Optimization of Electro-Discharge Texturing Parameters for Steel Sheets' Finishing Rollers

Exterior car-body parts are made of steel or aluminum sheets. Their formability and appearance after painting depends not only on the mechanical properties but also on their surface texture. The surface roughness characteristics, the roughness average Ra and the peak count Pc per centimeter depend on the texture of rolling mill's finishing rollers, their wear and the degree of removal by the rolling mill. The research was carried out on heat-treated finishing rollers on the surface of which a controlled texture was created by changing the electro-discharge texturing (EDT) parameters. Parameters and the number of electro-discharge texturing experiments were optimized using full four-factor experiment techniques at the upper and lower levels of the parameters in the form of 2⁴. The significance of the impact of individual EDT parameters and their interactions was identified based on the variance results. The ANOVA variance analysis results confirmed that the roughness Ra and the peak count Pc depend primarily on peak current (I_p), discharge peak voltage (U_p), pulse on time (P_ont) and pulse off time (P_offt). Optimization of the effect of the above parameters on the target roughness Ra_T,FR values and the peak count Pc_T,FR of finishing rollers was performed by the response surface methodology (RSM). Obtained regression models describe relationships between the input parameters of the electro-discharge texturing of finishing rollers and the output characteristics of the Ra_T,FR and the Pc_T,FR texture to a very high degree. The reliability of the electro-discharge texturing process of working rollers was assessed using the process capability index C_pk.