Z 1.4 Inspection Levels

Pharmaceutical sampling

Question

I am using a reduced switching rule and I don’t understand the meaning of the numbers in the first box. Total noncomforming less than limit number? What’s my limit number?Does production stability mean capability? Would I use 1.33?  The table has an arrow to reduced, so would I move to the next box?

Answer

The ANSI/ASQ Z1.4 standard has three inspection levels: normal, reduced and tightened inspection.  Initially you start at normal inspection, and can move to either tightened or reduced inspection depending on how lots are dispositioned.  Based on Figure 1 of the standard, the determination to move amongst the levels can be ascertained.  When you get to the reduced inspection level (Table II-C), you need to read the footnote (†).  It states “If the acceptance number has been exceeded, but the rejection number has not been reached, accept the lot, but reinstate normal inspection.”

A stable process or production is less about a capability index, and more about the control chart of the data showing a stable process.  In other words, the process is stable over time.

Steven Walfish

For more information about inspection, please view the resources found here.

ANSI Z1.4 Reduced Inspection

Question

If you have Ac=0 and Re=2 what do you do for 1? I have not used the reduced sampling before, so am curious what should be done in this instance.

Answer

If you review the footnotes for Table II-C of ANSI Z1.4, you will see that there is a note (†) that states: If the acceptance number has been exceeded , but the rejection number has not been reached, accept the lot, but reinstate normal inspection (see 10.1.4).  So in your case, with a single reject, you would accept and reinstate normal inspection.

Steven Walfish

Customer ISO Status In Jeopardy?

Question

My customer wants to get ISO 9001:2015 certified. He refuses to create a first-article, in-process, and final-inspection report. He has a router sheet that has a tiny space for final inspection brief information and the operator’s initials; no inspection data is available.
In his quality manual and processes he addresses “Time Studies” and “Statistical Process Control” but he refuses to record his inspection data because this “complicates and delays” his production. I told him this is a weakness in his QMS but he says it’s not. Will this issue jeopardize his ISO certification?

Answer

I would ask how the organization could present objective evidence with the requirements of Clause 8.5.1 including  – ‘shall implement production and service provision under controlled conditions.’

Charlies Cianfrani

Audit Versus Inspection?

Audit, audit by exception

Question

Would you please tell me what the differences between audit and inspection are?

Answer

This is a great question.   We can start with the definitions of inspection and audit per the new ISO 9000:2015 standard.  Inspection is “Determination of conformity to specified requirements”  (3.11.7)  and Audit is “systematic, independent and documented process for obtaining objective evidence and evaluating it objectively to determine the extent to which audit criteria are fulfilled”  (3.13.1).    Without parsing the words to much, the difference is one of scale:  Inspection is most often associated with inspecting a product or a service to make sure it is right, and an audit is most often associated with a higher-level review of the system that is designed to produce and inspect the product or service.    An audit of a manufacturing process wouldn’t just inspect the product, it would ensure (at a system level) that required inspections had already been performed on the product.  I have often made the differentiation in the following way… “An inspection is down in the grass, but to do an audit, you have to climb a tree.”  The reflects the difference in purpose and perspective for an audit.   Other authors, such as Arter, Sayle, and Russell refer to inspections as ‘backward looking’, that is, what was actually done to provide a product or service, while audits are ‘forward looking’.   Audits ensure that proper management controls are in place to ensure product quality into the future.   Instead of inspecting quality in (to a product produced in the past), an audit evaluates how well a quality system will predict and prevent quality problems (in the future).   My three favourite references are Quality Audits for Improved Performance by Dennis Arter, Management Audits, by Allan Sayle, and the ASQ Auditing Handbook, edited by JP Russell.

Thanks very much,

Denis J. Devos, P.Eng
A Fellow of the American Society for Quality
Devos Associates Inc.
(519) 476-8951
www.DevosAssociates.com

Inspection Sample Size

Question

  1. The customer expects certain levels of inspection: pull 157 bottles for visual testing, but then they also want 20 pulled for dimensional testing. Can’t the 20 additional bottles be a subset of the original testing sample?
  1. When calculating the lot, do you pull the samples before or after your calculations? Do the samples get included in the produced quantity or not?  For example: If the customer orders 10,000 bottles and the level 2 inspection pulls 200 bottles that drops the total shipped to the customer to 9,800 pieces.  If 10,200 bottles are produced then the inspection level increases so that 315 bottles need to be pulled for testing.  What is the correct sample size and production number?

Answer

Hello,

Here are the responses to your questions:

  1. Yes since the first inspection is visual, you can use a subset for the additional testing.
  1. The lot size is 10,000. You should be putting the samples back into the lot if they are not destroyed by the testing. You send what is contracted for.  You are sampling with replacement.

Jim Bossert

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

Combating contamination

Q: We want to ensure that we are receiving clean containers to package our products. How can we improve our incoming inspection process?

A: You should encourage your vendor to ship only clean containers. Then, be sure that the shipping and receiving process doesn’t cause contamination. If you can determine the source or sources of the contamination, the best fix is to remove the cause.

If that approach is not possible and you have incoming containers that may have some contamination, then consider the following elements in creating an efficient incoming inspection process.

1) How do you detect the contamination?

Apparently, you are able detect the container contamination prior to filling them, or are able to detect the effect of the contamination on the final product. Given that you are interested in creating an incoming test, let’s assume you have one or more ways to detect faulty units.

As you may already know, there are many ways to detect contamination. Some are faster than others, and some are non-destructive. Ideally, a quick non-destructive test would permit you to inspect every unit and to divert faulty units to a cleaning process. If the testing has to be destructive, then you’ll have to consider lot sampling of some sort.

There are many testing options. One is the optical inspection technique, which may find gross discoloration or large debris effectively. Avoid using human inspectors unless it’s only a short term solution, as we humans are pretty poor visual inspectors.

Another approach is using light to illuminate the contamination, such as a black light (UVA). Depending on the nature and properties of the contamination, you may be able to find a suitable light to quickly spot units with problems.

Another approach, which is more time consuming, is conducting a chemical swab or solution rinse and a chemical analysis to find evidence of contamination. If the contamination is volatile, you might be able to use air to “rinse” the unit and conduct the analysis. This chemical approach may require specialized equipment. Depending on how fast the testing occurs, this approach may or may not be suitable for 100 percent screening.

There may be other approaches for detecting the faulty units, yet without more information about the nature and variety of contamination, it’s difficult to make a recommendation. Ideally, a very fast, effective and non-destructive inspection method is preferred over a slow, error prone, and destructive approach. Cost is also a consideration, since any testing will increase the production costs. Finding the right balance around these considerations is highly dependent on the nature of the issue, cost of failure, and local resources.

2) How many units do you have to inspect?

Ideally, the sample size is zero as you would first find and eliminate the source of the problem. If that is not possible or practical, then 100 percent inspection using a quick, inexpensive, and effective method permits you to avoid uncertainties with sampling.

If the inspection method requires lot sampling, then all of the basic lot sampling guidelines apply. There are many references available that will assist you in the selection of an appropriate sampling plan based on your desired sampling risk tolerance levels.

Another consideration is the percentage of contaminated units per lot. If there is a consistent low failure rate per lot, then lot sampling may require relatively large amounts of tested units. You’ll have to determine the level of bad units permitted to pass through to production. Short of 100 percent sampling, it’s difficult (and expensive) to find very low percentages of “bad” units in a lot using destructive testing.

3) Work to remove original source(s) of contamination to permit you to stop inspections.

I stress this approach because it’s the most cost effective in nearly all cases. In my opinion, incoming inspection should be stopped as soon as possible since the process to create, ship and receive components should not introduce contamination and require incoming inspection to “sort” the good from the bad.

Fred Schenkelberg
Voting member of U.S. TAG to ISO/TC 56 on Reliability
Voting member of U.S. TAG to ISO/TC 69 on Applications of Statistical Methods
Reliability Engineering and Management Consultant
FMS Reliability
www.fmsreliability.com

Related Resources:

Digging for the Root Cause, Six Sigma Forum Magazine, open access

Many Six Sigma practitioners use the term “root cause” without a clear concept of its larger meaning, and similar situations occur in Six Sigma training programs. As a result, many practitioners overlook root causes. Read more.

The Bug and the Slurry: Bacterial Control in Aqueous Products, ASQ Knowledge Center Case Study, open access

When a customer reported a problem using the polycrystalline diamond (PCD) slurry supplied by Warren/Amplex, the company traced its product through the supply chain in order to identify the cause and quickly implement a solution. Read more.

Explore the ASQ Knowledge Center for more case studies, articles, benchmarking reports, and more.

Browse articles from ASQ magazines and journals here.

Dock to Stock

Suppliers, supplier management

Q: I have been tasked with implementing a dock to stock policy. Does an expert have any advice or information to share towards forming a dock to stock policy?

A: To begin, here is a brief definition of dock to stock (DTS):

Dock to stock is a receiving method whereby materials are delivered directly to point of use (storage or manufacturing), skipping the normal receiving inspection.

For most organizations, parts which are given a DTS status are those which have been “proven” to be compliant. It is common practice to perform a receiving inspection on the parts for a minimum of five deliveries (some companies choose 10).

After a supplier has proven to deliver a compliant product five times, that individual item/part number is given DTS status. It is then general practice for production/assembly departments or line personnel to verify compliance as needed. If a product is found to be noncompliant, it is put on a contingency list and must prove its validity again — usually through five to 10 compliant shipments before it is returned to DTS status.

Keep in mind that the DTS process is rarely used in some industries/companies. For example, a company certified to ISO 13485 (medical devices) would not use DTS due to FDA regulations — here’s an excerpt from 21 CFR 820.80 (b):

“Receiving Acceptance Activities: Incoming product shall be inspected, tested or otherwise verified as conforming to specified requirements.”

In short, determining how many acceptable shipments to qualify a supplier for DTS status is up to the company. Requesting a certificate of compliance with each shipment can tend to encourage a supplier to ensure their own quality, as does a yearly audit of the supplier’s facilities (if appropriate).

I hope using the guidelines above will help lead you toward your goal.

Bud Salsbury
ASQ Senior Member, CQT, CQI

Related Content:

Browse the free, open access resources below, or find more in the ASQ Knowledge Center.

Chinese OEM Reduces Returns With Improved Product Testing, ASQ Knowledge Center case study

When Continental Automotive Systems, Tianjin, China, began producing an electronic component known as the silver box, the return rate was more than 1,200 parts per million (ppm), versus a goal of less than 100 ppm. A Six Sigma improvement team used quality tools including trend charts, Pareto charts, and cause-and-effect diagrams to analyze the failure modes for the reported defects, finding that many were not being covered by product testing processes. Read more.

Cost-Effectiveness Based Performance Evaluation for Suppliers and Operations, Quality Management Journal

This research establishes a cost-effectiveness based  performance evaluation system for suppliers and operations. The purpose is to provide a methodology for “integrating supplier and manufacturer capabilities through a common  goal, profitability improvement, based on lowering the cost of purchased materials.”  Read more.

Expert Answers: Stock and Standards, Quality Progress

The advisability of implementing dock-to-stock is discussed. Read more. 

Ask A Librarian

Coordinate Measuring Machines (CMMs) and Digital Bore Gages

Gage R&R, Torque Wrence

Q: When inspecting diameters with tolerances of .0005 and below, are there any studies relating to the accuracy of different inspection methods, such as a coordinate measuring machine (CMM) versus a digital bore gage with setting ring combination?

A: The answer to this question can often be one of opinion and/or personal preference.  What I will present are my opinions, along with some known facts.

Non-contact measurement systems such as optical and laser equipment are bulky, expensive and impractical.  With these systems, the part must be taken to the system. This is not much good in a production environment.

While a CMM is without a doubt very accurate, they are also slow.  Like the optical or laser equipment, the parts must be taken to the system.  In many production situations it is more practical to check the part in the machine.  Also, even though CMMs come with reticulated heads, measuring at abstract angles or various depths is not always an option.  It is also wise to keep in mind that deeper bores would require longer stylus probes.  This is a situation that can introduce concerns of error and rapid movement can generate false contact readings with longer styli simply due to the motion.

A final thing to keep in mind is the high initial price of a CMM, as well as the maintenance costs.

Two and three point contact measurement is readily available.  Popular digital bore gages are calibrated to a master ring.  The rings themselves can be verified with a CMM or sent out for certification traceable to national standards. Most digital bore gages can be set up to interface with a statistical process control system. This is important when process control is vital.

Cylinder bore gages (generally two point contact) can sometimes have problems with linear accuracy. Analog versions can be more prone to operator error.

While two point systems will more readily detect ovality, where this is not a major concern, three point digital systems are, in this quality technician’s opinion, the best all-around option.

When I am inspecting parts in which ovality could be an issue, if the parts are readily portable, I will check a percentage with a CMM to verify their roundness.  However, for speed, accuracy, practicality, and price, a three point digital bore gage would be the way I would go to verify product with tight tolerances.

A final note: If parts are relatively small and can be in contact with other materials, robotics is often used with air gage instruments.  This is another expense but can be introduced in high volume manufacturing.

I hope this will help.

Bud Salsbury
ASQ Senior Member, CQT,CQI

ANSI/ASQC C1-1996 Supplier Testing

Schedule, calendar, timeline

Q: I need clarification on the following, please:

ANSI/ASQC C1-1996 — Specification of General Requirements for a Quality Program — has been included in the required specifications from a prospective customer. Section 3.3.4 states (in the last sentence) “Furthermore, the validity of certifications shall be periodically verified by the buyer through independent testing.”

What criteria (time-frame, suppliers, mills, etc.) should be used to comply with “periodically?”

What testing is to be performed for the required independent testing? Is it to be only a chemical analysis, or are mechanical tests to be performed as well?

Does this standard require independent testing of materials in purchased components such as gaskets, glass, bolts and fittings, or is “raw materials” only meant to be the base materials such as plate and sheet steel that we purchase?

A: To begin with, most establishments, including your customer, already know that materials most often come with material test certificates.  For example, when you order a sheet of steel from EMJ Metals or another supplier, they will supply a test certificate along with it.

The certificates include that data which would be most important to your customer such as chemical analysis, mechanical properties, ASTM specifications, etc. You are probably already aware of all this.

As for “periodic” and “independent” testing, here is my opinion:

If you have, in writing, a document stating that all purchased materials will be subject to receiving inspection and such inspections will verify that customer requirements have been met, that will be step 1.

For step 2, if you go to the web site of almost any materials supplier, they will have documentation (quality manual, ISO certification, etc.) which you can use as evidence they are a qualified supplier.

You can then contact that supplier and ask if they will verify, in writing, that they also test the material they are sending.  Steel suppliers, like most material suppliers, sell what they receive from the original mills.  The material certs they provide to you are made of tests the mills run.  A company such as EMJ, which I mentioned earlier, uses what is called a Niton tester to verify chemical make up of the product which they buy and in turn sell to their customers.

Finally, step 3: as with any quality management system, you must “do what you say you do.”  So, if you say that part of your receiving inspection includes hardness testing, be ready to provide evidence of that (incoming inspection reports).

In closing, I feel confident that if you prepare the steps noted above, or something similar and communicate this to your potential customer, they will be doubly satisfied with your company. Doubly because all of this would display evidence of an organization with a mature QMS.

Bud Salsbury,
ASQ Senior Member, CQT,CQI