Flow Time Analysis
(Ch 4 of MBPF)
And a cautionary tale
Flow Time Analysis
Inputs
Processing
System
Outputs
T Flow time = processing time + wait time (total time in the box)
Theoretical Flow Time is the time to process a typical
flow unit assuming NO waiting.
Flow Time Analysis
• Total amount of time for a flow unit to flow
from the entry to exit point of a process
– Includes delays and work
– Includes value added and NVA activities
• Shortening flow time often “good”
–
–
–
–
–
–
Decrease response time (Dell computer)
Reduce inventory (less $ tied up in WIP)
New product/service development (auto)
Robust to short product life cycles
Fast feedback on quality problems
An indicator of overall process excellence
Process Flow Charting
• Flow charts are graphical representations of
processes
• May capture inputs, outputs, activity network,
resources used, locations visited, decisions
or business logic, buffers and delays
• Many tools available, we’ll use iGrafx Process
as it is bundled with our MBPF text
– Very good flow charting engine
– Numerous templates for various kinds of common
business diagrams
– Also has a relatively easy to use and pretty
powerful process simulation capability. We will use
this.
To learn iGrafx Process, start by doing the Tutorial on “Creating Process
or Swimlane Diagram” which you can find in the iGrafx Tutorials menu
or iGrafx Help menu. This tutorial does NOT cover the simulation
features of iGrafx but instead just gets you started building process
diagrams. We’ll learn the simulation features as we move along in the
semester.
Process Flow Charts
Using PowerPoint or iGrafx Process
Activities/Subprocesses
Decision
Start/End
Events
Wait/
Buffer
Use AutoShape - Flowchart
Activity Precedence Use connection tool
Old Medical Transcription Process
Start Exam
Wait
Transcribe
into word
processor
•Diagnosis
•Plan of care
Print
Report
Physician dictates
into tape recorder
Wait
Physician
reviews
report
yes
End Process
Send report to
medical
records dept.
no
Changes?
Subprocesses and Cascading
Process Flow Charting in Practice
• Multi-disciplinary team
• Have each team member do own flow chart
– Why?
• Group facilitator or group tries to reach consensus on process
flow chart
– Yellow sticky notes
– Examine and revise by group
– Examine parts
• Don’t get buried in details
• Genuine disagreement may occur
• More flow charting resources
– A Fresh Look at Flow Charting
• http://www.q-skills.com/flowchrt.html
– Flow Charting Help Page
• http://home.att.net/~dexter.a.hansen/flowchart/flowchart.htm#Definition
– Flow Chart Overview
• http://deming.eng.clemson.edu/pub/tutorials/qctools/flowm.htm
Other Process Description Tools
• Swim lanes or Service System Maps
– Enhanced flow charting technique using
bands to delineate department participation
in process steps
– Variants can use color or other features to
represent more process information
– iGrafx Processes are of this type
• Process Activity Charts
– See next slide and Excel file
ProcessActivityChart.xls
Process Activity Chart
Page: ___ of ___
Process:
Date:
Developed By:
Current Process
Proposed Process
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Description
Time
Value Code
(V/N/C)
Example: X-ray
Symbol
Finding Theoretical Flow Time
Sequential Process
T
Start
1


T
1

T
2

T
3
2
Theoretical Flow Time

T  T1  T2  T3
3
Finish
Finding Theoretical Flow Time
Sequential & Parallel
Path 1: 1-3-5-7-8 (T1=80)
3
(20)
Start
7
(10)
1
(10)
2
(25)

5
(10)
4
(5)
T  max(T , T )  90
1
2
8
(30)
Finish
6
(10)
Path 2: 1-2-4-6-7-8 (T2=90)
T* is the length of longest path through the process
The path associated with T* is called the Critical Path
Activities on the Critical Path are called Critical Activities
Finding the Critical Path
• If process is “simple”, we can
– enumerate all the possible paths
– Calculate their length
– Find the longest path
• If process is complex, may be too many paths
to enumerate
– Various algorithms exist for this
– See Appendix of Chapter 4 in MBPF for Critical
Path Method
– Same method as used to find critical path in
project management networks (e.g. MS Project)
Observations about Critical Path
• Delaying an activity on CP will increase T*
• Activities NOT on CP can be delayed to some
degree without increasing T*
• Speeding up activities on the CP will
decrease T*
• Speeding up activities NOT on the CP will
NOT decrease T*
• The CP can change as we change the activity
times
• We are still assuming the activity times are
known deterministic quantities (no
randomness)
Flow Time Measurement
The Direct Method
• Observe the process over some specified,
extended period of time
• Take random (or exhaustive) sample of flow
units
• Calculate flow time, T, for each by
(tend – tstart)
• Calculate average T over sampled flow units
• Example: CalcFlowTime.xls
Flow Time Measurement
The Indirect Method
• Observe the process over some specified,
extended period of time, t
• Measure number of flow units, N, processed
over the time period, t
• Compute throughput, R=N/t
• At random points in time, count the number of
flow units in process. Compute the average of
these counts (we’ll call it I)
• Use Little’s Law to estimate T=I/R
Let’s revisit CalcFlowTime.xls
Actual Flow Time vs. Theoretical Flow Time
•
•
•
•
•
Most processes have numerous delays
Estimate avg. delay times and treat as activities
Value added vs Non-value added activities
See Example 4.7 (p86) for X-ray process example
Problem 4.1 in MBPF
1
(10)
Start
Start
1
(10)
Wait
(10)
2
(25)
2
(25)
3
(20)
Wait
(5)
T* = 55
Finish
3
(20)
Finish
TA = 70
Flow Time Efficiency = T*/TA = 55/70 = .786
Many real processes have very low Flow Time Efficiency
Levers for Managing Theoretical
Flow Time
•
•
We are ignoring waiting/delays for now
Three broad methods for reducing T*
1. Eliminate: Reduce work content of a
critical activity
2. Work in parallel: Move some work
content off of the critical path
3. Select: Modify the product mix
Eliminate
• Roots in scientific management and industrial
engineering
• Some combination of
– Eliminate NVAs (“work smarter”)
• Classic BPR example: Ford Accounts Payable
– Reduce # repetitions of task (“less rework”)
•
•
•
•
Build quality into process (poke-yoke)
Statistical process control
Design for manufacturability
Workforce training
– Increase speed (“work faster”)
• Incentives
• Better technology
• More resources
Work in Parallel
• Move work off CP to non-critical activity
• Move work off CP to “outer loop”
– Pre or post processing
– Examples: pre-authorization, pre-admission
testing, pre-registration
• Usually requires process redesign
• Often some enabling communications
technology required to facilitate parallel work
– Example: concurrent engineering facilitated by
CAD and high bandwidth networks allowing
transfer/sharing of large electronic files
Reengineering/Redesign
The fundamental rethinking and radical redesign of
business processes to achieve dramatic improvements
in critical contemporary measures of performance such
as cost, quality, service and speed.
Reengineering the Corporation, Hammer and Champy,
Harper Business (1993)
Process Reengineering
A 1st Look
• Radical
rethinking/redesign of
processes
• Clean sheet of paper
• Benchmark best practices
• Commitment from top
leadership
• Question unconscious
assumptions
• Value added vs. Nonvalue added activities
• Why redesign business
processes?
• How to go about
redesign?
• What is role of
information technology?
• Relationship to
continuous improvement,
total quality
management?
• Isn’t reengineering just
another word for layoffs
and downsizing?
BPR Life Cycle
• Process Analysis
• Idea Generation
– Establish a goal and Define Scope
– Generate Strategies
– Evaluate and Select
• Design and Implement
• Sustain
Why Redesign?
•
•
•
•
•
•
Current process “broken” (or may not exist)
No one seeing big picture
No one questioning business assumptions
Incremental improvement efforts insufficient
Go beyond perspective of “how we do things”
Processes critical to business success
Classic Reengineering
Principles
• Organize around outcomes, not tasks
• Have output users “do” the process
• Treat geographically dispersed resources as
though they were local
• Link parallel activities instead of integrating
results
• Put decision point where work performed and
build control into the process
• Capture information once, and at the source
“Reengineering Work: Don’t Automate, Obliterate”, Hammer and Champy,
Harvard Business Review (July-Aug 1990)
IHI: Redesign the System (p42-53)
•
•
•
•
•
•
•
•
•
•
•
Do tasks in parallel – info gather during waits
Use multiple processes – ED fast track
Minimize handoffs – reduce unit transfers
Synchronize – surgery starts at incision
Use pull systems – pull asthma from ED to clinic
Move steps closer together – registering ED patients in
treatment area
Use automation - PACS
Consider people to be the same system – self-scheduling
of surgery by surgeon office
Use multiple processing units – increase staffing
Extend the time of specialists – nurse aide
Convert internal steps to external – outsource
transcription
The 5-step BPR Framework
• Develop the Business Vision and
Process Objectives
• Identify the Processes to be
Redesigned
• Understand and Measure the Existing
Process
• Identify IT Levers
• Design and Build a Prototype of the
New Process
“The New Industrial Engineering: Information Technology and Business
Process Redesign”, Davenport and Short, Sloan Management Review
(Summer 1990)
The Fad That Forgot People
Reengineering didn’t start out as a code word
for mindless bloodshed. It wasn’t supposed to
be the last gasp of Industrial Age management. I
know because I was there from the beginning. I
was one of the ‘creators’.
The Fad That Forgot People, Davenport, T.H., Fast
Company, November 1995.
The Fad That Forgot People, Davenport, T.H., Fast Company, November 1995.
BPR – What Happened?
• Started as real people with real problems
– Ford Motor Co., Mutual Benefit Life, HP
• Synthesis of 3 concepts
– Technology
– Business processes
– Clean-sheet-of-paper approach
• Companies did stuff, academics and
consultants started to “model make”
• Davenport, Hammer and Champy wrote “bible”
articles and books
The Fad That Forgot People, Davenport, T.H., Fast Company, November 1995.
The Feeding Frenzy
• Top managers + big-time consultants+IT vendors = $$$
• Early successes were trumpeted
– Projects labeled “BPR”
– People always looking for “magic solution”
• Consultants started packaging BPR services
– Big $$$ contracts
– Executives needed to justify $$$ spent
– Layoffs quickest way to realize savings
• IT firms selling hardware, software AND
reengineering consulting
The Fad That Forgot People, Davenport, T.H., Fast Company, November 1995.
Reality Bites
• Massive layoffs labeled “reengineering”
• Alienation of good employees
– Treated as interchangeable cogs in corp. machine
– 25 yr old MBA’s making $80K as BPR “experts”
• Major project failures
• Consultants start repositioning for next wave
• And sell BPR to “rest of the world”
The Fad That Forgot People, Davenport, T.H., Fast Company, November 1995.
The Good Stuff
• Focus on business processes
• IT only useful if it helps people do work
• A Lesson: The bigger the hype, the greater
the chances of failure.
• Techniques and tools of BPR can still be
useful
The Fad That Forgot People, Davenport, T.H., Fast Company, November 1995.
The Next Big Thing
• Remember the lessons of BPR
• Don’t drop all your current approaches for the
“handsome newcomer”
• Don’t listen to most charismatic advocates,
listen to most reasoned advocates
• Talk softly
• Carry big ruler to measure real results
Defining Characteristics?
•
•
•
•
•
•
•
•
Statistical process control
Total quality management
Business process reengineering
Theory of constraints
Lean production methods
6-Sigma
Lean/6-Sigma
Operations research & management science
Process Capacity
• Recall flow basics
– R=flow rate
– T=flow time
– O=occupancy
O = RT (Little’s Law)
• Process capacity = Maximum sustainable
flow rate of a process
• A resource pool is a set of
interchangeable resources
How capacity gets used
Idle
Time
Busy
Unavailable
Find the bottleneck
T1=6 mins
C1 = 2 units
R1 = 2 / 6 = 0.333 pats/min =
20 pats/hr
Bottleneck is first activity.
T2=2 mins
C2 = 1 units
R2 = 1 / 2 = 0.5 patients/min = 30
pats/hr
Finding the Bottleneck Not Easy
• Complex business processes make finding
bottlenecks far from easy
• Process improvements can “shift the
bottleneck”
• GM and the C-More story
Problem 3.4 ER Flow Chart
• Read Problem 3.4 on p69
• This is first problem on HW3
• Let’s draw the flow chart in iGrafx Process