4V: Analyzing the Effects of Kinematic and Cutting Parameters

The rotary broaching process is critical for manufacturing dental and orthopedic implants from Ti6Al4V. Despite extensive research on machining titanium alloys, the rotary broaching of Ti6Al4V remains underexplored, particularly regarding the relationship between machining parameters and surface integrity. This study investigates the effects of cutting parameters and rotary broaching kinematics on surface roughness, microhardness, and texture. Hexagonal holes were machined into ϕ10×20 mm rods using Response Surface Methodology (RSM) for experimental design and analysis. Results indicated that feed rate and rotational speed are the primary factors affecting surface roughness, contributing 51% and 24.5% respectively, with roughness values ranging from 0.258 to 0.701 µm. Contrary to conventional orthogonal cutting theory, an increase in cutting speed led to higher cutting edge engagement frequency, adversely affecting surface texture and roughness due to the unique kinematics of rotary broaching. Additionally, microhardness of the broached samples increased from 341Hv to a maximum of 386Hv due to work hardening, primarily driven by feed rate and its effect on strain hardening of Ti6Al4V. Surface texture analysis revealed defects such as smears and grooves, caused by the ploughing effect and poor chip disposal, which could be mitigated by chamfering the pilot hole entrance.