Optimization of arc-PVD TiN coating process parameters by Taguchi technique

In this study an arc-physical vapor deposition (Arc-PVD) titanium nitride (TiN)-coating process was optimized using a Taguchi technique. In the first step, quality characteristics of coated tools and parameters of the coating process were defined according to customer requirements and scientific data, using quality function deployment (QFD) techniques and a cause-and-effect (Ishikawa, fishbone) diagram. The selected quality characteristics for the evaluation of coated tools were hardness, surface roughness, adhesion, and coating thickness. To optimize the coating process, bias voltage, reactive gas pressure, and cathode current were selected as coating process parameters. The substrate materials were HSS-E drill pins. Prior to the coating process, a similar surface preparation was applied to all samples in order to eliminate the effects of surface preparation parameters on the coating properties. Coating parameters (factors) were placed in an experiment matrix, L₉ orthogonal array, according to the Taguchi approach and chosen quality characteristics such that coating thickness, hardness, surface roughness, and adhesion were measured. Experimental results were analyzed by analysis of variance (ANOVA) to examine the effect of the process parameters on the quality characteristics. In this study, selected factors were placed in an L₉ orthogonal array. Nine trials were conducted and quality characteristics were measured. In the analysis stage of these quality characteristics, coating thickness was analyzed using ANOVA to determine optimal conditions for obtaining best coating thickness on the tools. According to the ANOVA, the optimum conditions for coating thickness of coated tools were found as cathode current 90 A, reactive gas pressure 5 mtorr, and bias voltage 150 V.