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    Discussion in 'Calculations' started by graphcomnsk, Dec 29, 2009.

    1. graphcomnsk

      graphcomnsk Member

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      The overall function of tool and manufacturing engineers embrace the entire span from participation in product development committees, through all process planning, method engineering and production, through the final inspection.
      At every stage in total manufacturing, these engineers are confronted with the dollar sign. Every better production is demanded at higher speed and lower costs.
      Analysis of Small – tool costs.
      The following analyzes are particularly applicable where production rates are small and fixed.
      Let N = number of pieces manufactured per year.
      C = cost of fixture
      I = annual allowance for interest of investment, %
      T = annual allowance for repairs, %
      D = annual allowance for depreciation, %
      S = yearly cost of setup
      a = saving in labor cost / unit
      t = percentage of overhead applied on labor saved
      V = yearly operating profit over fixed charges
      H = number of year required for amortization of investment out of earnings
      N = [C (I + T + D + M) + S] / [a (1 + t)]
      Tooling Economics In Combined Operations:
      Analysis may sometimes show that operations can be advantageously combined. The tool cost tooling may thus be reduced, or the production costs, or both.
      Costs of Combined Vs Separate Operations
      Costs Blanking Operation Forming Operations Total Blank and Form Combined Operations
      Tooling 40 30 70 50
      Setup 2 2 4 3
      Maintenance 2 2 2
      Processing 4 30 34 4
      Total Cost 48 62 110 59

      Process cost comparison
      During process planning, many possible methods of manufacturing may be reduced to a few based upon alternate process steps, use of available component, or combined operations. Under these conditions, a comparison of costs for different tools and process steps may quickly reveal the combination that will result in the lowest total cost/part.
      Let Nt = total number of parts to be produced in single run.
      Nb = number of parts for which the unit costs will be equal for each of two compared methods Y and Z (break even point)
      Ty = total cost for method Y
      Tx = total cost for method Z
      Py = unit tool process cost for method Y
      Px = unit process cost for method Z
      Cy,Cz = total unit cost for method Y and Z respectively.
      Then
      Nb = [Ty-Tz] / [Py-Pz]
      Cy = [Py Nt + Ty ] / Nt
      Cz = [Pz Nt + Tz] / Nt


      Effect of Tool Material on Minimum-cost Tool Life:

      The wear characteristics, as denoted by n [slope] value, show that economic life Tc for carbide tools is shorter than that of HSS tools. It is important to use higher speeds and shorter tool life for oxide tools.
      Performance Data For Various Tool Material
      Tool Material 1/n – 1 Values Tool Life, min Minimum Cost cutting speed Vc, sfpm
      Tc Tp
      HSS 7 35 14 107
      Tungsten Carbide 3 15 6 701
      Oxide 1 5 2 3500

      Economic Lot Sizes
      Economic lot sizes are calculated and employed to obtain the minimum unit cost of given part or material. This minimum is reached when the cost of planning, ordering, and setting up, handling, and tooling equal to the costs of storage finished parts. These costs may be equated and the lot size determined by mathematical calculation.

      Where C = Value of each pieces , k = annual caring cost , L = lot size (pieces) , m = monthly consumption (pieces), S = setup cost per lot, v = machining time / lot size (ratio)

      L = ? [24 x m x S] / {k x c x (1 + [m x V])}

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    3. mvalenti

      mvalenti Well-Known Member

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      Excellent Post!
       

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