MACHINING ECONOMETRICS Machinery's Handbook, 31st Edition
1222
For ASTM Class 20 gray cast iron, using hard ceramic,
ln ( V 1 ⁄ V 2 ) ln ( T 2 ⁄ T 1 )
ln (1490 ⁄ 2220) ln (15 ⁄ 45)
n
C
) V T 1
5932
. 036
n
1 # = = Selection of Optimized Data.— Fig. 22 illustrates cutting time, cycle time, number of parts before a tool change, tooling cost, and total cost, each plotted versus feed for a constant tool life. Approximate minimum cost conditions can be determined using the formulas previously given in this section. = = = First, select a large feed/rev or tooth, and then calculate economic tool life T E , and the economic cutting speed V E , and do all calculations using the time/cost formulas as described previously.
1000
t c t cyc # parts C TOOL C TOT
100
10
1
0.1
0.01
0.001
0.01
0.1
1
10
f, mm/rev
Fig. 22. Cutting Time, Cycle Time, Number of Parts Before Tool Change, Tooling Cost, and Total Cost versus Feed for Tool Life = 15 Minutes, Idle Time = 10 s, and Batch Size = 1000 Parts Example 11, Step by Step Procedure: Turning—Facing out: 1) Select a big feed/rev, in this case f = 0.9 mm/rev (0.035 inch/rev). A Taylor slope n is first determined using the Handbook tables and the method described in Example 10. In this example, use n = 0.35 and C = 280. 2) Calculate T V from the tooling cost parameters: If cost of insert = $7.50; edges per insert = 2; cost of tool holder = $100; life of holder = 100 insert sets; and for tools with inserts, allowance for insert failures = cost per insert by 4⁄3, assuming only 3 out of 4 edges can be effectively used. Then, cost per edge = C E is calculated as follows:
. 750 100 100 600 number of edges per insert cost of insert(s) 2 # + =
cutter body life in number of edges cost of cutter body
C
=
+
E
$ . 4 ⁄ 3 The time for replacing a worn edge of the facing insert = T RPL = 2.24 minutes. Assuming an hourly rate H R = $50/hour, calculate the equivalent tooling-cost time T V T V = T RPL + 60 3 C E / H R =2.24 +60 3 6⁄50 = 9.44 minutes 3) Determine economic tool life T E T E = T V 3 (1/ n − 1) = 9.44 3 (1/ 0.35 − 1) = 17.5 minutes 4) Determine economic cutting speed using the Handbook tables using the method shown in Example 10, V T C E E n = m/min = 280 / 17.5 0.35 = 103 m/min =
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