6184-7_tn07 - cha06369_tn07.qxd 2/12/03 7:01 PM Page 299...

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T ECHNICAL N OTE S EVEN technical note Assignable variation defined 300 Common variation defined Variation around Us 301 Upper and lower specification or tolerance limits defined Process Capability 302 Capability index ( C pk ) Capability index (C pk ) defined Process Control Procedures 305 Process control with attribute Statistical process control (SPC) defined measurements: using p charts Attributes defined Process control with variable measurements: Variables defined using X and R charts How to construct X and R charts Acceptance Sampling 311 Design of a single sampling plan for attributes Operating characteristic curves Conclusion 314 technical note seven PROCESS CAPABILITY AND STATISTICAL QUALITY CONTROL cha06369_tn07.qxd 2/12/03 7:01 PM Page 299
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This technical note on statistical quality control (SQC) covers the quantitative aspects of quality management. In general, SQC is a number of different techniques designed to evaluate quality from a conformance view. That is, how well are we doing at meeting the speciFcations that have been set during the design of the parts or services that we are pro- viding? Managing quality performance using SQC techniques usually involves periodic sampling of a process and analysis of these data using statistically derived performance criteria. As you will see, SQC can be applied to both manufacturing and service processes. Here are some examples of the types of situations where SQC can be applied: How many paint defects are there in the Fnish of a car? Have we improved our paint- ing process by installating a new sprayer? How long does it take to execute market orders in our Web-based trading system? Has the installation of a new server improved the service? Does the performance of the system vary over the trading day? How well are we able to maintain the dimensional tolerance on our three-inch ball bearing assembly? Given the variability of our process for making this ball bearing, how many defects would we expect to produce per million bearings that we make? How long does it take for customers to be served from our drive-through window during the busy lunch period? Processes that provide goods and services usually exhibit some variation in their output. This variation can be caused by many factors, some of which we can control and others that are inherent in the process. Variation that is caused by factors that can be clearly identiFed and possibly even managed is called assignable variation. ±or example, variation caused by workers not being equally trained or by improper machine adjustment is assignable varia- tion. Variation that is inherent in the process itself is called common variation. Common variation is often referred to as random variation and may be the result of the type of equip- ment used to complete a process, for example.
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This note was uploaded on 02/02/2012 for the course ADMON mpm taught by Professor 101 during the Spring '11 term at Colorado Technical University.

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6184-7_tn07 - cha06369_tn07.qxd 2/12/03 7:01 PM Page 299...

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