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6 Design for Six Sigma (DfSS)
The introduction lecture on this subject has been presented by Leszek
Biskup-Köstner from Siemens. Leszek defined Design for Six Sigma as a
method to design a new process/product (or redesign a fundamentally non-
competitive process) to satisfy customer requirements.
The need to apply the Six Sigma approach more upstream than in
production is well-known to come up after clearing up the mud. This is
well-illustrated with the tree in Fig. 6.1. The phrase low-hanging fruit has
been quite often used at the first conference during warning discussions
about making the proper choice of BB-projects.
Fig. 6.1 Famous tree to illustrate the classes of projects to attack
After solving and root-analysing the “ground-fruit” and “low-hanging fruit”
problems, the insight takes place that more than 60% of the roots of the
problems can be found in the development phase. At Philips we learned that
also from our experience with IOA (Industrial Opportunity Assessments). Fig.
6.2 is based on data from about 200 audits internal at Philips .
Fig. 6.2 Root causes of major changes in production
The most impressive picture presented by Leszek was Fig. 6.3, because it
illustrates very well the use of Sigma level at the lowest possible level of
“steps”, i.e. parts and process-steps. By accepting a too low sigma level at
these details you fall into the old pitfalls.
Design - Simulation
I.e. design Scorecards
Standard Spec Limits Step
Definition USL LSL Sigma
Fig. 6.3 Design Scorecard, showing the deeply deployed Sigma level
as key quality parameter
In analogy with the DMAIC phases in Six Sigma for manufacturing the
following five steps for Design for Six Sigma are defined (shown in Fig
Fig. 6.4 Overview of the structured five-step approach
of Design for Six Sigma
Table 6.1 Activities to be done & entities to be taken care of
1. Define 1
• Business goals
• Project goals
• Risk Analysis
• Influence of Customers and Processes
• Goals and scope
• Customer requirements (high level)
• Technical requirements
• High level plan
1.3 Project plan
• Project requirements
• Time line
So, write down why you are doing the project and how you split it up do be
able to do your project management properly. This is very common, the
The original sheets (see Appendix 4) mention also the tools to be used in each stage; no unknown
tools were mentioned. Simulation is highly advocated.
extra Six Sigma kind of start-up a project can not be read in these phrases,
but if you combine the column “step sigma” from Fig. 6.3 with this Table
than you realise that the intention is to have the goal of planning for Six
Sigma in mind together with all “common” steps of the Product Creation
Table 6.2 Activities to be done & entities to be taken care of
2.1 Customer Segmentation
• Identify Customers
• Segment Customers
• Prioritise Customers
2.2 Customer Requirements
• Customer Selection
• Data Collection
2.3 CTQ & Needs Analysis
• Prioritise Customer Needs
• Determine CTQs
• CTQ Analysis
• Risk Analysis
Understanding Customer needs was stated as being pivotal to a successful
project. Customer Segmentation, surveys, CTQs2 (Critical to Quality)
specification and using a structure tree for overview as preparation for
building a House of Quality (QFD) were mentioned as the detailed steps in
the Measure Phase. I like to add a proper use
and understanding of Kano's model in this phase as well.
Table 6.3 Activities to be done & entities to be taken care of
3.1 Process Requirements
• Define processes/product functions
• Allocate CTQs to process/functions
• Benchmark best performance and
3.2 High Level Design
• Process Description
• Deploy process/functional requirements to
• Define critical resources
3.3 Process capability
• Define evaluation criteria
• Obtain customer feedback
• Finalise design requirements
More or less the same as the key parameters in the APQP (Advanced Product Quality Planning)
approach of Ford from the early 1990s
• Risk Analysis
Starting with the overall requirements (i.e. CTQs) you will identify the
functions required of your product or service.
Table 6.4 Activities to be done & entities to be taken care of
4.1 Process Design
• Detailed process description
• Define critical to process (CTP)
• Control points, measurements
• Determine process capability
• Process simulation
• Risk analysis
4.3 Verification Plan
• Develop control strategy
• Develop control strategy
• Develop pilot test plan
The design step is similar to the analyse step with the major difference being
the level of detail of your design activities. In this step you get a good
overview which of the steps/parts will be critical if you have used the design
scorecards (see Fig. 6.3) properly. This is the most important extra that Six
Sigma has brought above the normal way of working.
Table 6.5 Activities to be done & entities to be taken care of
5.1 Execute Pilot
• Pilot testing
• Documenting results
5.2 Analyse Results and Implementation
• Compare results to specifications
• Start-up and testing
5.3 Project Closure
• Handout process documentation
• Transition to process management
• Project closure
The planned workshop after the introduction lecture on DfSS was skipped
because of the not-planned Six Sigma Club discussions.
6.2 AWARENESS WORKSHOP
Our Process Control group at CFT advocates and practices already for more
than ten years that you must move up-stream with improving activities. So, I
agreed completely with the presentation of Leszek, but did not find a really
new approach and/or new tools. As a result of mentioning this during
informal discussions I got a copy of the sheets of an internal GE DfSS
Awareness Workshop. Fig. 6.5 shows the place of this DfSS Awareness
Workshop in the total Training Roadmap. Also the Six Sigma Institute of
Mikel Harry is willing to train you in DfSS (Fig. 6.6). From this bundle of
sheets3 I have taken some sheets to give extra focus on the need to apply Six
Sigma in development as well.
Fig. 6.5 Example of GE Capital Quality Training Roadmap
Copies of this internal GE DfSS Awareness Workshop can be ordered from the author.
Fig. 6.6 Training program of the SSDI4 institute
Of course the workshop starts (see Fig. 6.7) with rephrasing the importance
of Six Sigma within General Electric, but Jack Welch also states that, if you
are not convinced, ".. you should take your skills elsewhere". Jack repeated
this message in USATODAY (1998-02-27): “With Six Sigma permeating
much of what we do, it will be unthinkable to hire, promote or tolerate those
who cannot, or will not, commit to this way of working”. Quite clear!
Fig. 6.7 Earnings at GE, but also a quite serious warning
Six Sigma Design Institute from Dr. Mikel Harry and Dr. Douglas Mader
Fig. 6.8 Detailed structure of the DfSS process at General Electric and the preferred tools to use
The DfSS process at GE is structured and very detailed, and it looks as if
nothing new can be read there. However, let us go into more detail for the
first step. In the Identify phase, customer wishes and product requirements
need to be identified to find all CTQ (critical to quality) variables. Not only
their target values, but also their limits. The broader definition of CTQ is:
Those characteristics of an item which, if non-conforming,
may prevent or seriously affect the unit performance,
reliability, producibility, or customer satisfaction of a
In my experience, QFD is seldom used and if it is, the action is stopped after
the first house. In this workshop, QFD is called the system for translating
customer requirements into company requirements at each stage from
research to product development, to engineering, and manufacturing to
marketing/sales and distribution. Applying the QFD tool in its full strength
delivers critical-to-quality characteristics (CTQs) from the second house,
key manufacturing processes from the third house and key process variables
from the fourth house. By the same deeply deployed use of the FMEA and
RCA tools, the change of forgetting a CTQ is minimised. The sheets of the
workshop illustrate that, after finding all CTQs in the identify phase, the
root causes of the CTQs must be found in the design phase, using e.g.
simulation and finite element methods (FEM) to model the relations.
A more general picture (Fig. 6.9) lists the three main classes of questions to
• Which parameters have great influence on Customer Satisfaction?
• Which failure modes can be expected?
• What failures did already happen and how can we prevent them?
The tools GE uses are not new (Fig. 6.9), they are operational at Philips as
well. However, the drive to find all CTQs and to be only permitted to
continue if the sigma level is acceptable (see also Fig. 6.3) quit rightly gives
this approach the name Design for Six Sigma.
Fig. 6.9 Three main tools to identify CTQs (=parameters critical to quality)
Looking for a metric to follow the implementation path through the entire
company, GE "only" uses the percentage of new drawings reviewed for
CTQs and the classification in simple sigma level categories of the so
chosen parameters. This still does not look very dramatic.
Fig. 6.10 Six Sigma Design metrics
However, the next slide makes it impressive (of course you can ignore the
message by convincing yourself that the figures are window dressing, but
please keep in mind that the sheets are taken from an internal workshop),
because of the speed of improvement. The change of 59% of all drawings
reviewed for CTQs via 73% to 84% is unbelievable large. And also the
improvement in sigma level from the bad category smaller than four to the
next category is quick.
Fig. 6.11 Overview of the performance during the first three quarters 1996
That's the difference between a lot of the Six Sigma companies and their
competitors: the knowledge is (maybe) the same, but GE (and others)
really DO it.
6.3 DFSS AT THE 1999 ASA QUALITY & P RODUCTIVITY
Preparing myself for the Lloret conference, especially for the DfSS subject,
I downloaded several presentations from the 1999 ASA Quality &
Productivity Research Conference. Reading these lectures strengthened my
feeling that the Six Sigma approach is having quite an impact, but did not
bring very much new with respect to methodology. But as with the scheme
of Fig. 6.8 it is easy to overlook the depth of DfSS, so I want to mention two
6.3.1 Fast Probability Integration
6.3.2 Engineering product
Fig. 6.12 Fast Probability Integration is a numerical method to speed up simulation
6.3.1 Fast Probability Integration
Fast Probability Integration is a numerical approach for probability
estimation, based on the approximate response surface and first-order
(mean) and second-moment (standard deviation) representations of the
uncertainties. Liping Wang  claims to do a two-minute FPI run instead
of an eight-hour Monte Carlo run for the same simulation (robust high-
pressure turbine efficiency) and even 65 minutes instead of a ten-day run
(GE aircraft engine study).
6.3.2 Engineering product
Gavin Finn introduces the concept op “engineering product” in his article
 as follows:
"Advances in technologies for the engineering design process have brought this part of the
product realization process far forward enough to be ready for Six Sigma approaches for
engineering. New design and engineering technologies have done for the engineering
process what Henry Ford did for manufacturing. No longer is the development of a new
model (or new product) the handiwork of a lone, skilled artisan. Now, teams of engineers
and designers, using common tools and methodologies collaborate in a highly orchestrated
process to conceptualize, detail, specify, and build almost every common and uncommon
product, from computer to toys.
The evolution of new work methods and tools for the engineering design process has
resulted in the creation of an engineering product, namely the digital product model. This
product can and should be subject to the rigor of a Six Sigma quality assurance process in
much the same manner as a physical product would be. This engineering product, or virtual
product, saves time in product development by eliminating the need for a physical mock-up,
and allows for early detection of interferences between components, and a number of trade-
off, or optimization studies.
The approach suggested here is to focus a Six Sigma program on the digital model, in
addition to the Six Sigma programs for the manufactured product. This new quality focus
will, by virtue of its intrinsic higher quality yield, also improve the product and process quality
with respect to the manufactured product."
By consequently applying the dpmo philosophy to the engineering product,
Gavin illustrates how the Six Sigma way of thinking can be profitably used
up-stream long before an actual prototype exists. Gavin states that the
available commercial design quality systems are able to analyse the digital
model in such detail.
For a detailed description I recommend reading the original article .
Overviewing the whole concept of Design for Six Sigma, I came to the
Companies that are able to get momentum in Design for Six
Sigma will speed up their PCP and avoid transferring from
development to production too early.