MACHINING ECONOMETRICS Machinery's Handbook, 31st Edition
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T k C E = cost per edge(s) is determined using two alternate formulas, depending on whether tools are reground or inserts are replaced: Cost per Edge, Tools for Regrinding: C 1 number of regrinds costof tool number of regrinds cost/regrind E # = + + ^ h Cost per Edge, Tools with Inserts: C number of edges per insert costof insert(s) cutter body life in number of edges costof cutter body E = + Note: In practice allow for insert failures by multiplying the insert cost by 4⁄3, that is, assuming only 3 out of 4 edges can be effectively used. Example 6, Cost per Edge-Tools for Regrinding: Use the data in the table below to calcu late the cost per edge(s) C E , and the equivalent tooling-cost time T V , for a drill. Time for cutter TOT C # = 1 1.5 Using the cost per edge formula for reground tools, C E = (40 + 5 3 6) ÷ (1 + 5) = $6.80 When the hourly rate is $50/hr, . . T T H C 60 1 50 60 68 9 16 minutes V RPL R E = + = + = ^ h Calculate economic tool life using T T n 1 1 E V # = − a k thus, T E = 9.17 3 (1⁄0.25 − 1) = 9.16 3 3 = 27.48 minutes. Having determined, elsewhere, the economic cutting time per piece to be t cE = 1.5 min utes, for a batch size = 1000 calculate: Cost of Tooling + Tool Change per Batch: . . . $ C C H T T T 60 60 50 1000 15 2748 916 417 TOOL CH R C V # # # # # + = = = ^ h Total Cost of Cutting per Batch: . . . $ C H T T T 60 1 60 50 1000 15 1 2748 916 1617 TOT R C V # # # # = + = + = a a k k Example 7, Cost per Edge-Tools with Inserts: Use data from the table below to calculate the cost of tooling and tool changes, and the total cost of cutting. For face milling, multiply insert price by safety factor 4⁄3 then calculate the cost per edge: C E =10 3 (5⁄3) 3 (4⁄3) + 750⁄500 = 23.72 per set of edges replacement T RPL , minute Cutter Price, $ Cost per regrind, $ Number of regrinds Hourly shop rate, $ Batch size Taylor slope, n Economic cutting time, t cE minute 40 6 5 50 1000 0.25 When the hourly rate is $50, equivalent tooling-cost time is T V = 2 + 23.72 3 60⁄50 = 30.466 minutes (first line in table below). The economic tool life for Taylor slope n = 0.333 would be T E = 30.466 3 (1⁄0.333 – 1) = 30.466 3 2 = 61 minutes. When the hourly rate is $25, equivalent tooling-cost time is T V = 2 + 23.72 3 60⁄25 = 58.928 minutes (second line in table below). The economic tool life for Taylor slope n = 0.333 would be T E = 58.928 3 (1⁄0.333 – 1) =58.928 3 2 = 118 minutes.
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