Month: September 2013

Statistical Methods and Control Charts

Analysis, Statistics, Control Charts, Statistical Methods

Question:
My question is regarding a threading process.  There is 100% inspection for go/no go check and about 5% rejection/rework.  The batch size is 5,000 nos and is completed in 3 days of production. Two such batches are produced in a month.

What type of control chart should be used to monitor the process? How should the process capability be calculated in this case?

Answer:
The type of control chart first depends on what type of data you are measuring.  If you are doing go/no go then you are limited to a “P” chart or a “C” chart.  A “P” chart looks at % good (or bad).  A “C” chart looks at the number of defects found.

If you are measuring thickness or strength, (something that can be measured), then you can use a X-bar/R chart or an X-bar/S chart depending on many samples are taken.

That is the simple answer; part of this depends on how you are taking samples and how often.  If samples are taken at the start and the finish, then I would probably recommend the “P” chart.

If you can measure throughout the manufacturing process, and you look at the type of defects, then I recommend a “C” chart.

Ideally, if you can get measurement data, you are better off with the X-bar/R or the X-bar/S charts.  These tend to be better predictors and it is easier to calculate capability.

With the capability for the go/no go data, you can get % defective, (or % good) and multiply that by 1,000,000 to get your capability estimate in defects per million.

Jim Bossert
SVP Process Design Manger, Process Optimization
Bank of America
ASQ Fellow, CQE, CQA, CMQ/OE, CSSBB, CSSMBB
Fort Worth, TX

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

Internal Lead Auditor/Auditor Qualifications

Audit, audit by exception

Question:

My manager and I have a question about internal lead auditor and auditor qualification. As stated in section 8.2.2 of ISO 9001:2008, “the organization shall conduct internal audits at planned intervals to determine whether the quality management system ….”

Our question is this; does the internal lead auditor and auditor have to be certified by an organization, or trained by a certified lead auditor? May a person read ISO 19011:2011 and with his/her experiences in his/her field then perform audit tasks as stated in section 8.2.2 of ISO 9001:2008? If yes, would an ISO registrar consider it to be a non-conformance finding?

Thank you in advance for taking time to answer our question.

Response:

Thanks for contacting ASQ’s Ask the Experts program.  With regard to your question, it is important to know that ISO 9001:2008 does not prescribe any specific requirements for the qualifications of persons conducting QMS audits.  ISO 19011:2011, provides guidance; not mandatory requirements for determining Auditor qualifications.  As you are aware, an internal audit is one of the most valuable tools that an organization has to determine the effectiveness of its quality management system as well as to identify opportunities for improvement.

For this reason, it is essential that the personnel or consultants used to conduct audit activities, have the qualifications and experienced needed to provide these services.  As a minimum, I would suggest that your internal audit personnel  attend Auditor classroom training accredited by ASQ, RABQSA or IRCA.  This training should be supported by arranging for their participation in future audits as an audit team member.  This audit should preferably be conducted by an individual who has a current certification as an ASQ CQA or an RABQSA or IRCA Lead Auditor.  Another consideration is to ensure that the Lead Auditor can provide an audit log as evidence of his/her past audit experience.  The Lead Auditor should also provide evidence of their continued training to maintain their competency as an Auditor.  Another key point is to ensure that the Lead Auditor has a working knowledge of your organization’s product line, processes or services.  The importance of using trained and experienced Auditors can’t be overstated.

Bill Aston
ASQ Senior Member
Managing Director of Aston Technical Consulting Services
Kingwood, TX
www.astontechconsult.com

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