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Tham khảo tài liệu 'metal machining - theory and applications episode 1 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Tool life 133 a ductile cast iron shows ceramic tools having a larger n-value than a carbide tool - for the white alumina n 1.2. This very high value indicates a mechanical wear mechanism reducing in intensity with increasing cutting speed. Figure 4.14 b for turning two different Ti-alloys with a carbide tool is an example of where a break point falls within the practical cutting speed range. Figure 4.14 c for face milling a grey cast iron shows a condition in which tool life decreases with reducing cutting speed. Taylor s equation - influence of feed and depth of cut Tool life is influenced by feed and depth of cut as well as by cutting speed. Additional life equations are fTn2 C2 dTn3 C3 4.3 and these may be combined with equation 4.2 replacing n there by n1 to give V1 n1f1 n2d1 n3T C 4.4 When tool life is limited by thermal damage mechanisms n1 n2 n3 i.e. cutting speed has a larger influence on life than does feed than does depth of cut reflecting the influences of these variables on cutting temperature. If however tool life is determined by chipping and fracture failures n2 and n3 can become smaller. 4.2.3 Tool life fluctuations It is almost impossible to keep cutting conditions exactly constant in practical machining. Even if it were possible it would be found that tool life and failure are phenomena based on probability. Fluctuations cannot be avoided in these. However the range of fluctuations is influenced by the damage mechanism. It is easy to imagine larger fluctuations when chipping or fracture rather than abrasion is the main mechanism. Figure 4.15 shows the cumulative probability of flank wear development after 1 min of P10 P10 B1112 Sintered steel 99 S 85 I 80 1 60 2 40 Q i 20 Z3 E Ổ 10 z TÌC-AI2O3 ceramic Inconel 718 VBmax 5 J- 0.02 0.05 0.1 0.2 0.5 1.0 2.0 Flank wear VB mm B112 - P10 V 200m min d 0.5mm f 0.1mm rev Sintered steel - P10 V 200m min d 0.5mm f 0.1mm rev Inconel 718 - Al2O3-TiC ceramic V 200m min d 0.5mm f 0.19mm rev Fig. 4.15 .
