Wire electrical-discharge machining (WEDM) is a process used to manufacture conductive hard metal components. It uses a continuously moving wire that serves as an electrode. Coating on the wire electrode allows for cooling of the wire electrode core and provides an improved cutting performance. The article "High- Performance Wire Electrodes for Wire Electrical- Discharge Machining-A Review" (J. of Engr. Manuf., 2012: 1757-1773) gave the following sample observations on total coating layer thickness (in mm) of eight wire electrodes used for WEDM:
21 16 29 35 42 24 24 25
Calculate a 99% CI for the standard deviation of the coating layer thickness distribution. Is this interval valid whatever the nature of the distribution? Explain.