Its primary focus is measurement systems where the readings can be replicated on each part. Under a product control philosophy this classification activity would be the primary reason for measuring a part. The customer and supplier s need to thoroughly understand the project requirements, what the deliverables will be and the methods by which both are to be achieved. Conducting preventive maintenance on a stable system, based on time series information, will be less wasteful than conducting preventive maintenance on a system with traditional techniques. For example, parts measured with a coordinate measuring machine during buy- off and then with a height gage during production; samples measured weighed on an electronic scale or laboratory mechanical scale during buy- off and then on a simple mechanical scale during production. .
Chapter I — Section B The Measurement Process 19 The next section deals with the effect of the measurement error on the product decision. This will aid in the development of the measurement equipment criteria and requirements affected by the location in the process. Simple measuring tools and devices i. The central theme here is communication. Many of the analyses are useful with other types of measurement systems and the manual does contain references and suggestions. Although the specific causes will depend on the situation, some typical sources of variation can be identified. In order to better understand the effect of measurement system error on product decisions, consider the case where all of the variability in multiple readings of a single part is due to the gage repeatability and reproducibility.
The objective is to stabilize the process. This may satisfy initial implementation requirements, but this documentation does nothing with regard to defining potential wear points, suggesting possible trouble areas or describing how to use the process. Note: The approach used in the 4th Edition is to compare standard deviations. Knowledge is gained of what the process is doing by evaluating the parameters or results of the process. Here are some guidelines: The team needs to evaluate the design of the subsystem or component and identify important characteristics.
Consequently, if an approach other than that described in this manual is used, a statement of such must be stated clearly in any results or summaries particularly those provided to the customer. Build tolerance should not be a mere given percent of product tolerance alone. If so, then the largest worst variation of the measurement system is small relative to the smaller of either the process variation or the specification limits. It may also cover performance standards for a more complex measurement system. Analytic studies are among the most important uses of measurement data because they lead ultimately to better understanding of processes.
Chapter I — Section D Measurement Source Development 32 Preventive Maintenance Considerations All too often, customers rely too heavily on suppliers for solutions. Effective documentation for any system serves the same purpose as a good map on a trip. . That possible relationship could be studied by using a statistical procedure called regression analysis to compare measurements of the critical dimension with measurements of the temperature of the feed material. P 12 F The measurement error just compounds the problem. Remember to use data to substantiate common assumptions about the measurement process.
Later, in some cases another part is measured and again the process may be adjusted. These guidelines serve to communicate acceptable standards. P 15 This chapter was written with the team philosophy in mind. The Measurement Life Cycle concept expresses the belief that the measurement methods may change over time as one learns and improves the process. .
Process control Is the process variation stable and acceptable? These are based on customer requirements and the functionality of the subsystem or component to the total system. Another use of measurement data is to determine if a significant relationship exists between two or more variables. The flow chart and initial discussion will facilitate the identification of the key individuals. These include: 1 Adequate discrimination and sensitivity. Management is also responsible for ensuring that those properties are used as the basis for selecting a measurement system. The effects of the various sources of variation on the measurement system should be evaluated over a short and long period of time. Now the process is running at 5.
It is not a job description for the buyer or purchasing agent. Edwards, Out of the Crisis, Massachusetts Institute of Technology, 1982, 1986. An exceptional condition could be a significant disparity with regard to price or delivery — this would not necessarily be discounted as a negative factor — one supplier may have discovered an item that others overlooked. Data collection methods and maintenance recommendations related to these activities can be obtained from the original manufacturer, or developed by plant engineering, manufacturing and quality personnel. If the reader chooses to increase the coverage level, or spread, of the total measurement variation to 99. Chapter I — Section B The Measurement Process 22 When a new process such as machining, manufacturing, stamping, material handling, heat treating, or assembly is purchased, there often is a series of steps that are completed as part of the buy-off activity.