Cost of Parts Fabrication

Table 16.10 lists the cost of parts fabrication in a nondimensional form from the manhours involved. Actual manhours needed to manufacture parts for each of the six Nacelle A stages can be obtained from the shop-floor engineering process sheets. Factored indices for Nacelle B can be established through DFM/A studies at the conceptual design stage.

At each stage of parts manufacture, manhours are given in fractions of the total manhours for all parts; manhour rates are invariant. The Nacelle B learning-curve factor for parts fabrication is about the same as for Nacelle A but not for the assem­bly. Nacelle B has fewer parts, thereby saving on costs.

manufacturing cost = rates x manhours x learning-curve factor

x size factor x manufacturing philosophy (16.3)

Table 16.10. Manhours fraction required to fabricate parts Nacelle A Nacelle B Total manhours cost for all parts 1.000 1.0878 Learning-curve factor 1.000 1.022 Parts in the forward-bulkhead assembly – Stage 1 (start): 0.056 0.120 Parts in primary assembly – Stage 2: 0.038 0.003 Parts in aft-bulkhead assembly – Stage 3: 0.111 0.130 Parts in first subassembly – Stage 4: 0.623 0.355 Parts in second subassembly – Stage 5: 0.073 0.294 Parts in third subassembly – Stage 6 (final): 0.099 0.098

Table 16.11. Manhour fractions required to assemble Nacelle A Nacelle B Total manhours required to assemble 1.0 0.7587 Learning-curve factor 1.0 0.735 Stage 1 (start): Forward-bulkhead assembly 0.1 0.032 Stage 2: Primary assembly 0.116 0.191 Stage 3: Aft-bulkhead assembly 0.056 0.141 Stage 4: First subassembly 0.27 0.241 Stage 5: Second subassembly 0.211 0.267 Stage 6: Third subassembly (final) 0.247 0.128

The rate and factor for Nacelle A are 1; details for Nacelle B are in Table 16.7. Subassemblies

Table 16.7 lists details for the Nacelles A and B nose cowl subassembly in six stages of processing. Table 16.10 lists subassembly costs in a nondimensional form in frac­tions of the total assembly manhours for all stages. Costs of the pure structure of the nacelle mould lines are separated from those of all other nonstructural compo­nents (e. g., anti-icing ducting, linkages, cables, and accessories) that are part of the complete EBU fitment for a nacelle that is ready for a turbofan engine. The costs of installing EBUs in the assembly process are considered but not the actual EBU cost. The assembly cost is expressed as follows:

assembly cost = rates x manhours x learning-curve factor

x size factor x manufacturing philosophy (16.4)

The rate and factor for Nacelle A are 1; details for Nacelle B are shown in Table 16.11. Savings are realized through the DFM/A study.

4. Cost of Support: Certain additional costs are incurred when a product fails to adhere to the desired quality during inspection. In that case, reworking and/or design concessions are required to salvage the product from rejection as scrap. These are the support costs – generally minor but difficult to determine. A flat – rate of 5% of the cost of material plus parts manufacture plus assembly is added as the support cost. DFM/A studies attempt to ensure design and manufacturing considerations that minimize support costs by making the product right the first time (i. e., the Six Sigma concept).

Cost of Amortization of the NRCs

Table 16.12 shows the two types of NRCs in nondimensional form. Amortization is performed for more than 200 aircraft – that is, distributed over 400 nacelle units.

Table 16.12. Nonrecurring costs Nacelle A Nacelle B Product design cost 1.0 1.1 Methods/tool design cost 1.0 1.1

5. Miscellaneous Costs: These are unavoidable (e. g., insurance and packaging) and unforeseen costs of contingencies involved in the supply chain and necessar­ily charged as a manufacturing cost. Normally, these costs are minimal; in this study, 3 to 5% of the costs of material plus parts manufacture plus assembly is used. In the industry, the exact costs are available.