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There are three general ways you can use measurement and control techniques to improve your product quality:
Reliability
The following graph, commonly called the "bathtub curve", illustrates the life or reliability of products. Some fail in their infancy (infant mortality) and those that survive, should go on to live a long trouble-free life before finally wearing out.
It is the purpose of Quality Assurance to determine through design verification testing that the product is able to provide that long, trouble-free life. Designed to be reliable, the product must then be manufactured to be reliable. It is the purpose of Quality Control to achieve this. Everything possible should be done to avoid poor workmanship and screen out latent defects, the typical causes of infant mortality failures.
Empowering production line people with the responsibility for the quality of their workmanship and providing them with the tools so they can verify that quality is a solution for the workmanship issue. The quality of the output of automated manufacturing equipment can be controlled by measuring and controlling the process variables and/or the product variables in real time during the manufacturing process. Latent defects can be screened out by testing incoming material.
As a final step, a screening procedure can be added for the finished product. These steps prevent inferior products, that would fail prematurely, from getting out to our customers and alienating them.
Quality Assurance
Quality Assurance pertains to product design and development. It involves testing practices aimed at scrutinizing our assumptions concerning our product's performance, reliability and manufacturability. It is sheer arrogance to believe that our product excels in these areas without first testing and verifying it.
Sometimes we need to go back and look at the basics. Consider
our product's principle of operation. Within that principle of operation are elements, the
individual quality of which determine the product's overall performance. Are we paying
enough attention to those elements and how our product's performance is affected when they
vary? Experimentation by measuring and varying the elements while measuring the result in
our product's performance provides us with a better understanding of our product. This
knowledge provides us with the basis for determining how we can optimize those elements
with respect to product design, manufacturing tolerances, manufacturing techniques and
which parameters to measure and control in production.
What we ultimately need is a system of QA techniques for measuring and
controlling the product design and development process so to arrive at a product that
meets the desired performance, reliability and manufacturability objectives. This avoids
the problems associated with underdesigning which may result in mass-produced
"lemons". It also avoids overdesigning which leads to higher cost products.
Machinability Testing
The better that we characterize our product and its behavior in the end
use environment, the more successful will our efforts at Quality Assurance be. Since it is
the physical world that our products perform in when they leave our factory, it is the
physical aspects of the product that we are concerned with here. How does our product
respond to the climates, forces, pressures, accelerations and vibrations that it becomes
subjected to in the real world? We might call this the physical perspective. It is
relevant to all products whether mechanical, electronic or electromechanical. By
physically testing our product we can determine if it is underdesigned or overdesigned. We
then proceed to another iteration until the product is optimally designed.
Quality Control
Quality Control pertains to manufacturing and involves the following procedures.
How To Do It
TQM requires that customer satisfaction be the concern of not just the sales department but that it be everyone's concern. Similarly, PQM requires that product quality be the concern not only of the Quality Department but that it, too, be everyone's concern. Design Engineers need to better understand the product's end use and service life environment before setting out to design it. Well defined, clearly understood design parameters, along with verification testing, provide the Quality Assurance that leads to the long, problem-free life today's customers expect from our products.
Design Engineers should also consider incorporating sensors and microprocessor control into the design of products. Doing so can improve the quality of our product's performance by measuring and controlling critical parameters. And with built-in health monitoring, our customer can be alerted to the need for maintenance rather than being surprised with a failure.
Manufacturing engineers and production people must assume greater responsibility for Quality Control as part of the manufacturing process. Infant mortality failures due to latent defects and poor workmanship not only alienate our customers but cost our company in warranty expenses. Maintaining satisfied customers who come back for follow-on purchases and decreasing warranty expenses do wonders for our corporate productivity.
So how do we achieve this quality-driven productivity? We do it with technology! A simplified view of technology is to see it as man's control of certain elements of nature once he has identified those elements, learned to measure them and to thereby control their behavior. Even the identification of elements is a result of measuring. Man first had to rely on his own inherent sensors to detect elements. But due to subjective errors, he had to develop tools to objectively measure the elements.
Today those tools are many. By using the right ones in a closed-loop
Product Quality Management system, we have the means for continuous product improvement.
The information gained from our QA and QC efforts becomes the basis for immediate design
revisions and future product redesigns.
Displacement Sensors used for Powergen Monitoring and Control
PQM shortens the time required to achieve a mature, reliable design by identifying product and process deficiencies early in the product life cycle. Rather than using our customer as the testbed for finding those deficiencies, we find them on our own, long before we've shipped out so many as to seriously harm our market share position. Instead, by practicing PQM, we improve our quality, increase our productivity, market share and profitability in one clean sweep.
PQM applies to large companies and small companies alike. We need
greater awareness and control of our product's performance, reliability and
manufacturabilty if we are to survive in the global economy of this twenty first
century. The way to succeed is to make use of available tools and their corresponding
techniques. 
(Parts of the above have been excerpted from the R.G. Associates' handbook, Product Quality Management Through Measurement & Control)
If you are an engineer or manager at a company or institution in the New England region (Connecticut, Massachusetts, Rhode Island, Vermont, New Hampshire and Maine), you may qualify to receive our handbook entitled, Product Quality Management Through Measurement & Control. Please visit our Free Book! page for more info.
Product Quality Management and PQM are trademarks of R.G. Associates, Inc. All worldwide rights reserved.
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