ABSTRACT
Data can be gathered in different forms. First, the purpose of the data must be determined. Only then can a decision be made as to what kind of data would best serve the purpose. There can be many purposes for collecting data in a manufacturing plant. Some common purposes are as follows:
Understanding of the actual situation ◾ . Data is collected to check the extent of the dispersion in part sizes coming from a machining process or to examine the percentage of defective parts contained in lots received. When the number of data items increases, they can be arranged statistically for easier understanding. Estimates can then be made concerning the manufacturing process or the machine and the condition of lots received through comparison with specified figures, standard figures, target figures, etc. Analysis ◾ . Analytical data may be used, for example, to examine the relationship between a defect and its cause. Data are collected by examining past results and making new tests. In this case, various statistical methods are used to obtain correct information. Process control ◾ . After investigating product quality, this data can be used to determine whether or not the manufacturing process is normal. Control charts are used in this evaluation, and action is taken on the basis of these data. Regulation ◾ . This data is used, for example, as the basis for raising or lowering the temperature of an electric furnace so that a standardized temperature level may be maintained. Actions are prescribed for each datum, and those measures must be taken accordingly. Acceptance or rejection ◾ . This type of data is used to approve or reject parts and products after inspection. There are two methods: total inspection and sampling. On the basis of the information obtained, a decision on what to do with the parts or products can be made.
