8.24 in the final colony structure. For each stiffener, 4 to 12 pieces must be welded together. To determine its mass, the lay-up bed is modeled as a light machine tool (see Section VIII.4.4.1). With a best-guess estimate of power consumption, these are the specifications of the lay-up bed: Dimensions Mass Power 25m x 25m x lm 312 Tons 100 kW VIII.5.3.2: EB Welding: There remains to set the size and number of EB welding heads to be used. First, the time allotted to various operations must be determined. On the average, one section must be produced every 17 hours. Allowing for some overlapping of operations, in these 17 hours one can expect the following distribution of time: Positioning and Clamping of Stock Welding Drilling and Bolting 10 Hr 3 Hr Hr For every hull section there are roughly 1200 pieces which must be positioned and clamped or an average of one every 30 seconds. There are 1600m of weld in each section so the welding head(s) must advance at a rate of 9m/min. The largest present EB devices are 100 kW (8.11). Appendix VIII.B shows that a 100 kW EB beam moving through 30 mm steel plate goes at a rate of Sm/min. Therefore, two welding heads are needed. A 100 kW welding head with support structure masses 800 kg (8.10) so the mass and power requirements are: Mass Power Each Unit 800 kg 100 kW Total 1600 kg 200 kW VIII.5.3.3: Drilling and Attachment of Major Stiffeners: Figure 8.6 is a flow chart of the fabrication operation, tracing the history of the hull section components through the fabrication shack. It
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