tailieunhanh - Machinability and Surface Integrity Part 2

Tham khảo tài liệu 'machinability and surface integrity part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Machinability and Surface Integrity 279 o Figure 147. Machinability testing utilising an accelerated testing procedure - a combination of the rapid facing and degraded tool tests 280 Chapter 7 on a moderately short timescale. Normally in many previous testing programs an uncoated cemented carbide P20 or P10 grade would have been used since these grades withstand both higher speeds and have better tool wear resistance to that of previously utilised cutting tool materials. However in this case an P25 grade was chosen which is a degradation from the optimum P20 grade but it should still perform satisfactorily. Furthermore the cutting speed was raised by times the optimum of 200 m min-1 with all facing operations being conducted at a constant surface speed 12 of 550 m min-1. Typical tool-life curves produce by the AWT technique are illustrated in Fig. 148 showing the expected three stages of flank wear. This flank wear being a function of the initial edge breakdown steady-state wear -as the insert s flank progressively degenerates and finally catastrophic insert edge breakdown - as the edge completely fails. Detailed metallurgical analysis can be made as to the reasons why some P M compacts performed better than others by reference to the literature on the metallurgical interactions between the tool and the compact - this subject being outside the scope of the present discussion. The facing-off secondary machining operation meant that after 10 facing passes a pre-programmed optional stop can then be applied to allow both tool flank wear and compact surface texture to be established. The faced-off surface texture results can then be superimposed onto the same graph -for a direct comparison of flank wear and for that of the machined surface texture parameter. Without going into too much detail of the specific aspects of the processing and metallurgical interactions present here on the composite graph some compacts abraded the cutting insert more than others while the