Applying Normal Probability Papers for Process Capability Definition

Abstract

This research deals with the subject of capability of production process for manufacturing identical products in accordance with established design specifications by comparing the spread of values of a statistical property that specifies the quality with the tolerance value for specifications. In order to reach this aim, normal probability papers were utilized as an effective means to carry out this comparison, which can be also used to define the percentage of defects outside the limits of specification for the property that specifies the quality. The use of normal probability papers was applied in calculating the capability of production process in one of plants for dry batteries, that is on the technological route for the production line for manufacturing a dry battery of large type, and on one battery manufacturing stages which is the operation of bending the cup of battery zinc, into which the mixture of heart cell (negative electrode) is placed. The cup of the zinc is then closed by a plastic insert. Specimens were taken from output of the process for 25 days and in 5 individuals for one specimen, and a control chart for average and standard deviation was then drawn, from which it is indicated that the process is statistically controlled allowing to use the normal probability papers to define the capability of the production process for this property. It is shown that the percentage of the total defects outside the limits of specification is equal to (8.31%).