32.1 Design for Quality

Traditionally, quality conformance in the production process can be said to be Quality after design (QaD) viz, applying quality control procedures during the production process only to ensure that the product conforms to the specifications given by the designers.

In his book, Quality by Design, Juran propounded his theory of QbD contrary to the traditional QaD, and emphasized that that quality could be planned, and that most quality crises and problems relate to the way in which quality was planned. QbD provides guidance to facilitate design of products and processes that maximize the product’s efficacy and safety profile, while enhancing product manufacturability and control. It is defined by Business Dictionary as a systematic process to build quality into a product from the inception to final output.

Juran’s emphasis on the above concept, as well as Taguchi’s experiments at Toyota as explained in Chapter 31, made several automobile manufacturers rethink the way the design process for a product is conceived, by adapting the principle of Quality by Design (QbD), by which detailed planning and checklists shall be prepared, to highlight all the factors that affect the production. These factors must be considered and analyzed before embarking upon the design procedure. This detailed planning builds quality into the design process as highlighted by Juran.

This term, QbD, is now replaced by a more popular term, Design for quality (DFQ), which is complementary to DFSS (Design for Six Sigma). It may be noted that while Six Sigma emphasizes the improvement of the process to achieve higher levels of quality, DFSS emphasizes meticulous planning in the design stage itself. Thus, while the former adapts the Define, Measure, Analyze, Improve, and Control (DMAIC) methodology, the latter adapts the Define, Measure, Analyze, Design, and Verify (DMADV) methodology, which is described more in later paragraphs.

It may also be noted that several books, as well as several six sigma practitioners relate the DMAIC methodology to QbD as they do equally to the six sigma process. The following paragraphs describe DMAIC as the methodology for achieving six sigma levels.

While DMAIC is described in detail in Chapter 24, it is cited here again to provide a contrast with DMADV or DFSS.

● Define the project goals and customer (internal and external) requirements.

● Measure the process to determine current performance.

● Analyze and determine the root cause(s) of the defects.

● Improve the process by eliminating defect root causes.

● Control future process performance.

This can also be represented below.

● Define the problem/defects

● Measure the current performance level

● Analyze to determine the root causes of the problem/defects

● Improve by identifying and implementing solutions that eliminate root causes

● Control by monitoring the performance of the improved process

The process of DFSS can be understood better by some of its explanatory definitions.

● A methodology for designing new products and/or processes.

● A methodology for redesigning existing products and/or processes.

● A way to implement the six sigma methodology as early in the product or service life cycle as possible.

● A way to exceed customer expectations.

● A way to gain market share.

● A strategy toward extraordinary return on investments.

It may be noted that this procedure is broadly similar to any other method improvement procedure followed by industrial engineers, which is explained more in Section 22.9 of Chapter 22 on Kaizen.

32.2 Design for Six Sigma

As explained in the previous paragraph, the six sigma practitioners have gone a step further by adapting DFSS to design a new product to achieve not only the high quality standards put forth by Juran, Taguchi et al., but to achieve the six sigma quality levels. The full impact the six sigma concept had on the modern manufacturing industries is explained in Chapter 24. This approach is similar to DMAIC methodology, which is explained in an earlier chapter, and consists of the steps detailed in the next paragraph.

Earlier, the design function and quality control function had separate identities and functions. But today it is DFQ (Design for Quality) and DFSS that has become part and parcel of the quality function, at least in coordinating with the design and development departments to ensure for application of DFQ and DFSS concepts for creating new products or process designs.

DFSS uses a process management and performance improvement strategy methodologies DMAIC or DMADV leading to Lean Six Sigma. As discussed in the previous paragraph, DMAIC is adapted to improve the existing process to achieve six sigma, while DMADV is adapted for designing new products and new processes that yield six sigma levels. This process of designing new products for six sigma is generally termed as Design for Quality (DFQ).

32.3 Acronyms for Methodologies Akin to DMAIC

The other acronyms used in DFSS are:

● DMAIC (Define, Measure, Analyze, Improve, and Control)

● DMADV (Define, Measure, Analyze, Design, and Verify)

● IDOV (Identify, Design, Optimize, and Validate)

● DCCDI (Define, Customer Concept, Design, and Implement)

● DMEDI (Define, Measure, Explore, Develop, and Implement)

While six sigma (DMAIC) requires a process to be in place and functioning, DFSS is applied during the design process with an objective of determining the needs of customers and the business, and driving those needs into the product solution duly created. In other words, DFFS is concerned with using tools, training, measurements, and verification so that products and processes are designed at the outset to meet six sigma requirements.

32.4 DMADV

DMADV is a DFQ methodology (Fig. 32.1) for the development of a new service, product, or process, as opposed to improving a previously existing one. The letters indicate:

● Define the problem/defects

● Measure the current performance level

● Analyze to determine the root causes of the problem/defects

● Design meticulously for the selected alternative

● Verify to validate that the design is acceptable to all stakeholders

This approach—Define, Measure, Analyze, Design, and Verify—is especially useful when implementing new strategies and initiatives because of its basis in data, early identification of success, and thorough analysis. Thus, it includes five phases as explained below and illustrated in Fig. 32.1.

32.5 Scope of DFSS

The scope of DFSS is as follows:

● Designing new products and or processes,

● Redesigning the existing products or processes,

● Developing products that meet the customers' expectations/demands,

● Predicting and improving quality before building prototypes.

We can say that DMAIC : DMADV :: Method Improvement study : Value Analysis.

32.6 Six Sigma Versus DFSS

We can summarize the differences between traditional six sigma and DFSS as follows:

32.7 Benefits of DFSS

1. Reduces the time to market the product because the customers’ voice is responded to in advance, making the product well accepted in the market.

2. Decreases the life cycle cost associated with the product. Taking action at the design stage is less expensive.

3. Increases understanding of different customers' expectations and their priorities related to the product/service attribute.

4. Reduces the number of design changes because the initial attempt itself tends to be an optimal design.

5. Enhances the organizations’ ability to manage risk in design process of products/services as all the problems are well thought out.

6. Reduces warranty costs as failures are less.

7. Increases robustness of the product because all variables are taken care of during the design stage.

8. Improves market share and business profitability as price is reduced and the products are accepted in the market.

32.8 Conclusion

Whereas several books relate DFSS procedure to DMIAC, some websites like Six Sigma and a few bloggers on the Minitab website say that the DFSS should not be related to DMAIC, but only to DMADV, indicating that the steps of Design and Verify are more essential to DFSS than merely Improve and Control. These versions indicate that even today, there is a controversy whether DMAIC or DMADV should be followed for DFSS. However, this author feels the distinction lies not in relation to DFSS, but in what context the procedure is applied. DMAIC focuses on improving an existing product or process, while DMADV focuses on creating a new product or process. The term D in other acronyms may mean Design for new products or redesign for existing products.