Quality Progress - October 2013 - 8

ExPERTANSWE Handling incoming inspections linked back to the supplier. The preferred that this practice results in biased, mislead- Q: How should we choose a sampling plan approach is to evaluate the supplier materi- ing information. As your inspection system for receiving inspection of parts that have al versus each applicable specification. This matures, you can replace the supplier data already gone through an inspection pro- may require you to inspect and accumulate with your in-house inspection results and cess at our supplier’s facility before being data on an interim basis. Over time, you gain confidence in your decisions. shipped to our facility? will obtain enough information to make an Jared Christensen Cedar Rapids, IA informed decision. Finally, consider detection. Is the defect I suggest that you compare your inhouse data to the supplier information at least once per year. Use a two sample t- hard to detect in subsequent processing test to see if there is a difference between A: This is an excellent question that every steps? If it is hard to detect, inspection the two data sets. If the difference is facility should address. I have a number of prior to use is more important. If the de- statistically significant, this is a red flag that suggestions that you may find helpful. fect is easy to detect, it is unlikely that the demands an explanation and may warrant defect will escape to the final customer, intensified inspection of future shipments. My first suggestion is to determine whether you have regulatory requirements so incoming inspection is less important. and factor those requirements into a docu- Assign a rank scale to each of these three using American National Standards Institute mented plan. If you work in a regulated factors, and multiply them together to (ANSI)/ASQ Z1.4 for attribute inspection and industry, such as medical devices, phar- obtain a risk priority number (RPN). In ANSI/ASQ Z1.9 for variables inspection.2,3 maceuticals or aerospace, you may be re- general, material with a high RPN number The ANSI plans include tables with sample quired to inspect incoming material prior to should be subject to incoming inspection sizes geared to the quality level that is de- use, even if the material has already passed for every lot or shipment, whereas mate- sired. The attribute plan includes switching a supplier inspection.1 Your facility also may rial with a low RPN can be subjected to rules for deciding when inspection should be bound by ISO standards to inspect—or periodic inspections, but no less than once be tightened or reduced. at least verify—the quality of incoming per year. material, and to hold the material until the The FMEA approach can be time As for the sampling plan itself, I suggest Incoming inspection costs money but does not increase the value of the material. required testing has been completed and consuming. As an alternative, ask the You may have regulatory requirements that appropriately documented. supplier for the raw data in addition to the compel you to inspect, but if you follow Next, I recommend that you perform certificate of acceptance. Obtain data for some of the suggestions outlined above, a risk assessment. The concepts used in at least three of the supplier’s production you can prioritize the inspection activities failure mode and effects analysis (FMEA) lots. More is better, but data for 10 lots are and achieve a high level of quality assur- include a risk assessment based on three sufficient for this purpose. Ask a quality ance at a minimum cost. factors: severity, occurrence and detection. engineer or statistician within your orga- Within the context of receiving in- nization to evaluate the supplier’s process spection, consider the impact of various indicator. Products with high Cpk values (> the final customer or will it merely cause 1.67) have low risk, so incoming inspection inconvenience with a potential loss of cus- may not be needed. Products that have tomer confidence and satisfaction? low Cpk values (< 1.33) should be inspected Occurrence is the frequency of the more frequently. defect within the population. At a mini- Keep in mind that a few suppliers may mum, review your supplier history data, cherry pick the samples prior to inspection. if available, and rank the suppliers based Samples with obvious defects are discard- on the frequency of product returns and ed and are never included in the accep- in-process rejects that can be definitively 8 Consultant and Master Black Belt capability using a Cpk metric or similar defects. Could the defect cause injury to Andy Barnett tance sample. The supplier may not realize QP • www.qualityprogress.com Houston RefeRences and note 1. For medical devices, see Code of Federal Regulations (CFR) Section 820.80. For pharmaceuticals, see CFR Section 211.84. 2. American National Standards Institute and ASQ, ANSI/ASQ Z1.4:2008—Sampling procedures and tables for inspection by attributes. 3. American National Standards Institute and ASQ, ANSI/ASQ Z1.9:2008—Sampling procedures and tables for inspection by variables for percent nonconforming. foR moRe infoRmation Borror, Connie M., The Certified Quality Engineer Handbook, third edition, ASQ Quality Press, 2009. http://www.qualityprogress.com

Table of Contents for the Digital Edition of Quality Progress - October 2013

Up Front
LogOn
Expert Answers
Perspectives
Keeping Current
Mr. Pareto Head
5S Shakeup
For the Greater Good
Turned On
Get There Faster
Career Corner
Standards Outlook
Quality in the First Person
QP Toolbox
QP Reviews
Back to Basics

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