Novel Application of a Crystal Process Controller and DOE to Improve Metallizing Results

A quartz crystal process controller has been adapted to control a 1.8 meter diameter production metallizer with greater flexibly and reproducibly than the standard configuration. Since the approach in metallizing is commonly that of completely evaporating a measured charge of aluminum, the thickness monitoring aspect of the controller was overridden and only the power ramp and soak capabilities were employed. A challenge is presented by parts which are deeper in proportion to their aperture than is ordinarily considered practical for metallizing in this type of equipment. The close distances to the filaments of the densely packed parts, the excess thickness of coating in some areas, and the steep angles of the surfaces to the incoming material tended to cause discoloration. Adequate coverage in the depths of the part require large charges of aluminum and long firing cycles. Design of Experiments methodology can be employed to find the best controller program parameters to give good part coverage, high reflectance, and long filament life. Practical results have been achieved by the approaches described.