COMSOAL Computer Method for Sequencing Operations for Assembly

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

Today’s Topics n Assembly Line Balancing u u By Hand « Overview « Example « Exercise By Computer « Using COMSOAL

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

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

Order of Precedence n 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 B, C 3 E Wrap Sandwich D 1 F Deliver Sandwich E 3

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

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

Cycle Time n Calculate the desired cycle time (Cd). u u If Joe’s Sub Shop has a demand of 100 sandwiches per day. The day shift lasts 8 hours. Cd = production time available desired units of output 8 hours x 60 minutes/hour 100 sandwiches Cd = 4. 8 minutes

Minimum Work Stations n Calculate theoretical minimum number of workstations (N). u If Cd = 4. 8 minutes j N= ti ti = completion time for task i Cd Cd = desired cycle time i =1 j = number of tasks

Minimum Work Stations n Calculate theoretical minimum number of workstations (N). u If Cd = 4. 8 minutes j N= ti i =1 N= 2+1+2+3+1+3 4. 8 Cd N = 2. 5 workstations 3 workstations

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

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

Line Efficiency n Evaluate the efficiency of the line (E). u If Ca = 4 minutes and n = 4 work stations. j E= ti i =1 E= 2+1+2+3+1+3 4*4 n. Ca E = 75. 0% effective

Trial and Error n Repeat until desired line efficiency is reached. Joe’s Sub Shop Workstation Task Element Time (min) Workstation Time (min) 1 A 2 4 C 2 B 1 D 3 E 1 F 3 2 3 E = 100. 0% effective 4 4

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

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

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

An Exercise n Calculate the desired cycle time (Cd). u If, there is a demand for 100 units to be produced every 12 hours. Cd = production time available desired units of output 12 hours x 60 minutes/hour Cd = 7. 2 minutes 100 units

An Exercise n Calculate theoretical minimum number of workstations (N). u If Cd = 7. 2 minutes j N= ti i =1 Cd ti = completion time for task i j = number of tasks Cd = desired cycle time

An Exercise n Calculate theoretical minimum number of workstations (N). u If Cd = 7. 2 minutes j N= ti i =1 N= 2+5+2+4+2 7. 2 Cd N = 2. 08 workstations 3 workstations

An Exercise n 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 ?

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

An Exercise n The most efficient set up of the line Workstation Task Element Time (min) Workstation Time (min) 1 A C B D E 3 2 5 4 2 5 2 3 E = 83. 3% effective 5 6

The Real World n A real world precedence chart Task Precedence Time (min) A — 3. 25 B A 4. 50 C — 12. 00 D B, C 1. 25 E D 5. 00 F A 0. 50 G C 1. 50 H D, F, G 25. 50 I H 3. 25 J I 6. 00 K A, G 1. 25

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

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

How it Works n The COMSOAL program proceeds in 6 steps as follows: u STEP 1: For each task, identify those tasks which immediately follow it in precedence order. u 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. u 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) u 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. u STEP 5: Randomly select from LIST C a task for assignment to the station. u 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? n n n Simplifies complex assembly line balancing problems Faster, easier, and more accurate than calculating by hand Saves time and money

References n n Russell, Roberta S. and Bernard W. Taylor III. Operations Management. 4 th ed. New Jersey: Prentice Hall, 2003. Graves, Robert, Dr. “Perspectives on Material Handling Practice. ” http: //www. mhia. org/bs/pdf/75021. pdf