• Reliability is the probability that an item will perform a require function under stated conditions for a stated period of time.

• A Reliability problem: A milling machine has three different bearings that fail in service. The distribution of each bearing is identical.

• When bearing fails, the mills stops, a repairperson is called and a new bearing is installed. The delay time of the repairperson’s arriving at the milling machine is also a random and variables having distribution is given in table 2.3.

• Different costs involved to change the bearing are shown in table 2.1. Table 2.4 shows simulation of 5 bearings under current method of operation. (in current method only those bearings are changed that are damaged).

• In current system it is assumed that life all bearings is exactly same. The cost of current system is estimated in table 2.5.

Different costs involved to change the bearing in proposed system is shown in table 2.6