"The old 7 statistical tools”
Quality pros have many names for these seven basic tools of quality, first emphasized by Kaoru
Ishikawa, a professor of engineering at Tokyo University and the father of “quality circles.”
Start your quality journey by mastering these tools, and you'll have a name for them too:
"indispensable."
1. Cause-and-effect diagram (also called Ishikawa or fishbone chart): Identifies many
possible causes for an effect or problem and sorts ideas into useful categories.
2. Check sheet: A structured, prepared form for collecting and analyzing data; a generic tool
that can be adapted for a wide variety of purposes.
3. Control charts: Graphs used to study how a process changes over time.
4. Histogram: The most commonly used graph for showing frequency distributions, or how
often each different value in a set of data occurs.
5. Pareto chart: Shows on a bar graph which factors are more significant.
6. Scatter diagram: Graphs pairs of numerical data, one variable on each axis, to look for a
relationship.
7. Stratification: A technique that separates data gathered from a variety of sources so that
patterns can be seen (some lists replace "stratification" with "flowchart" or "run chart").
FAILURE MODES AND EFFECTS ANALYSIS
Customers are placing increased demands on companies for high quality, reliable products. The
increasing capabilities and functionality of many products are making it more difficult for
manufacturers to maintain the quality and reliability. Traditionally, reliability has been achieved
through extensive testing and use of techniques such as probabilistic reliability modeling. These
are techniques done in the late stages of development. The challenge is to design in quality and
reliability early in the development cycle.
Failure Modes and Effects Analysis (FMEA) is methodology for analyzing potential reliability
problems early in the development cycle where it is easier to take actions to overcome these
issues, thereby enhancing reliability through design. FMEA is used to identify potential failure
modes, determine their effect on the operation of the product, and identify actions to mitigate the
failures. A crucial step is anticipating what might go wrong with a product. While anticipating
every failure mode is not possible, the development team should formulate as extensive a list of
potential failure modes as possible.
The early and consistent use of FMEAs in the design process allows the engineer to design out
failures and produce reliable, safe, and customer pleasing products. FMEAs also capture
historical information for use in future product improvement.
Types of FMEA's
There are several types of FMEAs, some are used much more often than others. FMEAs should
always be done whenever failures would mean potential harm or injury to the user of the end
item being designed. The types of FMEA are:
System - focuses on global system functions
Design - focuses on components and subsystems
Process - focuses on manufacturing and assembly processes
Service - focuses on service functions
Software - focuses on software functions
FMEA Usage
Historically, engineers have done a good job of evaluating the functions and the form of products
and processes in the design phase. They have not always done so well at designing in reliability
and quality. Often the engineer uses safety factors as a way of making sure that the design will
work and protected the user against product or process failure. As described in a recent article:
"A large safety factor does not necessarily translate into a reliable product. Instead, it often leads
to an overdesigned product with reliability problems."
Failure Analysis Beats Murphey's Law
Mechanical Engineering , September 1993
FMEA's provide the engineer with a tool that can assist in providing reliable, safe, and customer
pleasing products and processes. Since FMEA help the engineer identify potential product or
process failures, they can use it to:
Develop product or process requirements that minimize the likelihood of those failures.
Evaluate the requirements obtained from the customer or other participants in the design
process to ensure that those requirements do not introduce potential failures.
Identify design characteristics that contribute to failures and design them out of the
system or at least minimize the resulting effects.
Develop methods and procedures to develop and test the product/process to ensure that
the failures have been successfully eliminated.
Track and manage potential risks in the design. Tracking the risks contributes to the
development of corporate memory and the success of future products as well.
Ensure that any failures that could occur will not injure or seriously impact the customer
of the product/process.
Benefits of FMEA
FMEA is designed to assist the engineer improve the quality and reliability of design. Properly
used the FMEA provides the engineer several benefits. Among others, these benefits include:
Improve product/process reliability and quality
Increase customer satisfaction
Early identification and elimination of potential product/process failure modes
Prioritize product/process deficiencies
Capture engineering/organization knowledge
Emphasizes problem prevention
Documents risk and actions taken to reduce risk
Provide focus for improved testing and development
Minimizes late changes and associated cost
Catalyst for teamwork and idea exchange between functions
