Optimization of the PVD aluminium coating evaporation phase and the tungsten filament wire geometry

The PVD aluminum coating process is widely used in the automotive industry. It is becoming more widespread due to its economical and enviromental advantages compared to its alternatives. Product geometry and process design, in particular, have a direct impact on end-product quality. The most important out-puts of the process are the achievement of optical requierements, sustainable production and homogenity of the aluminium thickness. The purpose of this research is to describe the process conditions that directly affect the coating thickness under serial production settings while taking into account the industrial scale of the PVD aluminum coating equipment. For the optimization studies, Taguchi L27 experimental design method was used to determine the effects of the position of the part in two dimension, the distance between the substrat and vapour source, tungsten filament geometry, mass of the aluminum wire and machine pre-heating paramaters. The results were evaluated based on the aluminium coating thickness of the substrate. These studies were performed by using the industrial scale of PVD coating machine and optimized process conditions were determined. Taguchi's " the larger is better" evaluation criteria was chosen for the evaluation of the MİNİTAB® results. The most effective factors on the coating thickness of the substrate were determined as the subsrate position relative to the electrode and distance between the substrate and evaporation source. Increasing the closeness of the part to the source and using the middle position of the electrode caused the increase of the avarage coating thickness of the part and decrease the standart deviation of the coating. In this regard, sustainability and homogenity of the part were also improved. Contrary to expectation, steady increasement of the aluminum usage mass did not affect the coating thickness linearly or positively. However, disadvantages of aluminum mass for the tungsten filament types which were used in the studies were observed. The less effective factor on aluminum coating thickness is the type of the tungsten filament. Although basket type tungsten filament showed better perfomance compared to the others, camel and spiral type, all of them can be used in serial production by considering the advantages and disadvantages in total. In addition to the Taguchi experimental design studies, 3 different pre-heating parameters were also investigated and the verification studies of the experimental design were performed. It is the fact that when the pre- heating voltage is close to the evaporation voltage (7kV), aluminium wire stays in liquid phase more than usual and starts to drop on to the chamber ground. Thus, the coating thickness and sustaniability can be affected negatively. In conclusion, process conditions to increase the coating thickness have been determined in this study. These process conditions are expected to provide key inputs for the future product and process developments.