Computer Method for. Assembly Lines. Lindsay McClintock OPERMGT May 6, 2003

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1 COMSOAL Computer Method for Sequencing Operations for Assembly Lines Lindsay McClintock OPERMGT May 6, 2003

2 Today s Topics Assembly Line Balancing By Hand Overview Example Exercise By Computer Using COMSOAL

3 Assembly Line Balancing The process of equalizing the amount of work at each work station on an assembly line.

4 How to Balance a Line Specify the task relationships and their order of precedence. Draw and label a precedence diagram. Calculate the desired cycle time (C d ). Calculate the theoretical minimum number of workstations (N). Group elements into workstations recognizing cycle time & precedence. Evaluate the efficiency of the line (E). Repeat until desired line efficiency is reached.

5 Od Order of Precedence Specify the task relationships and their order of precedence. Joe s Sub Shop Task Work Element Precedence Time (min) A Receive Order 2 B Cut Bread A 1 C Prepare Toppings A 2 D Assemble Sandwich BC B,C 3 E Wrap Sandwich D 1 F Deliver Sandwich E 3

6 The Precedence Diagram Draw and label a precedence diagram. B 1 min A 2 min

7 The Precedence Diagram Draw and label a precedence diagram. B 1 min A 2 min C 2 min D E F 3 min 1 min 3 min

8 Cycle Time Calculate the desired cycle time (C d ). If Joe s Sub Shop has a demand d of 100 sandwiches per day. The day shift lasts 8 hours. C d = C d = production time available desired units of output 8 hours x 60 minutes/hour 100 sandwiches C d = 4.8 minutes

9 Minimum Work Stations Calculate the theoretical minimum number of workstations (N). If C d = 4.8 minutes N = j Σ t i i =1 C d t i = completion time for task i j = number of tasks C d = desired cycle time

10 Minimum Work Stations Calculate the theoretical minimum number of workstations (N). If C d = 4.8 minutes j N = Σ t i i =1 N = C d N = 2 5 workstations N 2.5 workstations 3 workstations

11 Order Work Stations Group elements into workstations recognizing cycle time & precedence. Workstation ti Task Joe s Sub Shop Element Time (min) Workstation Time (min) 1 A 2 3 B 1 2 C D 3 4 E 1 4 F 3 3

12 Line Efficiency Evaluate the efficiency of the line (E). If C a = 4 minutes and n = 4 work stations. E = j Σ t i i =1 nc a t i = completion time for task i j = number of tasks C a = actual cycle time n = actual number of workstations

13 Line Efficiency Evaluate the efficiency of the line (E). If C a = 4 minutes and n = 4 work stations. j E = Σ t i i =1 E = * 4 nc a E = 75.0% effective

14 Trial and Error Repeat until desired line efficiency is reached. Workstation Joe s Sub Shop Task Element Time (min) Workstation Time (min) 1 A 2 4 C 2 2 B 1 4 D 3 3 E 1 4 F 3 E = 100.0% effective

15 An Exercise A sample precedence chart Task Precedence Time (min) A 3 B A 5 C 2 D B,C 4 E D 2

16 An Exercise Draw and label a precedence diagram. A 3 min B 5 min

17 An Exercise Draw and label a precedence diagram. A 3 min B 5 min C 2 min D 4 min E 2 min

18 An Exercise Calculate the desired cycle time (C d ). If, there is a demand d for 100 units to be produced every 12 hours. C d = C d = production time available desired units of output 12 hours x 60 minutes/hour 100 units C d = 7.2 minutes

19 An Exercise Calculate the theoretical minimum number of workstations (N). If C d = 7.2 minutes N = j Σ t i i =1 C d t i = completion time for task i j = number of tasks C d = desired cycle time

20 An Exercise Calculate the theoretical minimum number of workstations (N). If C d = 7.2 minutes N = j Σ t i i =1 N = C d N = 2 08 workstations N 2.08 workstations 3 workstations

21 An Exercise Group elements into workstations recognizing cycle time & precedence. Workstation Task Element Time (min) Workstation Time (min)? A 3?? B 5?? C 2?? D 4?? E 2?

22 An Exercise Evaluate the efficiency of the line (E). E = j Σ t i i =1 nc a t i = completion time for task i j = number of tasks C a = actual cycle time n = actual number of workstations

23 An Exercise The most efficient set up of the line Workstation Task Element Time (min) Workstation Time (min) 1 A 3 5 C 2 2 B D 4 6 E 2 E = 83.3% effective

24 The Real World A real world precedence chart Task Precedence Time e( (min) A 3.25 B A 4.50 C D B,C 1.25 E D 5.00 F A 0.50 G C 1.50 H D,F,G I H 3.25 J I 6.00 K A,G 1.25

25 COMSOAL Computer Method for Sequencing Operations for Assembly Lines Developed by IBM Fast and Easy

26 How it Works 5 Common Heuristics Used Ranked positional weight Longest operation time (LOT) Shortest operation time (SHOT) Most number of following tasks Least number of following tasks

27 How it Works The COMSOAL program proceeds in 6 steps as follows: STEP 1: 1 For each task, identify those tasks which immediately follow it in precedence pecede ceode order. STEP 2: Place in LIST A for each task in the assembly, the total number of tasks which immediately precede it in the precedence diagram. STEP 3: From LIST A, create LIST B composed of the tasks which have zero predecessors. If no task remain unassigned to stations, then stop.

28 How it Works (con t) STEP 4: From LIST B, create LIST C composed of the tasks whose performance times are no greater than the available time at the station. If LIST C is empty, open a new station with the full cycle time available and go through h STEP 4 again. STEP 5: Randomly select from LIST C a task for assignment to the station. STEP 6: Update the time available at the station and LIST B to reflect the time consumed and the completed predecessors at this stage. If LIST B is empty update LIST A and return to STEP 3 otherwise return to STEP 4.

29 Why COMSOAL? Simplifies complex assembly line balancing a problems Faster, easier, and more accurate than calculating by hand Saves time and money

30 References Russell, Roberta S. and Bernard W. Taylor III. Operations Management. 4 th ed. New Jersey: Prentice Hall, Graves, Robert, Dr. Perspectives on Material Handling Practice.

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