Rexroth Tightening System 350 System Documentation - Rhino ...

294/316 Bosch Rexroth AG | Tightening Technology 10 Working with the System10.4 Results storage and statisticsExample(1)(2)T [Nm]0-5 σ -3 σ M+3 σ +5 σT+7 σM UGTM set sollT –T +T– T –= 5σM - M UG = 5σMOG- M = 7σT +– T = 7σFigure 10–57: Normal distribution with a set torque tolerance and including the average value(1) Analysis C lowerM OG(2) Analysis C upperThe result according to Fig. 10–57:7σC upper= ------- = 2.333σ5σC lower= ------- = 1.673σCritical machine capability index C mk = 1.67BS350 automatically calculates the critical machine capability index C mk .Summary – C m represents the maximum reachable value for C mk .– If the actual value reached for C m is smaller than the requested value for C m and C mk , the tighteningresult is insufficient.– If the actual value reached for C m is larger than the requested value and only C mk smaller, the requestedC mk might still be reached by moving the average value.– A tightening system that provides very good indices for a specific tightening case is not automaticallyequally suitable for other tightening cases.10.4.3.2 Process capability testIn the process capability test the question is answered as to whether the quality of the tightening over thelong term and under realistic conditions within the tightening process can be kept within the set tolerances.In contrast to the machine capability test, in the process capability test disturbances such as user influence,material batches, thread tolerance etc. are taken into consideration by the selection of the randomsample. The process capability test also needs a larger random sample (at least 100 OK tightenings undernormal conditions). Otherwise the procedure is the same as that for the machine capability test.The process capability index C p and the critical process capability index C pk are calculated according tothe same formulas as the machine capability index. A sufficient machine capability is absolutely necessaryfor a high process capability.System 350 | 3 608 878 040/05.2008