Design for Six Sigma

Control chart, data, analysis

Q: I am preparing a short training session for my company on the topic of Design for Six Sigma.  I am interested in looking at some examples of how other companies or organizations have used DFSS.  Is it possible to get case studies from ASQ on this topic?

A: Thank you for contacting ASQ and the Quality Information Center.  Design for Six Sigma (DFSS) can be defined as “robust design that is consistent with the applicable manufacturing processes to assure a fully capable process that will deliver quality products” (from The Quality Improvement Glossary by Donald L. Siebels).

For DFSS case studies, please visit ASQ’s website.

Z1.4 2008: AQL, Nonconformities, and Defects Explained

Pharmaceutical sampling

Q: My question is regarding the noncomformities per hundred units and percent nonconforming.  This topic is discussed in ANSI/ASQ Z1.4-2008 Sampling Procedures and Tables for Inspection by Attributes under sections 3.2 and 3.3 on page 2.  Regardless of the explanations provided, I find myself puzzled as to what the following numbers refer to in “Table II-A– Single sampling plans for normal inspection (Master table).”

Specifically, I am having problems understanding the following unit numbers just above the Acceptance and Rejection numbers (example, 0.010, 0.015, 0.025, 1000).  Do these represent percent noncomformities and if so,  does 0.010 = 0.01%, and conversely, how can 1000 = 1000%?

As you may see, I am very confused by these numbers, and I was hoping to have some light shed on this subject. Thank you for your answers in advance.

A: The numbers on the top of the table are just as the questioner stated: .0.010 = .01% defective.  That is the acceptable quality limit (AQL) number.  Generally, most companies want 1% or less, but as noted in the table, it does go up to 1000. It is extreme to think of something being more than 100%, but consider that it may be a minor or cosmetic defect that does not affect the function but just does not look good.  Scratch and dent sales are a common result of these higher numbers.

The AQL number is the worst quality level you would expect to find at this level.  The thing you have to remember is that these plans work best when the quality is very good or very bad.  If you are at the limit, you could end up taking more samples and spend a lot of time in tightened inspection.

Many people use percent nonconforming instead of percent defective, simply because of the connotation of “defective.” No one wants to say they shipped a defective product.  They may have shipped a nonconforming product that the customer could not use simply because their requirements were too strict, where another customer may be able to use the same thing because they have less stringent requirements.

Jim Bossert
SVP Process Design Manger, Process Optimization
Bank of America
Fort Worth, TX

For more on this topic, please visit ASQ’s website.

Does ISO 9001 Clause 7 Apply to Processes?

Manufacturing, inspection, exclusions

Q: Does clause 7 Product Realization in ISO 9001:2008 Quality management systems–Requirements apply to the design and development of manufacturing processes?

We have four facilities that are ISO 9001 certified under one certificate. One location designs the product, and the other facilities manufacture it. In the “design facility” we follow the requirements of clause 7. In the manufacturing facilities, we currently do not apply clause 7 for the process of developing the manufacturing processes.

A: ISO 9001 clause 7.3 is applicable to the design and development characteristics of a product.

ISO 9001:2008 clause 7.1 (Planning of Product Realization) and its reference to clause 4.1 (General Requirements) is more specific to product planning to ensure that the product quality objectives and the processes/resources are available to produce a product that will meet defined quality requirements as specified during design and development in clause 7.3.

Clause 7.1 requires that the planning process include identification of the inter-related processes (i.e., monitoring, inspection, product quality objectives, testing, records of conformity needed to verify the product requirements have been achieved.

The bottom line:  the product characteristics, quality objectives and inter-related processes must be documented.  If this is not fully achieved in the design and development process (clause 7.3), it must be included in the product planning process (clause 7.1). Please see clause 4.1.

Please keep in mind that your company’s ISO registrar will require evidence of conformity (records/documentation) to verify the requirements of clauses 4.1, 7.1 and 7.3 have been met.

Bill Aston
ASQ Senior Member
Managing Director of Aston Technical Consulting Services
Kingwood, TX

For more on this topic, please visit ASQ’s website.

Outsourcing and Quality

About ASQ's Ask the Standards Expert program and blog

Q: The company I work for has outsourced its manufacturing processes and will possibly be outsourcing some of its other processes (including its core quality operations) in the near future.  I am interested in ASQ articles that relate to the outsourcing of core company operations or how quality is affected overall by outsourcing.

A: Outsourcing can be defined as a “strategy to relieve an organization of processes and tasks in order to reduce cost, improve quality, reduce cycle times, reduce the need for specialized skill, and increase efficiency” (taken from The Quality Improvement Glossary by Donald L. Siebels).

For more on this topic, please visit ASQ’s website.

Using the 10:1 Ratio Rule and the 4:1 Ratio Rule

Q: Can you explain when I should be using  the 10:1 ratio rule and the 4:1 ratio rule within my calibration lab? We calibrate standards as well as manufacturing gages.

A: First, I will use the right nomenclature. What the user means is 10:1 and 4:1 Test Accuracy Ratio (TAR). That is, one uses standards 4 or 10 times as accurate as the Unit Under Test (UUT) to calibrate it with.

Unfortunately, the answer to the user’s question is NEVER if we were to use newer metrologically accepted practices.

The TAR is replaced by Test Uncertainty Ratio (TUR).  The ANSI/NCSLI Z540.3:2006 definition of TUR is:

“The ratio of the span of the tolerance of a measurement quantity subject to calibration, to twice the 95% expanded uncertainty of the measurement process used for calibration.”

*NOTE: This applies to two-sided tolerances.

The TUR is represented as a mathematical equation below:

Test Uncertainty Ratio (TUR) represented as an equation

Because of advances in technology, one can purchase highly precise and accurate instrumentation at the end user level, it gets challenging to find standards 4 or 10 times as precise with which to calibrate it and maintain metrological traceability at the same time (definition per ISO Guide 99:2007, Property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty).

Proper measurement uncertainty analysis of the UUT (including standards used with its uncertainty) identifies all the errors associated with the measurement process and ensures confidence that calibration is within the specification desired by the end user.

ISO/IEC 17025-2005: General requirements for the competence of testing and calibration laboratories, clause, third paragraph, also states that “When statements of compliance are made, the uncertainty of measurement shall be taken into account.”

This would also ensure confidence in the calibration employing the metrological and statistical practices recommended.

The other rule of thumb not to be confused in this discussion is to measure/calibrate with the right resolution. In the ASQ Quality Progress March 2011 Measure for Measure column, I wrote more on resolution with respect to specification and measurement uncertainty. The general rule of the thumb is if you want to measure/calibrate a 2-decimal place resolution device, you need at least 3-decimal place or higher resolution device.

This is a very good question posed and it is also unfortunately the most misunderstood practice among a lot of folks performing calibration.

Dilip A Shah
President, E = mc3 Solutions
Chair, ASQ Measurement Quality Division (2012-2013)
Secretary and Member of the A2LA Board of Directors (2006-2014)
Medina, Ohio

Related Content: 

Measure for Measure: Avoiding Calibration Overkill, Quality Progress

Evolution of Measurement Acceptance Risk Decisions, World Conference on Quality and Improvement

Measure for Measure: Calculating Uncertainty, Quality Progress

Is C=0 in Z1.4?

Chart, graph, sampling, plan, calculation, z1.4

Q: I have ANSI/ASQ Z1.4-2008 Sampling Procedures and Tables for Inspection by Attributes. I looked through it rapidly, and I still can’t find the C=0 plan directly, so I am a little confused. I thought C=0 is included in Z1.4. Is the C=0 plan spirit/concept contained in Z1.4 or does C=0 need to be calculated from the several tables in Z1.4? (if yes, which tables?).

A: Z1.4:2008 is a general sampling plan for attributes.  It is tabled by AQL with varying accept reject numbers.  The standard gives a framework for attribute inspection plans. Though Z1.4 does have some plans where C=0, they are NOT optimal to minimize the Type II error. For C=0 plans specifically, I would recommend purchasing Zero Acceptance Number Sampling Plans, Fifth Edition.  The value of the Z1.4 standard is the switching rules used for incoming inspection.

Steven Walfish
Secretary, U.S. TAG to ISO/TC 69
Statistician, GE Healthcare

For more on this topic, please visit ASQ’s website.

Measurement Tolerances and Techniques

ISO/IEC 17025:2017 General requirements for the competence of testing and calibration laboratoriesQ: I am looking for some information regarding blueprint tolerances and measurement tools used to measure certain features.

For example, can the same type of tolerance be applied over the length of 450 mm as it could be for a distance of 3 mm?  Is there additional measurement error or gage error that needs to be applied for longer distances?  If one uses a 1” micrometer for measuring a feature, does it make a difference in the measurement error by using the top end of the instrument versus using it to measure just very small features?

A: Thank you for your questions about measurement tolerances. First of all, since your questions were multi-layered, my answers will be as well. Nonetheless, I think I should be able to help you.

As for using the same type of tolerance for a dimension of 450 mm and a dimension of 3 mm, there is more than one answer. We’re talking about 17.7165 inches vs. .118 inches. The 3 F’s must first be considered.  That is Form, Fit, and Function.  In other words, where will this product be used?  If this will be for a medical product or for anything whatsoever where safety is a factor, the design engineer will most likely use a tighter tolerance. So both dimensions could be ± .001 or a more liberal ± .010.  The difference between the two sizes would just change the way they are manufactured.  For example: a 17.717 inch product with a tolerance of ± .030 could probably be rough machined or even made on a burn table.  If the size or location of the smaller dimension is critical, you would machine it with appropriate equipment and hold a tighter tolerance.  OK, enough Manufacturing 101 lingo.

With regard to measurement error, larger/longer dimensions can introduce the possibility of increased measurement error. However, if a “qualified” and experienced individual is doing the measurement, that should not be a major factor.  The same basic skills and standards would apply. The type of measurement equipment can make a difference.  In other words; if you use a Dial Caliper, you can probably rely on it to be accurate within .001-.002 inches.  If you use a 0-1 inch micrometer, you should be able to trust it’s accuracy within .0001 inch.

A qualified metrologist and/or a quality technician would know to check a micrometer at numerous points over its measuring range.  Measurement error should not increase significantly from one end to the other.  If it does, there is something wrong with the calibration or with the tool itself.

I know the above can be perceived as general answers, but I am confident you will see the specifics there as well.

Bud Salsbury
ASQ Senior Member, CQT, CQI

For more on this topic, please visit ASQ’s website.

ISO 14001 4.3.1 Environmental Aspects; Clarification of Intent

ISO 14004, Environmental Management System, EMS

Q: Based on Section 4.3.1 of ISO 14001-2004: Environmental management systems – Requirements with guidance for use, would an organization control, or be expected to influence, environmental aspects in the following situations:

  • Would an organization’s headquarters (or corporate office) control, or be expected to influence, the environmental aspects of its operating facilities?
  • Would an organization control, or be expected to influence, the environmental aspects of its suppliers, including contractors?
  • Would a regulatory agency control, or be expected to influence, the environmental aspects of other organizations subject to its regulatory requirements?

Clarification of Intent:

A: Clause 4.3.1 of ISO 14001:2004 requires an organization to identify the environmental aspects of its activities, products and services within the defined scope of its environmental management system (EMS) “that it can control and those that it can influence.”  This differs from the 1996 standard which used the phrase “that it can control and over which it can be expected to have an influence.”

The revised language removes one ambiguity in the 1996 version – some users incorrectly interpreted this phrase to imply that views of someone outside the organization must be considered when determining the environmental aspects the organization might influence. The intent of the new phrase in Clause 4.3.1 is to make it clear that the organization makes that determination.

Furthermore, as in the 1996 standard, the organization is obligated to identify environmental aspects only for those activities, products and services that are within its EMS scope, which again is decided by the organization (see Clause 4.1). Of these environmental aspects, the organization must decide which it can control and which are not within its control.  For those of its environmental aspects that it cannot control, the organization must decide if it can exercise influence over them

The Standard does not define criteria that an organization must use to determine its control of or influence over environmental aspects.  It is up to the organization to make that determination, on a case by case basis, considering its own unique factors, such as its governance structure, legal or contractual authority, its policies, local or regional issues, its obligations and responsibilities to interested parties, technological issues and implications on its own environmental performance. What might be appropriate for one organization might not be appropriate for others. It is important to note that it is possible for two different organizations or two different organizational units to control or influence the “same” environmental aspect.

In summary, an organization is only responsible for managing its own environmental aspects (those arising from activities, products, and services within its EMS scope) and only those aspects which it can control or which it can influence.

Regarding the three situations posed in the question:

1) Determining “control and influence” within a corporation or other hierarchical organization.   For purposes of identifying environmental aspects, the scope of the EMS is the key.  It delineates the activities, products, and services from which environmental aspects might arise and for which the organization needs to consider its control or influence.

If the EMS scope is restricted to corporate headquarters, the issue of control or influence pertains to the environmental aspects arising from headquarters’ activities, products and services.  It may be that some environmental aspects are not within corporate headquarters control, but instead are controlled by an operating facility.  In this case, corporate headquarters must consider whether it can influence those aspects that are within its scope and yet controlled by the operating facility.

If the EMS scope is restricted to one operating facility, the issue of control or influence pertains to that operating facility.  It may determine that some environmental aspects are not within the operating facility’s control, i.e., certain aspects may be controlled by another operating unit (such as headquarters or an engineering department).  The operating facility must consider whether it can influence those aspects that are within its EMS scope and yet controlled by another unit.

If the EMS scope includes both headquarters and the operating facilities, both headquarters and operating facilities need to consider their collective control or influence over the aspects within the scope of the EMS.

2)  Determining “control and influence” with regard to contractors and suppliers.   An organization is not responsible for the environmental aspects of its contractors or suppliers; it is responsible only for its own environmental aspects.   An organization may have environmental aspects associated with activities within its own EMS scope which are performed by contractors, or environmental aspects arising from materials or services purchased from suppliers.  For such aspects, the organization must consider what control it might have, e.g. through contracts, and what influence it might have, e.g. through purchasing power.

3) Determining “control and influence” for a regulatory agency.   When a regulatory agency identifies environmental aspects associated with its activities, products, and services, it must consider the same issues as other organizations; that is, it must determine the extent of control or influence it has over the identified aspects.  It is clear that such an agency may influence or even be perceived to control some environmental aspects associated with organizations that it regulates.  The important point is defining the regulatory agency’s environmental aspects that arise from the activities (e.g., setting water quality standards), products (e.g., discharge permits), and services (e.g., inspection) within its EMS scope.  Deciding which aspects are under the agency’s control or influence follows the same logic as for other organizations.

U.S. Technical Advisory Group (TAG) 207 Task Group on Interpretations

– – – – – – – – – – –

What are clarifications of intent?

The ISO 14001:2004 standard on environmental management systems has been negotiated over a period of years, with language carefully chosen to reflect delicate compromises and flexibility in their use and application.

Recognizing that questions of intent may arise from time to time in various settings, the U.S. TAG responds to questions regarding clarification of the ISO 14001 requirements. These responses reflect U.S. SubTAG 1’s understanding of the requirements as intended during its drafting. Responses are prepared by the SubTAG 1 Clarification of Intent Drafting Group, which consists of the Administrator, the U.S. SubTAG 1 Working Group experts and others who participated in the drafting of the ISO 14001 and 14004 standards. Responses are developed based on the group’s consensus understanding of the intent of the SC1 Working Group members who drafted the standard.

For more on this topic, please visit ASQ’s website.

Six Sigma Green Belt Projects

Data review, data analysis, data migration

Q: I teach a course called “Statistical Methods of Six Sigma” at an engineering college. I’m preparing students to take the ASQ Certified Six Sigma Green Belt exam if they are interested (it is not a mandatory requirement of my class).

Here’s my question — most of my students already have jobs lined up after graduation. Some of them are going to places where Six Sigma programs are already fully established. I do have one particular student who is expected to implement a Six Sigma program at the company that she is going to. It’s a small company, and they don’t already have a Six Sigma program in place.

If she passes the ASQ Green Belt exam and receives her Six Sigma Green Belt Certification, how does she go about getting a project approved if she’s working for a company that doesn’t already have existing Belts?

A: To ask a Green Belt to implement a Six Sigma program is not only ambitious, but also somewhat risky.  Green Belts have the least amount of experience in Six Sigma. Regardless, what this person should be doing is look at the company and decide what a good first project would be with an executive mentor.  The candidate should be looking at something that is important to the company and has impact to the business.  It should be something that requires some work and is not obvious to just anyone looking at the project.

Q: I think the expert more accurately posed what my real question is: how does a new grad working for a company that doesn’t currently have a Six Sigma Black Belt program find an executive mentor to approve or qualify her project?

I agree that she will need a Black Belt, but who will/can certify her project if there is not an existing Black Belt or Master Black Belt at her place of work?  (It is a small consulting firm for medical hospitals).

A: I recommend that she approach her local ASQ Section and inquire about mentors.

Jim Bossert
SVP Process Design Manger, Process Optimization
Bank of America
Fort Worth, TX

For more on this topic, please visit ASQ’s website.