Machinery's Handbook, 31st Edition
1218 MACHINING ECONOMETRICS Number of parts before tool change = N ch = 90⁄3 = 30 parts. Cycle time before tool change = T CYC = 30 3 (3 + 3) = 180 minutes
Example 5: Given cutting time, t c = 1 minute, idle time t i = 1 minute, N ch = 100 parts, cal culate the tool life T required to complete the job without a tool change, and the cycle time before a tool change is required. Tool life = T = N ch 3 t c = 100 3 1 = 100 minutes. Cycle time before tool change = T CYC = 100 3 (1 + 1) = 200 minutes. Calculation of Cost of Cutting and Grinding Operations.— When machining data varies, the cost of cutting, tool changing, and tooling will change, but the costs of idle and slack time are considered constant. Cost of Cutting per Batch: C C = H R 3 T C ⁄60 T C = cutting time per batch = (number of parts) 3 t c , minutes, or when deter mining time for tool change T ch = N ch 3 t c minutes = cutting time before tool change. t c = cutting time/part, minutes H R = hourly rate Cost of Tool Changes per Batch: $ $ min min C H T T T 60 CH R C RPL # # = = where T = tool life, minutes, and T RPL = time for replacing a worn edge(s), or tool for regrinding, minutes Cost of Tooling per Batch: Including cutting tools and holders, but without tool changing costs, $ $ $ $ min min min min hr hr C H T T H C 60 60 TOOL R C R E # # = = Cost of Tooling + Tool Changes per Batch: Including cutting tools, holders, and tool changing costs,
60
C
E
T T H RPL +
H 60 R
R
C C h Total Cost of Cutting per Batch: T TOOL CH C # # + = ^
60
C
E
T T H RPL +
H
f
p
R
R
1
C
T
=
+
#
60
C
TOT
Equivalent Tooling-cost Time, T V : The two previous expressions can be simplified by using T T
H C 60 R
E
thus:
= +
V RPL
T T T C V
H 60 R
C C ^
+ = h
# #
TOOL CH
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