MACHINING ECONOMETRICS Machinery's Handbook, 31st Edition
1220
Time for replacement of inserts T RPL , minutes
Number of inserts
Price per insert
Edges per insert
Cutter Price
Edges per cutter
Cost per set of edges, C E
Hourly shop rate
T V minutes
Face mill
2 2
10 10
5 5
3 3
750 750
500 500
23.72 23.72
50 30.466 25 58.928
End mill
1
3
6
2
75
200
4.375
50 6.25
Turning
1 30 6.44 With above data for the face mill, and after having determined the economic cutting time as t cE = 1.5 minutes, calculate for a batch size = 1000 and $50 per hour rate: Cost of Tooling + Tool Change per Batch: . . $ C C H T T T 60 60 50 1000 15 61 30466 624 TOOL CH R C V # # # # # + = = = ^ h Total Cost of Cutting per Batch: . . $ C H T T T 60 1 60 50 1000 15 1 61 30466 1874 TOT R C V # # # # = + = + = a a k k Similarly, at the $25/hour shop rate, ( C TOOL + C CH ) and C TOT are $312 and $937, respectively. 1 5 3 50 100 2.72 Example 8, Turning: Production parts were run in the shop at feed/rev = 0.25 mm. One series was run with speed V 1 = 200 m/min and tool life was T 1 = 45 minutes. Another was run with speed V 2 = 263 m/min and tool life was T 2 = 15 minutes. Given idle time t i = 1 minute, cutting distance Dist =1000 mm, work diameter D = 50 mm. First, calculate Taylor slope, n, using Taylor’s equation V 1 3 T 1 n = V 2 3 T 2 n , as follows: . ln ln ln ln n V V ' ' = = = Economic tool life T E is next calculated using the equivalent tooling-cost time T V , as described previously. Assuming a calculated value of T V = 4 minutes, then T E can be calcu lated from . T T n 1 1 4 025 1 1 12 minutes E V # # = − = − = a a k k Economic cutting speed, V E can be found using Taylor’s equation again, this time using the economic tool life, as follows, T T 263 200 45 15 025 2 1 1 2
n
n
V T V T # # = ^ ^ h
2 h 0.25
1
2
E
E
V V T T # = c E 1 2
263 12 15 # a
n
2
/min
278 m
k
m
=
=
E
Using the process data, the remaining economic parameters can be calculated as follows: Economic spindle rpm, rpm E = 1000 V E / π D = (1000 3 278)/(3.1416 3 50) = 1770 rpm Economic feed rate, F R E = f 3 rpm E = 0.25 3 1770 = 443 mm/min Economic cutting time, t cE = Dist / F R E =1000/443 = 2.259 minutes Economic number of parts before tool change, N chE = T E ÷ t cE =12 ÷ 2.259 = 5.31 parts Economic cycle time before tool change, T CYCE = N chE 3 ( t c + t i ) = 5.31 3 (2.259 + 1) = 17.3 minutes.
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online