An average of 20 new orders are started through a certain factory each month. On average, an order consists of 50 parts to be processed through 10 machines in the factory. The operation time per machine for each part = 15 min. The nonoperation time per order at each machine averages 8 hours, and the required setup time per order = 4 hours. There are 25 machines in the factory, 80% of which are operational at any time (the other 20% are in repair or maintenance). The plant operates 160 hours per month. However, the plant manager complains that a total of 100 overtime machinehours must be authorized each month in order to keep up with the production schedule. (a) What is the manufacturing lead time for an average order? (b) What is the plant capacity (on a monthly basis) and why must the overtime be authorized? (c) What is the utilization of the plant according to the definition given in the text? (d) Determine the average level of workinprocess (number of partsinprocess) in the plant.(a) MLT = 10(4 + 50x0.25 + 8) = 245 hr/order (b) Tp = (4 + 50x0.25)/50 = 16.5/50 = 0.33 hr/pc, Rp = 3.0303 pc/hr PC = (25x0.80)(160)(3.0303)/10 = 969.7 pc/month Parts launched per month = 20x25 = 1000 pc/month Schedule exceeds plant capacity by 1000 - 969.7 = 30.3 pc. This requires overtime in the amount = (30.303 pc x 10 machines)/(3.0303 pc/hr) = 100 hr. (c) Utilization U = (1000 pc)/(969.7 pc) = 1.03125 = 103.125% (d) WIP = (245 hr)(969.7 pc/mo)(1.03125)/(160 hr/mo) = 1531.25 parts The mean time between failures for a certain production machine is 250 hr, and the mean time to repair is 6 hr. Determine the availability of the machine.
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