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Product Layout All products go through one sequence of operations. Assembly line production is a good example. Line Balancing: Purpose is to balance a line , which means equal time at each station. Each station may have more than one operation. Sometimes we may not be able to balance a line perfectly because: (i) operation times are fixed (can not be sub divided) (ii) precedence relationships ------ drill before tap (iii) people/equipment factor ------ not at same rate

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Example: Toy Factory; Assemble Model K23675 Wagon Task # Description Time(Minutes) Task that must preceed 1. Position rear axle support and hand fasten four screws to nuts 0.75 * 2. Insert rear axle 0.18 1 3. Tighten rear axle support screws to nuts 0.15 1,2 4. and hand fasten four screws to nuts. 0.83 * 5. Tighten front axle assembly screws 0.25 4 6. Position rear wheel(#1) and fasten hub cap 0.20 1,2,3 7. Position rear wheel (#2) and fasten hub cap 0.20 1,2,3 8. Position front wheel (#1) and fasten hub cap 0.20 4,5 9. Position front wheel (#2) and fasten hub cap 0.20 4,5 10. Position handle shaft on front axle 0.13 1,2,3,. ......... 8,9 11. Tighten bolt and nut 0.15 10
1 2 3 4 5 6 7 8 9 10 11 0.75 0.18 0.15 0.20 0.20 0.20 0.20 0.13 0.15 0.83 0.25 N Total Cycle Time = T = 3 t i = t 1 + t 2 + . ... t 13 i =1 = 0.75 + 0.18 + . ... + 0.15 = 3.24 minutes Assume one shift operation = 8 hours = (60)(8) = 480 minutes Time allowed for breaks = 60 minutes Total productive time = P = 420 minutes/day Let us assume, we need to produce 500 wagons per day. Demand per day = D =500 Cycle time = C = P Demand = 420 500 = 0.84 minutes For a cycle time of C, minimum number of work station, N, is N = T Cycle Time = 3.24 0.84 = 3.86 need 4

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For a minimum number of 4 work stations, how to group the eleven different operation at each station? This grouping must satisfy the precedence relationship and total time at each station cannot exceed 0.84 minutes. Kilbridge and Webster’s Heuristic 1. Rank order operations according to number of predecessors. 2. Operations with least number of predecessors are assigned first. 3. In case of a tie, choose operation with longest operation time. 4. Total time at each work station should not exceed cycle time. 5. Precedence relationships must be satisfied. *************************************************************** Develop rank order for all operations Rank Operation No of Predecessors Time (ti) 1 1 0 0.75 2 4 0 0.83 3 2 1 0.18 4 5 1 0.25 5 3 2 0.15 6 8 2 0.20 7 9 2 0.20 8 6 3 0.20 9 7 3 0.20 10 10 9 0.13 11 11 10 0.15
Assignment of Operations To Work Stations 1. Work Station # 1 Choose operation # 4 ----- it has longest time Unassigned Time = 0.84 - 0.83 = 0.01 Time for remaining operations is greater than 0.01 2. Workstation # 2 Assign operation # 1 (least predecessors = none) Unassigned time = 0.84 - 0.75 = 0.09 Time for remaining operations is greater than 0.09

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