B using a tolerance time that is 50 greater than the

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stations needed on the line. (b) Using a tolerance time that is 50% greater than the cycle time, what would be an appropriate belt speed and spacing between parts? Solution : (a) T c = 60 0 96 48 ( . ) = 1.2 min T s = 1.2 - 0.05 = 1.15 min and E b = 1 - 0.07 = 0.93 Since M = 1.0, n = w = Minimum Integer 20 0 0 93 115 . . ( . ) = 18.7 19 workstations (b) Use T t = 1.5 T c = 1.5(1.2) = 1.8 min/station T t = s c L v . Rearranging, v c = s t L T = 5 18 ft . min. = 2.778 ft/min T c = p c s v . Rearranging, s p = T c v c = 1.2(2.778) = 3.33 ft/part 15.32 In the general assembly department of an automobile final assembly plant, there are 500 workstations, and the cycle time = 0.95 min. If each workstation is 6.2 m long, and the tolerance time = the cycle time, determine the following: (a) speed of the conveyor, (b) center-to-center spacing between units on the line, (c) total length of the general assembly line, assuming no vacant space between stations, and (d) elapsed time a work unit spends in the general assembly department. Solution : (a) T t = T c = 0.95 min v c = 6.2 0.95 s t L T = = 6.52 m/min (b) s p = v c T c = 6.52(0.95) = 6.194 m/car (c) L = 500(6.194) = 3097 m (d) ET = c L v = 3097 6.52 = 475 min Alternative method: ET = n T t = 500(0.95) = 475 min 15.33 Total work content for a product assembled on a manual production line is 33.0 min. Production rate of the line must be 47 units/hr. Work units are attached to a moving conveyor whose speed = 7.5 ft/min. Repositioning time per worker is 6 sec, and uptime efficiency of the line is 94%. Due to imperfect line balancing, the number of workers needed on the line must be four more workers than the number required for perfect balance. Manning level = 1.6. Determine (a) the number of workers and (b) the number of workstations are on the line. (c) What is the balance efficiency for this line? (d) If the workstations are arranged in a line, and the length of each station is 11 ft, what is the tolerance time in each station? (e) What is the elapsed time a work unit spends on the line? Solution : (a) T c = 60 0 94 47 ( . ) = 1.2 min, T s = 1.2 - 0.1 = 1.1 min For perfect balance, E b = 1.0. w = Minimum Integer 330 10 11 . . ( . ) = 30 workers. With 4 more workers than required for perfect balance, w = 30 + 4 = 34 workers . 121
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Assembly Lines-3e-S 07-05/06, 06/04/07 (b) n = 34 1.7 w M = = 20 stations (c) d = 34 11 330 34 11 ( . ) . ( . ) - = 0.118 = 11.8% (d) T t = 11 7.5 = 1.467 min (e) ET = 20(1.467) = 29.33 min Alternative method: L = (20 stations)(11 ft/station) = 220 ft, ET = 220/7.5 = 29.33 min 15.34 A manual assembly line is to be designed for a certain major appliance whose assembly work content time = 2.0 hours. The line will be designed for an annual production rate of 150,000 units. The plant will operate one 10-hour shift per day, 250 days per year. A continuous conveyor system will be used and it will operate at a speed = 1.6 m/min. The line must be designed under the following assumptions: balance delay = 6.5%, uptime efficiency = 96%, repositioning time = 6 sec for each worker, and average manning level = 1.25. (a) How many workers will be required to operate the assembly line? If each station is 2.0 m long, (b) how long will the production line be, and (c) what is the elapsed time a work unit spends on the line?
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