Machinery's Handbook, 31st Edition
1232 MACHINING ECONOMETRICS A comparison of feed rates for full slot ( ar / D = 1) and high-speed end milling ( ar / D = 0.03 and f z = 3.69 3 f z 0 = 0.628 mm) for tool life 45 minutes is shown in Fig. 26d. The points SL2, SL4, SL6 and HS2, HS4, HS6, refer to 2, 4, and 6 teeth (2 to 6 teeth are commonly used in practice). Feed rate is also plotted versus number of teeth z in Fig. 26e, for up to 16 teeth, still at f z = 0.628 mm. Comparing the effect of using 2 versus 6 teeth in high-speed milling shows that feed rates increase from 5250 mm/min (413 ipm) up to 18,000 mm/min (1417 ipm) at 45 minutes tool life. The effect of using 2 versus 6 teeth in full slot milling is that feed rate increases from 1480 mm/min (58 ipm) up to 3230 mm/min (127 ipm) at tool life 45 minutes. If 16 teeth could be used at ar / D = 0.03, the feed rate increases to F R = 44,700 mm/min (1760 ipm), and for full slot milling F R = 5350 mm/min (210 ipm).
100000
HS6
HS4
10000
HS2
SL6
SL4
T = 45, SL T = 45, HS
SL2
1000
0 1 2 3 4 5 6 7 8 9 1011121314151617 Number teeth
Fig. 26e. Feed Rate versus Number of Teeth Comparison of Slot Milling ( ar / D = 1) and High-Speed Milling at ( ar / D = 0.03) for 2, 4, and 6 Teeth at T = 45 Minutes Comparing the feed rates that can be obtained in steel cutting with the one achieved in the earlier referred DARPA investigation, using HSS and carbide cutters milling 6061- T651 and A356-T6 aluminum, it is obvious that aluminum end milling can be run at 3 to 6 times higher feed rates. This requires 3 to 6 times higher spindle speeds (cutter diameter 25 mm, radial depth of cut ar = 12.5 mm, 2 teeth). Had these tests been run with 6 teeth, the feed rates would increase up to 150,000–300,000 mm/min, when feed/tooth = 3.4 3 0.25 = 0.8 mm/tooth at ar / D = 0.03. Process Econometrics Comparison of High-Speed and Slot End Milling .—When making a process econometrics comparison of high-speed milling and slot end milling use the formulas for total cost c tot ( Determination of Machine Settings and Calculation of Costs starting on page 1216). Total cost is the sum of the cost of cutting, tool changing, and tooling: c tot = H R 3 ( Dist / F R ) 3 (1 + T V / T )⁄60 where T V = T RPL + 60 3 C E / H R = equivalent tooling-cost time, minutes T RPL = replacement time for a set of edges or tool for regrinding C E = cost per edge(s) H R = hourly rate, $
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online