Archive for the ‘Inspection’ Category

A Sampling Question

Monday, March 14th, 2011

A Six Sigma Green Belt student asked an interesting question about sampling. Here’s the question and my response.

QUESTION:
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Just a question that I thought I would run by you…
I work in the Automation industry, and am currently working on two production lines, and logging data for the parts being produced. One line is producing 60 parts per minute and I can thus log the data for every part. The other line is producing 240 parts per minute, and it is not possible to log the data for every part. I remember reading somewhere that in order to perform SPC you must take n consecutive samples (I think n was 5) every x number of cycles. What I need is definitive guidance on how to calculate n and x. I also need to know the statistical reason that n and x are used in order to explain this to the customer. Any feedback you can give me in relation to this would be greatly appreciated.

Regards,

AT in Irelend

RESPONSE:
======================
There is no rule that you need to sample n consecutive samples every x number of cycles. You are probably thinking of a technique known as PRE-Control, which is different than SPC. PRE-control also incorporates rules for deciding when to increase or decrease sampling frequency, stopping rules for processes, etc.. Personally, I don’t like PRE-Control for a variety of reasons, but if you have The Six Sigma Handbook, 2nd edition I discuss in starting on p. 661 or the 3rd edition starting on p. 465. My primary reason for disliking PRE-control is that it is a specification-based scheme (which I dislike in principle) and it will allow process variation to increase until it is as wide as the specs allow. SPC is all about reducing process variability to a minimum by identifying special causes of variation. When used in conjunction with Lean Six Sigma, SPC will also address common cause variation.

Instead of PRE-control I suggest that you consider using standard SPC control charts. I don’t know anything about your process so I can only offer general advice. If you’re already logging in metrics for 60 parts-per-minute I would be surprised if you’re not encountering problems like autocorrelation, which requires an adjustment to standard SPC such as using EWMA charts instead of classical control  charts. If you have autocorrelation and are not using the proper chart, then you will be experiencing a lot of “false alarms.” Processes seldom change by any meaningful amount in a matter of seconds, so you can probably extend the sampling interval. If you feel that you can economically sample 60 per minute, and that it is wise to do so, then you could sample this number of parts from the process running 240 parts per minute rather than checking every part. It would be best to choose the sample at random, rather than sampling every 4th part. Samples chosen using a fixed pattern are susceptible to problems if the process exhibits similar patterns. For example, if the process had 4 positions on a workstation then your 1-in-every-4 sample would always be sampling from the same workstation. Sometimes the patterns in the process are quite difficult to spot, and “Murphy’s Law” can strike at any time. Murphy’s Law states that anything that can go wrong, will go wrong.

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Does Lack of Ethics Explain China’s Quality Control Problems

Thursday, April 23rd, 2009

Explaining China’s Quality Control Problems – Alpha Consumer (usnews.com)

Kimberly Palmer, writing in the US News & World Report Alpha Consumer blog, relates her interview with Paul Midler, author of Poorly Made in China: An Insider’s Account of the Tactics Behind China’s Production Game. Midler attempts to explain why some Chinese-made products suffer from poor quality (when he’s done with this, he can do the same for the rest of the world!) Midler believes that a big part of the problem is miscommunication, but his explanation sounds more like a description of dishonesty than a mere failure to communicate. “ Manufacturing companies that produce a substandard product often know what the problem is with their product, but they don’t provide much of a hint to their customers,” says Midler. “This means that importing companies have to guess at where corners may have been cut. It’s a dangerous situation for all of us to be in, actually.” Other comments emphasize the point. For example:

  • “Should we have been surprised at what happened when we took our production orders to an economy that is different than our own, where controls are lacking, where business ethics are in short supply?”
  • “I became aware of how factories would make unilateral changes to products without informing their customers.”
  • “ So long as there are manufacturers who are trying to game the system by circumventing testing systems, consumers will have to be concerned about products coming from China.”
  • “… you also have some rather willful game playing where quality is manipulated in such a way so as to fool laboratory equipment and inspection.”

I’ve spent some time in China, and in other countries as well. I’ve found that people are people. I have no reason to believe that the Chinese I dealt with were any less ethical than the Americans I dealt with. In all cases I advised my employers and clients to follow Ronald Reagan’s doctrine for dealing with the Soviet Union: trust, but verify. Be sure that your suppliers have adequate quality management systems, process control systems, inspection systems, and documentation. Visit them to establish personal relationships and to verify firsthand that they do what they say. If needed (something you decide) put source inspectors in the supplier facilities. Conduct your own validation tests and receiving inspection.

Suppliers tend to understand when their customers are serious about quality. When they realize that they’re dealing with customers who take quality seriously, and back this up by putting verification and tracking systems in place, they tend to respond. If they don’t, your systems will detect it in time to protect your customers and your reputation. It works if the suppliers are across the street, or halfway around the world.

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IndustryWeek : China Must Do More Says EU as Unsafe Products Hit Record High

Tuesday, April 21st, 2009

IndustryWeek : China Must Do More Says EU as Unsafe Products Hit Record High.

Safety is an aspect of quality. Quality can be defined as conformance to customer requirements, and safety is certainly a customer requirement. I think that there are several issues here:

  1. Do the data show that products made in China are less safe than products made elsewhere? If so, who is responsible?
  2. Are product safety issues increasing?
  3. Finally, what can be done to improve product safety?

Are Chinese products less safe?According to RAPEX, the European Commission’s Rapid Alert System for dangerous consumer products, “It is clear … that Chinese products, and in particular, toys are overrepresented in the RAPEX statistics.” Chinese made toys, for example, account for about half of the toys sold in the EU, but they represent 80% of the RAPEX notifications. Regarding responsibility, the EU Consumer Commission assigns first responsibility to the manufacturers or their commercial representatives in the EU. I agree. Both the manufacturer in China and the organization acquiring and distributing these goods share responsibility for assuring the safety of their products.

Are safety issues increasing?While product safety issues are making more headlines, published data make it difficult to determine whether or not actual incidents are increasing. To determine this it would be best to have data in a form that could be displayed on a time-ordered chart, such as a control chart. However, the best I could find were data such as the EU’s statement “While the overall trade flow between the EU and China has greatly increased over the 2003-2006 period, the overall number of RAPEX notifications of Chinese origin has remained stable, even going down to 46% in the first six months of 2007.” Based on this it would seem that safety issues are either stable or, perhaps, declining.

What can be done to improve product safety? I’ve made numerous trips to China and visited many Chinese factories. I believe that China, and government agencies in Europe and US, is too focused on regulation and inspection. Advanced companies in the developed world abandoned this approach decades ago in favor of process control and continuous improvement. To be sure, inspection is still used. But it is merely used to confirm that the process controls continue to be effective. It’s a case of focusing on root causes rather than focusing on outcomes. Safety failures are not acts of God. They are a predictable and preventable outcome with one or more causes. Modern quality and safety is assured by understanding the processes in detail and acting to control process suppliers, inputs and actions to assure a quality result. Lean, Six Sigma and other methodologies are used to create excellent processes. Lean Six Sigma provides built-in process control using mistake-proofing, just-in-time production and delivery, visible factory displays, and a culture dedicated to product quality and safety.

When I go to my local fast food restaurant with my Grandson, I want to know that the toys he receives are safe. I’d feel a lot more confident if I knew that the manufacturer had process control and improvement in place rather than an army of inspectors and government regulators.

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Nuts-Inspection Won’t Improve Food Safety

Thursday, April 2nd, 2009

First peanuts, now pistachios. Not to mention spinach, almonds and host of other vegetables. Major salmonella outbreaks have been in the news a lot in recent years. The government and the food industry are working overtime to beef up guidelines on what companies need to do to keep consumers safe. USA Today reports that the salmonella outbreak in peanut products has sickened 691 and may have contributed to the deaths of nine in 46 states. While the Centers for Disease Control and Prevention says the last illness was reported on Feb. 24, products are still being sporadically recalled. The proposed solution is, usually, more regulation and more inspection.

I have some bad news: 100% inspection is not 100% effective. If you doubt this, set a timer for 60 seconds and try counting the Fs in this paragraph

Count the F’s. OFTEN UNREALIZED, FEATURE FILMS
ARE THE RESULT OF YEARS
OF SCIENTIFIC STUDY COMBINED
WITH THE EXPERIENCE OF OVER FIFTY YEARS.

Did you count 10 Fs? If so, you are in the minority. I’ve administered the “F-test” to students for many years and usually only 10%-20% find them all (even allowing for the trick F in the first sentence!) And this includes classes of inspectors. The effectiveness of inspection in real-world situations is much worse. An article in Test and Measurement World documented a very detailed study of inspection effectiveness on solder quality defects and found

Manual or automated optical inspection found only about 24% of all defects in these nine studies. In-circuit test covered about 26%. But the biggest eye opener came from functional test. If functional test were our only step, it would have caught no more than about 20% of the defects on those boards—and in most cases only around 10%. It couldn’t find solder problems or missing pull-up resistors, for example, because the boards usually still worked.

The truth is, it’s a lot easier to count Fs than it is to spot problems in a food processing facility. Inspection won’t get it done, and regulation will merely result in more paperwork and jobs for people who keep track of such things. So, what do I recommend? For starters, how about using a technology proven to help with such things? Specifically, food irradiation.

According to Idaho State University

Irradiation of food has been approved in 37 countries for more than 40 products. The largest marketers of irradiated food are Belgium and France (each country irradiates about 10,000 tons of food per year), and the Netherlands (which irradiates bout 20,000 tons per year).

The Center for Disease control confirms that Irradiation could also eliminate bacteria like Shigella and Salmonella from fresh produce, as well as a wide variety of other bacteria from other foods.

We know what to do. Others have proven that it is safe and effective. Let’s drop all of this feel-good chatter about inspecting and regulating quality and safety into our food supply and do what works.

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Measurement Error Kills Macho B

Tuesday, March 31st, 2009

If you live in Arizona, you’ve probably heard of Macho B. Macho B was believed to be the last surviving jaguar in North America. Southern Arizona is at the extreme northern boundary of the jaguar’s range and it was believed that no jaguars remained north of the United States border with Mexico. However, a snare set for a research tracking project tracking the movements of mountain lions and bears accidentally snared Macho B. Now one might wonder why officials didn’t simply let Macho B go, but that’s another story (and a long one.)

Macho B

It came to pass that Macho B ended up at the Phoenix Zoo. While there, zoo veterinarians tested him for kidney failures via a blood test. The test was positive and Macho B was euthanized. However, a pathologist at the University of Arizona’s Veterinary diagnostic Laboratory reviewed the tissue sample and concluded that Macho B’s test results could have actually indicated dehydration. The pathologist, Sharon Dial, said it is unproven dogma among some medical experts that blood levels alone can be used to “make a definitive statement that this animal will not survive.” Dial disagreed. “…I can say by looking at the kidneys that there is no structural reason why he would not have [survived]…For a supposed 15 year old cat, he had damned good looking kidneys.”

So, was Macho B doomed to a slow death due to kidney failure? Or did he have kidneys any 15 year old jaguar could be proud of? It’s a question of measurement variation, specifically reproducibility error. In Six Sigma work we are faced with such questions every day. So are others, although they may not know it until it’s too late to matter.

<strong>Macho B Update</strong>

PHOENIX – The Arizona Game and Fish Department yesterday formally placed one of its employees on administrative leave with pay as a result of an interim finding in the department’s ongoing internal administrative investigation into the events surrounding last year’s capture of the jaguar known as Macho B. The department took this action based on statements made by the employee during the course of the internal investigation, bringing about a need to consider taking administrative action to resolve concerns raised by the statements.

Under state personnel rules, placing an employee on paid administrative leave relieves the employee of duties, pending a determination on what final administrative action may be taken.

Department officials said the employee’s statements were related to the employee’s actions taken several weeks after the capture, recapture and euthanization of Macho B. The department continues to maintain that it did not direct any department employee to capture a jaguar, and that the department’s actions related to the capture were lawful.

Department officials added that the Game and Fish internal investigation cannot be considered completed until the department has an opportunity to review whatever findings may come out of a concurrent federal investigation being conducted by the U.S. Fish & Wildlife Service.

Information about events related to Macho B can be found here.

<strong>Game and Fish dismisses employee involved in jaguar capture</strong>

March 19, 2010

HOENIX – The Arizona Game and Fish Department today dismissed one of its employees as a result of the department’s ongoing internal administrative investigation into the events surrounding last year’s capture of the jaguar known as Macho B.

Dismissed was Thornton W. Smith, 40, a wildlife technician for 12 years with the department and one of the field biologists involved in the placement and monitoring of traps used in a black bear and mountain lion research project that resulted in the initial capture of Macho B.

The department dismissed Smith based on the employee’s own interview statements made during the course of the internal investigation. The statements related to Smith’s conduct that occurred several weeks after the capture, recapture and euthanizing of Macho B.

Smith’s statements and further investigation confirmed that he did not comply with verbal and written directions issued by supervisors and that he admitted to knowingly misleading federal investigators regarding facts surrounding the original capture of Macho B.

The department’s official letter that documents the grounds for dismissal was delivered to Smith earlier today.

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