Effect of lead on the machinability of brass alloys using polycrystalline diamond cutting tools

The international safety regulations are pushing the manufacturers of water systems and equipment to remove lead from material compositions due to the potential human hazard of lead absorption. The usage of green lead-free brass alloys is becoming mandatory in many important markets, demanding the manufacturers to quickly adapt their production techniques both casting and machining to this new reality. Regarding machining, lead has been used to facilitate the chip control, working as a natural chip breaker and reducing the tool wear. Therefore, the reduction of lead composition in brass alloys contributes to a machinability decrease of the materials leading to higher cutting forces, long chips and higher tool wear. This work focuses on the machinability characterization of three different brass alloys (leaded, medium-leaded and minimally leaded) by means of cylindrical external turning process with polycrystalline diamond inserts. A parametric study covering three different depths of cuts, three feed rates and four cutting speeds was conducted for three brass alloys with two repetitions. Cutting forces, chip morphology and surface roughness were analysed and compared between alloys. Complementary microstructural and mechanical characterization of the alloys were performed. Analysis of variance was performed to analyse the results. Cutting forces, power consumption, specific cutting pressure, roughness and chip morphology identification were used as comparison criteria among the tested materials. Results have demonstrated the decrease of machinability with the lead reduction, with higher cutting forces and longer chips. Polycrystalline diamond tools used in this work could be a good option to overcome the machinability challenges of the lead-free brass alloys.