DEGREE PROJECT IN MATERIALS DESIGN AND ENGINEERING, SECOND CYCLE, 30 CREDITS STOCKHOLM, SWEDEN 2018 Characterization of machinability in lead-free brass alloys KASIM AYTEKIN KTH ROYAL INSTITUTE OF TECHNOLOGY SCHOOL OF INDUSTRIAL ENGINEERING AND MANAGEMENT Abstract Recent legislation has put focus on the toxic nature of lead as an alloying element in brass products. Water supply systems are of biggest concern where suspected lead leakages from brass products are threatening human health. A comprehensive study has been conducted in order to characterize the machinability of lead-free brass alloys to provide the industry with necessary information to assist a replacement of the leaded alternatives. The characterization has focused on two particular machining processes, namely turning and drilling and has been based on cutting force generation and chip formation. While the turning tests aimed to characterize the machinability by comparing two lead-free alloys (CW511L and AquaNordic) with a leaded alloy (CW625N), drilling tests aimed to characterize machinability of the lead-free AquaNordic alloy particularly, with the main focus put on the impact of tool geometry on machinability. The results have shown that significantly higher cutting forces are generated during turning of lead-free alloys as compared to the leaded. There was, however, no significant difference between the two lead-free alloys regarding cutting forces while chip formation is improved for AquaNordic. Drilling tests have shown that the machinability of the lead-free AquaNordic alloy can be improved by increasing the tool rake angle and decreasing tool diameter. Based on the results from this thesis work, it has been concluded that the machinability of lead-free brass alloys is sufficiently good to be able to be adopted by the industry. However, improvement is necessary in order to fulfill the requirement needed to replace the leaded alternatives. Table of Contents 1. Introduction ................................................................................................................................ 1 1.1. Background ......................................................................................................................... 1 1.2. Aim and objective ................................................................................................................ 3 1.2.1. Turning – Alloy comparison .......................................................................................... 3 1.2.2. Drilling – Tool geometry comparison ............................................................................ 3 2. Brass as a workpiece material ..................................................................................................... 4 2.1. α –brass............................................................................................................................... 5 2.2. Duplex brasses .................................................................................................................... 5 2.3. Additional alloying elements................................................................................................ 6 2.3.1. Lead ............................................................................................................................. 7 3. Machinability .............................................................................................................................. 8 3.1. Machining theory ................................................................................................................ 9 3.1.1. Chip formation and morphology .................................................................................. 9 3.1.2. Cutting force generation ............................................................................................ 11 3.2. Effect of tool design on machinability ................................................................................ 12 3.2.1. Tool material and geometry aspects on drills ............................................................. 15 4. Literature review ....................................................................................................................... 17 5. Experimental ............................................................................................................................. 19 5.1. Methodology ..................................................................................................................... 19 5.2. Workpiece materials.......................................................................................................... 20 5.2.1. Turning – Alloy comparison ........................................................................................ 20 5.2.2. Drilling – Tool geometry comparison .......................................................................... 20 5.3. Cutting tools ...................................................................................................................... 21 5.3.1. Turning - Alloy comparison ........................................................................................ 21 5.3.2. Drilling - Tool geometry comparison .......................................................................... 21 5.4. Machining tests ................................................................................................................. 23 5.4.1. Turning ...................................................................................................................... 23 5.4.2. Drilling ....................................................................................................................... 24 5.5. Analysis ............................................................................................................................. 26 5.5.1. Cutting forces ............................................................................................................ 26 5.5.2. Optical analysis .......................................................................................................... 27 5.6. Comparative evaluation of chips ........................................................................................ 28 6. Results ...................................................................................................................................... 28 6.1. Turning .............................................................................................................................. 28 6.1.1. Force measurements ................................................................................................. 28 6.1.2. Chip morphology ....................................................................................................... 38 6.2. Drilling ............................................................................................................................... 42 6.2.1. Force measurements ................................................................................................. 42 6.2.2. Vibrations .................................................................................................................. 50 6.2.3. Chip morphology ....................................................................................................... 51 7. Discussion ................................................................................................................................. 55 7.1. Turning .............................................................................................................................. 55 7.1.1. Force measurement ................................................................................................... 55 7.1.2. Chip formation ........................................................................................................... 56 7.2. Drilling ............................................................................................................................... 57 7.2.1. Force measurement ................................................................................................... 57 7.2.2. Chip formation ........................................................................................................... 58 7.2.3. Vibrations .................................................................................................................. 58 7.3. Comments ......................................................................................................................... 59 8. Summary and conclusions ......................................................................................................... 60 8.1. Recommendations for machining of AquaNordic ............................................................. 61 9. Future work .............................................................................................................................. 62 10. Acknowledgements ............................................................................................................... 63 11. References ............................................................................................................................ 64 Appendix A ..........................................................................................................................................I A1. Chip formation and morphology ................................................................................................I A2. Cutting forces ..........................................................................................................................