Rexroth Tightening System 350 System Documentation - Rhino ...

10 Working with the System Tightening Technology | Bosch Rexroth AG 291/31610.4 Results storage and statistics-6σ +6σ-5σ +5σ-4σ +4σ-3σ +3σ-2σ +2σ-σ+σ(B)(A)68,27%95,46%99,75%99,9937%99,99994266%99,999999803%Figure 10–55: Normal distribution (Gauss graph) with standard deviation and its multiple(A)(B)Average valueTurning point of the distribution graph = standard deviationStandard deviationThe standard deviation σ (sigma) is the distance from the average value (mean) of the distribution graphto the turning point of the distribution graph (the point with maximum incline) with the dimensions of thecharacteristic (e.g. T [Nm], A [°]). It is larger than or equal to zero and smaller than the range R (see below).The range for the measurement results is described using the standard deviation.The distribution of the measurement values in percent is defined as follows within the normal distribution:– 68.27% of all measurement values are located in the range ± 1 σ– 95.46% of all measurement values are located in the range ± 2 σ– 99.75% of all measurement values are located in the range ± 3 σ– etc. as in Fig. 10–55.ExampleWhen the allowed tolerance of the torque is ±3 s, it means that from 1,000,000 tightenings, presumably2,500 tightenings will be outside of this tolerance (see Fig. 10–55).Range RThe range is the difference between the largest and smallest measurement value, in other words the differencebetween minimum and maximum. It describes the “outlier behavior” of the measurement values.With data in classes, the range is the difference between the upper class limit of the upper class and thelower class limit of the lowest class. The range of data in classes is thus cleared of “outliers”.10.4.3 Capability tests: machine capability, process capabilityThe goal of capability tests is:– To reach a result in the form of indicators (indices) about the suitability of a nutrunner/tightening system/tighteningprogram for a specific tightening case.– To compare general performance characteristics for various tightening devices objectively.System 350 | 3 608 878 040/05.2008