anupindi_mbpf3_ism_ch04
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School
Arizona State University *
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309
Subject
Industrial Engineering
Date
Dec 6, 2023
Type
docx
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4
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CHAPTER 4: FLOW TIME ANALYSIS
4.1 Objective
Chapter 3 introduced the three basic building blocks of process flow namely the (average) flow time,
(average) flow rate and (average) inventory.
It is followed by a sequence of three chapters, 4, 5 and 6,
which examine each one of these measures individually. Chapter 4 is concerned with flow time analysis.
The major point we wish to drive here is that flow time can be fruitfully divided into two components
namely waiting time and activity time (theoretical flow time).
The chapter analyses the theoretical time
in detail, postponing the analysis of waiting time to chapters 7 and 8.
4.2 Additional Suggested Readings
We assign Pizza Pazza (Kellogg case) as the major case for this module. (The Kristen Cookie Company,
(HBR case #9-686-093) is a fine alternative; see problem 2 at end of chapter). The case is simple and
accessible to most students, yet allows a rich discussion of the various factors that affect flow time such
as batch size, oven size and type, etc.
The discussion on theoretical flow time is based on the network flow framework of project management.
In class we often introduce the issue of parallel paths using the MBPF, Inc. example of building garages,
(see problem 3).
The example is small enough that the notion of critical path can be conveyed without
going through the formal path computations.
4.3 Solutions to the Problem Set
Solutions to Chapter 4:
4.1
a.
The first step is to find the average flow time for “time with judge” and “pay fine”.
This
can be done by averaging the ten observations given in the table.
These amount to 1.55minutes
and 2.4 minutes respectively.
Thus the theoretical flow time is 1.55 + 2.4 = 3.95 minutes.
b.
The theoretical flow time of the process can be estimated by taking the average of the
total time each defendant spent in the system.
This comes out to 120 minutes.
c.
The flow time efficiency is 3.95/120 = 3.3%
4.2
a.
The flow time of the two paths:
Path 1 (roof) : =
20+
45 +45 +25+ 40 =
175 minutes
Path 2 (base):
=
20+35+10 +30+25+ 40= 160
minutes
The critical path is path 1, and the flow time is 175 minutes.
b.
Activity 2 is not on the critical path
c.
The lead time will be reduced to 170 minutes.
4.3.
a.
b.
The critical path involves the food preparation.
The flow time is
4+18 + 12 = 34 minutes
c.
Cart preparation is not on the critical path
d.
The critical path will be reduced to 4+18 +10 = 32 minutes
The flow
time is 34 + 4 = 38 minutes
Prepare Food
18 Minutes
Prepare Cart
10 Minutes
Prepare Wine
Take Order
4 Minutes
Deliv
er
12
Minutes
Return and Debit
4 Minutes
4.4
a.
b.
The flow time is 50 minutes.
The critical path is the one of F1 (process and separate,
Activity A, Activity B, Loan Officer).
c.
Since activity A is on the critical path, the flow time will increase by 50%* 15 = 7.5
minutes, to 57.5 minutes.
4.5
F1
F2
Process
And
Separate
Activity
C
Loan
Officer
Activity
B
Activity
A
10
min
15
min
20
min
15
min
10
min
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a.
b.
The critical path is the one through the X-ray scanner.
The flow time is 30 + 40*1.5 + 60 = 150 seconds.
c.
The flow time efficiency is 150/530 = 28%
d.
The personal scanner is not on the critical path.
X –ray scanner
40 Seconds x 1.5 trays =
60 seconds
Personal scanner
30 Seconds
Prepare & place on
belt
30 Seconds
Retrieve &
reorganized
60 Seconds