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Operations Mgmnt.
Prof. Fandel: Chapter 16: Quality Control and SPC
| Question | Answer |
|---|---|
| Quality Control | A task to ensure that a good or service conforms to specifications and meets customer requirements by monitoring and measuring processes and making any necessary adjustments to maintain a specified level of performance. |
| 1:10:100 Rule | If a defect or error is identified and corrected in the design stage, it might cost $1 to fix. If it is first detected during the prod. process, it might cost $10. However, if the defect is not discovered until it reaches the customer, it might cost $100. |
| Quality at the Source | Means the people responsible for the work control the quality of their processes by identifying and correcting any defects or errors when they first are recognized or occur. |
| Statistical Process Control (SPC) | A methodology for monitoring quality of manufacturing and service delivery processes to help identify and eliminate unwanted causes of variation. |
| Common Cause Variation | The result of complex interactions of variations in materials, tools, machines, information, workers, and the environment. *Accounts for 80 to 95 percent of the observed variation in process. |
| T/F: Only Management has the power to change systems and infrastructure that cause common cause variation. | TRUE. |
| Special (assignable) Cause Variation | Arises external sources that are not inherent in the process, appear sporadically, and disrupt the random pattern of common causes. * Accounts for 15 to 20 percent of observed variation. |
| T/F: Only supervisors have the power to identify and solve special causes of variation. | FALSE. Both front-line employees and supervisors have the power ti identify and solve special causes of variation. |
| A process is in control: | When there are no specials causes the output of a process. |
| A process is out of control: | When special causes are present in a process. |
| Two basic mistakes when attempting to control a process: | 1) Adjusting a process that is already in control. 2) Failing to correct a process that is out of control. |
| Continuous Metric | One that is calculated from data that are measured as the degree of conformance to a specification on a continuous scale of measurement. |
| Discrete Metric | One that is calculated from data that are counted. |
| A process is said to be "in control" when the control chart has the following characteristics: | 1) No points are outside the control limits. 2) The number of points above and below the center line is about the same. 3) The points fall randomly above and below the center line. 4) Most points are near the center line, and few are close to the limits. |
| T/F: Small sample sizes keep costs lower; however, large sample sizes provide greater degrees of statistical accuracy in estimating the true state of control. | TRUE. |
| Sampling Frequency | Samples should be close enough to provide opportunity to detect changes in process characteristics as soon as possible and reduce the chances of producing a large amount of nonconforming output. |
| T/F: Large samples on a frequent basis are the most economical. | FALSE. Large samples on a frequent basis are normally not economical. |
| C-chart | Monitors the number of noncomformances (i.e., a count of the number of defects or errors) per unit, when the size of the sampling unit or number of opportunities for errors is constant. |
| c is the average number of nonconformances/unit. Control limits are given by: | UCLc = c + [3 x square root(c)] LCLc= c - [3 x square root(c)} |
| T/F: SPC is a useful methodology for process that operate at a high sigma level (Greater than 3-sigma). | FALSE. SPC is useful for processes that operate at a low sigma level (Less than or equal to 3-sigma) |
| T/F: For process with a high sigma level, few defects will be discovered even with large sample sizes. | TRUE. |
| Process Capability | Refers to the natural variation in a process that results from common causes. |
| Process Capability Study | A carefully planned study designed to yield specific information about the performance of a process under specified operating conditions. |
| Process Capability Index | A measure that quantifies the relationship between the natural variation and specifications. |
| Process Capability Index Equation | Cp = (USL -LSL)/6σ USL = Upper specification limit LSL = Lower specification limit σ = standard deviation of the process |
| Voice of the customer | Customer requirements, as expressed in the customers own terms. |
| Quality Function Deployment (QFD) | An approach to guide the design, creation, and marketing of goods and services by integrating the voice of the customer into all decisions. |
| T/F: QFD translates customer wants and needs into technical requirements of a product or service. | TRUE. |
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KAzetapi
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