com soal
TRANSCRIPT
COMSOALComputer Method for Sequencing Operations for Assembly Lines
Lindsay McClintockOPERMGT 345 – 004May 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 (Cd). 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 ShopTask Work Element Precedence Time (min)
A Receive Order — 2B Cut Bread A 1C Prepare Toppings A 2D Assemble Sandwich B,C 3E Wrap Sandwich D 1F Deliver Sandwich E 3
Specify the task relationships and their order of precedence.
The Precedence Diagram Draw and label a precedence diagram.
A2 min
B1 min
The Precedence Diagram Draw and label a precedence diagram.
A2 min
B1 min
C2 min
D3 min
E1 min
F3 min
Cycle Time Calculate the desired cycle time (Cd).
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
Cd =8 hours x 60 minutes/hour
100 sandwiches
Cd = 4.8 minutes
Minimum Work Stations Calculate the theoretical minimum number
of workstations (N). If Cd = 4.8 minutes
N = ti
Cd
j
i =1
ti = completion time for
task i
j = number of tasks
Cd = desired cycle time
Minimum Work Stations Calculate the theoretical minimum number
of workstations (N). If Cd = 4.8 minutes
N = ti
Cd
j
i =1 N =2 + 1 + 2 + 3 + 1 + 3
4.8
N = 2.5 workstations 3 workstations
Order Work Stations Group elements into workstations
recognizing cycle time & precedence.
Joe’s Sub Shop
Workstation Task Element Time (min)
Workstation Time (min)
1 A 2 3B 1
2 C 2 23 D 3 4
E 14 F 3 3
Line Efficiency Evaluate the efficiency of the line (E).
If Ca = 4 minutes and n = 4 work stations.
E = ti
nCa
j
i =1
ti = completion time for
task i
j = number of tasks
Ca = actual cycle time
n = actual number of workstations
Line Efficiency Evaluate the efficiency of the line (E).
If Ca = 4 minutes and n = 4 work stations.
E = ti
nCa
j
i =1 E =2 + 1 + 2 + 3 + 1 + 3
4 * 4
E = 75.0% effective
Trial and Error Repeat until desired line efficiency is reached.
Joe’s Sub ShopWorkstation Task Element Time
(min)Workstation Time (min)
1 A 2 4C 2
2 B 1 4D 3
3 E 1 4F 3
E = 100.0% effective
An Exercise
Task Precedence Time (min)
A — 3
B A 5
C — 2
D B,C 4
E D 2
A sample precedence chart
An Exercise Draw and label a precedence diagram.
A3 min
B5 min
An Exercise Draw and label a precedence diagram.
A3 min
B5 min
C2 min
D4 min
E2 min
Calculate the desired cycle time (Cd). If, there is a demand for 100 units to be
produced every 12 hours.
An Exercise
Cd =production time available
desired units of output
Cd =12 hours x 60 minutes/hour
100 units
Cd = 7.2 minutes
An Exercise Calculate the theoretical minimum number
of workstations (N). If Cd = 7.2 minutes
N = ti
Cd
j
i =1
ti = completion time for
task i
j = number of tasks
Cd = desired cycle time
An Exercise Calculate the theoretical minimum number
of workstations (N). If Cd = 7.2 minutes
N = ti
Cd
j
i =1N =
2 + 5 + 2 + 4 + 27.2
N = 2.08 workstations 3 workstations
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 ?
An Exercise Evaluate the efficiency of the line (E).
E = ti
nCa
j
i =1
ti = completion time for
task i
j = number of tasks
Ca = actual cycle time
n = actual number of workstations
An Exercise The most efficient set up of the line
Workstation Task Element Time (min)
Workstation Time (min)
1 A 3 5C 2
2 B 5 53 D 4 6
E 2
E = 83.3% effective
The Real World
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
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. 4th ed. New Jersey: Prentice Hall, 2003.
Graves, Robert, Dr. “Perspectives on Material Handling Practice.” http://www.mhia.org/bs/pdf/75021.pdf