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6 Design for Six Sigma (DfSS)

6.1 PRESENTATION

The introduction lecture on this subject has been presented by LeszekBiskup-Kstner from Siemens. Leszek defined Design for Six Sigma as amethod 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 inproduction is well-known to come up after clearing up the mud. This iswell-illustrated with the tree in Fig. 6.1. The phrase low-hanging fruit hasbeen 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 fruitproblems, 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 thatalso from our experience with IOA (Industrial Opportunity Assessments). Fig.6.2 is based on data from about 200 audits internal at Philips [1].

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Fig. 6.2 Root causes of major changes in production

The most impressive picture presented by Leszek was Fig. 6.3, because itillustrates 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 atthese details you fall into the old pitfalls.

Design - SimulationDFSS Steps

Spec Limits

USL LSL

Standard

DefinitionCTQStep

Step

Sigma

Process

SigmaOK?

VERIFY

Redesign

Yes

No

I.e. design Scorecards

Fig. 6.3 Design Scorecard, showing the deeply deployed Sigma levelas 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 Fig6.4):

n Define

n Measuren Analyse

n Design

n Verify

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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 Tablethan 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

Process.

Table 6.2 Activities to be done & entities to be taken care ofduring Measure-stage

2. Measure2.1 Customer Segmentation

Identify Customers

Segment Customers

Prioritise Customers2.2 Customer Requirements

Customer Selection

Data Collection

Prioritisation

Interviews

2.3 CTQ & Needs Analysis

Prioritise Customer Needs

Determine CTQs

CTQ Analysis

Risk Analysis

Understanding Customer needs was stated as being pivotal to a successfulproject. 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 inthe 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 ofduring Analyse-stage

3. Analyse

3.1 Process Requirements

Define processes/product functions

Allocate CTQs to process/functions

Benchmark best performance and

processes3.2 High Level Design

Process Description

Deploy process/functional requirements todesign requirements

Define critical resources3.3 Process capability

Define evaluation criteria

Obtain customer feedback

Finalise design requirements

2More or less the same as the key parameters in the APQP (Advanced Product Quality Planning)

approach of Ford from the early 1990s

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Risk Analysis

Starting with the overall requirements (i.e. CTQs) you will identify the

functions required of your product or service.

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Table 6.4 Activities to be done & entities to be taken care ofduring Design-stage

4. Design

4.1 Process Design

Detailed process description Define critical to process (CTP)

Control points, measurements4.2 Simulation

Determine process capability

Process simulation

Risk analysis4.3 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 beingthe level of detail of your design activities. In this step you get a goodoverview which of the steps/parts will be critical if you have used the designscorecards (see Fig. 6.3) properly. This is the most important extra that SixSigma has brought above the normal way of working.

Table 6.5 Activities to be done & entities to be taken care ofduring Verify-stage

5. Verify

5.1 Execute Pilot

Pilot testing

Documenting results

5.2 Analyse Results and Implementation Compare results to specifications

Start-up and testing

Training

5.3 Project Closure

Handout process documentation

Transition to process management

Project closure

The planned workshop after the introduction lecture on DfSS was skippedbecause of the not-planned Six Sigma Club discussions.

6.2 AWARENESS WORKSHOP

Our Process Control group at CFT advocates and practices already for morethan ten years that you must move up-stream with improving activities. So, Iagreed completely with the presentation of Leszek, but did not find a reallynew approach and/or new tools. As a result of mentioning this duringinformal discussions I got a copy of the sheets of an internal GE DfSSAwareness Workshop. Fig. 6.5 shows the place of this DfSS Awareness

Workshop in the total Training Roadmap. Also the Six Sigma Institute ofMikel Harry is willing to train you in DfSS (Fig. 6.6). From this bundle of

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sheets3 I have taken some sheets to give extra focus on the need to apply SixSigma in development as well.

Fig. 6.5 Example of GE Capital Quality Training Roadmap

3Copies of this internal GE DfSS Awareness Workshop can be ordered from the author.

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Fig. 6.6 Training program of the SSDI

4institute

Of course the workshop starts (see Fig. 6.7) with rephrasing the importanceof Six Sigma within General Electric, but Jack Welch also states that, if youare not convinced, ".. you should take your skills elsewhere". Jack repeatedthis message in USATODAY (1998-02-27): With Six Sigma permeating

much of what we do, it will be unthinkable to hire, promote or tolerate thosewho cannot, or will not, commit to this way of working. Quite clear!

Fig. 6.7 Earnings at GE, but also a quite serious warning

4Six Sigma Design Institute from Dr. Mikel Harry and Dr. Douglas Mader

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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 ifnothing new can be read there. However, let us go into more detail for thefirst step. In the Identify phase, customer wishes and product requirements

need to be identified to find all CTQ (critical to quality) variables. Not onlytheir 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

component.

In my experience, QFD is seldom used and if it is, the action is stopped afterthe first house. In this workshop, QFD is called the system for translatingcustomer requirements into company requirements at each stage from

research to product development, to engineering, and manufacturing tomarketing/sales and distribution. Applying the QFD tool in its full strengthdelivers critical-to-quality characteristics (CTQs) from the second house,key manufacturing processes from the third house and key process variablesfrom the fourth house. By the same deeply deployed use of the FMEA andRCA tools, the change of forgetting a CTQ is minimised. The sheets of theworkshop 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.

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A more general picture (Fig. 6.9) lists the three main classes of questions tobe asked: 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 aswell. However, the drive to find all CTQs and to be only permitted tocontinue 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 entirecompany, GE "only" uses the percentage of new drawings reviewed forCTQs and the classification in simple sigma level categories of the so

chosen parameters. This still does not look very dramatic.

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Fig. 6.10 Six Sigma Design metrics

However, the next slide makes it impressive (of course you can ignore themessage 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 drawingsreviewed for CTQs via 73% to 84% is unbelievable large. And also theimprovement in sigma level from the bad category smaller than four to thenext category is quick.

Fig. 6.11 Overview of the performance during the first three quarters 1996at GE

That's the difference between a lot of the Six Sigma companies and theircompetitors: the knowledge is (maybe) the same, but GE (and others)really DO it.

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6.3 DFSS AT THE 1999 ASA QUALITY & PRODUCTIVITYRESEARCH CONFERENCE

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 notbring very much new with respect to methodology. But as with the schemeof Fig. 6.8 it is easy to overlook the depth of DfSS, so I want to mention twopoints:6.3.1 Fast Probability Integration6.3.2 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 probabilityestimation, based on the approximate response surface and first-order

(mean) and second-moment (standard deviation) representations of theuncertainties. Liping Wang [10] claims to do a two-minute FPI run insteadof 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).

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6.3.2 Engineering product

Gavin Finn introduces the concept op engineering product in his article

[8] as follows:

"Advances in technologies for the engineering design process have brought this part of theproduct realizationprocessfar forward enough to be ready for Six Sigma approaches for

engineering. New design and engineering technologies have done for the engineeringprocess what Henry Ford did for manufacturing. No longer is the development of a newmodel (or new product) the handiwork of a lone, skilled artisan. Now, teams of engineersand designers, using common tools and methodologies collaborate in a highly orchestratedprocess to conceptualize, detail, specify, and build almost every common and uncommonproduct, from computer to toys.

The evolution of new work methods and tools for the engineering design process hasresulted 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 inmuch the same manner as a physical product would be. This engineering product, or virtualproduct, 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 focuswill, by virtue of its intrinsic higher quality yield, also improve the product and process qualitywith 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 usedup-stream long before an actual prototype exists. Gavin states that theavailable commercial design quality systems are able to analyse the digitalmodel in such detail.

For a detailed description I recommend reading the original article [8].

Overviewing the whole concept of Design for Six Sigma, I came to thefollowing conclusion:

Companies that are able to get momentum in Design for SixSigma will speed up their PCP and avoid transferring fromdevelopment to production too early.

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