Six Sigma versus DFSS

An often asked question centers upon the difference(s) between traditional Six Sigma DMAIC and Design for Six Sigma, or DFSS.  This holds especially true for companies that have DMAIC black belts and are uncertain regarding the applicability of yet another operational excellence initiative, given the overlap between these two Six Sigma programs. 

Simply put, DMAIC focuses upon existing situations, usually is reactive in nature, and tends to focus upon cost savings.  Conversely, DFSS focuses upon future product development, is proactive in nature, and focuses on expanded revenue via growth.  In a perfect world, all a company’s DMAIC black belts would eventually transition to DFSS as they wind down the number of cost savings projects (a.k.a. cost avoidance, elimination of cost of poor quality, etc.) and begin to concentrate upon growth through new product development.

REMEMBER: IF ALL YOU PERFORM IS CONTINUOUS IMPROVEMENT VIA SIX SIGMA DMAIC TOOLS, THE BEST THAT MAY BE HOPED FOR LONG TERM IS BEING THE BEST-IN-CLASS IN AN OUTDATED TECHNOLOGY. 

Functionally, all the DMAIC tools are heavily employed within DFSS, but the opposite is not true.  Also, DMAIC tends to lend itself to cross-functional personnel while DFSS, at least during a substantial portion of its roadmap, tends to require more engineering-oriented talent.  However, much of the DMAIC work within DFSS may easily be performed by traditional black belts, allowing the product development team to remain cross-functional, which is a mainstay of DFSS. 

From a tactical standpoint, a very simple explanation of the difference between DMAIC and DFSS:  DFSS begins with extensive customer requirements tools, and concept generation and selection tools, which are ultimately used to feed a high level House of Quality.  In DFSS, QFD is intensely integrated with Critical Parameter Management (CPM) via the creation of transfer functions.  This is the foundation of DFSS; the system HOQ in turn serially feeds the HOQ for the subsystem(s), components, and manufacturing capability assessments.  Most importantly, however, the statistical capabilities (Cp, Cpk, Pp, Ppk, etc.) are then driven back up this QFD system via transfer functions that are developed by known physical law, by the many statistical tools offered by DMAIC, or most often a combination thereof.  Again, remember that DFSS is a predictive tool, enabling the product development group to ascertain the in-line effects of their design before ever committing to product launch.

Excerpt from Genesis'  Executive Program

Software used to track DFSS

For information

The remaining tasks in DFSS tend to focus upon system reliability and robustness, especially in the presence of mitigating factors, or noise.  Statistical tolerancing tradeoffs are also made at this point, as a balance between cost and capability is created.  Usually, DFSS follows a rigorous Stage-Gate system of Concept, Design, Optimization, and Capability Verification.

Concept

The tools used during this stage that probably are not familiar to DMAIC black belts:

Understanding Customer Value

Markets and Their Segmentation

Voice of the Customer

Formal Interviewing Techniques

Voice of Technology

KJ Image Analysis

KJ Requirements Analysis

Pugh Concept Selection

Critical Parameter Management

This is where the deployment begins of QFD/CPM via the first, or system level HOQ.  Although ultimately engineering-oriented in nature, DFSS focuses very heavily upon the first HOQ, as it is the foundation of everything else that will follow within the Stage-Gate process.  Many companies believe they “know” the VOC and VOT, only to find that when they launch a product it either fails in the marketplace, fails technologically, or worse, both.

 Design

This is where the DMAIC tools begin to be employed.  The additional tools used during this stage that probably are not familiar to DMAIC black belts:

Design FMEA (Failure Modes and Effects Analysis)

Design for

Manufacturability

Assembly

Serviceability

Cost

Statistical Tolerancing

Remember that Critical Parameter Management (QFD/CPM) is continuing here.

 Optimization

Here is where extensive use of DMAIC tools occurs.  Keep in mind, however, that within a traditional DMAIC project, emphasis is placed upon what already is happening, whereas within DFSS the emphasis shifts to what will happen.

Capability Verification

The tools used during this stage that probably are not familiar to DMAIC black belts:

Robust Design (Taguchi-inspired methods)

Response Surface Modeling (usually reserved for DMAIC master black belts)

Sequential DOEs for Multiple Y Optimization (ditto)

Quality Loss Function (Taguchi)

Tolerance Balancing           

Reliability

Highly Accelerated Life Testing (HALT); “screening”

Accelerated Life Testing (ALT); “application”