Assembly Line Balancing
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Assembly-line balancing involves assigning tasks along an assembly line to workstations to minimize idle time and balance the workload. An unbalanced line can lead to wasted time and lower productivity, while a balanced line promotes efficient one-piece flow and minimizes waste. To balance a line, tasks are analyzed and assigned to workstations based on precedence and timing, with the goal of achieving a balanced workload across stations. This process can increase efficiency, productivity, and profits for an organization.
Assembly Line Balancing
- 1. Assembly-Line Balancing: An effective tool for improving Productivity 1. What is assembly-line balancing? to a workstation within an assembly line in order to meet the required production rate and to achieve a minimum amount of idle time. Line balancing is the procedure in which tasks along Assigning each task the assembly line are assigned to work station so each has approximately same amount of work. 2. Unbalance Line and Its effect High work load in some stages (Overburden) Maximizes wastes (over-processing, inventory, waiting, rework, transportation, motion) High variation in output Restrict one piece flow Maximizes Idle time Poor efficiency 3.Balanced Line and its effect Promotes one piece flow Avoids excessive work load in some stages (overburden) Minimizes wastes (over-processing, inventory, waiting, rework, transportation, motion) Reduces variation Increased Efficiency Minimizes Idle time
- 2. 4. How Can Assembly-Line Balancing Help Organization ? Increased efficiency Increased productivity Potential increase in profits and decrease in costs 5. Steps in Balancing an Assembly Line 1. List the sequential relationships among tasks and then draw a precedence diagram. 2. Calculate the required workstation cycle time. 3. Calculate the theoretical minimum number of workstations. 4. Choose a primary rule that will determine how tasks are to be assigned to workstations. 5. Beginning with the first workstation, assign each task, one at a time, until the sum of the task times is equal to the workstation cycle time or until no other tasks can be assigned due to sequence or time restrictions. 6. Repeat step 5 for the remaining workstations until all the tasks have been assigned to a workstation. 7. Evaluate the efficiency of the line balance. 8. Rebalance if necessary. Example of Assembly-Line Balancing Problem: The Model Z Bicycle is assembled in an assembly line. Four hundred and twenty bicycles are required each day. Production time per day is 420 minutes. Find the balance that minimizes the number of workstations, that stays within the workstation cycle time limitation, and that complies with task precedent constraints.
- 3. Example of Assembly-Line Balancing Cont. 1. Building the Model Z Bicycle: Assembly Steps and Times Task Task Time Task Description Tasks that must (in seconds) precede A 50 Connect the front tire to the bicycle — frame. B 16 Insert the handle bar. A C 14 Tighten handle bar with two screws B and nuts. D 55 Connect the rear tire to the bicycle — frame. E 20 Position chain mechanism to the D frame. F 17 Attach right hand brake to handle bar. C G 17 Attach left hand brake to handle bar. C H 17 Attach right side pedal. E I 17 Attach left side pedal. E J 13 Position chain onto chain mechanism. F,G,H,I K 14 Attach seat post. J 250
- 4. STEP 1. List the sequential relationships among tasks and then draw a precedence diagram 50 sec. 16sec. 14 sec 17 sec. A B C F s e 17 sec. c. 13 sec. 14 sec. 17 sec. G 55 sec. 20 sec. K J H s D E e 17 sec. c. I STEP 2. . Calculate the required workstation cycle time Convert minutes to seconds because task times are in seconds. CYCLE TIME = (PRODUCTION TIME PER DAY) /(OUTPUT PER DAY) = (60 sec. X 420 min.) / ( 420 bicycles) = 25,200 / 420 = 60 sec. STEP 3. Calculate the theoretical minimum number of workstations. NUMBER OF WORK STATIONS = ( SUM OF TOTAL TASK TIMES) / (CYCLE TIME) = 250sec’s / 60 sec’s = 3.97 = 4 (rounded)
- 5. Number of Following STEP 4.Choose a primary rule that will Task Tasks determine how tasks are to be assigned to workstations A 6 For this example, our primary rule is to prioritize tasks based on the largest B or D 5 number of following tasks. If there is a tie, our secondary rule C or E 4 is to prioritize tasks in the order of the longest task time. F, G, H, or I 2 In general, select rules that prioritize tasks according to the largest J 1 number of followers or based on length of time. K 0 STEP 5. Beginning with the first workstation, assign each task, one at a time, until the sum of the task times is equal to the workstation cycle time or until no other tasks can be assigned due to sequence or time restrictions. STEP 6. Repeat step 5 for the remaining workstations until all the tasks have been assigned to a workstation STEP 7.Evaluate the efficiency of the line balance. EFFICIENCY = (SUM OF ALL TASK TIMES))/(ACTUAL NO OF WORKSTATIONS)X(CYCLE TIME) = (250) / (5) X (60) = 0.83 OR 83 %
- 6. STEPS 5& 6. Balance made according to the Largest-Number-of-Following Tasks Rule. Stations Task Task Time Number of Remaining Feasible Task with Task with (in seconds) Following Unassigned Remaining Most Longest Tasks Time Tasks Followers Operating Time Station 1 A 50 6 10 idle None Station 2 D 55 5 5 idle None Station 3 B 16 5 44 C, E C, E E E 20 4 24 C, F,G, H, I,J C C 14 4 10 idle None Station 4 F 17 2 43 G, H, I G, H, I G, H, or I G 17 2 26 H, I, J H, I H or I H 17 2 9 idle None Station 5 I 17 2 43 J J 13 1 30 K K 14 0 16 idle None