63874-Ch15

# 1514 what is the difference between how the largest

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15.14 What is the difference between how the largest candidate rule works and how the Kilbridge and Wester method works? Answer : In the largest candidate rule, the algorithm begins with the work elements listed in descending order of their time values, whereas in the Kilbridge and Wester method, the algorithm operates on the work elements listed according to their precedence order in the precedence diagram. 15.15 In a mixed-model assembly line, what is the difference between variable-rate launching and fixed-rate launching? Answer : In variable-rate launching, the time interval between the launching of the current base part and the next is set equal to the cycle time of the current unit. Since different models have different work content times and thus different task times per station, their launch time intervals vary. In fixed-rate launching, the time interval between two consecutive launches is constant. The time interval in fixed-rate launching is an average based on the product mix and production rates of models on the line. 15.16 What are storage buffers and why are they sometimes used on a manual assembly line? Answer : A storage buffer is a location in the production line where work units are temporarily stored. As identified in the text, the reasons to include one or more storage buffers in a production line include: (1) to accumulate work units between two stages of the line when their production rates are different; (2) to smooth production between stations with large task time variations; and (3) to permit continued operation of certain sections of the line when other sections are temporarily down for service or repair. PROBLEMS Single Model Assembly Lines 15.1 A product whose work content time = 47.5 min is to be assembled on a manual production line. The required production rate is 30 units per hour. From previous experience, it is estimated that the manning level will be 1.25, proportion uptime = 0.95, and repositioning time = 6 sec. Determine (a) cycle time, and (b) ideal minimum number of workers required on the line. (c) If the ideal number in part (b) could be achieved, how many workstations would be needed? 102

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Assembly Lines-3e-S 07-05/06, 06/04/07 Solution : (a) T c = ( 29 60 0.95 30 = 1.9 min (b) w = Minimum Integer 47.5 1.9 = 25 workers (c) n = 25/1.25 = 20 workstations 15.2 A manual assembly line has 17 workstations with one operator per station. Work content time to assemble the product = 28.0 min. Production rate of the line = 30 units per hour. The proportion uptime = 0.94, and repositioning time = 6 sec. Determine the balance delay. Solution : T c = ( 29 60 0.94 30 = 1.88 min, T s = 1.88 - 0.1 = 1.78 min w = n = 17 workers and 17 stations E b = ( 29 28.0 17 1.78 = 0.9253, d = 1 - 0.9253 = 0.0747 = 7.47% 15.3 A manual assembly line must be designed for a product with annual demand = 100,000 units. The line will operate 50 wks/year, 5 shifts/wk, and 7.5 hr/shift. Work units will be attached to a continuously moving conveyor. Work content time = 42.0 min. Assume line efficiency = 0.97, balancing efficiency = 0.92, and repositioning time = 6 sec. Determine (a) hourly production rate to meet demand, and (b) number of workers required.
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