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A listing in reverse chronological order of articles by:
An earlier article focused on the conceptual application of appropriate sample sizes for X-bar charts. As we discussed, the purpose of control charts is to detect significant process changes when they occur. When the proper sample size is selected, X-bar charts will detect process shifts (that have practical significance) in a timely manner. [Read more…]
Imagine riding your motor scooter one sunny afternoon to your auntie’s home who lives near the sea, 20 miles from your home. On your trip there, the wind is at your back and the terrain slopes downward, resulting in an average speed of 25 mph. On the way home however, you’re motoring on a slight upward slope and into the wind, resulting in an average speed of 15 mph.
FMEA has an important relationship with risk management. This article provides an example of this relationship.
The suggested sequence is to first read the article “Relationship between FMEA and Risk Management” to learn about the interactions between FMEA and Risk Management at a high level. [Read more…]
In this article post, we discuss the suggested steps for planning a Designed Experiment.
It is critical to clearly define the problem before beginning experimentation. When the problem is not clearly defined and described, there will be confusion in designing and executing effective studies. To define appropriate responses to measure requires that the problem be understood and agreed on. Also, it is key to define the objectives of the actual experiment. If the problem is to reduce scrap rate, how much of a reduction is targeted? [Read more…]
“Component D” had some failures in its first 12 months. How many more would fail in 36-month warranty? ASQ’s Quality Progress Statistics Roundtable published the data and Weibull analysis. The data included left-censored failure counts collected at one calendar time. The Weibull analysis included actuarial failure forecasts. This article describes nonparametric alternatives to Weibull and quantifies extrapolation uncertainty. The nonparametric forecasts are larger than the Weibull forecasts. Alternative extrapolations of nonparametric failure rates from data subsets quantify uncertainty. [Read more…]
The purpose of control charts is to detect significant process changes when they occur. In general, charts that display averages of data/measurements (X-bar charts) are more useful than charts of individual data points or measurements. Charts of individuals are not nearly as sensitive as charts of averages at detecting process changes quickly. X-bar charts are far superior at detecting process shifts in a timely manner, and the sample size is a crucial element in ensuring that appropriate chart signals are produced. [Read more…]
While the construction of control charts is relatively straight-forward, often a more difficult question is “how do I know what process characteristic to control in the first place?” Clearly, controlling “everything” is not feasible or a smart use of limited resources. [Read more…]
I learned actuarial methods working for the USAF Logistics Command. We used actuarial rates to forecast demands and recommend stock levels for expensive engines tracked by serial number, hours, and cycles. I had a hunch that actuarial methods could be applied to all service parts, without life data. [Read more…]
In this article post, we formally define or describe the basic terminology that is commonly used in Design of Experiments. Some of the terms we have already been using in prior posts, but they will also be presented here for completeness. This is Part I of a two part article covering DOE Terminology. [Read more…]
Ergodicity means that cross-section probabilities equal longitudinal lifetime probabilities. (“Ergos” is Greek for “work.” Think of “ergonomics”.) Ergodicity means that we can estimate age-specific field reliability functions from cross-section data: ships (installed base) and returns (complaints, failures, service parts’ sales, etc.). Ships and returns provide information about lifetimes. Returns are the superpositions of failures of products or their parts started at different times. What does ergodicity have to do with toilet paper? [Read more…]
“If no one ever took risks, Michelangelo would have painted the Sistine floor.” – Neil Simon
FMEA and Risk Management are two distinct bodies of knowledge. This article explores some of the interactions between these two important methods. It is not intended to be a complete analysis of the similarities, differences, and linkages between FMEA and risk management. Rather, it is a high-level overview.
Imagine you were a rancher with a herd of cattle and a small field in which to graze them. One of your primary concerns include determining how many cattle the field could support. With too few cattle, you give up potential earnings that the field could readily sustain. But too many cattle consume the grass faster than the field could replenish it, resulting in malnourished cattle and degraded land quality.
Therefore, as a rancher with long-term prospects, inspecting and maintaining the field, planting new grass, and limiting the number of new cattle in the field all become a cornerstone of your business model. [Read more…]
Statistically based DOE provides several advantages over more simplistic approaches such “one-factor-at-a-time” experimentation. These advantages include:
Andrew Vázsonyi led an interesting life. He collaborated with mathematician Paul Erdös, he was co-founder of The Institute of Management Sciences, and he wrote “Which Door has the Cadillac: Adventures of a Real-Life Mathematician”. Around 1970, Andrew Vázsonyi interviewed for a teaching job in Sauder School of Business, University of British Columbia. During the job interview, he taught us Gozinto Theory. [Read more…]
Proper control chart selection is critical to realizing the benefits of Statistical Process Control. Many factors should be considered when choosing a control chart for a given application. These include:
