Machinery's Handbook, 31st Edition
MACHINING ECONOMETRICS 1233 Fig. 27 compares total cost c tot , using the end milling cutters of the previous examples, for full slot milling with high-speed milling at ar / D =0.03, and versus ECT at T = 45 minutes.
1
minutes 2,4,6 teeth marked
H-CURVE
SL2
SL4
SL6
HS2
0.1
HS4
T = 45, z = 4, SL T = 45, z = 6, SL T = 45, z = 2 , HS T = 45, z = 4, H T = 45, z = 6, HS
HS6
0.01
0.01
0.1
1
ECT , mm
Fig. 27. Cost 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 The feed/tooth for slot milling is f z 0 = 0.17 and for high-speed milling at ar / D = 0.03 the feed is f z = 3.69 3 f z 0 = 0.628 mm. The calculations for total cost are done according to above formula using tooling cost at T V = 6, 10, and 14 minutes, for z = 2, 4, and 6 teeth respectively. The distance cut is Dist = 1000 mm. Full slot milling costs are, at feed rate F R = 3230 and z = 6 c tot = 50 3 (1000⁄3230) 3 (1 + 14⁄45)⁄60 = $0.338 per part at feed rate F R =1480 and z = 2 c tot = 50 3 (1000⁄1480) 3 (1 + 6⁄45)⁄60 = $0.638 per part High-speed milling costs are, at F R =18000, z = 6 c tot = 50 3 (1000⁄18000) 3 (1 + 14⁄45)⁄60 = $0.0606 per part at F R = 5250, z = 2 c tot = 50 3 (1000⁄5250) 3 (1 + 6⁄45)⁄60 = $0.180 per part The cost reduction using high-speed milling compared to slotting is enormous. The cost for high-speed milling with 2 teeth is 61 percent (0.208⁄0.338) of full slot milling with 6 teeth ( z = 6). The cost for high-speed milling with 6 teeth is 19 percent (0.0638⁄0.338) of full slot for z = 6. Aluminum end milling can be run at 3 to 6 times lower costs than when cutting steel. Costs of idle (non-machining) and slack time (waste) are not considered in the example. These data hold for perfect milling conditions such as zero run-out and accurate sharpen ing of all teeth and edges.
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