To record the actual observation can have a marked

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to record the actual observation can have a marked effect on the reliability of the data. The value of the increase in the reliability of the data when recorded properly should be under estimated. The practice of recording a result only when it is outside specification is also not recommended, since it ignores the variation going on within the tolerance limits which, hopefully, makes up the largest part of the variation and, therefore contains the largest amount of information. Data should form the basis for analysis, decision and action, and their form and presentation will obviously differ from process to process. Information is collected to discover the actual situation. It may be used as a part of a product or process control system and it is important to know at the outset what the data are to be used for. For instance, if a problem occurs in the amount of impurity present in a product that is manufactured continuously, it is not sufficient to take only one sample per day to find out the variations between different operator shifts. Similarly, in comparing errors procedures, it is essential to have separate data from the outputs of both. These statements are no more than common sense, but it is not unusual to find that decisions and actions are based on misconceived or biased data. In other words, full consideration must be given to the reasons for collecting data, the correct sampling techniques and stratification. The methods of collecting data and not the ease of collection; there should not be a disproportionate amount of a certain kind of data simply because it can be collected easily. 2.4 Capability Index If a characteristic has single sided or double sided tolerance limits, you can calculate and display the capability indexes and in the mean value tracks and the qualitative tracks.
37/ ADTU OLE The process of capability index is a measurement of the smallest possible share of non-conforming units that results from the optimum distribution of characteristic values in the process. However, this value does not indicate, whether this is the case. The process capability index is a measurement of the expected share of non- conforming units in the process. The larger this value is, the smaller is the share of nonconforming units. The following formulae are used in the mean value tracks for the calculation: = (USL – LSL) / 6*s = min ((USL - `x), (`x – LSL)) / 3*s Here, the USL and the LSL are the tolerance range limits; x-bar and s are estimated values for the expected values for the expected value and the standard deviation of the original value distribution. S is calculated according to the process model of the control chart, either as the inner dispersion or total dispersion of the measured values. X is the overall mean value of the measured values.

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