Mitutoyo - Полный каталог инструмента - 2014 Английский язык
для размещения заказа - mitutoyo@mitutoyo-tools.ru
Quick Guide to Precision Quality Control
Measuring Instruments
Quality Control (QC) Histogram
A A system for economically producing products or services of a quality that meets A diagram that divides the range between the maximum and the minimum
customer requirements. measured values into several divisions and shows the number of values
Process Quality Control (appearance frequency) in each division in the form of a bar graph. This
makes it easier to understand the rough average or the approximate extent
of dispersion. A bell-shaped symmetric distribution is called the normal
Activities to reduce variation in product output by a process and keep this distribution and is much used in theoretical examples on account of its easily
variation low. Process improvement and standardization as well as technology calculable characteristics. However, caution should be observed because many
accumulation are promoted through these activities. real processes do not conform to the normal distribution, and error will result
Statistical Process Control (SPC) if it is assumed that they do.
Process quality control through statistical methods. Process Capability
Population Process-specific performance demonstrated when the process is sufficiently
standardized, any causes of malfunctions are eliminated, and the process is in
A group of all items that have characteristics to be considered for improving and a state of statistical control. The process capability is represented by mean ±3s
controlling processes and quality of product. A group which is treated based on or 6s when the quality characteristic output from the process shows normal
samples is usually the population represented by the samples. distribution. s (sigma) indicates standard deviation.
Lot Process Capability Index (PCI or Cp)
Collection of product produced under the same conditions. A measure of how well the process can operate within the tolerance limits of
the target characteristic. It should always be significantly greater than one.
Sample The index value is calculated by dividing the tolerance of a target characteristic
by the process capability (6s). The value calculated by dividing the difference
An item of product (or items) taken out of the population to investigate its between the mean (X) and the standard value by 3s may be used to represent
characteristics. this index in cases of a unilateral tolerance. The process capability index
assumes that a characteristic follows the normal distribution.
Sample Size
Number of product items in the sample. Notes: If a characteristic follows the normal distribution, 99.74% data is
within the range ±3s from the mean.
Bias
Value calculated by subtracting the true value from the mean of measured Bilateral tolerance
values when multiple measurements are performed.
Cp = —US6L-sL SL USL: Upper specification limit
Dispersion LSL: Lower specification limit
Variation in the values of a target characteristic in relation to the mean value. Unilateral tolerance ... If only the upper limit is stipulated
Standard deviation is usually used to represent the dispersion of values around
the mean. Cp = —U3SLs-X
Frequency Unilateral tolerance ... If only the lower limit is stipulated
Lower specification limit (LSL)
Cp = —X3-LsSL
Target process mean
Mean
Upper specification limit (USL)
Noncompliance
Bias Measured values
Dispersion/imprecision
Tolerance (USL - LSL)
A-21
mitutoyo@mitutoyo-tools.ru www.mitutoyo-tools.ru
