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# Session 10s - WORK SYSTEMS 2021-2022

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```OPER10500A
Operations Management
Design of Work Systems
&copy; DEPARTMENT OF LOGISTICS AND OPERATIONS MANAGEMENT, 2021
Conceptual Map
Conceptual Map
Time Study: Calculating NT and ST
Observed time (OT)
Performance rating (PR)
Normal time (NT)
NT = OT x PR / 100
Allowance factor (AF)
(as % of task time)
Standard Time (ST)
ST = NT x (1 + AF)
Example
Casing Sausages
From Work Measurement to Capacity Management
Cycle time
Production rate of a
workstation
Bottleneck
Utilization rate of a
workstation
Utilization rate of a
worker
Sequential vs
parallel processes
Continuous
improvement
Production rate of a
process
Cycle Time
Interval of time between the exit of two consecutive units at a stage, or at the
end of a process
Standard Time
Cycle Time
=
# of resources assigned to
Production Rate of a Workstation
Number of units produced per unit of time, generally in hours
(if one expresses the cycle time in hours per unit, the rate per hour is equal reciprocal
of the cycle time: units per hour)
Rate
=
(units/hour)
60 minutes
Cycle Time
OR
(in minutes)
Example:
• Cycle time = 15 minutes or 0.25 hour
• Rate = 4 units/hour (60/15 or 1 / 0.25)
1 hour
Cycle Time
(in hours)
Sequential versus Parallel Processes
SEQUENTIAL PROCESS
PARALLEL PROCESS
Process where a work is divided in a
series of specialized tasks. Employees are
assigned to a specific part of the process
Process where each employee realizes all
tasks, independently for the others.
1
2
3
4
1
3
2
4
1
3
2
4
1
3
2
4
1
3
2
4
Bottleneck
Acting on the Bottleneck
Acting on the Bottleneck
Identifying the Bottleneck
Acting on the Bottleneck
Operation
1
2
3
4
5
Rate
(Units/hr)
15
10
18
9
12
Where is the bottleneck?
1
2
3
4
5
Production Rate of a Process
Number of units produced during one unit of
time (e.g. 1 hour) by the process.
CALCULATION
• Sequential process: The rate of the
process is equal to the rate of the
bottleneck
• Parallel process: The rate of the
process is equal to the sum of rates of
each working station (performing all the
tasks) of the process
Cette photo par Auteur inconnu est soumise &agrave; la licence CC BY-SA
Example
Production Rate of a Process
A process is composed by 5 activities
whose standard times are:
1) 17 min
2) 18 min
3) 15 min
4) 16 min
5) 17 min
Calculate the production rate of:
• a sequential process in which each of
the five employees specializes in
performing one of the five activities, and
• a parallel process in which each of the
five employees performs the process
from activity # 1 to # 5
Sequential process
Parallel process
22/05/09
16
Utilization Rate of a Workstation
Sequential process:
Production rate of the bottleneck
Utilization rate of the
=
workstations of a stage
Production rate at this stage
Utilization rate of the
=
workstations of a stage
Cycle time of the stage
Cycle time of the bottleneck
Bottleneck
Exercise
Sequential Process
B
A
C
B
D
C
B
S.T
2 min
S.T.
9 min
S.T.
5 min
Standard
Time
# of
workers
A
B
C
D
2
9
5
1
1
3
2
1
Production
Cycle Time
Rate
(un./hr)
2,0
30
3,0
20
2,5
24
1,0
60
S.T.
1 min
Utilization
rate
66,7%
100,0%
83,3%
33,3%
Exercise
What is the Production Rate of this Parallel Process?
A
C
A
B
D
C
A
B
D
• Total st = 2+9+5+1=17
• PR = 60/17 = 3,53 units/h
• PR = 3,53*7=24,7 units/h
C
A
B
D
C
A
B
D
C
A
B
D
C
A
B
D
C
B
D
Utilization Rate of a Worker
When part of an operation is done by a machine,
the utilization rate of a worker is the proportion of
time worked by the employee versus the total
standard time of the operation.
(Total standard time – Machine time)
Total standard time
Exemple
Exercise
What is the utilization rate of the employee?
• (49,48,05)/49,34
= 84%
Continuous Improvement
• Removing one bottleneck will create a new
one.
• It is not advantageous to push the nonbottleneck resources to produce at full
capacity.
• In order to improve the utilization rate of
resources, we must try to balance, as much
as possible, the capacity of each
workstation
Exercise
Increasing the Production Rate?
B
A
C
B
D
C
B
S.T
2 min
The capacity
of the line is
limited by
S.T.
9 min
S.T.
5 min
Standard
Time
# of
workers
Cycle Time
A
B
C
D
2
9
5
1
1
3
2
1
2,0
3,0
2,5
1,0
Production
Rate
(un./hr)
30
20
24
60
S.T.
1 min
Utilization
rate
66,7%
100,0%
83,3%
33,3%
Solution
Balancing
B
A
C
B
D
C
B
S.T
2 min
Capacity as
increased to
23 units/h
S.T.
9 min
S.T.
5 min
Standard
Time
# of
workers
A
B
C
D
2
9
5
1
1
3,5
2
0,5
Production
Cycle Time
Rate
(un./hr)
2,0
30
2,6
23
2,5
24
2,0
30
S.T.
1 min
Utilization
rate
76,7%
100,0%
95,8%
76,7%
Continuous Improvement
• Eliminating waste
• Reducing standard times
• Reducing set-up times
(Single Minute Exchange Die,
SMED)
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