COMSOAL Computer Method for Sequencing Operations for Assembly Lines Lindsay McClintock OPERMGT 345 – 004 May 6, 2003

Today’s Topics Assembly Line Balancing  By Hand  Overview  Example  Exercise  By Computer  Using COMSOAL

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

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.

Order of Precedence Joe’s Sub Shop Task Work ElementPrecedenceTime (min) A Receive Order —2 B Cut Bread A1 C Prepare Toppings A2 D Assemble Sandwich B,C3 E Wrap Sandwich D1 F Deliver Sandwich E3 Specify the task relationships and their order of precedence.

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

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

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

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

Minimum Work Stations Calculate the theoretical minimum number of workstations (N).  If C d = 4.8 minutes N =  ti ti CdCd j i =1 N = N = 2.5 workstations  3 workstations

Order Work Stations Group elements into workstations recognizing cycle time & precedence. Joe’s Sub Shop WorkstationTask Element Time (min) Workstation Time (min) 1A23 B1 2C22 3D34 E1 4F33

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

Line Efficiency Evaluate the efficiency of the line (E).  If C a = 4 minutes and n = 4 work stations. E =  ti ti nCanCa j i =1 E = * 4 E = 75.0% effective

Trial and Error Repeat until desired line efficiency is reached. Joe’s Sub Shop WorkstationTask Element Time (min) Workstation Time (min) 1A24 C2 2B14 D3 3E14 F3 E = 100.0% effective

An Exercise TaskPrecedenceTime (min) A—3 BA5 C—2 DB,C4 ED2 A sample precedence chart

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

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

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

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

An Exercise Calculate the theoretical minimum number of workstations (N).  If C d = 7.2 minutes N =  ti ti CdCd j i =1 N = N = 2.08 workstations  3 workstations

An Exercise Group elements into workstations recognizing cycle time & precedence. WorkstationTask Element Time (min) Workstation Time (min) ?A3? ?B5? ?C2? ?D4? ?E2?

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

An Exercise The most efficient set up of the line WorkstationTask Element Time (min) Workstation Time (min) 1A35 C2 2B55 3D46 E2 E = 83.3% effective

The Real World TaskPrecedenceTime (min) A—3.25 BA4.50 C—12.00 DB,C1.25 ED5.00 FA0.50 GC1.50 HD,F,G25.50 IH3.25 JI6.00 KA,G1.25 A real world precedence chart

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

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

How it Works The COMSOAL program proceeds in 6 steps as follows:  STEP 1: For each task, identify those tasks which immediately follow it in precedence 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.

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 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.

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

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.”