Estimation of the efficiency of the appliance of the bolting machine

Machine Capability Index Calculation Method The machine repeatability index Cm is calculated as follows: Cm=T/6s where: T is the tolerance range, the difference between the maximum and minimum tolerances; s is the standard deviation. The standard deviation s is calculated as follows: s=1n-1Eni=1(xi-x)2 where: n is the number of measurements, typically 50; xi is the ith measurement; x is the average of 50 measurements value. The calculation method of the tolerance range T: T=Tmax-Tmin where: Tmax is the maximum tolerance value required by the process; Tmin is the minimum tolerance value required by the process.

The calculation method of the machine accuracy capability index Cmk is as follows: Cmk=(1-k)T/6s where k is the offset coefficient and k=2Bi/T.Bi is the offset between the measured data x and the nominal value of the standard center. The absolute value. Bi=|x-x0| where: x0 is the nominal theoretical nominal value of the process.

According to the requirements of European and American countries, the requirements for the machine capacity index Cm and Cmk of the new bolt assembly machine must be E1167; the requirements for the capacity index Cm and Cmk of the repaired bolt assembly machine must be E1133. The above is the sampling measurement at 50 times. The next request. If the number of sampling measurements is reduced by 10 times, the machine capacity index Cm and Cmk are increased by about 5%, respectively, but the sampling measurement data must be at least 20 times, otherwise the calculated machine capability index will be seriously distorted.

Example calculations The following is an example of the machine capacity index Cm, Cmk calculation method and process. For example, a unit purchased a single-head bolt assembly machine from Atlas with an accuracy of 3%. It is ready for the high-strength bolt assembly of M10@50 of 1019. The assembly process requirement is 55Nm5Nm, and it is required to accept this bolt assembly machine. Can the process requirements be met in mass production.

Firstly, install the bolt assembly machine according to the requirements of the manual, and then add a standard torque sensor of HBM with a precision of 012 in series at the joint sleeve. At this time, the bolt assembly machine is tested for 50 consecutive times. Test Data.

Test data table No. HBM standard torque sensor test value NmAtlas company working torque sensor test value 5 works according to the average value x of the working sensor. x work = (x1 + x2 +, + x50) / 50 = (55.31 +, +55.25) / 50 = 55.23 Find the working sensor standard deviation value s work. s work = 1n-1Eni = 1 (xi-x) 2 = 0.10 Find the average value x standard of the standard sensor.

x standard = (x1 + x2 +, + x50) / 50 = (56.40 + 56.20 +, +55.10) / 50 = 55.20 Find the standard sensor standard deviation value s standard. s standard=1n-1Eni=1(xi-x)2=0.29 or above It can be clearly seen that the standard sensor standard deviation value s standard and the working sensor standard deviation value s work nearly three times different, which is mainly the accuracy comparison of the working sensor. Low, low-precision sensors are relatively random. When an electrical signal is given, when the electrical signal is added or subtracted by 3%, the reading may be concentrated above and below the set nominal value, so the calculated standard deviation is relatively small; On the other hand, when the working sensor sends a signal to cut off the power, the actual reading may deviate from the nominal value set by the working sensor, and the calculated standard deviation is relatively large. This is why a standard sensor is connected in series on the bolt assembly machine.

It can be seen that the capacity index measured by the sensor of the Atlas bolt torque assembly machine is nearly three times that of the HBM standard sensor. The main reason is that the accuracy of the sensor of the Atlas bolt assembly machine is relatively low, generally 3%. The accuracy of the HBM standard sensor is relatively high, which is 012%. The sensor with low precision is obviously more random. Therefore, the lower the accuracy, the greater the machine capability index of the test and calculation; on the contrary, the higher the accuracy, the smaller the sensor test and the computing capacity index. Therefore, when calculating and evaluating the machine capacity index of the bolt assembly machine, it is necessary to use a high-precision sensor to evaluate the bolt assembly machine with lower precision.

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